Vol. 423: 69–82, 2011 MARINE ECOLOGY PROGRESS SERIES Published February 10 doi: 10.3354/meps08963 Mar Ecol Prog Ser Temporal differences across a bio-geographical boundary reveal slow response of sub-littoral benthos to climate change H. Hinz1, 2,*, E. Capasso1, 2, M. Lilley2, 3, M. Frost2, S. R. Jenkins1, 2 1School of Ocean Sciences, Bangor University, Menai Bridge, Anglesey LL59 5AB, UK 2Marine Biological Association of the UK, Citadel Hill, Plymouth PL1 2PB, UK 3Department of Biological Sciences, Swansea University, Swansea SA2 8PP, UK ABSTRACT: The English Channel is located at the biogeographical boundary between the northern Boreal and southern Lusitanian biozones and therefore represents an important area to study the effects of global warming on marine organisms. While the consequences of climatic change in the western English Channel have been relatively well documented for fish, plankton and inter-tidal benthic communities, data highlighting the same effects on the distribution of sub-littoral benthic organisms does, to date, not exist. The present study resurveyed a subset of sites originally surveyed from 1958 to 1959 along the UK coast of the English Channel. The main aims of this resurvey were to describe the present status of benthic communities and to investigate potential temporal changes, in particular distributional changes in western stenothermal ‘cold’ water and southern Lusitanian ‘warm’ water species. The increase in water temperature observed since the historic survey was pre- dicted to have caused a contraction in the distribution of cold water species and an extension in the distribution of warm water species. The temporal comparison did not show any clear broad-scale dis- tributional changes in benthic communities consistent with these predictions. Nevertheless, 2 warm water species, the sting winkle Ocenebra erinacea and the introduced American slipper limpet Crepidula fornicata, did show range extensions and increased occurrence, possibly related to cli- matic warming. Similarly, warm water species previously not recorded by the historic survey were found. The absence of broad-scale temporal differences in sub-tidal communities in response to cli- matic warming has been reported for other areas and may indicate that these communities respond far more slowly to environmental changes compared to plankton, fish and inter-tidal organisms. KEY WORDS: Climate change · Range-shifts · Benthic macro-fauna · Non-native species · English Channel · Long term monitoring Resale or republication not permitted without written consent of the publisher INTRODUCTION observational programmes across spatial gradients of perceived impacts (Kaiser et al. 2006, Hinz et al. Recognition of increasing anthropogenic pressure 2009). However, in attempting to understand how on the marine environment, particularly coastal sub- increasing pressure from drivers as wide-ranging littoral habitats, has stimulated wide-ranging research as pollution, aggregate extraction, urbanization, dem- into its impact at an ecosystem level. Experimental ersal fishing, eutrophication and climate change are studies have been invaluable in furthering our under- changing the benthic marine environment, the most standing of a variety of anthropogenic drivers and direct form of study is examining change through facilitating a move towards a more predictive science. time. In many marine habitats it has been the output Such work has taken on a variety of forms, from rela- of long-term studies which has most vividly demon- tively small-scale manipulative studies to larger-scale strated man’s influence in changing marine popu- *Address for correspondence: Menai Bridge. © Inter-Research 2011 · www.int-res.com Email: [email protected] 70 Mar Ecol Prog Ser 423: 69–82, 2011 lation and community structures (Myers & Worm surveys along the length of the English Channel (Holme 2003, Hays et al. 2005). 1961, 1966). Based on comparisons with the work of Despite the potential power of long-term studies, Ford (1923) and the general warming trend during this a relatively poor understanding of the long-term period, he postulated that species that were generally changes in sub-littoral soft sediments exists compared restricted to the western part of the English Channel to other marine habitats. For example, commercial (western species), with stenothermal life traits (adapted interest has dictated that decadal scale changes in fish to living at relatively cold stable ocean temperatures), populations are relatively well described (Pauly et al. would be negatively affected by any further warming, 2001, Myers & Worm 2003), and recognition of the ultimately leading to a reduction of such species in the importance of phytoplankton and zooplankton at the English Channel (Holme 1966). He further contem- base of the marine food chain has led to numerous plated that Lusitanian ‘warm water species’ (Cornu- long-term studies on these groups (Karl et al. 2001, brian and Sarnian species1) would extend their distrib- Beaugrand 2004, Hays et al. 2005). However, docu- utions in the channel and thrive especially in shallow menting long-term change in sub-littoral benthic soft coastal areas. Warm water species would not only sediments is hampered by the paucity of applicable increase their distributional range via migration and long-term datasets. Detailed historical surveys of sub- larval dispersal from the west (Cornubria or Cornish tidal benthic communities that include quantitative coast), but also from the Channel Islands (previously data pre-dating the 1970s are relatively rare. Existing ‘Sarnia’), arriving mid-channel on the southern coast of long-term studies are generally limited to European England (Holme 1966). seas, particularly the North Sea and English Channel, In 2006 we resurveyed parts of Norman Holme’s first and their output has demonstrated the effects of both benthic survey (Holme 1961), covering large extents of eutrophication (Kröncke & Rachor 1992) and demersal the southern coast of England. The main aims of the fishing impacts (Frid et al. 1999, Rumohr & Kujawski present resurvey were (1) to describe the current status 2000, Bradshaw et al. 2002, Kaiser & Spence 2002, of benthic communities and (2) to compare our data Capasso et al. 2010). with the historic survey in order to investigate poten- There have been few attempts to utilise benthic time tial changes in benthic communities. In particular, the series or datasets to assess changes in soft sediment paper focuses on the distributional changes of western benthic habitats as a consequence of climate change stenothermal ‘cold’ water and southern ‘warm’ water (but see Kröncke et al. 1998, Reiss et al. 2006, Frid et al. species in relation to climatic changes over the 48 yr 2009, Neumann et al. 2009). However, as early as the period spanning the 2 surveys. 1950s, it was recognised that monitoring this habitat in areas at the boundary of biogeographic provinces could provide indication of a changing climate (Holme MATERIALS AND METHODS 1961). The western English Channel is located at the biogeographic boundary between northern Boreal and Survey area. Between 1958 and 1959 Holme sam- southern Lusitanian fauna and has served as an impor- pled 167 stations along the southern coast of England, tant area for monitoring the effects of global warming extending from Penzance to Folkstone (Holme 1961). on marine organisms (Hawkins et al. 2003). Climatic Fifty of these sites were revisited in July 2006, across a conditions in the English Channel have changed con- similar spatial range (Fig. 1). siderably during the 20th century, with initial warming Sampling procedures adopted in 1958 by Holme. until the 1950s, a period of cooling after 1962 and sig- Holme sampled benthic communities along the English nificant warming since the 1980s (Luterbacher et al. Channel using an anchor dredge, a semi-quantitative 2004). While the consequences of climatic change have sampling gear designed to work in coarse sediments been relatively well documented for the western Eng- (see Holme 1961 for gear design). A single anchor lish Channel for fish (Southward et al. 1988, Genner et dredge sample was taken at each sampling station. al. 2004, 2010), plankton (Southward 1984, Pitois & Fox The geographical positioning of each station was ob- 2006, Gomez & Souissi 2007, Beaugrand et al. 2009) tained via a DECCA navigation system, and readings and inter-tidal benthic communities (Hawkins et al. were converted to latitude and longitude (Holme 1961). 2003, 2008, Herbert et al. 2003, 2009, Mieszkowska et Individual dredge samples were treated with consider- al. 2007), no such data exist for sub-tidal benthic or- able variation once onboard. Generally, a sub-sample ganisms. However, the large-scale surveys of Norman Holme (Holme 1961, 1966) do provide a baseline for 1Definitions: Cornubrian species are those species Holme the distribution of benthic species against which cur- typically found on the Cornish coast; Sarnian species are rent patterns can be compared. Between 1958 and those species Holme typically found off the Channel Islands 1963 Norman Holme conducted 2 large-scale benthic (previously ‘Sarnia’) Hinz et al.: Response of sub-littoral benthos to climate change 71 Fig. 1. Map of the 50 stations surveyed by Holme from 1958 to 1959 and resurveyed between July and August 2006. Numbered boxes indicate geographic regions (Regions 1 to 6) for which average sea surface temperatures for the 10 yr period prior to each respective survey were calculated (see Fig. 4) of the total catch was sieved over 2.2 mm, while the from the multivariate analyses (Stns 85, 112, 148, 173), rest of the catch was sorted for conspicuous animals, but were considered in the analysis of distribution with respect to their size or abundance, before being changes. The anchor dredge used in 2006 had similar hosed down on deck. In addition to or instead of the dimensions to the one used in 1958 (width × height × 2.2 mm mesh size, coarser sieving (at 5 and 11.5 mm) depth: 62 × 33 × 38 cm), although the mesh size used was carried out to process coarser sediment types. The (18 mm) was slightly larger.