https://arxiv.org/ftp/arxiv/papers/1804/1804.04719.pdf

there is a survey on target detection , you probably have to tailor your own technique to identify plankton accumulation.

https://ec.europa.eu/jrc/sites/jrcsh/files/20100602_infoday_madrid_cicuindes.pdf

https://www.asprs.org/wp-content/uploads/2010/12/Allensworth.pdf

Thanks, the third link is helpful to me. So far I've found that SAR can be used to monitor the oil spilling but not under the water surface.

Thanks Aldo. The first link is really helpful.