to sewage favor macroalgae with greater nutrient demands, such as sea lettuce 

 ( Ulva lactuca ) and the green algae, Enteromorpha sp . 



Turbidity may influence plant distribution. Turbidity is usually greater in 

 estuaries than in coastal waters, so plant growth (e.g., macroalgae) in 

 estuaries is limited to shallower waters. 



Phytoplankton, most zooplankton, and pelagic fish spend most, if not all, of 

 their lives within the water column. The bottom is occupied by benthic 

 invertebrates and demersal fish and, in shallow water, macroalgal species, 

 which are important producers. Waterbirds utilize the surface or near surface 

 estuarine subtidal waters for feeding and resting. 



Subtidal marine benthic invertebrates are of direct and indirect commercial 

 importance. Lobsters, scallops, and crabs, which are found in high salinity 

 subtidal areas of estuaries, have all supported major shell fisheries and a 

 significant portion of Maine's economy is dependent on these species. Clams 

 and worms are common in subtidal areas of estuaries and, although they are 

 rarely harvested there, their reproduction probably helps to replenish 

 depleted intertidal populations. The smaller invertebrates, such as amphipods 

 and worms, comprise the major food source of flounder and other bottom-feeding 

 fishes . 



Little research has been done on the subtidal estuarine benthic communities of 

 rock bottoms or aquatic beds in coastal Maine; therefore, the data presented 

 here are sparse. Two relatively detailed studies of estuarine unconsolidated 

 bottom sediments (Larsen 1979; and Larsen and Doggett 1978b) provide insight 

 into the effects of salinity on benthic invertebrate communities. 



Subtidal water column . The open water column is the habitat of pelagic 

 organisms, that is, those that do not have regular contact with the bottom. 

 These organisms include phytoplankton, zooplankton, pelagic fish, birds, and 

 marine mammals. 



The water column and the benthic environment interact. Some nutrients that 

 support phytoplankton growth are recycled in bottom sediments; some 

 zooplankton are larvae of benthic species, and pelagic fish 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. 



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

 year, but the pattern is not necessarily similar between estuarine and coastal 

 waters. Those differences are due to the characteristics of the individual 

 estuaries. In Maine, only Casco Bay and the drainage areas of the Penobscot 

 and Kennebec Rivers possibly would have significant organic discharge. 

 Possibly the continued summer-fall peaks of chlorophyll-a in upper Penobscot 

 Bay (figure 5-37) rather than the spring and fall peaks that are typical of 

 coastal waters are a result of high nutrient concentrations. This summer-fall 

 peak has also been reported in Great Bay, New Hampshire (Normandeau Associates 

 1974). However, in Penobscot Bay the source of nutrients may be either 

 freshwater inflow or upwelling from nutrient-rich deeper waters in the Gulf of 

 Maine (see "Plant Nutrients" above). 



5-78 



