Grazer effects on algal assemblages and mussel recruitment in two different mid‐intertidal communities in the Cook Strait, New Zealand

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<ul><li><p>This article was downloaded by: [Southern Taiwan University of Science and Technology]On: 11 November 2014, At: 17:46Publisher: Taylor &amp; FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK</p><p>New Zealand Journal of Marine andFreshwater ResearchPublication details, including instructions for authors andsubscription information:</p><p>Grazer effects on algal assemblages andmussel recruitment in two differentmidintertidal communities in the CookStrait, New ZealandNicole E. Phillips a &amp; Elanor Hutchison b ca Victoria University Coastal Ecology Laboratory, School ofBiological Sciences , Victoria University of Wellington , P.O. Box600, Wellington, New Zealand E-mail:b Victoria University Coastal Ecology Laboratory, School ofBiological Sciences , Victoria University of Wellington , P.O. Box600, Wellington, New Zealandc Department of Zoology , University of Otago , P.O. Box 56,Dunedin, New ZealandPublished online: 19 Feb 2010.</p><p>To cite this article: Nicole E. Phillips &amp; Elanor Hutchison (2008) Grazer effects on algalassemblages and mussel recruitment in two different midintertidal communities in the CookStrait, New Zealand, New Zealand Journal of Marine and Freshwater Research, 42:3, 297-306, DOI:10.1080/00288330809509957</p><p>To link to this article:</p><p>PLEASE SCROLL DOWN FOR ARTICLE</p><p>Taylor &amp; Francis makes every effort to ensure the accuracy of all the information (theContent) contained in the publications on our platform. However, Taylor &amp; Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor &amp; Francis. 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Terms &amp;Conditions of access and use can be found at</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Sout</p><p>hern</p><p> Tai</p><p>wan</p><p> Uni</p><p>vers</p><p>ity o</p><p>f Sc</p><p>ienc</p><p>e an</p><p>d T</p><p>echn</p><p>olog</p><p>y] a</p><p>t 17:</p><p>46 1</p><p>1 N</p><p>ovem</p><p>ber </p><p>2014</p><p></p></li><li><p>New Zealand Journal of Marine and Freshwater Research, 2008, Vol. 42: 297-3060028-8330/08/4203-0297 The Royal Society of New Zealand 2008</p><p>297</p><p>Grazer effects on algal assemblages and mussel recruitment in twodifferent mid-intertidal communities in the Cook Strait, New Zealand</p><p>NICOLE E. PHILLIPSELANOR HUTCHISON*</p><p>Victoria University Coastal Ecology LaboratorySchool of Biological SciencesP.O. Box 600Victoria University of WellingtonWellington, New Zealandemail:</p><p>*Present address: Department of Zoology, P.O. Box56, University of Otago, Dunedin, New Zealand.</p><p>Abstract Molluscan grazers were experimentallyexcluded for 24 months (December 2003 - December2005) from the mid-intertidal zone of the rockyshore at two sites at each of two locations inNew Zealand where intertidal communities differdramatically: Wellington Harbour (dominated bysessile invertebrates), and the Cook Strait (= south)coast (mostly bare rock). Excluding grazers resultedin immediate increases in foliose algae, and gradualincreases in filamentous algae. After 2 years, themean cover of both groups was similar in exclusionplots in both locations (22-24%). Crustose algaeand microalgae also increased in grazer exclusionplots, but mussel recruitment did not. There were nodifferences in response to grazer exclusion betweenthe two locations in the final algal assemblage ordensity of new mussel recruits, but the species ofmussel were different: Mytilus galloprovincialisrecruited in Wellington Harbour, and Xenostrobuspulex on the south coast. Thus, molluscan grazersin this system have a strong effect on the mid-zonealgal assemblage of the intertidal, and this effect wasgenerally similar across these two markedly differentintertidal communities.</p><p>M08004; Online publication date 2 September 2008Received 15 January 2008; accepted 18 June 2008</p><p>Keywords limpets; rocky intertidal; macroalgae;community structure; temperate reefs</p><p>INTRODUCTION</p><p>The dramatic impact that macro-invertebrategrazers can have on rocky intertidal assemblageshas been well documented from numerous studiesacross a variety of temperate systems (see reviewsby Lubchenco &amp; Gaines 1981; Hawkins &amp; Hartnoll1983; Underwood 2000). In mid to high intertidalzones, grazers often directly influence the abundanceand distribution of algae such that the removal orexclusion of grazers can result in dramatic increasesin algal cover and vertical distribution (Underwood1980; Lubchenco 1983; Cubit 1984; Jernakoff1985; Moreno &amp; Jaramillo 1985). Grazers canalso have profound effects on sessile invertebrates,both directly and indirectly. Recruitment of manybarnacle species is directly, negatively affected bygrazers that ingest new recruits or "bulldoze" themoff the substrate (Dayton 1971; Petraitis 1983;Miller &amp; Carefoot 1989). However, grazers mayalso influence recruitment of other sessile speciesindirectly via recruit responses to grazer effectson algae or microfilms, and these effects maybe either positive or negative (e.g., Underwoodet al. 1983; Jernakoff 1985; Menge et al. 1986;Petraitis 1990; Anderson 1995). Succession ofintertidal assemblages is also often dependent onboth direct effects of grazers (such as the removalof early colonising algal species and preferencesof different grazers for particular types or speciesof algae), as well as indirect effects via alteringspecies interactions (Lubchenco 1978; Lubchenco&amp; Menge 1978; Benedetti-Cecchi &amp; Cinelli 1993;Anderson &amp; Underwood 1997).</p><p>New Zealand has an extensive coastline and adiverse fauna of macro-invertebrate grazers (Creese1988). Asinmany other regions of the world, intertidalgrazer assemblages are often dominated by molluscssuch as limpets, which in New Zealand are diverseand often abundant in the rocky intertidal (Morton &amp;</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Sout</p><p>hern</p><p> Tai</p><p>wan</p><p> Uni</p><p>vers</p><p>ity o</p><p>f Sc</p><p>ienc</p><p>e an</p><p>d T</p><p>echn</p><p>olog</p><p>y] a</p><p>t 17:</p><p>46 1</p><p>1 N</p><p>ovem</p><p>ber </p><p>2014</p></li><li><p>298 New Zealand Journal of Marine and Freshwater Research, 2008, Vol. 42</p><p>Miller 1968; Menge et al. 1999; Dunmore &amp; Schiel2003). Nevertheless, the role that grazers play instructuring intertidal communities in New Zealandis still relatively unexplored (but see Rafaelli 1979;Menge et al. 1999; Dunmore &amp; Schiel 2003).</p><p>a t the southern tip of the North island, thereis a dramatic change in intertidal communitystructure over the relatively short distance (i.e.,</p></li><li><p>Phillips &amp; HutchisonGrazer effects on intertidal assemblages 299</p><p>movement of molluscs into the plots, but controlledfor potential effects the paint might have other thanto exclude molluscan grazers. The epoxy controlplots were also cleared and scrubbed similar to theexclusion and paint control plots, but only the fourcorners were marked with small buttons of epoxy.This treatment controlled for potential effects of theepoxy barrier itself. These treatments were similar tothose used by Menge et al. (1999). unmanipulatedplots were marked at the corners with epoxy buttonsand otherwise untouched.</p><p>We photographed all plots immediately beforeand after their establishment in December 2003, andsubsequently on a low tide every 3 months throughDecember 2005. Plots were examined monthly, andpaint reapplied as needed. occasionally molluscangrazers were found in the exclusion plots and wereremoved at this time.</p><p>We calculated the percentage cover of sessileorganisms for each quadrat using the random pointcontact method (Dethier et al. 1993). We overlaid50 randomly generated dots onto the image of eachquadrat, and identified the species underneath. Forease of plotting and analysis, algae were classifiedinto functional groups after Steneck &amp; Dethier(1994). a l l mobile invertebrates were identifiedand counted in each image.</p><p>In December 2005, after the final photographswere taken, plots were examined thoroughly,particularly for small juvenile mussels that mightbe hidden under or within the algal canopy that haddeveloped in the exclusion plots. We removed thealgal canopy from the exclusion plots to quantify thefinal percentage cover of encrusting algae that mayhave been otherwise obscured by the canopy.</p><p>Data analysisTreatment effects on algalcover and mussel recruitment</p><p>Treatment and spatial effects were particularlyof interest, and so were the only ones tested. Toidentify treatment effects, we used a nested a N o Vato examine the total number of grazing molluscsand total percentage cover of algae in the plotson two dates: after 1 year (December 2004) and2 years (December 2005). location (two levels:Wellington Harbour and south coast) and treatment(four levels: exclusion, paint control, epoxy control,and unmanipulated) were fixed factors. Sites wereconsidered a random factor nested within locationsand blocks were a random factor, nested within sitesand locations. We also included the treatment block(site, location) interaction. Post-hoc Tukey tests were</p><p>used to further explore significant differences (Zar1984). Proportional data often require transformationto fulfil assumptions of ANOVA, therefore algalpercentage cover data were arcsin square-roottransformed before analysis as recommended by Zar(1984). log10- (x + 1) transformation was the best atimproving homoscedascity for the molluscan data.all transformed data were examined for equality ofvariance using Cochran's test (Underwood 1997).</p><p>To examine mussel recruitment after 2 years ofmolluscan grazer exclusion, a nested a N o V a wasconducted on the total number of mussel juveniles inplots on the final sample date in December 2005. Thefactors were: location, treatment (both fixed factors),sites nested with location, blocks nested with site andlocation (both random factors), and the treatment byblock (nested within site and location) interaction.For this analysis only the exclusion and two types ofcontrol plots were used as some unmanipulated plotsin the harbour had adult mussels in them which mayconfound the results if mussel larvae use presenceof adults as a settlement cue (Pawlik 1992). Thesedata were log10- (x + 1) transformed before analysis.a l l statistical analyses were performed using thesoftware package JMP (v7).</p><p>Effects of molluscan grazer exclusionon algal community over 2 years</p><p>only using the exclusion plots, we used nestedaNoVas on three of the major algal functionalgroups that occurred in the plots (filamentousalgae, foliose algae, and microalgae) to examinedifferences among locations (fixed factor) with sitesnested within location, and blocks nested withinsites and locations (both random factors) on threedates: 3 months after the experiment started (i.e.,the first sampling date), after 1 year, and after 2years. Because we used photographs to quantifyalgal cover, we were unlikely to obtain an accurateestimate of crustose algal cover, as it may havebeen growing obscured beneath the algal canopies.Therefore, on the final date (December 2005) wequantified the percentage cover of crustose algaeafter the removal of the algal canopy.</p><p>We then used a nested a N o V a to examine thefinal species composition of the exclusion plots foreach of the dominant algal species or groups (non-calcareous crustose algae, microalgae, Ulva spp.,and Scytothamnus australis) across locations (fixedfactor), with sites nested within location, and blocksnested within sites and locations (random factors).all percentage cover data were arcsine square-roottransformed before analysis.</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Sout</p><p>hern</p><p> Tai</p><p>wan</p><p> Uni</p><p>vers</p><p>ity o</p><p>f Sc</p><p>ienc</p><p>e an</p><p>d T</p><p>echn</p><p>olog</p><p>y] a</p><p>t 17:</p><p>46 1</p><p>1 N</p><p>ovem</p><p>ber </p><p>2014</p></li><li><p>300 New Zealand Journal of Marine and Freshwater Research, 2008, Vol. 42</p><p>Mar04</p><p>Jun04</p><p>Sep04</p><p>Dec04</p><p>Mar05</p><p>Jun05</p><p>Sep05</p><p>Dec05</p><p>Sample dates</p><p>Mar Jun Sep Dec Mar Jun Sep Dec04 04 04 04 05 05 05 05</p><p>Fig. 1 Treatment effects on mean abundance of molluscan grazers ( 1 Se, n = 4) in experimental plots across sites.A, island Bay; B, Victoria university coastal ecology laboratory; C, Shelly Bay; and D, Worser Bay. Data werepooled across plots at each site.</p><p>RESULTS</p><p>exclusion plots were generally but not completelysuccessful in excluding grazing molluscs (Fig. 1).after 1 year and 2 years, the abundance of molluscangrazers was significantly lower in exclusion plotscompared with all other plot types (Table 1, Tukeytest, P &lt; 0.05). The number of molluscan grazersdid not vary across sites or location, but did vary byblocks after two years (Table 1). Molluscan grazersthat were occasionally found in low numbers inexclusion plots included the topshell M. aethiops,and winkle Austrolittorina spp., on two occasions thechiton S. pelliserpentis and on single occasions thecat's eye snail T. smaragdus, and limpets S. australis,C. denticulata, and C. ornata. The most abundantmolluscan grazers in control and unmanipulatedplots were C. denticulata, followed by M. aethiops,Austrolittorina sp., S. pelliserpentis and two otherCellana species, C. ornata and C. radians.</p><p>Total percentage cover of algae was much greaterin exclusion plots than any other plot type overthe entire 2-year course of the experiment (Fig.2). After both 1 and 2 years, the only significanteffect on algal cover was the treatment effect, where</p><p>algal cover in exclusion plots was greater than inany other plot type (Table 2, Tukey test, P &lt; 0.05),and no significant differences in algal cover acrosslocations, sites, or blocks.</p><p>After 2 years, there were no significant differencesin the number of mussel recruits for any effectsexamined (aNoVa, all factors and interactions,P &gt; 0.05). on average, after 2 years, there was atotal of four juvenile mussels per plot. althoughthe magnitude of mussel recruitment was similarin both locations, the species were different. a l lmussel juveniles from the harbour were identified bymorphology as the blue mussel M. galloprovincialis,and all mussels from the south coast were identifiedas the little black mussel Xenostrobus pulex.</p><p>in plots that excluded molluscan grazers, algalfunctional group composition changed over the 2years (Fig. 3, Table 3). Three mon...</p></li></ul>


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