Thursday, March 14, 2013

Small Fish and Coastal Carbon Cycles

You may not think that small fish such as anchovies- and their poop- can have a big impact on coastal ecology and food webs. A major characteristic of temperate coastal ecosystems is upwelling, where cold water from the open ocean moves to shallower water along the coast, bringing important nutrients with it. One of the transported molecules is carbon dioxide: algae at the ocean’s surface live in nutrient rich waters from upwelling (they need a combination of light and nutrients). They are consumed by copepods and other zooplankton, which are in turn consumed by “small forage fish” such as anchovies. Their fecal matter, which is rich in carbon, sinks into the deep sea, where it doesn’t work as a greenhouse gas to warm the planet. Scientists from Rutgers University and the Virginia Institute of Marine Science examined the sinking rates and contents of fecal matter of small forage fish in the Santa Barbara Channel. They found that pellets sink at a rate of about 2500 feet/day and that they contain up to 22 micrograms of carbon per pellet. When high numbers of forage fish gather in areas like the SB channel to feed, the rate of carbon fixation increases dramatically, up to as much as 251 mg per square meter per day.

The results of their study have important implications for many coastal areas with lots of upwelling, including the western coasts of North South America. The implications of changing ecosystems through fishing (especially the large-scale Anchovy fisheries of the west coast of Peru, which have suffered large declines and population “crashes” over the last 30 years) may be both larger than expected and have implications beyond the imagining of most scientists. Perhaps a fish-free diet may be one of the most effective ways to “go green” as our understanding of coastal and fishery ecology continues to change.

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