INTRODUCTION
The St. Georges Bay Ecosystem Project is a collaborative study between Government, harvesters, First Nations and the Interdisciplinary Studies in Aquatic Resources (ISAR) program at St. Francis Xavier University of the St. Georges Bay ecosystem. There are a number of social and ecological goals for this project (see Davis et al., 1999), two of which are the:
- Assemblage of the major bodies of information, data, and published material regarding the geology, oceanography, marine biology, ecology, fisheries, human occupation and use of the watersheds and marine waters.
- Employing these materials, construction of a dynamic, though preliminary, ecological model of the St. Georges Bay system.
In addressing the first goal, a lack of information on benthic fauna and community structure within the St. Georges Bay area was identified. Therefore, a comprehensive literature review was initiated to assess and summarize existing information on the benthic fauna and communities of nearby and relevant locations. Published information has been collected and is reported below for five principle areas:
The information presented has been principally drawn from the primary literature (i.e., published journals) with the more local information coming from secondary sources (government and University reports). It is recognized, as pointed out by Dunbar et al. (1980), "There is a real possibility that a great deal of faunistic information exists in unpublished form, especially in government marine laboratories". However, determination and gathering of this diffuse information was beyond the scope of this review. This review is drawn almost exclusively from English publications only, though it must be recognized that there is a large extant body of marine information published in French. In order to limit this review to relevant studies, a study or station within a study was only included if the water depth was less than 150 m (maximum depth to be expected within the study area), and subtidal (intertidal communities not included). This review incorporates American studies as far south as North Carolina. This is justified in that some of the physical parameters of St. Georges Bay area are, in many ways, more similar to the American coastal waters than to the northern Gulf of St. Lawrence (see Cameron and Mitchell, 1999). In order to incorporate as much relevant information as possible, studies in which the benthos was included as a secondary component (e.g., as part of a commercial lobster or scallop investigation) are also included in this review.
Four caveats must be borne in mind by the reader:
- There are differences
in sampling methods between studies and this will result in different
species, and different proportions of species, being captured. Therefore,
making detailed direct comparison between studies will probably not
reflect the actual benthic composition between the two or more studies.
Sanders (1968) recommends that to have data comparable, the type of
gear, methodology used in processing the sample, and the screen size
employed in washing the sample should be approximately similar. These
are not so between the variety of studies presented here.
- Sampling does
not capture all of the bottom fauna. Samples will be biased to certain
species/taxa and may give an incorrect picture of the details of the
benthic community/assemblage. Stickney and Stringer (1957) provide three
cases where this may be true: 1) when organisms are of such size and
shape that some will be retained by large mesh screens while others
will not, 2) When a species is collected in only scattered samples or
is represented by only one individual in but occasional samples, and
3) when organisms burrow too deeply into the substrate to be taken by
the sampler.
- Reporting detail:
Depending upon the purpose of the research, and the argument the author
of a paper is presenting, the level of detail within published works
ranges from species presence, biomass, and density to simple reporting
of the phyla present as a percentage of total species present. These
variations in information presented within papers further limits the
ability to compare across studies.
- Benthic fauna/communities exist in seasonally fluctuating environments. Results (particularly biomass) will depend upon the time of year of sampling. The majority of the sampling is done in the summer months, but there are fluctuations even within the relatively short time of early summer to late summer. As well, as Dexter (1944) points out, population changes occur from time to time [from unknown or undetermined stochastic events] which would alter the relative significance of many species in their community relationships.
While these caveats must be borne in mind, comparison of a large number of studies at a broader scale may dampen the fluctuations and so provide some reliable information on broad scale trends.
The following discussion is presented in order of geographic location with the most proximal areas presented first (Northumberland Strait, Gulf of St. Lawrence) and moving to more distant locations (American coastal studies) The level of detail reported herein decreases with increasing distance to reduce the probability of drawing erroneous conclusions from levels of detail not applicable over large areas. Within each broad location, the reported studies are presented in chronological order to the degree practical. For each study summarized the year of sampling, water depths and substrate type are presented where they were reported. One of the challenges of the benthic invertebrate literature is the use of scientific names without inclusion of classification to phyla/class. Unless the reader is intimately familiar with all benthic species, this may get confusing. In an attempt to clarify this, Appendix 1 contains an alphabetical list of invertebrate species mentioned in the text with their higher level classification, and Appendix 2 contains the same for algae and marine plants. As well, to the degree practical while maintaining readability, the classification has been given in the text to assist the reader.
Comments on Communities and Trophic Guilds
The following comments are intended to provide the reader with the background for the discussions through the text of this document.
The ecological literature contains a great deal of discussion regarding communities; whether they exist in reality or are sampling artifacts, what they represent, how to define them, etc. I will not discuss this but Mills (1969) and Jones (1950), though 30 and 40 year old papers, provide very good discussion of these issues in the marine environment. For the purposes of this review, I accept that communities are natural structures and intend the term in the form of Mills (1969): "Community means a group of organisms occurring in a particular environment, presumably interacting with each other and with the environment, and separable by means of ecological survey from other groups".
Benthic surveys have shown that areas having similar environmental conditions will support a benthic fauna of like composition (Peer, 1963). The environmental factors affecting community structure include substrate, salinity, water temperature, water energy, light, oxygen content and sedimentation (Jones, 1950; Logan et. al., 1983). The three most important factors are temperature, salinity and the nature of the substrate; where two of these factors are relatively homogenous, the third play a more significant role (Jones, 1950). So, over large areas of similar salinity and bottom temperature (e.g., Northumberland Strait) the substrate may be considered to be the more important variable affecting benthic fauna presence and community structure. In the deeper waters communities must shift from autotrophy to heterotrophy. Benthic marine organisms are predominantly either suspension or deposit feeders (Rhoads and Young, 1970), apparently due largely to the forms of the food supply in this environment. The inputs of energy reach the benthos below the euphotic zone in only two ways, either as current transported particles (food for suspension feeders) or as sedimented particles (food for deposit feeders); other trophic groups (e.g., carnivores, omniverous scavengers) are basically dependent upon these groups for energy (Wildish, 1983).