A survey on the populations of "Deer Cowries"

in the lower Florida Keys

Even in an offshore site well known as an El Dorado for shell collectors, 5 miles offshore Key West, not a single living, but numerous dead, mostly juvenile shells were found. According to local collectors, Deer Cowries were still abundant in this area in April of this year. We noticed in all sites visited, that the Thalassia grass-beds had suffered severe damage and were covered by wooly brown algae or a grey slimy substance originating from decaying algae.

 

During our stay in July, we made the following observations of things that deviated notably from what we used to see in the years before:

 

• Disappearance of living Cowries in the area between Marathon and Key West, as well as reefs 8 kilometers offshore from Key West. Only empty shells, mostly juveniles, were found, all seemed to have died at the same time earlier that year, judging from their fresh condition.

• The once flourishing population of the Flamingo Tongue Ovulid (Cyphoma gibbosum) and the rarer Cyphoma macumba at Bahia Honda State Park had all died off as well. Fresh, empty shells were found around the host corals, which had severe damage to their branches, which were partly overgrown with algae, denoting the death of the polyps.

• Other grazing gastropods, e.g. of the family Strombidae, had also died.

• Hunting or scavenging gastropods, such as the Horse Conch, the Fasciolariid Pleuroploca gigantea, were found alive.

• The areas usually covered in algae were denuded, or the Caulerpa-algae and Thalassia-leaves were covered by brown algae.

• Some larger sponges and few stone corals were found intact, but the smaller stone corals formerly abundant at Bahia Honda State Park, had died, apparently at the same time, judging from the fresh condition of the empty shells that were scattered in many places.

• The Lion Fish, an introduced species, had disappeared from all sites we visited. In 2010 we saw 3 to 4 centimeter long juveniles in abundance under our "Good Spot" in 2010 and reported our observation to the Department of Fish & Wildlife.

• The population of lobster under the "Good Spot" seemed more healthy than we had ever encountered it in the years before.

Number of living specimens of M. cervus counted between 2000 and 2015 in the "Good Spot". *2013 data is an estimate derived from a statement of a local shell dealer who reported collecting a "large number" of specimens on Facebook. The fluctuations we noticed on our visits were obviously due to prior visits of shell collectors during the respective year, e.g. in 2004, when rocks were found flipped over and not returned, which is an indication for the activities of irresponsible shell collecting.

©2020 by Molluscan Science Foundation