What factors influence the spread of invasive animal species in our oceans?
What factors influence the spread of invasive animal species in our oceans? This question was the focus for a team of experts from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), Bangor University (Wales, UK), and the University of Greifswald’s Zoological Institute and Museum in the context of the DFG-sponsored Research Training Group 2010 RESPONSE (Biological Responses to Novel and Changing Environments). The results of their study have just been released in the journal “Ecography”.
Crustaceans dominate the food webs of many costal habitats in our oceans. In addition, as ‘stowaways’ on board of vessels used in global shipping, many crab species have spread far beyond their natural homes. The Asian shore crab Hemigrapsus sanguineus is a good example of these invasive species: in just a few decades this species, native to the Pacific, has spread to many corners of the globe. By the 1980s, it had made its way to the Atlantic coast of North America, and by the 1990s, had gained a foothold in the coastal waters of Europe. In both North America and Northern Europe, this species is spreading farther and farther north, toward the rapidly warming polar waters. In the ecosystems they invade, these crabs can soon reach such high numbers that native species like the European shore crab Carcinus maenas are impacted or displaced. Furthermore, they exert considerable predation pressure in their new homes, often decimating e.g. marine invertebrates like mussels or young shore crabs, and taking these food sources away from other species in the process. This can produce lasting changes to the invaded ecosystems.
But how is climate change influencing the spread of invasive marine species? Invasive species are often characterised by a high tolerance for fluctuations in environmental factors like temperature and salinity, thus being more adapted to the effects of climate change in the oceans. The team of researchers, including members from the Alfred Wegener Institute, Bangor University (Wales, UK) and the University of Greifswald, especially focused on the early developmental stages of the Asian shore crab, and examined its microscopically small larvae, which grow as they float in the water column. Since it has been confirmed that the larvae of many marine organisms are more sensitive to environmental fluctuations than their adult counterparts, these larvae often represent a ‘bottleneck’ in the establishment of new populations.
Image: Adult specimen of Hemigrapsus sanguineus. (Credit: Alfred-Wegener-Insitut / Uwe Nettelmann)