Potential transport of harmful algae via relocation of bivalve molluscs

Abstract

Aquaculture and restoration activities with bivalve molluscs often involve moving individuals from one body of water to another. Our study tests the hypothesis that harmful algae ingested by source populations of shellfish can be introduced into new environments by means of these shellfish relocations. Cultures of several harmful algal strains, including Prorocentrum minimum, Alexandrium fundyense, Heterosigma akashiwo, Aureococcus anophagefferens, Karenia mikimotoi and Alexandrium monilatum, were fed to various species of bivalve molluscs, Crassostrea virginica, Argopecten irradians irradians, Mercenaria mercenaria, Mytilus edulis, Mya arenaria, Venerupis philippinarum and Perna viridis, to assess the ability of the algal cells to pass intact though the digestive tracts of the shellfish and subsequently multiply in number. Ten individuals of each shellfish species were exposed for 2 d to a simulated harmful algal bloom at a natural bloom concentration. The shellfish were removed after exposure, and maintained for 2 further days in ultra-filtered seawater. Biodeposits (feces) were collected after 24 and 48 additional hours, and observed under light microscopy for the presence or absence of intact, potentially viable algal cells or temporary cysts. Subsamples of biodeposits were transferred into both algal culture medium and filtered seawater and monitored for algal growth. Intact cells of most harmful algal species tested were seen in biodeposits. Generally, harmful algae from the biodeposits collected in the first 24 h after transfer re-established growing populations, but algae could less often be recovered from the biodeposits collected after 48 h. These data provide evidence that transplanted bivalve molluscs may be vectors for the transport of harmful algae and that a short holding period in water without algae may mitigate this risk. Further, preliminary results indicate that emersion may also serve to mitigate the risk of transport.

In vitro interactions between several species of harmful algae and haemocytes of bivalve molluscs

“…Thus, the transformation of A. fundyense cells into temporary cysts can be explained by a protective response to haemocytes. Similar in vitro observations of temporary cyst formation were made previously by Hégaret et al (2008a), and temporary cysts of A. fundyense have been observed in vivo in the stomachs and biodeposits of bivalve molluscs (Persson et al 2006;Hégaret et al 2007cHégaret et al , 2008bGalimany et al 2008b).…”

“…Contrastingly, in vivo exposure of C. virginica and C. gigas to A. fundyense and A. minutum, respectively, did not induce immunosuppression nor toxicity (Hégaret et al 2007b;Haberkorn et al 2010b). Temporary cysts of A. fundyense and A. minutum have been observed in the stomach, digestive gland and biodeposits of bivalves (Shumway et al 2006;Galimany et al 2008b;Hégaret et al 2008b;Haberkorn et al 2010b), indicating that the algal cells may transform into cysts as they pass through the digestive system. The release of toxic substances might then be reduced, causing less effect on bivalve tissues and haemocytes during in vivo exposures compared with in vitro experiments.…”

Effects of the toxic dinoflagellate Alexandrium monilatum on survival, grazing and behavioral response of three ecologically important bivalve molluscs

“…Various other potentially toxic dinoflagellate species have been documented to pass intact through the digestive tracts of bivalve molluscs (e.g. Shumway et al, 1985b;Shumway and Cucci, 1987;Bauder and Cembella, 2000;Springer et al, 2002;Hé garet et al, 2007Hé garet et al, , 2008a. For example, based upon inspection of fecal ribbons, Shumway et al (1985b) reported that O. edulis preferentially ingested the dinoflagellate P. minimum cells relative to other microalgal species; however, high incidence of fragments and intact cells of P. minimum in the fecal ribbons indicated that cells were only partially digested.…”

“…Cell viability was tested by inoculating feces collected from each animal after 24 and 48 h of depuration (Bauder and Cembella, 2000). Fecal samples (n = 10) were vortex-mixed and 1 ml of each fecal suspension was inoculated into each of two test tubes, one containing 10 ml of L1 growth medium, and one containing 10 ml of natural seawater (NSW, salinity 30; from CCMP, Boothbay Harbor, ME, USA) (Hé garet et al, 2008a). Controls consisted of 1 ml of A. monilatum stock culture inoculated into test tubes containing 10 ml of L1 medium (n = 10) and into tubes with 10 ml of NSW (salinity 30; n = 10).…”

Comparative study of predatory responses in blue mussels (Mytilus edulis L.) produced in suspended long line cultures or collected from natural bottom mussel beds

“…Alternative sources of mussel seed have included the development of methods for collection of seed from suspended cultures (Kamermans et al 2002(Kamermans et al , 2009). This method eliminates the risks of spreading unintended organisms, since transfer of seeds from one area to another potentially involves the risk of spreading of harmful algae (Hégaret et al 2008) or other harmful organisms.…”