Spatial Dynamics of Two Host-Parasite Relationships on Intertidal Oyster Reefs

Intertidal reefs comprised of the eastern oyster (Crassostrea virginica) have long experienced habitat loss, altering habitat patch characteristics of size and distance from edge to interior, potentially influencing spatial dynamics of host-parasite relationships. Using two parasitic relationships, one between eastern oyster host and parasitic oyster pea crab (Zaops ostreum) and the other between a xanthid crab (Eurypanopeus depressus) and a parasitic rhizocephalan barnacle (Loxothylacus panopaei), we examined how host-parasite population characteristics varied on intertidal reefs by season, reef size, and distance from edge to interior. Pea crab prevalence was more related to habitat characteristics rather than host density, as pea crab prevalence was the highest on large reefs and along edges, areas of comparatively lower oyster densities. Reef size did not influence densities of parasitized or non-parasitized xanthid crabs, but densities varied from edge to interior. Non-parasitized xanthids had significantly lower densities along the reef edge compared to more interior reef locations, while parasitized xanthid crabs had no significant edge to interior pattern. Organismal size had a varied relationship based upon habitat characteristics, as pea crab carapace width (CW) varied interactively with season and reef size, whereas CW of parasitized/non-parasitized xanthid crabs varied significantly between edge and interior locations. These results demonstrated that influential habitat characteristics, such as patch size and edge versus interior, are both highly species and host-parasite specific. Therefore, continued habitat alteration and fragmentation of critical marine habitats may further impact spatial dynamics of host-parasite relationships

Strong seasonality of Bonamia sp. infection and induced Crassostrea ariakensis mortality in Bogue and Masonboro Sounds, North Carolina, USA

Asian oyster Crassostrea ariakensis is being considered for introduction to Atlantic coastal waters of the USA. Successful aquaculture of this species will depend partly on mitigating impacts by Bonamia sp., a parasite that has caused high C. ariakensis mortality south of Virginia. To better understand the biology of this parasite and identify strategies for management, we evaluated its seasonal pattern of infection in C. ariakensis at two North Carolina, USA, locations in 2005. Small (<50 mm) triploid C. ariakensis were deployed to upwellers on Bogue Sound in late spring (May), summer (July), early fall (September), late fall (November), and early winter (December) 2005; and two field sites on Masonboro Sound in September 2005. Oyster growth and mortality were evaluated biweekly at Bogue Sound, and weekly at Masonboro, with Bonamia sp. prevalence evaluated using parasite-specific PCR. We used histology to confirm infections in PCR-positive oysters. Bonamia sp. appeared in the late spring Bogue Sound deployment when temperatures approached 25 °C, six weeks post-deployment. Summer- and early fall-deployed oysters displayed Bonamia sp. infections after 3–4 weeks. Bonamia sp. prevalences were ⩾75% in Bogue Sound, and 60% in Masonboro. While oyster mortality reached 100% in late spring and summer deployments, early fall deployments showed reduced (17–82%) mortality. Late fall and early winter deployments, made at temperatures <20 °C, developed no Bonamia sp. infections at all. Seasonal Bonamia sp. cycling, therefore, is influenced greatly by temperature. Avoiding peak seasonal Bonamia sp. activity will be essential for culturing C. ariakensis in Bonamia sp.-enzootic waters.9 page(s