Meiofauna and sediment chloroplastic pigments on the continental shelf off Louisiana, U.S.A.

Organic matter derived from phytoplankton blooms in the euphotic zone represents an important component of the flux of material to the bottom sediments. The relationship between the supply of phytodetritus to bottom sediments and the horizontal and vertical distribution of meiobenthos in the continental shelf of the Gulf of Mexico off the coast of Louisiana, U.S.A., was studied in February 1992. A total of 13 stations located in two areas was visited. One area (“off Mississippi” eight stations) was adjacent to the Mississippi River mouth and was directly influenced by the river plume, while the other (“off Cocodrie” five stations) was situated west of the Mississippi River mouth. The sediment chloroplastic pigment contents (Chl a and total pigments) were significantly higher off Mississippi, as were densities of harpacticoid copepods, while nematodes were significantly more abundant off Cocodrie. Vertical profiles of sediment pigments, harpacticoid, nematode, and total meiobenthic densities were also markedly different in the two areas. Densities of total meiobenthos, nematodes, and harpacticoids correlated significantly with the sediment total pigment and Chl a contents off Cocodrie, while no significant correlations were detected off Mississippi. This is an indication that meiofaunal abundances in the latter area, exposed to a constant supply of sedimenting organic matter, seem to be controlled by factors other than the abundance of phytodetritus as expressed by the sediment chloroplastic pigment content.