Bryozoa
Interactions with non-human organisms

Marine species are common on coral reefs, but seldom a significant proportion of the total biomass. In temperate waters, the skeletons of dead colonies form a significant component of shell gravels, and live ones are abundant in these areas. The marine lace-like bryozoan Membranipora membranacea produces spines in response to predation by several species of sea slugs (nudibranchs). Other predators on marine bryozoans include fish, sea urchins, pycnogonids, crustaceans, mites and starfish. In general marine echinoderms and molluscs eat masses of zooids by gouging pieces of colonies, breaking their mineralized "houses", while most arthropod predators on bryozoans eat individual zooids.

In freshwater, bryozoans are among the most important filter feeders, along with sponges and mussels. Freshwater bryozoans are attacked by many predators, including snails, insects, and fish.

In Thailand the introduced species Pomacea canaliculata (golden apple snail), which is generally a destructive herbivore, has wiped out phylactolaemate populations wherever it has appeared. P. canaliculata also preys on a common freshwater gymnolaemate, but with less devastating effect. Indigenous snails do not feed on bryozoans.

Several species of the hydroid family Zancleidae have symbiotic relationships with bryozoans, some of which are beneficial to the hydroids while others are parasitic. Modifications appear in the shapes of some these hydroids, for example smaller tentacles or encrustation of the roots by bryozoans. The bryozoan Alcyonidium nodosum protects the whelk Burnupena papyracea against predation by the powerful and voracious rock lobster Jasus lalandii. While whelk shells encrusted by the bryozoans are stronger than those without this reinforcement, chemical defenses produced by the bryozoans are probably the more significant deterrent.

In the Banc d'Arguin offshore Mauritania the species Acanthodesia commensale, which is generally growing attached to gravel and hard-substrate, has formed a facultative symbiotic relationship with hermit crabs of the species Pseudopagurus cf. granulimanus resulting in egg-size structures known as bryoliths. Nucleating on an empty gastropod shell, the bryozoan colonies form multilamellar skeletal crusts that produce spherical encrustations and extend the living chamber of the hermit crab through helicospiral tubular growth.

Some phylactolaemate species are intermediate hosts for a group of myxozoa that have also been found to cause proliferative kidney disease, which is often fatal in salmonid fish, and has severely reduced wild fish populations in Europe and North America.

Membranipora membranacea, whose colonies feed and grow exceptionally fast in a wide range of current speeds, was first noticed in the Gulf of Maine in 1987 and quickly became the most abundant organism living on kelps. This invasion reduced the kelp population by breaking their fronds, so that its place as the dominant "vegetation" in some areas was taken by another invader, the large alga Codium fragile tomentosoides. These changes reduced the area of habitat available for local fish and invertebrates. M. membranacea has also invaded the northwest coast of the US. A few freshwater species have been also found thousands of kilometers from their native ranges. Some may have been transported naturally as statoblasts. Others more probably were spread by humans, for example on imported water plants or as stowaways on ships.
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