I’m sorting fish we collected in Florida’s Pensacola Bay estuaries to study the effect that low oxygen levels are having on Atlantic croaker reproduction.
Croaker is one of the most common inshore fish along the coasts of the southeastern Atlantic Ocean and Gulf of Mexico. Low levels of oxygen, known as hypoxia, have been increasing dramatically in coastal waters around the world, largely from increased fertilizer run-off related to human activities like farming.
One of the most familiar of these places to us is called the “Dead Zone,” which is an area of almost no oxygen off the coast of Louisiana that covered about 7,900 square miles this past summer.
In these fish from Florida, we found that males and females had little ovarian and testicular growth, low egg and sperm production and low levels of reproductive hormones. And this was during a time of year when they would normally be preparing for reproduction. We also found that hypoxia decreases serotonin in the fishes’ brains.
We’re in the middle of a multi-year study of Atlantic croaker reproduction in the Dead Zone itself, where reproductive problems could seriously affect the sustainability of that population. As a part of this work, my colleague Professor Ed Buskey is looking at how hypoxia is changing benthic and planktonic copepod populations, which are critical components of the marine food web. Professor Wayne Gardner is in the area too, aiming to clarify how nitrogen flowing from the Mississippi River contributes to the formation of the Dead Zone.
Wish you were here,
Peter Thomas
This article also appeared in the Spring 2009 issue of Focus magazine.
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