Sea Turtles
Overview
Sea turtles are a vital part of the Mediterranean marine ecosystems but face increasing threats from human activity. The Aegean Sea, with its biodiversity hotspots provides essential feeding grounds for turtles all year round, mainly around the Posidonia seagrass meadows. There are also numerous small nesting beaches, where little, but still very important, nesting activity occurs during the late spring and summer months.
The Aegean Sea supports important populations of the Loggerhead and of the Green turtle, as well as a small population of the Leatherback Sea turtle.
By conducting research and monitoring of turtle populations in Archipelagos, we gain invaluable insights into their behaviours, nesting locations and most importantly the extent of the factors that threaten their survival. Turtles are facing serious threats including habitat destruction, impacts caused by tourism, pollution (mainly plastic pollution), as well as by-catch incidents, as well as the effects of climate change in the Mediterranean. According to current estimates, only 1 in 1000 turtle hatchlings survive to adulthood, while increasing human pressures make this even less likely, putting the sea turtle populations at an even greater risk of decline.
Partners
Archipelagos is a partner of the Mediterranean Science Commission (CIESM) JELLYWATCH program, which gathers baseline data on the frequency and extent of jellyfish outbreaks across the Mediterranean Sea for the first time.
Oceans around the world are being exposed to devastating destruction due to anthropogenic threats. Ecosystems commonly struggle to find stability, faced with overfishing, increasing sea temperatures and more. As key species struggle to cope with these factors, biodiversity finds itself susceptible to more primitive species groups such as jellyfish.
There are many trophic levels by which, when threatened, provide space for jellyfish blooms to infiltrate. Jellyfish thrive when oceans experience the following:
- A collapse of small fish that live closer to the sea surface, such as sardines or anchovies. These are species that feed on jellyfish and when their populations decrease, predation pressures on jellyfish plummet. Impacts are later amplified as jellyfish numbers begin to increase, remaining individuals of fish populations are often out competed for resources of zooplankton.
- Overfishing. As fish stocks are depleted due to human action, jellyfish populations increase. This initial action perpetuates the permanent removal of commercial fish from our oceans. Jellyfish prey upon the eggs and larvae of fish species, making it impossible for populations to not fall inferior to the already increasing number of jellyfish.
- Destructive fishing practices. Trawling and other methods of fishing that damage the seabed and all of its inhabitants, create optimal conditions for jellyfish. By removing all predators while simultaneously leaving behind a rocky damaged habitat, jellyfish are able to outcompete all remaining life.
Species
Common name
Loggerhead Turtle
Latin name
Caretta Caretta
Order
Testudines
Family
Cheloniidae
Life span
Between 45-65 years
Nesting behaviour
Loggerhead turtles nest on sandy beaches between May and September. Females lay five times a season with an average of 110 eggs per nest.
Weight
Averages around 135kg
Carapace length
Around 90cm
Population trends
Globally, loggerhead turtles are considered ‘Vulnerable’ by the IUCN Red List. The Mediterranean is home to one of 10 subpopulations and 86,000 nests per year, but little is known about this specific population.
Distinctive Features
Their skin ranges from yellow to brown in colour with a typically red to brown shell. They can be identified by their five vertebral scutes (shell plates) and hooked beak.
Diet
Crustaceans, molluscs, jellyfish and some fish species.
Main threats
Coastal development degrading nest sites, by-catch, plastic and light pollution and climate change.
Habitat
They spend most of their lives in shallow coastal waters and open ocean, only coming ashore to nest.
Interesting fact
Female loggerheads return to the beach they were hatched to lay their eggs.
All Media © Archipelagos Institute of Marine Conservation
Common name
Green turtle
Latin name
Chelonia mydas
Order
Testudines
Family
Cheloniidae
Life span
Up to 90 years
Nesting behaviour
Green turtles nest in the eastern Mediterranean between June and September. Females lay on average 110 eggs per nest.
Weight
Up to 190kg
Carapace length
Up to 114cm
Population trends
Globally, green turtles are considered ‘Endangered’ by the IUCN Red List as the number of mature females has declined by 48% to 67% over the past three generations. The Mediterranean is home to roughly 1,500 nests per year.
Distinctive Features
The green turtle is named for the colour of the fat under its shell and has a carapace that has various colour patterns over its life. They can be distinguished from loggerhead turtles by the presence of a single pair of prefrontal scales and four vertebral scutes.
Diet
They have a mainly herbivorous diet of seagrass and seaweeds.
Main threats
Coastal development degrading nest sites, by-catch, plastic and light pollution and climate change.
Habitat
They prefer shallow coastal waters and inshore bays
Interesting fact:
Green turtles can hold their breath for up to five hours!
All Media © Archipelagos Institute of Marine Conservation
Common name
Leatherback turtle
Latin name
Dermochelys Coriacea
Order
Testudines
Family
Dermochelyidae
Life span
Up to 50 years
Nesting behaviour
There have been no documented leatherback nesting sites in the Mediterranean.
Weight
Up to 500kg
Carapace length
Up to 1.8m
Population trends
Globally, leatherback turtles are considered ‘Critically Endangered’ by the IUCN Red List. The population remains migratory in the Mediterranean.
Distinctive Features
Recognisable by its size, dark colouration and soft, leather-like carapace made of skin and oily flesh (giving the turtle its name).
Diet
Primarily jellyfish, but they can feed on other soft-bodied organisms such as tunicates and cephalopods.
Main threats
Coastal development degrading nest sites, by-catch, plastic and light pollution and climate change.
Habitat
Leatherbacks are found primarily in the open ocean.
Interesting fact
Leatherbacks are the largest of all living turtles and one of the largest reptile species on Earth.
All Media © Archipelagos Institute of Marine Conservation
