Thursday, August 26, 2010

Black gill crabs turn up in Mississippi - Oil not a likely cause

Crabs with black gills recently turned up in Mississippi (wlox story). Local fishermen say they have never seen anything like it, but are worried these crabs are stained with oil. Black gills in crabs can be associated with disease ("black gill syndrome"), low oxygen levels, high levels of detritus, and pollution or a combination of the above.

Testing has so far indicated that oil is not involved, but that low oxygen levels and detritus are more likely causes (

“The FDA has advised that, following extensive sensory testing and chemical
analysis, tissue samples tested indicate that crabs from these previously closed
areas south of the barrier islands are safe for consumption,” stated a news
release from DMR and DEQ. “Testing for crab tissues includes specimens of
special interest, such as those with dark gills, brought to DMR’s attention by
concerned fishermen and the public; all of these samples have been determined to
be safe for consumption as well.”

Jewell said no exact cause has been determined for the dark gills found
on some crabs, but low dissolved oxygen levels and sediment are suspected.

“A lot of the low dissolved oxygen in our waters is because we have
very high temperatures,” he said. “That can be part of the issue, but I don’t
think it is any one thing.”

The crabs with dark gills that been brought to DMR by the public have
come from upper bay areas, he said. “There is a lot of sediment and a lot of
suspended sediment and that tends to get entrapped on the crabs’ gills,
particularly crabs that are stressed.”

The darkening is not found on any other crab organs, he said, “which
tends to indicate it has to do with respiration.”

Crab samples tested, including the dark gills, have returned as free of
oil or trace amounts in the parts per trillion range were found, he said.

“Anything they are finding is way below the NOAA protocol,” he

Sunday, August 1, 2010

New key for blue crab megalopae and juveniles

Adult blue crabs are distinctive. Olive shell set off with blue legs and claws and an undeniable fighting spirit. Young larvae and juveniles, however, are very difficult to distinguish from some of their close cousins. I had great news last week that a manuscript I have been working on since 2005 was accepted to the Journal of Crustacean Biology and is due out in early 2011. When I first started studying blue crabs in 2004, I was faced with the challenge of separating blue crab (Callinectes sapidus) megalopae from those of the lesser blue crab (Callinectes similis). I couldn’t make heads or tails of the problem because the original descriptions of the megalopae didn’t seem to match what I was collecting in the wild. A colleague was kind enough to pass along an unpublished manuscript by Ken Stuck and others that made separation of the species possible, if still not exactly easy at first. After contacting the authors of the original publication for permission, I combined data from the original manuscript with new data that I collected, and submitted the new manuscript. It includes drawings of both blue crab and lesser blue crab megalopae and juveniles and keys for separating them from similar species occurring along the US Atlantic and Gulf coasts. If a copy of the manuscript would be useful for your work, please contact me and I’ll send one your way.

Have new blue crab research your are publishing? Send a description and I'll include it in the blog.