Sea turtles are ancient marine reptiles that have navigated the world’s oceans for over 100 million years. Found in all the world’s oceans, they inhabit tropical and subtropical coastlines, with some species undertaking extensive migrations. Their long history and global presence highlight their diverse contributions to the health and balance of marine ecosystems.
Seagrass Meadow Health
Green sea turtles are primary herbivores in many shallow coastal waters, feeding extensively on seagrass meadows. Their grazing behavior is important for the health and productivity of these underwater grasslands. By consistently cropping seagrass, they prevent the beds from becoming overgrown, which can lead to reduced light penetration and anoxic conditions within the sediment. This regular grazing also stimulates new growth, increasing the nutritional value and density of seagrass leaves, which benefits other species in the ecosystem.
Healthy seagrass meadows provide ecosystem services, serving as nurseries and feeding grounds for diverse marine life, including many commercially important fish and shellfish. These meadows are also significant carbon sinks, sequestering large amounts of carbon from the ocean and burying it in their sediments. The absence of green sea turtles can lead to a decline in seagrass health, disrupting nutrient balance and compromising habitat structure for other marine organisms.
Coral Reef Integrity
Hawksbill sea turtles contribute to the structural integrity and biodiversity of coral reefs through their specialized diet. Unlike most marine animals, hawksbills primarily consume sponges, which can pose a threat to corals. Sponges compete with corals for space on the reef, and some species can grow rapidly, overgrowing and suffocating slower-growing corals.
By preying on sponges, hawksbill turtles help control sponge populations, preventing them from dominating the reef structure. This predation frees up space for corals to grow and thrive, supporting the biodiversity for which coral reefs are known. Coral reefs provide habitat and shelter for over 25% of all marine life, offering breeding grounds for numerous fish species and acting as natural protective barriers for coastlines. Without hawksbill turtles, sponges can proliferate, leading to degradation of the reef and a decline in its health and complexity.
Nutrient Cycling and Distribution
All sea turtle species facilitate the transfer and distribution of nutrients and energy across diverse marine habitats and between marine and terrestrial environments. Their long-distance migrations, spanning from open ocean foraging grounds to coastal feeding areas and nesting beaches, allow them to act as biological transporters. Waste products, such as feces, and even their carcasses contribute organic matter and essential nutrients like nitrogen and phosphorus to different parts of the ocean.
When nesting females come ashore, they deposit marine-derived nutrients onto beaches through their eggs and associated waste. While a portion of these nutrients returns to the ocean with hatchlings, a significant amount remains in the sand, enriching coastal vegetation and influencing beach ecosystems. This process links nutrient-rich marine systems to often nutrient-poor terrestrial beach environments, supporting dune stability and coastal plant communities.
Sediment Aeration and Turnover
Bottom-feeding sea turtle species, such as loggerheads and olive ridleys, perform an ecological service through their foraging activities. These turtles actively dig into the seafloor to unearth prey like mollusks, crabs, and other invertebrates. This digging behavior physically disturbs and aerates marine sediments, often referred to as a “tilling” action.
This physical disturbance prevents the development of anoxic (oxygen-depleted) conditions in the seabed, which can be detrimental to benthic communities. The aeration process also helps release trapped nutrients from the sediments, making them available for other organisms. The foraging activities of these turtles influence the distribution and health of bottom-dwelling communities, contributing to the functioning of the seafloor ecosystem.