A big increase in tourism on the Mediterranean coast of Spain correlates with a 70 percent decrease in mollusk shells during July and August and a 60 percent decrease in other months.
Shell removal can cause significant damage to natural ecosystems and organisms that rely on them, says lead author Michal Kowalewski, chair of invertebrate paleontology at the Florida Museum of Natural History at the University of Florida.
“This research is best described as a case study that evaluates shell loss due to tourism and then explores how this process may affect natural habitats,” Kowalewski says. “It’s too early to tell whether this depletion is substantial enough to trigger major environmental changes. However, our results suggest that we should not ignore this issue.”
For the study published in PLOS ONE, researchers conducted multiple monthly surveys from 1978 to 1981 and from 2008 to 2010 on Llarga Beach, a small stretch of shoreline on the coast of Spain.
Based on area hotel sales data, researchers estimate the number of tourists visiting the beach increased threefold over the last 30 years, with most visits during the summer. Over the same time period, the number of shells on the beach decreased by more than 60 percent.
The survey area has experienced no new commercial fisheries or urban development since the 1970s, suggesting human activity unrelated to tourism is unlikely to have contributed substantially to the shell loss, Kowalewski says.
Changes in ecosystem structure and local environmental conditions, which could potentially contribute to a natural decrease in shell numbers, were not observed.
Shell removal at Llarga Beach was higher during the summer, and shells were more abundant during the winter when fewer tourists visited the area. Although a popular destination, the beach is not a major tourist hot spot, and the shells found there are not beautiful, diverse, or valuable to collectors.
If a relationship between increased tourism and accelerated shell removal can be detected at a place that is not famous for its shells, it is likely that beaches known for their shells and frequented by collectors have had more substantial impact, Kowalewski says.
“Although significant research has been done on the impacts of human activity on live shellfish, including, recreational harvesting and curio collecting, we are still lacking rigorous studies estimating the scale of shell removal by humans,” Kowalewski says. “Shells are remarkable in that they serve multiple functions in natural ecosystems, from beach stabilization to building materials for bird nests.”
Shells also provide a home or attachment surface for diverse marine organisms, including algae, seagrass, sponges, and other micro- and macro-organisms. Hermit crabs use shells as their protective armor, while fish use shells to hide from predators.
These discarded exoskeletons of mollusks, including clams and oysters, are also important because most are made of calcium carbonate and in many coastal habitats they dissolve slowly and recycle back into the ocean.
Not so harmless
The study may prompt more systematic assessments of shell removal by tourists, says Geerat Vermeij, a mollusk shell expert and distinguished professor of geology with the University of California Davis who was not involved in the study.
“Molluscan shells are of prime importance to hermit crabs, and although sand beaches are not good places for such crabs, dead snail shells on mud-flats and rocky shores do form a primary resource for abundant hermit crabs. More subtly, many small organisms settle on dead shells, and so removing such shells will eliminate habitats for these colonists.”
Though tourism-related shell loss may one day prove harmful, more rigorous quantitative case studies are needed to fully understand the impact and develop reliable beach management practices aimed at shell protection.
Some countries already recognize the negative effects of shell removal, including the Bahamas, which limits the quantity of shells tourists can export without special permits.
“Humans may play a significant role in altering habitats through activities that many would perceive as mostly harmless, such as beachcombing and seashell collecting,” Kowalewski says. “It is important that we continue to investigate the more subtle aspects of tourism-related activities and their impact on shoreline habitats.”
Researchers from the Institut de Recerca de la Biodiversitat and Departament d’Estratigrafia, Paleontologia i Geociències Marines, Facultat de Geologia, Universitat de Barcelona, in Barcelona, Spain contributed to the study.
Source: University of Florida