Posted by admin | 11.01.2011 | Conservation, Marine Science

Scary Invader Stopped in its Watery Tracks

There is good news coming out of the Baltic Sea for those that are lovers of the white, flaky meat from cod. While populations took significant hits from decades of overfishing, a new invader was feared to further decimate its numbers by hitting it in the fish’s heartland.

Comb jellies are far from insidious looking. These luminous, globular members of the Ctenophora phylum are common and innocuous along the US’s East Coast. But once this animal moved beyond its natal range, there were large consequences. While comb jellies do have cilia to move about, they would have been unable to travel to the Black and Baltic Seas on their own; they traveled in the ballast water of commercial tankers.

The comb jelly spread rapidly after being introduced to the Black Sea basin in the 1980s. It devoured plankton, fish eggs, and larva. While problematic, the comb jelly became a real nuisance by its ability to reproduce. With no natural predators, a single comb jelly was capable of producing 14,000 eggs a day.

When the comb jelly was spotted coming into the Baltic Sea, many were concerned that it would hit the cod population hard – the Baltic is the most important cod spawning ground. But it appears cod can swim easier since the comb jellies won’t be making it to the central Baltic ground. No manmade solution was necessary to stop the threat; Mother Nature provided the ultimate obstacle. Researchers from DTU Aqua have confirmed that due to the lower salinity of the region, comb jellies aren’t able to reproduce.