I do have papers from the USA and Canada, however I am looking for other parts of the world where shellfish aquaculture is present and thriving such as China, Spain etc..
Usually, picophytoplankton occur in oligotrophic water, so not the places where bivalves aquaculture is developed. But you might find some information about coastal lagoons where bivalve aquaculture is important.
Are you latter comment, you are actually right. Here on the Canadian east coast we do find important biomass of picophytoplankton in rather small estuaries dominated by shellfish aquaculture. This said, those estuaries are enriched with important nutrient loads from runoffs (agricultural fields, golf courses etc...) promoting fast turnover for fast growing phyto like picophytoplankton.