Anemones, sponges, rockfishes, deepwater coral, basket stars, crinoids, big sessile invertebrates, and suspension feeders such as oysters, scallops, and mussels all have safe havens in rocky hard places. These animals must be able to withstand low temperatures, high winds, and intense waves. They must also be able to find food quickly when the conditions are not favorable for hunting.
Animals that live in rocky hard places tend to be filter-feeders, scavengers, or predators. Filter-feeding means that they eat algae or other small organisms that have accumulated in the water column. Scavengers eat dead organic matter that has fallen into the water. Predators hunt for food using their brains and muscles to catch their prey.
Animals that live in cold waters may have thick layers of fat to keep them warm. Fish with red blood cells instead of white blood cells are better at withstanding cold temperatures. Shellfish and other mollusks can close their shells to protect themselves from dangerous levels of heat and moisture. Animals that live in hot climates need large amounts of salt to maintain fluid balance. Without this excess salt, the body tissues would dissolve into water. Some creatures have special organs that release salt into the bloodstream when needed.
Deep-sea fish have adapted to life in extremely cold waters by containing lots of fat to keep them warm.
Mussels, barnacles, limpets, sea anemones, and predatory sea stars are common rocky shore groupings, each having a unique capacity to evade predation or thrive outside of the water. Mussels attach themselves to rocks using strong fibers called byssus, which also help them filter water. They release larvae into the water that drift down currents and eventually form new mussel colonies. Barnacles are related to spiders and crabs and they too attach themselves to surfaces with feathery extensions called peduncles. They lack true legs but instead have strong hooks that grip surfaces beneath the surface of the water or in soil. When food is available, barnacles grow large and heavy, using their weight to trap passing particles from the water or to break free if caught by a current.
Limpets are seed plants similar to aloe vera that grow in rock crevices and obtain moisture and nutrients from algae and other small organisms that live in the sand. They reproduce both sexually and asexually via spores. Limpet shells are white when fresh but turn brown with age. Sea anemones are related to jellyfish and have stinging cells called acontia that protect them from predators. They attach themselves to rocks with long strands of tissue called mesenteries and enclose small animals that fall into their gaping maws. Anemones use their tentacles to capture prey while feeding.
Invertebrates such as barnacles, mussels, oysters, tubeworms, limpets, chitons, snails, crabs, and starfish predominate on the rocky beach. Stationary filter-feeders include barnacles, mussels, and oysters. These organisms attach themselves to rocks in order to feed on water currents that carry organic matter into their shells or bodies where they can eat it.
Crabs are among the most important species in rocky intertidal zones because they help control the population of algae and other organisms which would otherwise deplete the food supply for more delicate marine creatures. In addition, they play an important role in moving nutrients from deeper waters up onto the beach during high tide. They do this by digging burrows and carrying away soil with their claws; some crab species also eat algae. There are three main groups of crayfish: freshwater, saltwater sea, and blackpool (or char). Freshwater crayfish are found in lakes and streams around the world, feeding on plants and decaying matter. They have long antennae used for sensing danger. Saltwater crayfish are similar to their freshwater counterparts but can grow to be two feet long. They live in estuaries, oceans, and large rivers. Blackpool crayfish are unique because they live in deep holes in the ground near fresh water. They are dark colored with white markings on their backsides.