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BENTHIC FAUNA/COMMUNITIES cont.

Back to Benthic Fauna/Communities, Part 1.

3.5 UNITED STATES COASTAL STUDIES

Benthic studies of the Atlantic coast of the United States were reviewed in addition to maritime and Gulf locations due to the lack of Canadian information and the recognition that the waters within Northumberland Strait and St. Georges Bay may be quite similar to more southern waters (see Cameron and Mitchell, 1999). Twelve locations along the American Atlantic coast between Massachusetts Bay, Massachusetts, and Cape Lookout, North Carolina, have reported studies between 1933 and 1973 and these are summarized below.

In 110 dredge hauls at Cape Ann, Massachussets Bay, between 1933 and 1937, Dexter (1947) found 48 invertebrate species. The water was shallow (maximum depth 10 m) and the substrate composed of fine mud (clay) deposits with occasional mixtures of sand, and some outcroppings of rocks. The community was described as Laminaria-Cancer characterized by Laminaria digitata, L. saccharina, and Cancer irroratus. Of the 48 species reported, the dominant ones (present in >20% of the hauls) were Asterias vulgaris (98% of hauls), Cancer irroratus (64%), Crangon septemspinosa (48%), Gammarus locusta (44%), Polineces heros (40%), Mytilus edulis (40%), Littorina littorea (38%), Lepidonotus squamatus (38%), isopods (36%), Pagurus longicarpus (30%), Nassarius trivittatus (26%), Chalina oculata (26%), hydroids (12-38%), and bryozoans (26-44%). Maximum densities per haul (mean densities not provided) of invertebrates ranged from one organism captured/60m² (0.016/m²) for uncommon organisms up to 0.56/m² (Crepidula fornicata), 0.62/m² (Carcinus maenas), 0.65/m² (Pagurus longicarpus), 0.66/m² (Crangon septemspinosa), 0.68/m² (Asterias vulgaris), 0.85/m² (Cancer irroratus), and 1.33/m² (Nassarius trivittatus).

Ipswich Bay, Massachusetts, was sampled during summer months between 1933 and 1940 using 58 dredge hauls at depths beween 3.5 and 24.5 m (Dexter, 1944). The substrate was of two types in the sampled areas - hard sand and rocky bottom. Including fishes, 110 species were identified as part of the bottom community in this bay. The most commonly captured invertebrate and algal species (>20% occurrence in dredge hauls) were:

Bryozoa - Bugulla flabellata, Membranipora spp.
Hydroza - Sertularia pumila, Obelia spp.
Annelida - Spirobis spirobis, Lepidonotus squamatus
Gastropoda - Lacuna vincta, Polinices heros
Crustacea - Gammarus sp., Caprella acutifrons, Aeginella longicornis, Idothea baltica, Pagurus longicarpus, Cancer irroratus, Crangon septemspinosa
Echinodermata - Strongylocentrtus drobachiensis, Echinarachinus parma, Asterias vulgaris, Henricia sanguinolenta
Tunicata - Molgula manhattensis
Algae - Laminaria saccarhina, Agarum cribrosum, Euthora cristata, Ulva lactuca, Chondrus crispus, Callithamnion sp. Gigartina stellata, Chaetomorpha sp., Enteromorpha sp.

In Ipswich Bay, maximum densities per haul (mean densities not provided) of invertebrates ranged from one organism captured/100m² (0.01/m²) for uncommon organisms up to 0.52/m² (Gammarus sp.), 0.93/m² (Asterias vulgaris), 1.0/m² (Sertularia pumila), 1.1/m² (Spirobis spirobis), and 5.31/m² (Echinarachinus parma) (Dexter, 1944).

In the late 1930s-early 1940s (sampling date not given) Menemsha Bight, Massachusettes, was examined for benthic fauna (Lee, 1944). Samples were taken from depths ranging from 2 to 25 m and substrates of two qualitatively described types - 1) fine to coarse sands, and 2) a soft fine clay. Typical species (>5 individuals/20 L sample) collected from the sand areas were Tellina tenera, Glycera dibranchiata, Emerita talpoida, Clymenella torquata, Gammarus locusta, Ampelisca macrocephala, and Echinarachinus parma. From the clay substrate equivalent species were Crepidula fornicata, Trophonia affinis, and Venericardia borealis. The eight most abundant species over the Bight (with range of average abundances) were Ampelisca macrocephala (3-33/20 L sample), Clymenella torquata (0-35/sample), Crepidula fornicata (0 at most stations, 423/sample in clay sediment), Echinarachinus parma (0-6/sample), Callocardia morrhuana (0-3/sample), Cyprina islandica (0-4/sample), Tellina tenera (0 at most stations, 9/sample at single zone of 15 stations) and Emerita talpoida (0 at most stations, 8/sample at single zone of 15 stations). The 20L sample of Lee (1944) represents an area of substrate of 0.5m² by 0.1 m sediment depth.

Greenwhich Bay, Rhode Island, was sampled in 1951-52 to assess the bottom invertebrate population (Stickney and Stringer, 1957). Water depth was from 3-9 m with a substrate of silt-mud, sand and a combination of these; median particle diameters ranged from 0.008 (mud) to 0.35 (sand) mm. One hundred and fourteen species were identified of which 37 were polychaetes, 32 molluscs (19 bivalves, 13 gastropods), 26 arthropods, and the remaining 19 representing Porifera (2 species), Coelenterata (4 sp.), Nemertea (2 sp.), Bryozoa (5 sp.), Echinodermata (2 sp.), Enteropneusta (1 sp.), and Tunicata (3 sp.). Three communities of these invertebrates were determined:

Ampelisca Community - muddy substrate and dominated by the amphipod Ampelisca spinipes (> 10,000 /m² in some places). Also present were Corophium cylindricum, Tharyx acutus, Tornatina canaliculata, Macoma tenta, and Podarke obscura.

Crepidula-Nereis-Neopanope Association - on shelly substrate and dominated by Crepidula fornicata. Also present Anomia simplex, Nereis succina, Neopanope texana, Libinia emarginata, Urosalpinix cinerea, Venus mercenaria, Bryozoa and Porifera.

Sand bottom community - Sand substrate inhabited by Ensis directus, Glycera dibranchiata, Crangon septemspinosa, Pagurus longicarpus, Dioptera cupreae, Haploscolops fragilis, Spio setosa, and Tellina tenera.

In addition to these discrete areas are transition zones between them which contain populations of members from more than one of the communities listed above. Dominant species within Greenwhich Bay were Ampelisca spinipes (42-978/m²), Corophium cylindricum (0-700/m²), Spiochaetopterus oculatus (2-362/m²), Nereis succinea (0-296/m²), Nassa obsoleta (7-282/m²), Pectinaria gouldii (0-266/m2), Podarke obscura (0-260/m²), Heteromastus filiformis (0-63/m²), and Venus mercenaria (average abundance 1-22 individuals/m²).

In the 1950's, another embayment, Buzzards Bay, Massachussets received a great deal of research. In 1955, 19 stations were sampled between 7 and 20 m depth over two substrate types, a sand bottom (median particle size 0.18-0.68 mm) and a silt-clay bottom (median particle size 0.01-0.04 mm) (Sanders, 1958). The results from these two substrates are presented in Table 19. Differences in the composition of the two communities are quite clear with the sand bottom dominated by the amphipods Ampelisca spinipes, Ampelisca macrocephala, and Byblis errata, together accounting for 36% (by number) of the community. The silt-clay community is not dominated by a single group; the five species of polychaetes listed comprise 29.6% of the community and bivalves (3 species) contribute an equal amount (29.1%) by number. Filter feeders are more common on the sand bottom while deposit feeders predominate on the silt-clay bottom.

Continued sampling in Buzzards Bay in 1956-57 resulted in the identification of 95 species in these years (Sanders, 1960). Samples were taken in 19 m of water with the majority (20 of 24 stations) of the substrate composed of 78-90% silt clay. Of the 95 species collected, 33 were polychaetes, 26 molluscs (12 bivalves, 14 gastropods), and 24 crustaceans. The remainder were oligochaetes, turbellarians, nemertines, sipunculids, enteropneustans, tunicates, anthozoans, and pycnogonids. The most commonly occurring species by number were the polychaetes Nephthys incisa, Ninoe nigripes, Lumbrinereis tenuis, the molluscs Nucula proxima, Callocardia morrhuana, Cylichna orzya, Turbonilla sp., and the crustaceans Hutchinsoniella macracantha, and Ampelisca spinipes. The polychaetes Nucula proxima and Nephthys incisa together comprise >76% of the benthic fauna, and 95% of the assemblage is formed from only 11 species (Nucula proxima, Nephthys incisa, Ninoe nigripes, Cylichna orzya, Callocardia morrhuana Hutchinsoniella macracantha, Lumbrinereis tenuis, Turbonilla sp., Spio filicornis, Retusa canaliculata, and Dorvillea caeca). In terms of biomass, the most significant species were Nephthys incisa (28.95% by weight), Bostrichobranchus pilularis (23.49%), Callocardia morrhuana (14.97%), Nucula proxima (13.98%), and Micrura leidyi (4.83%). An additional eight species (Arabella iricolor, Lumbrinereis fragilis, Ninoe nigripes, Nassarius trivittatus, Cerianthus americana, Flabelligera affinis, Cerastoderma pinnulatum, Yoldia limatula) each contributed less than 2%, but combined, these 13 species accounted for 95% of the measured biomass. Sanders (1960) estimates that a minimum of 87.5% of these organisms are deposit feeders with suspension feeders only representing about 4.3% of the community.

Table 19. Sampling conditions and benthic results (ranges and percentages) of Buzzards Bay sampling, 1955. Data from Sanders (1958)

Rhoads and Young (1970) suggest three trophic group distributions within Buzzards Bay:

1. Homogenous suspension feeder trophic group - Resulting when deposit feeders are largely excluded from the suspension feeder biotope by an inadequate food source in the sediment.
   
   
2. Homogenous deposit feeder trophic groups - Resulting when suspension feeders are largely excluded from the deposit feeder biotope by frequent resuspension of biogenically reworked sediments containing fine particles. Sediment instability and turbidity probably limiting for most suspension feeders.
   
   
3. Mixed trophic groups - Occurrence of a diverse suspension-feeder population on a mud bottom reworked by deposit feeders indicating physical stability of the bottom.

Meiofauna (nematodes, kinorhynchs, ostracods, copepods, turbellarians, halacarids, gastrotrichians, and cephalocarideans) were also sampled in Buzzards Bay by Weiser (1960) in 1957 at three of the stations used by Sanders (1958). Total density of organisms ranged from 1.69*105 to 1.86*106 individuals/m² with dry weights calculated as between 1 and 6 g/m². Nematodes (103 species) formed 89-99% of the total meiofauna with seven nematode species (Odontophora pugilator, Odontophora pupusi, Anticoma litoris, Dorylaimopsis metatypicus, Terschellingia longicaudata, Neochromadora pistillata, and Odontophora loffleri) each contributing >8% abundance. By number of individuals, the meiofauna was found to exceed the macrofauna by factors between 30 and 100 times, with a factor of 100 being the more common. Wigley and McIntyre (1964) report meiobenthos:macrobenthos ratios of 30:1 to 100:1 for a variety of studies in the eastern and western North Atlantic as well. The nematodes in Buzzards Bay could be grouped according to substrate and there was discerned an Odontophora-Leptonemella community in sandy habitats (corresponding to the Ampelisca macrofauna community) and a Terschellingia longicaudata-Trachydemus mainensis (kinorhynch) community in the silty habitat (corresponding to the Nucula proxima-Nephthys incisa macrofauna community).

A cruise in 1962 south of Marthas Vineyard, Massachusetts, sampled six stations at depths from 40-146 m (among deeper as well, not included here) over a substrate predominantly of sands and small gravels (median particle size 0.04-1.47 mm) (Wigley and McIntyre, 1964). Crustaceans (amphipods) dominated with densities ranging from 5 to 4,235/m² and wet weights of 0.02 to 33.07 g/m². Polychaetes were second ranging from 270 to 1,735/m² and 6.37 to 47.55 g wet weight/m². Polychaetes account for between 12 % (40 m) and 51.5% (69 m) of the total density, and when combined with the crustaceans account for >88% of all invertebrates in depths < 70 m. As percentage of total numbers molluscs ranged from 63 to 83% at less than 60 m and 2.8 to 37% between 60 and 100 m. At the greater depths (>70 m) the molluscs (27-30% of density) and echinoderms (15-38% of density) predominate. The greatest total density of fauna (>5,000 individuals/m²) occurred in the shallow water (<60 m) and was <2,000 /m² in all deeper stations. Between 40 and 100 m nematodes were found to generally comprise 78-94% of the meiofauna (One value of 39% was recorded at 51 m on a gravel substrate), with estimated total meiofauna densities of 1.27*105-9.88*105 individuals/m². The ratio of meibenthos density to macrobenthos between 40 and 100 m averaged 170:1 and ranged from 35:1 to 770:1 with four of the six station showing ratios between 170:1 and 185:1.

Sampling of an offshore transect from 2.5 to 200 m depth off of Cape Lookout, North Carolina, was conducted in 1965 (Day et al., 1971). Only those stations between 2.5 and 80 m depth are discussed here. The substrate ranged from fine to coarse sand (median particle diameters 0.15-0.609 mm). Thirty invertebrate species were collected at 2.5 m depth, 35 species at 5 m, 66 species at 10 m, 75 species at 20 m, 79 species at 39 m, and 77 species at 80 m. The species list of collected organisms in this area is considerably different from all other studies reported herein (i.e., is of a different biome than the more northern studies). Polychaetes showed the greatest diversity ranging from 13 species (2.5 m depth) to 50 species (20 m) per station. The number of species of other groups captured per station ranged from 4 (20 m) to 11 (39 m) for amphipods, 2 (5 m) to 13 (20 and 80 m) for bivalves, 2 to 4 for decapods at all depths, and 1-2 at all depths for gastropods and echinoderms. The most abundant organisms in depths of less than 80 m were amphipods and polychaetes. Of note with this survey is the very large sample size; the authors report 15,777 individuals of 619 species being identified.

In 1969 Cape Cod Bay, Massachusetts, was sampled for benthic organisms (Young and Rhoads, 1971). Water depths sampled ranged from 12 to 42 m and the substrate was composed of sand, silt, and clayey-silt (mean particle diameter < 0.75 mm). One hundred and thirteen species were reported consisting of polychaetes (46 sp.), molluscs (25 sp. [18 bivalves, 6 gastropods]), and amphipods (18 sp.). The remaining groups were isopods (3 sp.) Cumacea (5 sp.), mysids (3 sp.) echinoderms (5 sp.), cnidarians (3 sp.) and one species each of Ascidiacea, Archiannelidae, Oligochaeta, Nemertea, and Phoronida. Polychaetes, molluscs and amphipods comprise 94-98% of the macrofauna by number. Total densities of all species combined averaged 15,410 animals/m² with a maximum of 30,150/m² and the density of species (number species/0.1m²) ranging from 34 to 56. The most abundant macrofauna are all polychaetes (Euchone incolor, Capitella capitata, Spio limicola, Ninoe nigripes, and Asabellides oculata). Polychaetes also predominate in terms of biomass (24.5-91.8% of total ash-free dry weight) if hard parts (i.e., large bivalve shells, urchin tests) are excluded. Calculation of diversity indices within Cape Cod Bay (Brillouns index) resulted in values of H between 2.65 and 3.53 (mean H = 3.08). Deposit feeders are reported as being four to seven times as abundant than suspension feeding species in this bay.

O'Connor (1972) reported on 144 samples taken in Moriches Bay, Long Island, New York, in 1969-70. This is a shallow bay (mean depth 1.2 m) with three types of substrate - sand, clay-silt, and transitional between these two. He found bivalve molluscs the most abundant group on the sand substrate (4,136 individuals/m²), with polychaetes next in abundance (557 /m²), followed by gastropods (462 /m²) and amphipods (189 /m²). All other groups were present at less than 25 /m². In the clay-silt substrate amphipods were most abundant (662 /m²) followed by polychaetes (317 /m²), gastropods (269 /m²), bivalves (76 /m²) and tunicates (50 /m²). A square metre of the transition sediments supported 1,253 amphipods, 541 gastropods, 501 polychaetes, 486 bivalves, and 54 decapods. Total densities of all organisms combined ranged from 1,433 to 5,401 /m². Bivalves were found to dominate the biomass in the sand (36.1 g wet weight/m²) and transitional substrates (49.9 g/m²). In the clay-silt substrate polychaetes (17.7 g/m2) and tunicates (15.8 g/m2) predominated. With the exception of the polychaetes (5.5 g in sand, 10.6 g in transition sediments) in sand all other taxa were present at <2.1 g/m², in silt-clay at <7.5 g/m², and in the transition sediments at <5.3 g/m². Total biomass in sediments was calculated as 58.9 g/m² for sand, 71.9 g/m² for the transitional sediments, and 46.1 g/m² for the clay-silt substrate. The dominant species by weight in Moriches Bay were Mercenaria mercenaria, Mytilus edulis, Clymenella torquata, Bostrichobranchus pilularis, Molgula provisionalis, Neries succina, and Nassarius obsoletus. Suspension feeders were found to dominate in sandy (71.5% of biomass) and transitional (61.2 % of biomass) sediments. In clay-silt sediments deposit feeders form the majority (55.5%) of the biomass.

Two hundred and seven stations were sampled in Delaware Bay, Delaware, in 1972 and 1973 (Maurer et al., 1978). A total of 169 different species were collected in the two years from depths primarily (95% of stations) less than 15.5 m. This large number of stations sampled a very large variety of substrates, from 0-20% silt clay, to 70-100% silt clay. Annelids are reported as dominating (40.8% of total species), followed by arthropods (28.9% of species), molluscs (17.8%), ectoprocts (7.1%) and nemertean, cnidarians and echinoderms together accounting for 5.3% of species. Total density of organisms was low in this bay (722 individuals/m²), and most samples were dominated by only one or two species. The most commonly occuring species and their respective densities were:

• Tellina agilis (Bivalve, 57-62% occurrence, average density 45/m², maximum density 410-800/m²).
• Ensis directus (Bivalve, 34% occurrence, average density 62.5/m², maximum density 490-780/m²).
• Glycera dibranchiata (Polychaete, 24-29% occurrence, average density 5/m², maximum density 60-80/m²).
• Heteromastus filiformis (Polychaete, 24-28% occurrence, average density 17/m², maximum density 490/m²).
• Gemma gemma (Bivalve, 25% occurrence, average density 319/m², maximum density 2,290-4,160/m²).
• Mulinia lateralis (Bivalve, 16-21% occurrence, average density 26/m², maximum density 2,760/m²).
• Nucula proxima (Bivalve, 12-21% occurrence, average density 13/m², maximum density 250-630/m²).
• Nephthys picta (Polychaete, 16-18% occurrence, average density 2.5/m², maximum density 60/m²).
• Protohaustorius wigleyi (Amphipod, 14% occurrence, average density 8.4/m², maximum density 160-310/m²).

Using cluster analysis techniques, Maurer et al. (1978) determined nine separate faunal assemblages in the bay in 1972 and four in 1973. Deposit feeders were estimated to comprise 45% of the community, while suspension feeders form 24.8% and the remainder were carnivores (18.3%), omnivores (10.7%), and ectoparasite or commensals (1.2%). It was concluded that Delaware Bay comprises a mosaic of faunal assemblages, some of which fit the classic community concept but others are thought to represent species distributed along an environmental continuum rather than as discrete groups.

In Chesapeake Bay, Maryland, in 1973-74, as part of an enclosure predation study, the natural benthic fauna was examined (Virnstein, 1977). The area sampled was shallow water (1.4 m) of sand bottom. Of the 13 top ranked species 11 were annelids (10 of these polychaetes). In ranked order the dominant species reported were Peloscolex gabriella, Spiochaetopterus oculatus, Heteromastus filiformis, Streblospio bendeicti, Phoronis psammophila, Glycinde solitaria, Polydora ligni, Paraprionspio pinnata, Scolelepsis squamata, Scoloplos robustus, Eteone heteropoda, Nereis succinea, and Acteon punctostriatus. Average densities ranged from 89 Acteon punctostriatus/m2 to 3,971 Peloscolex gabriellae/m2. The polychaete density ranged from 105 Eteone heteropoda/m2 to 1,424 Heteromastus filiformis/m2. Of note is the complete lack of bivalves and crustaceans from the dominant species list. Phoronis psammophila is the only suspension feeder, the remainder of the dominant species are all deposit feeders.

As part of an experiment on clam predation, MacKenzie (1977) reports some predator densities in Long Island Sound, Connecticut. The crab Cancer irroratus density was estimated at 3.6-57.0/m2 (juveniles) and 0.7-1.1/m2 (adults). The mud crab Neopanope sayi was estimated at 7.5-53.8/m2 and the gastropods Urosalpinix cinerea and Eupleura caudata from 3.3-19.5/m2. Juveniles of the seastar Asterias forbesi ranged in density from 1.1-72.1 individuals/m2 and adults from 0.1-2.3/m2. Finally, the quahog Mercenaria mercenaria was present at <1 clam/m2.

Summary of U.S. Coastal Studies

As may be expected from sampling over an area as large as the eastern American seaboard, and consequently over a large variety of temperature, salinity and substrate characteristics, the resulting invertebrate communities are quite variable. Table 20 summarizes the number of dominant or common species by group from the studies reported here.

Table 20. Summary of number of reported dominant or common species by group for various U.S. studies. For sources of studies see text.

Total densities of fauna on and in appropriate substrate commonly range up to >5,000 individuals/m², with some notable densities including 1,735 polychaetes/m², 4,136 bivalves/m², and 4,235 amphipods/m². Deposit feeders are generally reported as being between 2 and 20 times as abundant as suspension feeders, though this is entirely dependent upon the substrate being sampled. The ratio of meiofauna to macrofauna is on the order of 100:1 to 170:1.

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