Withering syndrome of the black abalone, Haliotis cracherodii (leach): Water temperature, food availability, and parasites as possible causes

Withering syndrome (WS) has affected black abalone since the mid-1980s. We investigated the potential roles of elevated water temperature, food availability, and parasites (renal coccidia and rickettsiales-like procaryotes or RLPs) in this disease. Results from a temperature-feeding experiment suggested that elevated water temperature was not a direct cause of WS, but accelerated mortality. At a particular water temperature, both fed and starved abalone had similar survival. Abalone with WS fed on kelp until the animal reached the terminal stages of the disease, when visible atrophy of the foot muscle was easily observed. However, fed abalone held at an elevated water temperature, 20°C, had decreased survival relative to those held at 13°C. The lack of food in our investigations did not appear to be a direct cause of WS. In addition, no consistent statistically significant associations were identified between abalone condition and intensity of coccidian infection in both field and laboratory studies. No association was found between condition of the digestive gland and intensity of the RLP infection in our laboratory study. However, all abalone with degenerated digestive glands had visible signs of WS. Time to abalone death did not correlate with intensity of RLP infection, except in a pool of the 13°C treatments and possibly the 13°C starved treatment. Thus, at lower seawater temperatures, the RLP may affect survival. The significance of this observation may have resulted from small sample sizes. Only 22 abalone were included in the 13°C treatment, and 4 of these were in the starved treatment. These data suggest that further investigation of the role of the RLP in WS is needed.