By Maggie Wetzel

Imagine you wake up, a little confused but knowing you need to be somewhere. It is completely dark, with only a small light on the horizon. For some reason, deep down you know that is where you must go. You begin moving, slowly but surely, gaining more strength as you get closer. You’re almost there! Then BAM you run into a sticky, stinking mass. What in the world could it be?! You try and try to climb, but start to get tired and give up. You are eaten. 

 

Now that seems unlikely, probably a bit out of pocket… but that is what is happening to sea turtles. Sargassum Algae is taking over Southeast Florida beaches where turtles nest. Researchers sought to find out exactly how these mounds are impacting hatching turtles. They asked the questions: 1. What is the seasonal distribution of Sargassum at a SE Florida nesting beach and how does this timing relate to nesting and hatching production of Loggerhead turtles? 2. How do hatchling turtles respond to algae, both on land and after they enter the surf zone? 3. How can this information be used to estimate the impact of algal accumulation on hatchling recruitment?

First, let’s define a couple of key terms.

Sargassum	A pelagic algae that forms large mats that then wash up on shore.
Recruitment	Recruitment is any turtle that makes it past the first stage of life
Surf Zone	The area where waves break.

To answer these 3 questions, the scientist assessed the beach at Red Reef Park (shown above) for 63 evenings over the summer. This 67-acre area is a nesting site in Boca Raton, Florida. They chose this particular area because it was a favored nesting site for the turtles. The experiments were done over 43 observation evenings to determine the impact Sargassum accumulations had on turtles making it to sea. They were done at night since that is when the hatchlings emerge. 

Sargassum accumulations were measured in 3 separate locations at dusk. The locations were about 6 meters wide and 20 meters apart from each other. The width was measured in meters at its widest point and narrowest, and the height was measured in centimeters at its highest, lowest, and intermediate point. Pictures were taken each day as well, and the wind velocity and density were recorded.

To determine the seasonal distribution of Sargassum, wind velocity and direction was very important. They looked at the number evening during the first and second halves of the season that the wind came from an on shore direction which would favor Sargassum accumulation on the beach. They compared this to evenings with offshore winds. 

Hatchlings were collected from nests between late July to September. But don’t worry, no more than 25 turtles were removed from the nests! They were careful not to disturb other hatchlings in the nest too. The captured hatchlings were stored in a cooler with sand in total darkness with no AC. Although that may sound unpleasant, that is the ideal conditions for hatchlings to be in. They were freed after the trials were over, and made it safely to the ocean.

Turtles use visual cues to reach the ocean, so the experiments were designed to determine whether algal mats could act as a barrier, both onshore and in the surf zone. A rectangular arena was marked in the sand and swept clear of everything other than the algal mats. The turtle’s footprints were then used to track its progress during the trial time. The two main objectievs were: 1) see what proportion of hatchlings emerging were able to scale the natural accumulations on the beach on the night they emerged 2) find out the probability of hatchlings ability to reach the water with increasing heights of algal mats. Of course since its Florida, the experiments had to be abandoned some nights due to impending storms. 

The turtles in the surf zone were tracked by having glow-in-the-dark paint smeared on their shell. It was timed from the moment it reached the mat until it cleared in. 

The final results were as follows. 

1. What is the seasonal distribution of Sargassum at a SE Florida nesting beach and how does this timing relate to nesting and hatching production of Loggerhead turtles? 

As the months turned, as it got later into the year there was significantly less Sargassum accumulation. January through June it increases, and July to December it decreases. The July babies and early August were impacted the most by the abundance of mats. Poor babies should have just waited a little longer! Wind played no part in the Sargassum build up, as seen in figure 2.

2. How do hatchling turtles respond to algae, both on land and after they enter the surf zone?

78% of the 1967 turtle hatchlings made it to the ocean. Of the 22% that did not, the algal mats acted as a barrier. The higher the mat was, the less likely the turtle could cross it, as seen in figure 3. When they did approach the Sargassum, the highest chance of success was to directly scale it or find the gaps between mats. Some did diagonal, some zig zagged, some got entangled (10 did- 3 escaped, 7 did not). Some just stopped moving altogether! Two tried to burrow through it… that did not work. The worst though, is when some turned around when they reached the mat and crawled back to land. The longer it took for turtles to reach the water, the more likely they were to be eaten or become too exhausted. Through the surf the turtles seemed okay! 

3. How can this information be used to estimate the impact of algal accumulation on hatchling recruitment?

The research can estimate the impact of algal mats on hatchling recruitment for Loggerheads in the future. We can approximate how many turtles will make it to the ocean by the number of eggs and the abundance of algae. It may also be useful to see if the algal mats have effects on other species on sea turtles recruitment. It has been found that Green turtles are not impacted significantly by the mats. They nest later than Loggerheads, so the mats are no longer as high. More research is going to be done, but it is thought that green turtles and leatherbacks will also be better off due to their larger size. 

As we move into the future where these algal mats are becoming more of an issue by the year, it is extremely important to continue researching how it affects turtles. They are becoming such a larger issue due to increased nitrogen and phosphorus in the waters caused by the discharge of major rivers in the tropical Atlantic and Gulf of Mexico. The seasonality of the mats also aligns with Saharan dust inputs, African coastal upwelling and hurricane occurrences. The wind and velocity was not seen as significant to the accumulation of Sargassum, but in other studies it has been seen to be. I think this shows that their calculations might have been faulty. They noted that they took the first half of these measurements on an app on their phone rather than an anemometer. This definitely could have messed with their data and led to an incorrect conclusion. 

We need to monitor the populations to be sure that they are making it to the ocean. I strongly believe more research needs to be done concerning Kemp’s ridley, Olive ridley, Hawksbill and Flatback sea turtles. These are all species even smaller than the Loggerhead.. In this video you can learn more about the impact of sargassum on turtles and how to deal with the effects. 

 

Literature Cited
Schiariti, Joshua P., and Michael Salmon. “Impact of Sargassum Accumulations on Loggerhead (Caretta Caretta) Hatchling Recruitment in SE Florida, U.S.A.” Journal of Coastal Research, vol. 38, no. 4, 2022, pp. 725–34. JSTOR, https://www.jstor.org/stable/48676911. Accessed 18 Oct. 2022.