Last week out in the field working on our grouper movement project (see here for background) we found an interesting ectoparasite in the gills of a Nassau grouper. After expelling the tiny shrimp-like parasites from the grouper’s gills with a bilge pump, we counted about 800-900 individuals that were each about the size of a flea. We collected a few samples to take back to that lab and we discovered they are a type of isopod in the Gnathiidae family. Specifically, we think its Gnathia marleyi, a recently discovered species in the Caribbean by Paul Sikkel. It was first discovered in the US Virgin Islands and named after Bob Marley. Why Bob Marley you should ask? Well, through a quick google search I found an article that quoted Sikkel saying he named the species after Bob Marley because of his respect and admiration for Bob Marley’s music and that this gnathid species is “as uniquely Caribbean as was Marley”.
Gnathid isopods are a type of crustacean just like shrimp and crabs and are one of the most abundant crustacean parasites on reefs. They have two life stages: juvenile and adult. However, it is only in their juvenile stage where they eat and engorge themselves on the blood and mucous of their host. While they are considered to be ‘generalists’, studies have shown that they do show host preference such as the French grunt. To my knowledge, the Nassau grouper has not been recorded as a known host for G. marleyi (photo below). Lastly, I found an interesting study that showed gnathids prefer habitats with dead coral or sponges. In fact, their study suggests live coral may repel them (see here)! Another reason to protect and restore our reefs.