The Fisheries Blog –
A sea star is not usually the first example that comes to mind when picturing a voracious and fearsome top predator. However, many sea stars, the star-shaped echinoderms colloquially called “starfish” and often found in beach-motif decor, are just that: awesome top predators. Moreover, many sea star species are keystone species, or species that have a major impact on the diversity and functioning of their ecosystem. For instance, the sunflower sea star can grow to over 3ft (~1m) and move more than a meter per minute devouring everything in its path, particularly sea urchins and even fish.
The most well-known keystone sea star is the purple or orchre sea star. Scientists discovered that removing the purple sea star from their coastal intertidal habitat allows mussel populations to quickly cover these rocky habitats; the mussels in turn prevent other species from establishing themselves. Similarly, sea stars that prey primarily on sea urchins keep those populations from growing out-of-control and mowing down giant kelp forests that provide food and refuge to numerous aquatic species. Thus, a population of sea stars has important indirect impacts on many species throughout an ecosystem. Also because of their importance, many scientists quickly became alarmed when these top predators began disappearing a few year ago.