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Mollusks in Peril: Why Should We Care? By José H. Leal, Ph.D. Why All the Fuss about Mollusks? After all, they are small, slow-moving, slimy, “lowly” creatures that are barely noticed by most people. Right? Well, no. There is much more to them than just a trail of slime or pretty empty shells. Mollusks are the most diverse group of animals in the world’s oceans, and the second most diverse on Earth. They are present in virtually all of Earth’s natural environments and ecosystems, including deserts, cold mountain springs, rainforests, and the deepest ocean trenches. If nothing else, in addition to their status as a highly diverse and widespread group of animals, mollusks are also important to humans as food, as sources of inspiration for materials and products in contemporary science, medicine, and engineering. And let’s not forget about the beautiful shells they make. However, despite this fundamental relevance of mollusks in the big scheme of things, they have not received the consideration they warrant from conservation efforts nor the public attention they deserve. The Domino Effect. Organisms in natural ecosystems and food webs are all interconnected, and any disturbance that negatively affects one species (such as its permanent extinction) is likely to provoke a negative chain reaction that will interfere with a much larger number of species, in a cumulative and fast-paced manner. For instance, the extinction of a clam will negatively affect all species that eat that clam, and these adverse effects on the predators will in turn rapidly propagate within the food web. If enough species are critically affected, not only is the balance of nature forever altered, but our own fate as a species may be endangered in the long run. Because mollusks are such a large and widespread group, changes affecting mollusks as a group are potentially capable of having massive and irreversible effects on the planet’s biodiversity. Aren’t Extinctions Routine Events in Nature? Extinction is a natural process. Under normal conditions, the rate of extinctions is offset by the rate of speciation, which is the frequency of appearance of new species. But, because of human-induced modifications of the environment such as air and water pollution, clearing of natural areas for agricultural and urban development, and climate change, the current global rate of species extinctions is far higher than that for speciation. This disconnect between speciations and extinctions is one of the attributes of what Nobel Prize-winning atmospheric chemist Paul Crutzen termed the Anthropocene Epoch (spanning the last few centuries), when the human impact on the Earth's atmosphere, physical make-up, and living systems has been so relevant as to represent a new geological epoch. Molluscan Extinction Records Are Underrated. In an article published in June 2015 in the prestigious journal Proceedings of the National Academy of Sciences, Claire Régnier of the National Museum of Natural History (Paris) and her collaborators propose that the global number of extinct animal species, including mollusks, has been underestimated and may actually be about 175 times larger than the amount documented by the International Union for Conservation of Nature (IUCN). The IUCN publishes the Red List of Threatened Species, which is the benchmark widely used in conservation efforts and to measure the global decline in biodiversity. The IUCN extinction records are very low because the organization traditionally omits invertebrates (which include mollusks) from its scenarios. And invertebrates comprise 99% of all animal species diversity! The natural corollary to the conclusions of the work by Régnier and collaborators is that if those many species have already gone extinct in historical times, then a much larger number of them are endangered or critically threatened. Terrestrial, Marine, and Freshwater Mollusks Are In Peril. Human-induced environmental changes and ensuing extinctions have traditionally been more difficult to observe and document in the marine than in terrestrial and freshwater realms (e.g., it is more straightforward to gauge the effects of agricultural fields replacing natural land ecosystems and dams restricting water flow in rivers, to name just a few, than to assess the impact of equivalent changes in the ocean). For instance, despite the fact that there are almost twice as many known species of mollusks from the marine than from terrestrial environment, the number of recorded extinctions of land mollusks is about 100 times larger than that number for marine species. We now know that this smaller rate is an indication that extinctions of marine mollusks are not being properly assessed, rather than that they are not occurring. Marine species are severely threatened by human-induced changes, with many species vanishing before researchers have a chance to name and describe them. The Global Threats to Marine Species. Aside from localized problems in the coastal marine environment such as domestic and industrial pollution, development, urban and agricultural encroachment, and other geographically restricted sources of environmental degradation, marine mollusks are threatened by generalized, more widespread disturbances such as those associated with climate change. For instance, coral bleaching, the critical loss of energy-giving coral zooxanthellae caused by changes in ocean temperature, is now a global problem, affecting large areas in the marine tropics of the Atlantic, Indian, and Pacific oceans. The global “hot spots” for molluscan diversity coincide with coral reefs, as these latter are associated with a very large number of shallow-water molluscan species. As coral reefs decline, so will all the organisms connected with them. The Threat of Ocean Acidification. Ocean acidification is caused by the increased uptake of atmospheric carbon dioxide by sea water. More acidic sea water affects the shells of planktonic mollusks, thinning and opening holes in those delicate structures. Acidification is already a threat to several species of planktonic mollusks, including sea butterflies (pteropods). Sea butterflies are key links in open-ocean food webs, serving as food for many species of fish, which in turn feed larger animals such as sea birds, whales, and even polar bears. Epilogue. There you have, in a nutshell, why we should worry and discuss mollusks from the standpoint of a threatened, and to a large extent neglected, group of animals. I also gave you a brief description of the topics to be discussed and mulled over during (and after) the upcoming Mollusks in Peril Global Forum. Be there, voice your questions and concerns, help the community understand some of the problems that mollusks and everyone else face as we descend into the bowels of the Anthropocene Epoch.