Semibalanus balanoides

Researched By	Nicola White	Data Supplied By	MarLIN
Refereed by	Prof. Alan J. Southward
Taxonomy
Scientific name	Semibalanus balanoides	Common name	An acorn barnacle
MCS Code	R70	Recent Synonyms	Balanus balanoides
Phylum	Crustacea	Subphylum
Superclass		Class	Maxillopoda
Subclass	Cirripedia	Order	Thoracica
Suborder	Balanomorpha	Family	Archaeobalanidae
Genus	Semibalanus	Species	balanoides
Subspecies
Additional Information	No text entered
Taxonomy References	Rainbow, 1984, Fish & Fish, 1974, Howson & Picton, 1997, Hayward & Ryland, 1995b, Anderson, 1994, Bassindale, 1964
General Biology
Growth form	Conical	Feeding method	Passive suspension feeder, Active suspension feeder
Mobility/Movement	Permanent attachment	Environmental position	Epifaunal
Typical food types	Zooplankton, detritus	Habit	Attached
Bioturbator	Not relevant	Flexibility	None (< 10 degrees)
Fragility	Robust	Size	Small(1-2cm)
Height	Insufficient information	Growth Rate	23 - 160 µm/day
Adult dispersal potential	None	Dependency	Independent
Sociability	Gregarious
Toxic/Poisonous?	No
Additional Information	Semibalanus balanoides has a membranous base, while Balanus crenatus has a calacareous base. Semibalanus balanoides is preyed on extensively by the dog whelk Nucella lapillus and the shanny Lipophrys pholis. Feeding: Semibalanus balanoides feeds by extending thoracic appendages called cirri out from the shell to filter zooplankton or similar sized organic particulates from the water (Rainbow, 1984). In the absence of any current, the barnacle rhythmically beats the cirri. When a current is present Semibalanus balanoides holds the cirri fully extended in the current flow (Crisp & Southward, 1961; Southward, 1955). Barnacles feed most during spring and autumn when plankton levels are highest. Little if any feeding takes place during winter, when barnacles rely on stored food reserves. Feeding rate is important in determining the rate of growth. Barnacles feed when they are immersed so barnacles low on the shore are able to feed for a longer time and consequently grow faster than those high on the shore (Barnes & Powell, 1953). Moulting: Barnacles need to moult in order to grow. Frequency of moulting is determined by feeding rate and temperature. Moulting does not take place during winter when phytoplankton levels and temperatures are low. Growth: all barnacle species grow faster in early life and slower in later life. Growth rates recorded in the British Isles are given above (Anderson, 1994; Crisp & Bourget, 1985). Growth rate varies with a variety of biological and environmental factors, including current flow, orientation with respect to current, food supply, wave exposure, shore height, surface contour, and intra- or inter specific competition. Crisp (1960) concluded that un-interrupted current flow was the most important factor affecting growth and that growth was mainly determined by food intake. The influence of current, wave exposure and tidal level out-weighed latitudinal temperature influences in Semibalanus balanoides (Crisp & Bourget 1985). Individuals orientated with the rostral end, and hence the cirri, into the current flow gained a slight growth advantage over individuals of different orientation. Individuals that settled in pits grew slower than those on flat surfaces, perhaps since individuals in pits are removed from current flow, although should they out-grow the dimensions of the pits they grew normally (Crisp, 1960; Crisp & Bourget, 1985). At densities above 0.25/cm² barnacles compete for space, and, as soon as they touch, growth in diameter is replaced by growth in height, so that dry weight and volume continue to increase. However, at densities >1/cm² growth rate decreases with density. The presence of foliose species, e.g. filamentous algae, hydroids and bryozoans may also reduce growth, presumably due to reduced current flow over and food supply to the barnacles. (Crisp & Bourget, 1985). Growth is also reduced by the energy demands of reproduction and the presence of the cryptoniscid isopod parasite Hemioniscus balani. Parasites and epizoites: the midgut of Semibalanus balanoides is parasitised by the Gregarinid protozoan Pyxinioides balani while Epistylis horizontalis (a peritrich ciliate) lives on the gills and mantle (reviewed by Arvy & Nigrelli, 1969). Protozoan infestation may delay the release of nauplii. Metacercariae (a larval stage in the life cycle of trematodes) occur inside or near the gut of barnacles, e.g. Maritrema spp., a possible parasite of the turnstone (Arenaria intrepes morinella), terns or gulls, is found in Semibalanus balanoides (Rainbow, 1984; Arvy & Nigrelli, 1969). The cryptoniscid isopod Hemioniscus balani is a widespread parasite of barnacles, found around the British Isles, including Ireland, north to the Faroes and Oslo Fjord, and south to the Atlantic coast of France, as well as from Labrador to Massachusetts, New Scotland and Friday Harbour in the western Atlantic (Crisp, 1968). Hemioniscus balani is protandrous, the males becoming female after invading the host, eventually developing into a bloated, enlarged, star-shaped egg sac. An individual barnacle may contain up to 7 of theses parasites. Heavy infestation inhibits or destroys the gonads resulting in castration of the barnacle. (Rainbow, 1984; Crisp, 1968; Arvy & Nigrelli, 1969). The shell of British barnacles in the mid-shore may appear blackened due to the epizoic lichen Arthropyrenia sublittoralis (Rainbow, 1984). The crustose lichen Pyrenocollema halodytes can also grow on barnacle plates.
Biology References	Rainbow, 1984, Bennell, 1981, Fish & Fish, 1974, Crisp, 1960, Crisp & Southward, 1961, Stubbings, 1975, Barnes et al., 1963, Anderson, 1994, Crisp & Bourget, 1985, Crisp, 1968, Arvy & Nigrelli, 1969, Lewis, 1964, Bassindale, 1964, Thompson et al., 1998, Barnes & Powell, 1953
Distribution and Habitat
Distribution in Britain & Ireland	All coasts of Britain & Ireland, but sometimes is absent or rare in south-west Cornwall, the Isles of Scilly and south west Ireland.
Global distribution	Recorded in the north-east Atlantic from Spitsbergen to north-west Spain, on the Pacific coast of north America as far south as British Columbia and on the Atlantic coast as far south as Cape Hatteras; but missing from the Biscay coast of France.
Biogeographic range	Not researched	Depth range	Not relevant
Migratory	Non-migratory / Resident
Distribution Additional Information	In the 1950s the species was extremely rare in south-west Cornwall, and the far west of south County Cork (Crisp & Southward, 1958; Southward & Crisp, 1954; Southward, 1967). Since 1962, as sea temperatures decreased, its range spread westwards apparently from Lyme Bay (Southward, 1967). In 1998 it was found at Porthleven, although the population has declined recently (Southward, pers. comm.). Southward (1998) found that the record for the Azores by Nilsson-Cantell, in the Fauna of Scandinavia, was an error. Semibalanus balanoides is a boreo-arctic (i.e. northern) species. Its northern limits are closely paralleled by the summer limits of pack ice while its southern limits are controlled by high temperatures which prevent final maturation of gametes. The mean monthly sea temperature must fall below 7.2 °C in order for the barnacles to breed. Semibalanus balanoides is dominant in the eastern and northern regions of the British Isles. In the south west it gives way to chthamalid barnacles and it is sometimes absent or rare in south west Cornwall, south west Ireland and the Isles of Scilly. Semibalanus balanoides is less abundant on shores occupied by fucoid algae, because seaweeds prevent establishment of barnacle larvae or remove settled larvae by 'sweeping' across the rock (see reproduction). On shores exposed to strong wave action the upper limit of the barnacles distribution is raised because the shore is kept moist by spray. Semibalanus balanoides has a lower tolerance to desiccation than the chthamalid species due to a greater permeability of the shell plates. It is sometimes found sublittorally.
Substratum preferences	Bedrock, Large to very large boulders, Small boulders, Cobbles, Pebbles, Artificial (e.g. metal/wood/concrete)	Physiographic preferences	Strait / sound, Sealoch, Ria / Voe, Estuary, Open coast
Biological zone	Upper Eulittoral, Mid Eulittoral, Lower Eulittoral	Wave exposure	Extremely Exposed, Very Exposed, Exposed, Moderately Exposed, Sheltered, Very Sheltered, Extremely Sheltered, Ultra Sheltered
Tidal stream strength/Water flow	Very Strong (>6 kn), Strong (3-6 kn), Moderately Strong (1-3 kn), Weak (<1 kn)	Salinity	Reduced (18-30 psu), Full (30-40 psu), Variable (18-40 psu)
Habitat Additional Information
AMBI Group (Borja et al., 2000)	I
Distribution References	Rainbow, 1984, Bennell, 1981, Barnes, 1953, King et al., 1993, Stubbings, 1975, Barnes, 1958, Barnes et al., 1963, Lewis, 1964, Bassindale, 1964, Jenkins et al., 2000, Southward et al., 1995, Hawkins & Hartnoll, 1982, Crisp & Southward, 1958, Southward & Crisp, 1954, Southward, 1967, Southward, 1998
Reproduction/Life History
Reproductive type	Permanent hermaphrodite	Developmental mechanism	Planktotrophic, Lecithotrophic
Reproductive Season	Spawn February to April	Reproductive Location	Water column
Reproductive frequency	Annual episodic	Regeneration potential	No
Life span	6-10 years	Age at reproductive maturity	1 year
Generation time	1-2 years	Fecundity	Up to 10,000 eggs/brood
Egg/propagule size	Insufficient information	Fertilization type	Internal
Larvae/Juveniles Larval/Juvenile dispersal potential >10km Larval settlement period Insufficient information Duration of larval stage 1-2 months
Additional Information	Reproduction: Reproduction in barnacles is discussed in detail by Rainbow (1984), Barnes (1989), Klepal (1990), Barnes (1992), Anderson (1994) and the references therein. Key points follow. Semibalanus balanoides is an obligate cross-fertilising hermaphrodite. The barnacle penis is substantially longer than the body and is capable of searching an area around the adult to find a receptive 'functional female'. Copulation takes place in the UK from November to early December and although an individual 'functional male' may inseminate a single 'functional female' up to 6-8 times (dispensing all its seminal fluid), insemination by more than one functional male is required to successfully fertilise all the eggs. Up to 6 concurrent penetrations may occur (Rainbow, 1984; Anderson, 1994). After copulation the penis degenerates and is re-grown during summer ready for the following November. Penis and gonad development in the population is highly synchronous, and probably controlled by light and temperature regime since gonad maturation is inhibited by 15 °C or greater and a light period greater than 12h/day (Barnes, 1992). Fertilised embryos are held in two egg sacs and incubated in the mantle cavity over winter, during which the barnacle does not moult (anecdysis). Nauplii larvae are released from the barnacle between February and April, in synchronisation with the spring algal bloom. Hatching takes place later in the north and east of Britain. Synchronisation with the spring algal bloom is enabled by the release of a hatching substance, which is secreted by adult barnacles following ingestion of phytoplankton (Barnes 1957; Crisp 1956; reviewed by Clare, 1995). Hatching substance is released into the mantle cavity by the adult and has been identified as an eicosanoid, which may function by stimulating the release of embryonic dopamine (Clare, 1995). In response, the nauplii twitch repeatedly until they break free of the egg membrane and are released. The hatching factor is probably a complex mixture of hydroxy fatty acids, analogous to sex pheromones in insects (see Clare, 1995). 'Spawning' of nauplii in response to the spring phytoplankton bloom ensures that larvae grow and develop under optimum conditions when food supply is at its highest and have time to develop and lay down food reserves prior to settlement. Nauplii larvae are planktotrophic and develop in the surface waters for about two months. They pass through six nauplii stages before eventually developing into a cyprid larva. Cyprid larvae are specialised for settlement (see general biology). Peak settlement occurs in April to May in the west and May to June in the east and north of Britain. Semibalanus balanoides produces one brood per year of 5000 -10,000 eggs/ brood in mature adults but varies with age and location e.g. at Port Erin, Isle of Man fecundities of 2500-4000 eggs/ brood (max. 13,000) were reported while 400-8000 eggs / 1.5mg oven dried body weight were recorded in Scotland (Barnes, 1989). Reproduction may be affected by temperature, latitude, light, feeding, age, size, crowding, seaweed cover and pollution. High shore Semibalanus balanoides breed first and low shore specimens last (up to 12 days difference)(Barnes, 1989). Fertilization is prevented by temperatures above 10 °C and continuous light. Differences in breeding times with latitude are probably mediated by temperature and day length, e.g. in Spitzbergen fertilization occurs 2-3 months earlier than in the UK. Increased crowding or seaweed cover may decrease feeding and reduce fecundity. Barnacles grow rapidly in the first season after settlement. Newly metamorphosed larvae are very squat and only form the adult shape at 3 mm. Semibalanus balanoides may become sexually mature in the first year after settlement although this is often delayed until 2 years of age (Anderson, 1994). Life span of Semibalanus balanoides varies with the position on the shore. Barnacles low on the shore typically die in their third year, whereas those from near the mean level of high water neaps may live for five or six years. Recruitment: Settlement and subsequent recruitment is highly variable. Jenkins et al. (2000) reported variation in settlement and recruitment at all spatial scales studied (10s, 1000s of metres and 100s of km) in Sweden, the Isle of Man, southwest Ireland and southwest England and between 2 years, 1997 and 1998. Substantial variation in settlement and recruitment occurred between sites, but was not consistent between the two years studied. Variation in settlement explained 29 -99% of variation in recruitment across all sites, although not all variation in recruitment was explained by settlement at all sites. They also observed significant variation between replicate samples within sites in 1997. Recruitment was lower in southwest England than southwest Ireland even with similar settlement due to variation in post settlement mortality. Settlement density may also be influenced by onshore or offshore winds, resulting in irregular and sharp peaks of settlement, e.g. north Yorkshire or north west Scotland coasts (Kendall et al., 1985). Settlement density may be directly related to orientation of the shore to the prevailing winds. Settlement was enhanced by onshore winds in the Isle of Man (Hawkins & Hartnoll, 1982) but offshore winds and calm seas in Anglesey (Rainbow, 1984). Hawkins & Hartnoll, (1982) and Jenkins et al. (2000) suggested that failure to recruit in any one year is probably less likely when progeny are produced locally and disperse over short distances, whereas where dispersal is wide the chance of larvae encountering adult habitat is subject to varying hydrographic conditions, especially in offshore islands where isolation may exacerbate loss of larvae due to offshore transport. In poor years settlement occurred mainly in the later part of the season suggesting either that early larvae failed or were lost (Kendall et al., 1985), or that the phytoplankton bloom, and so release and development of larvae, was late. Macroalgae canopies inhibit cyprid settlement and sweeping of algal fronds or bulldozing by grazing limpets may cause high post-settlement mortality, up 82-97% under Fucus serratus canopy (Jenkins et al., 1999). Fucus serratus was found to inhibit settlement more than Fucus spiralis (which has a less dense canopy) and Ascophyllum nodosum (which floats upright in the water column). However, the long term survival of spat reaching >6mm under the canopy was enhanced, especially high on the shore due to reduced risk of desiccation under the canopy (Jenkins et al., 1999). The cyprids are capable of settling above their usual zone on the shore but their upper limit (below Chthamalus montagui) is maintained by their lower tolerance to temperature and desiccation when compared to chthamalids. Mortality in early life is highly variable, e.g. Kendall et al. (1985) noted that under highly desiccating conditions 70% of a single days input of barnacle spat to the upper shore died within 24 hrs, but overall, in 48 hrs in 1978 mortality was 13% however, in 1980, when intertidal was exposed to 27 °C, 48hr survival was reduced to 30%. Long term monitoring of intertidal barnacle populations in southwest England demonstrated a correlation between the relative abundance of Semibalanus balanoides to Chthamalus spp. and the planktonic ecosystem and sea temperatures over a 40 year period (1954-1987) (Southward, 1991; Southward et al., 1995). Semibalanus balanoides increased in abundance in cooler years and Chthamalus spp. in warmer years, possibly due to the increased survival of Semibalanus balanoides spat at lower temperatures and reduced desiccation (Kendall et al. 1985). At increased temperatures Chthamalus spp. are likely to produce more and earlier broods of larvae, and compete more effectively with Semibalanus balanoides which will suffer increased mortality at high to mid shore (Southward et al., 1995).
Reproduction References	Rainbow, 1984, Kendall et al., 1985, King et al., 1993, Stubbings, 1975, Anderson, 1994, Crisp, 1968, Arvy & Nigrelli, 1969, Walker, 1995, Crisp, 1974, Hill & Holland, 1985, Hui & Moyse, 1987, Barnes, 1989, Klepal, 1990, Barnes, 1992, Barnes, 1957, Crisp, 1956, Jenkins et al., 2000, Southward et al., 1995, Southward, 1991, Hawkins & Hartnoll, 1982