Scrippsiella spp. resting cysts, unlike many other dinoflagellate cysts, possess an outer layer of calcite beneath which is a thin sporopollenin wall. This feature may affect cyst survival through the digestive tract of benthic organisms, when they consume the cysts. The extent of digestibility is related to the degree to which grazing by benthic organisms could influence a benthic cyst population. To test consumption and digestion of a representative Scrippsiella cyst by one benthic grazer, the eastern oyster (Crassostrea virginica) was fed culture-produced resting cysts of the dinoflagellate Scrippsiella lachrymosa under controlled conditions. Cyst recovery from no-oyster, control containers was 97%; therefore, digestive destruction of cysts could be quantified as the difference between cysts added to experimental containers containing oysters and the number of intact cysts recovered after a period of oyster feeding. In each treatment, 18% of the cysts were destroyed after being ingested at a cell density of 43.4 cysts/mL and 11% were digested at a higher cell density (263.2 cysts/mL). Cysts were observed to become rounded and turn yellow after first losing the outer, calcareous wall as a first step in digestion. In fecal-pellet samples, contents from broken cysts could be found as well as intact cysts and rounded yellow cysts. Viability of ingested cysts was not evaluated, but it seems that Scrippsiella cysts are relatively resistant to digestion by oysters.
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Vol. 28 • No. 2