Feature Story                                                            January 2012

Will cold temperatures stop the Caribbean Creep?

A view of SERC's green village during snowmageddon Feburary 2010 (photo by Stephen Sanford).

Remember Snowmageddon 2010, the east coast snow storms that dumped 1-3 feet of snow over the mid-Atlantic? The February snowstorm was the largest in the region in nearly 90 years and resulted in the heaviest snowfall on record for Delaware (26.5 inches), and the third heaviest snowfall in Baltimore, Maryland with 24.8 inches. The storm made a big impression on Dr. João Canning Clode and other scientists at the Smithsonian Environmental Research Center (SERC), who began to wonder if the storm, and the December/January cold snap that preceded it, would result in increased mortality and possibly the disappearance of introduced marine species from southern climates.

Aided by the relatively recent increase in ocean surface water temperature, new marine invaders are beginning to spread northward along the southern and mid-Atlantic coasts from the Caribbean. This particular northern migration has been termed the “Caribbean Creep”, although the phenomenon of northward migration is not limited to this region. Many of the non-native species creeping northward are doing so because they are able to tolerate a broad range of temperatures. But what happens to these fair-weather travelers during a cold snap? In January 2010 a cold snap in the southeast led to higher mortality of several high profile species including manatees, sea turtles, and crocodiles. But there was also evidence that Caribbean Creep species, like the Green Porcelain Crab (Petrolisthes armatus), had declined dramatically as a result of the January chill. Green Porcelain Crabs have a very large presumed native range that includes the tropical eastern Pacific from Mexico to Peru and the western Atlantic from the Gulf Coast of Florida to southern Brazil and the eastern Atlantic from Senegal to Angola. But recently the crabs have moved north into Georgia and South Carolina. 

Dr. Canning Clode studing a Green Porcelain  Crab (Petrolisthes armatus).

To investigate further Dr. Canning Clode and his colleagues experimentally tested the cold-water tolerances of invasive Green Porcelain Crabs. Introduced crabs were collected in Georgia and brought to the lab where they were subjected to one of three temperature treatments. The first was a control treatment, which was held at a constant moderate winter temperature. The second was a cold treatment in which the temperature was fluctuated in such a way as to mimic the cold snap of January 2010. The third treatment tested extreme conditions, ones which would be expected in a more severe winter. 

They found that most of the crabs in the control treatment survived (83%), but many of the crabs in the cold treatments (61%) and all of the crabs in the extreme cold treatment died. Those crabs that did survive the cold treatments were sluggish, making them more susceptible to predation and possibly impacting their ability to feed. Prolonged exposure to cold temperatures may further compromise the crab’s ability to overcome cumulative cold events, as two other record cold snaps occurred in February and March 2010. The loss of over 60% of the population each time could explain the disappearance of this species in Georgia, suggesting that extreme cold temperature events may limit or prevent the northward spread of the invasive Green Porcelain Crab. Several climate models used to predict how species will react to climate change have predicted that climate change will result in the continued decline of global biodiversity over the next 100 years and the increased spread of introduced species. Many of these models have focused on temperature increases, but few have evaluated the impact of severe weather like cold snaps. For example, several studies have reported mass die-offs of shallow-water marine invertebrates in the winter but have not linked these to climate change models. Dr. Canning-Clode and collaborators suggest that these episodic cold weather snaps should be accounted for in future climate studies in aquatic environments, as it may be particularly valuable in explaining range expansions and the introduction of invasive species.

This study is published at PLoS ONE. For Dr Canning Clode “the core message of this paper is that yes, climate change is happening, but the cold is also part of this change. We believe these periodic cold events will limit the range expansion of Petrolisthes armatus as well as other Caribbean creep species”.

Canning-Clode, J, AE Fowler, JE Byers, JT Carlton, and GM Ruiz. 2011 ‘Caribbean Creep’ chills out: climate change and marine invasive species. PLos ONE 6(12):1-5 Available online

Written by Monaca Noble, SERC