THE BIOLOGY OF TOXOPNEUSTES ROSEUS IN RHODOLITH BEDS

IN BAJA CALIFORNIA SUR, MEXICO

A Thesis

Presented to

The Faculty of the Department of Biology

San Jose State University

In Partial Fulfillment

of the Requirements for the Degree

Master of Science

by

David Wayland James

August 1998

© 1998

David Wayland James

ALL RIGHTS RESERVED

ABSTRACT

THE BIOLOGY OF TOXOPNEUSTES ROSEUS IN RHODOLITH BEDS

IN BAJA CALIFORNIA SUK MEXICO

by

David Wayland James

The feeding, movement and covering behavior of Toxopneustes

roseus was investigated in rhodolith beds in the Gulf of California. Urchins

ate rhodoliths and nongeniculate coralline algal crusts almost exclusively

despite the availability of other algae. Large amounts of carbonate were

ingested. Individuals in a rocky habitat had larger jaws than those in a nearby

rhodolith bed, perhaps because food was less available and urchin densities

were higher in the rocky habitat. Urchins were highly mobile. While

individuals moved day and night, one population moved significantly more

at night. Diel movement may be a behavioral adaptation to avoid surge. The

ratio of covering material/body weight and the percent cover of material were

highest at the site with the most surge. Vvhile T. roseus consumed

rhodoliths, urchin movement may spread the grazing impact over large

areas. Bioturbation resulting from urchin feeding, movement and covering

activity may benefit the rhodoliths and contribute to bed persistence.

ACKNOWLEDGMENTS

There were many people who not only helped me complete my thesis

but supported me with both continuing and new friendships. I would like to

first thank my advisor, Mike Foster. He provided invaluable assistance,

comments, instruction, and also helped me approach and think about science

in a new way. He also introduced me to the Gulf of California and rhodolith

beds. I would also like to thank John Pearse for his advice and assistance in

the lab, Dr. James Nybakken for reviewing my thesis, and Chris Harrold for

sitting in on my thesis defense.

My thesis would not have been possible without the help, love, and

encouragement of Sophie James. Not only did she support my thesis and

trips to Baja, but she also provided half of my field support and data

collection. She kept a smile on her face during difficult field days and made

the whole experience more pleasurable. I was fortunate to have the assistance

of a good friend, Pete Hague, for the first half of my data collection. He

provided great company and took a load off my shoulders with his expertise

and efficiency.

There were many others who greatly helped my efforts. A huge thank

you goes to Rafael Riosmena-Rodriguez for his assistence with logistics,

numerous algal identifications, friendship, and providing much hospitality

with his wife Alejandra. Hector Reyes was kind enough to identify coral

v

species and provide information about invertebrates of the Gulf of California.

Mil gracias a toda la familia Cuevas por abrirnos las puertas de sus casas en la

Isla Pardito. Nos ofrecieron apoyo y amistad. Aldo Derose was very helpful

and built a trailer tough enough for Baja. Tom Brey was generous and

analyzed growth bands. Mike Graham and Shannon Bros gave much

appreciated statistical advice, and MLML librarians Joan Parker and Terry

Darcey fulfilled my endless requests for papers. Diana Steller and Lisa

Merrick provided much insight and information on Baja and rhodolith

communities. I would also like to thank my family for their love and

support.

I was very grateful for the funding from the David and Lucille Packard

Foundation, Gary Green and San Jose State University, the National

Geographic Society, and the Inter American Institute for Global Change.

vi

TABLE OF CONTENTS

Abstract iv Acknowledgments v Table of Contents vii List of Tables, Figures, and Appendix Vlll

Introduction 1

Materials and Methods 5 Study Sites 5 Density 6 Diet 8 Feeding Preferences 9 Coralline Algae Consumption 10 Aristotle's Lantern 11 Growth Bands 12 Movement 12 Covering Material 14

Results 16 Density 16 Diet 19 Feeding Preferences 21 Coralline Algae Consumption 22 Aristotle's Lantern 22 Growth Bands 23 Movement 23 Covering Material 25

Discussion 28

Literature Cited 39

Tables 47

Figures 51

Appendix 55

vii

LIST OF TABLES, FIGURES, AND APPENDIX

Table Title Page

1 Density of Toxopneustes roseus and algal bottom cover at El 47 Cardon in November 1996

2 Movement rates and distances of Toxopneustes roseus at El 48 Cardon and Diguet

3 Covering material and cover weight/body weight of 49 Toxopneustes roseus at El Cardon in November 1996, Diguet, and Pardito

4 Covering material of Toxopneustes roseus at El Cardon in 50 November 1996, Diguet, and Pardito

Figure

1

2

3

4

Locations of study sites in Baja California Sur, Mexico

Size-frequency distributions of Toxopneustes roseus at El Cardon in March 1996 and November 1996

Size-frequency distribution of Toxopneustes roseus at Diguet

Jaw length vs. test diameter of Toxopneustes roseus at El Cardon, Diguet, and Pardito

Appendix

Table

1 Amount of rhodoliths eaten by Toxopneustes roseus at El Cardon and Diguet

viii

51

52

53

54

58

INTRODUCTION

The sea urchin Toxopneustes roseus is common in rhodolith beds

(unattached, nongeniculate coralline algae) and rocky habitats in Baja

California Sur, Mexico. This sea urchin often forms large aggregations,

covering itself with rhodoliths as well as shell pieces and foliose algae (Foster

et al. 1997; D. James, pers. obs.). Little is known of the diet ofT. roseus, other

than it can consist of rhodoliths, nongeniculate coralline algal crusts and dead

coral (Glynn 1988; D. James, pers. obs.).

The relative size of Aristotle's lantern, a complex jaw apparatus

consisting of skeletal pieces, joints, muscles and ligaments (Hyman 1955), can

be used as an indicator of the amount and type of coralline algae eaten. Low

food availability leads to an increase in Aristotle's lantern size relative to the

test (Ebert 1980; Edwards and Ebert 1991; Levitan 1991). Levitan (1991) found

that when food was moderately limiting, the test decreased while some

growth occurred in the jaw, and Black et al. (1982) determined that lantern

length increased with increasing sea urchin density and differed between

habitats. Urchins with relatively larger lanterns had more material in their

guts and removed benthic algae from larger areas than individuals with

relatively smaller lanterns (Black et al. 1984). Larger jaws may have an

increased scraping strength (Black et al. 1984).

2

Movement patterns of sea urchins vary with species. Some sea urchins

have diel movement patterns and feed at night (Ebling et al. 1966; Fuji 1967;

Nelson and Vance 1979; Tsuchiya and Nishihira 1986), but this is not

universal (Glynn et al. 1979; Hay 1984; Shunula and Ndibalema 1986).

Nocturnal feeding behavior may serve to avoid fish predation (Nelson and

Vance 1979; Carpenter 1984). Food abundance may affect the daily distances

that urchin travel (Mattison et al. 1977; Russo 1979; Harrold and Reed 1985;

Andrew and Stocker 1986).

Many species of sea urchins cover themselves with algae, shell, and

other debris (Millott 1956; Lewis 1958; Sharp and Gray 1962; Dix 1970; Lees and

Carter 1972). This may serve as camouflage and protection from predators, or

it may increase stability during increased water motion since waves and surge

can inhibit the distribution, emergence and feeding of sea urchins (Lees and

Carter 1972; Lissner 1980; Lissner 1983; Foster 1987). Analyses of covering

material held by T. roseus in different habitats may help explain covering

behavior.

Feeding, movement and covering behavior of T. roseus may have

important effects on the distribution and abundance of calcareous algae in

rhodolith beds in this region. Bioturbation results from T. roseus feeding on

rhodoliths as well as moving through and over them/ and picking them up

(D. James pers. obs.). If T. roseus does not eat the entire rhodolith, then the

plant may benefit from being turned. However, other herbivorous sea

3

urchins can greatly alter algal species composition and relative abundance in

communities (Paine and Vadas 1969; Ogden et al. 1973; Estes and Palmisano

1974; Pearse and Hines 1979; Vance 1979; Foster 1982; Sammarco 1982; Ebeling

et al. 1985; Foster 1987; Andrew 1993). Grazing by T. roseus may reduce

rhodolith standing stock and increase carbonate sediment production.

Rhodolith grazing may be reduced if other preferred algae are available.

Sea urchins may have algal preferences, eating different algae depending on

availability (Leighton 1966; Vadas 1977; Vance and Schmitt 1979; Ogden et al.

1989; Schiel1982). They often feed on coralline algae, especially when young

or when other plants and foliose algae are unavailable (Vance 1979; Hawkins

1981; Schiel 1982; Chiu 1985; Kenner 1992; Guillou and Michel 1993).

Large aggregations of rhodoliths can be common and extensive in

nearshore environments worldwide (Bosence 1983). It is commonly thought

that these beds persist primarily in areas where turning and slight oscillatory

movements maintain individual rhodolith integrity and prevent fouling

(Steller and Foster 1995). Movement need not be frequent as rhodoliths may

remain static up to several months and still have living tissue over the entire

surface (Scoffin et al. 1985). Wave motion, currents and bioturbation may

periodically turn and move rhodoliths (Glynn 1974; Scoffin et al. 1985; Prager

and Ginsburg 1989; Guillou and Michel 1993; Steller and Foster 1995; Foster et

al. 1997).

The purpose of this study was to examine the diet, movement,

covering behavior and bioturbation of T. roseus to better understand the

biology of this species and the impact it has on rhodolith beds.

4

5

MATERIALS AND METHODS

Study Sites

Toxopneustes roseus was studied at 5 rhodolith beds in the Gulf of

California, Baja California Sur, Mexico (Figure 1). Most of the work was done

at two sites, El Cardon and Diguet. Additional observations and gut content

analyses were done at Manto de James and feeding observations were made at

Punta Bajo.

At El Cardon, the rhodolith bed occurred on a gradually sloping, sandy

substrate between 2.5 and 16.2 m deep. The bed consisted of live and dead

rhodoliths mixed together. Rhodoliths consisted of mostly Lithophyllum

margaritae with some Lithothamnion crassiusculum. Rhodolith sizes ranged

from 2-7 em in diameter. The algae Hypnea cervicornis and Spyridia

filamentosa were common and Caulerpa sertularioides, Sargassum

herporhizum and Hydroclathrus clathratus were seasonally abundant.

The bed at Diguet was shallower (2.7-4.6 m), relatively flat and more

exposed to surge. Rhodolith movement and urchin displacement from surge

were observed during sampling. Rhodolith patches were distributed across a

sandy bottom. Large L. margaritae (2-14 em diameter) were present in shallow

water with sparse Neogoniolithon trichotomun occurring deeper. Many

rhodoliths were covered with a layer of sand. The algae Cladophora

microcladioides, Enteromorpha intestinalis, Herposiphonia secunda,

Polysiphonia simplex and the colonial diatom Berkeleya hyalina were

common but not abundant. Codium simulans, Halimeda discoidea and

Hydroclathrus clathratus occurred occasionally.

6

Toxopneustes roseus was also studied around small rocky islands at

Isla Pardito. The bottom around the rocks consisted of rock, sand, and the

corals Pocillopora damicornis, P. meandrina and P. verrucosa. The algae

Lithophyllum imitans, N. trichotomun, C. microcladioides, E. intestinalis

and Sphacelaria didichotoma occurred on the rocks and dead coral rubble.

Toxopneustes roseus was present on rocks, at sand-rock interfaces and in coral

from depths of just below the low tide mark to 5.8 m. Urchins were very

abundant, reaching densities over 100/20 m 2• Urchin densities were not

measured quantitatively at Isla Pardito, but were observed.

Density

The density, size and depth distribution of Toxopneustes roseus at El

Cardon were determined in March and November 1996. Two 50 m transects

were sampled in March and three 270m transects in November. The

transects in November were parallel to shore and included the transects from

March. Transects were sampled in three depth zones: deep (11.6-9.6 m),

middle (9.4-7.5 m) and shallow (7.4-5.9 m), with two meters separating

quadrats in different transects. The shallow zone was not sampled in l\1arch

1996. Equal numbers of quadrats were sampled at each transect (March 1996:

n=36; November 1996: n=201). Random 20m2 quadrats (10m X 2 were

separated by at least one meter on each transect and oriented with the long

axis perpendicular to shore, starting on the transect at the deep end of the

zone. Quadrats were carefully searched and the number of individuals

counted, measured to the nearest millimeter, and their depth recorded.

Size-frequency modes were determined graphically.

Density and size distribution at Diguet were determined in December

1996. Four 200m transects parallel to shore were sampled (from offshore

towards shore). Fifty random quadrats were sampled in each transect.

Transect spacing, quadrat orientation and spacing, and density and size

determination were the same as at El Cardon. Urchin spatial patterns at El

Cardon in November 1996 and Diguet in December 1996 were determined by

calculation of Ip, the standardized Morisita index of dispersion (Krebs 1989).

The null hypothesis of random distribution was statistically tested using

equation X2 = Id(I,X-1) +n- I,X, where Id = Morisita's index of dispersion,

7

I,X =the sum of the quadrat counts, n =sample size, and df=n-1 (Krebs 1989).

Algal cover in the rhodolith bed at El Cardon was measured to

determine if the amount of rhodoliths and other algae affected urchin

density. Algal cover was determined using a point quadrat consisting of a 1.5

m bar and a 2 m string attached at both ends of the bar with 5 points tied on it

(Foster 1982). Bars were randomly placed and sampling points were

positioned on each side of the bar. All algae intersecting a 1 m vertical line

perpendicular to the substrate at each point were counted. Algal cover often

exceeded 100% because more than one alga may have intersected the line.

Rhodoliths smaller than 2 em were not counted. Twenty random points

were sampled every 10m along each transect.

8

Differences in density among depths at El Cardon were determined by

analysis of variance (ANOV A). The relationship between algal cover and

urchin density (dependent variable) at El Cardon was tested using multiple

regression. Only urchin density and algal cover data from the area of the bed

where T. roseus occurred were used for the algal cover analyses. Density and

algal cover data were log (X+0.1) transformed to improve normality. The

urchin and deep Caulerpa sertularioides data remained nonnormat

ANOV A was still used as it is robust to nonnormality (Underwood 1997).

Diet

Gut contents were determined for randomly selected urchins at El

Cardon in March 1996 (n=12) and November 1996 (n=20), Diguet in December

1996 (n=20), Pardito in December 1996 (n=20) and Manto de James in March

1997 (n=ll). Contents from all parts of the digestive system were removed,

9

preserved formalin, and held in alcohol until microscopic identification.

Over 100 pellets were analyzed per individual.

Feeding activity and food eaten was monitored by turning individuals

over and noting what was in their jaws. Feeding observations were made

during every day of sampling at all sites and seasons. At El Cardon, one night

dive each was made in March 1996 and November 1996. Over 100

observations were made at El Cardon in March 1996. In November and

December 1996, over 150 observations each were made at El Cardon and

Diguet, respectively. Over 50 observations were made at Pardito in December

1996. Observations were also made at Manto de James (n=50) and Punta Bajo

(n=20) in March 1997.

Feeding Preferences

Feeding preference experiments were done in the field at El Cardon in

November 1996 and at Diguet in December 1996. Preference was based on

which algae were included in the diet. Individuals were placed in plastic

containers (45x66x15 em) with screened lids (mesh size 1.6 mm). The

experiment was done at 10.4 m depth at El Cardon. Due to wind

the experiment for Diguet was run nearby at Pardito at 4.9 m depth with

urchins and algae from Diguet which were kept submerged and shaded

during transport.

1 0

Four treatments were used with three replicates each. Treatments

were: a control of rhodoliths and other algae alone, one urchin with

rhodoliths alone, one urchin with other algae alone, and one urchin with

rhodoliths and other algae. Other algae consisted of the green alga Caulerpa

sertularioides at El Cardon and the colonial diatom Berkeleya hyalina and the

green alga Enteromorpha intestinalis at Diguet. Algae were cleaned of

obvious debris and herbivores, blotted dry and weighed. Approximately 32 g

of rhodoliths and 11 g of C. sertularioides were used at El Cardon and 47 g of

rhodoliths, 0.2 g of B. hyalina and 0.4 g of E. intestinalis were used at Diguet.

The experiment was repeated three times at El Cardon and twice at Diguet.

Urchins used were approximately the same size and were pre-starved for 24

hours in containers with no algae. Individuals were left in each treatment for

48 hours.

Coralline Algae Consumption

Coralline algae consumption was determined by placing randomly

selected urchins in containers (see Feeding Preferences) for 24 hours.

Covering material was removed from each urchin to prevent feeding. Feces

from El Cardon November 1996 (n=13) were air dried in an enclosure for

24 hours. Daytime temperatures in this enclosure were 27-45° C and were

sufficient to thoroughly dry the samples. Samples from Diguet (n=12) were

1 1

stored in alcohol and dried in an oven at 90° C for 48 hours. Dried feces were

weighed to the nearest tenth of a gram, calcium carbonate was dissolved in

9% HCl, and the remaining fecal samples reweighed.

Feeding rate for 24 hours was assumed to be equal to fecal production

in 24 hours. Food has been observed passing through urchin guts as quickly

as 8-12 hours (Lewis 1964; Scoffin et al. 1980).

The relationship between fecal production and test diameter

(dependent variable) was determined by regression analyses. Test diameters

were log transformed to satisfy the assumption of normality.

Aristotle's Lantern

Random urchins were collected for measurements of Aristotle's

lantern and test diameter. As some individuals had slightly irregular test

shapes, the diameter of each individual was measured at three places to the

nearest tenth of a millimeter with vernier calipers and the mean diameter

used. Aristotle's lanterns were cleaned of organic material and separated

their elements by soaking in 5% NaOCl solution. The length of five

demipyramids (jaw structure) per individual Aristotle's lantern was

measured to the nearest tenth of a millimeter and the mean length used.

Demipyramid length was measured from the oral tip to the epiphysis

junction at the aboral end (Ebert 1980).

1 2

Among-site differences the relationship between demipyramid

length and test diameter were tested using analysis of covariance (ANCOV A)

comparing the slopes of regression between sites (independent variable) and

demipyramid length (dependent variable). The assumption of homogeneity

of variances was met by using ANOV A to test for among-site differences

ANCOV A residuals, which were not significant. A Matrix contrasts were

used to compare significantly different slopes among sites (Systat 1992).

Growth Bands

Growth bands on Aristotle's lanterns were identified to determine

annual growth increments. Brey et al. (1995) verified the annual formation of

growth bands on Aristotle's lanterns for the urchin Sterechinus neumayeri

(dark and dear bands). Demipyramids from individuals collected for

Aristotle's lantern analyses were ground smooth to a thickness of ::;;1 mm,

submerged in tert-butyl-methyl-ether and examined with a stereo microscope.

Movement

Movement rates at El Cardon in November 1996 and Diguet

December 1996 were determined by tagging individuals with anchor tags

(Olsson and Newton 1979). Urchins were tagged in place (not moved)

1 3

underwater and their test diameter measured to the nearest millimeter,

individuals were tagged at each site. Five days after tagging, there was 10%

mortality at El Cardon and 4% mortality at Diguet. However, individuals

dying from infections from tagging were observed moving and feeding.

Movement over 48 hours was compared between tagged (n=ll) and untagged

(control) individuals (n=7) at El Cardon in March 1996. Control urchins were

identified by test diameter measurements. Tagging did not significantly affect

movement over a 48 hour period (square root transformed; t-test: t=0.226;

df=16; p=0.825). Survey flags were placed 20 em from the urchin and polar

coordinates (distance from each urchin to the nearest em and direction to the

nearest 5°) to the flag were measured during each observation. To reduce

possible tagging artifacts, measurements were not used for analyses until at

least 24 hours after tagging.

Measurements were made at approximately 0730 and 1600 during the

day. Individuals were followed for 15 and 11 days at El Cardon and Diguet

respectively. Diel movements were sampled for 5 days at El Cardon and 4

days at Diguet by measuring movements at 0730 and 1600 during the same

twenty-four hour period. Twenty-four hour movements were calculated by

adding the day and night movements and standardizing them to exactly

twenty-four hours.

The differences between day and night movement rates were

determined by paired sample t-tests. El Cardon hourly rates were log (X+O.l)

1 4

transformed and Diguet hourly rates were log (X) transformed to satisfy the

assumption of normality. The relationship between size and 24 hour

movement was analyzed by linear regression using log transformed distances.

Covering Material

Covering material was determined from randomly selected

individuals (n=20) at El Cardon in November 1996 and Diguet and Pardito in

December 1996. Urchins and material on them were placed in ziplock bags

underwater for transport back to shore. Percent cover of material held was

determined by visual estimation. It was possible for an individual to have

over 100% cover because material was often layered. Covering material and

urchin weights were also determined to the nearest tenth of a gram.

Algal cover on the surrounding substrate was determined (see Density)

by haphazardly placing quadrat bars within one meter of the urchin.

Rhodoliths smaller than 2 em were not counted.

Covering material preference was determined indirectly by calculating

Ivlev's electivity indices (Krebs 1989) using the equation: E; = (ri- /( r; + ni),

where r; =the percentage of material i held and ni = the percentage of material

i in the environment.

1 5

Among-site differences in percent of covering material held and the

ratio of material held/body weight were determined by ANOV As. Multiple

comparisons were done with Tukey' s test.

1 6

RESULTS

Density

Most of the urchins at El Cardon in November 1996 occurred in all

depth zones along a 129 m section of the rhodolith bed. Only seven

individuals were found in quadrats sampled in the rest of the bed. The

highest mean density in the entire rhodolith bed at El Cardon was 1.0

urchins/20 m 2 in the middle (Table 1). Highest densities in a quadrat were 10

in the middle, 7 in shallow and 2 in deep. Urchin abundances in the middle

and shallow were twice as great as in the deep. While the abundance of

urchins differed among depths, differences were not significant (ANOV A:

F=0.16; df=2; n=201; p=0.86; power=0.79).

Dispersion changed with depth. Urchins in the middle and shallow

zones were dumped while individuals were randomly dispersed (usually

solitary and well dispersed) in the deep (Table 1). The middle and shallow

urchins were statistically different from a random distribution (middle:

X2=285.87; df=66; p<O.OOl; shallow: X2=223.94; df=66; p<O.OOl) and the deep

urchins were not statistically different from a random distribution (X2=66.75;

df=66; p=0.453). Although dispersion changed with depth, the relationship

between depth and test diameter was not significant (regression: n=144;

r2=0.01; F=1.44; p=0.24).

1 7

Rhodolith and Caulerpa sertularioides cover increased with decreasing

depth (Table 1). The cover of rhodoliths among depths was significantly

different (ANOVA: F=l2.29; df=2; n=90; p<O.OOl). Deep and middle rhodolith

cover were not significantly different (multiple comparison: p=0.123;

minimum detectable difference=0.15) but shallow was significantly greater

than deep and middle (multiple comparison: deep vs. shallow; p<0.001 and

middle vs. shallow; p=0.012). There was a significant difference in C.

sertularioides cover among depths (ANOV A: F=3.35; df=2; n=90; p=0.040).

Deep and middle were not significantly different (multiple comparison:

p=0.112; minimum detectable difference=0.07). Shallow was significantly

greater than deep, but not middle (multiple comparison: p=0.047 and p=0.923).

The relationship between urchin density and algal cover (live

rhodoliths and C. sertularioides) varied with depth. In deep, the relationship

was not significant (multiple regression: n=30; r2<0.01; F=0.05; p=0.95).

Although the multiple regression for the middle was significant and positive

(n=30; r2~0.21; F=3.61; p=0.04), neither regression was significant for rhodoliths

or C. sertularioides (rhodoliths: n=30; r2=0.10; F=3.01; p=0.09; C. sertularioides:

n=30; r2=0.07; F=2.05; p=0.07). However, there was a significant, positive

relationship between urchin density and C. sertularioides in shallow

(regression: n=30; r2=0.37; F=l6.08; p<O.OOl).

Along the 50 m section of El Cardon sampled in both March 1996

November 1996, density (mean±SE) was greater in the deep in March (n=13;

1 8

1.8±0.45) than in November (n=12; 0.8±0.22). In the middle, density was

greater in November (n=12; 1.5±0.49) than in March (n=13; 0.3±0. The

depth (m; mean±SE) that urchins occurred was significantly different between

March and November (Mann-Whitney U test: 2=7.15; p<O.OOl; March: n=47;

10.0±0.15; November: n=144; 7.9±0.12).

An apparent size-frequency mode at El Cardon in March 1996 was

centered around 90 mm (Figure 2). The mode was also centered around 90

mm in November 1996, but was more distinct. Similar sized individuals

were found during both sampling periods, ranging from 61-110 mm. Mean

sizes were 89.72 mm (SE=1.55; n=47) and 91.86 mm (SE=0.61; n=144) in March

and November, respectively. There did not appear to be any recruitment

events in March or November, as very few small urchins were found.

Almost all of the urchins at Diguet occurred in all transects along a 85

m section of the rhodolith bed. sampled quadrats in the rest of the bed,

only five individuals were found. Eighty-six percent of the urchins were in

the deepest transect. The density (n=200; mean±SE) in the entire rhodolith

bed at Diguet was 0.5±0.17 urchins/20m2• Urchins were aggregated

(standardized Morisita index of dispersion=0.50), with the most individuals

occurring in areas with highest rhodolith densities. Urchins were statistically

different than a random distribution (X2=2372.52; df=199; p<O.OOl). The

greatest number in a quadrat was 27 in the deepest transect. Urchins in the

rest of the transects were solitary.

1 9

There were two apparent size-frequency modes (one around one

around 109 mm) at Diguet in December 1996 (Figure 3). These may represent

past recruitment events. The mean size (mm±SE) of urchins at Diguet

(n=102; 99.01±1.25) was greater than at El Cardon in March and November

1996.

Urchins were very gravid at El Cardon in March 1996. Spermatozoa

were frequently released upon slight pressure on the gonads, and the ovaries

appeared well developed. Gonadal conditions appeared the same March

and November 1996 at El Cardon. Individuals were observed spawning on

several occasions at El Cardon in November 1996.

Gonads were very gravid at Diguet in December 1996. Urchins were

observed spawning in December 1996 and also in January 1997 (D. Steller,

pers. comm.). Urchins were gravid at Manto de James in March 1997.

Individuals were seen spawning at Los Islotes (near La Paz) in late August (H.

Hall, pers. comm.).

Diet

Entire rhodoliths and nongeniculate coralline algal crusts on rocks,

shells and dead coral were the only algae that Toxopneustes roseus was ever

observed feeding on at El Cardon, Diguet, Manto de James and Punta Bajo. At

El Cardon, Caulerpa sertularioides, Hydroclathrus clathratus, and Sargassum

20

herporhizum were seasonally abundant and Hypnea cervicornis and

filamentosa were common. These algae were never observed eaten, but were

frequently used as covering materiaL Berkeleya hyalina, Enteromorpha

intestinalis, Herposiphonia secunda and Polysiphonia simplex were common

at Diguet butT. roseus was never seen feeding on them. One individual at

Diguet was seen feeding on a rock and another on a sandy substance; it is

possible that they were eating diatoms or algal films as these were

occasionally seen on the sand.

Urchins fed on rhodoliths of all sizes and shapes. Individuals often

climbed larger rhodoliths and ended up tilted on their sides with the

rhodolith in their mouths. Individuals were also found on their sides eating

pieces of shell or dead coral with no visible algae. Urchins at all sites were

observed feeding during all hours of the day, and at night at El Cardon.

Gut contents consisted of mostly rhodolith pieces and some ground up

nongeniculate coralline algae at El Cardon. Gut contents at Diguet were

mostly ground up nongeniculate coralline algae and a few rhodolith pieces.

One piece of Cladophora sp. at El Cardon and five pieces of Cladophora sp. at

Diguet were found out of all the feces examined. Gut contents at Manto de

James consisted mostly of rhodolith pieces, some diatoms and one piece of

the bryozoan Reptadeonella hymanae.

At Pardito, urchins were observed feeding only on nongeniculate

coralline algal crusts on both rock and dead coral. One individual was seen

feeding on what appeared to be clean sand. In the shallow rocky area

nearshore at Punta Bajo, urchins were only eating geniculate and

nongeniculate coralline algae. Gut contents at Pardito consisted of mostly

ground up nongeniculate coralline algae and some E. intestinalis and

Sphacelaria didichotoma.

Feeding Preferences

21

Toxopneustes roseus was observed feeding on rhodoliths in all

treatments that included rhodoliths at El Cardon and Diguet. In the

treatment containers at El Cardon, urchins were never observed feeding on

Caulerpa sertularioides and no soft fecal pellets were seen in the containers

when individuals and algae were removed. No feeding on Berkeleya hyalina

or Enteromorpha intestinalis was observed in the containers at Diguet.

Urchins often used B. hyalina, C. sertularioides and E. intestinalis as covering

material in the containers, but no signs of grazing were observed on the algae.

Some E. intestinalis grew in all treatments, while C. sertularioides often

swelled slightly and B. hyalina deteriorated after 24 hours. Live rhodolith

fragments (2-10 mm) were found in the containers containing both rhodolith

treatments with urchins. These were most likely fragments dropped during

feeding. Details of this experiment are given in the Appendix.

22

Coralline Algae Consumption

Toxopneustes roseus produced large amounts of feces. Mean fecal

production in 24 hours was 3.87 g dry weight per individual (n=13; range 2.0-

5.8 g; SE=0.29) at El Cardon. This corresponds to 1.01 kg feces/20m2 /year

based on their overall rhodolith bed density. The mean size of urchins used

to determine the fecal production rate was 90.76 mm (n=13; SE=2.28). The

relationship between test diameter and fecal production was not significant

(n=13; i=0.080; F=0.961; p=0.348).

The mean fecal production in 24 hours was 8.19 g per individual (n=12;

range 2.7-10.7 g; SE=0.59) at Diguet. The amount of carbonate produced was

7.96 g per individual (n=12; range 2.7-10.3 g; SE=0.57). The amount produced

per year would be 1.48 kg carbonate/20 m 2 based on their overall rhodolith

bed density. Individual mean size for fecal production was 99.50 mm n=12;

SE=3.37). The relationship between test diameter and fecal production was

not significant (n=12; r2=0.020; F=0.207; p=0.659).

Aristotle's Lantern

The relationships between test diameter and jaw length were for

Cardon, Diguet and Pardito (Figure 4). Regression slopes for Diguet and

Pardito were not significantly different (ANCOVA: Site-Covariate interaction;

23

F=3.60; df=l; n::-..:42; p=0.065). Among all three sites, regression slopes were

significantly different (ANCOV A: Site-Covariate interaction; F=6.88; df=2;

n=63; p=0.002; A Matrix multiple comparisons, El Cardon<Diguet; El

Cardon=Pardito; Diguet>Pardito). While the slope of Diguet may have been

greater than Pardito, they-intercept was much lower, indicating most of the

urchins at Diguet had smaller jaws than urchins of a similar size at Pardito.

The slope of El Cardon was significantly lower than Diguet even though

similar sized urchins at El Cardon had larger jaws.

Growth Bands

Only demipyramids from five individuals were examined as they were

opaque with no obvious dear bands. Bands indicative of annual cycles were

missing from the jaws, but 8-9 lines were found on the tooth at the tip of one

demipyramid.

Movement

Hourly movement rate during the day was significantly greater than at

night at El Cardon (paired t-test: t=2.20; df=215; p=0.029). However,

difference in movement rates was not great (Table 2). Despite the longer

night period (15.5 hours vs. 8.5 hours) in November and December, 16

24

urchins moved greater mean distances during the day. Temporal movement

patterns varied among individuals in the population; twelve individuals had

mean night rates greater than their mean day rates.

At Diguet the night hourly movement rate was significantly greater

than the day rate (paired t-test: t=5.59; df=146; p<O.OOl). Day rates were similar

at Diguet and El Cardon, but the night rate was much greater at Diguet.

Twelve urchins had faster mean day rates, and two individuals had greater

mean day distances moved.

Spatial movement patterns varied greatly at both sites. Some

individuals remained in small areas by moving little, doubling back or

moving in a circle. Others ranged over larger distances.

There were not any obvious environmental variables (discussed

below) associated with the distance, direction, and speed of movement except

for differences in day versus night rates. Although there was a significant

positive relationship between urchin density and Caulerpa sertularioides

cover at El Cardon, individuals did not appear to move towards C.

sertularioides and frequently moved away from it. Urchins occasionally

moved across the depth gradient. Size was not related to movement and the

relationship between test diameter and mean distance moved over 24 hours

was not significant (El Cardon: n=48; r2=0.014; F=0.658; p=0.421; Diguet: n=48;

r2=0.059; F=2.883; p=0.096). Toxopneustes roseus was highly mobile, moving

at speeds up to 10 em/min, Maximum distances covered at El Cardon and

Diguet in 24 hours were 20.8 and 14.7 m, respectively.

25

Substrate appeared to affect individual location at Diguet. Sand

patches, 1-2 m in diameter, were frequent at this site. Urchins generally

avoided sand, moving on to rhodoliths or next to rocks which appeared to

provide protection from surge. The mean distance from individuals to the

nearest rhodoliths was 6.1 em (n=580; SE=0.4; range=0-90 em) while rhodolith

patches were spaced a minimum of 0.5 m apart. This suggests that urchins

searched for protection from surge. Individuals on sand were observed

sliding back and forth on the substrate when surge increased. Urchins in

areas of highest rhodolith densities moved the least and were the most

aggregated.

Bioturbation often resulted from movement. Urchins frequently

plowed trails through rhodoliths, and at El Cardon, Diguet and Manto de

James, individuals often buried themselves in rhodoliths, forming a pit.

Covering Material

In the rhodolith beds, covering material held was abundant, often

around 100% cover (Table 3). The percent cover of material held by podia was

significantly different among sites (ANOVA: F=31.49; df=2; n=60; p<0.001),

and all three sites had significantly different amounts of the various covering

material (multiple comparisons: p<O.OOl). Diguet had the highest percent

covering material and Pardito the lowest.

26

There was a significant difference among sites in the ratio of covering

material to body weight (ANOVA: F=40.63; d£=2; n=60; p<O.OOl). The ratio for

Diguet was significantly greater (multiple comparison: p<O.OOl) than El

Cardon and Pardito (Table 3). The ANOV A was not powerful enough to

detect a difference between El Cardon and Pardito (multiple comparison:

p=0.773; minimum detectable difference 0.21). However, the difference

between the means for El Cardon and Pardito was small (Table 3).

Available substrate for covering differed among sites. Rhodoliths at El

Cardon were generally smaller and weighed less than the rhodoliths and

coral fragments at Diguet. Dense rock and coral fragments were available at

Pardito.

Shells were the largest fraction of covering material at El Cardon,

followed by live rhodoliths and Caulerpa sertularioides (Table 4). The

electivity indices indicate that shell and sponge were positively selected.

More podia were attached to shell material than other material of the same

size. Dead rhodoliths were selected against more than live rhodoliths.

Live rhodoliths and coral rubble were the most numerous covering

material at Diguet. Sponges held by urchins were heavy/ weighing from 14.4-

105.4 g. The percent cover and electivity indices at this site indicate that

individuals picked up all available heavy material.

27

Shell and rock were the most common covering material on the

urchins sampled on rock and on sand next to rock at Pardito. Rocks small

enough to be picked up by podia were rare. Individuals observed on rock far

off the bottom usually held only small quantities of shell and rock. Those

among live and dead Pocillopora spp. held a high percentage of coral rubble.

Qualitative observations indicated that the length of time that

individual covering material was held varied. Urchins with easily

recognizable material carried it for two weeks without dropping it. However1

some individuals dropped and replaced some material within the same time

period. The composition of covering material at El Cardon changed between

March and November 1996. A higher percent of live rhodoliths was held in

March 1996, while shell cover was greater in November 1996 (D. James, pers.

obs.), suggesting covering material is probably not held on the order of

months. Large movements may precipitate the partial dropping of covering

material, as tagged individuals at Diguet were sometimes observed leaving

behind some of their covering when moving great distances.

The importance of covering material to the urchins was noted by the

response of their pedicellaria to material removal. Pedicellaria generally did

not attack hands when disturbed except when material was pulled off. More

pedicellaria attached to hands when handling urchins at Diguet compared to

El Cardon.

28

DISCUSSION

Toxopneustes roseus did not occur in high densities in the rhodolith

beds. However, urchins were usually aggregated and often formed high

density aggregations within portions of a rhodolith bed. Large, high density

aggregations were formed at Manto de Pepe, a rhodolith bed off Isla San Jose

(M, Foster, pers. comm.) and in both rocky and coral habitats at Isla Pardito (D.

James, pers. obs,), Toxopneustes roseus was not seen in the sandy and rocky

areas surrounding the rhodolith beds at El Cardon, Diguet, Manto de James,

and Punta Bajo,

Urchins are known to aggregate where food is abundant (Russo 1979;

Vadas et aL 1986), The aggregations of urchins in the rhodolith beds may

have been related to algal abundance, Individuals at Diguet occurred in the

areas with the highest rhodolith densities, and may be responding to

available food and protection from surge. The cause of aggregations at El

Cardon was not clear. The seasonal change in depth may have been due to an

attraction to C sertularioides as covering material and as a barrier that slowed

water movement.

Individuals may aggregate in response to spawning behavior.

monthly reproductive rhythm was found in Centrostephanus coronatus;

which doesn't aggregate (Pearse 1972). Toxopneustes roseus has been

observed spawning or in a very gravid condition during different times of the

29

year, and may have a similar spawning pattern which leads to aggregations.

Food availability in rhodolith beds is constant and may be high enough to

permit monthly spawning.

The lack of small urchins (refer back to size-frequency data) may be

caused by episodic recruitment. Some urchins recruit at very low levels

during most years (Pearse and Hines 1979). Presettlement and postsettlement

mortality may be high for roseus. It is also possible that larval transport

caused urchins to settle in other areas. Individuals smaller than one

centimeter were observed between rhodolith branches of partially buried

rhodoliths in the San Lorenzo Channel off La Paz (D. Steller, pers. comm.).

Recently settled T. roseus were observed buried in rocky rubble (H. Reyes1

pers. comm.).

Toxopneustes roseus fed almost exclusively on nongeniculate coralline

algae in rhodolith beds. None of the other available algae were preferred.

This pattern differs from the few studies of other urchins that live in

rhodolith beds, where only the juveniles were found to eat the coralline algae

(Freiwald 1993; Guillou and Michel 1993).

It is not clear why T. roseus did not eat other edible algae when

encountered. l\1any urchins eat Enteromorpha and Ulva (Kitching and

Ebling 1961; Ogden et al. 1989), yet T. roseus did not eat the former at Diguet,

or Ulva sp., Sargassum sp. or Padina sp. at a rocky site near La Paz where these

algae were extremely abundant (M. Foster, pers. comm.). Most eat

30

coralline algae only as a supplement to their diet or when preferred algae are

unavailable (Vance 1979; Chiu 1985; Harrold and Reed 1985; Kenner 1992).

The diet of T. roseus is also unique as few other urchins specialize on a single

plant type (Kempf 1962; Ogden 1976; Vadas 1977; Larson et al. 1980; Ogden et

al. 1989). Some of the available algae may have been avoided because of

chemical defenses. Caulerpa sertularioides contains caulerpin and complex

terpenoids and is resistant to herbivory (Norris and Fenical 1982; Paul et al.

1987). Sargassum spp. may contain polyphenolics (Norris and Fenical 1982)

but are not avoided by all urchins (Ogden 1976; Shunula and Ndibalema

1986).

Urchins at Pardito, the rocky site without a rhodolith bed, appeared to

also select nongeniculate coralline algae in their diet. While Enteromorpha

intestinalis and Sphacelaria didichotoma made up a large part of their diet,

these algae grew on the coralline algae, and thus may represent incidental

consumption. Hawkins (1981) found that the absorption efficiency of

Diadema antillarurn was higher for nongeniculate coralline algae than

endolithic filamentous and epipelic algae. If this is also true for T. roseus,

then it may have been more advantageous for them to select the coralline

algae at Pardito.

Toxopneustes roseus contributed a large amount of carbonate sediment

as a result of their feeding on rhodoliths. Urchins at El Cardon and Diguet

produced 3.87 and 7.96 g of carbonate/individual/ day. Glynn (1988)

31

determined individuals in rubble covered with nongeniculate coralline

algae and dead pocilloporid coral generated 1.57 g carbonate/individual/ day.

On an individual basis, carbonate production at El Cardon and Diguet was

much higher than values reported for Caribbean urchins and parrotfish,

which are well known sediment producers on tropical reefs. On a daily

individual basis, Diadema antillarum created from 0.63-1.44 g of new

carbonate and the parrotfish Scarus croicensis produced 3.0 g new carbonate

(Ogden 1977; Scoffin et al. 1980). More carbonate was ingested daily but 20-

50% of this was reworked or "old" carbonate (Hunter 1977; Ogden 1977;

Scoffin et al. 1980). Due to higher densities, Diadema antillarum produced

more new carbonate/m2 /year (4.6-5.3 kg), while Sparisoma viride and S.

croicensis produced 0.03 and 0.49 kg new carbonate/m2 /year, respectively.

While Toxopneustes roseus in rhodolith beds did not generate as much

carbonate per area (an estimated 51-74 g carbonate/m2/year), their

contribution is still large over time.

Toxopneustes roseus feeding rates may exceed the growth rates of the

rhodoliths. The growth rates of the rhodoliths Lithothamnion corallinoides

and Phymatolithon calcareum in Ireland were 88 and 249 g

carbonate/m2 /year (Bosence 1980). Lithophyllum incrustans, a nongeniculate

coralline algae in south-west Wales, had a growth rate of 379 g

carbonate/m2 /year (Edyvean and Ford 1987). However, coralline algal growth

rates vary seasonally and are higher in warmer water, such as Baja

California (Adey and McKibbin 1970). Rhodoliths in Baja California may

grow faster than these reported values.

32

Their feeding and movement rates suggest it was unlikely that urchins

ate entire rhodoliths. By eating only branch tips, most of the thallus is left

intact. Rhodolith fragments (2-10 mm) were also dropped during feeding.

Such fragments are likely capable of vegetative regrowth as 1-2 mm pieces of

rhodolith with pigmentation on the entire surface were observed in the field.

Damage to apices of rhodoliths can alter branching patterns (Bosence 1983;

Foster et al. 1997). Branching and growth may therefore be altered by T.

roseus grazing, and the potential effect of urchin herbivory on rhodolith

shape should be considered when interpreting factors that may have shaped

fossil and modern rhodoliths.

Clear bands in urchin jaws were found to be formed during periods of

slow growth caused by food deprivation and opaque bands formed during

rapid growth periods (Pearse and Pearse 1975). The lack of clear bands in the

urchin jaws suggests that a diet of coralline algae fulfills dietary requirements.

Toxopneustes roseus may grow at a constant rate.

The jaws at Pardito were relatively larger than at Diguet, further

suggesting specialization on coralline algae as these plants were less abundant

and urchin density was higher at Pardito. These larger jaw sizes in areas of

less available algae and higher urchin density are consistent with those

previously reported (Ebert 1980; Black et al. 1982; Black et al. 1984; Edwards

and Ebert 1991; Levitan 1991). Larger jaws may also facilitate scraping

coralline algae off rocks.

33

The difference in relative jaw sizes between El Cardon and Diguet may

be related to the method of feeding on nongeniculate coralline algae. Urchins

at El Cardon had more rhodolith bits in their guts while individuals at Diguet

had more scraped pieces of coralline algae. Larger lanterns may have more

strength, and additional strength may be necessary to constantly bite off pieces

of rhodolith. The similarity in relative jaw sizes between El Cardon and

Pardito may also be due to large jaws being necessary at El Cardon.

Although the test diameter and jaw length slopes of El Cardon and

Pardito were not significantly different, the slope for El Cardon suggests that

as individuals at this site get larger, their jaws will be relatively smaller than

at Pardito. This is also indicated by the larger urchins at El Cardon having

smaller lanterns than at Pardito.

Movement and covering material did not appear to be affected by

predation. Predation was never observed at El Cardon, and tests were not

destroyed or transported out of the area for at least 8 months. Evidence of

predation would most likely have been seen if it had occurred. There were

very few potential predators at Diguet (several fish in the family Balistidae)

and only one test was found with a molluscan drill hole. Potential fish

predators were very abundant at Pardito (Scaridae, Balistidae and Labridae),

but individuals with very little covering were commonly exposed on rocks

34

there. Cracked tests were never seen but occasional tests with holes drilled

them were observed. Local fishermen reported that octopus occasionally prey

on T. roseus. The well developed globiferous pedicellaria of T. roseus contain

venom which may deter most predators (Halstead 1988).

Toxopneustes roseus was very mobile. However, while there is an

inverse relationship between food availability and movement for many

urchins (Mattison et al. 1977; Russo 1979; Harrold and Reed 1985; Andrew and

Stocker 1986; Laur et al. 1986), this relationship clearly does not apply forT.

roseus. Urchins were surrounded by food in rhodolith beds, were always on

rhodoliths, and often carrying them. A consequence of their large

movements is that individuals did not remain in one area, which may

prevent all of the rhodoliths in a small area from being severely grazed.

Individuals may occupy different areas of a rhodolith bed over time.

During one observation at El Cardon in March 1997, only one dead and two

live tagged urchins were seen in the study area. It is unlikely that these

missing urchins died in the vicinity as old tagged tests persisted in the area

at least 8 months. The missing individuals probably moved out of the area.

Urchin densities appeared the same as in November 1996 and were most

likely similar due to new urchins moving into the area.

Toxopneustes roseus may move between rhodolith beds. At Requeson,

a rhodolith bed 5 km away from El Cardon, extensive searching by many

divers found that T. roseus was almost entirely absent in l\!Iarch 1996. Adult

35

urchin densities were similar at El Cardon and Requeson by November 1996.

It was unlikely that individuals were buried deep enough to be unnoticeable;

at Requeson, fine, anoxic sediment is present from several centimeters below

the top surface of rhodoliths at the deep margin of the rhodolith bed to 15-20

centimeters below the surface in the middle of the bed (Foster et al. 1997).

Toxopneustes roseus is probably not capable of surviving buried in fine,

anoxic sediment. The nearest rhodolith bed was 0.4 km away, suggesting that

urchins at Requeson moved a great distance on sand to get there. Individuals

were seen moving across large stretches of sand at Manto de James.

The diel movement at Diguet may be related to surge. There was

generally more wind and surge during the day at this site (D. James, pers.

obs.). Surge has been shown to decrease movement (Lees and Carter 1972;

Ogden et al. 1973; Lissner 1980; Tertschnig 1989), and Dance (1987) observed

that movement was negatively correlated with wind speed. The amount of

sand may also influence the timing of movements. Laur et al. (1986) found

that urchins moved slower in sand. When surge was present1 T. roseus was

more prone to being tumbled. Aggregations ofT. roseus occurred at Diguet in

areas of the highest rhodolith densities. These rhodoliths may have provided

protection from surge when individuals were buried in the sand, covered

with rhodoliths.

Surge also influences how much material is carried. Urchins at Diguet

were exposed to the most surge during this study. Rhodoliths at Diguet were

36

significantly larger than rhodoliths in Bahia Concepcion and lateral fusion

branches increased as depth decreased (Foster et al. 1997). Bosence (1983)

found that densely branched, lateral growing rhodoliths occur in high energy

areas. The amount and weight of covering material held by individuals at

Diguet would have increased their total weight. This material may have

helped anchor them on and around the sand, which covered 59.5±3.0

(mean±SE) percent of the bottom around the collected urchins. Covering

material may serve as a stabilizing force, as Lees and Carter (1972) found that

Lytechinus anamesus increased their covering during surge exposure, and

reduced it when surge ended and urchin movement increased. Individuals

at El Cardon and Pardito were exposed to less water motion and had similar

covering material/body weight ratios. Urchins at Pardito held less material

that weighed more than material at El Cardon, which resulted in similar

ratios.

Flat, stable substrate may also reduce covering material. Individuals at

Pardito on rocks in the shallowest water often had the least amount of

covering material, perhaps because there was more rock for the podia to

attach to and secure the urchin.

Toxopneustes roseus caused extensive bioturbation of rhodoliths.

Their feeding activity moved and turned rhodoliths, and plants were also

moved about when urchins picked them up or grabbed nearby ones.

37

Bioturbation resulted when covering material changed seasonally, and

rhodoliths were probably dropped and replaced over shorter time intervals.

Movement activity also resulted in bioturbation. Individuals often

plowed visible trails through the rhodoliths and frequently dug themselves

into the bed, creating pits up to 10 em deep. This activity is similar to that of

T. roseus in Panama which bury themselves in rubble during the day, and

emerge at night, extensively mixing the uppermost 10 em of substrate (Glynn

and Wellington 1983). Movement over rhodoliths no doubt causes

rhodoliths to shift their position, and the extent of movement suggests this

occurs over large areas. Bioturbation by urchins may be more important in

rhodolith beds at greater depths as Steller and Foster (1995) found that

rhodolith movement from water motion declined with increasing depth in a

rhodolith bed in Bahia Concepcion, Mexico.

Bioturbation also affected mats of the green alga Caulerpa

sertularioides. Urchins moved underneath the alga, plowing through the

rhodoliths and attached rhizomes. Caulerpa sertularioides appeared to be

uprooted and individual urchins also removed pieces of the plant for

covering material. Williams et al. (1985) report that the growth rates and

biomass accumulation of C. sertularioides were negatively affected by

bioturbation.

Rhodolith beds have a diverse assemblage infauna, epifauna and

cryptofauna (Steller 1993). While T. roseus may not be critical to bed

38

formation, their bioturbation may help maintain the integrity of the diverse

rhodolith community and the persistence of the beds. These positive effects

may more than offset negative effects from high feeding rates at high

densities. However, feeding impacts appear to be localized due to their large

movements.

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46

47

Table 1. Density (mean #±SE/20m2; n=201) of Toxopneustes roseus and algal bottom cover (mean %±SE; n=90) at El Cardon in November 1996. Data are untransformed. Ip = standardized Morisita index of dispersion ( -1 = maximum uniformity; 0 = randomness; + 1 = maximum aggregation; 95% confidence limits above 0.5 and below -0.5). P = probability of being statistically different than a random distribution using Morisita's index of dispersion (Id) and a chi-square distribution. Algal cover data are from the area of the rhodolith bed where most of the urchins occurred (see text).

Deep Middle Shallow

Urchin Density

0.4±0.08 1.0±0.25 0.8±0.20

Ip

0.02 0.52 0.52

p

0.453 <0.001 <0.001

Live Rhodolith

0.22±0.03 0.31±0.04 0.45±0.03

Caulerpa

0.16±0.04 0.28±0.04 0.30±0.04

48

Table 2. Movement rates and distances of Toxopneustes roseus at El Cardon and Diguet (mean±SE). Data are untransformed. Distances are standardized to 24 hours. El Cardon: urchins used= 48; movement data n = 216. Diguet: urchins used = 47; movement data n = 159.

El Cardon Diguet

Day Night 24 Hour Day Night 24 Hour Rate, Rate, Distance, Rate, Rate, Distance, cm/hr cm/hr em cm/hr cm/hr em

7.6±0.7 6.6±0.8 165.6±15.2 7.8±1.1 11.7±1.0 249.0±20.8

49

Table 3. Covering material and Cover Weight/Body Weight (n=20; mean±SE) of Toxopneustes roseus at El Cardon in November 1996, Diguet, and Pardito.

Percent Cover

Cardon Diguet Pardido

68.1±5.5 92.3±4.9 38.1±4.0

Cover Weight/ Body Weight

Cardon Diguet Pardito

0.18±0.02 0.52±0.03 0.21±0.03

50

Table 4. Covering material of Toxopneustes roseus at El Cardon in November 1996, Diguet and Pardito (%, n=20). Caulerpa =C. sertularioides. At El Cardon, urchin covering material Other = Spyridia filamentosa, Sargassum herporhizum and worm tubes; all were rare; substrate Other = S. filamentosa. At Pardito, Other = dead rhodoliths, bryozoans, urchin test and worm tubes.

El Cardon

Covering Material Substrate Electivity Mean± SE Mean± SE Index, Ei

Live Rhodolith 12.3±2.6 38.5±4.3 -0.52 Dead Rhodolith 8.0±1.3 53.0±4.1 -0.74 Shell 28.5±4.3 4.5±1.7 0.73 Sponge 6.5±1.8 5.0±2.1 0.13 Caulerpa 12.0±2.4 32.0±4.8 -0.46 Other 1.0±0.7 5.5±1.5 -0.71

Diguet

Covering Material Substrate Electivity Mean± SE Mean± SE Index, Ei

Live Rhodolith 47.8±6.2 35.5±2.8 0.15 Dead Rhodolith 9.9±1.5 0.5±0.5 0.90 Coral Rubble 20.6±3.9 3.5±1.3 0.71 Shell 1.4±0.6 1.5±0.8 -0.05 Sponge 2.2±1.4 0.5±0.5 0.62

Pardi do

Covering Material Substrate Electivity Mean± SE Mean± SE Index, Ei

Small Rock 10.7±2.9 0.0±0.0 1.00 Coral Rubble 2.8±1.0 2.5±1.2 Shell 21.3±2.0 1.0±0.7 0.91 Other 3.2±1.5 0.0±0.0 1.00

51

Figure 1. Location of study sites Baja California Sur, Mexico

12 March 1996

10

8

6

4

2

0

12

November 1996 10

8

6

4

2

60 65 70 75 80 85 90 95 100 105 110

Test Diameter, mm

Figure 2. Size-frequency distribution of Toxopneustes roseus at El Cardon in March 1996 and November 1996. March: n = 47; November: n = 144

52

53

6

4

2

o~--~~~~~~~~~~~~~~~~~~~~~~~

75 80 85 90 95 100 105 110 115 120

Test Diameter, mm

Figure 3. Size-frequency distribution of Toxopneustes roseus at Diguet in December 1996 (n = 102)

54

0 Cardon 27 Diguet

25

s 23 s ,..c::' D ~

gf 21

ClJ ~ !'?

"' 19

~ ~

17

15~--------L----------------F------------60

Figure 4. Jaw (demipyramid) length vs. test diameter of Toxopneustes roseus at Cardon, Diguet, and Pardito. Regression equations: Cardon= 9.83 + 0.12 9

Test; n = 21; r2 = 0.526; Diguet = -5.25 + 0.28 @ Test; n = 22; r2 = 0.838; Pardito =

3.41 + 0.21 e Test; n = 20; r2 = 0.830

APPENDIX

MATERIALS AND METHODS

Feeding Preferences

Feeding preference experiments were done in the field at El Cardon

November 1996 and at Diguet in December 1996 (see Feeding Preferences).

Preference was based on the amount of rhodoliths eaten.

55

Three treatments were used for each replicate. Treatments were: a

control of rhodoliths and other algae alone (n=3), one urchin with rhodoliths

alone (n=3), and one urchin with rhodoliths and other algae alone (n=3).

Algae were cleaned of obvious debris and herbivores, blotted dry and

weighed. Approximately 32 g of rhodoliths and 11 g of Caulerpa

sertularioides were used at El Cardon and approximately 47 g of rhodoliths,

0.2 g of Berkeleya hyalina and 0.4 g of Enteromorpha intestinalis were used at

Diguet. The experiment was repeated three times at El Cardon and twice at

Diguet. Urchins used were approximately the same size and were pre-starved

for 24 hours in the containers with no algae. Individuals were left each

treatment for 48 hours and then the final weight of algae was determined.

Differences in rhodolith weights among treatments were determined

by ANOV As. Multiple comparisons were done with Tukey' s test.

56

RESULTS

Feeding Preferences

The mean difference in rhodoliths eaten between the rhodoliths only

and rhodoliths and Caulerpa sertularioides treatments was only 1.33 g over 48

hours at El Cardon (Appendix Table 1). There was a significant difference in

changes in rhodolith weights in feeding preference treatments (ANOV A:

F=16.888, df=2, n=27, p<O.OOl). The control was significantly different than

both treatments (multiple comparisons: p<0.001 for control vs. rhodoliths

only; p=0.002 for control vs. rhodoliths and C. sertularioides). The amount of

rhodoliths eaten was not significantly different between the two treatments

(multiple comparison: p=0.194). The ANOVA was only powerful enough to

detect a difference of 2.42 g. However, the actual difference of 1.33 g is small

compared to 7.74 (the amount eaten 48 hours based on fecal production).

The difference in the mean amounts of rhodoliths eaten may be an

artifact of the urchin's need to cover themselves. Most of the individuals

used much of the available algae in the containers as covering material. This

activity, as well as the artificial setting of a plastic tub, may have caused a

reduction in their feeding rate.

At Diguet, the mean difference in rhodoliths eaten between the

rhodoliths only and rhodoliths with other algae treatments was only 1.17 g

57

over 48 hours (Appendix Table 1). There was not a significant difference

between treatments (ANOV A: F=3.270, df=2, n=18, p=0.066). The ANOV A

was only powerful enough to detect a 1.45 g difference. Compared to 16.38 g

(the amount eaten in 48 hours based on fecal production), a difference of

1.17 g is quite small. The lack of a difference between the control and other

treatments was probably due to the loss of sand in the rhodoliths. Sand was

stuck in between rhodolith branches and was loosened by the slight

movements of the containers in the surge.

58

Appendix Table 1. Amount of rhodoliths eaten by Toxopneustes roseus at El Cardon and Diguet (mean±SE). Sample size: El Cardon= 9; Diguet = 6. Other algae = Caulerpa sertularioides (El Cardon); Berkeleya hyalina and Enteromorpha intestinalis (Diguet).

El Cardon Diguet

Rhodoliths Only, g

4.04±0.48 4.63±1.08

Rhodolith Control: 0.19±0.49 (El Cardon); -1.63±0.26 (Diguet)

Rhodoliths and Other algae, g

2.71±0.60 3.47±0.93