Investigations of New England Marine Algae II: The Species Composition, Distribution and Zonation of Seaweeds in the Great Bay Estuary System and the Adjacent Open Coast of New Hampshire

Abstract

Seasonal collections were made at 9 sites within the Great Bay Estuary system and the adjacent open coast of New Hampshire-Maine. A total of 162 taxa of seaweeds were recorded, including 41 chlorophyceae, 45 phaeophyceae and 76 Rhodophyceae. A gradual reduction in species numbers and biomass was evident towards the head of Great Bay. The combined effects of wide ranging hydrographic conditions (particularly salinity) and limited substratum reduce the number of seaweeds in the estuary. Turbidity, pollution, ice scouring, reduced wave action and lower tidal amplitudes are significant, but are not of primary importance. Peak populations of seaweeds were found at an estuarine tidal rapid site (i.e., Dover Point) with strong tidal currents. The flora at the Dover Point tidal rapid site is open coastal in character, even though it is several kilometers inland from the open coast. Tidal currents may simulate the open coast, due to high O2, CO2 and nutrient contents, as well as reduced sediments. Both inter- and intraspecific competition for space are conspicuous in areas with tidal currents. The wide range of temperatures in the estuary causes pronounced seasonal differences in its flora. Many estuarine summer annuals are warm temperate species that are absent on the adjacent open coast. Perennials are more common on the open coast than in the estuary, presumably because of the greater stability of the coastal environment. Various changes in zonation patterns were evident inland from the coast. Many species showed a decrease in their upper limits. Several others remained at approximately the same level, while a few showed an increase in their upper limits. The species which exhibited depressed vertical limits seemed inflexible to changes of temperature and/or salinity, while the others were probably more flexible. Other environmental factors which cause changes in zonation patterns are discussed.