If someone were to ask you what sea turtles eat, how would you answer? Do they eat small fishes? Or sea planktons? Are they herbivores or carnivores? Or perhaps they are omnivorous? Well, there is no definite answer.
There are seven answers, just like how there are seven species of sea turtles in our oceans. As hatchlings, loggerheads and greens are omnivores, but as they transition into adulthood, the former become carnivores while the latter herbivores. Flatbacks feed on seaweeds and shrimps, among others, and hawksbills usually favour sea sponges. Kemp’s ridleys are meat-eaters, but olive ridleys are classified as omnivores, munching on sea cucumbers, fish, and various plants. Today, however, we shall be focusing on leatherbacks, who are often known as gelatinivores, devouring gelatinous prey such as jellyfish wherever they go.
Among the seven species, leatherback sea turtles are the largest, with a study showing that they could grow up to 640 kilograms in weight despite their specific jellyfish diet. As jellyfish are 95% water (which amounts to only 5 calories), leatherbacks usually consume up to 16,000 calories of the invertebrate, which is roughly 73% of their body weight. Among their favourite types of jellyfish to eat are lion’s manes and moon jellies, and they are usually found well deep in the depths of the ocean, seeing that leatherbacks can swim in high latitudes. These sea turtles tend to experience this high amount of consumption during the summer, before making a 9,000 miles migration journey in search of nesting beaches.
How do leatherbacks exactly feed on jellyfish and how are they capable of doing so? As humans, we are familiar with the venom jellyfish release when stinging the enemy. The venom comes from specialised cells called nematocysts and when made in contact with the human skin, the stung one gets could be awful and at times even fatal. Sea turtles however are reptiles, and their scales can protect them from these venoms. They are also blessed with spine-like projections called papillae which line down leatherbacks’ esophagus from the mouth which help them pierce and break down their prey once ingested.
While these characteristics might seem like a nightmare for jellyfish (they are), eating any other food other than invertebrates would likely damage their unique scissor-like jaws. This is why it is imperative for leatherbacks to prey on jellyfish on a large scale. Furthermore, they only require 22 seconds one average to catch one jellyfish and are usually able to swallow dozens in continuity. With a study showing that leatherbacks have a 100% success rate when hunting on jellyfish, it is no surprise that they can consume up to the aforementioned 16,000 calories of jellyfish.
Jellyfish exist in abundance throughout the seven seas and they are known to be resistant even in the most distressed environment. Leatherbacks help keep their population, as well as the oceans’ ecosystem—to an extent—in check. Nonetheless, it is worth noting that there are a great resemblance and little difference between jellyfish and plastic bags for hungry sea turtles roaming the waters for food. This simple mistake could be fatal for leatherbacks. They might be immune to jellyfish venoms, but even small pieces of plastics could cause blockage and internal injuries.
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