Flustra foliacea

Flustra foliacea is a common bryozoan throughout the temperate NE Atlantic. Colonies are predominantly found in the subtidal, but may often be washed-up along the coastline, particularly after storms. F. foliacea forms bushy colonies with stiff brown or light grey fronds. Fresh colonies have a distinctive lemon-like smell and grow to between 6 and 20 cm. F. foliacea attaches to hard substrates including stones and shells by an encursting basal portionof the colony. The colonies provide a microhabitat to a diverse assemblage of epifaunal species.

Colonies form a bushy clump of flat radiating fronds with terminally rounded lobes. Since F. foliacea is only lightly calcified, the colony as whole is flexible, allowing it move with the current. Zooids are approximately rectangular in shape and are arranged “back to back” to form bilaminar sheets. The frontal surface of the zooids is entirely membranous with no gymnocyst or cryptocuste preesnt. Four to five short, thick spines are arranged around the edge of the zooids. The polypide has13-14 tentacles and avicularia are present.

Colonies exhibit a degree of morphological plasticity, with frond width, and hence drag resistance, varying. Frond width is thought to be related to current speed.

Clumps of F. foliacea form a rich and diverse microhabitat, which provides a reasonably stable and perennial substrate for epizoobionts including other bryozoans species (e.g. Bugula, Scrupcellaria, Crisia and commonly Electra pilsoa). In the North Sea, the epizoobionts of F. foliacea can be divided into two distinct assemblages. In the northern North Sea, the assemblages are characterised by Amphiblestrum flemingii, Callopora dumerilii and Tricellaria ternate, while southern assemblages are characterised by Electra pilosa and Plagioecia patina. (Bitschofsky et al. 2011) Various predators, including sea urchins (Psammechinus miliaris), crabs, nudibranchs and pycnogonids (Achelia echinata), feed on F. foliacea and its associated epifauna.

Colonies are abundant subtidally throughout the British Isles. The species is distributed from the Barents Sea and Greenland south, but is thought not to extend below northern Spain.

Colonies grow through asexual budding. The growing season extends from March to September, with colonies remaining dormant from October to February. During the first year of growth, colonies grow as flat incrustations on the substratum, with erect growth beginning from the second year onwards. Annual growth checks, in the form of lines across the frond surface are frequently visible, and can be useful in ageing a colony. Colonies are typically expected to live for around 12 years.

Flustra foliacea is a cold temperate species that is most frequently found on coarse grounds which have stable, fixed substrata and strong currents. Colonies, however, are able to colonise the majority of hard substrata such as shells, stones or cobbles. The species occurs subtidally, but is often washed on to the strand line. F. foliacea has been recorded from brackish environments in the Bay of Fundy, Baltic Sea and the Netherlands (Winston, 1977).

The founding zooid (ancestrula) develops into a young colony, and later into an adult colony through asexual budding. Sexually produced embryos are brooded within the colony, before larvae are released. Larvae settle after liberation and metamorphose into an ancestrula.

Colonies are typically expected to live for around 12 years.

F. foliacea is often mistaken for seaweed, however, closer inspection of the fronds will reveal the very apparent zooids, confirming the colony as an animal species. Several other bryozoans are similar in shape and habitat to F. foliacea including other species of Flustra and Carbasea carbasea. In particular F. foliacea may be confused with Securiflustra securifrons (narrow-leaved hornwrack), but may be distinguished by broader fronds than S. securifrons. Additionally, the fronds of S. Securifrons are typically divided into wedge-shaped segments, unlike F. foliacea.

Female reproductive cells (ova) are orange in colour. They typically appear in August and move into the brood chambers (ovicells) during October. The sexually-produced embryos are brooded until larval release which commences in February. The larvae of F. foliacea are large non-feeding coronate larvae, which lack a shell and have a densely ciliated belt (the corona) for locomotion.

Colonies typically grow to between 6 and 20 cm. Zooids range from 0.4 by 0.2 -0.28 mm

Like all bryozoans, F. foliacea is a suspension feeder. It feeds on small phytoplankton using ciliated tentacles of the lophophore.