The onset of yolk-sac edema in Pacific herring (Clupea pallasi) due to environmental stressors present during an oil spill in an estuarine environment

OBJECTIVE: A natural resource damage assessment (NRDA) was conducted by federal and state trustees after the 2007 Cosco Busan oil spill (CBOS) in San Francisco Bay. Pacific herring embryos were collected from selected central bay sites and examined for early-life stage developmental injury; reported anomalies were thought to have derived from exposure to CBOS fuel oil. Chemical analyses of embryonic tissues did not demonstrate a clear pathway of CBOS exposure. Since the herring embryos were collected from shallow, dynamic estuarine waters, we conducted a controlled laboratory study to further investigate the possible effects on developing herring embryos caused by the fluctuating environmental stressors that naturally occurred in these shallow intertidal spawning areas (especially shifts in temperature, salinity, and ultraviolet light exposure that is intensified as a consequence of stranding in shallow water).

METHODS: This unique laboratory study evaluated effects on herring development caused by a suite of estuarine environ-mental stressors in the absence of CBOS by replicating near shore environmental conditions occurring at two sites within the central bay during the 2008 post-spill spawning. In addition to assessing developmental response endpoints such as body axis defects following a qualitative scoring process, we developed a new approach for assessment of pericardial and yolk-sac edema based on quantified measurements.

RESULTS: A significantly higher incidence and intensity of yolk-sac edema was observed in the embryos exposed to temperature and salinity changes, whereas pericardial edema did not occur in larval specimens at statistically significant levels compared to controls. Embryos exposed to ultraviolet light were associated with a higher incidence of body axis defects in larval specimens relative to the control. These experimental results indicate that fluctuating environmental conditions contributed to the abnormalities observed in naturally spawned herring collected during the post-spill spawning event.