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Conservation

Long-term monitoring reveals optimistic future for endangered limpets

Journal source: Espinosa, F., Rivera‐Ingraham, G. A., Ostalé‐Valriberas, E., & García‐Gómez, J. C. (2018). Predicting the fate of the most endangered marine invertebrate of the mediterranean: The power of long‐term monitoring in conservation biology. Aquatic Conservation: Marine and Freshwater Ecosystems, 28(6), 1283-1293. doi:10.1002/aqc.2944

Long-term monitoring protects biodiversity

Global climate change, invasive species, and habitat alterations are causing a significant loss in biodiversity, which is the variety of species living together in an ecosystem. Biodiversity is important because each organism contributes in unique ways to the functioning and health of an ecosystem. To protect biodiversity, scientists want to predict how species populations will change over time. Understanding how organism populations change and where they are found can help scientists inform managers about habitats that should be protected. In marine ecosystems, long-term monitoring is especially important for scientists to see how populations of species of concern are increasing or decreasing in over time.

In the Mediterranean Sea, a globally recognized “hot spot” of marine diversity, scientists are actively involved in long-term monitoring because these ecosystems provide habitat for many species of fish, mollusks, and crustaceans. Unfortunately, over-exploitation and habitat destruction have contributed to declines in biodiversity, and the Western Basin has the highest concentration of endangered species in all the Mediterranean.

Meet the Giant Limpet, an endangered marine invertebrate

One species that has captured the interest of scientists for long-term monitoring in the Mediterranean is the snail, Patella ferruginea (common name, Giant Limpet), which is considered the most endangered marine invertebrate in the Western Basin.

(Featured image) Limpets in their rocky intertidal habitat. Photo source: Flickr via Wikimedia Commons.

The Giant Limpet begins its life as a free-floating larva, which enables the species to disperse and establish various populations on rocks and other hard surfaces along marine intertidal zones. The Giant Limpet is considered a keystone species: other marine organisms higher up on the food chain depend on it for food.  This means the loss of the organism could change the ecosystem drastically. However, the Giant Limpet is threatened. For centuries, humans have been collecting the giant limpet to harvest for decorative purposes and for baiting fish. Additionally, urban development of coastal areas has fragmented and reduced limpet habitat, which has led to this limpet nearly disappearing from European coasts.

Map of the vicinity of the Strait of Gibraltar, where the study’s long-term limpet monitoring took place

While prospects seem bleak for this limpet, scientists have found unusually high numbers of the species along the Mediterranean coasts of the Bay of Cueta and near the Strait of Gibraltar. Long-term monitoring of limpet populations in these areas has provided scientists with data about abundance, recruitment, and average size of limpets. In turn, these data can be used to perform population viability analysis (PVA), an ecological tool used to predict a species’ risk of extinction and how long the species can last before reaching critically low population levels. Since high numbers of limpets were found in just one corner of the Mediterranean, while the rest of the population throughout the sea have virtually vanished, Espinosa and colleagues of the Marine Biological Laboratory in Seville, Spain, used monitoring data to predict the future of the giant limpet.

Long-term monitoring of limpets from 2007 to 2016 involved sampling from several coastal areas near the Strait of Gibraltar, each varying in their accessibility by humans. At each location, researchers counted and measured the shell size of limpets along transects, paths that help researchers estimate abundance of organisms in an area. These data were used to estimate population growth rate and the probability of the limpet going extinct after 50 years. The scientists also collected water measurements, including monthly water temperature and concentrations of chlorophyll α, a pigment found in marine algae that is used to estimate the number of algae in the water, to determine if these factors influenced populations of limpets.

What did they find?

The PVA showed that populations of limpets varied significantly over the 10-year monitoring period, and that limpet populations located at sites more accessible to humans declined over time. In contrast, higher limpet numbers were recorded from sites more difficult for humans to access. These sites were often fenced off and included artificial surfaces, such as concrete blocks and riprap commonly found in harbors to protect beaches from wave action. While sites with frequent human interactions had lower numbers of limpets compared to more restricted sites, the overall trend in the long-term data showed that the limpet population increased over time. High temperatures and high algae densities appeared to negatively affect  limpet population growth, as these conditions may attract hungry fish to dine on limpets.

An example of riprap, the structures that supported the highest overall numbers of limpets in this study. Photo source: Bureau of Reclamation via Wikimedia Commons.

Perhaps the most surprising find of this study was the unexpected importance of coastal development, in the form of artificial structures, in providing more space for higher numbers of limpets to live. While we may associate human development with habitat degradation, in this case, the addition of solid surfaces appears to be an important factor that has a positive effect on limpet populations.

The bigger picture

This study sheds light on why long-term data collecting is so important, as the data were used to analyze the viability of the limpet population in the coming decades. The study also showed that limpet populations thrived best on man-made structures that were rarely frequented by curious humans. Additionally, the high densities of Giant Limpets near the Strait of Gibraltar highlight the importance of limpet populations in this corner of the Mediterranean as a source of free-floating larvae to establish on nearby areas, further expanding the population into other regions of the sea, which would help reduce the risk of extinction. Since the authors identified where limpet populations were most abundant, on the manmade structures, conservation efforts can now focus on protecting those areas and potentially build more surfaces to further build up the population. In turn, by taking measures that would benefit limpet populations, the species associated with limpets can also be protected; protecting limpets could protect the biodiversity of these areas. As global changes continue to occur and as humans continue to modify the landscape, it will become increasingly important for more long-term monitoring programs to track populations of marine species.

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