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Oyster Reef Ecology and Restoration
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The Eastern oyster (Crassostrea virginica), was once very abundant in the Chesapeake Bay and supported an important industry. Overfishing, habitat destruction, and disease (Perkinsus marinus and Haplosporidium nelsoni) have decimated oyster populations. More than just an economic concern, as oysters disappeared, so have the important ecological functions – such as filtering phytoplankton and providing habitat for other species – which they provide. This has negative effects on water quality and on other species that live in the Bay. |
| To date, efforts to restore native oyster populations have resulted in only limited success. In response, the states of Maryland and Virginia proposed to introduce a non-native oyster species, Crassostrea ariakensis, to replace both ecological services and fisheries formerly supported by native C. virginica oysters. An Ecological Impact Statement (EIS) that includes both federal and state agencies is currently considering evidence on the potential benefits and risks of introduction C. ariakensis to Chesapeake Bay. |
Recently completed work:
The Marine Ecology lab has been involved in the EIS process since 2004, and has recently completed laboratory and field experiments to answer the following questions:
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What are the relative mortality rates of C. virginica and C. ariakensis larvae to predation by fish and gelatinous zooplankton?
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Will predation mortality differ for larvae of native and non-native oysters?
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Mortality rates of larvae are needed in order to model larval dispersal, model the potential for population growth, predict which of two candidate C. ariakensis strains (West Coast or South China strain) is suitable for introduction, or predict differential settlement of native and non-native oyster species in Chesapeake Bay. Essentially, mortality rates are critical pieces of information to making predictions on how well an introduced C. ariakensis would thrive.
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Crassostrea ariakensis (Asian oyster)
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During the summers of 2006 and 2007 we performed laboratory experiments exposing early stage (5-7 days old) and late-stage (12-14 days old) oyster larvae to predation by a visual predator (naked goby larvae [Gobiosoma bosc]) a non-visual gelatinous predator (ctenophore Mnemiopsis ledyii) and a non-visual sessile benthic predator (barnacles, Balanus spp.)Preliminary results suggest the relative preference of the ctenophore for oyster larvae does not appear to differ for early stage oyster larvae among species or strains; however preference may differ for late stage larvae.
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How do acquisition, prevalence, and intensity of Perkinsus marinus (Dermo) infection compare between C. ariakensis and C. virginica in the field?
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Infection with the parasite Perkinsus marinus, commonly known as 'Dermo', is a major cause of mortality for 2 and 3-year old oysters, and is a serious threat to successful oyster restoration in the Bay. Laboratory studies by others suggest that the Asian oyster C. ariakensis has faster growth and lower disease mortality than the native oyster (Calvo et al. 2001). While better survival against disease would make C. ariakensis a good candidate for introduction to the Bay, the potential for it to carry the disease may result in increased disease amongst remaining native C. virginica.
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Dermo (Perkinsus marinus)
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Graduate student Jenna Malek adds oysters to experimental cages
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In 2007 we conducted field experiments in the Rhode River with caged triploid (sterile, non-reproductive) C. ariakensis, and triploid and diploid C. virginica to see how exposure to, and distance from, infected native oysters influenced the progression of Dermo infections in each oyster type. All previously uninfected oysters in our experiments were grown from spat in the Rhode River beginning in 2006, and in 2007 we added infected oysters to select cages. We found that when in cages with infected oysters, Asian oyster individuals became infected as quickly as the native oyster, but that the intensity of infections was much less than that of the native oyster. Our study also generated data on relative growth and mortality rates of the three oyster types in the field. |
Graduate and post-doc work:
During the summer of 2008, members of our lab will begin new field studies on interactions between two different environmental factors and P. marinus infections in native oysters.
Post-doctoral researcher Darryl Hondorp will investigate if disease infection and transmission are impacted by diel-cycling hypoxia (early morning periods of low dissolved oxygen that occur when nighttime biological oxygen demand exceeds photosynthetic oxygen production the previous day).
Jennafer Malek, M.S. student at UMD-College Park, is interested in how susceptibility to infection is influenced by the oyster’s location with respect to tidal height. She will investigate whether oysters in the intertidal and subtidal zones are differentially infected by Dermo. Results of both studies may reveal areas that are more or less advantageous for oyster survival and growth, and therefore of concern to restoration efforts.
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