Chartella papyracea

Chartella papyracea occurs throughout the British Isles. The species is apparently restricted to the temperate east Atlantic, ranging from the southern North Sea through the English channel, the south and west coasts of the UK, the Irish Sea to the northern coast of Spain

Colonies are predominantly found in the shallow subtidal on hard substrates, but they may also colonise overhangs on rocky shores, near the low water mark. Chartella papyracea forms delicate tuft-like colonies with flattened branching fronds. Fresh colonies are brown or light grey and grow to up to 10 cm in height.

Colonies establish as an encrusting sheet of non-sexual feeding and non-feeding (kenozooids) zooids. Small delicate tufts of flat radiating fronds arise from a short flattened stem, diverging to both sides. Kenozooids border the edge of the fronds.

Chartella papyracea is only lightly calcified and the colony as whole is flexible, allowing it move with the current. Zooids are simple, approximately rectangular in shape and are arranged “back to back” to form bilaminar sheets. Short, thick spines protrude from the two distal corners of each zooid, furthest from the colony origin. The frontal surface of the zooids is entirely membranous and no gymnocyst is present.
Opercula (flap-like folds of the body wall which close the orifice) are lightly chitinized and avicularia are absent.

Chartella papyracea appears restricted to the temperate east Atlantic, ranging from the southern North Sea through the English channel, the south and west coasts of the UK, the Irish Sea to the northern coast of Spain. The species has been recorded as abundant from dredge samples off the north and west coast of France. Not thought to occur in the Mediterranean.

Distinguishing individual colonies of C. papyracea can be problematic. The holdfasts of adjacent colonies frequently come into contact, and multiple colonies may appear as one, although there is no fusion. Other colonies often become fragmented by mechanical disruption or partial overgrowth.

Colonies grow through asexual budding of new zooids at the periphery. Growth of Chartella papyracea is perennial, typically from early spring, throughout the summer to early October. Erect fronds die by detachment within 2-3 years, but the encrusting portion of the colony may live longer. Annual growth checks, in the form of lines across the frond surface are frequently visible.

Chartella papyracea is a cold temperate species that is most frequently found on hard substrates in the shallow subtidal. Colonies are also (rarely) found beneath overhangs on rocky shores, near the low water mark. The species occurs as a codominant with Bugula flabellata in communities colonizing vertical, shaded, sbulittoral rock surface in the the Bristol Channel.

The founding zooid (ancestrula) develops into a young colony, and later into an adult colony through asexual budding. Zooids formed in early spring are male (androzooids) and may become opaque white in colour as testis develop. Zooids developing later in the growing season are female (gynozooids). Sexually produced embryos are brooded within the colony, before larvae are released, around six weeks after gynozooid completion. Larvae settle after liberation and metamorphose into an ancestrula.

Fronds are expected to live for 2-3 years, but the encrusting part of the colony may exceed this. The life expectancy of a colony, as opposed to fronds, is difficult to assess in C. papyracea, mainly because of the difficultly in delimiting the extent of any one colony.

Chartella papyracea has a similar colony form to several other species in the family Flustridae. In particular C. papyracea may be mistaken for Flustra foliacea, but can be distinguished by the larger zooids and more delicate calcification than F. foliacea. Additionally, in F. foliacea, the fronds are broader and larger. Chartella papyracea can be distinguished from C. barleei -the only other species of the genus to occur in Britain - by the presence of short thick spines at each distal corner of the zooids, and the absence of avicularia.

The colony and individual fronds are hermaphroditic, but individual zooids are either male or female. Brood chambers (ovicells) are immersed within the zooid (endozooidal) and appear as small domed cap at the distal end (furthest from the colony origin) of the female zooids. The sexually-produced embryos, pale orange in colour, are brooded until larval release in the summer months and continuing into October. The larvae are non-feeding coronate larvae, which lack a shell and have a densely ciliated belt (the corona) for locomotion. Several generations of larvae are produced in a single summer breeding season.

Colonies typically grow up to 10 cm in height. Zooids are 0.5 by 0.2 mm

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