ENVIRONMENTAL AUDITING Evaluation of Tidal Marsh Restoration Comparison of Selected Macroinvertebrate Populations on a Restored Impounded Valley Marsh and an Unimpounded Valley Marsh within the Same Salt Marsh System in Connecticut, USA MYRON A. PECK PAUL E. FELL* ELIZABETH A. ALLEN JENNIFER A. GIEG CARL R. GUTHKE MICHAEL D, NEWKIRK Department of Zoology Connecticut College New London, Connecticut 06320, USA

ABSTRACT / Macroinvertebrates were examined on an impounded valley marsh in Stonington, Connecticut, that has changed from a Typha-dominated system to one with typical salt-marsh vegetation during 13 years following the reintroduction of tidal exchange. Animal populations on

this restored impounded marsh were evaluated by comparing them with populations on a nearby unimpounded valley marsh of roughly the same size.

Populations of the high marsh snail, Melampus bidentatus Say, were quantitatively sampled along transects that extended from the water-marsh edge to the upland; those of the ribbed mussel, Geukensia demissa Dillwyn, were sampled in low marsh areas on transects along the banks

of creeks and mosquito ditches. The occurrence of other marsh invertebrates also was documented, but their abundance was not measured. The mean density of Melampus was 332 + 39.6 SE/m 2 on the restored impounded marsh and 712 + 56.0 SE/m 2 on the unimpounded marsh. However, since snails were larger on the restored impounded marsh, the difference in snail biomass was less pronounced than the difference in snail density. Mean Melampus biomass was 4.96 +- 0.52 SE g dry wt/m 2 on the restored impounded marsh and 6.96 -+ 0.52 SE g dry wt/m 2 on the unimpounded marsh. On the two marshes, snail density and biomass varied in relation to plant cover and other factors. The density and biomass of Geukensia at the edge of the marsh were comparable on the restored impounded and unimpounded marshes. Mean mussel densities ranged from 80 to 240/m 2

and mean mussel biomass varied from 24.8-64.8 g dry wt/m 2 in different low marsh areas. In contrast, below the impoundment dike, mean Geukensia density was 1100 -+ 96.4 SE/m 2 and mean Geukensia biomass was 303.6 +- 33.28 SE g dry wt/m 2. A consideration of all available evidence leads to the conclusion that the impounded marsh is in an advanced phase of restoration.

Although there is a high concentration of coastal marsh restoration and creation sites in the northeast- ern United States, less research has been devoted to such activities in that region compared to the mid- Atlantic, Florida, Gulf of Mexico, and Pacific coasts (Shisler 1990). Furthermore, research on marsh res- toration has tended not to include detailed studies of macroinvertebrates, even though some of these ani-

KEY WORDS: Tidal salt marsh restoration; Macroinvertebrates; Melampus bidentatus; Geukensia demissa; Refer- ence marshes; Sampling methods

*Author to whom correspondence should be addressed.

reals may be good indicators of marsh condition and appear to inlluence plant productivity (Bertness 1984, 1985). Clearly there is a need for more research on marsh restoration in the northeastern United States that focuses on the invertebrate populations in addition to vegetation and other fimctional components.

In attempting to evaluate the restoration of a de- graded marsh, one is faced with the problem of a suitable reference standard. In many cases there are no detailed studies of the marsh prior to its degrada- tion. This is especially true with respect to animal populations. Even if such studies exist, comparison of the restored marsh with the marsh prior to its degra- dation may not be entirely valid. For example, if the

Environmental Management Vol. 18, No. 2, pp. 283 293 �9 1994 Springer-Verlag New York Inc.

284 M.A. Peck and others

predegradat ion study was conducted many years ear- lier, the marsh might have changed f rom that condi- tion over a period of decades due to natural factors. Ideally one also would like to be able to compare the restored marsh with a similar marsh in the same sys- tem that has never been degraded. In the case of impounded valley marshes, the restored marsh may be compared with regions of marsh below the im- poundment dike. I f no early study of the marsh exists and no suitable reference marsh is available, compar- isons must be made with other marshes described in the literature. However, this may be problematic, be- cause animal populations of di tferent marshes, even within a relatively small geographic region, may differ considerably (Fell and others, 1982).

Other questions that must be considered are: what components of the system should be studied and in what detail? These are iInportant questions because procedures for marsh assessment should be reason- ably comprehensive, broadly applicable and not overly labor intensive (Erwin 1990). With respect to ani- mal populations, it seems desirable to study in detail a few indicator species that (1) are typical of marshes over a broad geographical range and (2) can be quan- titatively sampled with relative ease. Such detailed quantitative studies can be supplemented by less com- prehensive studies of other auimals within the system.

This study evaluated the restoration of an im- pounded valley marsh at the Barn Island Wildlife Management Area in eastern Connecticut by assess- ing tile nmnerical size and biomass of certain macro- invertebrate populations. Such animal populations were compared to those of a similar, un impounded valley marsh about 1.3 km away. The pulmonate snail, Melampus bidentatus (Say), and the ribbed mussel, Geu- kensia demigsa (Dillwyn), were chosen as pr imary indi- cator species for the high marsh and low marsh, re- spectively. Melampus inhabits the higher elevations of tidal salt marshes along the Atlantic and Gul l of Mex- ico coasts of North America (Hausman 1932, Holle and Dineen 1957, Russel-Hunter and others 1972). It is especially prominent on marshes of the northeast- ern United States. This snail often occurs in large numbers in regions of high marsh covered by Spartina patens. (Air.) Muhl (saltmeadow hay), Distichlis spicata (L.) Greene (spikegrass), andJuncas spp., as well as in well-drained regions dominated by stunted Spartina alterniflora Loisel. (saltwater cordgrass) (Russel- Hunte r and others 1972, Price 1980, Hilbish 1981, Fell and others 1982, Joyce and Weisbcrg 1986). Sim- ilarly, Geukensicz is a major component of the macro- benthos inhabiting the lower elevations of salt marshes over much of the same geographical range as

occupied by Melamp~s (Kuenzler 1961, Rodriguez- Ort6ga and Day 1978, Bertness 1984, Lin 1989b). This mussel frequently forms dense aggregations in the tall S. alterniflora zone at the seaward edge of the marsh and along the banks of tidal creeks and mos- quito ditches, h may also extend up into the high marsh but is usually much less abundant there (Fell and others 1982, Bertness and Grosholz 1985, Bor- rero 1987, Lin 1989b). The populations of Melamp~s and Geukensia were sampled quantitatively and those of other tidal marsh invertebrates were sampled semi- quantitatively or qualitatively.

In an earlier study (Fell and others 1991), Melampus populations of the restored impounded marsh were compared with populations of this snail in marsh re- gions below the impoundment dike, but an assessment of low marsh invertebrates was not made. No significant difterences in tim numerical sizes of the Melampus pop- ulations were found. However, snail biomass was great- est on the restored impounded marsh because of the large size of the animals. The current report extends the evaluation of Meb~mpus populations on the restored im- pounded marsh and provides new information con- cerning invertebrate populations of the low marsh.

Site Description

The study area is part of the Barn Island Wildlife Management Area in Stonington, Connecticut (Fig- ure i). Within this system there are five valley marshes separated by ridges of forested upland ex- cept where they merge into a single more-or-less con- tinuous bayfront marsh border ing Little Narragansett Bay. All but one of the valley marshes have been im- pounded in an at tempt to create waterfowl habitat. The study was conducted on the westernmost marsh, an impounded marsh, and on the easternmost marsh, which has never been impounded.

Before it was impounded by a dike in 1946, the westernmost valley marsh had a floral composition strikingly similar to that of the un impounded valley marsh at the present time (Warren and others 1993). Following impoundment , it converted to a Typha an- gustifolia I , (narrow-leaved cattail)-dominated brack- ish marsh. Tidal flushing was partly restored to the marsh in 1978 by the installation of a 5-ft (I.5-m) -diameter culvert. In 1982 a 7-ft (2. l-m) -diameter culvert was added. The effected tidal exchange has resulted in a dramatic decline in Typha and the rees- tablishment of S. alterniflora and various high marsh plants (Sinicrope and others 199{)). Marshes below the impoundment dike consist of two types: stable S. pat- ens-dominated marshes and marshes on which S. pat-

Evaluation of Tidal Marsh Restoration 285

M B A R N ~ WILDLIFE

/12

IVEI~

Figure 1. Site map of the Barn Island Wildlife Management Area, showing the locations of different marshes: restored impounded marsh (RM), unimpounded marsh (UM), stable S. patens-dominated bayfront marshes (Wequetequock Cove, WC, and Bloom's Point, BP), and bayfront marshes on which S. pate~t~ has been largely replaced by stunted S. al- terniflora and fi~rbs (Pahner Neck, PN, and tteadquarters, HQ). Inset (upper right) shows the location of the Barn Island marshes in Stonington, Connecticut (short vertical arrow).

ens meadows have been largely replaced by st unfed S. alterniflora and forbs.

The unimpounded valley marsh (known as the Davis marsh) is roughtly comparable in size to the restored impounded marsh (Figure 2). The unim- pounded marsh has been mowed for sahmeadow hay for over 300 years; during the last 20 years, mowing has been done every three to four years. A large man- made ditch, probably dug during colonial times, runs along the upland border from the northwest corner of the marsh southward and then cuts across the mid- die of the marsh, joining the natural creek. In addi- tion, all but the stable bayfront marshes were ditched for mosquito control during the 1930s.

M e t h o d s

The distribution and abundance of invertebrates on the high marsh were determined by counting ani- mals within quadrats situated 5 m apart along transects that extended across the marsh from the water-marsh edge to the upland (Figure 2). The high marsh transects were positioned at tairly regular m-

Figure 2. l)etailed map of the restored impounded marsh and the unimpounded marsh, showing lt~e locations of high marsh transects (1-4). Sites where creek banks (A-C) and mosquito ditches (a and b) were sampled are indicated by tilled circles. Inset (upper right) shows the location of these marshes within lhe Barn Island system.

terwds ahmg the length of each valley so that different marstt regions were represented. Furtherntore, for each marsh, the number of quath'ats sampled in each type of vegetation was ronghly proportional to the relative surface area covered by h. (]onsequently, the samples were representative of the marshes as a whole.

Animals were collected using a 50-cm-sq wooden frame, 9 cm high, that was placed on the surface of tile Inarsh. The vegetation wilhin Ihe frame was clipped at the surface of the peat to facilitate collec- tion. Two people worked on each quadral, ct)l lecting from the periphery toward the center. This method of sampling resulted in an accurate enumeration of the stationary or slow-moving mollusks; however, since tile frame was light and did not fit tightly against the ground where the vegetation was dense, some of

286 M.A. Peck and others

the more active amphipods and isopods were able to escape under the frame.

Melampns was extensively sampled on the restored impounded marsh and the marshes below the im- poundment dike dur ing 1990 (Fell and others 1991). Since we wished to compare Melampns populations of the restored impounded marsh with those of the un- impounded marsh, which were sampled in 1991, it was necessary to resample some regions studied in 1990 to show that the populations had not changed. Large year-to-year variation in the size of Melampus populations has been observed on another Connecti- cut tidal marsh (Fell and Williams 1985). The resam- pied regions were areas covered by S. alterniflora along transect 3 of the restored impounded marsh and S. patens-dominated areas of the stable Wequetequock Cove marsh situated below the impoundmen t dike. Stunted S. alterniflora is the dominant high marsh plant of the restored impounded marsh; stunted S. alterniflora and S. patens represent the dominant forms of plant cover on the un impounded marsh (Warren and others 1993).

Low marsh invertebrates were sampled along the creek bank below the impoundment dike, as well as along the banks of the tidal creek and mosquito ditches of the restored and un impounded marshes (Figure 2). Animals were counted within quadrats sit- uated 3 m apart along the water-marsh edge. A 50- cm-sq quadrat f rame was hung vertically on metal spikes f rom the marsh edge dur ing low tide. Mussels were readily collected, but fiddler crabs had to be dug f rom their burrows. Since some of the burrows also had entrances outside the qudrats, a few crabs proba- bly escaped. The re fo re we could only estimate the relative abundance of these animals. Because the area of the low marsh (below about mean high water) is much less than that of the high marsh, the total num- ber of quadrats sampled and the distance between quadrats along the transects were reduced. In addi- tion, the number of quadrats sampled in the low marsh was kept to a minimum, because of the distur- bance such sampling creates.

Snails were measured to the nearest millimeter and mussels to the nearest 0.5 c m t o r determining the size distribution of these mollusks. Shell-free dry weights for different-sized Melampus and Geukensia were ob- tained by drying the soft tissues at 100~ until con- stant weights were reached. These values were then used to calculate biomass.

During the summer of 1991, high marsh sampling was conducted on 12 days between 23 May and 3July, while low marsh sampling was carried out dur ing 10 days between 2 July and 18 July. During the preced-

ing summer , 25 days between mid-June and early Au- gust were devoted to sampling high marsh regions above and below the impoundment dike of the west- ernmost valley system.

For statistical tests, one-way and two-way ANOVA (SPSS-X, 1986), as well as the Tukey multiple-range test, which accounts for multiple comparisons (Zar 1984), were used.

Results

Since Melampus bidentatus was sampled on the re- stored impounded marsh dur ing 1990 and on tile un impounded marsh in 1991, two regions of marsh that had been sampled dur ing 1990 were resampled in 1991 in order to determine if the populations had changed. Melampus density and biomass were not sig- nificantly different for the two years either in S. al- terniflora-covered areas along transect 3 of the re- stored impounded marsh or in S. patens-dominated regions of the bayfront marsh at Wequetequock Cove (Table 1). Consequently, we feel confident in compar- ing Melampus populations on the restored impounded marsh with those on the un impounded marsh even though they were sampled during different years.

Melampus was widely distributed on the restored impounded marsh and on the un impounded marsh. On both marshes it was found in >90% of tile high marsh quadrats (Table 2). The mean density of Melampta~ on the un impounded marsh was >2 times that on the restored impounded marsh. However, dif- ferences in Melampns biomass between the two marshes were less striking, because tile snails tended to be larger on the restored impounded marsh (Fig- ure 3). The mean shell-free biomass of Melampus on the un impounded marsh was only 1.4 times that of tile restored impounded marsh. On both marshes, drier areas dominated by S. alterniflora exhibited the same high Melampns biomass even though snail den- sity was significantly greater on the un impounded marsh. The biomass of Melampus in areas covered by S. patens also was similar on the two marshes but was lower than in areas dominated by S. altet~,ijTora (Ta- ble 2).

In drier areas of the restored impounded marsh covered by S. alternijTora, the density of Melampns was greater than in wet S. alternij'lora and snail biomass was greater than in areas covered by wet S. alterniflora and other high marsh plants (Tukey, p < 0.05). On the restored impounded marsh, Melampus density tended to be greatest in regions border ing the tidal creek and lowest in the often wetter regions near the upland covered by many of the same plant species (Figure 4).

Evaluation of Tidal Marsh Restoration 287

Table 1. Comparison of Melampus bidentatus populations on two marsh regions at Barn Island during the summer of two successive years"

Year Significance

Marsh region 1990 1991 (t test)

A. Restored marsh S. alterniflora (Y3)

N 20 20 Density 504 -+ 31.2 556 -+ 43.6 Biomass 8.44 -+ 0.44 9.60 -+ 0.76 Most abundan t size 9.1-10.0 9.1-10.0

B. Wequetequock Cove S. pater~

N 7 10 Density 828 -+ 132.0 760 -+ 73.2 Biornass 4.56 -+ 1.00 4.48 +- 0.52 Most abundant size 6.1-7.0 6.1-7.0

t = 0.95, df = 38, p = 0.346 t = 1.31, df = 31.13, p = 0.199

t = 0.48, df = 15, p = 0.639 t = 0.07, df = 15, p = 0.942

"Density = mean N -+ SE/mZ; biomass = mean g dry wt -+ SE/me; most abundant size = shell lengdl in ram.

Table 2. Frequency of occurrence, mean density (N _+ SE/m2), and mean shell-free biomass (g dry wt --- SE/m 2) of Melampus bidentatus in different high marsh areas of a restored impounded marsh and unimpounded marsh at Barn Island

Marsh Significance

Marsh area Restored U n i m p o u n d e d (t test)

All areas N 82 90 % occurrence 91 94 Density 332 -+ 39.6 712 - 56.11 Biomass 4.96 -+ 0.52 6.96 _+ 0.52

S. alterniflora-dominated N 19 47 Density 540 + 49.6 868 _+ 83.2 Biomass 8.16 ~- {I.72 8.28 -+ 0.80

S. patens-dominated N 11 31 Density 452 -+ 207.6 488 + 63.2 Biomass 4.68 +- 2.08 5.24 -+ 0.56

Wet S. alterniflora ~ N 30 5 Density 184 4- 45.2 816 +- 338.0 Biomass 3.36 + 0.72 6.68 -+ 2.72

Other high marsh b N 22 7 Density 300 -+ 57.2 580 -+ 161.2 Biomass 4.56 4- 0.84 6.28 -+ 1.48

t = 5.52, df = 157.52, p < 0.001 t = 2.80, df= 170, p < 0.01

t = 3.40, df = 63.85, p < 0.01 t = 0.11, dr= 56.11,p = I).917

t = 0.16, d] '= 11.90, p = 0.877 t = 0.26, d]'= 11.59, p = 0.800

t = 1.85, df= 4.14, p = 0.136 t = 1.59, df=33, p=O.122

t = 2.09, df = 27, p < 0,05 t = 1.02, dr= 27, p = 0,317

aAreas covered by S. aherniflora where there is standing water at low tide.

bAreas dominated by plants such asJunczts gerardi Loisel. (blackgrass) that were poorly represented on tlle marshes or mixtures of various high marsh grasses and forbs.

T h e snai ls a lso t e n d e d to be less a b u n d a n t a l o n g t h e

t r a n s e c t s i t u a t e d f u r t h e s t u p s t r e a m ( T a b l e 3), w h e r e

s o m e Typha pe r s i s t s a n d soil w a t e r sa l ini t ies a r e s o m e -

w h a t l o w e r t h a n a l o n g t h e o t h e r t r a n s e c t s (da ta n o t

s h o w n ) .

O n t h e u n i m p o u n d e d m a r s h , snail d e n s i t y a n d bio-

mass w e r e g r e a t e r in d r y a r eas d o m i n a t e d by S. alterni- flora t h a n in a r e a s c o v e r e d by S. patens ( T u k e y ,

p < 0.05). T h e Melampus p o p u l a t i o n was espec ia l ly ro-

b u s t in r e g i o n s o f t h e u n i m p o u n d e d m a r s h a l o n g

288 M.A. Peck and others

I 40 t N : 6,82 I

I

2030 1 . 0 ~ ~ ~

0 ~ l ; ~ [ ~

40_1 ~ N= 15, gg8

2O

lO

3 6 9 12 15

Shell Length (ram)

Figure 3. Size-frequency distribution of M. bidentatm on the restored impounded marsh (top) and the unimpounded marsh (bottom). N = number of snails in each sample.

the u p p e r extent o f the tidal creek (Table 3; Figure 5). On transect 1, mean snail density was 1200/m 2 and mean shell-free biomass was 10.5 g dry wt/m 2.

O the r high marsh invertehrates that were c o m m o n on the two marshes were the amph ipod , Orchestia gril- lus Bose, and the isopod, Philoscia vittata Say. How- ever, these more mobile animals were not sampled quantitatively, and therefore their abundances on the restored i m p o u n d e d and u n i m p o u n d e d marshes can not be compared .

Geukerr~ia demissa was sparsely distr ibuted in high marsh regions o f both the restored i m p o u n d e d and u n i m p o u n d e d marshes. However , on the unim- p o u n d e d marsh, mussel density was signiticantly greater (t test, t = 4.54, df = 97.45, p < 0.001), where it was >7 times that on the restored i m p o u n d e d marsh. On both marshes, this mussel occur red at the greatest f requency toward the ups t ream end of the creek valley (Table 4). On the res tored i m p o u n d e d marsh, the f requency o f occurrence o f Geukensia was greatest in areas covered by S. alterniflora and the mean density o f mussels was lowest in areas domi- nated by S. patens. In contrast, on the u n i m p o u n d e d marsh, Geukensia occur red at relatively high fre- quency in areas covered hy S. patens as well as in areas covered by S. alterniJlora and tile mean densit.y o f Geukensia t ended to be highest in S. patens-dominated areas.

Geukensia also was found along the hanks o f the main tidal creek and mosqui to ditches o f both marshes (Table 5). T h e mean density and biomass o f

TRANSECT I / ~ ~ L 4 0 O0

~ L IS ' I i i I 0 , I ' I ]W

.800

.400

.0 ~

z -800

.400

.0

[ - I I ' I I I I I ] I I I I I I I I I ~ I I I I I I I 0 20 40 80 80 100 120

800

400

0 ] i i i i i i i i i i i,t i i i i i i I

"-; 2,000.

Z 1,600.

1,200.

800.

400.

80 60 40 20 0 D i s t a n c e F r o m W a t e r (m)

Figure 4. Distribution of M. bidentatus and dominant plants aloug four transects on the restored impounded marsh. For transects I-3E, the tidal creek is on the left and the upland is on 1he right; tor transects 3W and 4, the creek is on the right and the upland is on the left. (Sa, S. alterniflora; W, wet S. alterniflora; Sp, S. paten.~; O, other high marsh). Plato species are indicated where they represent >50(~ of cover.

(;eukensia were similar a long tile creeks o f the restored i m p o u n d e d marsh and u n i m p o u n d e d marsh. How- ever, below the dike o f the restored i m p o u n d e d marsh, the density o f mussels was at least fbur times h igher and their biomass > 6 times greater than else- where a long the creeks. T h e density o f Geukensia in mosqui to ditches was three times h igher on the re- s tored i m p o u n d e d marsh than oil tile u n i m p o u n d e d marsh, but mussel biomasses were comparable on the two marshes, because mussels in ditches o f the re- s tored i m p o u n d e d marsh tended to be small.

O the r c o m m o n macroinver tebrates o f tile low marsh were crabs and annelids. T h e fiddler crabs, Uca pugmax and Uca minax, occurred along the pr imary creek and within the mosquito ditches of the restored i m p o u n d e d marsh and u n i m p o u n d e d marsh, al- t hough they appeared to be somewhat more abun- dant on the latter (Table 6). Uca minax was tk)und only at the ups t ream end o f the tidal creeks and in mos- quito ditches. Few Uca pugnax wcre present along the

Evaluation of Tidal Marsh Restoration 289

Table 3. Mean density (N • SE/m 2) and mean shell-free biomass (g dry wt _+ SE/m 2) of Melampus bidentatus along different transects of a restored impoiunded marsh and an unimpounded marsh at Barn Island a

Transect

Marsh 1 2 3 4 Significance

(Tukey)

Restored N Density

Biomass

Unimpounded N Density

Biomass

8 I 1 46 17 100 • 66.0 448 • 110.0 328 + 38.4 388 • 138.0

1.40 • 0.84 6.04 • 1.44 5.64 • 0.60 4.12 • 1.40

19 31 16 24 1208 -+ 67.2 804 • 109.6 392 • 48.8 408 +_ 72.0

10.48 -+ 0.60 8.28 +- 1.04 4.92 • 0.56 3.88 • 0.68

NS

p < 0.05

p < 0.05

~Transect 1 was situated toward the headwaters of each tidal creek and successive transetls were hwawd progressively downstream. All transects extended across the marshes perpendicular t<+ dae creeks. Means sharing a common underline d<~ not dil[{q" sign|fit andy.

creek below the i m p o u n d m e n t dike. T h e polychaete, Nereis (= Neanthes) succinea Frey and Leuckart , was seen a long the creek banks of both marshes and was especially c o m m o n on the restored i m p o u n d e d marsh where it also occurred within mosquito ditches.

Discussion

Melampus bidentatu~', Geukensia demissa, Uca spp., and o ther tidal marsh inver tebrates have become re- established on a restored i m p o u n d e d valley marsh within the Barn Island Wildlife M a n a g e m e n t Area in Connect icut . Before restorat ion began in 1978, al- most three four ths of the marsh was covered by Typha and nearly 20% of it was unvegeta ted . Now more than a decade after the re in t roduc t ion of tidal f lushing,

Spartina alterniflora together with o ther tidal marsh plants has largely replaced Typha and colonized the unvege ta ted areas (Sinicrope and others 1990). Al- t hough no in fo rma t ion is available conce rn ing inver- tebrate popula t ions on the i m p o u n d e d marsh pr ior to at tempts at restorat ion, it is doubt fu l that typical tidal salt marsh species were presen t (Fell and others 1991 ). T h e presence of such animals on the marsh in 1990 suggests that res torat ion of a typical tidal salt marsh c o m m u n i t y has occurred. However, species composi- t ion alone is not sufficient for evaluat ing restorat ion; the numer ica l size and/or biomass of popula t ions must also be considered. In addi t ion, t0r animals, the size s t ructure of their popula t ions may be ano the r impor t an t pa rame te r fbr assessment.

Al though Melampus occurs at modera te popu la t ion densities on the restored i m p o u n d e d marsh, its mean densi ty there is somewhat lower than on the bayf ron t

Figure 5. Distrihution ofM. bidentatu+~ and dominant plants along four transects on the unimpounded marsh. For all nanstx:t.~, tile tidal creek is on tile right. A large ditch that runs along the upland is on the left for trasects 1-3; and a ditch (tug through open marsh is on ttte left for transect 4. (Sa, S. altern!/lora; W, wet S. alterni[lom; Sp, S. pate+~; O, other high marsh. Plant species are indicated where they represent > 50% {}f cover.

290 M.A. Peck and others

Table 4. Frequency of occurrence and mean density (N - SE/m 2) of Geukensia demissa in different high marsh areas of a restored impounded marsh and an unimpounded marsh at Barn Island

Marsh

Restored Unimpounded

Marsh area N % occurrence Density N % occurrence Density

Transect 1 8 25 3.00 - 2.48 19 68 10.52 +- 3.40 2 11 27 1.08 -+ 0.56 31 52 6.32 - 2.00 3 46 17 0.68 + 0.24 16 38 7.24 -+ 3.56 4 17 6 0.24 -'- 0.24 24 25 4.84 + 2.20

Vegetation type S. alterni)%ra.dominated 19 21 0.84 ~ 0.40 47 40 4.24 - 1.00 Wet S. alterniflora 30 23 0.92 - 0.32 5 60 5.60 -+ 3.00 S. patens-dominated 11 9 0.36 -+ 0.36 31 55 10.96 -+ 3.12 Other high marsh 22 9 1.08 - 0.92 7 29 8.56 + 5.92

All areas 82 17 0.88 - 0.28 90 46 6.96 - 1.32

Table 5. Mean density (N -+ SE/m 2) and mean shell-free biomass (g dry wt -+ SE/m 2) of Geukensia demissa in different low marsh regions of a restored impounded marsh, a marsh below the impoundment dike, and an unimpounded marsh at Barn Island

Marsh Significance

Marsh area Restored Below dike Unimpounded (t test)

Main creek, A and B N 12 Density 144 - 17.6 Biomass 29.6 -+ 3.52

Main Creek, C N Density Biomass

Mosquito ditches, a and b N 12 Density 240 -+ 41.6 Biomass 64.8 - 9.80

m

m

12 156 -+ 29.6

32.4 +- 5.12

4 4 1100 + 96.4 232 + 32.4

303.6 -+ 33.28 24.8 - 3.36

m

m

12 80 --+ 11.2

54.4 _ 6.32

t = 0.29, df =- 22, p = 0.774 t = 0.44, df = 22, p = 0.667

t = 8.55, df = 6, p < 0.001 t = 8.34, df = 3.06, p < 0.05

t = 3.70, df = 12.56, p < 0.05 t = 0.90, df = 22, p = 0.378

marshes below the i m p o u n d m e n t dike (Fell and oth- ers 1991) and less than hal f that on a nearby un i m-

p o u n d e d valley marsh (Figure 6). T h e popula t ion densit ies of Melampus on the res tored i m p o u n d e d marsh and the u n i m p o u n d e d valley marsh are most similar toward the mouths of the tidal creeks. T h e u p p e r par t o f the u n i m p o u n d e d marsh suppor ts a high densi ty and biomass of Melampus. Much of this

area is covered by short S. alterniflora. In contrast , on the u p p e r par t of the res tored i m p o u n d e d marsh, the Melampus popula t ion exhibits a lower and less un i - form abundance . Along the most ups t ream transect where relic Typha persists, Melampus densi ty tends to be low. In addi t ion, the Melampus popula t ion is small

in areas of wet S. alterniflora, which before res tora t ion efforts began were p r edominan t l y devoid of vegeta-

t ion (Sinicrope and others 1990). More than a th i rd of

the quadra t s sampled on the restored i m p o u n d e d marsh were of this type. Both the f auna and flora of

the u p p e r por t ion of the restored i m p o u n d e d marsh indicate that res torat ion there is less complete than it is fu r the r downst ream.

Melampus tends to be substantial ly larger on the restored i m p o u n d e d marsh compared to the un im- p o u n d e d marsh a nd the marshes below the i m p o u n d - m e n t dike. Consequent ly , the d i f ference in snail bio- mass is less s tr iking than the d i f ference in snail densi ty between the res tored i m p o u n d e d marsh a nd u n i m - p o u n d e d marsh, a nd snail biomass actually is greater on the marsh region above the dike than it is below (Figure 6). In fact, in relatively dry regions covered by S. alterniflora, the biomass of Melampus is the same on

Evaluation of Tidal Marsh Restoration 291

Table 6. Mean density (No. + S.E,/m 2) of Uca pugnax and Uca minax in different low marsh regions of a restored impounded marsh, a marsh below the impoundment dike, and an unimpounded marsh at Barn Island

Marsh

Restored Below dike Unimpounded

Marsh area U. pugnax U. minax U. pugnax U. minax U. pugnax U. minax

Main creek, A and B N Density 18.4 • 5.72

Main creek, C N Density

Mosquito ditches, a and b N Density 28.8 • 4.72

12 - - 12 0.4 --- 0.32 - - 41.6 -+ 7.24 2.8 • 1.24

4 4 1.2 • 1.00 0 5i.2 -~ 12.36 0

12 - - 12 0.8 +- 0.44 - - 31.2 • 3.32 3.2 • 1.28

800_

E

:~ 400- , , . , . ,

Z,

Q 0-

35 g3 82 g0

T--

_g SM CM R'M U'M

_8 D

E

_4

_0 .s ~ n

Figure 6. Mean density (clear bars) and mean biomass (lined bars) ofM. bidentatus in different marsh areas at Barn Island. (SM = stable S. pate~-dominated hayfront marsh; CM = bayfront marshes on which S. patens has been largely replaced by stunted S. alterniflora and forbs; RM = restored impounded valley marsh; UM = unimpounded marsh). The number of quadrats sampled on each marsh area is indicated above the bars and standard errors are repre- sented by vertical lines above the bars.

the restored impounded and unimpounded marshes even though snail density is significantly greater on the latter.

The large size of Melampus on the restored im- pounded marsh may be due to a more rapid growth rate resulting from a larger/better food resource. Food preference studies have shown that Melampus ingests both live and dead marsh grasses and that it does not discriminate among different grasses with any marked consistency. However, grass detritus is chosen more often than blue-green algae or sulfur bacteria (Rietsma and others 1982). On the other hand, old S. alterniflora detritus is preferred over newly formed S. alterniflora detritus, and snails grow

more rapidly on the latter diet. In this case, food choice by and growth of Melampus are inversely corre- lated with the phenolic content of the plant material (Rietsma and others 1988). An analysis of food re- sources and an elucidation of the population dynam- ics of Melampus on the restored impounded marsh might enhance our understanding of the restoration process.

Geuher~ffa demissa occurs at low density on the high marsh regions of both the restored impounded marsh and unimpounded marsh, but was more abundant on the latter. On the higher regions of the unimpounded marsh, it occurs with greatest frequency toward the upstream end of the tidal creek where Melampus also is most abundant. Peak abundances of these two mol- lusks may be related to low levels of predation (Vince and others 1976, Joyce and Weisberg 1986, Lin, 1989a), a high quantity/quality of food (Rietsma and others 1988, Lin 1989b), and/or a favorable physical environment (Lent 1969, Price 1980, McMahon and Russell-Hunter 1981, Kraus and Crow 1985).

Geukensia has been reported on the high marsh elsewhere in New England (Fell and others 1982, Bertness and Grosholz 1985). However, mussels in this marsh region generally are characterized by low populations density, small size, and low growth rates, and there is little or no recruitment of juveniles here. It appears that most mussels occurring on the high marsh may have been carried there by winter ice rafts. (Bertness and Groshoiz 1985).

Geukensia is present at moderate densities along the banks of the main creeks and mosquito ditches of both the restored impounded marsh and the unim- pounded marsh. The greatest density and biomass of Geukensia were found immediately below the im-

292 M.A. Peck and others

poundment dike. The abundance of mussels there may be due to a downstream influence of the dike (Luckenbach and others 1990). For example, it seetns probable that a buildup of water on the seaward side of the dike during high tide may result in a longer period of submergence for the mussels.

Uca pugnax also was found along the banks of the main creek and mosquito ditches of the restored im- pounded marsh and the unimpounded marsh. This crab appeared to be less abundant along the creek below the impoundment dike than elsewhere. The scarcity of Ucapugnax below the dike may be related to the large number of mussels there. Uca minax occurs in small numbers on both marshes and is apparently restricted to mosquito ditches and the upper ends of the tidal creeks. Uca minax prefers areas of lower salin- ity than does Uca pugnax. This, together with other factors, including competition between the two spe- cies, apparently determines their distribution (Teal 1958, Miller and Maurer 1973, Daiber 1982, Ringold 1979).

The presence, distribution, and abundance of var- ious macroinvertebrates on the restored impounded marsh in comparison to marshes below the impound- ment dike and to a nearby unimpounded valley marsh indicate that restoration is in an advanced phase. This conclusion is strengthened by the use of two different types of reference marshes, which present different advantages and disadvantages for comparisons. Com- parison of the restored impounded valley marsh to marshes below the impoundment is clearly desirable because these are components of the same small en- tity. However, marsh fauna change along the length of tidal creeks/rivers (Miller and Mauer 1973, Parker 1976, Fell and Williams 1985) and dikes also may alter downstream marshes (Luckenbach and others 1990). Comparison of the restored impounded valley marsh with a similar unimpounded valley marsh within the same general system eliminates some of the concerns mentioned above, but each valley marsh will have some unique characteristics that will influence the dis- tribution and abundance of plant and animal popula- tions.

This study assesses the condition of a marsh 13 years after restoration efforts were initiated. Unfortu- nately no information is available concerning the stages by which the present condition was achieved. Comprehensive studies that tocus on the progressive changes occurring on recovering marshes should be undertaken.

Sampling the high marsh at close intervals along transects that extend from the water-marsh edge to the upland border gives a more comprehensive pic-

ture of the marsh than does more selective sampling, because it covers most or all of the marsh zones and may reduce sampling bias. However, in-depth sam- pling along transects can be very time consuming. Although the present study is too large and labor intensive to serve as a model for most efforts to evalu- ate animal populations on restored or created marshes, it is hoped that the information provided here will aid in the design of less comprehensive stud- ies that can adequately assess the condition of marsh fauna.

Acknowledgments This study was supported by a grant from the Long

Island Sound Fund of the Connecticut DEP. The help of Robert Askins with the statistical analysis is greatly appreciated.

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