Journal of the Marine Biological Association of the United Kingdom

Research Article

High densities and depth-associated changes of epibenthic megafauna along the Aleutian margin from 2000–4200 m

F.J. Fodriea1 p1 c1, L.A. Levina1 and A.E. Rathburna2

a1 Integrative Oceanography Division; Scripps Institution of Oceanography, 9500 Gilman Drive, MC 0218, La Jolla, CA 92093-0218, USA

a2 Department of Paleontology and Paleoceanography; Indiana State University, 159 Science Building, Terre Haute, IN 47809, USA

Abstract

The Aleutian margin is a dynamic environment underlying a productive coastal ocean and subject to frequent tectonic disturbance. In July 2004, we used over 500 individual bottom images from towed camera transects to investigate patterns of epibenthic megafaunal density and community composition on the contiguous Aleutian margin (53°N 163°W) at depths of 2000 m, 3200 m and 4200 m. We also examined the influence of vertical isolation on the megafaunal assemblage across a topographic rise at 3200 m, located 30 km from the main margin and elevated 800 m above the surrounding seafloor. In comparison to previous reports from bathyal and abyssal depths, megafaunal densities along the Aleutian margin were remarkably high, averaging 5.38±0.43 (mean±1 standard error), 0.32±0.02 to 0.43±0.03 and 0.27±0.01 individuals m−2 at 2000 m, 3200 m and 4200 m, respectively. Diversity at 2000 m was elevated by 15–30% over the deeper sites (3200–4200 m) depending on the metric, while evenness was depressed by ~10%. Levels of richness and evenness were similar among the three deeper sites. Echinoderms were the most abundant phylum at each depth; ophiuroids accounted for 89% of individuals in photographs at 2000 m, echinoids were dominant at 3200 m (39%), and holothurians dominated at 4200 m (47%). We observed a 26% reduction in megafaunal density across the summit of the topographic rise relative to that documented on the continental slope at the same depth. However, the two communities at 3200 m were very similar in composition. Together, these data support the modified ‘archibenthal zone of transition’ framework for slope community patterns with distinct communities along the middle and lower slope (the upper slope was not evaluated here). This study fills a geographical gap by providing baseline information for a relatively pristine, high-latitude, deep-sea benthic ecosystem. As pressures grow for drilling, fishing and mining on high-latitude margins, such data can serve as a reference point for much-needed studies on the ecology, long-term dynamics, and anthropogenically induced change of these habitats.

(Received October 06 2008)

(Accepted March 16 2009)

(Online publication July 09 2009)

Correspondence:

c1 Correspondence should be addressed to: F.J. Fodrie, Department of Marine Sciences, University of South Alabama & Dauphin Island Sea Laboratory, 101 Bienville Boulevard, Dauphin Island, AL 36528, USA email: jfodrie@disl.org

p1 Current Address: Department of Marine Sciences, University of South Alabama & Dauphin Island Sea Laboratory, 101 Bienville Boulevard; Dauphin Island, AL 36528, USA