Climate Change and Coral Reef Connectivity

Coral Reefs (2009) 28:379-395 DOI 10.1007/s003 3 8-008-0461-9 REV IEW Climate change and coral reef connectivity P. L. Munday • J. M. Leis • J. M. Lough • C. B. Paris • M. J. Kingsford • M. L. Berumen • J. Lambrechts Received: 1 August 2008/Accepted: 9 December 2008/Published online: 14 January 2009 © Springer-Verlag 2009 Abstract This review assesses and predicts the impacts temperature might enhance the number of larvae surviving that rapid climate change will have on population connec the pelagic phase, but larger increases are likely to reduce tivity in coral reef ecosystems, using fishes as a model reproductive output and increase larval mortality. Changes group. Increased ocean temperatures are expected to to ocean currents could alter the dynamics of larval supply accelerate larval development, potentially leading to and changes to planktonic productivity could affect how reduced pelagic durations and earlier reef-seeking behav many larvae survive the pelagic stage and their condition at iour. Depending on the spatial arrangement of reefs, the settlement; however, these patterns are likely to vary greatly expectation would be a reduction in dispersal distances from place-to-place and projections of how oceanographic and the spatial scale of connectivity. Small increase in features will change in the future lack sufficient certainty and resolution to make robust predictions. Connectivity could also be compromised by the increased fragmentation Communicated by Ecology Editor Prof. Peter Mumby of reef habitat due to the effects of coral bleaching and ocean acidification. Changes to the spatial and temporal P. L. Munday ( H ) • J. M. Lough • M. J. Kingsford ARC Centre of Excellence for Coral Reef Studies, scales of connectivity have implications for the manage James Cook University, Townsville, QLD 4811, Australia ment of coral reef ecosystems, especially the design and e-mail: [email protected] placement of marine-protected areas. The size and spacing of protected areas may need to be strategically adjusted if P. L. Munday • M. J. Kingsford School of Marine and Tropical Biology, James Cook University, reserve networks are to retain their efficacy in the future. Townsville, QLD 4811, Australia Keywords Climate change • Population connectivity • J. M. Leis Global warming • Larval dispersal • Habitat fragmentation • Australian Museum, Sydney, NSW 2010, Australia Marine-protected areas J. M. Lough Australian Institute of Marine Science, Townsville, QLD, Australia Introduction C. B. Paris Rosenstiel School of Marine and Atmospheric Science, Most coral reef animals have a complex life cycle with a University of Miami, Miami, USA demersal adult stage that is relatively site attached and a pelagic larval stage that is subject to dispersal. For such M. L. Berumen Biology Department, Woods Hole Oceanographic Institute, species, connectivity between populations inhabiting dif Woods Hole, MA 02543, USA ferent patches of reef is expected to be maintained primarily by the dispersive larvae (Sale 1991). The scale of J. Lambrechts larval dispersal can vary greatly both within and among Centre for Systems Engineering and Applied Mechanics, Université catholique de Louvain, B-1348 Louvain-la-Neuve, taxa (Sale and Kritzer 2003; Kinlan and Gaines 2003; Belgium Shanks et al. 2003); some larvae may disperse just a few Ô Springer 380 Coral Reefs (2009) 28:379-395 metres from where they were spawned, others may disperse et al. 2003; Hoegh-Guldberg et al. 2007). Key environ 10s-100s km to populations on distant reefs (Gaines et al. mental variables for coral reef ecosystems include water 2007). Several factors are known or expected to influence temperature, circulation patterns, water chemistry (e.g. pH, the scale of dispersal and the magnitude of settlement salinity and nutrient supply), sea level, occurrence of resulting from dispersal. These factors include the pelagic tropical cyclones and sources of climatic anomalies such as larval duration (PLD), water currents that the eggs and El Niño-Southern Oscillation (ENSO) events. All of these larvae experience, behaviour of the larvae, the number of variables are likely to be affected by climate change, which reproductive propagules produced and the proportion that in turn will affect the distribution of coral reef organisms, survive to settlement, and the availability of suitable hab the structure of reef communities, and the function of key itat for the settling larvae (Cowen 2002; James et al. 2002; ecological processes, such as population connectivity. Cowen et al. 2007; Gerlach et al. 2007; Leis 2007). Climate Predicting how climate change will affect connectivity change has the potential to affect all these factors and, thus, in coral reef ecosystems is important because dispersal of significantly alter patterns of biological connectivity in larvae between reefs is a key component of population coral reef ecosystems (Munday et al. 2008a). dynamics for most coral reef organisms (Caley et al. 1996; Population connectivity is a whole-of-life process that Armsworth 2002). The number of reproductive propagules depends on adults producing eggs and larvae that disperse produced by adults, the spatial scale of dispersal during the between patchily distributed populations and the survival pelagic phase, the number of larvae surviving to settlement of those offspring in the new population until they breed and their success in recruiting to the benthic populations and reproduce (Pineda et al. 2007). The length of the larval could all be affected by climate change, with potentially phase and the current regime experienced by larvae could far-reaching implications for the dynamics and sustain obviously influence the dispersal pattern of a small, pelagic ability of adult populations. Understanding the scale of animal. Behavioural attributes of the larvae, such as ver connectivity is also an important consideration for tical migration, swimming ability and orientation towards designing effective networks of marine-protected areas reefs or other important cues, could also influence dispersal (MPAs) (Jones et al. 2007; Almany et al. 2009) and patterns. These behaviours, and the timing of their devel managing coral reef fisheries. The scale of population opment during the pelagic stage, appear to be critically connectivity helps determine the optimal size and spacing important in determining dispersal outcomes and the spa of reserves for the conservation of biodiversity and the tial scales over which dispersal takes place (Armsworth potential for larval dispersal and recruitment to non-reserve 2000; Paris and Cowen 2004; Cowen et al. 2006; Leis areas (Botsford et al. 2001; Shanks et al. 2003). Finally, the 2007). degree of connectivity between populations will influence In most marine organisms, cumulative mortality during the ability of populations of coral reef organisms to adapt the pelagic stage is extremely high, and therefore, small to rapid climate change through the exchange of favourable changes in mortality rates have a large effect on the genotypes between populations (Munday et al. 2008a). numbers of individuals surviving to settlement (Caley et al. This review assesses the likely effects that rapid climate 1996). Furthermore, any spatial variation in mortality pat change will have on connectivity of reef fish populations. terns would have a substantial influence on the spatial Fishes are used as model organisms because connectivity pattern of dispersal. Due to the high mortality expected in of fish populations has been an area of intense research marine larval stages, dispersal of demographic significance over the past decade (Cowen et al. 2007) and much more is can only be expected over a limited distance (Cowen et al. known about the ecological patterns of connectivity in 2000), although long distance dispersal by small numbers fishes than most other coral reef organisms. First, the of larvae can still be important in maintaining genetic environmental changes that rapid climate change will bring connectivity between populations (Planes 2002). Finally, to to coral reef ecosystems are outlined, particularly those make the transition to a reef-based existence, those larvae changes that are likely to have significant impacts on that survive the pelagic stage must find appropriate settle population connectivity. The effects that these environ ment habitat, and often their settlement requirements are mental changes will have on adult reproduction, larval very specific (Ohman et al. 1998; Holbrook et al. 2000, dispersal and recruitment patterns are then considered in Leis and Carson-Ewart 2002). detail, as well as the effects that climate-induced habitat Human activities since the late 18th century have fragmentation could have on population connectivity. The changed the composition of the atmosphere, causing the benefits and utility of biophysical models for predicting the global temperature to warm rapidly (Trenberth et al. 2007). effects of climate change on coral reef connectivity are Coral reef ecosystems, although located in the world’s discussed and, finally, the implications of changes in con naturally warmest marine waters, are considered to be nectivity patterns for the design and placement of MPAs particularly vulnerable to rapid climate change (Hughes are considered. Ô Springer Coral Reefs (2009) 28:379-395 381 Many of the predictions made in this review are highly ~70% of the global average. This correlation is useful for speculative because of uncertainty about

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