What Do Sea Turtles Eat In Hawaii?

Sea turtles have been swimming in Hawaii’s ocean waters for over 100 million years. If you’ve been lucky enough to spot one of these ancient mariners during your Hawaiian vacation, you may have wondered: what are they eating out there?

In short, the green sea turtle and hawksbill sea turtle species found in Hawaii have diverse diets consisting of seagrasses, algae, sponges, jellyfish, and more.

Types of Sea Turtles in Hawaii

Green Sea Turtles

The green sea turtle is the most common species of sea turtle found in Hawaiian waters. An estimated 2,000 green sea turtles feed in Hawaii’s shallow, algae-rich coral reefs and lagoons. Green sea turtles received their name from the greenish color of their cartilage and fat, not their shells.

Their shells can range from shades of brown to shades of olive green with radiating streaks.

Green sea turtles primarily feed on marine algae and sea grasses. Their favorites in Hawaii are nutrient-rich red and green algae as well as sea lettuce and manatee grass. They use their strong jaws to scrape algae off reefs and rocks.

An adult green sea turtle can consume over 10 pounds of algae per day!

Some key facts about green sea turtles in Hawaii:

• Nesting populations can be found on beaches of French Frigate Shoals in the Northwestern Hawaiian Islands
• Listed as threatened under the Endangered Species Act since 1978
• Major threats include habitat loss from coastal development, plastic pollution, fisheries bycatch, and climate change

Hawksbill Sea Turtles

Although less common than green sea turtles, hawksbills also frequent Hawaiian waters and reefs. An estimated 30-40 hawksbill sea turtles live around Maui and 150-200 around the Main Hawaiian Islands.

Hawksbills get their name from their narrow, pointed beak which they use to reach into cracks and holes of coral reefs to look for food. Their diet consists primarily of sponges as well as sea anemones, jellyfish, shrimp, mollusks like squid, and a variety of algae.

Some key facts about hawksbill sea turtles in Hawaii:

• They nest on remote beaches in the Main Hawaiian Islands but most nesting happens in the Northwestern Hawaiian Islands
• Population declined approximately 80% since the 1950s due to loss of nesting habitat
• They face threats from illegal trade of their shells for jewelry and decorations

Protecting Hawaii’s sea turtles is important not only for conservation efforts but also for the tourist economy. Sea turtles are one of Hawaii’s iconic animals that visitors love to see on snorkeling and diving tours.

Maintaining healthy oceans and reefs allows sea turtle populations to rebound so future generations can enjoy seeing them too!

Green Sea Turtle Diet

Seagrasses and Algae

Green sea turtles are primarily herbivorous, feeding on seagrasses and algae as their main sources of nutrition. The seagrass beds in Hawaii provide an abundant buffet for the green sea turtles to graze on.

Some of the common seagrass species that green turtles eat include Thalassia testudinum and Halophila decipiens. These seagrasses contain proteins, lipids, carbohydrates and minerals that are vital for the turtles’ growth and development.

In addition to seagrasses, green turtles also consume multiple species of marine algae, including red, green and brown algae. Gracilaria spp., Ulva spp., and Caulerpa spp. are some of the common algal species found in Hawaii that contribute to the green turtle’s diet.

The algae provide vitamins, omega-3 fatty acids and other beneficial nutrients.

Jellyfish

While primarily herbivorous, green sea turtles do occasionally feed on animal matter like jellyfish, sponges and other marine invertebrates. Several species of jellyfish are found in the waters around Hawaii, including the moon jellyfish and the box jellyfish.

When available, green sea turtles will feed on jellyfish to supplement their diet.

Jellyfish provide a good source of protein and amino acids for the turtles. However, jellyfish lack some of the vital nutrients like calcium that the turtles need for shell development. Therefore, green sea turtles only feed on jellyfish opportunistically and do not rely on them as a primary food source.

Sponges and Other Invertebrates

In addition to supplementing their herbivorous diet with jellyfish, green sea turtles also occasionally feed on sponges, shrimp, crabs and molluscs found in Hawaii’s reef ecosystem. Sponges are rich in iodine, which helps support thyroid function in the turtles.

Crustaceans like shrimp provide amino acids, omega-3s and vitamin B12.

However, green sea turtles feed on these animal-based foods only sparingly. Research shows that their diet generally consists of over 90% plant material, with animal matter constituting less than 10%. Their specialized digestive system is evolved to breakdown fibrous plant material rather than animal tissue.

Hawksbill Sea Turtle Diet

Sponges

Hawksbill sea turtles are specialized sponge-eaters, with sponges making up the majority of their diet. In fact, some research suggests that sponges can account for up to 95% of a Hawksbill’s diet!

Hawksbills use their narrow, pointed beaks to reach into crevices and extract sponges. Their favorite sponges tend to be the ones with high protein and calcium content. In Hawaii, some prime sponge-hunting spots for Hawksbills include coral reefs and rocky areas near shore.

Some of the most commonly eaten sponge species in Hawaii include Geodia mesotriaena, Plakortis angulospiculatus, and Cinachyrella kuekenthalli. Hawksbills often repeatedly visit the same sponge patches to feed.

Other Invertebrates

In addition to sponges, Hawksbills also eat other marine invertebrates like sea squirts, jellyfish, shrimp, crabs, mollusks, and sea urchins. However, these only make up a small portion of their overall diet.

For example, a study that examined the stomach contents of 12 juvenile Hawksbill turtles in Hawaii found that only around 5% of their diet consisted of other invertebrates like hydroids, bryozoans, and mollusks (source).

Algae

Hawksbills occasionally supplement their main sponge diet with some marine algae as well. However, algae is not a significant part of their nutritional intake.

A combination of sponges and other nutrient-rich invertebrates gives Hawksbills the right balance of protein, lipids, carbohydrates, and calcium they need. Their specialized diet allows them to thrive in coral reef environments across Hawaii and the world.

Threats to Hawaii’s Sea Turtles and Their Food Sources

Climate Change and Ocean Warming

Climate change poses a major threat to Hawaii’s sea turtles. As oceans warm, this can negatively impact turtle nesting beaches and food supplies. Studies show that warmer sand temperatures lead to a highly skewed sex ratio, with more female hatchlings (NOAA).

Higher temperatures also increase the risk of disease outbreaks among hatchlings. What’s more, rising sea levels can degrade nesting habitats as beaches shrink or become inundated.

In terms of food sources, warming oceans alter patterns of ocean circulation and nutrient availability. This can reduce the abundance of seagrasses and algae that green sea turtles rely on. Coral reef ecosystems that support turtles may also decline due to mass coral bleaching events.

On the other hand, some turtle prey species like jellyfish could potentially thrive under climate change.

Coastal Development

Development along Hawaii’s coastlines poses risks like artificial lighting that can disorient nesting turtles and hatchlings. Construction activities can also directly damage turtle nests or make beaches less suitable for nesting.

For instance, seawalls and erosion control structures can degrade or shrink nesting habitats over time.

In terms of food impacts, dredging and filling wetlands for coastal development destroys vital seagrass and algae beds that green sea turtles depend on. Runoff pollution from roads, buildings, and other infrastructure can also contribute to declines in coral reefs and seagrasses that are important food sources.

Marine Debris

Hawaii’s beaches and ocean waters contain high levels of plastic and other marine debris. Sea turtles often mistake debris items like plastic bags for jellyfish or other prey. A 2015 study found plastic in the guts of nearly half of green turtles examined in Hawaii (NOAA).

Consuming debris can injure turtles internally, block digestion, reduce feeding and nutrient uptake, and sometimes cause death.

Large amounts of marine debris floating at sea or washing onto nesting beaches also degrade critical turtle habitats. Hatchlings can get trapped under piles of debris on beaches. Research even shows that microplastics end up polluting Hawaii’s seagrass beds to the detriment of green sea turtle diets.

Conclusion

To summarize, the two species of sea turtles calling Hawaii’s waters home have varied diets. While green sea turtles focus more on seagrasses and algae, hawksbills prefer sponges and other invertebrates. Both play important roles in balancing Hawaii’s marine ecosystems.

As these ancient reptiles face mounting threats from climate change, habitat loss, and pollution, it is crucial that we make efforts to protect both sea turtles and their food sources for generations to come.

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