Perkinsus marinus in coastal Georgia, USA, following a prolonged drought

Abstract

Oysters Crassostrea virginica are 'keystone' estuarine species in the southeastern USA, providing essential fish habitat, food for human consumption, filtration of water bodies, and protection against shoreline erosion. Relatively few oyster pathology studies have been conducted in Georgia. The parasitic protozoan Perkinsus marinus was first observed here in the 1960s, but has not been investigated since the late 1990s, when increasing oyster infection levels were apparent. In the late 1990s and early 2000s, the region suffered a prolonged drought, resulting in elevated salinities and the proliferation of various diseases in the marine environment. By 2003, salinities had returned to normal levels, but the effect of the drought on oysters was unknown. In June 2003, oyster reefs throughout Chatham County were sampled to evaluate the prevalence and intensity of P. marinus. The disease appears to have remained prevalent in the coastal waters of Georgia (100% prevalence at some sites), but the intensity was low, ranging from 0 to 1.83 on a scale where heavy infections rated a score of 5. While the disease did not occur at levels high enough to cause oyster mortalities, further monitoring, particularly on a temporal scale, is warranted.

Effects of controlled air exposure on the survival, growth, condition, pathogen loads and refrigerated shelf life of eastern oysters

“…Off‐bottom oyster aquaculture is practiced throughout the world because it can improve oyster growth and shell shape, eliminate predation, reduce siltation and allow opportunities to expose oysters to air to control biofouling (Comeau, ; Jory, Carriker & Iversens, ; Parsons, ; Walton, Davis & Supan, ). Aerial exposure has also been reported to increase oyster survival, extend refrigerated shelf life, and possibly reduce the impacts of pathogens (Adams, Walker & Heffernan, ; Gillmor, ; Littlewood, ; Littlewood, Wargo, Kraeuter & Watson, ; Power et al., ).…”

Assessment of Infection Prevalence and Intensity of Disease-Causing Parasitic Protozoans Perkinsus marinus and Haplosporidium nelsoni in Georgia Oysters

“…This study suggests that the prevalence of P. marinus and H. nelsoni on the Georgia coast appear to have increased since their first occurrences in Georgia oyster populations [13]. Despite this apparent increase, subsequent studies in coastal Georgia since that period have similarly not detected reduced health or mortality in disease-infected oysters [20,27,41,43], including the current study. Thus, it is possible that local oyster populations in Georgia are resistant or more resilient to infections from these parasites [58,59] or tolerant of co-stressors (i.e., temperature) that might lead to reduced oyster health and even death.…”

“…Unlike the prevalence surveys, P. marinus intensity showed a negative response to salinity and dissolved oxygen when accounting for other water quality variables, in the coastwide survey. While other studies have found that Dermo may increase with salinity [ 34 , 42 ], it is possible that Dermo may peak at intermediate–high salinities and decrease as salinity becomes oceanic [ 43 ]. Likewise, lower oxygen conditions can affect oyster immune responses, leading to higher prevalence, intensity, and progression of Dermo disease in oysters [ 17 , 39 ].…”

Demography of the ecosystem engineer Crassostrea gigas, related to vertical reef accretion and reef persistence

“…Additional measurements are provided in the supplementary material. Dry shell weight was determined after dissecting the oyster, separating the tissues from the shell, and airdrying the shell at room temperature for 2 days (Power et al, 2006;Mann et al, 2009). …”