Sanibel Sea School passes second year mark in sand dollar research project
The Sanibel Sea School just surpassed the second year mark for their sand dollar research project, which is already revealing interesting data.
Sanibel Sea School Lead Marine Science Educator Johnny Rader said the research project began in 2015 after they scooped thousands of sand dollars the size of their pinky nail in the water using their hands.
“That’s 4 to 9 millimeters. We wanted to figure out their density and their distribution. We also realized that there hadn’t been much done,” he said of studying sand dollars.
Rader said a type specimen is kept in an archive for every animal studied.
“The type specimen for this particular sand dollar came from Sanibel,” he said. “We started studying it then, just to learn more about how its distributed and its density on Sanibel because we found that during that time its density was in mass number.”
A couple things could have happened the summer the tiny juveniles were found. He said there could have been a large spawning event where tons of gametes were released, or the spawning event resulted in cloning.
The mass amounts of those tiny juvenile sand dollars were found all over Sanibel the summer of 2015, which prompted the 10 year research project in September of the same year.
“What I have found to be really interesting is in those two years we haven’t necessarily had that spawning event again, but we’ve been able to monitor these sand dollars grow over the course of these two years,” Rader said.
A small committee, three teachers from Canterbury School, Rader, Sanibel Sea School Executive Director Dr. Bruce Neill and Sanibel Sea School Director of Education Nicole Finnicum, was formed for the research project. The Sanibel Sea School education staff goes out once a month for the field research.
“We do this year round,” Rader said.
Every single month the team hits the beach to measure the sand dollars at Sundial Beach Resort & Spa due to their satellite campus, and Buttonwood.
“On our charts you can see distinct populations,” he said.
A population, or settlement, starts as a plankton, which floats around in the water for up to a dozen days. Rader said the sand dollar is bilateral symmetric at the beginning and then they metamorphosis into the flatten shape in parts of five.
“They have a dual life cycle. They are platonic where they are free floating in the water and then they settle down. We don’t know the exact cues of what makes them settle down into that juvenile form of sand dollars,” he said. “We haven’t had a mass settlement since then, but we noticed that next December there was another settlement.”
Rader said there has been settlements in the winter and summertime at Bowman’s Beach.
“That’s pretty common for echinoderms, so sand dollars, sea urchins. They have one mass spawning during the lunier cycle in the summer months and then a smaller, but still spawning event in the wintertime,” he said.
The research project is trying to track the populations to see where they go.
Rader said some of the interesting statistics they have found thus far is the sand dollars do not always show growth month after month.
“We have noticed that there are these areas where they are not growing,” he said. “That’s why I have started to do the embryology, so I have been making them release gametes, their reproductive cells, eggs and sperm.”
Rader said the sand dollar stores their eggs and then mass releases them.
“Eggs are an expensive commodity, or it is very energy expensive. So, the thought process is those months that we find there is no growth, they are storing that growth energy and relocating it into more of a reproductive state. They are trying to put more energy to producing egg and sperm that they are to growing in size themselves,” he said.
When they are out in the field, they take their research vessel, a paddleboard, and a caliper to measure the sand dollar in millimeters.
“We are still trying to determine what makes an adult an adult. Again with my embryology, I’m seeing how large they have to be to start carrying reproductive cells,” Rader said, which is about two years. “We’ve been basing a lot of our research and hypothesis on other echinoderm species.”
In addition to using a caliper, they also use a transect measuring tape.
“It goes out for 30 meters. Every meter out we collect, count all the adults in one meter square,” Rader said, while using scuba equipment. “Every meter I start my count over.”
The adults are also measured for size frequency to determine how much growth has occurred.
A different system is used for the juveniles. Rader said they throw out a quadrate, one square meter, haphazardly and collect all the juveniles in that square meter. They are then placed in a bin.
“By measuring each individual one in that square meter we will get how many there are in the square meter. Measuring them at the same time will also give us the density,” he said.
A juvenile, Rader said has not been found in more than a year on Sanibel. Bunche Beach, however has juvenile sand dollars.
“We don’t know if these populations are moving along Sanibel,” he said.
Through their research, they had found that die offs happen during a weather event, such as a hurricane, as well as when nine arm sea stars eat the juveniles.
“They actually eat outside of their body, so they take their stomach and wrap it around and digest the skin and leave the skeleton behind,” Rader said.
One location takes up to 90 minutes to complete the data collecting. If juveniles are present the time spent at the location increases.
While out on the beaches, Rader said they do spend time educating people about the difference between a live and dead sand dollar. The sand dollars with skin and spines are still alive, he said.
At the end of the research Rader hopes to understand the spawning events a little more clearly. If, in fact, they spawn closer to the full moon.
“The exact time of when sand dollars spawn is what I would like to figure out. Also the relationship between growth and reproduction,” Rader said.