The Marine Life Information Network

Description

Recorded distribution in Britain and Ireland

A warm-water species recorded on the south and west coasts of Britain as far north as Orkney and along the Scottish east coast south to Aberdeen. The Isle of Wight is its eastern limit in the English Channel. It is relatively abundant on Irish coasts.

Global distribution

Crisp et al. (1981) noted that its distribution extends through the western and eastern Mediterranean and down the north African coast to Mauritania.

Habitat

Recorded in the high to mid eulittoral zone on exposed to moderately exposed rocky shores. Its vertical distribution overlaps with that of Chthamalus stellatus and Semibalanus balanoides.

Depth range

Identifying features

• Shell wall of six solid plates.
• Kite-shaped operculum opening.
• The joint between the terga and scuta crosses the centre line less than one third of the way down towards the rostrum.
• Tissue inside opercular aperture is usually blue/pale blue with brown and black markings.
• Junction between terga and scuta is concave 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, the more sheltered locations in which it was found and its different pattern of zonation (Southward, 1976).

Listed by

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Taxonomy

Biology

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 cirral beat frequency than those at lower levels. However, Southward (1955; 1964(b)) found no similar trends.
Southward (1955) found that there was no cirral beat of Chthamalus stellatus / Chthamalus montagui in still water and that cirral beating was only induced at a current of approximately 10 cm/sec. The cirral beating frequency is also related to temperature, as 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 of 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 cirral 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).

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 from dogwhelks due to their smaller size in comparison with Semibalanus balanoides and often higher position on the shore. Other predators which pull shells or cirri of barnacles off the rock include crabs, amphipods, shore fish such as shanny Lipophrys pholis, and sometimes herring gulls (Moore & Kitching, 1939). 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). Gubbay (1983) showed that Chthamalus montagui could withstand a compressive force of 42 N and a much lower tensile force of 7.4 N, and that a membranous base adhered to the substrate better than a calcified base. 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

Habitat Information

Geographical distribution. Crisp et al. (1981) have described the distribution of Chthamalus stellatus and Chthamalus montagui. Chthamalus montagui occurs all around the western seaboard of Britain and all around Ireland. It is absent from part of Liverpool Bay. It occurs in Orkney but not Shetland and extends south down the east coast of Scotland to Aberdeen. Its distribution on the east coast is more or less continuous, extending from the north of Scotland, along the west coasts of Britain and along all coasts of the Irish Sea. Records detailing its worldwide distribution are limited, but it is probable that their range extends further south to Mauritania, through the western and eastern parts of the Mediterranean Sea. It is rare or absent from offshore islands. It is common in the northern Adriatic and occurs at locations in the Aegean and Black Seas.

Vertical distribution. Chthamalus montagui is dominant over Chthamalus stellatus in more sheltered sites (Southward, 1976; Crisp et al., 1981; Burrows et al., 1992). Where their distributions overlap Chthamalus montagui has a greater vertical distribution above 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). Near its northern limit in Scotland Chthamalus montagui is limited to a narrow band at the top of the shore due to competition with Semibalanus balanoides (Kendall & Bedford, 1987), and the influence of lower temperatures. Poor settlement of Chthamalus spp. also usually occurs. The higher the species occurs up on the shore, the more resistant to desiccation influences they tend to be (Southward, 1955b). 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 distribution of Chthamalus spp. is not affected by small increases in algal cover. However, rapid increases to 100 % can lead to a massive decline in barnacle populations, declining to almost zero in a year or two (Southward, 1991). Hawkins & Hartnoll (1982) found that the lower shore level limit was controlled by the presence of algal turf.

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 and competition. Chthamalus spp. are warm water species, with their northern limit of distribution in Britain. They tend to be more tolerant to temperature increases and desiccation than Semibalanus balanoides. Southward (1976) found that in Cornwall and Devon, where the barnacle is common, it dominates the upper half of the barnacle zone. 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 temporary decrease in sea temperatures (Southward, 1991). Since 1981 there has been a general increase in Chthamalus (Southward, 1991), maybe corresponding with gradual climate warming. Southward & Crisp (1954) noted that in 1948-51, during high temperatures in the British Isles Chthamalus 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, 1955b).

Life history

Adult characteristics

Larval characteristics

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 Chthamalus stellatus and Chthamalus montagui, below.

Fertilization. Sexual maturity of Chthamalus montagui was attained at a rostro-carinal diameter of 4.4.5-6.4 mm (O'Riordan et al., 1992). Chthamalus montagui is able to breed in its first year (Burrows, 1988; Southward & Crisp, 1954), after 9 to 10 months of settlement (Southward & Crisp, 1954). 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). Barnacles generally reproduce by cross-fertilization, but Chthamalus has been shown to self-fertilize when isolated (Barnes & Barnes, 1958; Barnes, 1989); this usually occurs high up on shore. However, it has been noted that in self-fertilized individuals oviposition is delayed (Barnes & Barnes, 1958; Barnes, 1989) and the resulting eggs can be slightly abnormal and are considered less viable (Barnes, 1989). Egg masses (egg lamellae) are brooded in the mantle cavity (O'Riordan et al., 1995; Barnes, 1989).

Breeding season. 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/July and August. 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 the maturation of each brood ovarian and penis re-development takes place (O'Riordan et al., 1995; Barnes & Barnes, 1965; 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 of other Chthamalus species. 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 (Burrows et al., 1992). Southward & Crisp (1956) noted that the interval between broods in Chthamalus stellatus and Chthamalus montagui became shorter at higher temperatures. The onset of the breeding season was noticed by Crisp (1950) to spread up the shore level over several months. Brooding in Aberystwyth was noted to be from May or June to August (Kendall & Bedford, 1987), with approximately 80 % containing a naupliar mass. Cyprid settlement occurred from late July to early September at a sea temperature of 15.3 to 18.8 °C (Kendall & Bedford, 1987). In northern Spain, the brooding period tends to be longer, between April and early October, with 30 % containing a naupliar mass (Kendall & Bedford, 1987). The breeding period, period of larval settlement and density of recruits are all reduced near the northern limits of its distribution. Crisp (1950) suggested that for Chthamalus montagui and Chthamalus stellatus in the United Kingdom, breeding commenced earlier with decreasing longitude and easterly longitude. Breeding of Chthamalus stellatusand 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). In the Mediterranean, the breeding season usually occurs in July and August (Mizrahi & Achituv, 1990, in O'Riordan et al., 1995). Experiments by O'Riordan et al. (1995) showed that in their first year Chthamalus stellatus and Chthamalus montagui breed once or more, and more than once thereafter.

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; Burrows, 1988, in Kendall & Bedford, 1987). Chthamalus montagui will only breed if temperatures exceed 15°C (Patel & Crisp, 1960).

Recruitment and lifespan. Towards the northern limits of the species distribution annual recruitment is low (Kendall & Bedford, 1987) and individuals have an increased longevity (Lewis, 1964). The normal lifespan of Chthamalus stellatus / Chthamalus montagui at mid-shore level is considered to be approximately 2-3 years (Southward & Crisp, 1956). However, growth is more rapid and the mortality rate is greater lower down on the shore (Southward & Crisp, 1956).

Fecundity. Burrows et al. (1992) found that the number of eggs per brood for Chthamalus montagui ranged between 1,030 and 1,803 in Britain, depending on body size and weight. It was also noted by (Burrows et al., 1992) that the fecundity generally increased with lower shore levels colonized, with estimations of one to two broods per year at high shore levels, two to over three at mid-shore levels, and over two to over four at low shore levels.

Physical pressures

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Additional information

Policy/legislation

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Status

Non-native

Importance information