MERCURY AND PLANKTON IN TROPICAL MARINE ECOSYSTEMS: A REVIEW

Abstract

Mercury (Hg) is an exogenous and harmful metal that accumulates in the tissues of organisms along food chain.  Bioaccumulation  by  plankton  is  therefore  of  great  significance  for  understanding  marine  processes concerning Hg accumulation and biomagnification throughout the food chain. Plankton has a short life cycle and plankton species composition respond quickly to environmental changes in the water column, making it a water quality indicator. There is a consensus that Hg enters the food chain via phytoplankton, and then is accumulated by the other links in the chain, via trophic transfer. While Hg is bioconcentrated from water by  phytoplankton,  comparatively  little  is  known  about  the  concentrations,  dynamics,  and  controls  on  Hg bioavailability  in  marine  ecosystems.  Plankton  is  one  of  the  last  matrixes  studied  by  Hg  researchers  in  a systematic manner. As the base of food chain, these organisms have been the subject of several studies on the biological effects of Hg contamination in coastal ecosystems worldwide, such as in Australia, coast of California  (USA)  and  Baltic  Sea.  However,  few  studies  in  the  literature  have  focused  on  tropical  marine ecosystems. In this review, mercury data on tropical marine plankton is presented based on previous studies on the Tropical Pacific, in Arabian Sea, Gulf of Thailand and the South Atlantic. These studies have contributed to our understanding of mercury behavior, fate, and transport of this element in tropical marine ecosystems. The lack of results in the scientific literature about Hg in marine plankton could be attributed to difficulty in  collection,  preparation  and  analysis  of  this  type  of  samples.  Collection  is  dependent  of  parameters  like luminosity, moon phase, tidal cycle, depth of the water column and physical and chemical parameters of water that influence in the quantitative and qualitative taxonomic groups of plankton present.