Benthic Ecology in an Estuarine Tidal Rapid

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Abstract
The distribution and abundance of selected benthic plants and animals were evaluated under varying current regimes at Dover Point, New Hampshire, USA, an estuarine tidal rapid site. Pronounced spatial changes in current veolcities occur across the tidal channel at Dover Point, varying from negligible at the margins to 5.5 knots in mid-channel. Two parallel bridges cross the channel, each having 8 hexagonally shaped piers. The maximum number of taxa per pier were located in areas of moderate currents, where a variety of current-sensitive and current-tolerant species existed. The lowest number of taxa per pier occurred in areas with strong ebb tidal currents. Of the 7 most conspicuous intertidal organisms on the bridge piers, Semibalanus balanoides had the highest percentage coverage and the broadest tolerance to currents. Porphyra umbilicalis and Blidingia minima were found in high current regimes, with the latter missing some current due to its high level in the zonation. Mytilus edulis occurred in ebb-dominated areas, but it was sporadically distributed, presumably because of extensive predation. Gigartina stellata was restricted to intermediate currents with some reduced intertial populations, perhaps due to ice scouring. Ascophyllum nodosum and Fucus vesiculosus var. spiralis were absent and/or stunted in the mid-channel ares with strongest currents; they were also vertically restricted from low intertidal areas with strong currents. The abundance of P. umbilicalis and F. vesiculosus var. spiralis, showed a significant inverse linear relationship suggesting the occurrence of interspecific competition. Extensive interspecific competition between Chondrus crispus and M. edulis was noted. Examples of widespread predation and grazing by several invertebrates are discussed. The average stature and abundance of Ascophyllum and Fucus were statistically examined for correlations with current velocity. A variety of comparison between the Dover Point and Lough Ine, Ireland tidal rapids are made.