Abyssal Community Structure of the Benthic Infauna of the Eastern Equatorial Pacific: DOMES Sites A, B, and C

Abstract

Eighty 0.25m² box cores were collected and analyzed to determine the faunal composition, species diversity and sample similarity of the benthic communities of three sites in the eastern Equatorial Pacific. (The results are part of a baseline survey of the fauna of the manganese nodule province of the Pacific.) The bottom topography of this region is characterized by abyssal hills, with a relief of 50 to 300 meters, at a depth of 4350 to 5150 meters.

Macrofaunal density ranged from 36–268 individuals per m². A significantly higher density was found at site C, when compared to sites A or B. Numerically, the fauna was dominated by polychaetes (40.1%), tanaids (19.5%), isopods (11.7%) and bivalves (8.4%). Meiofauna was present in high abundances (62% of the total metazoan fauna), even though the screen size used (300 µm) was too large to retain the majority of them. Biomass of the macrofauna ranged from 0.0156–1.5708 grams wet weight per m².

Deposit feeders comprised 81% of the total macrofauna, while suspension feeders accounted for 19%. This predominance of deposit feeders was also reflected in the trophic structure of the polychaetes, accounting for approximately 89% of the total number of individuals. Site C had the highest percent of suspension feeders, while site A had the lowest.

Species diversity was found to be extremely high and comparable to the results obtained from other deep sea investigations. A very obvious feature of the fauna was the rarity with which most of the species were encountered. As a result reliable estimates of the total number of species in these communities could not be made.

Species similarity analysis suggests there is a higher degree of faunal affinity within a site than between sites. The only obvious environmental difference between the sites is a possible east-west gradient in organic flux.