Bryozoans; Lace Coral
Bryozoans, more commonly known as “lace corals”, form colonies of hundreds of minute (one millimetre long) box-like individual animals, called zooids. Because many bryozoan colonies form hard, limestone skeletons resembling corals they are often confused with true corals. In fact, the individual bryozoans animals (zooids) are much smaller and more complex than coral polyps. Some zooids have been modified to perform a specialised function other than feeding, such as reproduction, defence, nutrient storage and cleaning. Each individual lives in its own dwelling known as a “zooecium”, and from a single individual, many identical animals are budded off to form large colonies. Each zooid has a ring of feeding tentacles surrounding the mouth and an operculum at one end that opens to allow the feeding tentacles to emerge. The muscle that pulls the tentacles back if the zooid is disturbed is the fastest contracting in the animal kingdom. Each zooid has a well developed digestive system, with mouth, stomach and anus, as well as a nervous and muscular system. The body walls have connecting passages which enable nutrients to floe through the colony. Lace coral bryozoans are suspension feeders, capturing food particles using their cluster of ciliated tentacles known as lophophores .
Bryozoan larvae have a short-lived, non-feeding planktonic stage that lasts for one hour from the time of fertilisation, before settling and metamorphosing into the founding individual of a new colony. From there the budding of new zooids and subsequent zooids increase the size of the colony to up to 16 centimetres in diameter comprising of tens of thousands of feeding individuals. Bryozoans are often among the first animals to settle and grow on bare patches of reef. Lace coral bryozoans form rigid perforated and highly folded calcified structures which form layers over shells, rocks and algae, they vary in colouration from cream to orange or yellow.
Lace coral bryozoans are common in sheltered waters that are not turbid from depths of 3 to 20 metres. They occur from Western Australian waters to New South Wales and around Tasmania.
Occurrence at the Busselton Jetty:
The delicate lace coral bryozoan can be observed scattered amongst the invertebrate growth on the jetty pylons.
Image by: S. Teede