Managing Perkinsus marinus in the Gulf of Mexico: The Dermowatch Program


Apr. 2004


Soniat, TM
Foret, M
Ray, SM
Kortright, EV
Robinson, L

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Throughout its range from Mexico to Maine, Perkinsus marinus is a major cause of mortality in eastern oysters, Crassostrea virginica. The parasite was first described from Louisiana oysters as Dermocystidium marinum, from which its common name Dermo is derived. Because there is no economical or feasible treatment of infected oysters, the only effective approach to control Dermo is proper management. The parasite is more prevalent at high water temperature (T) and high salinity (S) and is thus most problematic during late summer and on the seaward side of estuaries. Possible management techniques include maintaining freshwater inflows, diverting fresh water into high-salinity estuaries, early harvest of infected oysters, and moving infected oysters to low salinity waters. (The movement of infected oysters to low salinity environments is not recommended in estuaries lacking frequent freshets, because this practice may lead to the long-term establishment of the parasite in the upper estuary). The DermoWatch Program was established to more effectively manage Dermo in the Gulf of Mexico. DermoWatch is a web site (, a monitoring program, and an online community for the management of P. marinus. The web site contains an embedded model that calculates a time to critical level (t-crit) of disease from an initial level of disease and water T and S. Thus, samples of oysters are collected and water T and S are measured. An initial weighted incidence (i-WI) of parasitism is determined using Ray's fluid thioglycollate method. A critical WI (c-WI) is set at 1.5. Water T, S, i-WI are inputs to the model and by simulation a t-crit is determined as the number of days to reach c-WI, assuming no change in T or S. Six public reefs and three private leases in Galveston Bay have been sampled monthly since December 1998. New Texas sites and Louisiana sites are being added. The web site displays the most recent data from each site on the home page and archives all data, such that an historical record is maintained. A web-accessible Dermo Calculator provides anyone with data on T, S, and i-WI the opportunity to calculate a t-crit and explore the dynamics of disease progression. An obvious limitation of the approach is that single values of T and S, taken at the time the oysters are sampled, are used to represent environmental conditions for the entire month. We are testing the utility of a continuous monitoring station to better predict disease progression ( Stationid = 105). Studies are also being conducted on the relationship of levels of disease (WI) to oyster mortality. A clearer understanding of the relationship between WI and mortality will help us to more precisely establish a c-WI.


pgs. 311-312


bays, coastal waters, cultured organisms, disease control, environmental factors, infestation, marine molluscs, mortality, oysters, parasitic diseases, protozoan diseases, salinity effects, temperature effects