Meiofaunal Densities and Copepod Species Composition in a Louisiana, U.S.A., Estuary

Estuarine meiofauna was collected at two Gulf of Mexico sites for a 15month period. Comparisons of major taxon densities and meiobenthic copepod species composition, densities, and diversity were described for an intertidal vegetated (Spartina alterniflora) marsh site and a nearby subtidal, non-vegetated bayou site. Intertidal marsh total meiofauna averaged 540-10 cm-2, of which 83% were nematodes and 14% were copepods. The subtidal site averaged 2,300 10 cm-2 total meiofauna; 97% were nematodes and 2% were copepods. Marsh copepod collections were dominated by Nannopus palustris and Enhydrosoma woodini, together comprising 69% of all copepods. Bayou collections were dominated by Pseudostenhelia wellsi and Cletocamptus helobius, which constituted 80% of all copepods. About eight species were collected monthly at each site, and most of these occurred at both sites. However, all abundant copepod species, except Halicyclops coulli, differed in abundance between bayou and marsh stations. Similar values for total meiofauna, nematodes, and total copepods are typical for previously studied Atlantic estuaries when equivalent vegetated and non-vegetated habitats are compared. Between coastlines, copepod species compositions overlap, and dominant species differ, but diversity is only slightly higher in Atlantic estuaries. Seasonal cycles of abundance and reproduction are known for meiofauna from several estuarine habitats (Bilio, 1966; Coull, 1973; Coull & Vernberg, 1975). The most thoroughly investigated estuaries are along the North American Atlantic coast. Habitats include subtidal sands and muds (Coull & Bell, 1979; Coull & Fleeger, 1977; Hogue, 1978) and intertidal Spartina alterniflora marshes with studies from both the low (Fleeger, 1979, 1980; Higgins & Fleeger, 1980), and high marsh (Bell, 1979, 1983; Brickman, 1972). Distributional patterns of meiobenthic copepod species across a subtidal to high marsh gradient also have been described from Atlantic marshes (Coull et al., 1979). Knowledge of Gulf of Mexico estuarine meiofauna distribution, abundance, and reproduction is poor in contrast to that for the Atlantic coast. Only the studies of Fleeger et al. (1983), based on Lake Pontchartrain and the more recent work of Phillips & Fleeger (1985), report seasonal cycles. Several studies, however, have characterized meiofauna in detail over a portion of a year (see Chandler & Fleeger, 1983; Day et al., 1973; Fleeger et al., 1982; Sikora & Sikora, 1982), and generally indicate that Gulf meiofauna share abundance and taxonomic similarities with equivalent Atlantic habitats. The lack of seasonal data from the Gulf, especially in the marsh and surrounding creeks (bayous), is unfortunate. Louisiana marshes are expansive in I thank T. Chandler for help with computer analysis (ordination models) and for advice on statistical methods. The Louisiana State University Council on Research provided partial support for this work. TRANS. AM. MICROSC. SOC., 104(4): 321-332. 1985. ? Copyright, 1985, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.127 on Sun, 26 Jun 2016 06:54:24 UTC All use subject to http://about.jstor.org/terms TRANS. AM. MICROSC. SOC. area, and vegetative area has been correlated to yields of commercial fisheries (Turner, 1978). Recent evidence suggests that meiofauna, especially copepods, are significant in the diets of estuarine-dependent fish and shrimp (Hicks & Coull, 1983). Furthermore, certain species appear to require grazing time on the marsh surface for a portion of their energy intake (Weisburg & Lotrich, 1982), or favor marsh or shallow fringing creeks for foraging (Miller & Dunn, 1980; Minello & Zimmerman, 1983). Thus, seasonal data on meiofauna abundance, reproduction, and species composition are valuable to those who model or synthetically conceptualize trophic dynamics in the marsh-estuarine complex. The purpose of this investigation was to determine patterns of meiofauna abundance, copepod species composition, and reproduction over a 15-month period. Two sites [a subtidal, non-vegetated bayou (creek) site and an intertidal, between S. alterniflora, site] were chosen in a Louisiana marsh complex to quantitatively compare such cycles from the Gulf of Mexico with the better known Atlantic locations. MATERIALS AND METHODS Sampling sites were located in a Spartina alterniflora marsh complex near Port Fourchon, Louisiana (29?10'N; 90?10'W), directly behind an overwash barrier beach on the Gulf of Mexico. The intertidal site was among short (40 cm) S. alterniflora, located on the streamside levee. The subtidal site was in a slow-moving, tidally-flushed bayou (creek) fringing the marsh. Tides in this area are wind-dominated, and as a result, tidal height and water cover over the marsh were irregular. The bayou site was always submerged, from 1 m to a few cm. Salinities ranged from <3-26%o. Sediments were similar at the two sites, each about 85% silt-clay. Many macroepifauna are resident in these marsh complexes (see Day et al., 1973). Nineteen collections, usually monthly, were made from April 1978-June 1979. One locale was sampled at each site until March 1979 when an additional locale, approximately 10 m from the first, was added at each site. These additional locales were tested for within-habitat variability (Hurlbert, 1984). Samples were collected by hand-coring with modified plastic syringes (2.6cm diameter). Replicates were collected at random points within a 2-m radius of the center of each locale. Three to five replicates were taken from each locale, all to a depth of 4 cm. Cores were fixed with 10% formalin and stained with rose bengal in the field. In the laboratory, samples were sugar-floated (see Fleeger, 1979) or passed through 0.5and 0.063-mm sieves, sonified (Thiel et al., 1975), and then sorted under a dissection microscope. All metazoans were identified to major taxon. Copepods (adults and copepodites) were identified to species, sexed, and reproductive condition noted. Data are given and analyzed as monthly aggregates. MANOVA (SAS-GLM, SAS Institute, Inc., 1982) was used to analyze spatial and temporal variability of nematodes, copepods, nauplii, and major species 322 This content downloaded from 157.55.39.127 on Sun, 26 Jun 2016 06:54:24 UTC All use subject to http://about.jstor.org/terms VOL. 104, NO. 4, OCTOBER 1985