Hydrobiologia 204/205 : 331-338, 1990 .S. C. Lindstrom and P. W. Gabrielson (eds), Thirteenth International Seaweed Symposium .

331© 1990 Kluwer Academic Publishers . Printed in Belgium .

Seasonality of standing crop of a Sargassum (Fucales, Phaeophyta) bedin Bolinao, Pangasinan, Philippines

Gavino C. Trono, Jr. & Arturo 0. LluismaMarine Science Institute, College of Science, University of the Philippines at Quezon City, Philippines

Key words: biology, phenology, Philippines, Sargassum, seaweed, standing crop

Abstract

The seasonality of standing crop of a Sargassum bed was investigated by conducting monthly samplingfrom February 1988 to July 1989 . Environmental parameters of water movement, salinity, number ofdaytime minus tides, and water temperature were also measured . An intra-annual pattern of variationin standing crop of Sargassum crassifolium, S . cristaefolium, S. oligocystum, and S . polycystum wasobserved. Standing crop was generally lowest in February, March, April, or May, and highest inNovember through January . Sargassum accounted for about 35 to 85% of the monthly algal standingcrop of the bed, and the observed variation in overall standing crop of the bed generally reflected thestanding crop of Sargassum . The seasonality of the standing crops of the associated algal divisions alsofollowed an annual cycle, but their maximum and minimum standing crops did not coincide with thoseof Sargassum . Individually, as well as collectively, the standing crops of the Sargassum spp . were poorlycorrelated with the environmental factors observed .

Introduction

The increasing commercial harvesting of Sargas-sum as raw material in the manufacture ofseaweed meal is reflected in the significantupward trend in the export of this product to othercountries during the last few years . In 1987, some4,188 metric tonnes of Sargassum meal worth P 10million (about US$476,000) were exported(Bureau of Fisheries & Aquatic Resources Statis-tics). However, no data on the amount ofSargassum utilized locally in the manufacture ofanimal feeds are available . The gathering ofSargassum currently is concentrated in centralVisayas and northern Mindanao, where fisher-men claim that the unregulated gathering ofSargassum has resulted in the destruction of beds,

which in turn has caused the decline of fish stocksin the area .

Herein, we report on one aspect of studies weare pursuing to gather basic information on thebiology and phenology of Sargassum beds to serveas a basis for formulating a management schemefor the rational utilization of the resource .

Materials and methods

The study was conducted from February 1988 toJuly 1989. The site is located on Bolinao at thereef edge about 1.5 km north-northeast of the isletof Dewey on Santiago Island (Fig . 1). TheSargassum bed extends about 100 m landwardfrom the reef crest and more than 200 m seaward .

332

CAPEBOLINAO

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UP MSIKilometers

Marine6 Laboratory

119,'54'

5,6'

The rocky-coral substratum, with coarse sandand coral rubble, gently slopes seaward . Theseaward limit of the bed is located in about 8 to11 m of water where Dictyopteris sp. co-domi-nates . The study site is exposed to strong wavesand currents during the north-east (October toMarch) and south-west (June to September)monsoon seasons.

A permanent reference point (wooden post)was established at the reef crest. A calibrated linewas tied to the post at the reference point andextended 100 m seaward across the shallow sub-tidal portion of the bed (wave-exposed) . A secondcalibrated line was extended from the referencepoint 100 m landward across the intertidalportion of the bed (protected) . The lines were

Fig . 1 . Location of the study site .

5,8'

permanent . A portion of the intertidal bed isexposed during extreme low tides, but is con-stantly wetted by waves .

A pair of modified belt transects positionedparallel to the two sides of the calibrated lines atthe intertidal and subtidal portions of the bedwere sampled using 0 .25 m2 metal quadrats . Themetal quadrats were randomly dropped at 10-mintervals along the belt transects using the lines asguide. A total of 42 biomass samples were col-lected monthly . All algae inside the quadrat werecollected and sorted, and the wet weights of all thespecies in the samples were recorded . The spatialand temporal distributions of the Sargassum spp .and associated species were analyzed using thedata on biomass. These were correlated, using

Correlation Analysis (a subprogram of MICRO-STAT*), with the monthly data on water move-ment (expressed in diffusion index factor, DF,values, Doty, 1971 a), salinity, absolute number ofdaytime minus tides per month (i .e . the number ofdays in a month when lower low water is lowerthan the mean lower low water between 0600 and1800 h), and water temperature . Daytime minustides were taken into account because the occur-rence of such tides often results in partial to com-plete exposure to air of the intertidal portion of thebed and exposure to very shallow water of thesubtidal portion .

Results

Species composition and the contributions of the dif-ferent plant groups to total biomass

The bed was generally dominated throughout theyear by four species of Sargassum, S. crassifoliumJ . Agardh, S. cristaefolium C . Agardh, S. oligo-cystum Montagne, and S. polycystum C . Agardh(Fig. 2). Associated with Sargassum spp . were 73species of macrobenthic algae : 30 Chlorophyta,29 Rhodophyta, and 14 Phaeophyta, unidentifiedfilamentous Cyanophyta, and three species ofseagrasses. The latter were recorded only at theinnermost limit of the bed .

Fig. 2 shows the monthly contributions of thedifferent plant groups to total standing crop .Standing crop ranged from 510 to 2,129 g wetwt M-2 and averaged 1,192 g wet wt M -2 . Thefour Sargassum species accounted for about 61of the average. During the months of Novemberthrough January, Sargassum spp. attained anaverage of 1,508 g wet wt m _ 2, or about 83 % oftotal standing crop . The other phaeophytanspecies contributed 25% , Chlorophyta 6%,Rhodophyta 6 % and seagrasses 1 % to totalstanding crop . The Cyanophyta contributed aninsignificant amount .

* MICRO STAT is a statistical software package, Copyright1978-85 by Ecosoft, Inc.

Standing crop seasonality

For Sargassum, lowest standing crops wereobserved in March and April of 1988 and inMarch through May of 1989, and the highest fromNovember 1988 through January 1989 (Fig . 2) .Low standing crop was also observed in Junewhen rough sea conditions caused by a passingtyphoon removed a large amount of biomass . InOctober, only the inner protected portion of thebed was sampled due to very rough sea conditionsalso caused by a typhoon . Since Sargassumaccounted for about 35 % to 85 % of the monthlytotal standing crop in the bed, the seasonal var-iation of the mean total algal standing crop merelyreflected the seasonal variation of the meanSargassum standing crop .

The seasonality of the standing crops of theindividual Sargassum species followed the samegeneral trend as that of total Sargassum standingcrop, with lowest values in March, April, and/orMay, gradually increasing in the succeedingmonths, attaining highest values in Novemberand/or December . Sargassum crassifolium andS. polycystum attained highest standing crops inDecember (647 and 447 g wet wt m -2, respec-tively), and S. cristaefolium and S. oligocystum inNovember (430 and 282 g wet wt m-', respec-tively) .

The associated plant groups (Fig . 2) had highstanding crops from February to May and lowstanding crops from June to January .

Spatial distribution of biomass

Fig. 3 shows the mean total, as well as the meanfor Sargassum spp ., of monthly standing crop forthe inner and outer portions of the bed . Onaverage, the mean total biomass recorded for theouter wave-exposed (subtidal) portion of the bedwas slightly higher (1,261 g wet wt m -2) than forthe inner protected (intertidal) part of the bed(1,156 g wet wt m - 2) . Standing crop in the outerportion was greater than in the inner portion dur-ing November through January, the months ofhighest standing crop in the bed . Approximately

3 33

334

700m

600

500

400

300

200

100

0

- S. crassifollium S. polycystum

S . cristaefollium. . . S. oligocystum

F M A M J J A S O N D J F M A M J J88

89

Fig. 2. Monthly mean standing crop of the different Sargassum species and algal divisions

∎1 Sargassum (inner)M Others (inner)M Saraassum(outer)ED Others(outer)

FMAM J JASONDJFMAM JJ88

89Fig. 3 . Monthly mean standing crop of algal divisions in the inner and outer portions of the bed .

80% of the total biomass sampled in the subtidal

showed high and significant correlations withportion during this period was contributed by

some of the environmental factors . The specificSargassum spp., particularly S. crassifolium and

correlations with environmental factors variedS. cristaefolium, which were more abundant in theouter portion of the bed . On the other hand, rela-tively higher standing crops were recorded in theinner portion of the bed from May to Septemberin

I.1988 . Sargassum standing crop in this portion

40DAY-MINUS TIDES

35

of the bed consisted chiefly of S. polycystum and

35

WATER MOVEMENT30

30 1

4S. oligocystum .

25

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25 O mThe associated algal groups recorded generally

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higher standing crops in the inner portion of the

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From February, 1988 to July, 1989, algal species

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average of about 594 g wet wt M-2 (50 .4 %) to the

36-

X35N

30mean total standing crop in the inner portion of

34 \

1r\\the bed and only 276 g wet wt M-2 (24.2 %) in the

33

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,,

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Correlation with environmental factors

Individually, as well as collectively, Sargassumspp. showed insignificant correlations (Table 1) Fig. 4. Monthly data on water movement (± std. deviation),with the environmental factors (Fig . 4). Some of water temperature, absolute number of day minus tides, andthe more abundant associated species, however,

salinity (± std . deviation).

29

28----TEMPERATURE

SALINITYJ FM AM J J A SON DJ FM AM J J88

89

5

0

335

3 3 6

Table 1 . Correlation coefficients of standing crops of the most abundant species in each division and of whole divisions with

* p < 0 .05 .** p < 0 .01 .a Sargassum excluded.

even within divisions . Halimeda opuntia (L.)Lamouroux andH. macroloba Decaisne, the mostabundant chlorophytes, showed significant corre-lations with temperature and salinity, respec-tively, whereas the less abundant Caulerparacemosa (Forsskaal) J . Agardh and Valoniaaegagropila C. Agardh did not show significantcorrelations with any environmental factors .However, chlorophytes as a whole were not sig-

nificantly correlated with any of the environ-mental factors . Dictyota cervicornis Kuetzing andHormophysa cuneiformis (J. F. Gmelin) Silvashowed significant correlations with daytimeminus tides, whereas Turbinaria conoides showedsignificant correlations with water temperature,daytime minus tides and salinity . The rest of themore abundant phaeophytes, including Sargas-sum spp., showed insignificant correlations . As a

physical parameters .

Species Meancontributionto division'smonthlystanding crop,in

Watertemperature(°C)

Salinity Daytimeminustides

Watermovement(DF)

ChlorophytaCaulerpa racemosa (Forsskaal) J . Agardh 14.12 -0.50 0 .45 -0.17 0.01Halimeda macroloba Descaisne 6.32 0.37 - 0.63 * 0.46 -0.40H. opuntia (L.) Lamouroux 46.20 0.68* -0.81** -0.34 -0.47Valonia aegagropila C. Agardh 6.38 -0.33 0 .24 0 .24 0 .00

PhaeophytaDictyota cervicornis Kuetzing 9.13' 0 .27 0.22 - 0 .53 * 0 .46Hormophysa cuneiformis (J . F . Gmelin) Silva 30 .38' -0.20 0.29 0 .67** 0 .17Padina spp . 8 .37' -0.36 0.51 -0.30 0 .35Sargassum crassifolium J. Agardh -0.19 0.27 0 .26 0 .47S. cristaefolium C . Agardh 0.20 -0.14 -0.26 0 .27S. oligocystum Montagne 0.23 -0.24 0.00 0 .28S. polycystum C. Agardh -0.07 -0.14 0.27 0 .17Turbinaria conoides (J. Agardh) Kuetzing 29.24 a - 0.75 ** 0 .61 * 0.69** 0 .13T. ornata (Turner) J. Agardh 15 .41 a -0.55 0 .32 0.18 0 .30

RhodophytaActinotrichia fragilis (Forsskaal) Boergesen 12 .23 -0.45 0 .61* -0.17 0 .21Amphiroa foliacea Lamouroux 27.01 -0.55 0 .73 ** 0 .35 0 .58A . fragilissima (L.) Lamouroux 16 .46 0.65* -0.63* -0.50 -0.15Mastophora rosea (C . Agardh) Setchell 5.39 -0.24 0 .42 -0.33 0 .16

Chlorophyta 5 .68 0.32 -0.22 0.04 -0.14Phaeophyta (excluding Sargassum) 25.34 - 0.75 ** 0.87** 0.59** 0 .47Sargassum 62.36 -0.04 0 .08 0 .34 0 .43Rhodophyta 5 .55 -0.41 0 .60 * 0 .23 0 .32Total (incl. sea grasses) 100 .00 -0.24 0 .33 0.59** 0.60*

whole, however, Phaeophyta showed significantcorrelations with water temperature, salinity, anddaytime minus tides. Rhodophyta showed a sig-nificant correlation only with salinity althoughAmphiroa foliacea and A. fragilissima, two of themore abundant rhodophytes, showed significantcorrelations with water movement and tempera-ture, respectively, and with salinity . Mastophorarosea was insignificantly correlated with theenvironmental factors measured .

Discussion

In the present studies, temporal variation in thestanding crop of the Sargassum bed follows anannual pattern if no unusually rough seas (such asones generated by typhoons) occur . For Sargas-sum, the lowest standing crops were observed inFebruary, March, and/or April, and the highestduring November, December, and January. Theoccurrence of the maximum standing crop of Sar-gassum coincided with the occurrence of low tem-peratures, which normally prevail from Novemberto January . This observation is in agreement withthe observations of DeWreede (1976) andMcCourt (1984) that tropical Sargassum tends tobe most abundant during the cooler months of theyear. After this period of maximum standing crop,a rather abrupt reduction follows, indicatingSargassum dieback. During January or February,Sargassum spp . undergo senescence, and growthfrom new recruits begins in March through May .The only exception seemed to be S. polycystum,which remained vegetative throughout the year byregenerating new shoots from persistent rhizoidalholdfasts . Data obtained during the same periodshowed that Sargassum spp., except S. poly-cystum, attained highest fertility during January orFebruary, before the sudden reduction in standingcrop .

The low standing crops observed in June andOctober of 1988 were believed to be due to theoccurrence of unusually rough seas during thesemonths. Had these seas not occurred, the trend instanding crop seasonality would have beenapproximately monomodal (i .e . with only one

33 7

high point) for the year . The data gathered in 1989appear to support this supposition. Storms, how-ever, are acknowledged to significantly affectstanding crop and could influence algal biomassmore strongly than the seasonal factors such aslight and temperature (de Ruyter van Steveninck& Breeman, 1987 ; Doty, 1971b) . Sargassum,being large, frondose, and buoyant, is liable to getdetached from the substratum or from its holdfastby unusually strong water motion . In the Philip-pines, the tropical cyclone season is from Junethrough December (Parong et al., 1985), andrough sea conditions were observed in the areaduring these months even when storms did notdirectly pass over the area . In no month, however,was there a complete disappearance of any Sar-gassum species, even S. cristaefolium, which wasreported to completely disappear from reefs inGuam during certain months (Tsuda, 1972) .

The temporal variation in the standing crop ofthe associated algal divisions followed a basicpattern, namely, attainment of highest standingbiomass in the early part of the year, followed bya somewhat abrupt reduction, then followed by agenerally gradual rise (e .g . non-SargassumPhaeophyta and Rhodophyta) or fall (e .g. Chloro-phyta). The pattern appears similar to that ofSargassum in being apparently annual, but gen-erally lagged two to three months behind Sargas-sum .The poor correlations between Sargassum

standing crop and the environmental factors sug-gest that Sargassum standing crop is not simplyrelated to the environmental factors considered inthis study. Poor correlations were also observedbetween standing crops of other, non-Sargassumspecies and environmental factors . Poor corre-lations could be due to natural lack of straight-forward relationships between particular speciesand environmental factors, interference betweenor among factors, interference by unpredictableevents such as unusually strong water motion, orimportance of factors other than those consideredin this study, such as biological interactions .Trono & Saraya (1987) observed that the abun-dance of associated species is significantlyinfluenced by the amount of cover provided by

338

large dominant benthic macrophytes such as Sar-gassum spp. and Hormophysa cuneiformis . Ante-cedent effects (Doty, 197lb) could likewise affectcorrelations between standing crops and environ-mental factors . A correlation between the stand-ing crop of a species and one or more environ-mental factors does not necessarily produce acorrelation between the standing crop of the divi-sion to which it belongs and the same environ-mental factors .

Acknowledgements

This study is part of a research grant to the seniorauthor by the Philippine Council for Aquatic andMarine Research and Development (PCAMRD) .The figures were made by Mr . R. Cada.

References

DeWreede, R. E., 1976 . The phenology of three species ofSargassum (Sargassaceae, Phaeophyta) in Hawaii . Phy-cologia 15 : 175-183 .

Doty, M . S ., 1971a. Measurement of water movement inreference to benthic algal growth . Bot. mar . 14 : 32-35 .

Doty, M. S ., 1971b . Antecedent event influence on benthicmarine algal standing crops in Hawaii . J. exp . mar . Biol.Ecol . 6 : 161-166 .

McCourt, R. M., 1984. Seasonal patterns of abundance, dis-tributions and phenology in relation to growth strategies ofthree Sargassum species . J. exp. mar. Biol. Ecol. 74 :141-156.

Parong, E. M ., N . C . Lomarda, & A . S . Santos, 1985 . Opera-tional Manual Tropical Cyclone Forecasting. PAGASA-National Weather Bureau, Quezon City .

Ruyter van Steveninck, E . D. de & A. M. Breeman, 1987.Population dynamics of a tropical intertidal and deepwater population of Sargassum polyceratium(Phaeophyceae). Aquat . Bot . 29 : 139-156 .

Tsuda, R. T ., 1972 . Morphological, zonational and seasonalstudies on two species of Sargassum on reefs of Guam .Proc . int. Seaweed Symp. 7 : 40-44 .

Trono, G. C., Jr . & A. Saraya, 1987. The structure anddistribution of macrobenthic algal communities on the reefof Santiago Island, Bolinao, Pangasinan . Phil. J . Sci.Monogr. 17 : 63-81 .