Fouling on recreational boats in the western English Channel
Description
The movement of fouled leisure craft is recognized as a major vector for the spread of sessile marine non-indigenous species (NIS) along coastlines. Datasets are presented on the taxa found in the biofouling of the external wetted surfaces of recreational boats (sailing yachts and motor cruisers) in one coastal marina in Devon (SW England) and four coastal marinas in western Brittany (NW France). Visual inspections of the hull surface and ‘niche’ areas (rudder, propeller etc.) for sessile biota were carried out on 71 Devon and 50 Brittany boats immediately upon their removal from the water for maintenance, with field recording of suitable taxa and collection of specimens requiring laboratory identification. Twenty-four sessile NIS (23 invertebrates and one brown alga) were recorded. The distribution of fouling taxa between open hull surfaces and niche areas was documented. Hull inspections were carried out from 2008 to 2011 in Devon, England, at a single marina. French inspections all took place in 2011 and involved four marinas in Brittany, France. Twenty-two species recognized as non-indigenous in Great Britain were recorded on the Devon boats and 18 French NIS on the Brittany boats. The upright-growing bryozoan Tricellaria inopinata was the most frequently occurring species on Brittany boats and jointly the most frequent, along with the barnacle Austrominius modestus, on the Devon boats; T. inopinata occurred on c. 90% of boats in both data sets. A second upright bryozoan, Bugula neritina, was found on c. 60% of boats in both data sets, while two colonial ascidians, Diplosoma listerianum and Botrylloides violaceus occurred on c. 60% of Brittany and Devon boats respectively. The unitary ascidian Asterocarpa humilis was notably more frequent in Brittany (present on 26 out of 50 boats) than in Devon (2 out of 71 boats). This observation matches the rapid infilling of sites by A. humilis seen in SW English marinas between 2010 and 2013, while Brittany marinas were already all colonized by 2010. Devon boats carried an average of 4.32 NIS (with a range of one to eight NIS per boat, while Brittany boats averaged 5.54 NIS per boat, ranging from zero to 12 NIS per boat. Thus, none of the Devon boats were free of NIS while 6% of Brittany boats lacked NIS. On the Devon boats, the number of NIS recorded on the niche areas (mean 4.47) was significantly greater than on the open-hull areas (mean 2.35). The same distinction between niche and open-hull areas was observed in the Brittany boats: niche areas mean 3.94 species, open-hull mean 2.42. Information on patterns of boat maintenance and usage from questionnaire-guided interviews with boat owners is also provided.
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Boats were surveyed at a single English marina in Devon (SW England) and four different French marinas in NW Brittany (NW France). The actual collecting of biological data was comparable between England and France; one surveyor participated in both sets of surveys, ensuring correspondence of the practical survey process and taxonomic understanding. In both England and France, hull fouling was investigated on land soon after the removal of leisure craft from the water for maintenance. In England this involved the scheduled craning of a boat out of the water by marina personnel up onto a ramp above the water level where it was temporarily propped upright. The researchers were allowed access to the newly exposed underside of the boat for approximately three minutes before marina personnel started removing any fouling with a high-pressure water hose. During the period of access all wetted regions of the boat were inspected by three researchers, species noted, photographs taken, and specimens collected for subsequent identification. In addition to non-indigenous species, other algal and sessile invertebrate taxa (i.e. natives and those considered cryptogenic) were recorded. Plastic scrapers were used for collecting specimens to avoid damaging the boat’s surfaces. Initial identifications were then made at the marina with the specimens spread out in a tray of seawater, with examples preserved as necessary in 70% ethanol for lab identification. In 2011 only, separate records were made of A) fouling on general hull surfaces normally receiving conventional antifouling and B) so-called ‘niche’ areas, difficult or inappropriate to treat with regular antifoul paints: the base of the keel, the propeller plus propeller shaft, and the rudder. In France, a proportion of boats was inspected in the same circumstances as in Devon, soon after the boat was lifted or hauled out of the water by marina staff. Other boats were grounded on a ramp at high tide by the owner to become exposed as the tide fell. In either case a single researcher spent 10 minutes examining the exposed underside of each boat, separately recording fouling on the hull, propeller plus shaft, rudder, base of keel and openings of inlet/outlet pipes. Laboratory identification of specimens was based on morphology using dissecting stereomicroscopes and standard identification literature. External taxonomic advice was sought as necessary. Taxonomic names used here have been updated according to WoRMS. In the English marina the boat’s owner was interviewed by one of the three researchers with the aid of a questionnaire before or after the period of access to the boat to record fouling. However, boats were often lifted by the marina staff without the owner being present, in which case the owner questionnaire could not be completed. In France every boat’s owner was present and was interviewed with the aid of a questionnaire by a second researcher while the hull inspection was going on.