Marine Algal Ecology in a New Hampshire Tidal Rapid

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Abstract
The species composition and abundance of the benthic organisms at the Piscataqua River tidal rapid show pronounced spatial variations, depending upon the current regimes and substrate. Few benthic plants and animals are present on vertical promontories that are exposed to strong tidal currents (40-80 cm/s) and pronounced shearing effects, while adjacent back-eddy areas with sloping substrate show a more diverse flora and fauna. A comparison of the zonation and differential tolerances to water motion of the major intertidal organisms is summarized. Ascophyllum nodosum was the most sensitive species to strong tidal current; it showed a conspicuous suppression of its lower distributional limits and a reduced stature in exposed habitats. In contrast, the fucoid alga Fucus vesiculosus var. spiralis, the gigartinalean red algae Chondrus crispus and Gigartina stellata and the barnacle Balanus balanoides were more tolerant to tidal currents. The algal flora at the study site is open coastal in character, particularly within the subtidal zone. A mixture of organisms occurs at the Piscataqua River tidal rapid. That is, organisms in the upper shore, such as Ascophyllum, are more typical of sheltered conditions, while those on the lower shore are robust open coastal species such as Laminaria digitata.