After processing the video footage from our first week of stationary camera deployments, we noticed we were not alone. Most people just recognize her as a shark, but that’s an understatement. She’s a tiger shark. Locals have taken to calling her Tony the Tiger. National Park Service biologists and technicians have yet to encounter one in their many years of diving around Buck Island so my team and I are confident we won’t be crossing paths with Tony while scuba diving.
NPS has been working with multiple collaborators to study the movements of sharks within the monument using acoustic telemetry. Given these recent sightings of Tony in our video footage, NPS biologists are eager to see if they can cross reference these sightings with detections from acoustic receivers installed near our camera monitoring site. We hope to find that Tony is one of the individuals that was tagged in previous years.
Tiger sharks are natural predators to sea turtles. Their serrated teeth allow them to tear through the turtle’s carapace (shell). Even though Tony has been feeding on our study subjects, we’re happy that she’s here. The presence of apex predators is one of the signs of a healthy ecosystem. Believe it or not, they play an important role in structuring seagrass ecosystems. They balance the food web as well as prevent lower levels from exhausting resources.
Healthy seagrass ecosystem = Abundant greens turtles = Tiger sharks
It’s important to understand the significance of top-down control in natural ecosystems in order to better establish conservation and management baselines that could predict ecosystem responses to natural and anthropogenic change.
Green turtles in the Caribbean feed selectively on the seagrass Thalassia testudinum; however, they do not graze at random. Rather, they maintain “grazing plots” of young blades of T. testudinum by consistently recropping them. By routinely cropping these plots, they’re increasing their protein intake while keeping lignin consumption low, essentially making their food more digestible. This grazing pattern also increases nitrogen content over time, yielding a higher nutrient diet. Lignin is a complex organic polymer deposited in the cell walls of many plants, making them rigid and woody. Also, lignin has been repeatedly identified as the major chemical component controlling the digestibility of cell walls; therefore making it more difficult to break down. In ungrazed blades of T. testudinum, lignin levels are 100% greater than in blades from grazed strands. When establishing a new grazing plot, green turtles will bite at the base of the tall T. testudinum blades and allow the upper, older portions that are high in lignin and covered in epiphytes to float away. Thus, the digestive efficiencies of green turtles and forage quality are enhanced by their specialized feeding behavior.
We have been placing stationary cameras in established grazing plots and have witnessed this maintenance behavior. I am excited to see what other behaviors we’ll be able to observe.
“Consider the sea turtle when you boat where they feed;
injuries can be avoided if we just reduce our speed.
Consider the sea turtle when you’re at the beach;
trash, holes and castles make the sea hard to reach.
Consider the sea turtle when installing outdoor lights;
they misguide hatchlings when they are high and bright.
Consider the sea turtle when you shop at the store;
plastic bags are deadly when they float beyond our shore.
Consider the sea turtle when you spend the day fishing;
lines, hooks and nets can prevent them from swimming.
Consider the sea turtle when using balloons;
if they land in the water they cause certain doom.
Consider the sea turtle when you want to fertilize;
runoff from rain will cause bad algae to rise.
Consider the sea turtle and work together;
because our actions can impact sea turtles forever.”
When my friend Ashley shared this poem with me all I could do was smile. I love how it addresses major issues in a simple, understanding way. This poem is a great example of how we can inform the public and get them interested enough to pay attention to these topics. With minimal effort on our part, we can have BIG impacts on our surroundings.
Leatherback sea turtles are the largest of all living turtles, weighing up to 2000 pounds. They’re also the most pelagic (open ocean dwelling), while other sea turtle species spend most of their lives in neritic (nearshore) environments. Unlike other sea turtle species, leatherbacks lack a bony carapace (shell). Instead of scutes (scales), their carapace is composed of a layer of thin, tough, rubbery skin that is strengthened by thousands of tiny bone plates. This allows them to expand their lungs while they dive to depths deeper than 1,000m to feed, primarily on jellyfish. Like the green turtles I’m working with, leatherbacks are also listed as an endangered species.
Dr. Kelly Stewart, Southwest Fisheries Science Center (NOAA), leads a field program at Sandy Point National Wildlife Refuge in St. Croix. The program focuses on genetically fingerprinting leatherback hatchlings as they leave the beach after emerging from their nests. The purpose of her study is to determine the age to maturity. This is an important measure that allows scientists to evaluate population status and design management strategies to protect this long-living, slowly maturing species. While obtaining this measure seems simple, it is particularly difficult to do so for sea turtle populations, especially for pelagic species like leatherbacks.
I had the opportunity to volunteer with her interns in patrolling the beach at Sandy Point National Wildlife Refuge for nesting leatherbacks. First patrol began at 7:30pm and last patrol was at 3am. The beach was divided into sections that had to be cleared, checked for turtles, every 45 minutes. This was not an easy task by any means. We had to walk up and down the beach, exposed to the elements (rain, insects, etc.) until just before sunrise. I couldn’t imagine having to do it on a regular basis for several months … and then I held my first hatchling. At that very moment, something clicked and it all made sense. Roughly one in one thousand hatchlings survive to adulthood. Very little is known about the life history of leatherbacks, largely because they spend most of their lives in pelagic environments. I would happily trudge through sand all night to help find out more about these fascinating creatures.
I spend a lot of my time counting. It’s essential for the research I’m helping with at Buck Island Reef National Monument (BUIS). I count in order to determine seagrass and macro-algal species composition, structural complexity, and percent cover of seagrass. These values will allow my mentor, Alexandra Gulick, to characterize and compare turtle grazed and ungrazed meadows at Buck Island. This will also allow us to determine what the turtles are eating. Caribbean green turtles are known to primarily eat Thalassia; however, we are noticing that they are also consuming Syringodium at BUIS.
The algae I count: Halimeda spp., Caulerpa spp., Penicillus spp., Acetobularia spp., and Udotea spp.
The seagrass I count: Thalassia testudinum, Syringodium filiforme and Halodule wrightii
I also count green turtles. The other day Alexandra, Ashley and myself spent an early morning conducting visual surveys for foraging green turtles in the seagrass meadows to determine the period of peak grazing activity. We’ll be deploying stationary cameras within grazed meadows to look at how different seagrass pasture characteristics (all the things I count) affect green turtle foraging behavior. Deploying cameras during the peak grazing period increases our chances of observing green turtles. And once we get them on camera, I’ll be observing and analyzing their foraging behavior (e.g. grazing duration, bite counts, intake, etc.), AKA counting.
Seagrass ecosystems are incredibly important foundational ecosystems that provide a variety of ecological and economic services. These ecosystems, and the animals that rely upon them, have been threatened and disrupted by rapid declines and degradation in seagrasses worldwide. Much of the loss can be linked to anthropogenic stressors. Green turtles are the only herbivorous sea turtle species and are the primary consumers of seagrasses worldwide. Green turtle populations have been severely overharvested by humans over the last 200 years and are currently listed as a threatened/endangered species. However, populations are beginning to increase in some areas as a result of long-term conservation efforts. Given the rapid decline in seagrass coverage globally, there is growing concern that the altered ecosystems of today may not be able to sustain grazing by green turtle populations as they did two centuries ago. When an endangered species recovers, what ecological role does it fulfill if its ecosystem has been altered by anthropogenic activities? This is only one of many questions being asked by my mentor, Alexandra Gulick (Graduate Student, Archie Carr Center for Sea Turtle Research, University of Florida). To begin to answer this prodigious question, she must start by investigating the fundamental factors that drive this plant-herbivore interaction. I’m here to help Alexandra execute two of her ecological objectives.
- Evaluate the productivity of naturally grazed and ungrazed seagrass meadows.
- Evaluate the effects of seagrass pasture characteristics on green turtle foraging behavior.
Accomplishing said objectives will then allow her to model the carrying capacity of Caribbean seagrass pastures for recovering green turtle populations.
Buck Island Reef National Monument (BUIS) was established in 1961 under President John F. Kennedy and was later expanded in 2001 under President Bill Clinton. It was the first fully marine protected area in the National Park Service system. The monument includes Buck Island (176 acres) and 18,839 acres of submerged land and coral reef systems. Buck Island is an uninhabited island 1½ miles off the northern coast of St. Croix, and is surrounded by a barrier reef and large expanses of seagrass meadows. Conducting this research at BUIS offers a unique opportunity to study green turtle grazing dynamics and habitat use. Fortunately, the seagrass ecosystem supports both juvenile and adult turtles throughout the year which is uncommon. Also, over the last decade NPS resource managers have documented increases in green turtle nesting and foraging populations. When combined, these factors make BUIS more than ideal for studying green turtle and seagrass interactions. I am thrilled to be a part of this research and partake in sharing it with the world.
Laura Palma reporting for duty! Destination: US Virgin Island St. Croix
I hail from the distant land of Miami Florida, born and raised. It’s also where I attained a Bachelor of Science in Marine Biology from Florida International University. As a recent graduate, I can tell you I don’t have money. But what I do have are a very particular set of skills; skills I have acquired as a scientific diver. That is what drew me to this particular internship. But diving alone was not enough to hook me line and sinker; the opportunity to explore and study a new ecosystem and organism, seagrass beds and green sea turtles, is what sealed the deal. I have never worked with sea turtles or conducted intensive research with seagrasses, something I won’t be able to say by the end of this internship.
While I’m here I intend to take full advantage of the opportunity MOSAICS has given me not only from the research perspective but also from the National Park Service (NPS) aspect. I’m curious to experience what it will be like working for NPS and whether it will be a good fit for me. As most of my experience has been with academic institutions, this internship will allow me to expand my career experience with other agencies. I’ve only been here six days and already I’ve had the pleasure of interacting with some great scientists including several from NOAA. I hope this experience will help me determine if graduate school will be my next feat.
I’d like to give a big thank you to my project mentor, Alexandra Gulick (Graduate Student, Archie Carr Center for Sea Turtle Research, University of Florida) and my NPS supervisors, Clayton Pollock (Biologist) and Zandy Hillis-Starr (Chief of Resource Management) for offering me this opportunity.