Cancer borealis
Cancer borealis ("Jonah crab") is found in the mid- to lower intertidal zone under algae and among rocks. This predator eats blue mussels and other invertebrates. The remains of this crab are often found in the upper intertidal zone, evidence of bird predation.

Carcinus maenas
Carcinus maenas ("green crab") is found under algae and small rocks, and it eats other invertebrates in the mid- to lower intertidal zones. This crab is native to Europe and is an invasive species. The green crab is smaller than the Jonah crab.

Homarus americanus
Homarus americanus ("American lobster") is a bottom-dwelling predator and scavenger. The American lobster is found throughout the Gulf of Maine, where it is commercially important. The lobster is found in rocky, subtidal habitats but, rarely, can be observed in lower intertidal pools.

Idotea balthica
This herbivorous crustacean, an isopod, feeds on a variety of algae including large rockweeds (Ascophyllum, Fucus). It is common in the mid- and lower intertidal zones but is hard to see because its color usually matches the algae it is feeding on. This behavior helps it resist predation by fish. Individuals vary in color from yellow to brown to deep burgundy.

Semibalanus balanoides
Semibalanus balanoides ("barnacles") are sessile filter feeders. Larvae settle in the spring and attach head down to the rock. They make heavy calcified plates, which protect them from predation and drying stress, and begin to sweep phytoplankton into their digestive system by catching them with modified, feathery limbs that sweep out into the seawater from the plates. Semibalanus balanoides can be found from the low to high intertidal zones. Individuals lower in the intertidal zone and in high intertidal pools are larger than individuals that settled in the high intertidal zone. The larger individuals are in habitats where they are covered by water for a longer period of time each day, and this protects them from stress and provides them with more opportunities to feed.
Planktonic crustaceans- Copepods make up a large proportion of the zooplankton in many parts of the world with Krill being prevalent in the Antarctic Ocean. They are very important in that they take the energy trapped by phytoplankton, the tiny floating plants that live in the surface water layers and make them available to larger animals that cannot filter out the tiny phytoplankton, but can filter the larger zooplankton.
Planktonic Crustaceans in vast quantities are eaten by fish and baleen whales, the larger planktonic species are also eaten by squid and small birds and other animals that hunt them individually rather than by filter feeding.

Juvenile herring hunt for the very alert and evasive copepods in schools: The copepods can sense with their antennae the pressure-wave of the approaching herring and react with a fast escape jump. The length of the jump is quite consistent. The fish arrange in a grid of this characteristic jumplength. The copepods can dart about 80 times before they tire out. It takes 60 milliseconds to spread out the antennae again, and this timeslot is utilized by the herring to finally snap a copepod. A single juvenile herring would never be able to catch a large copepod. picture used permission of Uwe Kils published under GNU Free Documentation License, Version 1.2
Barnacles- These are a difficult prey due to their calcareous shell which can be clamped tight shut, they also tend to be individually quite small, so it can be a lot of effort for little food reward to open them up. There are however specialist predators that feed on them such as some Gastropod Molluscs that drill through the shell with a specialized radula.
Decapod Crustaceans- crabs, lobsters, shrimp and crayfish amongst others. These are particularly attractive prey as they have very muscular tails which are designed to beat quickly and propel them backwards, also the large claws have much muscle so making an attractive prize for a predator. They are difficult animals to eat however as those large claws can be formidable weapons, also they tend to have a very strong resilient carapace made basically of chitin and toughened with large amounts of calcium carbonate (limestone).