Estuarine, Coastal and Shelf Science 60 (2004) 729e735

www.elsevier.com/locate/ECSS

Barnacle distribution in Lough Hyne Marine Nature Reserve:a new baseline and an account of invasion by the introduced

Australasian species Elminius modestus Darwin

Jennifer Lawson, John Davenport), Alan Whitaker

Department of Zoology and Animal Ecology and Environmental Research Institute, University College Cork,

Lee Maltings, Prospect Row, Cork, Republic of Ireland

Received 23 December 2003; accepted 23 March 2004

Abstract

The distribution and abundances of the following species of barnacles were established in autumn 2001 within the Lough HyneMarine Nature Reserve: Cthamalus stellatus, Cthamalus montagui, Semibalanus balanoides, Elminius modestus, Balanus crenatus andVerruca stroemia. The results of the survey showed a clear distinction between the vertical distribution and the abundance of

barnacle species inside Lough Hyne, and those sites sampled in the Rapids and outside the Lough. The Lough is now dominated bythe introduced Australasian species E. modestus. This species was first recorded outside Lough Hyne in 1956. By 1988 it was foundoccasionally throughout the Lough, and appreciable numbers were recorded in 1990e1991. It has now replaced all other species in

some parts of the North Basin. At sites subject to freshwater influence it is totally dominant, including in the highly sheltered Goleensite where intertidal barnacles have not previously been recorded. It is suggested that, once established in the North Basin, thesheltered nature of the Lough, combined with high summer temperatures and limited circulation, fostered retention of larvae and

heavy spatfall of E. modestus.� 2004 Elsevier Ltd. All rights reserved.

Keywords: Lough Hyne Marine Nature Reserve; barnacles; invasion; Elminius modestus; introduced species; invasive species

1. Introduction

Lough Hyne is one of the most studied marineenvironments in the world, having attracted investiga-tors since the 19th Century. The Lough consistentlyexhibits general salinities of 34.6e34.8 (Kitching, 1991)and is regarded as fully marine. It is a statutory marinenature reserve and it is important that marine reservesbe monitored, so that trends or changes in the flora andfauna are identified (Costello and Myers, 1991; Littleet al., 1992).

This study was prompted by apparently increaseddensities of the introduced Australasian barnacle speciesElminius modestus Darwin on the shores of the Lough.The objectives of the study were to investigate the

) Corresponding author.

E-mail address: jdavenport@zoology.ucc.ie (J. Davenport).

0272-7714/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.ecss.2004.03.011

distribution of all barnacle species around LoughHyne’s shores, looking in particular at the introducedspecies, and determining how the distribution might berelated to environmental factors.

Elminius modestus is a small sessilian barnacle, nativeto New Zealand and southern Australia, and introducedto European waters by ships or flying boats prior to1943 (Bishop, 1947; Stubbings, 1950). It has sincebecome well established and widespread in Europeancoastal waters (Flowerdew, 1984). Elminius modestuswas reported to be present in small numbers outside (butnot inside) Lough Hyne in 1956 by Beard (1957); thiswas also the first record of its presence in Ireland.Further investigation indicated that it had initially beenintroduced by shipping somewhere in the sheltered inletsof Cork harbour, probably during 1955 (Crisp, 1958).

In 1955 Ebling et al. (1960) carried out an extensivesurvey of the distribution of common plants and animalson the shores of Lough Hyne. This included mapping of

730 J. Lawson et al. / Estuarine, Coastal and Shelf Science 60 (2004) 729e735

the distribution and abundances of Cthamalus stellatus(which had not then been differentiated into Cthamalusmontagui Southward and Cthamalus stellatus Poli), andSemibalanus balanoides Linnaeus. Elminius modestus wasnot present either in the Lough or the sites surveyed inBarloge Creek at that time.

Little et al. (1988) were the first to record the presenceof Elminius modestus inside the Lough. They also differ-entiated the chthamalids into Cthamalus stellatus andCthamalus montagui and found no significant differencein distributions between the two surveys as far as chtha-malids were concerned. However, they and Little et al.(1992) found general barnacle cover to have increasedconsiderably between 1955 and 1991 due to a consistentincrease in Semibalanus balanoides between years and thearrival of E. modestus. Little et al. (1992) recorded E.modestus from most parts of the Lough (they did notstudy the Rapids or Barloge Creek), but in general thespecies’ numbers were equal to or less than S. balanoides.

The sites examined in the present study allow effectivecomparison with these earlier investigations and the re-sults obtained permit identification of changes in densityand distribution of barnacles over the last 10e15 years.The data also form the most wide-ranging and detailedavailable survey of barnacles within Lough Hyne andprovide a quantitative baseline for future studies.

2. Materials and methods

Lough Hyne (51(30# N, 9(18# W) is situated on thesouth coast of County Cork, Ireland. A total of 17 siteswere sampled (Fig. 1 and Table 1) in summer 2001. Tenof these were located within the Lough, four at theRapids, and another three in Barloge Creek. These siteswere chosen to encompass the range of habitats found atLough Hyne, and also to coincide where possible withlocations previously sampled (Ebling et al., 1960; Littleet al., 1992). The location of each of the sites wasrecorded (Table 1) using Garmin GPS for future refer-ence purposes.

To determine the vertical distribution, and relativeabundance of the barnacle species, three replicate tran-sect surveys were carried out at each site. Surveyswere conducted in a vertical, contiguous manner, using10!10-cm quadrats, and encompassed the range of dis-tribution of the barnacles from upper to lower shore. Inmost cases the shores were near-vertical, so that 10-cmquadrats corresponded closely with 10-cm changes invertical height. At the Goleen (Site 4) the shore slopewas shallow and in this case (for calculation of kite dia-gram coordinates), it was assumed that the slope wasconsistent over the distributions of the barnacles. Withineach quadrat the numbers of each barnacle species werecounted and recorded. Shore heights were also estab-lished for each site, relative to chart datum, using

cross-staff and pole. Note that the tidal range withinLough Hyne is far less than outside. Information on thehydrography of Lough Hyne is available from previousstudies (Bassindale et al., 1957; Kitching, 1991).

Salinity measurements were taken, for each site,using a Goldberg refractometer accurate to a salinity of

Fig. 1. Map of sampling sites. Lough Hyne’s general location is close

to 51(30#N, 9(18#W. Irish National Grid coordinates are given at the

bottom right of the figure. Precise GPS latitude and longitude values

for the 17 sites are given in Table 1.

Table 1

Names, identifying numbers and precise GPS locations of sites shown

in Fig. 1

1. North Wall N 51(30.352# W 9(18.043#2. Freshwater Hill N 51(30.380# W 9(18.388#3. Kelly’s Pier N 51(30.264# W 9(18.488#4. Goleen N 51(29.805# W 9(18.150#5. Goleen Cliff N 51(29.881# W 9(18.139#6. North Labhra N 51(30.080# W 9(18.139#7. Southeast Labhra N 51(30.070# W 9(18.007#8. South Castle N 51(30.118# W 9(17.964#9. Northwest Castle N 51(30.134# W 9(18.048#

10. Whirlpool Cliff N 51(30.067# W 9(17.741#11. Top of Rapids N 51(29.992# W 9(17.756#12. Middle of Rapids N 51(29.971# W 9(17.747#13. Lower Rapids N 51(29.928# W 9(17.743#14. Dromadoon N 51(29.976# W 9(17.73315. Barloge Creek N 51(29.791# W 9(17.696#16. Barloge Quay N 51(29.685# W 9(17.776#17. Bullock Island N 51(29.597# W 917.570#

731J. Lawson et al. / Estuarine, Coastal and Shelf Science 60 (2004) 729e735

1. Where possible, two salinity recordings were made;one after a dry period and another after a rainy period.Readings were taken at the sea surface and at depths of5, 10 and 20 cm. At points where there were freshwaterinputs (Goleen, F.W. Hill, and Kelly’s Pier), readingswere also taken at depths of 1 and 2 cm.

3. Results

The results are summarised here. The full barnaclespecies count data and other relevant information isheld in two places: the library of the Marine BiologicalAssociation of the United Kingdom and the LoughHyne data archive of the Department of Zoology,Ecology and Plant Science, University College Cork.

The results of this survey showed a clear distinctionbetween the distribution and abundance of barnaclespecies inside Lough Hyne, and those sites sampled inthe Rapids and outside the Lough. Fig. 2 shows thatElminius modestus was by far the most dominantbarnacle species inside Lough Hyne in terms of bothabundance at each site and distribution around theLough. At sites of significant freshwater input an evengreater dominance could be seen. Three such sites areFreshwater Hill (2), Kelly’s Pier (3) and Goleen (4). Atthese sites E. modestus was completely dominant andoccurred to the exclusion of all other species in someinstances. At Freshwater Hill, E. modestus was the onlybarnacle species present. At Kelly’s Pier the only otherspecies found comprised a few Semibalanus balanoides atthe bottom of the transect. At the Goleen site E.modestus was again the only intertidal species present,but Balanus crenatus Bruguiere and Verruca stroemia(O.F. Muller) were found on large submerged stones atthe base of the transect. Surface salinity levels at allthree of these sites (but none of the others) were oftensubstantially reduced below the general 34 of the Lough,though more so during or after periods of rain. Underconditions of strong freshwater inflow at FreshwaterHill (2) the entire (shallow) water column was fresh atlow tide. Surface films (of varying thickness) of very lowsalinity (0e5) spread to Kelly’s Pier (3), so barnacles atthese sites were regularly exposed to low salinity,especially on the prolonged ebb tide of the Lough.

Other noteworthy features of barnacle distributionswithin the Lough were the dominance of Elminius mod-estus at the Castle Island sites (6e9) as well as peripheralsites 1e11, and the distribution of Verruca stroemia. Thelatter species was present at most sites (except CastleIsland) from the Rapids to the North Wall (1). Althoughit is a widespread species from the Mediterranean toNorway (Hayward and Ryland, 1995), it has attractednegligible attention before in studies of the Lough.

Vertical distribution and abundances of barnacles atthe Rapids and Barloge Creek sites were very different.

The Middle of Rapids (12) and Dromadoon (14) siteswere located opposite each other and displayed similarpatterns of distribution and abundances. The species atthese sites showed fairly even distributional ranges andabundances. Chthamalus montagui was present over thegreatest vertical range and was present at its highestabundances at the mid/upper shore levels. Chthamalusstellatus, Balanus crenatus and Verruca stroemia domi-nated the lower shore, with C. stellatus extending to themid shore level and displaying its highest abundance inthe quadrats where the numbers of C. montagui dropped.

At the Lower Rapids (13) site all species presentdisplayed similar vertical distributional ranges, butSemibalanus balanoides was clearly the most abundant.Elminius modestus had its highest abundance at the mid/lower shore level where S. balanoides began to fade out.There were also high abundances of Verruca stroemia onthe lower shore. This same pattern of distributionalrange and dominance amongst species was found at theBarloge Creek site (15), which is the closest outside siteto the Rapids.

At Barloge Quay (16) the vertical distributionalranges for Elminius modestus, Semibalanus balanoides,and Chthamalus montagui were again similar to eachother. However, C. montagui was restricted more to themid-shore than the other two species, but there it wasdominant. Elminius modestus and S. balanoides showedthe same vertical range of distribution, but S. balanoideswas by far the more abundant of the two species at thissite. At the mid/lower shore level S. balanoides andChthamalus stellatus dominated in terms of abundance.As would be expected, B. crenatus showed the greatestabundance at the lowest intertidal level sampled at thissite.

At Bullock Island (17), Elminius modestus and Semi-balanus balanoides again had almost identical ranges ofvertical distribution, but S. balanoides was dominant interms of abundance on the mid/upper shore levels.Elminius modestus had its highest abundances on thelower/mid shore level where S. balanoides began todecrease. Cthamalus montagui and Chthamalus stellatusalso had higher abundances than E. modestus at the mid-shore level; with C. stellatus the more dominant of thechthamalids on the mid/lower section of shore and C.montagui becoming more dominant on the mid/uppershore. Verruca stroemia and Balanus crenatus were alsopresent on the lower shore and V. stroemia was slightlythe more abundant of the two species.

4. Discussion

The results of this survey clearly show that Elminiusmodestus is now by far the most dominant barnaclespecies inside the Lough. However, the species, althoughpresent, is not dominant in the Rapids or Barloge Creek

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Fig. 2. Vertical distribution of barnacles in Lough Hyne in summer 2001. Abundance data (linear scale from 0 to 10 000 barnacles m�2) are presented

as kite diagrams. EM, Elminius modestus, SB, Semibalanus balanoides, CM, Cthamalus montagui, CS, Cthamalus stellatus, BC, Balanus crenatus, VS,

Verruca stroemia. Numerals on each diagram correspond with sites described in Table 1 and Fig. 1.

733J. Lawson et al. / Estuarine, Coastal and Shelf Science 60 (2004) 729e735

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Fig. 2 (continued )

outside Lough Hyne. By referring to previous studies ofthe distribution and abundance of barnacle species atLough Hyne (Ebling et al., 1960; Little et al., 1988,1992), temporal changes in relative abundances can beidentified. Elminius modestus was not recorded in theLough in Ebling’s survey in 1955; at that time the Loughwas dominated by chthamalid species, while Semi-balanus balanoides was absent from many of the sitessampled within the Lough (Ebling et al., 1960). Littleet al. (1988) reported occasional E. modestus at the northend of the Lough. When Little et al. (1992) resurveyedthe sites of Ebling et al. in 1990, E. modestus was presentat all sites except for one, Goleen (4). However, it wasnot the dominant species and its abundances anddistribution were similar to those recorded for thechthamalids and S. balanoides. Since that time thenumbers and dominance of E. modestus have dramat-ically increased to the levels recorded in the presentsurvey. There are a number of factors that may haveencouraged the proliferation of E. modestus within theLough; these include salinity, shelter, elevated summerwater temperature (Lough Hyne shows pronouncedseasonal thermal stratification in the Western Troughand western portions of the South Basin; Rawlinsonet al., in press) and an enclosed space that mayretain larvae, allowing a competitive species such as E.

modestus to increase rapidly under favourable condi-tions.

Elminius modestus has a longer season of reproduc-tion and continuous settlement than any other barnaclespecies in British/Irish waters (Crisp and Chipperfield,1948). Barnacle recruitment is variable because it isdependent on a suite of environmental and biologicalfactors, including wind direction, temperature, latitude,light, feeding, age, size, crowding, seaweed cover andpollution (see Southward, 1987 for review). Successdepends on settlement being followed by a period offavourable weather (Barnes, 1989). Elminius modestus isa cross-fertilising hermaphrodite, which can breed al-most continuously throughout the year. Under favour-able conditions it has been known for broods to bereleased every 10 days. However, O’Riordan andMurphy (2000) found that ovaries were not well-developed in nearby Cork Harbour during wintermonths. Cyprid larvae were found on the shore betweenMay and October. Newly metamorphosed E. modestusgrow rapidly and can reach maturity in about 8 weeks.Release of Semibalanus balanoides larvae takes placebetween February and April with peak settlementbetween April and June (Fish and Fish, 1996). Elminiusmodestus has the ability to settle at higher shore levelsthan S. balanoides and also in the subtidal zone (Foster,

734 J. Lawson et al. / Estuarine, Coastal and Shelf Science 60 (2004) 729e735

1971). These adaptations, together with the widetemperature range tolerated during larval developmenthave contributed to the species’ success (Harms, 1984).

Preliminary results from intertidal settlement panels intheNorthBasin fromOctober 2000 toOctober 2001 showE. modestus to be extremely dominant in terms of cypridsettlement andmetamorphosis. The results so far indicatethat the settlement rate of E. modestus may be over 300times that of S. balanoides, with the highest settlementsoccurring in AugusteSeptember and in AprileMay(D. Watson, 2002, personal communication).

Low tide at the few localised sites of freshwater inputcan expose barnacles to very low salinities, in some casesdown to 0. The results of the present survey showedElminius modestus to be particularly dominant at thesesites, where it was sometimes the only barnacle speciespresent. Experiments have shown that E. modestus isparticularly tolerant of lowered salinities; it can adapt toconsiderably lower salinities than Semibalanus bal-anoides, even as low as 2.5 (Bhatnagar, unpublisheddata; Foster, 1970). The ability of E. modestus to remainactive in extremely low salinities may help to explain whyit has outcompeted the other species at the freshwaterinput sites. However, as the rest of the Lough is fullymarine, low salinity does not explain why E. modestushas become so dominant in the Lough as a whole.

The maximum fetch in the Lough is not more than1 km, so the shores are all very sheltered (Little, 1991).It has been noted in previous studies that Elminiusmodestus is not characteristic of exposed shores, where itis often sparsely distributed, and does not displace eitherSemibalanus balanoides or Chthamalus stellatus. It ismore successful in sheltered inlets and estuaries (Crispand Southward, 1959; Crisp, 1958; Foster, 1971; South-ward, 1987). The results found in the present survey areconsistent with these earlier observations, and help toexplain the marked difference in the relative abundanceof E. modestus inside the Lough compared with theRapids and Barloge Creek sites. The finding of E.modestus in quantities at the Goleen site appearsparticularly relevant, as the surveys of Ebling et al.(1960) and Little et al. (1992) showed no intertidalbarnacles whatsoever at this highly sheltered (andfreshwater-influenced) site.

Lough Hyne has an unusual tidal regime in which thetide floods for about 4 h and ebbs for about 8.5 h(Bassindale et al., 1957). This stems from the Lough fillingand emptying through the narrow, shallow Rapids. Theresulting strong ebb and flood currents in the Rapidsprobably account for the lower densities of Elminiusmodestus there, since the species is characteristic of lowenergy sites. The current can reach speeds of 3 m s�1 overthe sill of the Rapids during outflow (Kitching, 1991).However, atWhirlpoolCliff (10), which bears the brunt ofthe fast incoming current, E. modestus maintains itsdominance (Fig. 2), but these conditions only occur at

Whirlpool Cliff during inflow, which is of much shorterduration than the outflow, so that for most of the timeWhirlpool Cliff is sheltered from water movement.

In the summer months the temperature of the surfacewaters of the Lough rises considerably (Kitching, 1991).This increase in the temperature of the surface watersduring the summer months may be particularly favour-able for Elminius modestus, a warm-water species, andmay enhance its breeding success, thus contributing toits dominance within the Lough. It has been shownexperimentally that E. modestus has increasing repro-ductive success at higher temperatures (Harms, 1984).The rate of larval development in both E. modestus andSemibalanus balanoides is strongly influenced by watertemperature. Semibalanus balanoides is a boreal cold-water species and therefore optimum development of itslarvae occurs at lower temperatures of 6e12 (C,whereas the warm-water E. modestus has its highestsurvival at 24 (C. Elminius modestus begins to breedwhen the water temperature exceeds 6 (C, and sonauplii can be found in the plankton from May toOctober and substantial settlement takes place fromJune to October (Harms, 1984). It is conceivable thatglobal climate change has contributed to the success ofE. modestus and the relative decline of S. balanoides (cf.Occhipinti-Ambrogi and Savini, 2003), since Ireland isan area where Lusitanian and boreal species meet, but itis inevitable that the presence of an invasive species willconfuse any climate-related signals from native species.

Enclosed waters disperse pelagic larvae less readilythan open coastal waters. Thus the introduction of thesame number of Elminius modestus larvae into an areawhere the water exchange and dispersal is limited willresult in a more local and denser spat fall (Crisp, 1958).Whilst up to 90%of thewater in the SouthBasin ofLoughHyne is replaced by water from the Rapids in about tentides, in the North Basin 90% replacement takes anestimated 26e27 tides (Bassindale et al., 1957). LoughHyne, particularly the North Basin, is therefore an idealenclosed situation, favouring dense fall of E. modestuscyprids. It took roughly 30e35 years for E. modestus toprogress from its first foothold immediately outside theLough to presence (but not dominance) throughout theLough. It has only taken a further 10 years to becometotally dominant amongst barnacles in theNorthBasin. Itseems probable that this is due to the very low turnover ofwater in that basin. Also, recently completed planktonstudies (Rawlinson, personal communication) indicatethat there is a net input of biomass and numbers ofplankton at the Rapids during most tidal cycles. Therelatively slow initial rate of invasion of the Lough by E.modestus contrasts with its generally fast rate ofcolonisation of harbours and estuaries (e.g. Barnes andBarnes, 1960). It spread from the SE of England toShetland between 1943 and 1978 (Hiscock et al., 1978).However, in the latter cases it is probable thatmuch of the

735J. Lawson et al. / Estuarine, Coastal and Shelf Science 60 (2004) 729e735

colonisation was mediated by shipping, which repeatedlyintroduces propagules to the innermost parts of enclosedareas. In Lough Hyne shipping is not a factor,

The success of Elminius modestus poses other ques-tions. Little et al. (1992) noted that barnacle cover ingeneral had increased in the Lough between the 1960sand 1990 at the expense of macroalgal cover. This trendhas been enhanced in the last decade by the advance ofE. modestus, even though populations of a major algalgrazing invertebrate (the sea urchin, Paracentrotuslividus) have collapsed during the same period (Barneset al., 2002). The full impact of a new major suspension-feeding organism (which is also distributed subtidally inthe shallow North Basin) on the ecology of Lough Hyneis as yet unclear, but it seems certain that E. modestusfully merits the label of ‘invasive’, i.e. it is an introducedspecies that is ecologically harmful (see Boudouresqueand Verlaque, 2002 for definitions).

Acknowledgements

Declan O’ Donnell of the Wildlife Services kindlygave permission to carry out work in the Lough Hynemarine reserve. John Bohane is thanked for hiscontinuing support of research at the Lough. The firstauthor (J.L.) received much help from fellow studentsduring the course of the study.

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