Basketball-sized alien bryozoan could threaten native fish habitat
Science Centres: Aquatic Biodiversity and Biosecurity
NIWA scientist Dennis Gordon with two of the alien bryozoans.
Scallop fishers in Golden Bay have been reporting large, brittle colonies of an unidentified bryozoan clogging their dredges. The species, which can grow to the size of a basketball, was first thought to be the endemic ‘cornflakes coral’ (Hippomenella vellicata) that forms similar colonies off nearby Separation Point. However, studies by NIWA, funded by the Ministry of Fisheries (Marine Biosecurity), have revealed that the nuisance bryozoan is an alien species, Biflustra grandicella, previously known only from Chinese coastal waters.
The colonies are found on the seafloor of Golden Bay at depths of about 20 to 27 m. The species was first noticed in the bay last December and seems to be fairly widespread. No one knows how it got there. Identifying it has been difficult because Biflustra grandicella closely resembles another much more widespread alien species of Biflustra that was found on the hull of a badly fouled Australian LPG tanker in Wellington in 1998. Fortunately, that species was dead or dying and does not appear to have established in New Zealand.
According to published reports by Chinese scientist Xi-Xing Liu, B. grandicella is one of the commonest fouling bryozoans from the north to the south of China, where it encrusts almost any underwater object. The Golden Bay colonies are the first documented record of the species outside Chinese waters.
Published descriptions of Chinese specimens suggest that the Golden Bay colonies may be larger. The Golden Bay colonies also have a fairly rapid growth rate based on anecdotal reports and the ‘cleanness’ of their surfaces (i.e., very few species have been found attached to the Golden Bay colonies). The cleanness of the colony may also be a result of deterrent chemicals produced by the colony, but this has yet to be established.
One reason why these large colonies of B. grandicella are causing concern is their similarity to endemic Hippomenella vellicata. Along with ‘Tasman Bay (or hard) coral’ (a bryozoan called Celleporaria agglutinans), H. vellicata is found at similar depths and in similar habitats as B. grandicella, off Abel Tasman National Park. Despite producing deterrent biochemicals, large colonies of H. vellicata attract the young of commercial fish species by providing shelter and food (including a wide variety of encrusting and mobile invertebrates). If B. grandicella does invade the habitat of H. vellicata and out-competes it, there may be a decline in the diversity of encrusting invertebrates and other associated organisms, which could affect the attractiveness of bryozoan habitat to young fish.
Unlike most bryozoans which produce short-lived non-planktonic larvae, B. grandicella produces planktonic larvae that may live for many days or even weeks. This means we could expect B. grandicella to spread quickly and widely beyond Golden Bay, depending on tidal currents and local circulation.