There are more than 100 freshwater fish species, varying from the giant European catfish (in the Tagus International Natural Park) to some small and endemic species that live only in small lakes (along the western portion of country, for example). Some of these rare and specific species are highly endangered because of habitat loss, pollution and drought. Up-welling along the west coast of Portugal makes the sea extremely rich in nutrients and diverse species of marine fish; the Portuguese marine waters are one of the richest in the world. Marine fish species are more common, and include thousands of species, such as the sardine (Sardina pilchardus), tuna and Atlantic mackerel. Bioluminescent species are also well represented (including species in different colour spectrum and forms), like the glowing plankton that are possible to observe in some beaches.
What type of glowing species can be found on some beaches in Portugal?
plankton