Spider crabs find a new home

Over the past few weeks, the CEI reef team has made great progress with their West Indian spider crab (Mithrax Spinosissimus) project. Dr. Iain McGaw, a visiting scientist, is leading the charge to investigate the potential use of M. spinosissimus to remove biofouling organisms from aquaculture cages. When organisms settle upon net cages, their growth can reduce water flow, and has the potential to cause the nets to sink. The process of using one aquatic organism to feed or control another is known as integrated multi-trophic aquaculture (IMTA). This often reduces the input of wastes or the need for chemical treatment which can release pollutants into the surrounding environment. Dr. McGaw hopes to show how spider crabs could be used as a sustainable, environmentally friendly alternative. Currently biofouling is controlled using chemical or power-washing methods which introduce a lot of dead material into the environment.

Spider crabs are a great candidate for IMTA because they are large, non-aggressive and are keen grazers on algae and encrusting invertebrates. Their consumption of algae has been found to rival that of other reef dwelling fish and they tend to have a quite broad preference with respect to the types of organisms they will consume. However, there has been little research into the ability of spider crabs to clean algae from aquaculture cages. The cage being used in this study was built by CEI in 2012 to house cobia (Rachycentron canadum). There were several problems with this aquaculture project, mainly the issue of large predatory fish finding a way into the cage and eating the study species! Several years on and the netting is now covered in green algae, fire coral, sponges and a wide variety of other encrusting organisms.  The top of the cage floats at 40 feet below the surface whilst the bottom rests on the sea floor at 80 feet, with algae-encrusted nets suspended in between.

Divers explore the old aquaculture cage. Photo credit: Kelly Martin

Divers explore the old aquaculture cage. Photo credit: Kelly Martin

At the start of March, the reef team took ten spider crabs from the CEI wet lab to the cage to begin the experiment.  The divers placed one crab on ten of the twelve sections that comprise the top half of the sphere-shaped structure.  The crabs are each enclosed by a small wire cage, which are secured to the algae-encrusted netting with zip ties. Several days later, the reef team went to check up on the crabs in their new homes.  They swam around the cage and checked on each of the ten crabs; all of them appeared healthy, but unfortunately one crab had died.  Dr. McGaw believes this crab was likely molting its exoskeleton, which would have made it more vulnerable to the change in environment from the wet lab to the open ocean. However, the other nine crabs appeared happy and healthy and were clearly eating the algae on the large cage.

A spider crab rests on the algae-encrusted netting. The crabs are enclosed in small cages to prevent them from escaping which allows the team to monitor their consumption of algae. Photo credit: Daisy Buzzoni

A spider crab rests on the algae-encrusted netting. The crabs are enclosed in small cages to prevent them from escaping which allows the team to monitor their consumption of algae. Photo credit: Daisy Buzzoni

Last weekend the reef team returned to the dive site to assess how the crabs were doing after their first week on the cage.  Once again, the crabs appeared quite content and some had completely cleared the netting of growth. The next phase of this experiment will be to collect more spider crabs from the patch reefs and place them inside the aquaculture cage in order to determine long term survival rates and assess feeding, growth and health of the individuals. This exciting project is just starting to take off, so stay tuned for more updates!

Tales of the turtle team

As we wave goodbye to our recent visitors, the CEI turtle team would like to extend a huge thank you to the two fabulous Earthwatch teams who shared our enthusiasm for everything, from chasing turtles to scouring the algae beards off the hulls of our boats. The volunteers were as diverse as the underwater world, ranging in age from 15 to 80! As a non-profit that seeks to promote scientific research and education, Earthwatch collaborates with the Cape Eleuthera Institute by sending teams of ready-handed volunteers to help the Sea Turtle Research & Conservation team investigate the mechanism used by juvenile green turtles (Chelonia mydas) to select a foraging habitat. As evolution would have it, sea turtles are darn crafty underwater, often outwitting the many humans and various equipment required to catch and tag them. Our Earthwatch groups provided us with the help we needed in order to employ two different turtling techniques: rodeo and siene netting.

The first Earthwatch team consisted of seven adult volunteers with a variety of backgrounds, from yoga teachers to obstetricians, demonstrating that a passion for sea turtle conservation knows no occupational boundaries. This team were turtle chasing fiends, catching a total of 21 turtles in just one week, including 6 turtles that were new to the CEI tagging program. One of these new turtles, who we called Drewl, was just 22 centimetres long and set the record for the smallest turtle we have ever captured in Deep Creek. When not tagging turtles, Team 1 could be found conducting scientific longlines, assisting with data entry, and witnessing a necropsy performed on a bottlenose dolphin for the Bahamian Marine Mammal Stranding Network. At the end of the week, Earthwatch Team 1 paid a visit to Sheryl’s - a local restaurant ran by The Island School’s very own kitchen staff member, Sheryl Anderson. It was here that they discovered their new favourite seafood, the invasive Red Lionfish. Overall, team 1 had a diverse and busy week - fins were lost (and then found), vans broke down (and were then pushed by strong independent women), and cassava chips were shared. We didn’t think the first group could ever be matched in excellence, but then we met Earthwatch Team 2.

Earthwatch volunteers record biological measurements of a sea turtle they caught from a boat using the ‘rodeo’ technique.

Earthwatch volunteers record biological measurements of a sea turtle they caught from a boat using the ‘rodeo’ technique.

Earthwatch Team 2 was made up of 13 students from Dover-Sherbourne High School, MA, their two teachers and one Earthwatch Institute chaperone. This group had the opportunity to get involved with some of the other research projects at CEI, including longlining for sharks and assessing the health of seagrass around the coast. In addition to catching 15 turtles, the group of students had the chance to measure a Caribbean reef shark (Carcharhinus perezi) caught on a scientific long line. They also assisted graduate student, Izzy Lake, with her Master’s research investigating potential anthropogenic effects on seagrass beds. During a trip to the North of the island, the students visited the Glass Window Bridge, a particularly impressive spot, where they could see the contrast between the rough Atlantic Ocean and the tranquil Caribbean Sea. Among these exciting activities, they also went snorkelling with sea horses, jumped into a 600 foot deep blue hole, and watched bats flutter overhead in the Rock Sound Caves.

The volunteers from Dover-Sherbourne High School gather for a group photo on the shoreline of a creek where they spent the day spot-seining to catch turtles.

The volunteers from Dover-Sherbourne High School gather for a group photo on the shoreline of a creek where they spent the day spot-seining to catch turtles.

The positive attitudes, inquisitive minds, and go-getter mentality of both groups made for effortless teaching. We hope that both teams now understand the importance of the shallow coastal habitats around Southern Eleuthera that act as foraging grounds for Green Turtles during the juvenile and sub-adult phases. The CEI turtle team investigates the spatial dynamics of these immature green turtles and the processes of site selection and resource use within their foraging grounds. Identifying these fine-scale distribution patterns will contribute to a better understanding of habitat use within discrete aggregations of foraging sea turtles, and highlight essential habitats for this endangered species.

If you want to get involved or learn more about our work find us on our website or like the CEI and Tracking Sea Turtles in The Bahamas Facebook pages.

 

Fishing for knowledge in The Bahamas

The CEI reef team are working in partnership with the Institute for Social Ecological Research (ISER) Caribe on an interdisciplinary research project to understand the ecology and social perceptions of the parrotfish fishery in The Bahamas. There is a wealth of information concerning the ecological role of parrotfish in Bahamian waters, but the economic and social value of the fishery remains unknown. The data collected will create the foundation for an innovative educational and social marketing campaign to promote sustainable fisheries use and management in The Bahamas.

The nature of this project combines both ecological and social perspectives into assessing the status of parrotfish.  We hope that by surveying local populations we can obtain traditional knowledge passed on through generations of families, some of whom depend on the ecosystem for their livelihood. The questionnaires may also help to increase awareness about the importance of parrotfish and stimulate interest in the end campaign strategy.

The first implementation phase of this project focuses on the human interaction with the Bahamian marine ecosystem. In order to understand the perceptions of local stakeholders, the reef team is actively implementing ethnographic research methods to gather social ecological data. In just three weeks, the team has conducted 22 fishermen surveys and 16 consumer surveys. The information gathered thus far has provided key insight on local economic dynamics and social connections between the three main research sites: Tarpum Bay, Rock Sound and Deep Creek.

Research assistant Roxy de Waegh interacts with local children whilst waiting for fishers to return to the docks in Tarpum Bay.

Research assistant Roxy de Waegh interacts with local children whilst waiting for fishers to return to the docks in Tarpum Bay.

In addition to conducting fisher and consumer surveys, the CEI reef team has had the absolute honor to collaborate with the local Deep Creek Middle School (DCMS). The DCMS eighth graders joined the reef team in the field, where they lead interviews with local fishermen and consumers from their settlements. The Grade 8 students demonstrated the power of youth by using their local knowledge, creativity and enthusiasm to make the surveys more efficient and definitely more fun! They explored the complexity of fishing-as-livelihood versus conservation-minded-fishing and proposed to illustrate their ideas by designing a comic book and music video.

Students from Deep Creek Middle School interview a retired fisherman at his house in Rock Sound.

Students from Deep Creek Middle School interview a retired fisherman at his house in Rock Sound.

As the CEI reef team continues to conduct their interviews, in the hopes of reaching a total of 90 surveys, the socio-economical and ecological connections are becoming clearer and evermore intrinsic. It is essential to incorporate the human dimension as part of our marine ecosystem, and not as a separate entity. The team continues to work hard to find local fonts of knowledge who can add invaluable stories, opinions and information to the survey database. They hope to finish data collection within the next few months, but in the meantime keep a look out for the DCMS music video coming your way soon!

Catching Crabs By Moonlight

Over the past few weeks, the CEI reef team has gone on three night dives in search of the nocturnal West Indian spider crab (Mithrax spinosissimus).  At the start of February the team of research technicians and interns headed out to their first dive site, known as Cathedral, just a few hundred meters off the south-west coast of the Cape. They observed a variety of nocturnal creatures, like huge spiny lobster (Panularis argus) and mantis shrimp (Odontodactylus scyallarus), but unfortunately no crabs.  After nearly 40 minutes of searching they abandoned the dive, hopped back on the boat and drove a few minutes north to the next site, Tunnel Rock.  The team navigated the large rocks and surrounding reefs for another 40 minutes and saw lots of exciting animals, such as a porcupinefish (Diodon holocanthus) and a green turtle (Chelonia mydas), but still no sign of the elusive spider crab.

The following evening the team decided to try again in a different location, journeying north of the CEI campus to the patch reefs. The interns snorkeled out to examine the first reef from the surface, and were excited to find several huge crabs foraging on the reef below. The team quickly pulled on their SCUBA equipment and descended the 3 or 4 meters to the sea floor. They were shocked when they saw the huge crabs up-close, they knew that spider crabs are the biggest crabs in the Caribbean, but were still not prepared to come face to face with a crab over 1 foot across.

It has been several years since a captive crab study has been carried out at CEI and, without an experienced crab catcher, the team weren’t sure how difficult the crabs would be to handle. Nevertheless, intern Daisy Buzzoni approached the closest spider crab nestled under a ledge of the reef. She positioned her handheld nets around the crab and gradually inched them towards each other. The crab sprang into action and scurried quickly to its left, straight into one of the nets! Using the same technique, the team moved between the small patch reefs and managed to catch 5 more sizeable crabs. Over the past few weeks, the reef team has been on more crab catching expeditions and has caught over 30 of them!

Reef team intern, Daisy Buzzoni, proudly holding the huge spider crabs she caught from the patch reefs using handheld nets. These crabs were transported back to our wet lab in a tank full of saltwater on the boat. 

Reef team intern, Daisy Buzzoni, proudly holding the huge spider crabs she caught from the patch reefs using handheld nets. These crabs were transported back to our wet lab in a tank full of saltwater on the boat. 

Over the next few months, the diet and behavior of these crabs will be studied by a visiting scientist, Dr. Iain McGaw, to assess how crabs could be used to control algae build up in aquaculture operations. Most systems currently use power washing or chemicals to remove the accumulations of algae, which have been shown to pollute the surrounding environment. Iain hopes that crabs could provide a more ecologically friendly and sustainable method of maintaining productive aquaculture systems.  

This spider crab has made itself at home in a piece of PVC tubing in one of our wet lab tanks. We put these tubes in the tanks to provide the crabs with a habitat similar to the ledges and holes they would shelter under on the reefs.

This spider crab has made itself at home in a piece of PVC tubing in one of our wet lab tanks. We put these tubes in the tanks to provide the crabs with a habitat similar to the ledges and holes they would shelter under on the reefs.

The crabs collected by the reef team are quite settled into their new home and thriving in the saltwater tanks in our wet lab. They will stay here for several weeks, whilst Iain assesses what species of algae is favored by these crabs and what time of day they are engaging in the most foraging behavior. These crabs will also be studied by Logan Zeinert, a research technician for the reef team. After studying them in the wet lab, Logan will move the crabs to a large algae encrusted structure just off the coast of the Cape. This site, known locally as “The Cage”, was previously used to house Cobia as part of an old CEI aquaculture project, but since it’s decommission, has accumulated a thick layer of algae. Once moved here, Logan will monitor the crabs and their consumption of this algae to calculate the efficiency of their feeding.

Keep checking our Blog and Facebook page to stay up to date with news from the reef team and all the other projects at CEI.

Caught By Surprise

Every day on a shark research boat is exciting, but hauling in a huge tiger shark (Galeocerdo cuvier) is definitely a once in a lifetime experience. At the start of February the shark team, led by Research Technician Christian Daniell, set one of their first longlines of the new year and caught the biggest female tiger shark that CEI has seen on a shallow water survey in over 2 years.

The longline was set just a few kilometers off the south-east of Cape Eleuthera. After a 90 minute soak time, the team began hauling the line and were excited to find 3 Caribbean reef sharks (Carcharinus perezi), each shark bigger than the previous one. The team measured, tagged and safely released these sharks and were feeling content with their work. However, they were not heading home any time soon – hooked on one of the last gangions was a huge female tiger shark, over 3 meters in length! They could not believe their luck but soon jumped into action and secured the giant shark to the side of the boat. The interns were in awe of the incredible creature but worked efficiently to measure and tag the shark and then release it quickly.

Research Technician, Christian Daniell secures the large tiger shark to the side of the research boat to allow the interns to measure the shark safely.

Research Technician, Christian Daniell secures the large tiger shark to the side of the research boat to allow the interns to measure the shark safely.

Large tiger sharks are commonly found across The Bahamas and the chance to see, or even dive with them, attracts many tourists and brings great revenue to the area. However, these migratory sharks tend to hunt in deep waters and are rarely seen this close to shore. CEI’s long term shark monitoring program uses mainly shallow water longlines and therefore tends to catch juveniles or smaller sharks. Over the past few years, CEI has caught and tagged many juvenile tiger sharks on its shallow water longlines but has not caught a mature tiger shark since the spring of 2014.

The measurements of this unexpected catch will be added to CEI’s long-term longline database but will also be used by Christian Daniell, Research Technician, who is currently collecting data for his independent project. Christian hopes to spend his time here comparing the populations of sharks between 2008 and now. He will use both longlines and Baited Remote Underwater Video Surveys (BRUVS) to collect data and compare it to those published in a 2011 study by Dr. Edd Brooks. This comparison is particularly interesting as it may indicate how the implementation of a shark sanctuary in The Bahamas in 2011 has affected shark populations around the Cape. It is hoped that this prohibition of shark fishing will have increased and diversified local shark populations, and will provide evidence to support protective legislation in other places across the world.

CEI continues to monitor the shark populations around the Cape, follow us on Facebook and Instagram to stay up to date with our exciting catches!