Download Mollusks in Peril: Why Should We Care? By José H. Leal, Ph.D. Why

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.