Scientists believe that hawksbill turtles
may maintain the health of coral reef systems by grazing on sponges, which if left to grow unchecked, outgrow the corals, cover them up and kill the reef. Because of this, researchers believe that declining numbers of hawksbill turtles may be a factor in the inability of reefs to resist increasing pressures from pollution, algal overgrowth, overfishing and climate change.
Essential for maintaining healthy ecosystems
are largely herbivorous, and their constant grazing on sea grasses increases the healthiness and growth rate of seagrass beds. Leatherback turtles
, which forage in the open ocean throughout their life, are the top predators of oceanic jellyfish. These jellyfish, in turn, eat larval fish. As the numbers of leatherbacks in the ocean decrease, jellyfish numbers may increase locally and eat more larval fish, leaving fewer fish to grow into adults. A wide variety of marine ecosystems dependent on these fish, and indeed commercial fisheries, may end up suffering from this cascading effect.
Marine turtles return to inshore areas for the nesting season and lay hundreds of eggs each season. In doing so, they provide a source of nutrients that plays a vital role in coastal dune ecosystems. The eggs and hatchlings provide food for many predators, and the empty shells and eggs that don't hatch provide nutrients that can be recycled by invertebrates and micro-organisms. In turn, these nutrients are used by plants, which help stabilise dune structure. In this way, turtles transport nutrients from productive far-away feeding grounds to nutrient-poor coastal ecosystems, and play a vital part in their stability.
Marine turtle's gender - not genetically determined
Male turtles stay at sea for all of their lives, and only females ever come ashore to lay their eggs on sandy beaches - usually the exact same beach where they were born. Unlike many animals, a marine turtle's gender is not genetically determined, but is dependent on the temperature of the sand where the egg develops. Female hatchlings result from higher temperatures, while males are produced by cooler temperatures. Different beaches and different positions in the nest can both affect the eventual gender of the hatchling.
The long journeys and numerous threats
Like humans, marine turtles take many years to become reproductively mature - it may take up to 30 years for some species before a female is able to lay eggs. In between hatching and returning to their nesting beach to lay eggs, most marine turtles migrate vast distances.
Leatherback and loggerhead turtles
for example, travel across the entire Pacific Ocean between feeding and nesting grounds - a journey of over 12,000 kilometres one way or more than one third of the way around the world. Other species stay much closer to home - for example the flatback turtle does not move outside the waters of the northern Australian continental shelf.
The long time to reach maturity and the many natural dangers fact by hatchlings and juveniles through their incredible migrations mean that as few as 1 in 1,000 eggs may survive to adulthood.
The history & cultural significance behind marine turtles
Turtles have been of major cultural, traditional, social and economic significance to many coastal communities in the Asia Pacific region for centuries. For example, according to Hindu mythology, the India deity Vishnu was reincarnated as "Kachhapa" - a turtle, holding the burden of the world on its back.
Turtle meat and eggs have provided valuable sources of sustenance, while shells were sought after for ceremonial and ornamental purposes. Hawksbill turtle shells made into jewellery, ornaments, and utensils have been a part of trade in the Asia Pacific region for centuries.
Turtle eggs - in great demand for food & medicine
Large amounts of turtle eggs are consumed in the South East Asian sub-region. The exploitation of eggs initially started as a traditional source of food within local communities. Customary beliefs about the aphrodisiac and medicinal properties of turtle eggs have also encouraged a huge commercial market for the eggs within South East Asia.
The expansion of European civilisation across the globe in the 1600s and 1700s depended in part upon adequate food supply for ships' crews. Marine turtles were a ready and seemingly inexhaustible source of food. The northern hemisphere’s subsequent fondness for turtle soup in the Victorian era led to large-scale commercial turtle harvesting, putting many turtle populations under even more severe strain. Turtle harvesting and canning factories were still operational in places like Western Australia as late as the 1970s.
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