She tried it once: eating seagrass. “Just because I was curious what those turtles like about it.” But the blade Thalassia testudinum in other words turtle grass that Fee Smulders put in her mouth could not immediately be called a culinary delicacy. “Unlike seaweed, seagrass is never eaten by humans. Only the seeds are popular in Southeast Asia.”
Apart from the taste nothing but praise for Thalassia testudinum, and roughly seventy other seagrass species worldwide. Smulders beams when she talks about the subject. “Maybe I see it a bit as my mission to promote seagrass, yes. Sometimes I see students come in and think: wow, what’s interesting about this?’ But once they see that swaying underwater greenery, and discover that it is bursting with life in between – crabs, shrimp, fish, rays – the enthusiasm comes soon enough.”
As a student at the University of Amsterdam, Smulders was not an immediate fan of seagrass either. “It’s less colorful than coral, so it gets less attention. In our first year, we all had to give a presentation about a section from the textbook. I was assigned the topic ‘seagrass and seaweed’. One paragraph, there was no more information, and most of it was about seaweed.” While they are really two very different groups. “Seaweeds are multicellular algae, quite primitive in form and function, without vascular bundles and a root system. Seagrasses are real plants that, like whales, have evolved back to marine life. They are the only plants that can bloom completely underwater in the sea and spread their seeds.” Her own fascination came in her third year of study, during fieldwork in Portugal. “We did experiments there with seagrass – we looked at what happened if you added extra salt or sulphite – and I found it so fascinating that I decided to take a master’s degree in marine biology. That summer I obtained my diving license in Thailand.”
turtle grazing
Smulders is now a PhD student at Wageningen University doing research on seagrass in a bay near Bonaire. “It grows in the shade, behind coral reefs, and is really a nursery for fish. They grow up in the shelter of the grass. The leaves are as long as your forearm, so that’s a great hiding place.” In addition, it also serves as food. Not only for the fish, but especially for turtles. They don’t call it for nothing turtle grass.” And it is that turtle grazing that Smulders is particularly interested in.
“The green turtle, which is the most common species in that area, has been very bad in the past. But in recent decades, their numbers are rising again thanks to conservation projects. At Bonaire, we estimate that the population in the 700-hectare bay now consists of about 500 animals. Those turtles hatch from their eggs, go out into the ocean, float around for a while, return to shore, and then they mainly eat sea grass. They are grazing for up to eight hours a day, which is adding up.” However, that success story creates a new problem: overgrazing. „On Bonaire we see that the grazing zone is moving further and further towards the coast, the turtle grass is disappearing. Bad news for the coastal zone – because it is well protected thanks to the dense root network – and for the turtles themselves. They dig, or rather graze, their own seafarer’s grave. Because they are so much Thalassia testudinum eat, see another invasive seagrass species Halophila stipulacae his chance. That species seems to increase in places where sea turtles graze a lot, and is smaller than the turtle grass. As a result, it offers less protection for fish. And turtles don’t like to eat it.”
Floating barrel
To investigate the exact influence of the grazing behavior of the turtles, Smulders conducted various grazing experiments with the help of students. “We mainly compared the seagrass composition inside and outside the cages we installed. Some cages had large openings, so that fish could still get in and turtles couldn’t. Other cages were even inaccessible to fish.” In general, the biologists spent about 5 hours underwater per fieldwork day. “We brought along a floating barrel to store seagrass samples and a special water-resistant notebook.” In addition, they also mounted special ‘homemade’ cameras on the shells of various turtles. “This way we could immediately see where and how much the sea turtles graze.”
During one of those film sessions, not in Bonaire but in the Bahamas, Smulders noticed that the turtles showed very different behavior on the spot. “They were very aggressive towards each other, going hard at boats instead of avoiding them. What turned out? They were fed by tourists, with squid. As a result, they received a lot of protein, they were just like bodybuilders. They had no appetite for seagrass at all.” But there was something else going on in the Bahamas, in an area where there were no tourists: the sea turtles lived with tiger sharks. “As a result, they were constantly on their guard, and they never grazed in one place for very long. The sharks influenced turtle behavior.”
Smulders would like to do further research into these shark-turtle interactions in the future. „And to the CO2-storage by seagrass, which is gigantic. Did you know that seagrass produces more CO . per square meter2 is stored than by rainforest? It’s super productive, and there’s very little breakdown. Unless, as in the Mediterranean, boats drop anchor right over a seagrass meadow. Then there is a lot of CO . locally2 free because the seagrass dies.”
Seagrass is one of the least protected underwater ecosystems. “That’s why I like to act as a seagrass ambassador.”
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