Friday, January 11, 2013

What's for dinner?

A rapid marine invasion is currently occurring in the western Atlantic. In the mid-1980s lionfish (Pterois volitans) were released in Florida. Since then, they have become established in >4 million km2 of the western Atlantic, Caribbean, and Gulf of Mexico. 

The problem is that these invasive lionfish reach higher densities and larger sizes than in their native range (Indonesia). Their hunting method is unlike that of any Atlantic predator as they use prey herding to catch fish and crustaceans which they ingest as a whole (prey can be half their own body size).

This has an immense impact on the native reef fish populations in the western Atlantic. Furthermore, little is known of how lionfish numbers are kept stable within their native range. The problem until recently was the lack of an in-depth understanding of their diet which in turn would help to assess the impact on the native species. Given their hunting mode, lionfish could prey on most fish species within their gape size limits.

The only solution to the problem is to look at the stomach content of lionfish which is problematic when relying only on morphology. Two studies utilized DNA Barcoding of lionfish stomach content to identify prey species for a better estimate on the breadth of the diet of these invaders. A first paper by Mexican scientists came out last summer and described efforts to analyze the prey composition of lionfish collected along the Mexican part of the Mesoamerican Coral Reef. Two days ago we (researchers from Canada and the US including myself) were able to add some more information to this. Our fish were collected at reef sites off southwest New Providence, Bahamas. The results of both studies are similar. Not surprisingly DNA Barcoding considerably increased the resolution of the diet studies. The number of fish species found in comparable number of stomachs analyzed was around 35 with some overlap. Differences are likely the result of regional fauna differences. However, the overall picture is alarming as prey fish are indeed members of most groups that fit within the gape size range of lionfish and it seems that the latter are not picky. Actually both studies also found evidence for cannibalism. Lionfish eat juvenile lionfish as long as they have the right size. But fish is not the only item on the menu as the Mexican group showed that 1/4 of the diet consisted of crustaceans mainly decapods.

Invasive species are often generalists. The ecological implications of these findings are profound because of the large number of interspecific interactions they can create or disrupt, particularly in species-rich ecosystems like coral reefs. Only taxonomically well-resolved diet information combined with prey availability data can help to identify the species most at risk from lionfish predation.

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