Phytoplankton: Manna from Below

By guest blogger Christina Albright-Mundy Phytoplankton is comprised of over 5,000 algal species, most of which fall into one of the...

By guest blogger Christina Albright-Mundy
Phytoplankton is comprised of over 5,000 algal species, most of which fall into one of the following classifications:  coccolithophores, cyanobacteria, diatoms or dinoflagellates.  This conglomeration forms the base of the oceanic food web, just as land plants form the base of the terrestrial food web.  Like plants, phytoplankton is photosynthetic, creating sugar molecules using carbon dioxide, available nutrients and sunlight.  A side effect of photosynthesis is the release of oxygen into the water column and into the atmosphere.  It was the release of this oxygen over 2 billion years ago that formed earth’s current atmosphere composition of 21% oxygen and 78% nitrogen.  Still today, phytoplankton is responsible for 70-80% of the oxygen we breathe.

Phytoplankton production is limited by nutrient availability in the water column.  Nitrogen, phosphorous, silicon, iron, zinc, copper and manganese are the nutrients required for phytoplankton to reproduce and photosynthesis.  Of these, iron and manganese are the limiting factors due to their low concentration in the water column.  A shortage of these nutrients will result in a decline in phytoplankton production.

The importance of phytoplankton is often overlooked.  Every aquatic organism has phytoplankton to thank for its existence, as all food webs in the ocean can be traced back to phytoplankton.  Besides the little thing of oxygen production, humans also owe thanks to phytoplankton for sustenance and economic relief.  In some regions, marine animal protein is responsible for 50% of the human diet.   Factory farms in developed countries use this same protein to feed livestock and farmed fish.  The business of fish in the US alone is worth $70 billion dollars annually and is credited with the creation of 1 million jobs.

On the flip side, phytoplankton is capable of bringing destruction to an ecosystem when excessive nutrients are present, leading to harmful and toxic blooms.  During a bloom when excessive phytoplankton is present in the water, visibility deteriorates, sunlight penetration of the water column is reduced, coral reef damage occurs and the availability of dissolved oxygen drops.  Should the phytoplankton bloom release toxins, large fish kills and negative impacts on human health can occur.  The most infamous example of this type of bloom is a “red tide”.  With this excessive phytoplankton bloom, the water along the coastline takes of a reddish hue and is notorious for killing large numbers of fish.

Humans impact phytoplankton production directly and indirectly by their actions.  Excess nutrient deposition in the ocean by waste water runoff, alterations of food webs due to overfishing, and oil spills have the potential to affect phytoplankton development.  Indirectly, global climate change is resulting in warmer atmospheric and oceanic temperatures.  As the polar ice caps melt, freshwater is released into our oceans, altering the saline contents of the waters.  As air temperatures increase, surface water temperature will also increase.  Phytoplankton is affected by both salinity and temperature, any changes to these components can independently affect when and if a bloom occurs, and with what intensity.

A future concern for phytoplankton development is oceanic mining.  As we quickly deplete terrestrial mineral sources, scientists and mining corporations are looking to the oceans to solve our deficit.  Of most concern is the proposed extrapolation of manganese nodules.  Manganese is used in the production of steel and human demand for this mineral is high.  The large amounts demanded would most certainly alter the concentrations available in the water column for phytoplankton development.  As with everything else, it is the lowest common denominator that affects phytoplankton development and this type of mining could have ocean wide and world wide consequences.