No Noctiluca were seen at this time. So I have no idea what this may be. It is most likely not a Noctiluca ingesting anything.
Marine, during one of the lowest tides of the year.
Many dinoflagellates have a cyst phase of their life cycle and it's somewhat equivalent to a resting stage- so when conditions aren't quite right, they turn into a cyst and then germinate when conditions are more favorable. I do not know lots about Protoperidinium cysts, but here's a link to some Alexandrium cyst work that is being done within Puget Sound. It's pretty interesting stuff: https://catalyst.uw.edu/workspace/banasn/14943/82760.
Hope that answers your question.
The dinoflagellates (Greek δῖνος dinos "whirling" and Latin flagellum "whip, scourge") are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth. Many dinoflagellates are known to be photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey, (phagotrophy). In terms of number of species, dinoflagellates form one of...