Health and survival of red abalone Haliotis rufescens from San Miguel Island, California, USA, in a laboratory simulation of La Niña and El Niño conditions.

The variability in Southern California's marine climate is dominated by the El Niño-Southern Oscillation, with cycling between El Niño events (characterized by warm water, low productivity, and frequent storms) and La Niña events (which exhibit the opposite conditions). Relative to the mainland and other Channel Islands, San Miguel Island (SMI) consistently maintains cooler water temperatures and supports significant populations of red abalone Haliotis rufescens, presumably owing to increased food production and diminished expression of the bacterial disease known as withering syndrome. We conducted a laboratory experiment to examine the effects of La Niña and El Niño conditions on the health and survival of red abalone from SMI. Six replicate tanks per treatment, each containing six abalone, were subjected to one of the following three temperature regimes (treatments): Bodega Bay, California ambient (AMB; mean, 11.4 degrees C), SMI La Niña regime (LAN; mean, 13.8 degrees C), and SMI El Niño regime (ELN; mean, 16.5 degrees C). After 328 d, survival in the ELN treatment was significantly lower than in the AMB and LAN groups. A body condition index was significantly lower in the ELN group than in the AMB group, and the LAN group was in between. A visual score of body shrinkage was significantly higher in both the LAN and ELN groups than in the AMB group. Other clinical signs of withering syndrome and the prevalence and infection intensity of the causative agent, Candidatus Xenohaliotis californiensis, increased as temperature increased in the three treatment groups from AMB to LAN to ELN, although the differences were not statistically significant. Generally, we found that increased temperature resulted in elevated disease expression, although less than observed in previous studies that used farmed abalone and higher, less variable temperature regimes. Water temperature modulates the effect of withering syndrome in wild red abalone, and very strong El Niño events are predicted to result in significant mortality at San Miguel Island.