Sea turtles (Chelonioidea), also known as marine turtles, are an ancient species and have been around for roughly 150 million years, swimming through our oceans since the late Jurassic period when dinosaurs still roamed the earth. They can live for approximately 80 years! Currently, we can distinguish seven sea turtle species in Earth's oceans. Unfortunately, five out of seven species of sea turtle are classified as endangered. Each one of the species plays a different, but equally important and crucial role in maintaining the balance and well-being of marine habitats. We should take a closer look and analyse the turtles and their habitats, diet, and life cycle in more detail!
Anatomy of a sea turtle
The anatomy of the sea turtle hasn't changed much in the million years they've roamed the oceans, but let's face it - it's hard to improve on perfection! Sea turtles' bodies have been streamlined to work perfectly in the sea with very few modifications.
The main characteristic of every sea turtles is their hard oval or heart-shaped shell which protects them from predators and abrasion. The shell's outer layer consists of firm but flexible horny plates (scutes) and is composed of keratin covering bones and cartilage, with the spine attached to the carapace - the top side of the shell. Together with the bottom shell – plastron, carapace creates a skeletal box, as they join together along each side of the body.
Only one species of sea turtles don't have this distinctive feature – Leatherbacks, as the name suggests, have a soft leather-like tissue in the shell's place, that covers bony plates underneath. Unlike land turtles, sea turtles are unable to retract their head or limbs under the shell. This is why they developed prominent upper eyelids that protect their eyes.
Sea turtles' limbs – flippers – allow them to swim fast, sometimes on long distances. The front flippers are wide and long, and they help turtles to swim through the ocean and depending on the species, fore flippers usually have one or two long claws. The shorter hind flippers work as a rudder for steering and stabilisation.
Even though they don't have ears, sea turtles have the ability to hear – they can respond to vibrations and low-frequency sounds. All chelonians also lack teeth, instead, they grow horny beaks made of keratin, and their jaw shape is adapted to best suit their diet.
Although the different species vary in size, adult male and female sea turtles of the same kind are equal in size. The only thing that allows us to tell the male and the female apart is the tail – slightly longer in male turtles as this is where their reproductive organs are located. Size is not the only thing that differs the sea turtles' species – the other primary factor is their colour! It ranges from black, through reddish- and greenish-brown, to olive green and yellow.
Sea turtle life cycle
Sea turtles start their lives as a cluster of eggs buried in a nesting pit that's been dug high up on a beach by their mother. The mother, as well as other mothers, will head to various beaches, dig their nests and lay their eggs.
The turtles will remain here until the eggs are ready to hatch. Not all the eggs in the nesting pit will hatch, however, out of the 150 – 200 eggs that are laid, around 20% of them will never hatch.
For sea turtles it's all about the numbers, once the eggs have hatched roughly a month and a half after they were laid, the turtles dig out of the nesting pit, and in mass, they face the perilous task of reaching the ocean. Here they encounter a whole new set of dangers. On this journey, the hatchlings must dash past various possibly life-threatening obstacles and predators like crabs and seagulls.
Upon reaching the ocean, the remaining turtles now have the repelling force of the waves to contend with, as well as a whole new set of predators, from large fish and seabirds, through dolphins and sharks. Once the turtles reach open waters, they will congregate around anything that floats, that can offer them some level of protection and camouflage from predators. The turtles will remain in these places just floating around the ocean for many years as they grow, feeding on things like small fish or plant matter. Only around 50% of the turtles that made it into the ocean will survive this long.
Within next couple of years, roughly around a decade, the hatchlings will increase in size until they reach the point of maturity. Once this happens, they will head out to look for a mate and swim back towards the beaches they were hatched on, completing the cycle. Sadly, nowadays only around 1% of the turtles survive up to this point, which is incredibly bad news for the sea turtle population and that's the reason why they're on the endangered species list.
Types of sea turtles
Loggerhead - Caretta caretta
Status – Vulnerable - around 50,000 remain.
Anatomy - Anatomy - Loggerhead turtles have enormous heads with massive, strong jaws and a heart-shaped, bony carapace without ridges. Its front flippers are short and thick with two claws, while its rear flippers usually have three claws.
Size (Carapace length) - 2.5 to 3.5 feet (80 to 110 cm).
Adult weight - Between 155 and 375 pounds (70 to 170 kg).
Colour - Adult loggerhead turtles have a reddish brown carapace with a yellowish-brown plastron. Hatchlings have a dark-brown carapace with flippers pale brown on margins.
Habitat – Loggerheads are most commonly found in shallow water around continental shelves in the Pacific, Atlantic and Indian oceans. They are also found in coastal bays and estuaries; this is because this is where they prefer to feed.
Diet - Primarily carnivorous loggerheads feed mostly on shellfish that live on the bottom of the ocean. Their large heads and powerful jaw muscles help them to crush shellfish giving them access to the sustenance inside easily. They will eat a variety of invertebrates such as; clams, muscles and horseshoe crabs.
Breeding habits – Females reach maturity when they're 35 years old. They usually mate every 2-3 years and then nest in the warmer months. They come back to the nesting site at the beach every two weeks to lay around four clutches of 100-120 eggs. Loggerheads nest 2-3 times per season which falls from April through early September.
Green turtle - Chelonia mydas
Status – Endangered - between 85,000 and 90,000 nesting females remain.
Anatomy – Anatomy – Green turtles have a single pair of prefrontal scales (scales in front of the eyes) and has a small, blunt head with a serrated jaw. The carapace is bony without ridges, its colour varies and is oval shaped with large non-overlapping scales. Each flipper has one visible claw.
Size (Carapace length) - 3 to 4 feet (83 – 114 cm). It is the largest of sea turtles.
Adult weight - between 240 and 420 pounds (110 – 190 kg).
Colour - The carapace colour varies from olive-green and pale to bright yellow, brown and black tones. The plastron varies from white, dirty white or yellowish in the Atlantic populations to dark grey-bluish-green in the Pacific populations. Hatchlings are dark-brown or nearly black with white underneath and white flipper margins. The name of the green turtle comes not from the carapace colour, but from the colour of their flesh.
Habitat – Most commonly found around islands, in bays, and in protected shores with seagrass beds. However, they are occasionally spotted in the open ocean, though, this is rare. They can be found, i.e., on The Galapagos, Coastal East Africa, and Coral Triangle.
Diet – A green sea turtles diet changes as it ages, when the shell is under 10 inches, they eat a varied diet of worms, small crustaceans, aquatic insects, and algae. When over 10 inches, their diets become mainly herbivorous, consisting of seagrass and algae.
Breeding habits – Green sea turtles have to travel a long way to mate, sometimes even as far as 1600 miles or 2600km. Just as other sea turtles, the females travel to the beach for the nesting process. They lay around 85-200 eggs per clutch and do so 3-4 times per season. Nesting season varies among the population, but it usually falls from late May to early September.
Leatherback - Dermochelys coriacea
Status – Vulnerable - between 20,000 and 30,000 nesting females.
Anatomy - Head has a deeply notched upper jaw with 2 cusps. The leatherback is the only sea turtle that lacks a hard shell. Its carapace is large, elongated and flexible with 7 distinct ridges running the length of the animal. Composed of a layer of thin, tough, rubbery skin, strengthened by thousands of tiny bone plates, the carapace does not have scales, except in hatchlings. All flippers are without claws.
Size (Carapace length) - 4 to 6 feet (130 – 183 cm).
Adult weight - 660 to 1,100 pounds (300 – 500 kg).
Colour - The carapace is dark grey or black with white or pale spots, while the plastron is whitish to black and marked by 5 ridges. Hatchlings have white blotches on carapace.
Habitat - Primarily found in the open ocean, as far north as Alaska and as far south as the southern tip of Africa, though recent satellite tracking research indicates that leatherbacks feed in areas just offshore. Known to be active in water below 40 degrees Fahrenheit, the only reptile known to remain active at such a low temperature.
Diet - Leatherbacks have delicate, scissor-like jaws. Their jaws would be damaged by anything other than a diet of soft-bodied animals, so they feed almost exclusively on jellyfish. It is remarkable that this large, active animal can survive on a diet of jellyfish, which are composed mostly of water and appear to be a poor source of nutrients.
Breeding habits – Leatherbacks, unlike other sea turtles, don't always come back to the same beach for nesting. Also their nesting season falls for the opposite time of the year - they prefer to nest in autumn and winter months. On the top of this, they lay more eggs than any other sea turtle – with astonishing 12 clutches with 60-85 eggs per single nesting! Leatherbacks nest 5-7 times per season approximately every 10 days, but only every other or third year.
Hawksbill - Eretmochelys imbricata
Status – Critically endangered - around 8000 remain.
Anatomy – Hawksbills are one of the smaller sea turtles. Their name came from their narrow head and pointed beak, which brings a hawk to mind. Younger turtles have heart-shaped carapaces, which stretch out into more oval shape as they grow. Their beautiful carapace is what hawksbills are best known for – the hard, bright-coloured scutes are overlapping, creating a distinctive pattern on the shell, but also protect them from most predators. They also have a pair of claws on each flipper.
Size (Carapace length) – 2.5 to 3 feet (71 – 89 cm).
Adult weight – 101-154 lbs (46 – 70 kg).
Colour – The carapace usually is amber coloured with some brown and black streaks that create patterns. Males are usually slightly more brightly-coloured than females.
Habitat - Hawksbills are found mainly in coral reefs. This species inhabits tropical oceans, and the most abundant populations occur in the Caribbean Sea, Seychelles, Indonesia, and Australia. They usually avoid swimming in deep waters, and keep somewhat close to the coast.
Diet – Hawksbills are omnivorous, which means they eat both plants and animals - they mainly live off sponges found on coral reefs, algae, molluscs, crustaceans, and jellyfish. They play a crucial role in maintaining marine ecosystems and the health of coral reefs and seagrass beds.
Breeding habits –The mating season is usually from April-November (September-February for hawksbills inhabiting the Indian Ocean). Nests between 3 to 6 times per season every 2 to 4 years. They lay around 140 eggs per nesting.
Kemp's ridley - Lepidochelys kempii
Status – Critically endangered – approximately 1,001-10,000 nesting females remain.
Anatomy – These are the turtles that are significantly smaller in size than the others. The species characteristic features are its parrot-like beak and their carapace, which is often almost round and consists of only five pairs of scutes. They have one claw on front flippers and one or two on the back flippers.
Size (Carapace length) – 2 feet (around 60 cm).
Adult weight - 100 lbs (45 kilograms).
Colour – Carapace is an olive colour, with the off-white to pale yellowish plastron.
Habitat – This is the rarest and world's most endangered sea turtle species. They can usually be found in shallow waters near the Gulf of Mexico, but also as far north as Nova Scotia.
Diet – Kemp's ridleys are omnivores; they mainly feed on crabs, which are their favourite food. They also eat jellyfish, and occasionally molluscs and seaweed.
Breeding habits - Females mature at the age of ten to twelve years. This species nests every two years in arribadas - 'mass arrival,' with approximately three clutches of about 90 eggs in one season, which falls from March to August. They often travel hundreds of miles to reach their nesting beach, usually the same beach they hatched from.
Olive ridley - Lepidochelys olivacea
Status – Vulnerable - approximately 800,000 nesting females remain.
Anatomy – Along with Kemp’s ridleys, olive ridleys are the smallest of the sea turtles. The olive ridley has a quite small head and slightly smaller shell in comparison with the Kemps. The carapace is bony without ridges and consists of 6 large scutes, it's heart-shaped, nearly rounded, and smooth, with slightly upturned edges. Females have a somewhat more rounded carapace than males. Both the front and hind flippers have 1 or 2 claws, sometimes with an extra claw on the front flippers.
Size (Carapace length) - 2 to 2.5 ft (60-75 cm).
Adult weight – Up to 100 lbs (45 kilograms).
Colour - Named for its olive green coloured shell and skin, and a rusty coloured carapace. Hatchlings are black when wet with greenish sides.
Habitat - Olive ridleys are found in coastal bays and estuaries only in warmer waters, including tropical and subtropical waters of the southern Atlantic, Pacific, and Indian Oceans. They typically forage offshore in shallow waters.
Diet – Ridleys are omnivorous they primarily dine on crustaceans - crabs and shrimps, but also molluscs, jellyfish, small invertebrates, tunicates and fish eggs.
Breeding habits – Ridleys nest up to 3 times a year in a 5 -7 days long mass nesting called Arribada, where thousands of females that have reached the maturity at the age of 12, come together and return to the same beach where they hatched, to lay eggs. Females typically lay about a hundred eggs, in the season from June to December. Sadly, approximately only one hatchling survives to reach adulthood for every 1000 hatchlings that enter the sea waters.
Flatback - Natator depressus
Status – Deficient data/vulnerable – approximately 10,000 nesting females remain.
Anatomy - Unlike other sea turtles, the Flatback has an extremely flat, smooth carapace with slightly upturned ridges - and that's where its name derives from. The oval carapace is much thinner than those of other turtles, which means that they can easily get hurt while hitting hard surfaces. Flatbacks also have a distinctive pair of prefrontal scales at the front of the head, and four side scutes on each side of the carapace.
Size (Carapace length) – 3.2 feet (up to 1m).
Adult weight - 198 pounds (90 kg).
Colour - The carapace of a flatback turtle is yellow-grey or olive-green just like it's flippers, but the rest of the body is between yellow and light green. The plastron is usually pale yellow.
Habitat -Flatbacks prefer inshore waters, bays, coastal coral reef and grassy shallows. They stay away from rocks and rocky seabed, leaning towards soft-bottomed seabed habitats that are far from reefs. This turtle species have the smallest distribution of all turtles, and it is restricted to the waters of Australia and Papua New Guinea in the Pacific.
Diet - Like other turtles, flatbacks are omnivores. Its diet is varied and consists of, e.g., soft corals, shrimp, small lobster, algae, small fish, seaweed, seagrass, jellyfish, molluscs, as well as sea cucumbers.
Breeding habits - this species lay a significantly smaller number of eggs than the other species – with an average of 50 per nest at the time. Some females nest up to four times per season with the interval between each event between 13 and 18 days. Flatbacks breed during any time of the year, but this activity increases during the summer months of June, July and August.
Why are sea turtles endangered?
Sea turtle populations all over the world have been declining rapidly in recent decades. Sea turtles are under a threat of extinction caused by human activities. Some of the threats sea turtles must face nowadays are, e.g., destruction of nesting sites and coral reefs, pollution of the oceans, as well as overconsumption of turtles' meat, leather, and shells. On the top of this, hundreds of thousands of sea turtles are accidentally caught and die in fishing gear every year. Not even to mention all the predators baby turtles have to encounter on their way from the nesting sites to the oceans' waters!
The turtles' reproduction is directly affected by climate change – because the turtles' gender is determined by the temperature eggs to have been exposed to, warmer temperatures will shift the gender ratio of hatchlings, resulting in having more female turtles than male ones.
- Sea turtle world.http://www.seaturtle-world.com/
- Conserve turtles.org.https://conserveturtles.org/
- NOAA's Southeast Fisheries Science Centerhttps://www.sefsc.noaa.gov/
- World turtle trust.http://world-turtle-trust.org/index.html
- World wildlife.https://www.worldwildlife.org/
- World Wide Fund https://www.wwf.org.uk/
- ecomarbelize - anatomy http://www.ecomarbelize.org/anatomy.html
- Types of sea turtles. https://www.thoughtco.com/types-of-sea-turtles-2292019
- Defenders.org – sea turtles.https://defenders.org/sea-turtles/basic-facts
- 'Sea Turtles: A Complete Guide to Their Biology, Behavior, and Conservation'bBy James R. Spotila access via Google Books