Most of the ocean-derived food resources are harvested in the marine subtidal 

 zone. In the Gulf of Maine these resources include pelagic fishes, such as 

 herring and mackerel; demersal fishes such as haddock, cod, and flounder; and 

 invertebrates, such as lobster, scallops, and shrimp. These and other 

 commercial species depend on the energy base of the phytoplankton and 

 macroalgae, as well as on the zooplankton, benthic invertebrates and other 

 fishes at intermediate trophic levels (see "Food Webs" above, chapter 11, 

 "Fishes," and chapter 12, "Commercially Important Invertebrates"). 



Levels of knowledge of the various biological groups occupying the marine 

 subtidal zone vary considerably in Maine. Little research has been done on 

 macroalgal and invertebrate communities in the Gulf of Maine. Environmental 

 influences on the abundance and distribution of many species of plants and 

 animals are not well understood. 



Class: open water (water column) . The water column is the environment of 

 pelagic organisms, i.e., those that do not have regular contact with the 

 bottom. These organisms include phytoplankton, zooplankton, squid, pelagic 

 fish, birds, and cetaceans. Interaction takes place between the water column 

 and the benthic environment in coastal waters. Some nutrients that support 

 phytoplankton growth are recycled in bottom sediments, some zooplankton are 

 larvae of benthic species, and pelagic fishes often lay their eggs on the 

 bottom. The marine water column habitat is contiguous with the estuarine 

 water column habitat. Organisms in the water column move, or are transported, 

 extensively between marine and estuarine systems. Pollutants in the estuarine 

 water column are transported into the marine water column. The water column 

 extends over the entire subtidal zone and encompasses 100% of the subtidal 

 area inland of the headlands. Also included in the water column habitat is 

 the subtidal area from the headlands to the 300-foot (100-m) depth contour. 

 The distribution of the water column by region is the same as that of the 

 subtidal subsystem. 



In the Gulf of Maine, phytoplankton production is not constant throughout the 

 year. The first bloom of phytoplankton (chlorophyll-a photosynthetic pigment 

 is used as an index of the abundance of algae) appears in the spring and is 

 associated with physical and chemical factors (see "Hydrography" above). This 

 bloom terminates because of the depletion of nutrients (see "Nutrients" 

 above). The second bloom is in the fall after the overturn of water, when the 

 nutrient supply is replenished. 



The overall seasonal pattern is generally repetitive and predictable. The 

 exact timing and number of peaks of the blooms, particularly the spring bloom, 

 varies from year to year and with location (see figure 4-21). Usually, the 

 spring bloom occurs earlier in southern regions and progresses northward 

 across the Gulf of Maine and coastal waters of Maine from late February 

 through May. The spring bloom is composed mainly of diatom species. The 

 stratified warm waters of summer support dinof lagellates . 



The general seasonal pattern described above may be altered when certain 

 processes occur that enhance the supply of nutrients to the phytoplankton (see 

 "Nutrient Cycle" above) . The extent of this variability in the 

 characterization area is unknown but it appears that higher phytoplankton 

 production may be occurring in the eastern regions (5 and 6) than in the 

 western regions (1 to 4), probably due to upwelling. Areas of localized 



4-61 



10-80 



