Chthamalus stellatus

Researched By	Karen Riley	Data Supplied By	MarLIN
Refereed by	Prof. Alan J. Southward
Taxonomy
Scientific name	Chthamalus stellatus	Common name	Poli's stellate barnacle
MCS Code	R47	Recent Synonyms	None
Phylum	Crustacea	Subphylum
Superclass		Class	Maxillopoda
Subclass	Cirripedia	Order	Thoracica
Suborder	Balanomorpha	Family	Chthamalidae
Genus	Chthamalus	Species	stellatus
Subspecies
Additional Information	Before 1976 Chthamalus montagui was considered a variety of Chthamalus stellatus, but in 1976 was identified as a distinct species, due to differences in its vertical zonation on the shore and morphology, particularly in the shape of the opercular plates, setation of the smaller cirri. (Southward, 1976).
Taxonomy References	Hayward & Ryland, 1995b, Hayward et al., 1996, Fish & Fish, 1996, Howson & Picton, 1997, Southward, 1976, Rainbow, 1984, Crisp et al., 1981, Bassindale, 1964, Bassindale, 1964
General Biology
Growth form	Conical	Feeding method	Active suspension feeder
Mobility/Movement	Permanent attachment	Environmental position	Epifaunal, Epilithic
Typical food types	Generally feeds on plankton.	Habit	Attached
Bioturbator	Not relevant	Flexibility	None (< 10 degrees)
Fragility	Robust	Size	Small(1-2cm)
Height	Insufficient information	Growth Rate	ca. 10-55 µm / day
Adult dispersal potential	None	Dependency	Independent
Sociability	Gregarious
Toxic/Poisonous?	No
Additional Information	Feeding Chthamalus stellatus / Chthamalus montagui generally feed on small plankton. They can consume diatoms, but were found not to grow under a regime dominated by diatoms (Barnes & Barnes, 1965). Normal feeding of chthamalids involves a cirral beat. This cirral beat is also noted to be a respiratory mechanism (Anderson & Southward, 1987). However, in high wave exposure they tend to hold their cirri out stiffly against the water current for a long period of time, retracting when food is captured (Crisp, 1950). Barnacles living in wave exposed conditions may benefit from this passive suspension feeding habit where cirral beating and consequent energy expenditure are minimised (Crisp, 1950). Rates of cirral beat decrease with age and size, but increase with temperature (Anderson & Southward, 1987). Green (1961) reported that barnacles higher up on shore had a higher cirrial beat frequency than those at lower levels. However, Southward (1955; 1964(b)) found no similar trends. Southward (1955) found that there was no response of Chthamalus stellatus / Chthamalus montagui in still water and that cirrial beating was only induced at a current of approximately 10 cm / sec. The extension response was also sometimes shown. The cirrial beating frequency is also related to temperature, shown by experiments by Southward (1955). Chthamalus stellatus / Chthamalus montagui barnacles kept at a temperature of 0 °C did not react to touch after an hour. He also found that they remained inactive at a temperature up to 5 °C. Between 5 and 30 °C there was a linear increase to 10 beats every 10 seconds. This slowly declined above 33 °C and dropped rapidly at 36 °C. Although the species resisted coma above a temperature of 40 °C, all cirrial beating ceased at 37.5 °C. Respiration Sessile barnacles have a pair of gills: pleats of the mantle wall, attached to the mantle cavity (Stubbings, 1975). Rainbow (1984) also stated that the cirri might also play an important role in respiration. There is usually a slow respiratory pumping beat, with varied emergence of the cirri. Moulting Barnacles need to moult in order to grow. Feeding rate and temperature determine the frequency of moulting. Moulting does not take place during winter when phytoplankton levels and temperatures are low (Crisp & Patel, 1960). Growth Once the barnacle is fixed in place it is unable to detach again (Crisp, 1955). All species grow faster in early life and slower in later life, and chthamalids tend to become tubular when crowded (Southward & Crisp, 1965). The 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. Growth in Chthamalus spp. takes place along the whole internal surface of the one layered plates (Bourget, 1977). The growth rate for Chthamalus stellatus / Chthamalus montagui has been reported by Barnes (1956; Crisp & Bourget (1985) as between 10 - 55 µm per day (relatively slow) in the linear phase. Crisp (1950) noticed that Chthamalus stellatus / Chthamalus montagui reached a maximum size of 0.2 to 1.4 cm. Chthamalus stellatus / Chthamalus montagui was found to have a lower growth rate than many other species of barnacles (Relini, 1983). The species reached a basal diameter of 2-2.5 mm in 3 months, 3.5-4 one year later, up to 8 mm in the 2nd year of growth, but generally no more than about 5-6 mm (Relini, 1983). Sometimes a decrease in size was noticeable, due to abrasion. This low growth rate was found to be associated with a low metabolic rate, or low oxygen consumption, by Barnes & Barnes (1965). Benedetti-Cecchi et al. (2000) observed that Chthamalus stellatus barnacles in the north west Mediterranean were significantly larger the higher up shore that they were found. However, no significant difference in growth rate was noted by Benedetti-Cecchi et al. (2000), with the growth rate of juveniles being between 0.4 and 0.8 mm per year, and that greater mortality of young and adults in a low shore environment. Parasites and epizoites Healy (1986, in O'Riordan et al., 1992) observed the parasitic isopod, Hemioniscus balani in Chthamalus stellatus and Chthamalus montagui in Ireland, although it was never present in Lough Hyne populations. However, Southward & Crisp (1954) found that although it attacks and sterilises Semibalanus balanoides individuals, it does not normally attack chthamalids on British shores. Further Information The dog whelk, Nucella lapillus, feeds on barnacles. The species of Chthamalus spp. are less at risk of this due to their smaller size in comparison with Semibalanus balanoides, but nevertheless it can still have a negative impact on their abundance. Other predators which pull shells or cirri of barnacles off the rock, include crabs, amphipods, shore fish such as wrasse and sometimes herring gulls (Moore & Kitching, 1939), in particular, the shanny Blennius pholis (Kendall & Bedford, 1987). Another possible predator is the polychaete, Eulalia viridis (Moore & Kitching, 1939). Chthamalus spp. is also known to be displaced by Patella spp. and smothered by Mytilus spp. and algae at lower shore levels (Moore & Kitching, 1939). Empty barnacle cases provide homes for small periwinkles, , small bivalves and the isopod, Campecopea hirsuta (Fish & Fish, 1996). In order to protect themselves from changes in temperature, desiccation and a lowering of salinity, intertidal barnacles are usually able to close their aperture tightly (Moore & Kitching, 1939).
Biology References	Barnes & Barnes, 1965, Anderson & Southward, 1987, Crisp, 1950, Southward, 1964, Crisp & Patel, 1960, Stubbings, 1975, Crisp, 1955, Southward & Crisp, 1965, Bourget, 1977, Crisp & Bourget, 1985, Relini, 1983, Benedetti-Cecchi et al., 2000, Moore & Kitching, 1939, Southward, 1955, Crisp et al., 1981, Southward & Crisp, 1954, Barnes et al., 1963, Kendall & Bedford, 1987, Bassindale, 1964, Southward, 1964(b), Bassindale, 1964
Distribution and Habitat
Distribution in Britain & Ireland	A southern, warm-water species recorded on the south and west coasts of the British Isles as far north as the Shetland Isles. The species is less abundant along the channel towards The Isle of Wight, its eastern limit.
Global distribution	Occurs in The Black Sea, along most of the Mediterranean coast, and further south in Tunisia, Madeira, the Azores, and Cape Verde Islands. No recorded exist further south of this point.
Biogeographic range	Not researched	Depth range	Mid to lower eulittoral
Migratory	Non-migratory / Resident
Distribution Additional Information	Geographical distribution Crisp et al. (1981) described the distribution of Chthamalus stellatus and Chthamalus montagui. Chthamalus stellatus is abundant along western coasts of Britain and Ireland. It does not occur in the central Irish Sea. It occurs in northern and north-eastern Scotland including at exposed locations in Shetland.. In France it is abundant westwards from Roscoff, is absent from the Bay of St. Malo, and is less common east of Roscoff. Chthamalus stellatus occurs along Irish coasts from Antrim around to Wexford, although it only occurs in abundance along the west coast. The species is less abundant along the channel towards the Isle of Wight, its eastern limit. Individuals recorded as Chthamalus stellatus in the Indian and Pacific Ocean are, in fact, other species of the stellatus group. Vertical zonation Chthamalus stellatus is dominant over Chthamalus montagui at exposed sites (Southward, 1976; Crisp et al., 1981). Where the species overlap, Chthamalus montagui has a greater vertical distribution, extending above and below that of Chthamalus stellatus (Burrows et al., 1992) and, while Chthamalus montagui is more common between MHWS & MHWN, Chthamalus stellatus is abundant lower down at MTL and below (Pannacciulli & Relini, 2000). Chthamalus stellatus inhabits the lower half of the intertidal, but in wave-exposed or wet and shady places they occur higher up on shore (Crisp et al., 1981; Pannacciulli & Relini, 2000). Physical factors such as exposure to seawater, desiccation and poor food supply limit the distribution of barnacles on the upper shore, whereas competition for space, predation and strong wave action limit the distribution at low and mid shore levels (Pannacciulli & Relini, 2000). The higher the species occurs up on the shore, the more resistant to desiccation influences they tend to be (Southward, 1955). The distribution of Chthamalus spp. is not affected by small increases in algal cover. Hawkins & Hartnoll (1982) found that the lower shore level limit was controlled by the presence of algal turf. However, rapid increases to 100 % algal cover can lead to a massive decline in barnacle populations to almost zero in a year or two (Southward, 1991). Substratum preference Barnacles attach themselves to hard, rough surfaces and are rarely found on chalk cliffs (Moore & Kitching, 1939). Moore & Kitching (1939) also suggested that this may be because the surface is smooth, washed away easily, or too porous (making it possible to be dried out from below). Temperature dependence / competition Chthamalus spp. prefer warm temperatures, whereas Semibalanus balanoides prefers low temperatures. This is reflected by the changes in their distribution with changes in climate. For example, in the severe winter of 1962-63 Chthamalus populations declined (Southward, 1967) while Semibalanus balanoides increased, and in the temperature rise of 1988-89 the trend was reversed (Southward, 1991). Long term trends are also evident. A decline in Chthamalus populations and an increase in Semibalanus balanoides occurred between 1962 and 1980, corresponding with a decrease in sea temperatures (Southward, 1991). Since 1980 there has been a general increase in Chthamalus spp. (Southward, 1991), maybe corresponding with gradual climate warming. Southward & Crisp (1954) noted that in 1948-51, during high temperatures in the British Isles Chthamalus spp. dominated over Semibalanus balanoides, and from 1952, during lower temperatures there was a resurgence of Semibalanus balanoides. Southward (1991) noted a two year phase lag between temperature trends and changes in barnacle abundance in Plymouth. Chthamalus spp. are more abundant in waters where the mean temperatures are above 10 °C for several months of the year (Southward, 1955).
Substratum preferences	Bedrock, Large to very large boulders, Artificial (e.g. metal/wood/concrete)	Physiographic preferences	Open coast
Biological zone	Mid Eulittoral, Lower Eulittoral	Wave exposure	Exposed
Tidal stream strength/Water flow	Very Strong (>6 kn), Strong (3-6 kn), Moderately Strong (1-3 kn)	Salinity	Full (30-40 psu)
Habitat Additional Information
AMBI Group (Borja et al., 2000)	I
Distribution References	Burrows et al., 1992, Hayward & Ryland, 1995b, Hayward et al., 1996, Moore & Kitching, 1939, Southward, 1976, Pannacciulli & Relini, 2000, Southward, 1955, Southward, 1991, Southward, 1967, Crisp et al., 1981, Southward & Crisp, 1954, Barnes, 1953, Barnes et al., 1963, Bassindale, 1964, Hawkins & Hartnoll, 1982, Bassindale, 1964
Reproduction/Life History
Reproductive type	Self-fertilization, Permanent hermaphrodite	Developmental mechanism	Planktotrophic
Reproductive Season	Early to mid-summer	Reproductive Location	As adult
Reproductive frequency	Annual episodic	Regeneration potential	No
Life span	3-5 years	Age at reproductive maturity	<1 year
Generation time	1-2 years	Fecundity	To ca 3,400 eggs per brood
Egg/propagule size	Insufficient information	Fertilization type	See additional information
Larvae/Juveniles Larval/Juvenile dispersal potential 100-1000m Larval settlement period Insufficient information Duration of larval stage 11-30 days
Additional Information	Before 1976 there was no distinction between Chthamalus stellatus and Chthamalus montagui. Since 1976 the existence of two separate species was recognised (Southward, 1976). Therefore, papers pre-1976 on Chthamalus stellatus have been recorded as for both species, below. Fertilisation Sexual maturity of Chthamalus stellatus was attained at a rostro-carinal diameter of 4.0-6.8 mm (O'Riordan et al., 1992). A pre-1976 observation by Southward & Crisp (1954) suggests that Chthamalus stellatus is able to breed in its first year after 9 to 10 months of settlement. Sperm is activated by the oviducal gland and transferred to the oviducal sac via the penis of a neighbouring barnacle (Barnes, 1989). 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' (Rainbow, 1984). Fertilised egg masses (egg lamellae) are brooded in the mantle cavity (O'Riordan et al., 1995), outside the body (Barnes, 1989). Barnacles generally reproduce by cross-fertilisation, but Chthamalus spp. have been shown to self-fertilise when isolated (Barnes & Barnes, 1950; Barnes & Crisp, 1956; Barnes, 1989); this usually occurs high up on shore. However, it has been noted that oviposition is delayed (Barnes & Barnes, 1950; Barnes, 1989) and the resulting eggs can be slightly abnormal and are considered less viable (Barnes, 1989). Breeding season The onset of the breeding season in the United Kingdom was noticed by Crisp (1950) to spread up the shore level over several months. Southward (1978) suggested that Chthamalus montagui breeds one to two months later than Chthamalus stellatus. However, Crisp et al. (1981) found little difference in SW Britain, with the main breeding peak in June and August (O'Riordan et al., 1995). Throughout the breeding season most individuals produce several broods (Burrows et al., 1992; O'Riordan et al., 1992), with a small percentage of the population remaining reproductively active throughout the year (O'Riordan et al., 1995); Barnes, 1989). After maturation of each brood ovarian and penis re-development takes place ( O'Riordan et al., 1995; Barnes & Barnes, 1965; Barnes & Barnes, 1977; Burrows, 1988; Anderson, 1994). According to Hines (1978) temperature and food availability are the main factors controlling the duration of the breeding season and the embryonic development rate. In fact, Burrows (1988, in Kendall & Bedford, 1987) found the onset of the breeding season to be correlated with a sea temperature of 10 °C or above. Breeding of Chthamalus stellatus and Chthamalus montagui usually takes place earlier in the year in continental Europe than in the British Isles (Relini & Matricardi, 1979; Relini, 1983; Miyares, 1986, all in O'Riordan et al., 1995). Crisp (1950) suggested that for Chthamalus montagui and Chthamalus stellatus in the United Kingdom, breeding commenced earlier with decreasing longitude and easterly longitude. However, in the Mediterranean the breeding season usually occurs in July and August (Mizrahi & Achihuv, 1990, in O'Riordan et al., 1995). Breeding of Chthamalus stellatus in France occurs in April (Barnes, 1992), and correlates with mean air and sea temperatures of 11 - 12 °C, and maximum temperatures of 14 °C. Barnes (1992) found that at an upper temperature limit of 20 - 21 °C in the sea and 24 - 25 °C in the air reproductive activity decreased. Southward & Crisp (1956) noted that the interval between broods in Chthamalus stellatus and Chthamalus montagui became shorter at higher temperatures. Barnes & Barnes (1965) found that in high suspended solids and low salinity there was a decrease in the number of eggs per brood of Chthamalus stellatus in Europe. Older barnacles are able to breed at a smaller size than younger barnacles. For instance, experiments by O'Riordan et al. (1992) showed that in their first year Chthamalus stellatus and Chthamalus montagui breed once or more, and more than once thereafter. Chthamalus stellatus / Chthamalus montagui are very tolerant of high periods of emersion, yet Patel & Crisp (1960) found that when barnacles which were brooding eggs were kept out of the water, a second batch of eggs was not produced. Embryonic development In both Chthamalus stellatus and Chthamalus montagui it took approximately 23 days for embryos to develop completely in vivo at 15 °C (Burrows et al., 1992), whereas Burrows (1988, in Kendall & Bedford, 1987) found that at 15 °C it took 26 days, and Achituv & Barnes (1976) reported a value of 25 days, although the temperature is not known. Fecundity Burrows et al. (1992) found that the number of eggs per brood of Chthamalus stellatus ranged between 1,274 - 3,391 in Britain, depending on body size and weight. It was also noted by Burrows et al. (2000) that the fecundity generally increased with lower shore levels colonized, with estimations of 1-2 broods per year at high shore levels, 2 to over three at mid shore levels, and over 2 to over 4 at low shore levels. Fecundity in protected areas such as harbours is usually lower, possibly due to increased turbidity (Barnes, 1989). However, in Archachon (France) in highly turbid waters the effect was not so noticeable, probably due to higher nutrient concentrations (Barnes, 1989). Annual recruitment and lifespan Life span of Chthamalus stellatus / Chthamalus montagui is considered to be approximately 2-3 years (Southward & Crisp, 1950). However, growth is more rapid and the mortality rate is greater lower down on the shore (Southward & Crisp, 1950).Towards the northern limits of distribution annual recruitment is low (Kendall & Bedford, 1987) and they have an increased longevity (Lewis, 1964).
Reproduction References	Burrows et al., 1992, Barnes & Barnes, 1965, Crisp, 1950, Southward, 1976, O'Riordan et al., 1992, Barnes, 1989, Rainbow, 1984, O'Riordan et al., 1995, Crisp et al., 1981, Burrows, 1988, Anderson, 1994, Hines, 1978, Barnes, 1992, Patel & Crisp, 1960, Southward & Crisp, 1954, Barnes & Barnes, 1968, Southward & Crisp, 1956, Southward, 1978, Lewis, 1964