|Déjà-vu all over again; tell-tale tangles|
|By Harry G. Lee|
Around mid-afternoon on April 6, 2008, Bill Frank was making his customary rounds during a minus low tide at Mayport Naval Station beach, when he noticed a larger-than-usual something-or-other in the distance, about 25 yards south of the boulders comprising the south jetty of the St. Johns River entry. As he approached, it became apparent that this was not a Horse Conch or giant whelk but rather a tangle of heterogeneous marine life (Fig. 1). On closer inspection it was found to be studded with the shells of small mollusks, mostly hermit-crab-inhabited gastropods. By instinct he bagged the whole thing up and stowed it in his back pack. After toting the ”heavy mess” (Bill’s words) around for a couple of hours and getting soaked as a consequence, he finally got back to his car and headed home.
Knowing he had an entire shell collection in this half cubic ft. conglomeration, he asked me to evaluate the part of the assortment comprised of molluscan remains. We tacitly admitted a sense of déjà-vu as Brian Lloyd had provided his mom, Charlotte Thorpe with a similar tangle eight years earlier, and it proved to be a sheller’s equivalent of a Vegas slot-machine jackpot (Lloyd, 2000, 2000a).
I was able to extract the mollusk shells from this mix of algae, sea whips, marsh grass, parchment worm casings, whelk egg cases, etc, and here is what was there (phylogenetic order):
That’s 1625 shells of 35 species. All but two of bivalve species were represented by single valve(s), often not fully preserved. The majority of gastropod shells showed evidence of hermit crab occupancy, and very few living mollusks were encountered. In both groups exceptions are noted above.
Brian Lloyd’s one cubic ft. tangle was “collected” by being foul-hooked while he was whiting-fishing in the surf at Katherine Hanna Park, Atlantic Beach on 4/24/00. It was composed of “a discarded fishing rig entangled with algae, dead seawhips, marsh grass, a large parchment worm, sponges, and an empty whelk case” (Lloyd, 2000, 2000a; Fig. 4). Although somewhat larger in volume, the tangle’s description sounds essentially the same as Bill’s 2008 material and invites comparison. Brian’s tangle was handed over to his mom, and I was able to identify 3952 shells of 60 species.
Brian’s top ten species were [rank and number in Bill’s tangle]:
and Bill’s top ten [rank and number in Brian’s tangle]:
Why the hermit-crabs concentrated in these tangles is not clear, but such gregarious behavior has been observed in other situations such as among intertidal rocks in various localities. The relative abundance of the Sharp Nassa (Figs. 2, 3) and the Dovesnails stands out, and, as Charlotte indicated (Lloyd, 2000, 2000a) in the case of the Nassa snails, this numerical dominance of members of this family (Nassariidae) is encountered in shallow water ecosystems of other parts of the world. The same can be said of the Dovesnails of many species in many disparate geographic areas.
There are other similarities and differences in these analyses, but the similarities are the more striking. I think it safe to conclude that the composition of the molluscan fauna, at least the smaller species, on our beaches hasn’t changed appreciably over the first eight years of this millennium.
Acknowledgements: I thank Charlotte Thorpe for Fig. 4 and Bill Frank for Figs. 1, 2 and 3.
Lloyd, C., 2000. A remarkable catch. Shell-O-Gram 41(4): 1, 3-5. July-August.
Lloyd, C., 2000a. A remarkable catch. American Conchologist 28(3): 4, 24. Sept.