|A Remarkable Catch|
|By Charlotte Lloyd|
On April 24th of this year my son Brian was surf fishing for Whiting at Katherine Hanna Park in Atlantic Beach, Florida. He felt something pulling on his line and reeled in a discarded fishing rig entangled with algae, dead sea whips, marsh grass, a large parchment worm, sponges, and an empty whelk egg case. This "biomass" was teeming with a zillion (his description) hermit crabs in miniature shells. Recognizing several species of Epitonium, he put the tangle in his bucket, added seawater, and went home to call and tell me what he had for me. I was on my way to give a shell program to senior citizens, and it was several hours before I could pick up the bucket; consequently the hermit crabs expired. First glance told me it would be worthwhile to examine the shells more closely.
Once home I photographed the "catch," and then came the task of removing the hermit bodies from the shells. I found the "panning for gold" method to be the most successful. With water running into the bowl with the shells, most of the hermit crab bodies, being less dense than the shells, washed out and over the bowls rim.
I identified the hermit crabs as Pagurus longicarpus Say, 1817, a small and plentiful crab along our coast. Its well-developed soft and somewhat coiled abdomen is inserted into a dead mollusk shell it carries around as portable protection.
I noticed large numbers of Phrontis acuta (Say, 1822), the Sharp Nassa, so I thought it would be interesting to compare the numbers of different species to come up with a count. Phrontis acuta is a small 8-12 mm. species that has a glossy sturdy structure with strong pointed beads on the whorls. The beads occasionally have a narrow brown spiral line connecting them. Dr. Harry G. Lee was excited to hear about the catch and offered to identify all of the shells (see the list with identification and shell counts at the end of article). At final count, I recorded an amazing 3,952 shells with 2,088 being Phrontis acuta for 53% of the total. The 1,864 other shells were distributed among 59 different species.
Why so many Phrontis acuta? The family Nassariidae, the mud snails, are shallow water, usually intertidal dwellers. They occur in large colonies and are scavengers. Several months ago I witnessed a closely related Nassarius species of the Indo-Pacific in the surf at Nuku Hiva Island in the Marquesas. This mollusk was very active in the surf zone. Each wave would pick up the tiny snail several feet off of the bottom where it would use its mantle to maneuver/glide to the bottom to feed again. There must have been thousands in an area of about five square meters. I can only surmise that locally Phrontis acuta has the same habit and is a lot more common in our surf than I had originally thought.
The question also arises as to why so many hermit crabs were on the biomass entanglement. What are the gains of coexistence - food, protection, reproduction? We do know that some hermit crabs like the company of their peers. Any shell collector can tell of turning a rock and finding hundreds of hermits "hanging out together." The mass could also have been a "lunch wagon" on which the hermits could hitch a ride and feed as it rolled along the bottom.
Some live shells were found on the mass. These included Astyris lunata, Lunarca ovalis, Anadara transversa and Musculus lateralis. Also, two fossil species were identified - Carditamera arata (Conrad, 1832) and Gemophos lymani (M. Smith, 1936). There were quite a few single shells of bivalves in the entanglement.
One week later I called Brian to tell him he was right about the Epitonium, that there were eight species identified, and that the total number of shells in the catch was 3,952. His reply was, "Wow, - Mom just think how many jumped or fell off when I was reeling it in!"
Below is a listing of shells and the number of each species obtained from the tangle of tackle, seagrass, Busycon eggcase, etc., angled by Brian Lloyd and lent to H. G. Lee on 4/27/00: