Significant mortalities of the Pacific oyster, Crassostrea gigas, have been reported worldwide since the 1950s. The impact these re-occurring mortality events have had on the C. gigas industry has highlighted the necessity to determine the factors that may be causing these mortalities. This study investigated the possible role of ostreid herpes virus (OsHV-1) in C. gigas mortalities over 2 successive summers at 2 study areas in Ireland. A single sample of adult C. gigas, which had been experiencing mortalities at one of the sites was screened. Successive cohorts of C. gigas spat obtained from a hatchery outside Ireland was relayed to both sites in 2003 and in 2004. Spat were screened each year prior to relaying. Samples were collected every 2 weeks and mortality counts were recorded and observed at both sites. Polymerase chain reaction (PCR) analysis and subsequent sequencing indicated that a previously undocumented variant genotype of OsHV-1 was present in the single cohort of adult C. gigas and in seed and juveniles at both sites, in both years. Analysis suggests that the Irish OsHV-1 μvar variant genotype is closely related to OsHV-1 μvar, first described in France in 2008.
Interannual and seasonal variation in recruitment of serpulid tube worms was monitored at two depths at each of four sites between February 1999 and January 2001 in Bantry Bay, Ireland. In both years, a single peak in recruitment was observed. The timing of the peak was similar in both years, but the magnitude of the peak differed significantly. More individuals recruited onto the underside than on the upperside of the horizontally orientated panels. A higher density of recruits was observed at a depth of 7 m than at 4 m during recruitment maxima. There was little variability in recruitment rates either within or between sites. The proportions of Pomatoceros triqueter and P. lamarckii recruiting per deployment were examined. Juvenile mortality was high. Based on ongrowing laboratory experiments, the dominant species was P. lamarckii. Serpula vermicularis was also present in low abundance. Examination of the spatial patterns of distribution of the serpulids indicated that the recruits were aggregated within panels. The degree of aggregation was correlated with the overall density of recruitment per panel.
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