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Poli's stellate barnacle (Chthamalus stellatus)

Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help

Summary

Description

An intertidal barnacle with six solid wall plates, an oval-shaped operculum opening, and a membranous base. Juveniles have a kite-shaped opercular opening. The rostral plate is relatively narrow, plates are of roughly equal size, and its rostral plate is not fused with the rostrolateral plates. Usually conical in shape, however when crowded may become tubular. It may reach a diameter of approximately 14 mm, depending on habitat, food availability and level on the shore. The tissue inside the opercular aperture is bright blue with black and orange markings.

Recorded distribution in Britain and 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.

Habitat

Recorded in the mid to low eulittoral zone on exposed rocky shores. Its vertical distribution overlaps with Chthamalus montagui and Semibalanus balanoides.

Depth range

Not relevant

Identifying features

  • Shell wall of six solid plates.
  • Oval-shaped operculum opening.
  • Joint between the terga and scuta crosses the centre line at one third or more of the distance towards the rostrum.
  • Tissue inside the operculum opening is usually bright blue with brown and orange markings.
  • Junction between the terga and scuta is convex towards rostral plate.
  • Shell base is membranous.

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).

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Biology review

Taxonomy

PhylumArthropoda
FamilyChthamalidae
GenusChthamalus
Authority(Poli, 1791)
Recent Synonyms

Biology

Typical abundanceHigh density
Male size rangeUp to 1.4cm
Male size at maturity
Female size rangeSmall(1-2cm)
Female size at maturity
Growth form
Growth rateca. 10-55
Body flexibilityNone (less than 10 degrees)
Mobility
Characteristic feeding methodActive suspension feeder, See additional information
Diet/food source
Typically feeds onGenerally feeds on plankton.
Sociability
Environmental positionEpifaunal
DependencyIndependent.
SupportsNone
Is the species harmful?No

Biology 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).

 

 

Habitat preferences

Physiographic preferencesOpen coast
Biological zone preferencesLower eulittoral, Mid eulittoral
Substratum / habitat preferencesArtificial (man-made), Bedrock, Large to very large boulders
Tidal strength preferencesModerately Strong 1 to 3 knots (0.5-1.5 m/sec.), Strong 3 to 6 knots (1.5-3 m/sec.), Very Strong > 6 knots (>3 m/sec.)
Wave exposure preferencesExposed
Salinity preferencesFull (30-40 psu)
Depth rangeNot relevant
Other preferencesNo text entered
Migration PatternNon-migratory / resident

Habitat 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).

Life history

Adult characteristics

Reproductive typeSelf-fertilization
Reproductive frequency Annual episodic
Fecundity (number of eggs)1,000-10,000
Generation time1-2 years
Age at maturity9 - 10 months
SeasonMay - August
Life span2-5 years

Larval characteristics

Larval/propagule type-
Larval/juvenile development Planktotrophic
Duration of larval stage11-30 days
Larval dispersal potential Greater than 10 km
Larval settlement periodInsufficient information

Life history 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
  • Lifespan 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).

Sensitivity reviewHow is sensitivity assessed?

Physical pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
Substratum loss
 High Moderate Moderate High
Barnacles are permanently attached to hard rough surfaces. Therefore, loss of substratum due to activities such as spoil dumping or land claim will result in loss of individuals in the area. If suitable substrata remains within the area, colonization of juvenile barnacles is possible. Intolerance is assessed as high. Recoverability is likely to be moderate (see Additional Information section below).
Smothering
 Intermediate High Low Moderate
Chthamalus stellatus / Chthamalus montagui have been shown to be relatively unaffected by smothering by oil. Monterosso (1930) showed experimentally that the species can survive complete smothering by petroleum jelly for approximately two months, by respiring anaerobically. Complete smothering caused by the Torrey Canyon oil spill yielded similar results; A few Semibalanus balanoides died, yet Chthamalus stellatus / Chthamalus montagui seemed unaffected, while at Booby's bay more than 90 % had managed to clear an opening in the oil film (Smith, 1968). Although oil had very little effect on individuals, it is likely that smothering by sediment can clog breathing apparatus. Recruitment to the smothered area will also be reduced. Therefore intolerance is assessed as intermediate. Recoverability is likely to be high (see Additional Information section below).
Increase in suspended sediment
 Low Very high Very Low Moderate
Barnacles are likely to be able to tolerate a slight increase in suspended sediment concentration. A large increase in siltation to 100 mg/l for one month is likely to block breathing apparatus and impose an energetic cost of cleaning the gills. Intolerance is therefore assessed as low. Recoverability is likely to be very high as feeding and respiratory structures are likely to be clear of particles within a short space of time.
Decrease in suspended sediment
 Tolerant Not relevant Not sensitive Not relevant
A decrease in suspended sediment concentration is unlikely to affect Chthamalus stellatus populations.
Desiccation
 Low Very high Very Low Moderate
Chthamalus stellatus is a warm water species, with its northern limit of distribution in Britain. It tends to be more tolerant to desiccation than Semibalanus balanoides. The higher the species occurs up on the shore, the more resistant to desiccation influences they tend to be (Southward, 1955). Cracks and crevices offer further protection from desiccation. Southward (1958) reported an internal temperature of 28.8 °C in an air temperature of 13.7 °C. Therefore, intolerance is assessed as low. Recoverability is likely to be very high (see Additional Information section below).
Increase in emergence regime
 Intermediate High Low Moderate
According to Hines (1978) temperature and food availability are the main factors controlling the duration of the breeding season and the embryonic development rate. With an increase in emergence, the period of time covered by the water would decrease, and the time available for feeding and breeding would also decrease. This is likely to reduce the growth rate and reproduction. There is also likely to be a shift downwards on the shore due to competition between Semibalanus balanoides. Intolerance is assessed as intermediate. Recoverability is likely to be high (see Additional Information section below).
Decrease in emergence regime
 Low High Low High
Barnacle populations are likely to be tolerant to a decrease in emergence. With a decrease in the emergence regime, the feeding time and breeding possibilities are likely to increase. Adults of Chthamalus stellatus can survive permanent submersion (Barnes, 1953). However, competition between Semibalanus balanoides is likely to play an important role in the changes in species distribution. It is likely that the distribution of Chthamalus stellatus will move further up the shore, with no noticeable difference in the range. Intolerance is assessed as low. Recoverability is likely to be very high (see Additional Information section below). 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.
Increase in water flow rate
 Low Very high Very Low Moderate
An increase in water flow rate is likely to lead to a higher growth rate and annual recruitment. Intolerance is assessed as low. Recoverability is likely to be very high (see Additional Information section below).
Decrease in water flow rate
 Low Very high Very Low Moderate
A decrease in the water flow rate is likely to lead to a decrease in food availability and recruitment. Intolerance is assessed as low. Recoverability is likely to be very high (see Additional Information section below).
Increase in temperature
 Tolerant* Not relevant Not sensitive* High
Chthamalus stellatus would be favoured by an increase in temperature based on the following information:
  • Chthamalus stellatus is a warm water species, with its northern limit of distribution in Britain. It tends to be more tolerant to temperature increases than Semibalanus balanoides.
  • Southward (1958) reported an internal temperature of 28.8 °C in an air temperature of 13.7 °C. Therefore, a slight increase in temperature can lead to a much larger increase in temperature inside the barnacle during exposure to air and the sun.
  • Since 1975 there has been a general increase in the abundance of Chthamalus stellatus (Southward, 1991), perhaps corresponding with gradual climate warming. Southward (1991) noted a two year phase lag between temperature trends and changes in barnacle abundance in Plymouth.
  • Chthamalus sp. is most abundant in waters where the mean temperatures are above 10 °C for several months of the year (Southward, 1955b). Burrows (1988, in O'Riordan et al., 1995) found the onset of the breeding season to be correlated with a sea temperature of 10 °C or above.
  • Southward & Crisp (1956) noted that the interval between broods in Chthamalus stellatus became shorter at higher temperatures.
    • Therefore intolerance to an increase in temperature is likely to increase reproduction, the rate of larval and embryonic development and, therefore, recruitment.
  • At an upper temperature limit of 20 - 21 °C in the sea and 24 - 25 °C in the air reproductive activity decreased (Barnes, 1992). Intolerance is assessed as tolerant* in the British Isles.
Decrease in temperature
 High Low High High
During the severe winter of 1962-63, over the majority of the species range, they were able to withstand the cold. However, greater mortalities were noted to occur a month or two after the coldest weather (Crisp, 1964). Chthamalus spp. populations declined (Southward, 1967) while Semibalanus balanoides increased, and in the temperature rise of 1988-89 the trend was reversed (Southward, 1991). A decline in Chthamalus spp. populations and an increase in Semibalanus balanoides occurred between 1951 and 1975, corresponding with a decrease in sea temperatures (Southward, 1991). Southward & Crisp (1954) noted that in 1948-51, during high temperatures in the British Isles Chthamalus spp. dominated over Semibalanus balanoides, and during 1951-52, 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). In fact, Burrows (1988, in O'Riordan et al., 1995) found the onset of the breeding season to be correlated with a sea temperature of 10 °C or above (Burrows et al., 1992).
  • At an upper temperature limit of 20 - 21 °C in the sea and 24 - 25 °C in the air reproductive activity decreased (Barnes, 1992 (3)). Southward & Crisp (1956) noted that the interval between broods in Chthamalus stellatus and Chthamalus montagui became shorter at higher temperatures (in 5).In both Chthamalus stellatus and Chthamalus montagui it took approximately 23 days for embryos to develop completely in vivo at 15 °C (4), whereas Burrows (1988, in O'Riordan et al., 1995) 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 (5).
    • intolerance to a decrease in temperature is assessed as high. Recoverability is likely to be low (see Additional Information section below).
    Increase in turbidity
    		 Low Very high Very Low Moderate
    Barnes & Barnes (1968) found that in high suspended solids and low salinity there was a decrease in the number of eggs per brood of Chthamalus stellatus / Chthamalus montagui. Fecundity in protected areas such as harbours is usually lower, possibly due to increased turbidity (Barnes, 1989). Intolerance is assessed as intermediate. Recoverability is likely to be moderate (see Additional Information section, below.)
    Decrease in turbidity
    		 Tolerant Not relevant Not sensitive Not relevant
    A decrease in turbidity is likely to lead to an increase in the quantity of flagellates available in the water column. Therefore, the species is assessed as 'tolerant'.
    Increase in wave exposure
    		 Tolerant Not relevant Not sensitive Not relevant
    Chthamalus stellatus colonizes exposed rocky shores. An increase in wave exposure is therefore unlikely to affect the species greatly. However, its vertical distribution has been found to increase with increasing wave exposure (Foster, 1971(b)).
    Decrease in wave exposure
    		 Intermediate Moderate Moderate High
    Chthamalus stellatus colonizes exposed rocky shores. A decrease in wave exposure below 'exposed' is likely to result in replacement of Chthamalus stellatus with Chthamalus montagui, which favours more sheltered environments. A decrease in the level of wave exposure may also cause a shift in the community towards fucoid algae, which prevent barnacle larvae settlement. Intolerance is assessed as intermediate. Recoverability is likely to be moderate (see Additional Information section below).
    Noise
    		 Tolerant Not relevant Not sensitive Not relevant
    Barnacles are unlikely to be affected by noise.
    Visual presence
    		 Tolerant Not relevant Not sensitive Not relevant
    Barnacles are unlikely to be affected by visual presence.
    Abrasion & physical disturbance
    		 Intermediate High Low Low
    Cracks and crevices offer protection from some abrasion. Small abrasive forces, such as erosion from suspended sediment, has been noted to cause a decrease in barnacle size (Relilni, 1983). On a larger scale, Gubbay (1983) showed that Chthamalus montagui could withstand a compressive force of 42 newtons (N) and a much lower tensile force of 7.4 N, perhaps equivalent to trampling pressure. It is likely, due to Chthamalus stellatus and Chthamalus montagui being morphologically similar, that these values would be similar for Chthamalus stellatus. However, larger forces are likely to be more harmful to individuals. Therefore, intolerance is assessed as intermediate. Recoverability is likely to be high (see additional information section below).
    Displacement
    		 High Moderate Moderate High
    Once the barnacle is fixed in place it is unable to attach again (Crisp, 1955). Intolerance to displacement is therefore assessed as high. Recoverability is likely to be moderate (see Additional Information section below).

    Chemical pressures

     IntoleranceRecoverabilitySensitivityEvidence/Confidence
    Synthetic compound contamination
    		 Intermediate Moderate Moderate Very low
    Barnacles have a low resilience to chemicals such as dispersants, dependant on the concentration and type of chemical involved (Holt et al., 1995). They are less intolerant than some species (e.g. Patella vulgata) to dispersants (Southward & Southward, 1978). However, the barnacle population suffered indirectly as a result of the mass mortality of grazers. The resultant bloom of algae, and growth of fucoids, within 6 months, grew over and killed surviving barnacles (Hawkins & Southward, 1992). Therefore, intolerance to synthetic chemicals is assessed as intermediate. Recoverability is likely to be moderate (see Additional Information section, below).
    Heavy metal contamination
    		 Low High Low Very low
    Barnacles accumulate heavy metals and store them as insoluble granules. No information is available as to the effects of heavy metals on Chthamalus stellatus, but a larger amount of information was found with respect to a barnacle from the same family, Semibalanus balanoides. It is possible that sensitivities to heavy metals may be similar in both species. Clarke (1947) investigated the intolerance of Semibalanus balanoides to copper, mercury, zinc and silver. He found that 90 percent of barnacles died when held in 0.35 mg/l Cu carbonate for two days. Zinc, mercury and silver killed 90 percent of barnacles in two days at concentrations of 32 mg/l, 1 mg/l and 0.4 mg/l respectively. Pyefinch & Mott (1948) recorded median lethal concentrations of 0.32 mg/l copper and 0.36 mg/l mercury over 24 hours for this species. Barnacles may tolerate fairly high level of heavy metals in nature, for example they are found in Dulas Bay, Anglesey, where copper reaches concentrations of 24.5 µg/l, due to acid mine waste (Foster et al., 1978). Therefore, intolerance is assessed as low. Recoverability is likely to be high (see Additional Information section, below).
    Hydrocarbon contamination
    		 Low High Low Moderate
    Chthamalus stellatus/ Chthamalus montagui have been shown to be relatively unaffected by smothering by oil. Monterosso (1930) showed experimentally that the species can survive complete smothering by petroleum jelly for approximately two months, by respiring anaerobically. Complete smothering caused by the Torrey Canyon oil spill yielded similar results; A few Semibalanus balanoides died, yet Chthamalus stellatus / Chthamalus montagui seemed unaffected, while at Booby's bay more than 90 % had managed to clear an opening in the oil film. On further examination these individuals were found to be in good condition, with no oil present in the gut (Smith, 1968).
    However, detergents used to clean up the oil lead to a decline in Chthamalus spp. populations. In areas which where large amounts of detergents had been used, there was much greater mortality, and in Kynance cove the population was wiped out completely (Smith, 1968). Therefore, intolerance to hydrocarbons is assessed as low. Recoverability is likely to be high (see Additional Information section, below).
    Radionuclide contamination
    		 No information Not relevant No information Not relevant
    Insufficient
    information.
    Changes in nutrient levels
    		 Intermediate High Low Low
    Little data exists on the effects of increased nutrients on barnacles. A slight increase in nutrient levels may be beneficial for barnacles by promoting the growth of flagellates. However, Holt et al. (1995) predict that smothering by ephemeral green algae is a possibility under eutrophic conditions. Intolerance to nutrient levels is assessed as intermediate. Recoverability is likely to be high (see Additional Information section, below).
    Increase in salinity
    		 Tolerant Not relevant Not sensitive Not relevant
    Chthamalids only occur in full salinity water, therefore an increase in salinity is unlikely to exert a noticeable effect. The species is recorded as not intolerant of an increase in salinity.
    Decrease in salinity
    		 High High Moderate Moderate
    Barnacles are able to acclimatise over a number of days to reduced salinity (Rainbow, 1984), with their closing response is triggered at a lower salinity (Moore & Kitching, 1939). However, the behavioural avoidance is associated with anaerobiosis and low metabolic activity (Barnes et al., 1963). 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 / Chthamalus montagui. If salinities decrease below 21 psu all cirral activity of barnacles normally associated with full salinity waters, ceases (Foster, 1971). Therefore, intolerance to a decrease in salinity is assessed as high. Recoverability is likely to be high (see Additional Information section, below).
    Changes in oxygenation
    		 High High Moderate Moderate
    Southward (1955) conducted experiments on the relationship of cirral activity in Chthamalus stellatus / Chthamalus montagui, connected with feeding and respiration, to decreased oxygenation, by passing nitrogen through the water at 6 ml per minute at 13 °C. He found that in all cases a decrease in oxygen concentration lead to a decrease in cirral activity and that, after 15 minutes, the mean cirral beat had decreased from 3.1 to 2.9 beats per second. After 30 minutes exposure, cirral beat had completely ceased and the barnacle remained inactive. It was further observed that the scuta and terga remained slightly open with the cirri often protruding.
    Barnacles have to obtain oxygen from the water through their cirri including by cirral beating in still water. Since cirri stop beating in response to lowered oxygen levels, it seems likely that intolerance will be high. Therefore, intolerance to oxygen levels is assessed as high. Recoverability is likely to be high (see Additional information section, below).

    Biological pressures

     IntoleranceRecoverabilitySensitivityEvidence/Confidence
    Introduction of microbial pathogens/parasites
    		 Intermediate High Low Low
    Healy (1986, in O'Riordan et al., 1992) observed the crustacean parasite, Hemioniscus balani, in Chthamalus stellatus and Chthamalus montagui in Ireland, although it was never present in Lough Hyne. However, Southward & Crisp (1954) found that although it attacks and sterilises Semibalanus balanoides individuals, it does not attack Chthamalids, at least not in the British Isles. Therefore, intolerance to microbial pathogens / parasites is assessed as intermediate. Recoverability is likely to be high (see Additional Information section, below).
    Introduction of non-native species
    		 Low High Low Moderate
    The Australasian barnacle Elminius modestus was introduced to British waters on ships during the second world war. Although the species does well in estuaries and bays, where it can displace Semibalanus balanoides and Chthamalus montagui, Chthamalus stellatus generally occurs in more exposed locations where Elminius modestus is likely to be less abundant or absent. Therefore, intolerance to non-native species is assessed as low. Recoverability is likely to be high.
    Extraction of this species
    		 Not relevant Not relevant Not relevant Not relevant
    Not relevant.
    Extraction of other species
    		 Low High Low Low
    Collection of intertidal algae may damage barnacles by abrasion from trampling. Intolerance is assessed as low. Recoverability is likely to be high (see Additional Information section, below).

    Additional information

    Southward & Crisp (1954) suggested that Chthamalus stellatus is able to breed in its first year after 9 to 10 months of settlement. 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)

    Importance review

    Policy/legislation

    - no data -

    Status

    Non-native

    Importance information

    -none-

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    Datasets

    1. Centre for Environmental Data and Recording, 2018. Ulster Museum Marine Surveys of Northern Ireland Coastal Waters. Occurrence dataset https://www.nmni.com/CEDaR/CEDaR-Centre-for-Environmental-Data-and-Recording.aspx accessed via NBNAtlas.org on 2018-09-25.

    2. Cofnod – North Wales Environmental Information Service, 2018. Miscellaneous records held on the Cofnod database. Occurrence dataset: https://doi.org/10.15468/hcgqsi accessed via GBIF.org on 2018-09-25.

    3. Fenwick, 2018. Aphotomarine. Occurrence dataset http://www.aphotomarine.com/index.html Accessed via NBNAtlas.org on 2018-10-01

    4. National Trust, 2017. National Trust Species Records. Occurrence dataset: https://doi.org/10.15468/opc6g1 accessed via GBIF.org on 2018-10-01.

    5. NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.

    6. OBIS (Ocean Biodiversity Information System),  2023. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2023-06-06

    7. Outer Hebrides Biological Recording, 2018. Invertebrates (except insects), Outer Hebrides. Occurrence dataset: https://doi.org/10.15468/hpavud accessed via GBIF.org on 2018-10-01.

    8. South East Wales Biodiversity Records Centre, 2018. SEWBReC Myriapods, Isopods, and allied species (South East Wales). Occurrence dataset: https://doi.org/10.15468/rvxsqs accessed via GBIF.org on 2018-10-02.

    9. South East Wales Biodiversity Records Centre, 2018. Dr Mary Gillham Archive Project. Occurance dataset: http://www.sewbrec.org.uk/ accessed via NBNAtlas.org on 2018-10-02

    Citation

    This review can be cited as:

    Riley, K. 2002. Chthamalus stellatus Poli's stellate barnacle. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 06-06-2023]. Available from: https://www.marlin.ac.uk/species/detail/1323

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    Last Updated: 28/01/2002