Nematodes are the most abundant marine invertebrate taxon in the world. As such, they compose the bulk of the meiobenthic biomass, are a food source for higher trophic levels (Gee 1989; Coull 1990), but they are most important in sediment biogeochemical processes (Aller and Aller 1992). Although they only make up 18% of the total benthic biomass, nematodes cycle twenty times their mass in carbon annually (Platt & Warwick 1980). In a recent study, nematodes accounted for > 40% of the total uptake of ¹⁴C-labelled detritus in microcosms (Ólafsson et al. 1999). Besides direct consumption of detritus, nematodes are thought to facilitate remineralization and uptake of detritus by other organisms. Net incorporation and turnover of detritus into Nepthys incisa (Polychaeta) doubled in the presence of meiofaunal nematodes (Tenore et al. 1977). Tietjen (1980) hypothesized that nematodes facilitate this detrital conversion by i) mechanical breakdown of the detritus, ii) excretion of limiting nutrients to bacteria, iii) producing films conducive to bacterial growth, and iv) by bioturbating sediments around detritus. The importance of nematodes in the ecology of sediment communities is unquestioned. (Photo courtesy of AWI-Bremerhaven)

    Given their intimate association with sediments, natural populations of nematodes are no doubt exposed to high levels of sediment-bound toxicants from agricultural runoff, urban runoff, or other anthropogenic sources. Normally, their ecological role in benthic processes would make understanding the contaminant impacts on their populations important, but their complex taxonomy is outside the expertise of most investigators. This has hampered assessment of the effect of toxicants on their population dynamics.

    Within the past 10 years, emerging DNA technology provides powerful approaches to not only identify effectively cryptic species but also to isolate genes that may be directly impacted by environmental stresses. In a sense, changes in allelic composition at these loci serve to mark sweeping changes in the populations of organisms that may represent concomitant changes in their ecological impact in the estuary. The polymerase chain reaction (PCR; Mullis et al. 1986; Saiki et al. 1988) allows for isolation of these genetic markers from individuals, even of small meiobenthos like nematodes (Schizas et al. 1997).

    Large-scale genome projects focusing on invertebrate models have greatly increased our knowledge about the number and variety of genes in metazoans. Of these, the nematode genome project on Caenorhabditis elegans represents the only metazoan whose entire nuclear genome is well-mapped and the majority of proteins sequenced (Chervitz et al. 1998). Using this and data for other organisms that are accessible on the internet through GenBank, exciting new possibilities arise for the isolation of genes from previously unstudied organisms via PCR. In this case, we will use information about nematode genetics to create a new model by isolating genes from individuals of the common marine, free-living nematode Cylindrotheristus miamiensis Hopper 1969 . Such a model system will monitor toxicological response at the molecular level that is ecologically relevant to the estuarine environment.

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