DEEP WATER BENTHIC ALGAL 

 ZONATION IN THE GULF OF MAINE 



Robert L. Vadas and Robert S. Steneck 



Dept. of Botany and Plant Pathology 



and Center for Marine Studies 



University of Maine 



Orono, Maine 04469 



ABSTRACT 



Algal community structure is described for a deep-water rock 

 pinnacle in the Gulf of Maine. Three depth zones of algal 

 dominance are apparent and consist 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 are also present but 

 inconspicuous. Upright macroscopic filamentous and thin sheet- 

 like forms were not observed on the pinnacle. Sea anemones 

 ( Metridium senile ) dominate some vertical faces and abrupt 

 prominences in the shallowest regions of the pinnacle (to 24 m) 

 and locally appear to set the upper vertical limits of kelp and 

 possibly foliose reds. Laminaria sp. forms an open park-like 

 canopy from 24 to 30 m whereas Agarum cribrosum the deepest kelp, 

 grows as isolated individuals to 40 m. Peyssonnelia sp. and 

 Leptophytum laeve are the deepest occurring fleshy and calcareous 

 crusts, 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. 



INTRODUCTION 



Globally, marine plants account for most of the primary 

 production on earth. In many productive coastal regions, a 

 significant portion of the production is from attached macroalgae 

 (Mann, 1973). The vertical limit of this production, however, is 

 restricted to relatively shallow depths which differ from place to 

 place depending on oceanographic conditions. To assess the 

 potential contribution of benthic macroalgae to global marine 

 productivity, we need to know the depth limits or extinction 

 depths ( sensu Sears and Cooper, 1978) of these plants. Although 

 research has been conducted on extinction depths of tropical 

 plants, relatively few studies exist for cold water habitats. 



In the past decade the use of scuba, manned submersibles, 



