Refuge Notebook • Vol. 17, No. 45 • November 6, 2015 Local seashells provide more than just a home for hermit crabs by Jennifer Peura Gastropod shells collected near St. Lawrence Island were studied to assess if their populations affected hermit crab populations. After beachcombing at low tide, perchance coin- of calcium carbonate, the major compound in shells, ciding with a full or new moon to maximize your suc- coral, the exoskeleton of lobsters and crabs, and (im- cess, be it at Captain Cook State Park or Homer’s portantly to Sockeye lovers) pteropods. Pteropods are Bishop’s Beach, you’re likely to end up with a small the major food source of krill, which in turn is the ma- collection of shells, crab exoskeletons, or other rem- jor food source for juvenile salmon. Sea shells also nants of marine life. Even without regard to the ac- provide habitats for multiple fish species at different tual animals whose exoskeleton remains are now sim- stages in their life cycle, notably to hide from preda- ply just seashells that adorn the mantle in your living tion. Shells are used by shorebirds to build nests, by room, the shells themselves have other ecological val- barnacles as a substrate to grow on, and by hermit ues. crabs for protection. The breakdown of shells provides nutrients for or- The lowly hermit crab you might purchase from ganisms that live in the ocean’s benthos (or bottom). PetCo is often assumed to be a textbook example of This nutrient recycling is integral to the availability one species that can’t exist without another in close 86 USFWS Kenai National Wildlife Refuge Refuge Notebook • Vol. 17, No. 45 • November 6, 2015 proximity. That is to say, as a responsible hermit crab and to acquire food, making bivalves sensitive to tox- owner, your aquarium should hold gastropod (slugs, ins even as they serve as a vector for humans to ingest snails, whelks and periwinkles) shells of various sizes toxins. that your growing pet crustacean can use as disposable Unfortunately the same issue is true for the once houses. lucrative fisheries of Long Island and Hudson Bay. So you might think that hermit crab populations After Hurricane Sandy, 76 clammers filed a lawsuit are dependent on gastropod populations. It turns out against the City of New York claiming wastewater that’s not the case. As a graduate student at Southern from a treatment facility that lost power contaminated Illinois University, I studied exactly that question by their fishery. Prior to Sandy, many blamed overhar- examining populations of hermit crabs and gastropods vesting of clams caused the demise of that fishery, sampled at 52 sites around St. Lawrence Island with a which resulted in Manhattan chowder frequently (and trawl net by the U.S. Coast Guard’s icebreaker Healy. ironically) served with clams imported from Florida. Although I tortured the data collected from the 10,000- Like many other fisheries, the impact of harvesting square-mile study area with lots of different analyses, such a large portion wasn’t considered until the popu- I couldn’t find any evidence to support the commonly lation was in peril. However, is that the whole story— held idea that hermit crab populations are geographi- overfishing and pollution? There’s evidence that an- cally limited by gastropods. Further research is needed other factor is in play as well, and it starts at the be- to explain how gastropod shells were available to her- ginning of the bivalve’s life cycle. mit crabs without the living gastropods being present, Poor larval growth and survival was first observed even after accounting for migration by populations in oysters in 2005 with decreased fertilization rates and elsewhere—a mystery that remains unanswered. increased juvenile mortality due to the unavailability Closer to home, there is another mysterious issue of calcium carbonate. Clams, crabs, lobsters and coral that plucks hard on the heart strings of those who re- struggle from day one to grow because of a lack of the member Clam Gulch, just a few years ago, playing host fundamental building block of their shells. Calcium to a heavy flow of Alaskans setting up shop with clam carbonate is decreasing in marine systems, and it’s due cannons and buckets full of razor clams. During the to a chemical reaction taking place in every ocean of past two years, however, the abundance of razor clams the world. When atmospheric carbon dioxide levels has been shockingly low. The rapid population decline rise, their concentrations in the ocean increase as well, resulted in suspending all clamming activity from the causing a chemical reaction that makes the available mouth of the Kenai River to Homer in hopes that we carbonate less able to bind with calcium. This creates a set up future generations with a successful clam fish- more acidic environment with calcium carbonate lev- ery. els sometimes low enough to inhibit larvae from ma- The question of “where are the clams?” reaches be- turing into shelled clams. yond our Kenai Peninsula beaches. The same question The finding of a simple seashell on a beach canbea is being asked in every state along the Pacific and At- reminder that gastropods and bivalves are both impor- lantic oceans. Clam fisheries are abruptly declining, tant but vulnerable to environmental change. While causing those whose livelihood depends on a respon- water treatment experimentation is underway to help sibly maintained clam fishery to desperately search for clam and oyster hatcheries rebound, I try to leave the an answer and a solution. The Boston Clamdigger’s beach with a little less trash than when I arrived in Association filed a lawsuit against Swissport, a com- hopes that my small efforts may help the plight of pany that provides Boston Logan International Air- these shellfish. port with fuel. The lawsuit claims that the loss ofhar- Jen Peura is a seasonal biotech at the Kenai Na- vestable clams in Boston Harbor was influenced by a tional Wildlife Refuge. Find more information at http: huge fuel spill in 2010. Clams and other bivalves (mus- //www.fws.gov/refuge/kenai/ or http://www.facebook. sels, oysters and scallops) filter water for movement com/kenainationalwildliferefuge. USFWS Kenai National Wildlife Refuge 87.