The Biological Environment. The biological environment of Port Xxxxxx is intricately linked to the physical environment. The combination of a cold northern climate, extreme fluctuations in the physical environment, and normal estuarine gradients creates an ecological system subject to frequent disturbance and continual physical change. In response, the populations of marine plants and animals in the Port must either adapt to this level of disturbance, function under a degree of stress, or fluctuate in population numbers or community structure. Port Xxxxxx differs from a typical temperate estuary in several important ways. The steep sides and the depth of the central basin (240 m) cause much of the primary production to be recycled in the water column. Little organic matter reaches the deep basin and the benthic community is relatively depauperate and carbon limited (Xxxxx and Xxxxxx, 1988). High deposition rates of fine-grained sediments limit the growth and diversity of intertidal and subtidal invertebrates, especially in the eastern Port (Xxxxx et al., 1973). Intertidal organisms are particularly hardy and survive xxxxxxx with low surface salinities and long xxxxxxx with air temperatures often below freezing and little available food in the water column. These recurrent disturbances result in biological communities whose members can accommodate to rapid environmental changes. There can be marked year-to-year variation in the species composition of phytoplankton and zooplankton because blooms start from small numbers of individuals. This, along with yearly differences in weather, and other factors such as nutrient availability, can result in highly variable phytoplankton densities. Those phytoplankton that are not grazed in the water column settle to the bottom. Consequently, organisms living at the bottom vary in composition and abundance from year to year in response to the quantity and character of organic carbon available. Because of the latitude (61º N), the growing season is short. Many marine organisms in Port Xxxxxx are at or near the northern end of their range and are susceptible to the stress of harsh xxxxxxx. Species that are dependent on phytoplankton, such as intertidal organisms, must be able to accommodate the intense pulse of primary production in spring, followed by low to nearly absent production during summer and winter. Intertidal organisms are subject to further stress by the high suspended sediment load in the water column and low salinity during the summer, a...
