EXECUTIVE SUMMARY
The St. Georges Bay Ecosystem Project is a collaborative study between Government, harvesters, First Nations and St. Francis Xavier University of the St. Georges Bay ecosystem. A lack of information on benthic fauna and community structure within the St. Georges Bay area has been identified by Davis et al. (1999), thus a comprehensive literature review was initiated to assess and summarize existing information on the benthic fauna and communities of nearby and relevant locations. The information has been principally drawn from the primary literature and is delimited by depths of 0 to 150 m, and north-south geography of the northern Gulf of St. Lawrence south to North Carolina. This large area of coastline was grouped and reported on as five separate zones - Northumberland Strait, Gulf of St. Lawrence, Nova Scotia (Atlantic Coast), New Brunswick (Bay of Fundy), and American coastal studies.
Only a small number of studies of the benthos have been conducted within Northumberland Stait; within this channel it appears that polychaetes are present in the greatest species abundance followed by amphipods, bivalves, gastropods, and non-amphipod crustaceans and echinoderms. Algal species are dominated in terms of species number by Rhodophytes, followed by Phaeophytes and Chlorophytes. Invertebrate biomass ranges up to 1,400 g/m2 with bivalves, gastropods, polychaetes and echinoderms making up the majority of the contribution. An extensive study (Caddy et al., 1977) provides an indication of the diversity and abundance of the benthic fauna within this area.
The Gulf of St. Lawrence is ecologically divisible into southern and northern areas with different species compositions between the two areas. Within the southern Gulf the bivalves, gastropods and polychaetes appear to be the dominant organisms. In terms of biomass, bivalves appear to contribute to a greater degree than gastropods. Polychaetes are variable, ranging from the greatest contributor of biomass to the least of the three principle groups. In the northern Gulf, including the St. Lawrence River estuary, crustaceans are a more significant component of the benthic invertebrate presence. Individual species (e.g., whelks, seastar species) appear to dominate the benthos to a greater degree in the northern Gulf, whereas in the southern Gulf the communities tend to be composed of multiple species in a particular guild (e.g., several vertebrate and invertebrate species acting as predators). Polychaetes continue to contribute significantly to the benthic community in the northern Gulf of St. Lawrence.
Very little work has been done along the Atlantic coast of Nova Scotian shores with respect to benthic fauna or communities. Polychaetes have been reported on and in some areas may form up to 95% of the benthic biomass. Annelids in general were found in St. MargaretŐs Bay to contribute the greatest to the caloric content of the benthic community, followed by echinoderms, arthropods and molluscs.
The reported studies from the Bay of Fundy describe communities from two substrate types - soft sediment and hard surface. Within the soft sediments there is great variability depending upon sampling site and time of year.
Benthic studies from the eastern American States were included as well. 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. Total densities of fauna on and in appropriate substrate were high.
The 42 studies summarized range over a large area and a diversity of environments, yet they contain a good deal of consistency in results. However, there has been an obvious loss of emphasis on benthic studies in recent years with very few studies being conducted within the last 20 years.
Within water depth and substrate conditions relatively similar to St. Georges Bay the greatest number of individual species per phyla/class appears to belong to the polychaetes. The classes which contributed the next greatest species numbers were the bivalve and the gastropod molluscs. Species presence of non-amphipod crustaceans are variable in their representation, depending upon the location being sampled. Amphipods are not consistently reported, though at some locations they obviously form a large contribution to the total species diversity. The echinoderms are consistently represented with low species number. The remainder of the species consist of nematodes, tunicates, hydroids, bryozoans, cnidarians, cumaceans, poriferans, polyplacophorans, and several associated phyla present only in minor quantities.
As generalizations, polychaetes, bivalves, gastropods and echinoderms appear to often form the bulk of the invertebrate biomass in northern Atlantic waters, with polychaetes contributing to a greater degree if shells and tests are excluded. Larger, but less commonly occurring taxa, such as decapod crustaceans, form only a minor component of the benthic biomass. Often the bulk of the biomass is represented by only a few species.
Deposit and suspension feeders were generally reported to dominate the benthic communities, though other trophic guilds (browsers, carnivores, omnivores, ectoparasites) are also present. Meiofauna appears to outnumber macrofauna by at least two orders-of-magnitude. The substrate plays a dominant role in structuring the benthic community and determining what taxa are present.
The St. Georges Bay study area substrate is composed of a variety of distinct sediment types as well as mixtures of these types. Therefore, it should be expected that there will be a large number and variety of benthic communities within the study area, and the determination of these requires field sampling.
This review has resulted in three recommendations:
I. Collect unpublishedinformation from government/consultants offices to expand the local database. As well, review the French language publications.
II. Sample St. Georges Bay for benthic fauna and community structure. Sampling is necessary and critical if information is to be gathered on the benthos of St. Georges Bay.
III. Focus sampling on:
1) Determination/analysis of feeding guilds;
2) The magnitude of the meiofauna abundance; and
3) Interactions between the surface benthic fauna and the community in the water column.