Benthic Macrofauna and Habitat Monitoring on the Continental Shelf of the Northeastern United States I . Biomass

Information on long-term temporal variability of and trends in benthic community-structure variables, such as biomass, is needed to estimate the range of normal variability in comparison with the effects of environmental change or disturbance. Fishery resource distribution and population growth will be influenced by such variability. This study examines benthic macrofaunal biomass and related data collected annually between 1978 and 1985 at 27 sites on the continental shelf of the northwestern Atlantic, from North Carolina to the southern Gulf of Maine. The study was expanded at several sites with data from other studies collected at the same sites prior to 1978. Results indicate that although there was interannual and seasonal variability, as expected, biomass levels over the study period showed few clear trends. Sites exhibiting trends were either in pollutionstressed coastal areas or influenced by the population dynamics of one or a few species, especially echinoderms. Introduction _ In the northeastern United States, the basic definition and spatial distribution of benthic communities and dominant taxa are becoming known (Pratt 1973, Wigley and Theroux 1981, Theroux and Grosslein 1987); however, temporal variability and trends have received less attention. There have been few long-term (>3 years) benthic studies in the northwestern Atlantic and fewer yet that have considered biomass as a variable. Benthic community biomass and production have long been of interest to fishery ecologists, e.g., Peterson (1918), Blegvad (1928, 1951), and McIntyre (1978), particularly as they relate to the quantity of food available to fishery species and as a primary component in ecosystem models. See, for example, Cohen et a1. (1982), Lunz and Kendall (1982), and Overholtz and Tyler (1986). Biomass, as with other benthic community-structure variables, can also be used for environmental monitoring. For example, biomass changes have been related to organic enrichment, resulting from eutrophication or waste discharges (Pearson and Rosenberg 1978, Cedarwall and Elmgren 1980). Biomass estimates are usually less affected than other benthic community-structure variables, e.g., species richness or numbers of individuals, by sortingefficiency errors. This is because most biomass is from larger, more common species (Coleman 1980, Cedarwall and Elmgren 1980, Glemarec and Menesguen 1980). Biomass estimates can also be influenced by other factors such as the intermittent occurrence of rare, large individuals of certain species. As noted by Coull (1985), long-term data sets may be necessary, in themselves, to propose credible hypotheses. Wolfe et al. (1987) and Lewin (1986) also noted that longterm studies are less likely to miss infrequent, but important, perturbations in the ecosystem. This report summarizes and provides a preliminary analysis of the range of temporal variability and possible trends in wet weight biomass for 27 sites, well distributed on the northeastern continental shelf of the United States. These were monitored during 1978-85 as part of NOAA's Northeast Monitoring Program (Reid et al. 1987). This report also includes results from earlier studies at some of the same sites. This long-term data set augments the extensive, earlier spatial distribution studies of the area by Wigley and Theroux (1981), Steimle (1985), and Theroux and Grosslein (1987). Analysis of other community-structure variables (numerical abundance, species composition, and richness) is being prepared, with a more rigorous statistical analysis of habitat relationships.