Amphipods of the deep Mississippi Canyon, northern Gulf of Mexico: ecology and bioaccumulation of organic contaminants
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In five summer cruises during the period 2000-2004, seventy-four box cores were collected from eleven locations from the Mississippi Canyon (480- 2750m, northern Gulf of Mexico), and an adjacent transect (336-2920) to understand the community structure and trophic function of amphipods and for measuring the bioaccumulation of polycyclic aromatic hydrocarbons, (PAHs). Amphipods were discovered to be an important component of the macrofauna of the Mississippi Canyon (40 % of the total faunal abundance). Seventy two species, belonging to nineteen families, were collected from the study area with 61 species from the canyon and only 38 species from the non-Canyon transect. The head of the canyon (480m) was dominated by dense mats (15,880 ind/m2) of a new amphipod (Ampelisca mississippiana). The logarithm of the amphipod abundance decreased linearly with depth. The species diversity (H`) exhibited a parabolic pattern with a maximum at 1100m. The differences in amphipod abundances and biodiversities were correlated with the variation in the amount of available organic matter. The depression in diversity in the canyon 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 the structural complexity of the canyon. Annual secondary production of A. mississippiana was 6.93 g dry wt m-2, based on size-frequency method and corresponding to an estimated univoltine generation from a regression model. The production/biomass ratio (P/B) was 3.11. Production of this magnitude is comparable to shallow marine ampeliscids but are high for the depauperate northern Gulf of Mexico. The effect of the organic contaminants and the bioavailability to the amphipods was determined through measuring the bioaccumulation of the PAHs. The distribution of PAHs in sediments was different from the distribution in the organisms suggesting preferential uptake/depuration or uptake from pore or bottom waters. The average bioaccumulation 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 for other benthic invertebrates. The average bioaccumulation factors were highest for dibenzothiophenes (up to 132) and alkylated PAHs and lowest for parent high molecular weight PAHs.
Soliman, Yousria Soliman (2007). Amphipods of the deep Mississippi Canyon, northern Gulf of Mexico: ecology and bioaccumulation of organic contaminants. Doctoral dissertation, Texas A&M University. Available electronically from