ZONATION OF DEEP WATER BENTHIC ALGAE IN THE GULF OF MAINE1

Abstract

ABSTRACT Algal community structure is described for a deep‐water rock pinnacle in the Gulf of Maine. Three depth zones of algal dominance were apparent consisting of 1) leathery macrophytes (to 40 m), 2) foliose red algae (to 50 m) and 3) crustose algae (fleshy crusts to 55 m and coralline crusts to 63 m). Microscopic filamentous and erect calcareous algae were also present but inconspicuous. Upright macroscopic filamentous and thin sheet‐like forms were not observed on the pinnacle. Sea anemones (Metridium senile) dominated some vertical faces and abrupt prominences in the shallowest regions of the pinnacle (to 24 m) and locally appeared to set the upper vertical limits of kelp and possibly foliose reds. Laminaria sp. formed an open park‐like canopy from 24 to 30 m whereas Agarum cribrosum, the deepest kelp, grew as isolated individuals to 40 m. Peyssonnelia sp. and Leptophytum laeve were the deepest occurring fleshy (to 55 m) and calcareous crusts (to 63 m), respectively. The occurrence of these algae at record depths for the Gulf of Maine and for cold water marine environments may be the result of an absence of large herbivores and the high productivity potential of the benthos in these relatively clear waters. By compiling data on depth distribution patterns world‐wide, it is evident that the three zone structure of algal morphologies observed in the Gulf of Maine is a global phenomenon.