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BENTHIC FAUNA/COMMUNITIES cont.

Back To Benthic Fauna/Communities, PART 1.

3.3 NOVA SCOTIA (ATLANTIC COAST)

Benthic assessments have been reported for the Atlantic coast of Nova Scotia for only four locations, and for the most part (i.e., West Dover, Shelburne Harbour, and Lunenburg Bay) the benthic descriptions were a secondary component of a project; thus they are not comprehensive. As the Gulf of St. Lawrence has been shown to have very different communities due to differing environmental conditions, so too, the more exposed Atlantic coastline may be expected to possess different benthic communities from the sheltered Northumberland Strait.

Seventeen stations in St. Margaret's Bay were sampled at depths between 28 and 62 m in 1966 and 1967 (Brawn et al., 1968). Caloric content was determined rather than faunal density or biomass and the standing crop within this bay during the summer was found to average 76 kcal/m² and range between stations from 8-174 kcal/m². Annelids contributed 42% of the total caloric content followed by echinoderms (35%), arthropods (12%) and molluscs (11%). The arthropods contributed the greatest mass-specific content (>1.05 kcal/g live weight) while the annelids contributed 0.463-1.06 kcal/g, molluscs 0.374-0.791 kcal/g, and echinoderms 0.114-0.633 kcal/g. As well, the substrate quality appears to affect the total calories per square metre, peaking where there were almost equal amounts of fine sand (44% of material between 0.037-0.25 mm) and silt with clay (52% of material <0.037 mm). On either side of this peak the caloric content per square metre declines (See Figure 2 in Brawn et al., 1968). The authors suggest that as a rough approximation the biomass in grams wet weight per square metre may be multiplied by 644 cal/g (their mean value) to convert biomass to caloric content. Miller et al. (1971) published an energy flow diagram for St. Margaret's Bay and provide the following biomass estimates (kcal/m2) - lobsters (1.7), brittle stars (2.0), seastars (4.0), periwinkles (12.0), mussels (13.6), and sea urchins (87.1).

In 1967-68 St. Margaret's Bay was sampled for the polychaete Pectinaria hyperborea (Peer, 1970). Samples were collected from 60-80 m water depth within bottom deposits consisting of fine aerobic mud. This was an area of known high P. hyperborea density (1.4-478 individuals/m²; mean=100.4 /m2, n=24 stations). Production estimates ranged from 0.07 to 15.6 g/m², with all of the stations producing >5 g/m² laying within the deep, muddy areas of the bay.

The spatial organization and abundance of polychaetes was also investigated in St. Margarets Bay between 1977 and 1981 (Volkaert, 1987). Sampling at depths of 46 m in substrates of clay-silt (fine sand 12-21%, silt 46-67%, clay 19-37%) 58 and 62 polychaete species were identified at two separate stations with the combined sites representing 67 species. Polychaetes formed 95% of the benthic fauna sampled. Total benthic biomass was estimated at 227.47 g wet weight/m². Polychaete mean densities ranged from <1 individuals/m² (24 species) to >1,000 individuals/m² (Aricidea sp. [juveniles] and Cossura longocirrata [juveniles]). Filter feeders formed 10.4% of the fauna and surface deposit feeders 23.9%. The remaining trophic groups were burrowers (25.4%), herbivores (7.5%), carnivores (31.3%) and unknown (1.5%).

Elner and Campbell (1987) provide brief descriptions of two sites in southern Nova Scotia sampled in 1979-81 - a macroalgal bed (Lobster Bay) and an urchin barren (Shelburne Harbour). Depths at each station ranged from 3 to 10 m and the substrates at each consisted of cobbles and boulders densely embedded in a shell-sand matrix. At the macroalgal (ungrazed by urchins) site macroalgae (predominantly Chondrus crispus and Laminaria spp.) were present at near 90% cover and the invertebrates present were gastropods (predominantly Buccinum undatum), the bivalves Mytilus edulis and Modiolus modiolus, polychaetes, amphipods, the crabs Pagurus spp., Hyas spp., Cancer spp. and Carcinus maenas, and the seastar Asterias spp. In contrast, at the urchin barren site, fleshy macroalgal cover (mainly Desmarestia) was reduced to <3% cover and most of the algal biomass was the crustose coralline, and urchin resistant, Corallina officinalis. Sea urchins (Strongylocentrotus drobachiensis) dominated, with densities between 29 and 90 individuals/m². Other invertebrates present included Littorina littorea, Acmaea testudinalis, Tonicella sp., Mytilus edulis, Modiolus modiolus, the brittlestar Ophiura spp, Homarus americanus, Cancer irroratus and borealis, and Asterias spp.

Densities of 0.4 scallops (Placopecten magellanicus)/m2, 3.71 seastars/m² for Asteria vulgaris and forbesi, 0.03 rock crabs (Cancer irroratus)/m² and <0.05 moon snails (Lunatia heros)/m² were reported for Lunenburg Bay based on sampling in 1990 (Hatcher et al., 1996). Water depth in this area is approximately 8 m (below low tide) and the substrate is large cobble with kelp, grading through shale gravel and shell fragments, to mud and silt at the channel margins. Within this same bay in 1991-1992 mean scallop densities were estimated at 0.525/m², Asterias spp. densities at 0.8-1.2/m², and rock crabs at 0.02/m² (Barbeau et al., 1996). Sampling in 1991-92 was done in <10 m water depth on substrates of shell fragments, medium to fine granite slate, and cobble on silty sediment, grading to sands and silt size sediments as it shoals near the shoreline.

Drummond-Davies et al. (1982), in a mark-recapture population estimate in West Dover during 1977 estimated a biomass of 26.3-61.0 g/m² for Cancer irroratus in a kelp bed of depth 1-9 m. They refined their estimate to 52.1-61.8 g/m² which they equated with approximately 0.5 crabs/m².

Summary of Nova Scotia (Atlantic Coast)

Very little work has been done along the Nova Scotia shores with respect to benthic fauna or communities. Polychaetes have been reported on and in some areas (with appropriate substrate) may form up to 95% of the benthic biomass. Annelids in general were found in St. Margaret's Bay to contribute the greatest to the caloric content of the benthic community, followed by echinoderms, arthropods and molluscs. However, on a mass-specific basis the arthropods contribute the greatest caloric content, followed by the annelids, molluscs and echinoderms. Typical species within these groups reported in the literature for this area are:

Bivalves: Mytilus edulis, Modiolus modiolus, Placopecten magellanicus
Gastropods: Buccinum undatum. Littorina littorea, Acmeae testudinalis, Lunatia heros
Polychaetes: Pectinaria hyperborea, Aricidea sp., Cossura longocirrata
Arthropods: Pagurus spp., Cancer irroratus, Cancer borealis, Carcinus maenas, Homarus americanus, Hyas spp.
Echinoderms: Asterias spp., Ophiura spp.

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3.4 NEW BRUNSWICK (BAY OF FUNDY)

The Bay of Fundy, separating New Brunswick from Nova Scotia, has been the subject of few studies since Whiteaves (1901) summarized early work in the 19th Century by Verrill, Stimpson, Ganong and others (Caddy, 1970). This current literature review found no relevant studies on the benthic fauna or communities within the bay prior to 1966, and in the intervening 30 years since then only six relevant studies have been published.

During 1966-1967, 196 dredge hauls were retrieved from depths of 55-128 m in the Bay of Fundy. Caddy (1970) describes the results of these surveys. The substrate is composed of rock, gravel, sand and mud but was not sampled in detail and quantified. One hundred and thirty invertebrate species were found forming five faunal assemblages, with three of these assemblages appearing to be correlated with substrate type (Table 15). Due to the dredge hauls extending over large areas (up to 1.5 km long), it is likely that the collection incorporated more than one community and so faunal assemblages were described rather than communities. The 130 invertebrate species came from nine taxa (Table 16) with molluscs contributing the greatest species number (36; [18 bivalves, 14 gastropods]), followed by poriferans (21), echinoderms (18), polychaetes (17), bryozoans (16) and crustacean (12). The remaining groups contributed approximately 7% of the total species number.

Table 15. Constituent species of the benthic assemblages and related substrate type from Bay of Fundy sampling 1966-1967. Data from Caddy (1970).

Table 16. Distribution of 130 invertebrate species by Phyla/Class from Bay of Fundy sampling 1966-1967. Data from Caddy (1970).

Wildish et al. (1972) determined two animal assemblages in L'Etang Inlet, Bay of Fundy in 1970-1971, prior to the discharge of effluent from a hardwood pulp mill into this environment. Their study site was a shallow water inlet (0-20 m deep) with a substrate of mud, shell, gravel, and sand. The assemblages are:

1. Euryhaline assemblage on inshore mud - Nephthys ciliata, Neries virens, Mya arenia, Macoma balthica
2. Stenohaline assemblage on inshore mixed mud/sand/shell gravel - Lumbinereis fragilis, Ninoe nigripes, Nephthys incisa, Astarte sp.

Calculated mean densities of individuals and species, and biomass, for this sampling period based on 116 grab samples reported by Wildish et al. (1972) are presented in Figure 4. The overall mean densities for individual animals was 182.2 /m², for species density was 36.36 species/m², and the mean biomass was 139.24 g/m². The mean individual density appears to peak in spring and during the sampling period samples ranged between 10 and 772 individuals/m². Mean species density remained quite constant, with samples ranging from 3 to 112 species/m². Biomass per month ranged from 2.54 g/m² (August) to 1,532 g/m² (April), with the mean biomass fluctuating through the year between approximately 25 and 300 g/m². Biomass appears to peak in this area in spring and late Autumn, and decline to low levels through winter and summer. Stations were revisited in L'Etang Inlet in 1972 and 1975 (Wildish et al., 1977) but these data are not included here as the pulp mill had been operating since 1971 discharging effluent into the inlet and so the benthic assemblages no longer represented 'natural' conditions.

Figure 4: Mean biomass (upper), and density of individuals and species (lower) over time in L'Etang Inlet, New Brunswick, 1970-71. Data from Wildish et al. (1972).

In a review of the marine and coastal systems of the Passamoquoddy region, Wildish (1983) provides data on four estuaries (L'Etang, St. Croix, Digdeguash, Musquash) and the Saint John Harbour. In depths ranging from 1 to 28 m, on substrate ranging from fine sand to fine silt the mean number of species at these locations combined was 17.16 species/m² and ranged from 2 to 68 species/m². The mean number of individuals/m² was 199 with a range from 3 to 1,390 /m². One value of 1,208,470 /m² (St. Croix estuary, 1974) was excluded from this analysis as being so influential as to make the mean unrepresentative and is almost three orders of magnitude larger than the next highest value. Mean densities for the individual areas are provided in Table 17.

Table 17. Means and standard deviations of species and individuals densities (/m²) in four water bodies in New Brunswick. Digdeguash estuary was excluded due to single sample only and extreme value from St. Croix referred to in text is also excluded. Data from Wildish (1983).

Within Passamoquoddy Bay, Logan et al. (1983) recognized four distinctive communities on hard surfaces (e.g. boulders, rock ledges, etc.) - 1) Crustose coralline algae, 2) Terebratulina septentrionalis (Brachipoda), 3) man-made structures, and 4) shell substrates. The crustose coralline community is characterized by the widespread occurrence of several species of encrusting coralline algae and is generally a moderately shallow community (i.e., 20-40 m) dominated by suspension feeders and herbivorous browsers. The Terebratulina septentrionalis community is the most important hard substrate community in Passamoquoddy Bay in terms of total biomass and is dominated by chitons, hydroids, anenomes and bryozoans in addition to T. septentrionalis. It is generally under boulders in depths of 0-20 m, progressively emerging with increasing depth to become completely emergent below 50 m. This community is also dominated by suspension feeders and browsers. The other two communities are very localized to two surfaces: man-made structures such as weir poles, wharf pilings and floats, and to abandoned valves of bivalve shells. The number of species present within these communities is greatest for the crustose coralline and least for the shell substrates (Table 18). Differences in species number between these communities are greatest for the Mollusca, Arthropoda and Echinodermata.

Table 18. Number of species per taxon from four benthic communities in Passamoquddy Bay, New Brunswick based on 15 years of sampling. Table modified from Logan et al. (1983). An equal number of species does not imply the same species are present in the different communities. For list of species present, and relative abundance, see Logan et al. (1983).

Summary of New Brunswick (Bay of Fundy)

The reported studies from the Bay of Fundy describe communities from two substrate types Ð soft sediment and hard surface. Within the soft sediments there is great variability depending upon sampling site and time of year. Species density ranges from approximately 3-112 species/m², individual density from 10 to 772 individual/m² and biomass from approximately 2.5 Ð 1,500 g/m². On hard substrates molluscs have the greatest species diversity, forming up to 30% of all species in the two most widespread hard surface communities. Echinoderms represent approximately 11-14% on the surfaces, arthropods ~12%, coelenterates 9-11% and annelids <10%.

In towing over large areas, and so presumably several substrate types, the percentage composition of the catch by group becomes quite even. There were 18 bivalve species, 14 gastropods, 17 polychaetes, 12 crustaceans and 18 echinoderms collected by Caddy (1970). However, these do not represent distinct communities but rather combined assemblages over 1.5 km length tows.

Representative (numerically 'dominant/common') invertebrates reported for the Bay of Fundy include:

Bivalves: Spisula spp., Modiolus modiolus, Chlamys islandica, Hiatella arctica, Placopecten magellanicus, Anomia spp., Mya arenia, Macoma balthica, Astarte spp.
Gastropods: Buccinum undatum, Colus stimpsoni, Neptunea decemcostata, Clione vastificia.
Polychaetes: Polydora spp., Thelepus cincinnatus, Nephthys ciliata, Nephthys incisa, Nereis virens, Ninoe nigripes, Lumbrinereis fragilis.
Arthropods: Pagurus spp., Hyas coarctatus.
Echinoderms: Asterias vulgaris, Henricia spp. Crossaster papposus, Solaster endeca, Gorgonocephalus articus, Hippasterias phryginia.

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3.5 U.S. Coastal Studies