The rocky intertidal biotopes of Helgoland: present and past

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<ul><li><p>ORIGINAL ARTICLE</p><p>Inka Bartsch Ian Tittley</p><p>The rocky intertidal biotopes of Helgoland: present and past</p><p>Received: 1 April 2003 / Revised: 1 April 2004 / Accepted: 10 July 2004 / Published online: 6 November 2004 Springer-Verlag and AWI 2004</p><p>Abstract Nineteen of the 57 littoral rocky shore biotopesand 4 of the 26 variants as well as 1 sublittoral fringebiotope classied for Britain and Ireland have been re-corded on Helgoland in this baseline study. Most of thewave-cut platform is at sublittoral and lower littorallevels and most high eulittoral biotopes are conned tonarrow zones on seawalls. Large areas of gently slopinglower eulittoral and also boulder areas adjacent to sea-walls are characterised by a mixture of two or morebiotopes. Only 4 of the 23 littoral biotopes and variantsare characterised by faunal species. Comparison withpast descriptions of intertidal communities suggestscontinuing presence of most of the autochthonous bio-topes over the past 80 years but also change due to theinvasion of the macroalgae Mastocarpus stellatus andSargassum muticum over the past 20 years. One previ-ously recorded cave biotope and a sublittoral seagrasssite have become extinct due to habitat loss while otherbiotopes probably have extended their range due tohabitat increase. The presence of 4 intertidal biotopes(20%) considered rare or scarce in Britain supports therecognition of Helgoland as a site of special conserva-tion in a regional and international context.</p><p>Keywords Littoral biotopes Biodiversity change Helgoland Non-native species</p><p>Introduction</p><p>A lack of integrated information for marine ecosystems,particularly knowledge of the composition and distri-bution of communities of plants and animals and asso-ciated habitats, is a hindrance both to scientic studyand to the development of scientically based policiesfor managing the resources of the coastal zone (Foster-Smith 2001). This applies to Helgoland and Dune de-spite intensive study of the islands marine fauna andora over the past 150 years (see Kuckuck 1894, 1897a,1897b, 1897c; von Dalla Torre 1889; Caspers 1938;Ziegelmeier 1957, 1966; Kornmann and Sahling 1977,1983, 1994; Gillandt 1979; Janke 1986, 1990; Reichert2003).</p><p>Marine biotopes</p><p>The classication of marine biota as biotopes and theirspatial recording, as with vegetation mapping on theland, was developed as a practical tool to assist con-servation and site management of marine biodiversity,environmental impact assessment, monitoring man-agement practices, and the prediction of possible fu-ture changes (Kent and Coker 1992; Connor et al.1997a, 2003; Tittley et al. 1998). The underlying con-cept implies that a biotope in a particular area is anassemblage of species that may occur recurrentlywithin a larger region (Kent and Coker 1992). Thusobservation of the temporal and spatial dynamics ofbiotopes and/or biotope complexes via mapping and/or remote sensing will provide biodiversity informationat a grosser scale or higher hierarchical level in anecological classication than the species level. Theranked classication of ecological units as developedby Connor et al. (1997a, 1997b, 2003) indicates simi-larity by the position in the hierarchy. It also creates abasis for ecological comparison both within and be-tween biogeographical regions (cf. Tittley and Neto2000).</p><p>Communicated by K. Wiltshire</p><p>I. Bartsch (&amp;)Alfred Wegener Institute for Polar and Marine Research,Am Handelshafen 12, 27515 Bremerhaven, GermanyE-mail: ibartsch@awi-bremerhaven.deTel.: +49-471-48311404Fax: +49-471-48311425</p><p>I. TittleyNatural History Museum, London, SW7 5BD, UK</p><p>Helgol Mar Res (2004) 58: 289302DOI 10.1007/s10152-004-0194-2</p></li><li><p>Previous studies of marine communities on Helgoland</p><p>Ecological studies that describe the marine communitiesof Helgoland and Dune are few and largely concern thealgal vegetation; however, Janke (1986, 1990) and Re-ichert (2003) described in detail the intertidal fauna anddominant ora and their distribution on the northeastcoast of Helgoland. Kuckuck (1897a) undertook the rstdescription of the principal intertidal algal communitiesand presented a few photographs but most of hisobservations and photographs have been lost. Subse-quently Nienburg (1930) dened the species assemblageson seawalls surrounding the red sandstone clis, theintertidal and subtidal red sandstone wave-cut platform,sublittoral stones and cobbles (Gerollzone) on theseabed of the north harbour, and the chalk reefs of DuneIsland. Schmidt (1928) undertook a similar study of thealgal communities of the clis and wave-cut platformsand provided a few photographic records. Den Hartogs(1959) classication of the algal communities diered inits quantitative and phytosociological approach. SCU-BA diving enabled Luning (1970) to chart for the rsttime the vertical distribution of the sublittoral algalvegetation. Tittley (1982) undertook transect studies onthe few remaining lengths of natural red sandstone cliand also articial seawalls and harbour walls. Brunger(1989) again used the phytosociological approach forintertidal communities, providing additional quantita-tive data. De Kluijver (1991) described sublittoral ani-mal-dominated communities in detail.</p><p>Aims and objectives</p><p>The principal aim of this study was to identify the bio-topes present on Helgoland (excluding Dune Island)using the British biotope classication and thereby totest its applicability. A second aim was to comparedescriptive ecological data from past studies with datafrom the present survey to obtain a temporal perspectiveon the stability of the intertidal biotopes.</p><p>Methods</p><p>Present biotopes</p><p>Fieldwork was undertaken on seven occasions (1224July 1999, 1323 June 2000, 1624 June 2001, 2529April 2002, 1013 September 2002, 1016 March 2003,and 16 July 2003) to record the intertidal biotopes onHelgoland. Biotopes were identied using the ap-proaches of Connor et al. (1997a, 1997b, 2003), Foster-Smith (2001), and Hiscock (1996). As neither map noraerial photographs of the intertidal region were availableduring the eldwork period of 1999 to 2002, the acces-sible intertidal region was characterised photographi-cally and supported by topographical sketches. Theboundaries of communities were outlined in the sket-</p><p>ches. An approximate identication of communities wasachieved by matching the visually abundant cover andunderora species with descriptions in Connor et al.(1997a). Species abundance data (percent cover ofmacrobenthos in 0.500.50 m quadrats) were taken atpoints in areas subjectively chosen to be representativefor the respective biotopes or mixture of biotopes. Thepresupposed biotopes were sampled around the islandand with n5. This generated a total of 182 quantitativequadrat points. The positions of sampling quadrats wererecorded using a dierential global positioning system(DGPS) with an accuracy of 17 m (ESYS GmbH,Berlin). Figure 1 shows the intertidal area and the namesand locations of sites mentioned in the text. The quan-titative data were iteratively compared with the biotopedescriptions in Connor et al. (1997a, 2003). Seasonalvariation was identied by recording the same sites inspring, summer, and autumn. This biotope survey pre-supposed a knowledge of the biota, and a clear, if sub-jective, impression of the types of community (see Kentand Coker 1992; Dierschke 1994). Habitat informationincluding topography, substrate, relative wave exposureaccording to the prevailing winds and relative height onthe shore was also noted throughout the study. Salinityis fully marine except at a few sites where there isfreshwater run-o down the clis.</p><p>Site map</p><p>Figure 1 was created in 2003 on the basis of threegeoreferenced black-and-white orthophotographs pro-vided by the Landesvermessungsamt Schleswig Holstein,Kiel, Germany at a scale of 1:7000 with a resolution of0.4 m showing Helgoland and its intertidal region. Theoriginal photographs (Agfa Aviphot Pan 200) were ta-ken on 26 May 2001 around low water. The digital or-thophotographs were enlarged to a scale of 1:200 or1:300 and all visible geomorphological structures weredigitised and classied using ArcView 3.2 (ESRI, Ger-many). Colour eld photographs supported this task.The slight mismatch of about 0.5 m at the transitionzone between the orthophotographs was adjusted. As nodigital elevation information was available, the outlineof ridges was followed along lines of similar grey tonesand thus is somewhat subjective.</p><p>The biotope classication for Britain and Ireland</p><p>Identication of biotopes in the British classication isthrough a hierarchy of ranked units or a matrix ofinformation on habitats and species assemblages (Con-nor et al. 1997a, 2003). The primary divisions of the</p><p>Fig. 1A, B Digitised map of Helgoland and its intertidal zone. Aand B show a continuous map that is separated only for reasons ofspace</p><p>c</p><p>290</p></li><li><p>291</p></li><li><p>classication concern physical features, rstly rock orsediment substratum, secondly wave-exposure condi-tions, and thirdly shore level. The classication thuscombines biological and physical features and in thisway diers from the marine phytosociological approachof den Hartog (1959). The largest unit of biologicalfeature is the biotope complex and it contains one ormore biotopes. Variants [also referred to by Connoret al. (1997a, 1997b) as sub-biotopes] describe variationtypes within a biotope. Rockpool, cave biotopes, andephemeral biotopes are classied separately. Connoret al. (1997a, 2003) provide a full ecological descriptionfor each biotope complex, biotope, or variant in theclassication; the characterising species and their abun-dance are given, and the associated species are listed.Each unit of the classication is given a code that indi-cates the physical and biological features present;information on the distribution and frequency of eachbiotope is also given.</p><p>Past biotopes</p><p>Past information on the ecology of the marine ora andfauna of Helgoland was collated and reviewed from thepublished literature. The ecological and communityinformation given was interpreted to identify the prin-cipal intertidal communities according to the Britishbiotope classication. This information was used toidentify dierences and/or similarities in intertidal bio-topes of Helgoland with time.</p><p>Results</p><p>The biotopes and complexes recorded</p><p>The intertidal marine biotopes identied in the presentsurvey are listed in Tables 1 and 2. The tables give anoverview of the names, the codes adopted from Connoret al. (2003), the visually dominant species on Helgo-land, the substrate, relative height on the shore, spatialoccurrence, and the observed seasonality. The identi-cation (ID) numbers are for easy comparison of biotopesbetween all three tables and the text. Of the 57 intertidalrock and cave biotopes itemised in Connor et al. (1997b,2003) 19 have been recorded for Helgoland. Addition-ally, 4 variants described by Connor et al. (2003) and 1sublittoral fringe biotope were also recorded and 1 newvariant is proposed.</p><p>Habitat complex: features on eulittoral rock (lichens,caves, rockpools, and ephemeral seaweeds; FLR)</p><p>Biotope complex: lichens or small green algae on supra-littoral rock (FLR.Lic) Four biotopes of this complexwere well developed in the upper eulittoral and supra-littoral on Helgoland. Although Verrucaria spp. formed</p><p>discoid patches on erratic basalt blocks, the biotopeFLR.Lic.Ver (see Connor et al. 2003) was not present.</p><p>FLR.Lic.YG (ID 1) The biotope characterised byyellow and grey lichens occurred principally in thesupralittoral on manmade structures but was notinvestigated in detail.</p><p>FLR.Lic.Pra (ID 2) The Prasiola stipitata biotopeformed a thin adherent layer of small thalli at supralit-toral levels on manmade and natural substrata near birdroosts; the biotope extended to spray-zone levels wherethe characterising species were Rosenvingiella polyrhiza(Rosenvinge) P.C. Silva and P. calophylla (Carmichaelex Greville) Kutzing. It was best developed in spring.Extensive pure stands of R. polyrhiza occurred in Marchand July 2003 and further investigation is needed toverify a distinct Rosenvingiella biotope.</p><p>FLR.Lic.Bli (ID 3) The biotope characterised byBlidingia spp. was recorded commonly in summer as adistinct green band on natural and manmade substrataat mean high water level (MHW); in spring, by con-trast, it was noted as a discontinuous band. It is espe-cially well developed on concrete tetrapods (coastalarmouring) together with Porphyra umbilicalis (Linna-eus) Kutzing but is rare on natural red sandstone. InMarch 2003 it was observed locally overgrowing abarnacle biotope.</p><p>FLR.Lic.UloUro (ID 4) The UlothrixUrospora bio-tope occurred abundantly in spring as an adherent layerof laments on red sandstone rocks and boulders atupper mid-littoral shore levels below the biotopes char-acterised by Blidingia spp. and EnteromorphaPorphyraspp. Ulothrix and Urospora spp. occasionally occurredamong the latter and the biotope was not found in itsexpected position at eulittoral fringe levels above theBlidingia-biotope. In spring it formed a dark-greenband in places discoloured by epiphytic diatoms while insummer it was replaced by dense stands of Enteromor-pha spp.</p><p>Biotope complex: rockpools (FLR.Rkp) This habitat onHelgoland mostly comprised shallow channels that re-mained in direct contact with the sea during low tide.Three biotopes and one variant were commonly re-corded on the wave-cut platform.</p><p>FLR.Rkp.G (ID 5) The green seaweeds (Enteromor-pha spp. and Cladophora spp.) in shallow upper shorerockpools biotope was recorded in limited extent onhorizontal surfaces of harbour walls. The species con-tent, seasonality, and spatial extent require furtherinvestigation.</p><p>FLR.Rkp.Cor (ID 6) Corallina rockpools were acommon and characteristic feature of the wave-cutplatform and showed seasonal facies. Those without</p><p>292</p></li><li><p>Table 1 The intertidal marine biotopes of Helgoland, visually dominant species. Biotope codes and names according to Connor et al.(1997b, 2003). The identication (ID) numbers enable easy comparison between tables and text. Author names of species are only added ifnot mentioned elsewhere in the text</p><p>ID Biotope code Biotope name Visually dominant species at HelgolandVersion 03.02</p><p>1 FLR.Lic.YG Yellow and grey lichens on supralittoral rock Species composition needs further investigation2 FLR.Lic.Pra Prasiola stipitata on nitrate-enriched</p><p>supralittoral or littoral fringe rockP. stipitata Suhr ex Jessen</p><p>3 FLR.Lic.Bli Blidingia spp. on vertical littoral fringe soft rock B. minima (Nageli ex Kutzing) Kylin, B. marginata(J. Agardh) P.J.L. Dangeard ex Bliding, Porphyraumbilicalis</p><p>4 FLR.Lic.UloUro Ulothrix acca and Urospora spp. on freshwater-inuenced vertical littoral fringe soft rock</p><p>Ulothrix spp., Urospora penicilliformis (Roth)Areschoug, Bangia atropurpurea</p><p>5 FLR.Rkp.Ga Green seaweeds (Enteromorpha spp. andCladophora spp.) in shallow upper shore rockpools</p><p>Species composition needs further investigation</p><p>6 FLR.Rkp.Cor Corallina ocinalis, coralline crusts and brownseaweeds in shallow eulittoral roc...</p></li></ul>