- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Biology and Ecology
- Water Tolerances
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Pathway Vectors
- Impact Summary
- Environmental Impact
- Risk and Impact Factors
- Gaps in Knowledge/Research Needs
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Chthamalus proteus Dando & Southward, 1980
Summary of InvasivenessTop of page
C. proteus is a small, tan intertidal barnacle. It typically occurs from the high to mid-intertidal zone particularly in sheltered embayments and harbours but also in semi-exposed locations along the open coast. A native of the Gulf of Mexico, Caribbean and the Southwest Atlantic, it has been accidentally introduced to the Hawaiian Islands, Midway, Guam and French Polynesia. It is a substrate generalist with a relatively short larval life span and time to first reproduction. This species is not on an alert list nor listed as a regulated pest. Its ecological impacts have been little studied, but in some locations, C. proteus attains high densities (approaching 100 percent cover) and can settle heavily on other intertidal organisms (Zabin, 2005). Field experiments in Hawaii indicate the native pulmonate limpet Siphonaria normalis is negatively impacted by the presence of C. proteus, and that settlement of other organisms may be inhibited by the barnacle (Zabin, 2005).
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Arthropoda
- Subphylum: Crustacea
- Class: Maxillopoda
- Subclass: Thecostraca
- Superorder: Thoracica
- Order: Sessilia
- Family: Chthamalidae
- Genus: Chthamalus
- Species: Chthamalus proteus
Notes on Taxonomy and NomenclatureTop of page
Chthamalus proteus was only recently separated from two other species, Chthamalus fragilis and Chthamalus bisinuatus, by Dando and Southward (1980), using morphological characteristics and enzyme electrophoresis. Specimens examined by the authors that were determined to be C. proteus included material referred to as Chthamalus stellatus bisinuatus, C. bisinuatis and C. fragilis. The separation of C. proteus from its congenors has also been supported by a molecular analysis using two mitochondrial genes (COI and 16S rRNA) (Wares, 2001).
DescriptionTop of page
C. proteus is a small (typically 6 mm shell length) tan to white intertidal barnacle. It is highly variable in external appearance; characteristics of the shell and opercular valves are changeable with age and environmental conditions. The orifice is usually kite-shaped, although less so than in C. montagui. In young individuals the articulations between pairs of terga and scuta appear to be nearly straight with the occuludent margin appearing almost perpendicular; however, this articulation is always sinuous internally and becomes more externally visible as the individual ages (Dando and Southward, 1980).
C. proteus was only recently separated from two other Chthamalus species, C. fragilis and C. bisinuatus, by Dando and Southward (1980). These two species co-occurwith C. proteus in the northern and southern portions of its range, respectively. Dando and Southward (1980) identified morphological characteristics, which, except in the case of very small individuals, can be used to confidently distinguish C. proteus from C. fragilis, which it superficially resembles. The ratio of the width of the adductor muscle insertion to the width of the scutum measured at the same level and the double occludent angle (Dando and Southward, 1980) are both greater in C.proteus than in C. fragilis. In addition, the ratio of the height to width of the first maxilla (Dando and Southward, 1980) is greater in C. proteus than in C. fragilis in most of the specimens measured. Illustrations of the variations in the morphology of terga and scuta (Dando and Southward, 1980) should be extremely useful in distinguishing this barnacle from other Chthamaloids. Descriptions in Dando and Southward (1980) detail further distinctions between C. proteus and several other congenors, including C. fragilis, C. angustitergum, C. binsinuatus, C. montagui and C. stellatus. Unfortunately, nearly all of these require dissection, making it difficult to distinguish between species in the field, especially between young, un-eroded specimens.
DistributionTop of page
The native range of C. proteus presumably extends from southern Florida in the Gulf of Mexico, throughout the Caribbean and into South America along Atlantic Coast as far as Parana State, Brazil. Dando and Southward (1980) report populations from Florida, Texas and Alabama in the USA, from numerous Caribbean Islands, from Belize, Panama and Columbia and from various sites in Brazil. They surmise that the range is continuous along the Gulf and Caribbean coasts of Mexico, although no records exist for this region. Dando and Southward (1980) also note an absence of specimens from Trinidad south to northeastern Brazil, corresponding to the low salinity area created by the Amazon and Orinoco rivers, but do not indicate whether adequate sampling of this area was indeed carried out.
C. proteus now occurs throughout most of the main Hawaiian Islands and has been reported from Midway Island, Guam, in the Marianas and Mangareva and Moorea, in French Polynesia. In its non-native range, it has been mostly reported from harbour areas, but in some locations it has spread into bays, lagoons, and fishponds as well as the open coast rocky intertidal. C. proteus may be elsewhere in the tropical and warm-temperate Pacific; many of these locations are not routinely surveyed and the resemblance of C. proteus to other Chthamaloid barnacles could result in this species going undetected in a new location for some time.
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Atlantic, Southwest||Widespread||Native||Not invasive||Zabin et al., 2007|
|Pacific, Eastern Central||Localised||Southward et al., 1998; Zabin, 2005; Zabin et al., 2007||First reported in 1993. Kauai, Oahu, Molokai, Maui, Hawaii Island.|
|Pacific, Western Central||Localised||Southward et al., 1998; Zabin, 2005||First reported in 1998. Midway, Guam, Mariana, Mangareva, Moorea.|
|USA||Present||Present based on regional distribution.|
|-Alabama||Present||Native||Dando and Southward, 1980||Dauphin Island|
|-Florida||Widespread||Native||Dando and Southward, 1980||Apalachee Bay, Alligator Port; south of St Petersburg Beach to Mullet Key; Naples.|
|-Hawaii||Localised||Introduced||1973 (not found) - 1993 (first||Invasive||Southward et al., 1998; Southward et al., 1998; Zabin, 2005; Zabin et al., 2007||Kaui, Oahu, Molokai, Maui, Hawaii Island.|
|-Texas||Widespread||Native||Dando and Southward, 1980||Rockport|
Central America and Caribbean
|Antigua and Barbuda||Localised||1970||Native||Southward, 1975||Rock, wooden piling, also common in the English Harbour.|
|Belize||Present||Native||Dando and Southward, 1980|
|Cuba||Present||Southward, 1975||Reported as C. bisinuatus by Southward. Esperanza. Collected by Pilsbry as C. fragilis.|
|Curaçao||Widespread||1920||Native||Southward, 1975; Dando and Southward, 1980; Zabin et al., 2007||Reported as C. bisinuatus by Southward (1975). On mangroves, shells, stones, boat hulls. Spaanse Water, St Jorisbaai, Piscadero Bay, Barbara Beach, Willemstad.|
|Grenada||Widespread||Native||Southward, 1975||Reported as C. bisinuatus by Southward (1975). Common on mangroves, wood pilings and rock.|
|Guadeloupe||Widespread||Native||Southward, 1975||Reported as C. bisinuatus by Southward (1975). Many on mangroves.|
|Jamaica||Widespread||Southward, 1975||Reported as C. bisinuatus by Southward (1975). Collected by Polisbry (1916) as C. fragilis. Kingston Harbour and Port Royal.|
|Martinique||Present||Native||Southward, 1975||Reported as C. bisinuatus by Southward (1975). Few on rock.|
|Netherlands Antilles||Widespread||Southward, 1975||Reported as C. bisinuatus by Southward (1975). Recorded in 1933 by Nilsson-Cantell as multiple species. Bonaire; Lagoen but not found in Lac.|
|Panama||Widespread||Native||Dando and Southward, 1980; Zabin et al., 2007||Colon (Galeta Point), Portobelo Bay|
|Puerto Rico||Present||Native||Southward, 1975; Zardus and Hadfield, 2005||Reported as C. bisinuatus by Southward (1975). Few on magroves near La Parguera.|
|Saint Lucia||Present||Native||Southward, 1975||Reported as C. bisinuatus by Southward (1975). Few in harbour.|
|Trinidad and Tobago||Widespread||1970||Native||Southward, 1975; Dando and Southward, 1980||Reported as C. bisinuatus by Southward (1975). Tobago, few on rocks; Trinidad, on rock and wood, common to all intertidal localities, Port of Spain, Scotland Bay, Monos Island, Galera Point and Balandra Bay.|
|United States Virgin Islands||Widespread||1939||Southward, 1975; Zardus and Hadfield, 2005||Reported as C. bisinuatus by Southward (1975). Last reported by Nilsson-Cantell as C. fragilis. St Thomas; Charlotte Amalie; Brewers Bay; Range Cay; St John.|
|Brazil||Present||Present based on regional distribution.|
|-Bahia||Widespread||Native||Zabin et al., 2007||Caravelas on mangroves, cement structures, basalt.|
|-Rio de Janeiro||Localised||Native||Zabin et al., 2007||Camboinhas, Niteroi.|
|-Sao Paulo||Localised||Native||Zabin et al., 2007||Ubatuba, granite rock|
|Colombia||Present||Native||Dando and Southward, 1980||Near Santa Marta|
|Venezuela||Widespread||Native||Southward, 1975||Reported as C. bisinuatus by Southward (1975). Margarita Island.|
|French Polynesia||Localised||Introduced||Zabin, 2005; Zardus and Hadfield, 2005||A Southward, personal communication in Zabin, 2005. Rikitea, Mangareva and Cook's Bay, Moorea.|
|Guam||Localised||Introduced||Zabin, 2005; Zardus and Hadfield, 2005||Apra Harbour|
|US Minor Outlying Islands||Localised||Introduced||Southward et al., 1998; Zabin, 2005; Zabin et al., 2007||Midway, Lagoon Wharf|
History of Introduction and SpreadTop of page
The first report of C. proteus outside of its native range was from Oahu, Hawaii in 1998 (Southward et al., 1998.). Through subsequent discussions with marine biologists in Hawaii, it appears that the barnacle was not present (or in numbers too low for detection) before 1973 (C Matsuda, Kapiolani Community College, Honolulu, Hawaii, personal communication, 2002) and that the earliest record of its presence is 1993, when it was found in Pearl Harbour but misidentified as the native Nesochthamalus intertextus (J Brock, University Of Hawaii, Honolulu, Hawaii, personal communication, 2000). In 1995, a photographer who was preparing a book on the common intertidal and shallow water organisms in Hawaii photographed it because it was widespread and abundant in Kaneohe Bay, on the windward side of Oahu (J Hoover, Honolulu, Hawaii, personal communication, 2002). He sent a specimen to barnacle taxonomist William Newman and the correct identification was then made. By 1996, C. proteus was reported from much of the south coast of Oahu, from harbour sites on Kauai and Maui and by 1998 from Midway Island and Apra Harbour in Guam (Southward et al., 1998). Subsequent surveys between 1998 and 2004 revealed that the barnacle was widespread on Oahu and less common, but present, on Hawaii Island and Molokai and on Mangareva and Moorea in French Polynesia (Zabin et al., 2007).
The pattern of distribution in its non-native range suggests that shipping is the main vector by which C. proteus is spread. In the Hawaiian Islands, the barnacle’s widespread distribution and high abundance on the island of Oahu suggests that it has been on this island the longest and/or has been introduced multiple times here. Nearly all large commercial and military vessels coming to Hawaii go directly to Oahu, so both vector and opportunity are greatest here. Goods are primarily transported to the other main Hawaiian Islands via inter-island barges from Oahu. The scenario of consequent spread of the barnacle from Oahu to other islands via shipping is also supported by the fact that C. proteus is mainly found in harbours on the other islands.
While ballast water is a possible means of transport for C. proteus, there is some evidence that larvae are somewhat sensitive to conditions of food and temperature (Zardus and Hadfield, 2005). Hull fouling could potentially transport large numbers of healthy, gravid adults and is thus likely a more effective method. C. proteus has been observed heavily fouling the hulls of the inter-island barges (Godwin, 2003). Zabin (2005) reported collecting C. proteus from small craft in its native range; this is another potential vector to the islands.
Although C. proteus could potentially spread throughout the Hawaiian Islands via natural larval dispersal (assuming favorable currents and sufficiently long larval life spans), vessel traffic between islands is likely a more efficient mode of inter-island transport. If barnacles on boat hulls release larvae in port, they are inoculating these areas with a larger and more regular supply of larvae than might be expected via natural dispersal. While vessel traffic may be largely responsible for the spread of this invader around an island, dispersal in the plankton to nearby sites ’down current’ from established populations may also play a major role.
Molecular analysis using sequences generated from mitochondrial DNA (COI) found four distinct clades from samples collected in the native range: one endemic to Panama, one endemic to Brazil and two from the Caribbean (Zardus and Hadfield, 2005). All four lineages were represented in the Hawaii population, suggesting multiple source populations. The majority of the Hawaiian specimens were of the Brazilian type; the Panamanian type was least represented. This, coupled with the observation that C. proteus is not found in areas of lowered salinity, led Zardus and Hadfield (2005) to suggest that a major route of introduction of C. proteus to the Pacific was around Cape Horn rather than through the Panama Canal. If this is the case, they suggest that perhaps the barnacle reached the more southern islands of the Pacific before coming to Hawaii. While it is true that C. proteus is not found in areas with long-term lowered salinity, it is able to tolerate full strength fresh water for at least 5 hours, the time it takes to transit the Panama Canal (C Zabin, University of Hawaii, Honolulu, Hawaii, personal communication, 2008); thus survival of the passage through the canal should be possible.
Zardus and Hadfield (2005) also noted that the different clades were not evenly distributed throughout the Hawaiian Islands, and suggested that, a) the spread of C. proteus around the islands was likely largely promoted by vessel traffic, rather than by natural larval dispersal from established populations, which would tend to homogenize populations; b) C. proteus may have been transported directly to the smaller islands rather than going through Oahu in some cases.
IntroductionsTop of page
|Introduced to||Introduced from||Year||Reason||Introduced by||Established in wild through||References||Notes|
|Natural reproduction||Continuous restocking|
|French Polynesia||<2004||Hitchhiker (pathway cause)||Zardus and Hadfield (2005)|
|Guam||<1997||Hitchhiker (pathway cause)||Zardus and Hadfield (2005)|
|Hawaii||Caribbean||1973-1993||Hitchhiker (pathway cause)||Yes||Southward et al. (1998); Zabin (2005); Zardus and Hadfield (2005)|
|US Minor Outlying Islands||<1998||Hitchhiker (pathway cause)||Southward et al. (1998)|
Risk of IntroductionTop of page
At the moment, except for the island of Oahu, in its invaded range C. proteus is primarily limited to harbourharbours (Zabin et al., 2007). Over time, it can be expected to increase in density within harbour areas due to continued inoculations from vessel traffic and larvae released by resident populations. From these initial points of entry and establishment, C. proteus can be expected to spread into adjacent protected and semi-protected waters.
Given its life history, specifically its short time to sexual maturity and a relatively short larval life span (Zabin et al., 2007), C. proteus is capable of rapid spread. Considering that C. proteus probably attained its present distribution around Oahu in 30 years or less, with favorable currents, the barnacle can be expected to become widely established in suitable habitats around the other main islands in Hawaii within 2–3 decades. Places less often reached by currents or by boat traffic, areas of high wave exposure, high algal cover and brackish waterways are at lower risk of invasion by C. proteus.
Boat traffic from Hawaii, Guam and from other locations in the Mariana Islands and French Polynesia where the barnacle is established is the most likely vector for continued spread of C. proteus to additional islands in the Pacific. Vessels most likely to spread the invader are those that have been in residence in infested waters for extended periods of time, as these are most likely to have collected high densities of adult barnacles. The barnacle has been reported from both large commercial (Godwin, 2003) and small pleasure craft (fiberglass and wooden sailboats and the fiberglass bottom of a Zodiac.).
Given its relatively wide environmental tolerances (Zabin et al., 2007), C. proteus should be able to invade other Pacific islands, particularly those without high cover by other sessile intertidal species. In areas with higher numbers of predators, such as fish or crabs that might prey on barnacles, distribution may be restricted to the high intertidal zone. Since it does not appear to settle readily on old coral rock (Zabin et al., 2007), distribution may also be limited by the availability of appropriate hard substrata on tropical islands lacking other types of shoreline rocks. Thus, C. proteus is likely to first appear on manmade materials in harbours and adjacent mangrove systems that do not receive continuous freshwater input.
Individuals of C. proteus have been found on commercial vessels preparing for departure from Hawaii to the US mainland (LS Godwin, Bernice P Bishop Museum, Honolulu, Hawaii, personal communication, 2000). Based on the latitudinal range displayed in the Atlantic, and its tolerance of waters at least as cold as 16º C (Zabin et al., 2007), this barnacle should be able to invade areas from approximately San Diego southwards. As Chthamalus species are often hard to distinguish in the field, it is entirely possible that C. proteus would go undetected for a period of time on the West Coast of the USA and Mexico, and perhaps is there now. Predicted rate of spread to the mainland is dependent on the amount of ship traffic with barnacle-fouled hulls, their residence time in port, and the perhaps reduced survival of C. proteus in cooler waters.
This barnacle is not currently on a quarantine list nor is it likely to be introduced intentionally to any new locations.
HabitatTop of page
Investigations by Zabin and others (Zabin, 2005; Zabin et al., 2007) indicate that habitat use is, in general, similar between sites in the native range and Hawaii. C. proteus is most abundant in the calm waters of bays and harbours. However, large, fecund individuals were found in semi-protected sites, sometimes in high densities. The barnacle was rarer in truly open-coast settings: it was not found it at any such sites investigated in Curaçao, Netherlands Antilles and at only two such sites in Panama. It was present at six high-energy sites on Oahu (Zabin et al., 2007), although in such locations it is typically found in low abundance or in protected microhabitats. On Oahu, the one exception to this general pattern is along wave-beaten shores at the Kaneohe Bay Marine Corps Base. There, it is found in relatively high abundance co-occurring with the native barnacle Nesochthamalus intertextus above rocks covered with encrusting coralline algae, the limpets Cellana spp. and the helmet urchin, Colobocentrotus atratus, a typical high-energy intertidal assemblage (Zabin, 2005). All of these individuals of C. proteus were quite small (mean approximately 4 mm rostrocarinal length), and it is not clear whether this is a viable population.
C. proteus appears to be a substratum generalist; it is found on rocks, metal and cement structures, plastic, mangroves, and barnacles and other hard-shelled organisms both in Hawaii and in its native range. At all locations surveyed in both its native and non-native range, C. proteus was found in highest densities on artificial substrata (Zabin et al., 2007). Such substrata are typically correlated with low to moderate energy sites, so the effects of substratum cannot be separated confidently from the effects of wave energy. It was conspicuously absent on old coral or limestone rock. Southward and Newman (1977) commented on the general unsuitability of coral rock for attachment by barnacles with membranous bases like C. proteus, hypothesizing that the porosity of this rock type leads to increased desiccation risk.
C. proteus is strictly an intertidal organism occurring from the high intertidal to about the zero tide mark: it has not been reported from the shallow subtidal zone. Zabin et al. (2007) found that its vertical distribution varies between sites, generally reflecting the difference in tidal excursion at each location, i.e.,higher in Hawaii than in Curaçao or Caribbean Panama and higher in wave splashed vs. calm areas. Brazil was an exception to this:at one site at a river mouth, C.proteus was restricted to the mid- to low-intertidal range, probably due to the presence of a fairly continuous freshwater lens bathing the high intertidal.
Although Zabin et al. (2007) did not determine its exact salinity tolerance, the barnacle is conspicuously absent from areas that have continuous freshwater input, both in its native range and in Hawaii. Earlier work reports C. proteus missing from areas with salinities lower than 22 ppt (Southward, 1975; Dando and Southward, 1980).
C.proteus appears to tolerate a fairly wide range of water temperatures: extreme highs of 38ºC recorded in shallow waters of the Galeta reef flat of Panama (Cubit 1990) and lows of 16ºC during some upwelling months in southeastern Brazil (Neto, 2003). It is also apparently able to survive in both clear and turbid waters and is highly tolerant of disturbed environments, growing well in polluted harbours and lagoons. Numerous individuals were surviving on an oiled seawall at Galeta, and several individuals were found settled on beach tar covering intertidal rocks in Curaçao (Zabin, 2005).
Habitat ListTop of page
|Coastal areas||Present, no further details|
|Intertidal zone||Principal habitat||Natural|
Biology and EcologyTop of page
Zardus and Hadfield (2005) used using sequences generated from mitochondrial DNA (COI) to examine population structure in C. proteus in its native and Pacific range. They found four distinct clades from samples collected in the native range: one endemic to Panama, one endemic to Brazil and two from the Caribbean. This population structure was present in the Pacific as well: all four lineages were represented in the Hawaii population, suggesting multiple source populations and little mixing via natural larval dispersal. Although all of the clades were represented in the Pacific specimens, not all clades were represented equally and not all were present on all islands. The Panamanian clade was least represented. Most of the Hawaiian barnacles fell into the Brazilian clade, suggesting this as a major source region or that barnacles of this genotype are surviving best in Hawaiian waters. Zardus and Hadfield (2005) found that genetic differences among islands were significant, although they accounted for only a small amount of the total genetic variation observed, the majority being explained by variability across all localities. Localities within each island did not significantly differ from one another and partitioning localities into three ship traffic classes (military, commercial, pleasure craft) explained only a tiny fraction of the total variation and was not significant.
C. proteus has many of the ’weedy‘ life history characteristics that make for a good invader: rapid growth following settlement, early onset of reproduction, year round production of propagules, quick larval development time, and the ability to spread via human mediated pathways. Generation time is also relatively short: Zabin et al. (2007) observed one barnacle, 6 weeks post-settlement, with eggs, and many barnacles with eggs within two months.
Like many barnacle species, chthamaloids are hermaphrodites. Fertilization is internal and developing eggs are brooded by the parent until they are ready to be released as swimming larvae. While self-fertilization has been reported in other Chthamalus species, it is not known whether C. proteus can self-fertilize.
In a two-year study, Zabin et al. (2007) surveyed the reproductive status of C. proteus monthly at two locations in Hawaii. Adult barnacles with developing eggs and un-hatched nauplii were found in varying abundance at all times of the year. Five distinct peaks of production were observed over the study period: in the spring and autumn of both 2002 and 2003 and winter 2001-2002. A less distinct peak in the winter of 2002-2003 was also observed. The peaks of production were approximately synchronous between the sites with a mean of 46% percent of the animals carrying propagules during peaks of production. At both sites, greater numbers of propagules were associated with larger shell size when tested by linear regression.
Data were also collected from single-date surveys of reproductive status at additional sites in Hawaii and in Curaçao, Panama and Brazil. The percentage of reproductive individuals across all sites was within the range seen in Hawaii, with the exception of three survey points in Brazil which were well above all others. Mean shell length was not appreciably different among the three regions, however fecundity per body size did vary with region. Hawaiian and Caribbean barnacles were similarly fecund relative to shell size, but Brazilian representatives produced greater numbers of propagules per shell size. Subsequent to these findings, average egg-length was compared between 30 individuals each from Camboinhas, Brazil and Pearl Harbour, Hawaii. Eggs in Hawaiian individuals averaged 166 µm (SD 11.4) in length whereas in Brazilian samples they averaged 183 µm (SD 17.9); these differences were statistically significant.
Zabin et al. (2007) also confirmed seven larval stages for C. proteus: six naupliar stages followed by a cyprid. The developmental period varied with temperature and diet. At low food concentration (Isochrysis galbana at 125,000 cells/mL) at 28°C, the earliest cyprids were seen on the ninth day, whereas at 25°C they were observed on the 17th day. At high food concentration (Isochrysis galbana at 250,000 cells/ml) there was no difference between temperature treatments, with the first cyprids seen on the eighth day. Fed a high concentration mixed algal diet (Isochrysis galbana and Skeletonema costatum at a total concentration of 250,000 cells/mL), cyprids also appeared on the eighth day at 28°C but two days later at 24°C.
There is no evidence based on field observations or experiments of obligative associations between C. proteus and other organisms. While the native pulmonate limpet Siphonaria normalis facilitates the settlement of C. proteus in some locations in Hawaii (Zabin and Altieri, 2007), the barnacle is also present in locations where the limpet is not found. Similarly, while individuals of C. proteus recruited in higher numbers to PVC plates coated with extract from the barnacle Balanus reticulatus than they did to plates coated with extract from conspecifics (Zabin, 2005), C. proteus can be found in abundance in the absence of B. reticulatus. The barnacle was found on mangrove prop roots (Avicennia sp. and Rhizophora spp.) both in Hawaii and its native range, but this is only one of many substrate types it uses (Zabin et al., 2007).
Essentially, in both its native and non-native range, the barnacle appears among the intertidal flora and fauna typical to each area: other barnacle species, limpets, snails, oysters, algae, sponges, tunicates and hydroids. Chthamalus angustitergum, a Caribbean native common on exposed coasts, co-occurs with C. proteus in more protected environments in the native range. These two barnacles were seen overgrowing each other in Curaçao and Panama. In Brazil, C. bisinuatus occurs in the upper strata of the intertidal zone from exposed to protected shores with C. proteus below and a wide zone of overlap between the two.
Without experimental work, it is not possible to confidently describe the fundamental (versus realized) ecological niche of C. proteus, but some observations about the barnacle are suggestive: it attains highest densities in a number of sites where it is the only sessile organism in the high intertidal zone (Zabin et al., 2007). In Hawaii, populations lower in the intertidal were frequently overgrown by oysters, and in Curaçao, where tidal range is very small, the barnacle was, at three locations, found buried but alive under layers of algae, hydroids, sponges and tunicates (Zabin et al., 2007). At one location in Hawaii, the lower limits of the distribution of C. proteus appear to be at least partially controlled by competition with algae. Barnacles were not present on or under the algae, but clean settlement plates attached to the substrate over the algae were readily settled on (C Zabin, University of Hawaii, Honolulu, Hawaii, personal communication, 2008). All of these observations suggest that C. proteus is not generally a good interference competitor for settlement space, but that it likely survives by being able to live in locations where few other organisms can (like the very high intertidal or turbid waters) and by being the first to arrive on new substrate. It may also be able to withstand periods of overgrowth by other organisms.
Water TolerancesTop of page
|Parameter||Minimum Value||Maximum Value||Typical Value||Status||Life Stage||Notes|
|Depth (m b.s.l.)||Optimum||-0.3-80 m tolerated. Not tested experimentally. Can occur throughout intertidal zone, depends on tidal range as well as wave splash (Zabin et al., 2007)|
|Salinity (part per thousand)||22||36||Optimum||Short periods of full freshwater tolerated. Tested tolerance up to 4 hours (Zabin, 2005)|
|Turbidity (JTU turbidity)||Optimum||Not quantified. Qualitative: occurs in muddy to full tropical open coast seawater (Zabin et al., 2007)|
|Velocity (cm/h)||Optimum||Not quantified. Qualitative: from protected harbours and lagoons to protected micro-habitats within high wave exposure rocky intertidal sites (Zabin et al., 2007)|
|Water temperature (ºC temperature)||Optimum||Not tested experimentally. Tolerated range of 16-38 from observation of existing populations (Zabin et al., 2007)|
Notes on Natural EnemiesTop of page
There is some suggestion, at least at one of the Hawaiian sites studied by Zabin et al. (2007), of size-dependent mortality, which may result from predation by a common native whelk, Morula granulata (Thaididae). The whelk is a generalist, readily consuming C. proteus and the native barnacle N. intertextus in the laboratory (V Fread, University of Hawaii, Honolulu, Hawaii, personal communication, 2008). These and other whelks were present at the open coast intertidal sites investigated in Hawaii, but were generally absent from the more typical fouling assemblages in harbours and embayments.
Predatory snails, including Morula spp., were found at a number of sites where C.proteus was present in Panama and at one site in Curaçao where C. proteus was absent, but C. angustitergum was present. In Brazil, the whelk Stramonita haemastoma is commonly found in the low intertidal zone on exposed shores, and wasobserved preying on C. proteus (FB Pitomo, Universidade Federal Fluminense, Niteroi, Brasil, personal communication, 2008).
Large grazers such as chitons and limpets which might inadvertently ingest or ‘bulldoze’ young barnacles off the substrata were found at a number of sites inthe Caribbean surveyed by Zabin et al. (2007). In Curaçao, these were nearly always present where the barnacle wasabsent, but in Panama, they co-occurred with the barnacle, although generally lower inthe intertidal zone. Hawaii has few chitons and its patellid limpets are generally restrictedto high-energy coasts, where C. proteus is not usually found. Fish and crabs may also be predators on C. proteus, but their importance and differences in predation between the sites is unknown.
As far as could be determined from observations, there is no clear indication of predation as a major control of the barnacle either in its native range or in Hawaii, although the barnacle’s success in fouling assemblages might be attributed to lowered predation in these areas. Grazing by chitons and limpets might be a factor in determining the lower limits of C. proteus in open coast settings in its native range; this is not likely to be important in Hawaii due to the rarity of chitons and the general restriction of patellid limpets to high wave exposure sites.
Means of Movement and DispersalTop of page
C. proteus could easily be transported intra-regionally via natural larval dispersal given favorable currents. Given its relatively short larval life span it is not likely to spread via currents over long distances. The most effective vector for continued spread both regionally and internationally is commercial and private vessels. While transport in ballast water is a potential mechanism, hull fouling is the more probable mode.
Pathway VectorsTop of page
|Ship ballast water and sediment||Potential vector for larvae; speculative, not observed||Yes||Yes|
|Ship hull fouling||Frequency unknown; adults observed on boat hulls in native and invaded range||Yes||Yes||Zabin, 2005|
|Water||Potential vector for larvae from established populations.||Yes||Yes||Zabin, 2005; Zabin et al., 2007|
Impact SummaryTop of page
Environmental ImpactTop of page
The impacts of C. proteus on native organisms have not been fully investigated. No work has been done to date on the larval ecology of the barnacle and how larvae might impact other organisms. Impacts, if they exist, are likely to be the greatest in bays and harbours where larvae from established populations are retained. C. proteus sometimes settles heavily on the shells of the native whelk, Morula granulata, and on the limpets Cellana spp. (opihi) and Siphonaria normalis. The effects of this overgrowth have not been investigated. Of these three native species, only the opihi are of conservation significance, as they are under severe harvesting pressure.
Zabin and Altieri (2007) used field experiments and surveys in Hawaii to examine interactions between the barnacle and the pulmonate limpet S. normalis. In experiments in which the limpets were free to move between manipulated plots, limpets made their home scars in highest numbers on plots free of barnacles, at intermediate levels in plots with low numbers of barnacles and at lowest levels in plots with high numbers of barnacles. Zabin and Altieri, (2007) hypothesized that the presence of barnacles even in low numbers may interfere with the ability of the limpet to make a home scar and/or may not be optimal substrate over which to graze.
In another study, Zabin (2005) found no effects on a native barnacle, Nesochthamalus intertextus in terms of recruitment, growth or mortality following the removal of C. proteus from plots on a seawall in Hawaii where both species occur. There were also no effects of the native on the non-native barnacle in similar experiments.
However, Zabin, (2005) did find that Balanus reticulatus, another non-native barnacle in Hawaii, was negatively impacted by the presence of C. proteus in field experiments. When C. proteus was removed from settlement panels, B. reticulatus settled in higher numbers relative to control panels from which C. proteus was not removed. In a follow-up experiment, plates on which B. reticulatus was the numerical dominant and plates on which C. proteus was dominant were placed in the field for six weeks. B. reticulatus recruited in higher numbers to plates with high numbers of conspecifics relative to plates dominated by C. proteus, regardless of substrate availability. Zabin (2005) hypothesized that by recruiting rapidly to new substrate C. proteus is thus able to pre-empt settlement by the larger, faster-growing B. reticulatus. (Ironically, B. reticulatus and the limpet S. normalis appear to facilitate settlement of C. proteus. While an impact on another non-native species is unlikely to be of conservation consequence, this finding does suggest that C. proteus may interact with other intertidal organisms in a surprising and subtle manner.
Risk and Impact FactorsTop of page Invasiveness
- Proved invasive outside its native range
- Has a broad native range
- Abundant in its native range
- Highly adaptable to different environments
- Is a habitat generalist
- Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
- Pioneering in disturbed areas
- Tolerant of shade
- Highly mobile locally
- Long lived
- Fast growing
- Has high reproductive potential
- Has high genetic variability
- Modification of natural benthic communities
- Monoculture formation
- Threat to/ loss of native species
- Competition - monopolizing resources
- Highly likely to be transported internationally accidentally
- Difficult to identify/detect in the field
- Difficult/costly to control
Gaps in Knowledge/Research NeedsTop of page
Perhaps the most critical gap in knowledge is in understanding the impacts or potential impacts that this barnacle may have in its new range. Very little is known about its ecological role in its native range, including the true extent of that range. Among the most puzzling aspects of this invasion is why it did not occur until fairly recently, many decades after the first Caribbean organisms began to appear in Hawaiian waters. It could be instructive to know whether it was a change in the vector, the organism, the donor region, the host region or some combination of these that opened the door to this invasion.
ReferencesTop of page
Dando PR; Southward AJ, 1980. A new species of Chthamalus (Crustacea: Cirripedia) characterized by enzyme electrophoresis and shell morphology: with a revision of other species of Chthamalus from the Western Shores of the Atlantic Ocean. Journal of the Marine Biological Association of the United Kingdom, 60:787-831.
Pilsbry HA, 1916. The sessile barnacles (Cirripedia) contained in the collections of the US National Museum; including a monograph of the American species. Bulletin of the United States National Museum, 93.
Southward AJ; Burton RS; Coles SL; Dando PR; DeFelice R; Hoover J; Parnell PE; Yamaguchi T; Newman WA, 1998. Invasion of Hawaiian shores by an Atlantic barnacle. Marine Ecology Progress Series, 165:119-126.
Southward AJ; Newman JA, 1977. Aspects of the ecology and biogeography of the intertidal and shallow-water balanomorph cirripedia of the Caribbean and adjacent sea-areas. FAO Fisheries Report. Rome, Italy: FAO, 407-425.
Zabin CJ; Altieri A, 2007. A Hawaiian limpet facilitates recruitment of a competitively dominant invasive barnacle. Marine Ecology, Progress Series, 337:175-185. http://www.int-res.com/abstracts/meps/v337/p175-185/
Zabin CJ; Zardus J; Pitombo FB; Fread V; Hadfield MG, 2007. A tale of three seas: consistency of natural history traits in a Caribbean-Atlantic barnacle introduced to Hawaii. Biological Invasions, 9:523-544.
ContributorsTop of page
04/01/08 Original text by:
C Zabin, Smithsonian Environmental Research Center & Univ. California, Davis Romberg Tiburon Cen. for Env. Stud, 3152 Paradise Drive, Tiburon, CA 94920, USA
Distribution MapsTop of page
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