Bonamiosis status in natural Ostrea puelchana beds in San Matías Gulf (Patagonia, Argentina), 14 years after an epizootic

Abstract

Between 1995 and 1996, Bonamia exitiosa caused an epizootic in San Matías Gulf, Argentina, that spread from a commercial culture site of Ostrea puelchana to natural beds located at the northeastern coast of the gulf. A mortality rate of 95% was registered in cultured oysters, and oysters from natural beds were also affected. The aims of this study were to assess the parasite prevalence in oyster beds and the demographic structure 14 yr after the epizootic. Two different oyster beds were studied during 2009 and 2010. Parasite prevalence was studied related to oyster aggregation, density, sex, and oyster size. Prevalence reached 35.3% at Las Grutas and 18.9% at Banco Reparo and was proportionally associated with density. Prevalence was also associated with the type of aggregation in Banco Reparo, where carrier oysters were more infected. Infection was independent of sex category, and infected oysters were larger than the non-infected ones. Oyster density decreased markedly compared to previous studies in both beds and mean sizes were lower, while prevalence doubled. Because of the persistence of the beds in this period, disease seems to control the population structure.KEY WORDS: Ostrea puelchana · Bonamia exitiosa · Epidemiological study · Survey of prevalence · Patagonia · Argentina Resale or republication not permitted without written consent of the publisher Contribution to DAO Special 7 'Microcell parasites of molluscs'Dis Aquat Org 110: [135][136][137][138][139][140][141][142] 2014 most affected natural beds were Banco Reparo (BR), located at the mouth of SAB, 4 km away from the culture site, and the bed at Las Grutas (LG), located 20 km from the culture site. The dispersal pattern of B. exitiosa suggested that the disease may have modified the density and population structure of O. puelchana through mortality in different beds close to the affected area. These dense natural beds have been only reported in the shallow subtidal of the northern coasts of the SMG, the southernmost limit of this oyster's distribution (Pascual et al. 2001). The microspatial organization of the individuals within the beds has been categorized by Morriconi & Calvo (1989) and Pascual (1993) as displaying 3 types of aggregation, reflecting the unusual reproductive stra tegy of O. puelchana. These were (1) free adult individuals, (2) clusters of adults, and (3) carrier oysters with dwarf males settled in the anterior border of the concave valve, which is a unique adaptation of this particular Ostrea species.Epizootic events documented for marine invertebrates occur rapidly and can produce drastic consequences, such as the devastation of stocks of cultivated oysters (Cranfield et al. 1991, Jonsson & André 1992, Doonan et al. 1994, Cranfield et al. 2005, Kroeck & Montes 2005. Often the translocation of infected oyster stocks has greatly accelerated the spread of disease (Grizel 1985). Both density and population structure can be rapidly affected (Cranfield et al. 2005). Kroeck & Montes (2005) described a re duction in B...

Microcell parasites of molluscs: introduction to DAO Special 7

“…Research has been published by several teams working in many of these B. exitiosa systems (e.g. Hine et al 2001, Kroeck & Montes 2005, Corbeil et al 2006, Abollo et al 2008, Hill et al 2010; see also Audemard et al 2014, Oehrens Kissner et al 2014, Ramilo et al 2014a. Most of the work on Bonamia species has focused on either B. ostreae, B. exitiosa, or Bonamia sp.…”

“…Thirteen of the papers in this DAO Special, including separate reviews on both Mikrocytos (Abbott & Meyer 2014) and Bonamia (Engelsma et al 2014), present new insights into Mikrocytos and Bonamia diversity and distributions (Abbott et al 2014, Hill et al 2014, Ramilo et al 2014b), diagnostics (Flannery et al 2014, Ramilo et al 2014c, ultrastructure (Hine et al 2014), and infection dynamics (Audemard et al 2014, Laing et al 2014, Lynch et al 2014, Oehrens Kissner et al 2014, Ramilo et al 2014a, and capture major developments in the field since the last review of these genera (Carnegie & Cochennec-Laureau 2004). The fourteenth, by Spiers et al (2014), points to continuing uncertainty concerning the identity of B. roughleyi and reminds us that 'microcells' may well include more taxa than Bonamia and Mikrocytos.…”