MEPS 364:119-127 (2008)  -  DOI: https://doi.org/10.3354/meps07490

ABSTRACT: In near-shore marine ecosystems, organisms inhabit an interface between marine and terrestrial environments where both systems interact in complex ways. These interactions may occur along gradients in biophysical conditions that vary over spatial and temporal scales. These environmental conditions are known to drive many biological processes with resulting influence on a given species life history. In the present study we examined spatial variation in indices of reproductive fitness, namely fecundity, egg volume, and egg biochemistry in the red sea urchin Strongylocentrotus franciscanus along a spatial gradient of decreasing wave energy and increasing terrestrial influence in Barkley Sound, British Columbia, Canada. Stable carbon (δ¹³C) isotopic analysis was used as a bioindicator of (1) the influence of terrestrially derived carbon in egg production and (2) the concomitant effects of assimilation of terrestrial carbon on egg quality. Stable nitrogen (δ¹⁵N) isotopic analysis was used to assess trophic status among and within locations and relate this back to the strength of the gradients. We found that urchins in the lowest energy wave environment released the most eggs compared to all other locations. Egg volume was similar across all sites in the present study; however, within each site, mean egg volume varied among female urchins. Egg biochemistry (e.g. protein, carbohydrate and lipid levels), a proxy for egg quality, was the same at all sites, although analysis of percent carbon, a proxy for lipids, suggested a trend in increasing levels as distance from high wave energy environments increased. No obvious spatial pattern in δ¹³C was observed, suggesting that input of terrestrial organic material is well diluted in Barkley Sound. With respect to δ¹⁵N, we found little variation in trophic level at which foraging takes place. In contrast there were different δ¹³C and δ¹⁵N levels when comparing egg to tube foot tissue, suggesting that temporally S. franciscanus was feeding on different food sources or that for these tissue types urchins differentially assimilate carbon and nitrogen isotopes.

KEY WORDS: Urchin · Stable isotopes · Barkley Sound · Terrestrial–marine interactions · Egg biochemistry