The Tropicalisation of Western Atlantic Seagrass Beds
This project is an opportunity to explore the broader impacts of climate change on the ecology of seagrass ecosystems and the species supported by them, in an NSF funded project being led by The Smithsonian Institution in collaboration with The Centre for Ocean Research and Education, starting May 2018.
Seagrass meadows are among some of the most productive marine ecosystems on earth, supporting a diverse assemblage of species and offering living space and shelter to a range of ecologically important fauna. As primary producers, seagrass meadows create rich feeding grounds for herbivorous species such as manatees and turtles as well as epibenthic predators, like stingrays. In addition, the iconic Bahamian queen conch rely on seagrass beds for adult life-history stages.
The functional significance of seagrass ecosystems are considered critical in the overall dynamics of coastal and nearshore environments, as they provide structure, reduce disturbance and sedimentation rates, as well as typically enhancing biodiversity. Through these processes, seagrasses are considered a class of ‘ecosystem engineer’ and essentially structure habitats, creating nutrient gradients among sediments.
Climate change is altering the ecological functioning of a broad range of terrestrial and marine communities and while prior work has addressed the direct effects of climate on organismal functioning, many studies fail to consider how alterations in biotic interactions (via shifts in species ranges and food web dynamics) might serve to obscure, or even amplify, the direct effects of climate on ecological structure.
This exciting project will involve coordinated field experiments conducted across 20 degrees of latitude among multiple institutions, incorporating the geographic range of turtle grass (Thalassia testudinum) to investigate effects of tropicalisation and increased herbivory on the function of foundational species and associated flora and fauna.
Updates will be posted here, and on our Instagram Page.
- Update 1 -
As the project gets underway, all components are continuing smoothly. The project's duration has also been extended, resulting in continual monitoring of the site for a full year. Such an extension enables seasonal changes to be observed as well as the initial focus on grazing and nutrient effects that may result from climate change. A large barracuda approximately 4 feet in length has also taken up residence within the experimental array, highlighting the importance of seagrass meadows as keystone ecosystems in The Bahamas.
-Update II -
Having just completed our first subsampling period, the experiment is well underway not just here, but in the nine other locations throughout the western Atlantic. We have been consistently collecting data every two weeks since April and will continue to do so until the project’s conclusion in June 2019. Among our bi-weekly data harvesting and maintenance schedule, we conduct grazing surveys or assays, which uses standardised lengths of seagrass attached to sisal ropes and pegged into the canopy, where we then record for a three-hour period to see who is taking chunks out of the blades. The site itself has changed dramatically, with intense turtle grazing and the cages themselves are acting as aggregation devices, where we see vast schools of bar jack, juvenile grunts, dozens of green turtles and down in the thick canopies we see conch, West-Indian sea eggs (a type of urchin), squid, mantis shrimp and moray eels.
We also conduct fish an invertebrate transect surveys, clean the cages, monitor light availability and experimentally manipulate nutrient availability among plots. The project continues to provide us with a fantastic education platform, whereby we incorporate local students and visiting groups into these data collection activities as part of our educational programming. Scientists from The Smithsonian Institution continue to visit regularly and assist us with the more time intense and laborious four-monthly subsampling activities, and we are expecting them again in January 2019.
-Update III -
In April of 2019, we welcomed Dr. Olivia Rhoades from The Smithsonian Institution back to Eleuthera, where, in collaboration with the CORE team, we collected our final samples from this network array in what was an intense 11 days of diving, snorkelling, free diving, cage removal, E-DNA processing, biodegradation assessments, grazing assays, predation assays, drone surveys, sediment core retrieval, epiphyte scraping, green biomass drying and weighing and a whole host of other tasks, to ensure that this project was a success - and it was. We are grateful for the support of The Smithsonian Institution in their assistance with this enormous ‘break-down’ task, and we are eagerly anticipating each of the sites within this network of collaborators to finalise their data collection, so we can begin the long road of analysis that lays ahead.
This was CORE’s first major collaboration, and emotions ran high towards the end, where we had to say goodbye to our new colleagues and friends that have been working with us over the past 14 or so months, to make this project a reality. Thank you to Dr. Justin Campbell, Dr. Olivia Rhoades and Scott Jones for your support, professionalism and mentorship for the countless young people from Eleuthera and beyond who were actively involved in this project.
Image courtesy of Shane Gross