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Conserving biodiversity

Investigating climate change impacts on the Bahamian black land crab

Research

By Kelly Foss

An ocean sciences doctoral student is shining a light on the Bahamian black land crab — literally.

Bill Bigelow crabbing at night under the light of a head torch.
Photo: Submitted

“They’re nocturnal animals, and when we go out and collect data on population size or community demographics in the bush, it’s all under head lamps,” said Bill Bigelow.

Ocean dependence

So why is an ocean sciences student interested in a terrestrial animal?

“From a biological standpoint, even though they are a land animal, they depend on the ocean for part of their reproductive cycle,” said Mr. Bigelow, who is supervised by Dr. Iain McGaw, Department of Ocean Sciences, Faculty of Science. “During the Caribbean rainy season, there’s a mass migration to the ocean where they release their eggs.”

“How does a land animal breathe through gills?” — Bill Bigelow

The black land crab evolved from the sea hundreds of millions of years ago and has managed to hang on to some of the physiological traits of its marine ancestors since that time.

“Surprisingly, they continue to breathe through gills, which begs the question, how does a land animal breathe through gills?” he asked. “Those are core components of this project — understanding their biology and the importance of different habitats for them to survive and thrive.”

Exploring with students from the Deep Creek Middle School in South Eleuthera.
Photo: Submitted

A question of balance

Because the crab depends on moisture from rain to live, Mr. Bigelow looked at how different levels of dehydration influenced their blood chemistry, or osmolality.

Water helps them maintain homeostasis, or balance. As the crabs lose moisture and dehydrate, the availability of water in their blood becomes increasingly concentrated, he says.

“Once we understood that psychological response, we then asked how this would influence their feeding patterns and activity levels.”

Mr. Bigelow is still in the analysis phase, but says early trends show that as the crabs become more dehydrated, they eat less.

“It’s probably due to the fact that they don’t have the energy,” he said. “But their selection of food seems to change, as well. When dehydrated, they prefer things that are more broken down, pre-digested, so to speak, over more bulky food stocks.”

Drier and warmer

In the Caribbean, a variety of climate models predict a drying and warming scenario by mid-century due to climate change.

So, Mr. Bigelow feels it’s important to understand what impact these changes may have on the black land crab, as it is a significant component of the Bahamian economy and environment.

“We might not see these crabs here in the not-so-distant future.” — Bill Bigelow

They’re an important food resource and they have a “huge” function in the ecosystems, but there is a deficit in the research surrounding them, he says.

“For an animal that breathes through gills and is dependent on rain moisture, having no rain in months could potentially not bode well for them. And yet, the Bahamas goes through very distinct dry and wet periods, so where do they go and how do they survive? It looks like they actively seek out small nooks and crannies in very specific microhabitats and retreat there for those dry months.”

Protecting habitats

Mr. Bigelow has connected with local harvesters to help him identify those particular habitats that are so important to the black land crab.

Educational outreach with students at the Harbour Island Green School.
Photo: Submitted

“We want to support harvesters in identifying areas they think should be preserved and then amplify their voices,” he said. “We hope to report our findings to the Bahamas National Trust and the Bahamian government, to really push legislature to reserve these habitats, because if they don’t, we might not see these crabs here in the not-so-distant future.”

Mr. Bigelow is also working with Dr. Owen O’Shea, an adjunct professor at Memorial University and CEO of the Centre for Ocean Research and Education (CORE) in Eleuthera, the Bahamas.

They are carrying out interactive surveys and town hall meetings with the goal of engaging local Bahamians in a two-way knowledge transfer about the black land crab fishery.

The central mission of CORE is to promote the value of conserving biodiversity through research, education and outreach in the communities of Eleuthera and surrounding islands. This is achieved through a grassroots approach, building capacity through the inclusion of these communities in applied research programs.

Bill Bigelow interviewing a local stakeholder about the cultural and economic significance of the land crab fishery.
Photo: Submitted

Local perceptions and knowledge

Mr. Bigelow agrees social science is an important part of his project.

“If you don’t talk to the people who know a subject best, you’re missing out on critical data. The heart and soul of this project is working in the community, with the community and for the community.”

Funding for this research has been provided through a Social Sciences and Humanities Research Council (SSHERC) Partnership Engaged Grant.


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