Red tide
Noctiluca scintillans?

Red tide at Adventure Bay 11 February 2020
About this species
Individually these critters are tiny and not usually visible to the naked eye. There are documented cases in Tasmania in which dense 'red tides' of Noctiluca, a type of phytoplankton, has bloomed in response to a combination of increased nutrient loads and warming waters. Note: because there are multiple species that can cause red tides, species-level identification of sightings should be considered tentative unless a sample has been verified under a microscope. Read more…