Relatively speaking, there aren’t that many species of marine reptile you are likely to run into on a dive. However, the charisma and love they elicit are enough to fill the ocean. Perhaps none are more beloved than all 7 species of sea turtles. Similar to their terrestrial cousins, they are evolutionary dinosaurs, changing very little in the eons of their existence. For centuries, this ancient form served them perfectly, but even with the love of modern ocean-goers, they are now finding survival in this human age increasingly more perilous.
Sea Turtle Reproduction
These migratory species are found across the oceans, but are typically born on tropical and subtropical shores. In fact, unlike fresh water turtles who are prone to sunbathing on stable ground or emerging logs, sea turtles never step flipper on land except for when they are hatching, or when they return to lay eggs. Famously, sea turtles return to their natal beach to lay the next generation. The female crawls up onto shore and uses her large flippers to dig a hole big enough for anywhere between 50 and 350 eggs. She then will kick sand back over the eggs, completely disguising the nest. This whole process can take upwards of 60 minutes. She can do this up to 8 times per season. Where the eggs are placed has an indirect impact on the sex of the offspring. Sex in turtles, alligators, and crocodiles is determined after fertilization by the temperature at which the eggs are incubated. Only a few degrees can make all the difference. Any egg incubated below 81.86°F (27.7°C) will become male. Eggs incubated above 87.8°F (31°C) will become female. Eggs incubated between the two temperatures will become a mixture of male and female. Because global temperatures are on the rise, and even the deepest sand temperatures are following that trend, this could have vast impacts on sex ratios.
After about 50-60 days, the eggs will hatch and the babies will make a run to the relative safety of the sea. This is historically the most dangerous time in the entirety of a sea turtle’s life. On average, one egg from each clutch will make it to adulthood. Birds, snakes, dogs, racoons, crabs, and fishes will prey on the small and vulnerable young. Some species, such as the Kemp’s Ridley and Olive Ridleys will try to combat these odds by overwhelming the predators with numbers. Hundreds to thousands of sea turtles will nest at once so all the young hatch simultaneously. With thousands of baby sea turtles making sprinting to the sea, predators can’t possibly capture all of them and some have a greater chance of making it to safety.
Eggs that never hatch will decompose and provide important nutrients to the beach communities and dune vegetation. The plants that they nourish create important erosion control for fragile beach ecosystems. Once the hatched turtles have made it to the open sea, the young of almost every species is vegetarian. They feed on seagrass and algae and help keep seagrass beds biodiverse and healthy.
Sea Turtle Anatomy
Instead of a shell, they have a carapace on their backs and a plastron on their bellies. Because they essentially spend the entirety of their life swimming in water, they are more fusiform than terrestrial turtles. But, to become so fusiform, sea turtles had to lose the ability to retract their legs and neck. The resulting affect is that sea turtles can migrate thousands of miles every year, but they cannot protect their appendages in the same way a terrestrial turtle can. As the turtle ventures around the ocean, it does pick up some unexpected company. Up to 29 species of sea turtle-specific barnacles live off the the literal backs of these nomadic reptiles. Just like the barnacles embedded in whale’s skin, the small arthropods attach themselves to the carapace or plastron, and sometimes even the flippers of sea turtles, capitalizing on the micro plankton feast in all the waters the sea turtle host visits. There isn’t any evidence these barnacles hurt their hosts, mostly the turtles don’t seem to notice the barnacle’s presence.
What turtles most certainly notice is the higher presence of salt in marine environments than those of their freshwater ancestors. To compensate for the higher salt concentration outside of the body, many vertebrates like fish and mammals produce high salt concentration urine to rid the body of excess salts. However, reptilian kidneys are not capable of doing so; instead they have a lachrymal gland near their eyes that produce incredibly salty tears. So if you’ve ever seen a sea turtle, or other marine reptile appear to sneeze or shake their head violently, they are probably releasing these salty drops and expelling them far from their face.
How long do Sea Turtles breed?
Sea turtles can take up to 50 years to reach sexual maturity. They mate in the sea, while staying afloat to breath. The females can then swim thousands of miles to return to the beach of their birth and start the cycle all over again. Once mature, they mate and lay eggs every 2-4 years. This will continue until they breath their last, somewhere around 80 years. So the low survival rate per clutch, combined with the relatively small breeding potential throughout a turtle’s life make them a vulnerable group to changes in the ecosystem or unnatural predation. They cannot replenish their number quickly should a large disturbance take place.
Threats to Sea Turtles
Unfortunately, that is just what is happening to their number, from almost every angle. Not only are sea turtles poached for their meat, leathery skin, and shells, they are often unintentionally caught as bycatch. This means that they get stuck in nets, long lines, and trawls meant for other species. Because turtles are reptiles, they must come to the surface to breath air. When they are caught in fishing gear, they cannot make it to the surface in time and drown. Even if a turtle remains free its entire life, it is sure to be affected by human waste. Plastics are found in every ocean at this point, and many look and smell like food to an unsuspecting sea turtle. Once ingested, the plastic never breaks down. Instead it perpetually takes up space in the turtle’s digestive system, blocking nutritious food from being digested and absorbed. So turtles will starve because their bellies are too full. Turtles can also get caught in plastic rings, causing deformations while the turtle grows.
Oil spills are especially disastrous for sea turtles of all ages. Oil tends to float, so when a turtle comes to the surface to breath, it is coated in the oil. While they attempt to take in air through their nostrils, the oil is inhaled and ingested as well. The inside of their lungs and digestive tract is covered in oil, eventually causing it to become so sick it can no longer swim. Female sea turtles can pass oil compounds on in their eggs, and oil that reaches nesting beaches can penetrate into the eggs of the unborn turtles.
Speaking of eggs on nesting beaches, they have been facing novel threats in the past century from human development. As the coasts become developed for human use, sand is disturbed, inaccessible, or eliminated entirely. Females have nowhere safe to lay their eggs, and eggs that are lain are vulnerable to human activity overtop of them. Seagrass beds and mangroves, traditionally used as nurseries for the young turtles, are disappearing at alarming rates. It is no wonder that every species of sea turtle is listed on the IUCN endangered list.
Running into a sage, unbothered sea turtle on a dive is always a delight. However, it is only going to become more rare of a thrill the worse we treat the oceans. Or perhaps most importantly, the worse we allow the oceans to be treated.
‘Sea Turtle Business’ was written by Roya
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