Carbon stable isotopes reveal relative contribution of shelf-slope production to the Northern California Current pelagic community

Miller, Todd W., Richard D. Brodeur, Greg H. Rau

Limnol. Oceanogr., 53(4), 2008, 1493-1503 | DOI: 10.4319/lo.2008.53.4.1493

ABSTRACT: To better delineate the relative contribution of shelf and slope production to the northern California Current (NCC) pelagic community, we examined the cross-shelf distribution of δ13C in 19 species of nekton, three species of Cancer decapod larvae, five gelatinous zooplankton, two dominant euphausiid species (Thysanoessa spinifera and Euphausia pacifica), calanoid copepods (Acartia sp. and Pseudocalanus sp.), and particulate organic matter (POM). Results showed 13C enrichment from nearshore shelf sites relative to offshore slope sites at all trophic levels. For POM, a significant trend in δ13C with log chlorophyll a (Chl a) was observed, with high Chl a values associated with shelf primary production. Copepods, gelatinous zooplankton, and nekton showed a significant linear decrease in δ13C with distance offshore. Nekton and gelatinous zooplankton associated with very nearshore shelf waters (<10 km distance offshore) had the highest δ13C values, whereas those off the slope (>20 km offshore) were more depleted in 13C. A comparison of results from nonparametric analysis of the pelagic community data to environmental variables also showed variables associated with the shelf and oceanic waters, with distance offshore, sea surface temperature (10 m in depth), and bottom depth being significant. Because pelagic systems are highly dynamic in space and time, our study indicated that δ13C could be used as an indicator of relative nearshore and offshore production across multiple trophic levels, even in active upwelling ecosystems such as the NCC.

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