Why these zebra-striped sea slugs are the unsung heroes of our underwater meadows

Nature · Published 29 September 2026 Swipe more like this →

In short: Eelgrass sea hares look like tiny, gelatinous blobs, but they are vital environmental cleaners. By grazing on algae that coats seagrass, they ensure sunlight reaches the plants, allowing meadows to thrive. This delicate balance, supported by sea otters, keeps entire estuary ecosystems functioning in the face of nutrient pollution.

Eelgrass sea hares, sometimes called Taylor’s sea hares, are small mollusks easily identified by their zebra-striped bodies and bunny-like head tentacles. Despite their appearance, which resembles a spoonful of green jello, they perform a critical ecological service. They do not consume the seagrass itself; instead, they use rows of tiny teeth to scrape away microscopic algae that accumulate on the blades. This cleaning process is essential because it prevents algal mats from blocking the sunlight that the seagrass requires to grow.

The relationship between the sea hare and its environment is part of a complex food web, particularly visible in Elkhorn Slough, an estuary near Monterey Bay. For decades, this area has struggled with nutrient overload from agricultural runoff, which triggers excessive algae growth. However, the reintroduction of sea otters to the slough in the 1980s triggered a trophic cascade. By preying on crabs—which are natural predators of the sea hares—the otters allowed the sea hare population to flourish. This increase in the slug population resulted in cleaner seagrass blades, effectively counterbalancing the negative impacts of the algal blooms.

This interaction highlights the importance of biodiversity in maintaining habitat health. The eelgrass beds at Elkhorn Slough provide a sanctuary for a wide array of species, including Dungeness crabs, clams, skeleton shrimp, and various fish. While sea hares and nudibranchs are both types of sea slugs, they represent distinct groups within the mollusk family. The ongoing research into these dynamics, led by scientists such as Brent Hughes and Katharyn Boyer, underscores how top predators can influence the structure of an entire ecosystem and the cycling of nutrients within it.

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