Turning on the Heat: Ecological Response to Simulated Warming in the Sea Dan A. Smale1*, Thomas Wernberg1,2, Lloyd S. Peck3, David K. A. Barnes3 1 School of Plant Biology, Oceans Institute, University of Western Australia, Perth, Western Australia, Australia, 2 Australian Institute of Marine Science, Oceans Institute, University of Western Australia, Perth, Western Australia, Australia, 3 British Antarctic Survey, Natural Environment Research Council, Cambridge, United Kingdom Abstract Significant warming has been observed in every ocean, yet our ability to predict the consequences of oceanic warming on marine biodiversity remains poor. Experiments have been severely limited because, until now, it has not been possible to manipulate seawater temperature in a consistent manner across a range of marine habitats. We constructed a ‘‘hot-plate’’ system to directly examine ecological responses to elevated seawater temperature in a subtidal marine system. The substratum available for colonisation and overlying seawater boundary layer were warmed for 36 days, which resulted in greater biomass of marine organisms and a doubling of space coverage by a dominant colonial ascidian. The ‘‘hot-plate’’ system will facilitate complex manipulations of temperature and multiple stressors in the field to provide valuable information on the response of individuals, populations and communities to environmental change in any aquatic habitat. Citation: Smale DA, Wernberg T, Peck LS, Barnes DKA (2011) Turning on the Heat: Ecological Response to Simulated Warming in the Sea. PLoS ONE 6(1): e16050. doi:10.1371/journal.pone.0016050 Editor: Stuart Humphries, University of Hull, United Kingdom Received August 25, 2010; Accepted December 6, 2010; Published January 14, 2011 Copyright: 2011 Smale et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Funding was sourced from the University of Western Australia’s postdoctoral development award to DS (AUD 30K). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: daniel.smale@uwa.edu.au Introduction A multitude of biologically significant environmental changes are projected to occur as a consequence of anthropogenic climate change [1]. Increasing temperature is arguably the most important change, as temperature influences physiological and ecological processes across biological scales, from genes to ecosystems. Current knowledge of observed and expected biological changes – and the ecophysiological mechanisms that drive them – on land far exceeds that from ocean systems, largely because of the costly, logistically-challenging nature of marine research and the inaccessibility of aquatic habitats [2]. For example, unlike in terrestrial habitats, where cloches have been used to experimen- tally elevate temperature over short to medium timescales to investigate community-level responses to simulated global warm- ing [3,4], there have been few controlled manipulations of temperature in the sea. Although it is logistically difficult to manipulate seawater temperature for ecological field experiments, previous studies have utilized natural or man-made thermal gradients to examine biological responses to seawater warming over varying timescales [5,6]. For example, thermal discharge plumes from coastal power plants have provided the opportunity to collect valuable field data to show comprehensive and unexpected changes in marine community structure in response to seawater warming [6,7]. Longer term warming driven by thermal discharge plumes has also facilitated empirical tests of ecological theories [6] However, while such approaches are clearly valuable, they are inherently either unreplicated or spatio-temporally confounded and also it is not possible for the researcher to exert control of the warming regimes or treatments. Another common approach that ecologists have adopted examine the influence of environmental drivers on marine biodiversity involves the use of settlement panels, which provide artificial habitat for the settlement and growth of sessile marine organisms. Settlement panels act as uniform, comparable replicates that can be used to conduct manipulative experiments on the influence of key physical and biological processes on community structure. Assemblages colonising settlement panels have been subjected to controlled manipulations of, amongst other factors, physical disturbance, light levels, sedimentation, nutrient enrichment, competition and grazing pressure (e.g., [8,9,10,11]). Here, we developed this approach by manipulating temperature on and around settlement panels to conduct highly novel in situ experiments on the response of natural communities to simulated oceanic warming. Results A ‘hot-plate’ system, in which electrically heated settlement plates were warmed in an experimental array (comprising 8 hot plates and 8 control plates), was deployed at 6m depth in the fully- saline (35 psu) mouth of the micro-tidal Swan Estuary in Perth, Australia (Fig 1A). The plate surface available for colonisation and the boundary layer of water surrounding the plate were warmed to 0.67uC (60.11 s.d., based on 860 hourly observations) above ambient temperature, in situ, for 36 days (Fig. 1B). The temperature of the Swan River decreased considerably during the deployment, which was conducted in autumn, but the temperature differential between hot plates and control plates remained relatively constant throughout the experiment (Fig. 1B). A typical fouling assemblage, dominated by colonial ascidians, PLoS ONE | www.plosone.org 1 January 2011 | Volume 6 | Issue 1 | e16050