69 



found mciofauna to be very sensitive to the treatments. Harpacticoids exhibited a graded response of decreasing 

 diversity with increasing exposure to pollutants, but diversity profiles for nematodes were virtually unaffected. 

 Diversity was not useful in detecting the pollution gradient in the field study, but community differences were 

 distinct and species level data gave no more information for discrimination than did higher groupings (Heip et 

 al. 1988). Macrofauna phyla groupings also were just as adequate for distinguishing the pollution gradient as 

 were species level data (Warwick 1988a). Based on the field and mesocosm studies Warwick (1988b) came to 

 the following list of conclusions on the relative utility of meiofauna and macrofauna in detecting environmental 

 impacts. 



• Macrofauna: 



widely studied, and there are many species which are known stress indicators; 



longevity results in community structure exhibiting integrated responses over the long-term; 



world-wide taxonomic literature means they are easy to investigate; 



methodologies for sampling and analysis are well developed. 



• Meiofauna: 



sampling is inexpensive and less labor intensive; 



lower levels of taxonomic discrimination produce results which are as good as species analyses 



(macrofauna also); 



short generation times mean fast response potentials; 



because of short generation times, small size, and direct benthic development, community responses 



are measurable at temporal and spatial scales which can be reproduced in experiments (e.g., 



mesocosms); 



copepod species were most sensitive to discriminate polluted sites than other meiofauna or 



macrofauna species. 



The most remarkable result from these studies is that identifications at higher taxonomic levels are as good as 

 species identifications. This indicates that it may be possible to obtain up to 80% of the information one needs 

 with the expenditure of the first 25% of the funds. The results also indicate that meiofauna and macrofauna can 

 indicate impacts at different levels of the ecosystem of interest. Finally, harpacticoid copepod species are the 

 most sensitive indicators of stress in both field and mesocosm studies. 



SEEP STUDY 



Southern California has an abundant amount of natural hydrocarbon seeps. Curiously, it was found that there 

 are higher densities of benthic macroinvertebrates living in seep sediments than in normal sandy sediments (Spies 

 and Davis 1979; Davis and Spies 1980). Organic enrichment, via heterotrophic hydrocarbon degrading bacteria 

 and chemoautotrophic sulfide-oxidizing bacteria and nematodes, was hypothesized to explain the high densities 

 of macroinfauna at the Isla Vista seep (Spies and DesMarais 1983). We investigated mechanisms that control 

 tropho-dynamic benthic processes as a function of active petroleum seepage (Spies et al. 1988). Meiofaunal, 

 bacterial, and microalgal populations were followed over two annual cycles to determine if they were responding 

 to fluctuations in the abundance of bacterial and microalgal food. 



Bacterial biomass and productivity exhibited a strong graded response, increasing with increasing hydrocarbon 

 seepage (Table 8). Nematode density was also greater at the station with the most active seepage rates. On 

 temporal scales, when bacteria biomass and production decreased from the first to second year, so also did 

 nematode density (Table 8). These strong links between nematodes and bacteria indicate that seeping petroleum 

 has an enhanced effect on the detrital (bacteria based) food web. Benthic metabolism increased sharply along 

 the petroleum gradient (Montagna et al. 1986; Bauer et al. 1988). Although the nematodexopepod ratio is 

 controversial, it increases with the increasing petroleum gradient. Harpacticoids and Chi a are more dense and 

 abundant at the comparison site than at the seep sites (Table 8). When Chi a decreased, harpacticoid density 

 decreased (Table 8). These strong links between harpacticoids and microalgae, and decreases in both 

 populations with increasing seepage indicate that seeping petroleum may have a deleterious effect on the grazing 

 (microalgal based) food chain. 



