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Predicting the effects of marine climate change on the invertebrate prey of the birds of rocky shores

MICHAEL A. KENDALL,

1

,

2

* MICHAEL T. BURROWS,

2

,

3

ALAN J. SOUTHWARD

2

&STEPHEN J. HAWKINS

2

1

Plymouth Marine Laboratory, Prospect Place, Plymouth PL1 3DH, UK

2

MarClim Project, Marine Biological Association UK, Citadel Hill, Plymouth PL1 2PB, UK

3

Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, Oban, Argyll PA37 1QA, UK

By the end of the 21st century models of climate change predict that the air temperatureover most of the British Isles will increase by between 2 and 3

°

C and sea-level will rise by40–50 cm. Over that period it will become windier and mean wave height will increase, aswill the frequency of storms. These changes in climate and weather will impact the intertidalzone of the UK and will cause distribution changes in many of the common invertebratespecies that live there. Where these changes are severe they may well impact on patternsof distribution of ducks and wading birds. In the British Isles a number of organisms liveclose to their geographical limits of distribution. Some of these species might be expectedto extend their range as climatic restraints are relaxed. Species currently limited by cool sum-mers or winter cold will move northwards. In most cases the effects on the distribution ofwaterbirds will be small. For example, the replacement of the Northern Limpet

Patella vul-gata

by the Southern Limpet

P. depressa

is unlikely to adversely affect Eurasian Oystercatch-ers

Haematopus ostralegus

. Of wider concern is the possibility that as climate warms theabundance and productivity of brown algae will decrease. This is likely to have two signific-ant effects for waders. First, it would represent a loss of potentially rich feeding groundsfor species such as Ruddy Turnstone

Arenaria interpres

that feed on small easily desiccatedinvertebrates living on or below the seaweed. Secondly, as algae die or are broken away theresulting debris is exported to sediment habitats where it considerably boosts the

in situ

pro-duction of bacteria at the base of the food web. An increase in sea-level will only have a majorimpact on the extent of rocky shore invertebrate communities where shore topography pre-vents the upward migration of the biota. Where a seawall limits shores, for example, bio-logical production will be curtailed as the area available for colonization decreases. Increasesin the size of waves and the frequency of storms will mimic increasing exposure and therewill be a significant reduction in algal production in areas that are affected.

The majority of scientists agree that the Earth’s clim-ate is getting warmer. Analysis of global air temper-atures from 1856 to the present show the 1990s tobe the warmest decade and 1997 and 1998 as thewarmest years (Jones

et al

. 1999). Ocean temperatureshave increased in parallel with those of the atmos-phere. Long-term records from the English Channel(Fig. 1) show that from the early 1980s sea temper-ature increased slightly until 1990. During thefollowing decade there was an increase of almost

1

°

C. This was far greater than any change in the pre-vious 100 years. In its warm phase, annual mean seasurface temperature off Plymouth is 11.5–12.2

°

Cwhereas during its cold phase the correspondingtemperature is 10.0–11.5

°

C. As computer modelsforecast that by 2080 UK mean air temperatures willrise by between 1.5 and 3.2

°

C, the trend in inshoresea temperature is likely to continue. As global tem-perature rises, the volume of water in the oceans willexpand and the polar ice caps will reduce in volume.This will cause sea-levels to rise by a predicted worldaverage of 13 cm by 2020, rising to 40 cm by 2080.In some parts of the UK sea-level rises may be

*Corresponding author.Email: mak@pml.ac.uk

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Predicting effects of climate change on invertebrates

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partially offset by coastal sinking (Hulme

et al

.2002).

Given that there will be substantial changes in clim-ate in the coming decades it is necessary to makepredictions concerning the magnitude and natureof the changes to coastal biodiversity that will alsooccur. For some coastal habitats this might be diffi-cult, but predictions for changes in the biota of rockyshores are substantially aided by long running archivedata from a number of UK and European sourcesas well as by a rich literature on the biology of thecomponent species. The Marine Biodiversity andClimate Project (MarClim) looks at the long-termrecords of variations in the abundance of rocky shorespecies, analyses them simultaneously and makesmodels for the future biota of the UK. This projectbegan in mid 2001 and as yet full analyses are un-available. However, preliminary predictions forshallow water life around the coasts of Scotland havealready been made (Hiscock

et al

. 2001). Should awarming of the sea influence the abundance/qualityof the prey of waterbirds or change the biota of inter-tidal habitats in which they forage, local or evennational patterns of bird distribution will be affected.The qualitative nature of such changes is predictableand will exacerbate the altered patterns of distribution

that are already recorded as a response to milderwinters between the mid 1980s and the late 1990s(Rehfisch

et al

. 2004). Changes at overwinteringsites will be over and above any impact to Arctic-nesting species that might result from a compressionof breeding habitat (Rehfisch & Crick 2003). Herewe discuss the probable nature of changes to theinvertebrate fauna of the rocky seashore togetherwith predictions of the response of some waterbirds.

EFFECTS OF CLIMATE ON THE DISTRIBUTION OF ROCKY SHORE SPECIES

The geographical distribution of the dominantBritish and Irish intertidal rock species was mappedin the 1950s (Southward & Crisp 1956, Crisp &Southward 1958). The fauna includes a number ofcommon species that are either at or close to theirnorthern or southern geographical limits of distribu-tion. There has been little subsequent research tocontradict the conclusions of Hutchins (1947) andLewis (1964) that species with north–south patternsof distribution have their geographical limits set bytemperature. Lewis (1976) proposed that speciesclose to their northern distributional limits in the UKwere limited by the severity of winter conditions,whereas those approaching their southern limitof distribution were limited by summer conditions.Crisp (1964) demonstrated that in the particularlysevere winter of 1962/63 the range of a number ofsouthern species was reduced. Such extreme condi-tions undoubtedly serve as a check on the expansionof the range of a species but it is highly unlikely thatwinter conditions alone set distributional limits.

Lewis and his co-workers (Lewis

et al

. 1982,Kendall & Lewis 1986, Lewis 1986, 1996, 1999,Kendall & Bedford 1987) investigated the way inwhich climate affects a suite of dominant rocky shorespecies including the southern barnacle

Chthamalusmontagui

and the top-shells

Osilinus

(

Monodonta

)

lineata

and

Gibbula umbilicalis

. Studies on the tro-chids suggested that as species approached theirnorthern limit of distribution they spawned andrecruited over a far shorter season than in the centreof their range. Nevertheless, populations close totheir northern limits do produce gonads and spawnannually (Kendall & Lewis 1986) and animals trans-planted beyond their normal range can develop andspawn (Lewis 1986). Northern species at the south-ern edge of their range are unlikely to be limited bythe failure of gonad development, although their

Figure 1. (a) Annual variation in mean sea surface temperaturein the English Channel off Plymouth. The dashed line shows thesmoothed trend. From Meteorological Office Hadley Centre gridsquare 50–51°N, 4–5°W. (b) Long-term variability in theabundance of warm water barnacles of the genus Chthamalusand the cold water barnacle Semibalanus balanoides.

42

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reproductive season may well switch to an earliertime of the year (Bhaud 1982). In the case of thenorthern barnacle

Semibalanus balanoides

, at itsnorthern limit in the Arctic it spawns in mid summer(Feyling-Hansen 1953), in the centre of its range inApril–May (Kendall

et al

. 1985) and close to itssouthern limit in February/March (Barnes & Barnes1976). The distribution of this species on southernshores (Barnes & Barnes 1976), observations ofsettlement success (Kendall

et al

. 1987, Jenkins

et al

.2000) and experimental manipulations (Wethey1984, Jenkins

et al

. 1999) all suggest that desiccationof individuals recently settled from the planktonlimits its southerly extension.

C. montagui

is a southern species that reaches itsnorthern limit of distribution in northwest Scotland.Unlike

S. balanoides

,

C. montagui

has the potential tospawn successive broods of larvae whenever food andwarmth permit. M.P. Myares (unpubl. data) recordedthat in Spain larval settlement onto the seashoretakes place over much of the year. By contrast, Ken-dall and Bedford (1987) showed that in west Walesthere is only a single settlement period. In southwestEngland, Burrows

et al

. (1992) recorded as many asfour broods of larvae produced annually.

PREDICTING THE FUTURE FAUNA OF ROCKY SHORES IN THE BRITISH ISLES

The MarClim Project will make predictions aboutthe future composition of the biota of rocky shoresunder a range of climate change scenarios. For manyelements of the marine biota this would be a daunting

task, but the fauna of the rocky shore is comparat-ively easy to quantify and as a result there is a richliterature. For similar reasons, many schemes formonitoring the impact of humans on the environ-ment have included the study of rocky shores andthese have provided, and in some cases continue toprovide, a wealth of data. Both the information inthe literature and that in databases accrued by mon-itoring organizations will be combined by MarClimto provide a powerful basis for the prediction of thefuture composition of rocky shore communities. Thedata resources available to the MarClim project aresummarized in Table 1. Importantly, many of the datasets that will be considered cover the last decade ofrising sea temperatures; unfortunately, however, manyof the other principal data sets were suspended inthe late 1980s as a result of changes in national sci-ence policy. Although regrettable, if new surveys areundertaken within the next few years using compar-able methodology it will still be possible to assess theextent of change during the 1990s. MarClim will re-survey as many as possible of the principal sites usedin earlier surveys and will re-map the distribution ofthe main rocky shore species of the British Isles.

The distribution of the biota of rocky shores in theBritish Isles is complex and is set by the interplay ofbroad-scale factors, principally climate and oceaniccirculation patterns, and local-scale processes such asbiological interactions or variables relating to coastaltopography (e.g. aspect, rock type exposure) and localhydrography (e.g. current strength, turbidity, tidalrange). To predict the effects of climate change on thedistribution of individual species it will be necessary

Table 1. Principal datasets to be used within the MarClim programme.

Category Geographical coverage Original collector Years in record

Intertidal organisms SW England, Isle of Man A.J. Southward 1950–1987Intertidal organisms UK, France and Portugal S.J. Hawkins 1980–2001Intertidal organisms UK, northern France Rocky Shore Surveillance Group (J.R. Lewis) 1964–1987Intertidal organisms Anglesey Coastal Surveillance Unit (E. Jones) 1974–1984Intertidal organisms Southern England R. Herbert 1982–2001Intertidal organisms Shetland Shetland Oil Terminal Advisory Group 1978–2001Intertidal organisms UK/Europe D.J. Crisp TBCIntertidal organisms UK/Europe H. Barnes TBCIntertidal organisms Orkney Orkney Marine Biology Unit TBCInshore fish (power stations) UK CEGB 1981–2001Birds Europe WeBS 1984–Hydrography, plankton & fish Plymouth MBA 1903–1987Sea temperature Plymouth T. Richards 1967–2001Hydrography Port Erin D.J. Slinn, J.R. Allen, T. Shammon 1904–2000Sea temperature Guernsey R. Sendall 1988–2000Sea temperature Worldwide Hadley Centre 1880–2001

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Predicting effects of climate change on invertebrates

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to extract broad-scale signals from the noise causedby local-scale factors. Once the relationship betweenthe abundance of a species and climate has beencharacterized, it will be possible to create predictivemodels that will simulate patterns of distributionunder the various climate change scenarios. Thisstage of the project lies in the future but data alreadyanalysed indicate clearly the way in which climatechange will have an impact on the flora and inverteb-rate fauna of rocky seashores.

Many rocky shores in the north of the British Islesare covered by the barnacle

S. balanoides

, a northernspecies seldom found in any abundance beyond South-ern England. As

Semibalanus

declines it is generallyreplaced by

C. montagui

and

C. stellatus.

The relativedynamics of these barnacles in southwest Englandhave been the subject of long-term study, the results ofwhich are summarized in Figure 1(b) (from Hawkins

et al

. 2002) and should be viewed in conjunctionwith Figure 1(a). Figure 1(b) demonstrates that as

Semibalanus

populations decline, the

Chthamalus

species increase and vice versa. This relationship ismediated by climate via its effects on inshore seatemperature. Figure 1(b) is based on a data set thatceased in the late 1980s, but monitoring of barnaclepopulations has continued at a reduced number ofsites. The most recent data show that since 1985 thewarm-water barnacle species increased in abundance(Southward 1991, S.J. Hawkins & A.J. Southwardunpubl. data). It should be noted that although seatemperatures have now reached levels observed in1949–51, recent observations show that

S. balanoides

remains fairly common in the Plymouth area,although recruitment may be failing. Such informa-tion on the relative population dynamics of inter-tidal barnacles in relation to inshore sea temperaturecan be used as the basis for prediction of the effectsof the warming of inshore waters.

OTHER SPECIES

Climate-driven species-level change also seems tohave taken place in numerous other intertidal organ-isms during the study period, including the SouthernLimpet

P. depressa

and the warm-water top-shells,

O.

(

Monodonta

)

lineata

(Southward

et al

. 1995) and

G. umbilicalis

(N. Mieszkowska unpubl. data). Figure 2shows that

P. depressa

declined in abundance andrange between the warm period of the 1950s and thecooler 1980s (S.J. Hawkins & A.J. Southwardunpubl. data). A number of other common species,which are expected to respond to the warming of

inshore waters, are listed in Table 2. A more completelist is given by Hiscock

et al

. (2001).

OTHER EFFECTS

Fucoid algae are characteristic of all but the mostexposed intertidal areas of the northern Europeanrocky seashores; in the infra-littoral zone they arereplaced by larger laminarian species. Brown algaehave a substantial effect on the composition of thecommunity in which they live and on that of nearbyassemblages. They have a direct role as a food sourcefor grazing species, particularly gastropod snails, andas structural support for such animals as hydroids,ascidians and bryozoans. Fucoids also give shelterfrom heat and desiccation by keeping the rockbeneath them moist and cool during the low waterperiod. This makes it possible for animals and plantsthat are sensitive to desiccation to survive in anotherwise hostile environment. In this way, smallcrustaceans, sea anemones, hydroids, bryozoa andpolychaete worms may be maintained by the pres-ence of fucoid algae. Dead algae also sustain thebiota on nearby sediment beaches where low

in situ

production is substantially boosted by the energythat comes from their decomposition. The strand-line community is also totally dependent on algalproduction.

Fucoid algae are a feature of northern shores (Bal-lantine 1961) and will be influenced by climatechange. As sea and air temperatures increase it isprobable that fucoid cover on moderately exposedshores will decline and as a consequence the bio-diversity of rocky shores and the productivity of adja-cent sediment assemblages will decline. The loss offucoid algae, broadly related to temperature increase,may well be exacerbated by the effects of increasesin storminess that are predicted as a consequence ofglobal warming. Depending on their aspect relative towind-driven seas, some rocky shores will become moreexposed and as a consequence their biological prop-erties will change. In addition to the loss of algae,increased storminess will widen both barnacle andlichen zones in the high shore, increase the shore heightreached by red algal assemblages and replace barnacle/limpet associations by those dominated by mussels.

The predicted sea-level rise is unlikely to have aconsiderable effect on most macrotidal rocky shores.In the majority of cases the strong slope of the sea-shore continues well above the level of high water.As sea-levels rise so the physical zones occupied byeach species will move up the shore, but as there is

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free space available at the top of the shore no specieswill be displaced. The major exceptions to this pre-diction will be in places where there is a wave-cutplatform beneath cliffs or where the natural seashorehas either been topped by an artificial sea wall orgives way to sediment. In both cases, rising sea-levelwill compress existing patterns of zonation.

EFFECTS ON INVERTEBRATE PREY OF BIRDS

Although a great variety of birds may feed on rockyseashores, very few are specialists relying exclusively

on that habitat. At Robin Hoods Bay (North York-shire, UK) only nine bird species regularly fed onthe rocky shore. Of these nine species there was asingle passerine, the Rock Pipit

Anthus petrosus

, theremainder being either gulls or waders (Feare &Summers 1985). The Ruddy Turnstone

Arenariainterpres

and the Purple Sandpiper

Calidris maritima

are species particularly closely associated with inter-tidal rocky shores, where both species feed on smallmolluscs and crustaceans that live under stones,beneath macro algae or in cracks and crevices. Eura-sian Oystercatchers

Haematopus ostralegus

are morespecialized, being predators of limpets and mussels

Figure 2. The distribution and abundance of Patella depressa around southwest England and Wales during the 1950s (�) and early1980s (�). The diameter of the symbols is proportional to the abundance.

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Predicting effects of climate change on invertebrates

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(Coleman

et al

. 1999). Although Dunlin

Calidrisalpina

and Common Redshank

Tringa totanus

areoften seen on rocky shores, they are largely transientsthat specialize in feeding on sand or mud. The Com-mon Eider

Somateria mollissima

is characteristic ofrocky habitats in northern Britain, where it feedslargely on mussels

Mytilus edulis

. In light of theobservations on the effects of climate on the popu-lation dynamics of the more important rocky shoreinvertebrate species, it is possible to predict theimpact such changes might have on waterbirds. Thefollowing predictions can be made:

1

Climate change is unlikely to have a significanteffect on the amount of biomass available for birdpredation. Where large, more conspicuous speciesare concerned the major effect will be to change thebalance between competing species. Thus in the southof England

P. depressa

will become more abundant

than the Northern Limpet

P. vulgata

and

C. montagui

and

C. stellatus

will replace

S. balanoides

. It is likelythat in species where reproductive success increases,the mean size of adult animals will decrease. Thismight have an impact on the efficiency with whichprey are handled.

2

There will be a decline in the abundance of fucoidalgae and as a consequence small soft-bodied inver-tebrates that the algae protect from heat and desic-cation will be less common. This might have animpact on species such as the Ruddy Turnstone.

3

The decline in fucoid algae will have an adverseimpact on the productivity of both sediments andstrand line. Both habitats have their own avifauna,which might suffer as a consequence.

4

Increased storminess will cause a limited increasein exposure and as a consequence an increased areaof seashore will be dominated by mussels

Table 2. Some common rocky shore species that are expected to respond to climate change in UK waters.

Species Current distribution North/South

CnidariaAnemonia viridis Widely recorded on west coast of Britain & Orkney; absent from east coast SBunodactis verrucosa Southern species recorded at a few locations in SW Scotland & Shetland SActinia fragacea A southern species, present in the Channel as far east as Brighton S

AnnelidaSabellaria alveolata A southern species; reaches SW Scotland

CrustaceaChthamalus stellatus A southern species as far as NW Scotland and Shetland SChthamalus montagui Southern species common on north and west coasts of Scotland, S

present in Orkney and Shetland; occasionally in N. North SeaSemibalanus balanoides A northern species reaching its southern limit in SW Britain NBalanus perforatus Only recorded in SW Britain as far north as S Wales in British Isles SClibanarius erythropus Southern species. Northern limit Channel Islands SHaliotis tuberculata Southern species found as far north as Channel Islands STectura testudinalis A northern species commonly recorded throughout Scotland but reaching N

its southern limit in the Irish SeaPatella vulgata A northern species reaches its southern limit in Portugal NPatella depressa A southern species which reaches its northern limits at Anglesey S

in the British IslesPatella ulyssiponensis Commonly recorded on the west coast of Britain and present in Orkney; S

as far south as Filey in North SeaGibbula umbilicalis A southern species commonly recorded on the west coast of Britain. S

N limit on north coast of ScotlandGibbula pennanti Southern species found as far north as Channel Islands SOsilinus (Monodonta) lineata A southern species which reaches its northern limits in Northern Ireland S

and AngleseyMalaraphe neritoides A southern species commonly recorded throughout Britain SOnchidella celtica Southern species; reaches Cornwall SParacentrotus lividus A southern species abundant in parts of SW Ireland but only sporadically S

recorded occurrences in SW England and at a few locations on the west coast of Scotland

Strongylocentrotus droebachiensis A northern species confined to the east coast of the British Isles; Nprobably occurs on all North Sea coasts of Britain

46 M. A. Kendall et al.

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EFFECTS OF CHANGES IN BIRD NUMBERS ON ROCKY SHORE INVERTEBRATES

In the previous section of this paper the potentialeffects of changes in the invertebrate fauna of littoralrock on waterbirds were outlined. However, theinteractions between birds and invertebrates are notall necessarily ‘bottom-up’. Changes in bird popula-tions are likely to affect invertebrates. Should theabundance of Arctic-nesting shore birds be reducedas a result of tundra being replaced by forest (Zöckler& Lysenko 2000), a significant source of predationon small molluscs and crustaceans will be lost andas a result some populations might expand. Underwarmer conditions, Common Eider might retreatnorthwards and, as a consequence, their predationon mussel beds might be reduced and hence theirspatial coverage might extend.

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