Amphipods of the deep Mississippi Canyon, northern Gulf of Mexico: ecology and bioaccumulation of organic contaminants

摘要

In five summer cruises during the period 2000-2004, seventy-four box coreswere collected from eleven locations from the Mississippi Canyon (480- 2750m,northern Gulf of Mexico), and an adjacent transect (336-2920) to understand thecommunity structure and trophic function of amphipods and for measuring thebioaccumulation of polycyclic aromatic hydrocarbons, (PAHs). Amphipods werediscovered to be an important component of the macrofauna of the Mississippi Canyon(40 % of the total faunal abundance). Seventy two species, belonging to nineteenfamilies, were collected from the study area with 61 species from the canyon and only38 species from the non-Canyon transect. The head of the canyon (480m) wasdominated by dense mats (15,880 ind/m2) of a new amphipod (Ampeliscamississippiana). The logarithm of the amphipod abundance decreased linearly withdepth. The species diversity (H`) exhibited a parabolic pattern with a maximum at1100m. The differences in amphipod abundances and biodiversities were correlated withthe variation in the amount of available organic matter. The depression in diversity in thecanyon head is thought to be competitive exclusion resulting from the dominance by A.mississippiana, but the high species richness is presumed to be a function of thestructural complexity of the canyon.Annual secondary production of A. mississippiana was 6.93 g dry wt m-2, basedon size-frequency method and corresponding to an estimated univoltine generation froma regression model. The production/biomass ratio (P/B) was 3.11. Production of thismagnitude is comparable to shallow marine ampeliscids but are high for the depauperatenorthern Gulf of Mexico.The effect of the organic contaminants and the bioavailability to the amphipodswas determined through measuring the bioaccumulation of the PAHs. The distribution ofPAHs in sediments was different from the distribution in the organisms suggestingpreferential uptake/depuration or uptake from pore or bottom waters. The averagebioaccumulation factor (4.36 ? 2.55) and the biota sediment accumulation factor(0.24?0.13) for the total PAHs by the ampeliscids were within the range reported forother benthic invertebrates. The average bioaccumulation factors were highest fordibenzothiophenes (up to 132) and alkylated PAHs and lowest for parent high molecularweight PAHs.