Trophic Importance Of Epiphytic Algae In Mississippi Seagrass Beds

Multiple stable isotope analyses were used to examine food web dynamics in seagrass ("Halodule wrightii") beds located off the northwestern shore of Horn Island in Mississippi Sound. Stable isotope ratios for carbon (delta13C), nitrogen (delta15N), and sulfur (delta34S) were measured on material collected from May 1989 through November 1992. The delta13C and delta34S values of most consumer organisms clustered near those measured for epiphytes, macroalgae, and plankton, rather than that of seagrass blades. Trophic levels, as determined by delta15N, could not be clearly separated. Stable isotope data, in combination with high measured rates of primary production, strongly suggest that epiphytic algae are the major source of organic carbon for higher trophic levels in this system. The contribution of "H. wrightii" appears to be minimal, at best. The overall picture that is emerging based on the present and previous studies is one of the major trophic importance of benthic microalgae (i.e. epiphytes and sediment-associated microflora) in coastal food webs. Grant no. NA16RG0155-02