Chief Science Correspondent
For millions of years, the icy cold waters surrounding the Antarctic continent were isolated from the rest of the planet. As these critical regions of the Southern Hemisphere become warmer, the boundaries are no longer so clear. These warmer conditions have made way for the possible invasion of a likely disastrous predator: the king crab.
The media has been quick to take note of a recent study, published in an early edition of Proceedings of the Natural Academy of Sciences. Just six pages long including references, the paper presents evidence that a reproductively viable population has formed on the outer continental slope surrounding the West Antarctic Peninsula (which is one of the most rapidly warming regions on Earth).
The ecology of the waters surrounding Antarctica is unique, and has been studied as a model for how ancient marine ecosystems once functioned. Sea stars and nemertean worms are the top predators in the system, and most fauna have thin shells. Thus, shell-crushing crustacean invaders pose a massive threat to these vulnerable organisms.
To date, scientists have collected a great amount of evidence that the air surrounding the Antarctic Peninsula is warming; however, scientists are not certain how the changes in air temperature will impact ocean temperatures in the near future. To date, summer water temperatures in the region have risen 1.5 degrees Celsius over the past 50 years.
Although king crabs have not yet been found on the continental shelf, individuals from two species have been found on the continental slope, which is deeper, warmer and farther from the coastline (see image below).
Currently, these populations are still thermally excluded from the upper shelf, the portion closest to land. However, the authors reported that current temperatures do not exclude the populations from the lower region of the shelf. They determined that other physical factors, such as salinity, sediment and hydrostatic pressure do not limit these invading species.
From the photographic survey on the outer shelf, the authors also concluded that the king crabs would encounter an abundance of prey and few predators (most likely seals and fish). Furthermore, as an invasive species, king crabs hold an advantage in the ecosystem: they may not be recognized as prey by the potential predators in the region.
I believe the conclusions of the study would have been stronger if the authors had examined the concurrent effects of these variables. For instance, thermal and haline tolerances are often interrelated, meaning that thermal tolerance may be further limited under certain salinity conditions (and vice versa). In other words, the distribution limitations of these species may be more complex than was indicated in this study.
That said, the implications of this study are very important, and the photographic survey method is very impressive. Antarctic biology data tends to be limited, and by generating these seafloor images the authors have gained access to visual data from a world that was, until recently, almost completely unknown.