Zostera Marina Bed and Nearby Unvegetated Sediments in Damariscotta River, Maine (USA)

ELSEVIER Journal of Sea Research 41 (1999) 321±332

Spatial and diurnal distribution of invertebrate and ®sh fauna of a Zostera marina bed and nearby unvegetated sediments in Damariscotta River, Maine (USA)

Johanna Mattila Ł, Glen Chaplin, Michele R. Eilers, Kenneth L. Heck, Jr., Jonathan P. O'Neal, John F. Valentine Dauphin Island Sea Lab, P.O. Box 369±370, Dauphin Island, AL 36528, USA Received 7 January 1998; accepted 12 December 1998

Abstract

Fish, epibenthos and macroinfauna were collected in a Zostera marina bed and nearby unvegetated sediments in the estuary of the Damariscotta River, on the mid-coast of Maine. Samples of epibenthic fauna and ®sh were collected at low tides both during day and night, and samples of infauna at low tides during the day. The mean density of Zostera shoots in the study area was 335 m2. Abundance and species number of ®sh were greater at night than during the day and greater in eelgrass beds (Z. marina) than in unvegetated habitats. Daytime ®sh collections were dominated by Atlantic silversides (Medinia medinia), while juvenile winter ¯ounder (Pseudopleuronectes americanus) dominated night collections. Also Zostera-associated epifaunal abundances and number of species were signi®cantly higher at night than during the day. Mysis stenolepis, Idotea balthica and Littorina obtusata were dominant species in the epifauna samples. Of the total of 37 invertebrate species encountered, only ®ve occurred both in the infaunal and epifaunal samples. Nineteen different taxa were collected from the benthic core samples. The most abundant invertebrate infaunal taxa were sipunculids, the polychaete Nereis virens, and oligochaetes. Infaunal invertebrate abundances and species diversity were signi®cantly higher in eelgrass beds than in unvegetated sediments. The abundance and number of species of benthic invertebrates were also positively correlated to seagrass biomass. Community diversity values .H 0/ were relatively low but ®t well in the general pattern of decreasing diversity towards northern latitudes.  1999 Elsevier Science B.V. All rights reserved.

Keywords: spatial variation; diurnal variation; ®sh; invertebrates

1. Introduction 1982) ranging from Greenland to Spain in the eastern Atlantic and from Arctic Canada to North Carolina Zostera marina L. is the most common seagrass in the western Atlantic (Setchell, 1935). Z. marina is species in temperate coastal areas (Homziak et al., also common throughout the Paci®c Ocean (Setchell, 1935; Kikuchi, 1966, 1980). It is the only seagrass species in the Baltic Sea (Rasmussen, 1973), and it Ł Corresponding author. Present address: HusoÈ Biological Sta- tion and Dept. of Biology, AÊ bo Akademi University, BioCity, also occurs sporadically in the Mediterranean (Be- Artillerigatan 6, FIN-20520 AÊ bo, Finland. Fax: C358 22154748; nacchio, 1938). E-mail: johanna.mattila@abo.® Eelgrass increases habitat complexity and pro-

1385-1101/99/$ ± see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S1385-1101(99)00006-4 322 J. Mattila et al. / Journal of Sea Research 41 (1999) 321±332 vides living space and shelter for a greater variety of know about Zostera-associated fauna in the north- animal species and greater abundances of individuals ern temperate zone comes primarily from the Baltic than the adjacent unvegetated habitats (Rasmussen, Sea (e.g. Petersen and Boysen Jensen, 1911; Petersen, 1973; Adams, 1976a,b; Orth et al., 1984; Orth, 1992; 1918; Lappalainen, 1973; Rasmussen, 1973; Lappa- BostroÈm and Bonsdorff, 1997). Many ®sh and in- lainen and Kangas, 1975; Lappalainen et al., 1977; vertebrate species use eelgrass meadows as feeding Pihl Baden and Pihl, 1984; Pihl Baden, 1990; Mattila, and nursery grounds (Petersen, 1918; Heck and Orth, 1995; BostroÈm and Bonsdorff, 1997). 1980a), including many economically important ®sh This study describes the diurnal and spatial dis- and shell®sh. Eelgrass meadows are commonly re- tribution of the ®sh and invertebrate fauna of a tem- garded as among the highly productive near-shore perate Zostera marina bed and a nearby mud ¯at on habitats (Thayer et al., 1975; Orth, 1977; Pihl Baden the northeast coast (43ëN latitude) of North America. and Pihl, 1984). In particular, we consider how seagrass biomass is In general, there is a positive correlation between related to animal species richness and abundance, Zostera biomass and faunal abundance, biomass, and describe day±night patterns in faunal abundance and diversity as shown for ®sh (Adams, 1976a), decapods composition, and compare our results with previous (Heck and Orth, 1980b), and other benthic inverte- studies that have used similar sampling methods. brates (Lappalainen and Kangas, 1975; Homziak et al., 1982). However, Nelson (1980) did not ®nd any signi®cant amphipod abundance±seagrass biomass 2. Material and methods correlation, nor did Pihl Baden and Pihl (1984) ®nd any correlation between the biomass of Zostera and 2.1. Study site the abundance of epifauna. Diurnal variation in ®sh densities has been ob- Samples were collected in a Zostera marina bed served in many shallow areas. Usually the catches and in a nearby mud ¯at (at a distance of about are bigger by night than by day. This variation is of- 500 m) located in the shore area at Darling Marine ten explained with the daily activity patterns of ®sh Center (43ë560N, 69ë350W) (Fig. 1), Walpole, in the (Adams, 1976a,b; Horn, 1979; Orth and Heck, 1980; estuary of the Damariscotta River, Maine. The tidal Bayer, 1981). Fish may sleep or be more active (e.g. range in this area is approximately 2.5 to 4 m, with feeding) during the night time, both of which may two tidal cycles per day. The tidal current is about result in increased susceptibility to capture (Gray 0.8 km h1 during ebb and ¯ood tides. The salinity and Bell, 1986). usually ranges from 28 to 32½, but for shorter Vertical distribution of Zostera-associated epi- periods it can drop to as low as 24½ (T. Miller, fauna has been studied only little, but Nagle (1968) pers. commun., 1997). The water temperature varied found in the Cape Cod area that organisms abundant between 16 and 18ëC during the sampling period of on Zostera blades occurred in reduced numbers in 7 to 12 September 1996. The depth of the Zostera the sediments surrounding the leaves, while abundant bed and the mud ¯at was approximately 0.5 to 1.5 m infaunal animals had few representatives as epifauna. during low tide. Seagrass density was measured with Many studies have described the Zostera-associa- a 100-cm2 quadrat that was haphazardly tossed into ted fauna from the mid-Atlantic coast of North Amer- the seagrass bed. All shoots inside the frame were ica, particularly in the Chesapeake Bay and North Car- then counted (n D 20). olina waters (e.g. Nagle, 1968; Briggs and O'Connor, 1971; Orth, 1973; Marsh, 1973, 1976; Nelson, 1979, 2.2. Sampling of ®sh and decapods 1980; Heck and Orth, 1980b; Orth and Heck, 1980; Homziak et al., 1982; Virnstein et al., 1984; Heck et Fish and epibenthic decapods were collected with al., 1989, 1995). By comparison, much less is known a 6.35-mm mesh haul seine, 1.6 m high and 8.1 m about Zostera-associated fauna along the northeast long. In the grass habitat, a metal chain was added coast of North America above 40ëN latitude (but see to the bottom of the seine to increase the catch LalumieÁre et al., 1994; Heck et al., 1995). What we ef®ciency. This chain was not used in the mud J. Mattila et al. / Journal of Sea Research 41 (1999) 321±332 323

habitat. Both sites were sampled daily during both day and night low tides, with two replicate hauls taken each time (Table 1). Each replicate haul was 30 m long; thus an area of about 243 m2 was sampled by each replicate. After each haul, the seine was carefully lifted from the water so that organisms remained in the seine bag. The seine was then carried to the shore where the organisms were removed and separated. In the laboratory all ®sh and decapods were identi®ed, weighed, measured and counted.

2.3. Sampling of infauna

Benthic core samples were taken in the seagrass bed and in the unvegetated area located between the seagrass bed and the shore line. A PVC corer with a 10-cm diameter (bottom area 78.5 cm2) was driven into the sediment to a depth of 10 cm to collect each sample. Sampling sites were chosen `semi-ran- domly' so that areas with different seagrass densities=biomasses were covered. Samples were taken in an unvegetated area, on the onshore edge of the bed, in the center of the bed, and on the offshore edge of the bed (Table 1). Besides the macrofauna, blades, rhizomes and roots of eelgrass were also collected in the vegetated area. In the laboratory, samples were rinsed over a 0.5-mm sieve to remove ®ne sediments. All samples were treated alive. Vegetation was removed by hand, separated into leaves, rhizomes and roots, dried at 60ëC for a minimum of 24 h, and then weighed to determine above-ground and below-ground biomass in units of dry weight (DW) (š1 mg accuracy). All organisms were sorted and identi®ed to the lowest possible taxon, and then enumerated.

2.4. Sampling of Zostera-associated epifauna

Epifaunal samples were collected with transparent plastic bags (125 dm3, height ¾120 cm). These bags were placed over a couple of individual plants and the shoots were severed just above the sediment surface. The bags were then divided into 20-cm sections by tying cable ties at 20-cm intervals along Fig. 1. The study area in the Damariscotta River, Maine. Study the shoots and also closing the bags with a cable sites in the seagrass and mud ¯at areas are shown. tie above the shoot tips. A total of 21 samples were collected from the eelgrass bed both during the night and day low tide (Table 1). 324 J. Mattila et al. / Journal of Sea Research 41 (1999) 321±332

Table 1 Number of samples and sampling methods of different faunal groups in seagrass and mud habitats; sampling time is also indicated.

Type of fauna Time Habitat seagrass bed bare mud ¯at Fish and decapods day 2 haul seines a 2 haul seines night 2 haul seines a 2 haul seines Infauna day 7 sediment cores 3 sediment cores Zostera-associated epifauna day 21 bag samples night 21 bag samples a With a metal chain attached to the bottom of the seine.

In the laboratory, the sample bags were opened plant was 3.44 (š0.12, n D 223); thus, the average section by section and all animals collected were re- total density was 1152 leaves m2. Mean leaf length moved, identi®ed and counted. Eelgrass leaves were was 52.8 cm (š0.9, n D 576) and the range was counted and the length of each leaf was measured. 7 to 124 cm. The mean above-ground biomass was 56.2 g DW m2 (š18.4, n D 7) and the average 2.5. Numerical and statistical analyses below-ground biomass was 198.0 g DW m2 (š41.5, n D 7). The total seagrass biomass varied between Species diversity .H 0/ was estimated using the 48.9 and 437.8 g DW m2 (x š s:e: D 254:2 š 54:6 Shannon±Weaver index (Shannon and Weaver, 1963) gm2). according to: Xs 3.2. Fish and decapods 0 H D pi LNpi iD1 A total of 1182 ®shes belonging to thirteen where s D total number of species, pi D ni =n, species were seined from the grass habitat (Fig. 2a). the proportion of the total number of individuals Atlantic silversides (Menidia menidia) were the most belonging to the ith species. abundant species (50.7% of total abundance) dur- Differences in the spatial distribution (seagrass bed ing the day, whereas winter ¯ounder (Pseudopleu- vs. mud ¯at) and temporal (day vs. night) of the ®sh ronectes americanus) was the most common species and zoobenthos were analysed by t-test or Mann± (59.8% of the total abundance) during the night. In- Whitney rank comparisons if the populations in the dividuals of winter ¯ounder caught during the day samples were not normally distributed (Sokal and (mean length x D 4:9 š 0:1 cm) were signi®cantly Rohlf, 1995). Also spatial and diurnal differences in smaller than individuals caught during the night mean sizes of ®sh and decapod species were analysed (x D 6:3 š 0:1cm;t-test, t D 5:335, p < 0:001). with t-tests. Diurnal variation in vertical distribution No other species showed any size differences be- of Zostera-associated epifauna was analyzed with tween the day and night seinings. Threespine stickle- the 2-test. Correlations (Pearson Product Moment back (Gasterosteus aculeatus), fourspine stickleback Correlation) between the biomass of vegetation and (Apeltes quadracus) and grubby (Myoxocephalus ae- species richness and abundance were also calculated. naeus) were also common both during the day and the night. These ®ve species made up 97% during the day and 93% of the catches during the night. 3. Results American eel (Anguilla rostrata) was collected in the grass bed only during the night. 3.1. Seagrass Other species previously observed in the seagrass area include inland silverside (Menidia beryl- The mean density of Zostera was 335 shoots m2 lina), longhorn sculpin (Myoxocephalus octodecem- (š39, s.e., n D 20), and the mean leaf number per spinosus), pollock (Pollachius virens) and white hake J. Mattila et al. / Journal of Sea Research 41 (1999) 321±332 325

Fig. 2. Total abundance of ®sh species during day and night samplings in (a) the seagrass area, and (b) the mud ¯at. * D one ®sh. Solid bars D night catch, stippled bars D day catch. Note the logarithmic scale.

(Urophycis tenuis) (C. Vickery and K.L. Heck Jr., caught on the bare mud ¯at. Very few individuals University of South Alabama, unpubl. data), but they were caught during the day (Fig. 2b). All mud species were not caught during seining. During the sampling were also found in the seagrass. period, striped bass (Morone saxatilis), adult rock A larger number of species and individuals and crabs Cancer irroratus and green crabs Carcinus greater total biomasses were collected at night. The maenas were also caught in gillnets during the night diel differences were most pronounced in the mud (J. Mattila, unpubl. data). These species probably use (Fig. 2b). Species-speci®c mean sizes of individu- the seagrass habitat as a feeding ground. als did not differ for any species that occurred in Only 40 ®shes belonging to four species were both habitats. Fish diversity indices .H 0/ were sig- 326 J. Mattila et al. / Journal of Sea Research 41 (1999) 321±332

Table 2 Total density (N) and diversity (H0) of different types of fauna as sampled during day and night in a seagrass bed and at bare mud ¯ats in the Damariscotta River in September 1996

Type of fauna Time of the day Parameter Habitat seagrass bed bare mud ¯at Fish day N 541 7 H0 1.28 š 0.21 0.10 š 0.12 night N 600 33 H0 1.37 š 0.14 0.64 š 0.16 Infauna day N 2693 š 902 1486 š 740 H0 1.07 š 0.17 0.69 š 0.57 Zostera-associated epifauna day N 8.1 š 1.8 ± H0 1.16 š 0.13 ± night N 21.1 š 3.4 ± H0 1.53 š 0.09 ±

Total density for ®sh is given as number of individuals caught in seines, for infauna as ind m2 and for epifauna as number of individuals per sample. Standard errors of the mean densities are indicated for infauna and epifauna samples. Standard errors of the mean diversities are given for all samples. ni®cantly higher in the seagrass than on the bare outside the bed 1486 ind m2 (š740) (Table 2). One mud ¯at (Table 2). In the mud ¯at, there was also sample taken in the unvegetated area also contained a statistically signi®cant difference in H 0-values be- a large abundance (12 484 ind m2) of sipunculids. tween the day and night values (Mann±Whitney test, The sample was considered to contain an atypical ag- T D 10:50, p Ä 0:0001). No such difference (t-test, gregation of worms for the unvegetated habitat, and t D 0:54, p D 0:632) was noted in the grass bed. it was omitted from all statistical analyses. The three Four decapod species were also caught in the sea- most abundant taxa in the eelgrass bed were sipun- grass bed. The most common species was Crangon culids, the polychaete Nereis virens and oligochaetes. vulgaris (mean length 38:3š5:4mm(s.e.),n D 749) Invertebrate abundance showed a signi®cant cor- followed by Carcinus maenas (mean carapace width relation with Zostera-biomass (Fig. 4a), although the 37:3 š 16:2 mm, n D 56). A few individuals of the total species number did not (Fig. 4b). The total crab Cancer irroratus .n D 1/ and caridean shrimp above- and below-ground biomass of Zostera var- Eualus sp. .n D 4/ were also caught in the grass bed. ied between 2.6 and 438.0 g DW m2 (x š s:e: D Crangon (mean size 35:4 š 5:3 mm, n D 480) and 188:8 š 50:6gDWm2, n D 10). On average, 22% Carcinus (mean size 53:0 š 12:2, n D 43) were also of the total biomass was above-ground biomass. The the most common decapod species on the bare mud H 0 value of the invertebrates in the seagrass bed ¯at. There was no signi®cant difference in the size was on average 1:07 š 0:17 and outside the bed of Crangon between the habitats, but Carcinus was 0:69 š 0:57 (Table 2). signi®cantly larger on the mud ¯at than in the grass bed (t-test, t D5:30, p < 0:0001). Cancer (mean 3.4. Zostera-associated epifauna size 77:1 š 9:0 mm, n D 43) was relatively common on the mud ¯at but not in the seagrass. A total of nineteen species was recorded from the epifauna samples. The most abundant species 3.3. Infauna were Mysis stenolepis, Littorina obtusata and Idotea balthica (Fig. 5). As with the ®shes, species num- Nineteen different taxa were collected from the ber (Mann±Whitney test T-value 3.73, p < 0:001) benthic cores (Fig. 3). The mean total abundance in and total abundance (t-test, t D 3:73, p D 0:001) the seagrass bed was 2693 ind m2 (š902, s.e.) and were signi®cantly higher during the night low tide J. Mattila et al. / Journal of Sea Research 41 (1999) 321±332 327

Fig. 3. Abundance of infaunal species (mean number per m2 š s.e.) in the seagrass and mud-¯at sites. Solid bars D mud ¯at, stippled bars D seagrass. Note the logarithmic scale. than during the day low tide. These differences were species per sample) and in the 80 to 100 cm section mainly due to higher night time densities of M. during the night (0:7 š 0:4 species per sample). Only stenolepis (t-value D2.91, p D 0:006), L. obtusata gastropods (Littorina spp.), bivalves (Mytilus edulis), (t-value D2.67, p D 0:011), I. balthica (t-value amphipods (Aeginella longicornis and Caprella lin- D 2.26, p D 0:030), and Littorina rudis (t-value D earis), and isopods (Idotea sp.) were found in the 3.96, p < 0:001). About 50% of the animals were topmost 20 cm of the leaves. found in the leaf segments between 20 and 60 cm above the bottom (20±40 cm: 25% and 27%; 40± 60 cm: 25% and 23%; day and night, respectively) 4. Discussion when the animal occurrence was related to available leaf surface (Fig. 6). During the day, leaf tips were A total of 35 invertebrate species and thirteen ®sh occupied proportionately less than during the night. species were found in samples from the eelgrass habi- However, there was no statistically signi®cant dif- tat. In the bare mud habitat, a total of thirteen inver- ference in the vertical distribution between the day tebrate and four ®sh species were found. The average and night samples ( 2-test, 2 D 20:0, d.f. D 16, density of benthic invertebrates in the core samples in p D 0:220). the Zostera bed was 2693 ind m2. These densities are The diversity values were signi®cantly higher in similar to those observed in other temperate Zostera the night samples .x D 1:530 š 0:090/ than in the meadows of higher latitudes (Lappalainen, 1973; day samples .x D 1:160 š 0:132/ (Mann±Whitney BostroÈm and Bonsdorff, 1997). In the mid-Atlantic test, T D 364:5, p D 0:030). The average species region, lower invertebrate densities in Zostera mead- number was also highest in the lower part of the ows have often been observed both on the European leaves and decreased with increasing height. The west coast (Roscoff, France: 990 to 1310 ind m2;Ja- highest species number was recorded in the 20 to cobs, 1980) and the American east coast (Beaufort± 40 cm segment (1:9 š 0:4 species per sample during Morehead City, North Carolina: 700 to 1000 ind m2; the day and 3:8 š 0:4 species per sample during the Thayer et al., 1975). However, in Chesapeake Bay, night), and the lowest species number was recorded Orth (1973) found high summer densities of benthic in the 60 to 80 cm section during the day (0:6 š 0:3 invertebrates (2350 to 14 725 ind m2). 328 J. Mattila et al. / Journal of Sea Research 41 (1999) 321±332

vertical distribution of invertebrates in Zostera meadows (Nagle, 1968). The species number and abundances of epifaunal species associated with Zostera leaves were higher during the night than during the day. We believe that this pattern is mainly caused by the diel activity patterns of crustaceans such as Crangon vulgaris and Mysis spp., which may bury themselves in the sediment during the day, becoming more active and motile during the night. In seagrass beds, physical conditions such as oxygen saturation may vary drastically within short time intervals. Oxygen saturation may drop to near zero for several hours during night low tides (Broekhuysen, 1935). Low oxygen content during the night may markedly affect activity patterns of both invertebrates and ®sh, and force mobile species that are normally bottom dwellers higher up the water column, which could partly explain the increased animal abundances observed in the night samples. Fish species collected in the Zostera meadow in the Damariscotta River are primarily cold-water species whose ranges extend from the Arctic to the mid-Atlantic coast of the United States (Bigelow and Schroeder, 1953). Eight of the species collected in the Zostera meadow (Anguilla rostrata, Apeltes quadracus, Gasterosteus aculeatus, Menidia meni- Fig. 4. The relationship between (a) the total invertebrate abun- dia, Microgadus tomcod, Myoxocephalus aenaus, dance (r2 D 0:663, p D 0:034, n D 9), and (b) number of Pseudopleuronectes americanus and Syngnathus fus- 2 : : species in the benthic core samples (r D 0 468, p D 0 173, cus) are also commonly found in seagrass meadows n D 9) and the total Zostera marina biomass (sum of above- ground and below-ground biomass). in Cape Cod, Massachusetts (Heck et al., 1989). More ®sh were caught during the night than during the day, although the day±night difference in the The positive correlation between benthic inverte- grass bed was not as marked as in some other sea- brate abundance and seagrass is also consistent with grass habitats (Adams, 1976a; Horn, 1979; Orth and the ®ndings of most earlier studies (Lappalainen Heck, 1980; Bayer, 1981). Several factors may cause and Kangas, 1975; Adams, 1976a; Heck and Orth, the number of ®sh to increase in night catches. The 1980b). In our study, the differences observed be- higher abundances at night may be due to ®sh from tween the seagrass site and the bare mud-¯at site deeper areas that visit seagrass meadows in greater could theoretically also have been caused by the dif- numbers during darkness. Such a nocturnal activity ference in location instead of presence=absence of pattern may be a means of avoiding daytime preda- seagrass only. This, however, is unlikely, and since tors. In our study, the American eel was found in the the results accord well with earlier results from other Zostera meadow only during the night. On the other areas, we are convinced that the biomass of seagrass hand, some bigger predators, such as striped bass is the main factor explaining differences in faunal and adult decapods (Cancer irrogatus and Carci- abundances. nus maenas), were also caught with gillnets in the Only ®ve invertebrate species were common to eelgrass bed during the night. These species most the samples taken with the benthic corer and the epi- likely use the meadows as feeding areas, as eel- fauna bags. This is consistent with earlier results on grass meadows are known to be important feeding J. Mattila et al. / Journal of Sea Research 41 (1999) 321±332 329

Fig. 5. Abundance of Zostera marina-associated epifauna (mean number per sample š s.e.) per sample during day (stippled bars) and night (solid bars) sampling. areas for many ®sh species. For example, Adams shown that smaller fourhorn sculpins inhabit Zostera (1976b) found that 56% of the food consumed by beds to a greater extent than adjacent unvegetated ar- eelgrass-associated ®sh species is also produced in eas. In our study area, individuals of winter ¯ounder the grassbeds. caught in the daytime sampling were smaller than Seagrass beds are commonly considered to be individuals caught in the night sampling. However, refuges for juveniles and small individuals. We found the small individuals were present during both peri- that the average size of Carcinus maenas was smaller ods (2.3±6.7 cm by day and 2.5±9.6 cm by night; in the seagrass than in the mud ¯at. Since the mud one larger individual (29 cm) was also caught during ¯at is a simple habitat where predation risk is likely the day low tide). It is possible that more large indi- to be higher than in the complex seagrass habitat, it is viduals come in during the night to feed and that the likely that the smaller Carcinus maenas used the sea- smaller ones stay within the seagrass bed throughout grass as a refuge and nursery area (Heck and Orth, the day for better protection. 1980a,b). LalumieÁre et al. (1994) have analogously Quantitative ®sh abundances are hard to estimate from seine catches, since catch ef®ciency may vary considerably according to species and the time of the day (Gray and Bell, 1986). However, an attempt was made to roughly estimate the number of ®sh per square metre at the study sites. For this purpose, the seining ef®ciency was assumed to be 50% for all species in both habitats (compare Kjelson, 1977). The approximate daytime abundances were then calculated to be 1.12 ind m2 in the Zostera meadow and 0.01 ind m2 in the mud ¯at. The corresponding densities during the night low tide were 1.23 ind m2 and 0.07 ind m2. Sogard and Able (1991) estimated Fig. 6. Vertical distribution of epifauna on Zostera marina leaves during the day and night low tides. The occurrence of epifauna ®sh densities in New Jersey estuaries (Zostera and in each leaf zone is expressed in proportion to actual available Ulva lactuca habitats) during September to range surface area in that respective zone. between 7.3 and 9.7 m2. Atlantic silversides dom- 330 J. Mattila et al. / Journal of Sea Research 41 (1999) 321±332 inated their catches (2.5 to 4.2 ind m2). Adams 5. Conclusions (1976a) estimated the ®sh populations in Zostera meadows in Beaufort, North Carolina, to be about The Zostera bed studied in the Damariscotta River 0.8 to 2.0 ind m2 in September. Our density esti- supported signi®cantly higher numbers of species mations were relatively low compared to the mid- and individuals of both invertebrates and ®sh than Atlantic ®sh densities. Since seining is a relatively the nearby bare mud ¯at. Densities were higher at unreliable method of quantitative sampling, we may night than during the day. The invertebrate densi- have overestimated the catch ef®ciency of our sam- ties were similar or even higher than densities found ples. Adams (1976a) used both seine and trawl to in most other Zostera areas. Totally, 35 invertebrate collect his samples. The ef®ciency of these gear species were found in the Zostera bed. In con- was most likely close to ours, and so were also the trast, ®sh densities were low compared to reports abundance estimates. Sogard and Able (1991) col- of mid-Atlantic ®sh densities. A clear distinction lected their samples with a throw trap which is a was found in the vertical distribution of invertebrate relatively good quantitative sampling method (Pihl species; fourteen taxa were found only in the epi- and Rosenberg, 1982), and consequently the abun- faunal Zostera samples. The ®sh fauna consisted of dance estimates in Sogard and Able's study were primarily cold-water species that are typical also in also clearly higher than ours. Any underestimate of the mid-Atlantic region of the North American coast. true densities by seine catches is likely to be greater in seagrass beds than in bare sediments. This means that in our study the differences between seagrass Acknowledgements bed and mud ¯at are likely to be greater than actually reported. We thank the Director of Darling Marine Cen- Species richness and diversity values in the ter (University of Maine) Dr. Kevin Eckelbarger for Damariscotta River study area were relatively low providing us with excellent working facilities, and compared to eelgrass areas in the mid-Atlantic re- are especially grateful to Timothy Miller for logis- gion of North America (Nagle, 1968; Briggs and tical help and useful advice and information. Three O'Connor, 1971; Adams, 1976a; ; Nelson, 1980; anonymous reviewers provided helpful comments Orth and Heck, 1980; Thayer et al., 1984; Fonseca that profoundly improved the style and contents of et al., 1990; Heck et al., 1995), but both ®sh and the manuscript. Financial support was provided by infaunal diversity in the eelgrass bed were higher the Dauphin Island Sea Lab and the Academy of than in the non-vegetated area nearby. LalumieÁre et Finland, which are thankfully acknowledged. al. (1994) did not ®nd any support for high species diversity in a Zostera bed in the James Bay. Their study did not, however, contain any comparisons References with adjacent non-vegetated habitats. LalumieÁre et al. (1994) propose the shortness of the growing sea- Adams, S.M., 1976a. The ecology of eelgrass, Zostera marina son and harsh climate as reasons for low diversity (L.), ®sh communities, I. Structural analysis. J. Exp. Mar. in the James Bay. The diversity values calculated Biol. Ecol. 22, 269±291. for fauna in the Damariscotta River Zostera meadow Adams, S.M., 1976b. Feeding ecology of eelgrass ®sh communities. Trans. Am. Fish. Soc. 105, 514±519. ®t well in general latitudinal diversity patterns for Bayer, R.D., 1981. Shallow-water intertidal ichtyofauna of the Zostera in temperate areas (i.e. decreasing diversity Yaquina Estuary, Oregon. Northwest Sci. 55, 182±193. with increasing latitude; e.g. Setchell, 1935; Virn- Benacchio, N., 1938. 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