Fossil records indicate that marine turtles have lived within the world’s oceans for over 100 million years, making them one of a few living links with the time of the dinosaurs.
Sea turtles are well adapted for life in the ocean, their streamlined body and strong flippers propel them effortlessly through the water and also serve well for digging nesting chambers on the beach.
Turtles are reptiles; they have lungs to breathe air from the surface, scutes (rough scales) covering their bodies and are cold-blooded.
They are ectothermic (meaning they rely on their environment for warmth) this is one of the reasons why sea turtles prefer to live in warm tropical to temperate waters.
Marine turtles are a highly migratory species with strong site fidelity to breeding and foraging grounds. They utilise both marine and terrestrial environments to fulfil different stages of their life cycle. Turtle populations are vulnerable to disruption due to the specifics of their breeding cycles:
These traits mean that marine turtles are highly vulnerable to human impacts and are very slow to recover from population decline.
Although marine turtles spend the majority of their lives in the ocean, adult female marine turtles come ashore to lay eggs in the sand above the high tide line. Females lay on average, two to six clutches per season. In between laying clutches, turtles remain close to the nesting beaches before returning to their foraging grounds at the end of the season.
Successful incubation requires marine turtle eggs to be buried in well-ventilated, humid, sandy sites that are not subjected to flooding or erosion, and have a temperature range that stays within 25-35⁰C for the duration of incubation. Marine turtles have temperature dependent sex determination. This means that the temperature during incubation determines the sex of hatchlings, with higher temperatures producing predominantly females. We can assume that hatchlings in the Southern ranges, such as on the Gold Coast beaches will be predominantly male, especially at the beginning and end of the season, with some females being produced in the middle.
Hatchlings emerge from the nest and orient towards the sea using the low light horizon. After entering the water, hatchlings use a combination of natural cues (such as wave direction, current, and magnetic fields) to navigate and travel into deeper offshore waters. Crawling out of the nest, crossing the beach and swimming away is thought to imprint the hatchlings with the cues that allow individuals to return to their natal region for breeding as adults.
Hatchlings rely on the internalised yolk sac for energy during the first few days of life. Once they reach the open ocean they will begin to forage for food in the upper water column favouring things such as sea weed and small marine invertebrates.
4) Pelagic Juvenile
After the hatchling leaves its natal beach and swims offshore it enters it’s next life-stage referred to as the post-hatchling or pelagic juvenile stage. In general, hatchlings disperse into oceanic currents such as the East Atlantic Current (EAC), which offer a relative amount of safety to the small reptiles. The turtles will stay in these pelagic environments for some years until they grow into juveniles and are large enough to settle in coastal feeding habitats.
5) Juvenile – Adult
After leaving the oceanic habitat, juvenile turtles (i.e. not sexually mature) generally ‘recruit’ or take up residency in continental shelf waters where they inhabit sub-tidal and intertidal coral and rocky reefs and seagrass meadows and deeper soft-bottomed habitats. Prime turtle feeding areas include the Moreton Bay Marine Park, the Broadwater and along man made seawalls and training walls found at our creek entrances.
All species of sea turtle dig an egg chamber equal to the length of their rear flippers and excavate a body pit whilst doing so (Bustard 1972). They will use all four flippers to excavate the body pit and then just the rear flippers to dig the egg chamber. Depth is dependent on the species, for Loggerhead and Green sea turtles it is approx. 60-70cm deep. Once complete she will begin to lay her eggs, this will take approx. 20 mins, it is believe they go into a trance like state during this period, however they can still be disturbed and may abort the process if they feel threatened, once she has finished she will then fill in the nest with her flippers before returning to the ocean to rest.
Much of this information was taken from ‘Recovery Plan for Marine Turtles in Australia, Commonwealth of Australia 2017’ , please follow the link for further information.
Having reviewed the turtles life history lesson you will now understand that sea turtles need a variety of habitats throughout their life. Here on the GC we have both feeding areas and nesting areas and it is crucial that we look after them if we want to give the turtles the best chance of survival. The seagrass meadows of Moreton Bay Marine Park and even further South into GC waterways are known turtle feeding areas. Turtles also like to graze on algae, sponges, jellyfish and invertebrates living on natural and artificial reefs including our rock walls along the coast.
Turtles return to nest on beaches from the region they hatched, above the high tide line and usually in vegetated dunes. While our Gold Coast sand dunes have been modified over time causing changes and reductions in native vegetation diversity, we have seen turtles return to some of our beaches. Ensuring that the sand dunes are in good condition is vital to turtle nesting success, please be mindful of trampling dune vegetation when you are enjoying the beach.
Turtles are also important members of marine ecosystems. Their feeding habits help to maintain delicate marine food webs by keeping certain species in check such as sea jellies . Hawksbills help to keep coral reefs healthy by eating a variety of sponges which compete with coral for space. As climate change and other human impacts threaten coral reefs across the globe, it is increasingly important that animals such as the Hawksbill continue to keep coral reefs healthy.
Turtles contribute vital nutrients to marine ecosystems through material leftover from nesting such as egg shells, unhatched eggs and even hatchlings, which provide nourishment for dune vegetation. Hatchlings are also an important food source to a variety of predators such as fish, crabs and sea birds and adult turtles are important prey for larger marine creatures such as sharks and Orcas.
Together with dugongs, Green Turtles have another important roll as ‘Seagrass Groundskeepers’. Seagrass meadows are an ecosystem engineer and are relied on by many species for survival. By grazing on seagrass and macroalgae, Green turtles help to keep the meadows productive. They also recycle nutrients, making them available to a plethora of other animals and plants. Healthy seagrass beds are important nurseries and habitat for invertebrates and fish, including commercially valuable species. By keeping seagrass meadows healthy the turtles are protecting our food security.
If you are interested in finding out more about seagrass, Watergum monitors seagrass meadows here on the Gold Coast. Click here for Watergum Seagrass.
Despite global efforts to protect and conserve sea turtles, turtle populations have declined significantly, and of the seven species found in the world, three are classified by the United Nations as Endangered, and three as Critically Endangered.
In Australia sea turtles are protected under the Commonwealth Environment Protection Biodiversity Conservation Act 1999 (EPBC Act). Most of the significant nesting areas (‘rookeries’) for all species of turtles in eastern Queensland have been declared protected habitat under this Act and include key sites such as Mon Repos Conservation Park, Woongarra Marine Park and the Moreton Bay Marine Park.
Here on the Gold Coast, we have a number of sea turtle species visiting that are listed as nationally vulnerable, endangered or critically endangered in Australia. ‘Vulnerable’ means that the species may become endangered if threats to survival continue where as ‘Endangered’, indicates that the species may become extinct if the threats to survival continue.
It is an offense to handle or interfere with sea turtles at any life stage. Please become familiar with the responsible turtle watching guidelines discussed in the following lessons.
If you find a sick or injured sea turtle, call the Sea World Rescue Team who are available 24/7 on;
07 5588 2222 (9:00am to 5:00pm)
07 5588 2177 (After Hours)
Please save these numbers in your phone so you are prepared!
If you assist in anyway (e.g. remove a lure) you must inform QPWS within 72 hours.