Tidepool plankton.......

During a recent training session for Beach Naturalists I was showing plankton in LOTE area.  I was asked if the sample I was showing was concentrated sea water or if that's how dense the plankton was naturally.
It was concentrated many times through the use of a plankton net......so natural density was not what was shown in the sample. 

However there are situations where the concentration of plankton...even zooplankton can be quite high in the natural setting....as in this image of a tide pool at Constellation Park Marine Reserve....5-17-11.