Molluscs

Crabs, shellfish, clams,...

Blue mussels, edulis mytilus, are effective filter feeders

Blue mussel beds can clean fjords and bays

A project conducted by researchers from Denmark's Technical University showed that 18 hectares of blue mussels in Skive Fjord reduced the levels of algae low enough to prevent oxygen depletion.

The main issue with fertilization of coastal waters causing algae bloom stems from the massive amounts of dead algae sinking to the bottom in thick layers. As they rot, they consume and deplete oxygen, choking huge swathes of the seabed, leading to widespread bottom death. This is a big issue along coasts of agricultural areas.

Cephalopods - Jet-powered Masters of Disguise

Most cephalopods—the group in which scientists classify octopuses, squid, cuttlefish and nautiluses—can change color faster than a chameleon. They can also change texture and body shape, and if those camouflage techniques don’t work, they can still “disappear” in a cloud of ink, which they use as a smoke-screen or decoy.