A survey on the populations of "Deer Cowries"

in the lower Florida Keys

Since the year 2000, we have visited the lower Florida Keys on a regular basis, monitoring the populations of Deer Cowries, Macrocypraea cervus (See photo) and M. zebra, as well as the ash-cowry, Luria cinerea, in a restricted area southwest of Marathon Key.

 

In one place (which shall not be disclosed here, but in our group it has always been known as "The Good Spot"), an exceptionally large number of these large Cowries thrived in the ledges of rocks along the shore, at 1 to 3 meters depth.  During seven visits during the past 15 years, the number of Deer Cowries encountered alive was recorded, and between 10 and 30 specimens were collected, which did not seem to have an impact on the number of shells observed in the following year (see diagram below).

 

On the previous visit in July 2010, the population was in a remarkably good state, with specimens hiding everywhere in the ledges of the bridge pylons, under rocks, and even exposed during daytime. A local collector reported seeing several specimens in March/April of this year, in this same spot.

When we revisited this place in July, we noted a large number of fresh dead, mostly juvenile shells in the gutters between the pylons, but did not see a single living animal. We found a single fresh dead L. cinerea only, and noticed that also other gastropods that feed by grazing on the substrate (Strombus raninus, S. gigas, S. alatus) had also died off. On subsequent searches in other areas between Marathon and Key West, the same scenario was encountered.

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