Plankton blooms: Causes and Consequences

Phytoplankton need nutrients and light for photosynthesis to occur and grow at very high rates. To limit the growth of phytoplankton and have healthy coastal ecosystems, I feel we need to reduce nonpoint source point pollution AND nutrient/fertilizer runoff from farmlands and cities. For the record, jellyfish are zooplankton and consume or eat phytoplankton. Click here or on the pdf file to read the full article or an excerpt below.

 

A bloom of Karenia brevis viewed from the air. This "crimson tide" is only composed of small dinoflagellates, but it can have devastating consequences for a coastal ecosystem. Source: http://microbewiki.kenyon.edu/index.php/File:Red_tide_genera.jpeg

Other phytoplankton blooms are harmful not because of the toxins that they produce, but because of the processes that happen when the blooms die off: massive amounts of phytoplankton die and sink to the bottom where they are decomposed by bacteria. These bacteria use oxygen to consume the dead phytoplankton, creating large portions of the water column that are low in oxygen. Fishes and some zooplankton avoid these low oxygen zones, but gelatinous zooplankton seem to be able to withstand low oxygen conditions. These low oxygen regions are often referred to as “dead zones” because very few animals can live there. A dead zone occurs regularly in the summertime in the northern Gulf of Mexico and has been expanding in recent years. Reducing nutrient/fertilizer runoff from farmlands and cities is therefore crucial to limiting the growth of phytoplankton and maintaining healthy coastal ecosystems.

 

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