MEPS 411:127-136 (2010)  -  DOI: https://doi.org/10.3354/meps08677

ABSTRACT: Generalist fishes provide an effective measure of the composition of basal carbon source pools fueling benthic communities, by integrating inputs across major consumer groups. In Doubtful Sound, New Zealand, shallow water invertebrate communities differ from those in other areas in Fiordland due to low salinity caused by freshwater output of a hydroelectric power station. To investigate whether the composition of basal carbon sources supporting this benthic community differed from that in unaltered sites, we sampled a generalist wrasse, Notolabrus celidotus, from altered and unaltered habitats throughout Fiordland, and quantified its δ¹³C, δ¹⁵N, δ³⁴S and the abundance of its fatty acids. N. celidotus from the altered sites in Doubtful Sound had significantly lower δ¹³C, δ¹⁵N and δ³⁴S than those collected from similar habitats throughout the Fiordland region, indicating a higher proportion of chemosynthetically fixed organic matter for Doubtful Sound N. celidotus and the invertebrate community upon which they feed. Relatively high abundances of cis-vaccenic acid (18:1ω7c) in fish from Doubtful Sound and δ¹³C values that were ~–33‰ for 18:1 isomers confirmed the incorporation of chemosynthetic bacteria, and indicated that the original source of carbon was forest litter. Despite these differences in carbon supply to N. celidotus, analysis of otolith sections revealed no differences in growth rates among sites. The results of this study demonstrate that a shift in invertebrate composition can be indicated by higher order consumers. In Doubtful Sound, decreased abundance of filter-feeding bivalves has reduced the flux of marine derived carbon through the benthic community to higher trophic levels relative to more pristine sites in Fiordland.

KEY WORDS: Notolabrus celidotus · Stable isotopes · Fatty acid biomarkers · Compound specific δ¹³C · Food web