The Effect of Salinity On Experimental Infections of A Hematodinium SP. In Blue Crabs, Callinectes sapidus

Abstract

The parasitic dinoflagellate Hematodinium sp. parasitizes blue crabs along the Atlantic seaboard of the United States. Infections in blue crabs have only been reported from waters where salinity is >11 practical salinity units (psu). Blue crabs maintain a hyperosmotic internal concentration at low salinities (0-5 psu), roughly comparable to 24 psu, and should be capable of maintaining an infection in low-salinity waters even if Hematodinium spp. cells are intolerant of low salinities. We tested this notion by observing the effect of low salinity on the progression of disease in crabs experimentally infected with the parasite. Blue crabs were acclimated to 5 psu or 30 psu salinity treatments. They were inoculated with Hematodinium sp. and necropsied 3, 7, 10, and 15 days post-inoculation. The low-salinity treatment did not have an effect on the proliferation of Hematodinium sp. infections in blue crabs; moreover, a greater proportion of infections in crabs in the low-salinity treatment developed dinospore stages than did those in the high-salinity treatment, indicating that salinity may affect the development of the parasite. However, dinospores from in vitro cultures rapidly became inactive when held in salinities <15 psu. Our experiments indicate that Hematodinium spp. can develop in blue crabs at low salinities, but that the parasite is incapable of transmission in this environment, which explains the lack of natural infections in crabs at low salinities.

Overwintering of the parasitic dinoflagellate Hematodinium perezi in dredged blue crabs (Callinectes sapidus) from Wachapreague Creek, Virginia

“…In H. perezi, macro-and micro-dinospores develop in separate in vitro cultures; but we have not observed possible zygotes, rather spore stages give rise to filamentous trophonts (Li et al, 2011). Dinospores from naturally sporulating crabs and those from cultures survive up to 7 days at 21-23 o C but do not form cysts (Li et al, 2011;Coffey et al, 2012).…”

Molecular detection of the parasitic dinoflagellate Hematodinium perezi from blue crabs Callinectes sapidus in Louisiana, USA

“…Our findings agreed with those of previous studies that did not detect this pathogen in blue crabs from Louisiana's coastal marshes. H. perezi appears to require salinities above 11 ppt (Messick & Shields 2000, Shields & Overstreet 2007, Coffey et al 2012; salinities in the coastal marshes of Louisiana are often below 11 ppt (Boesch et al 1994) but generally higher offshore (Brown 2015). The distribution of infected adults is consistent with a negative effect of low salinities on H. perezi in Louisiana's marshes that does not fully extend to higher salinity offshore habitats.…”

Disease, parasite, and commensal prevalences for blue crab Callinectes sapidus at shedding facilities in Louisiana, USA

“…Because salinities at shedding facilities in Louisiana are usually <10 ppt (Table 1), transmission of H. perezi between crabs in the shedding tanks is not possible (Coffey et al 2012). Conversely, infected crabs can be transported to the facility where the infection develops until the crab molts and is removed from the tanks.…”

“…H. perezi causes morbidity and mortality of infected crabs after destroying hemocytes and hemocyanin (Taylor et al 1996, Lee & Frischer 2004). It has not been directly correlated with mortalities in shedding systems because this parasite has only been found in wild blue crabs at salinities greater than 11 ppt, and the potential transmissive state of the parasite is not active below 20 ppt, both higher than typical salinities of shedding systems (Newman & Johnson 1975, Messick & Shields 2000, Coffey et al 2012. However, H. perezi could infect a pre-molt crab that was caught in a high salinity area and transported to the shedding tanks.…”