Spatial Synchrony in Coral Reef Fish Populations and the Influence of Climate

Abstract

We investigated spatial patterns of synchrony among coral reef fish populations and environmental variables over an eight-year period on the Great Barrier Reef, Australia. Our aims were to determine the spatial scale of intra- and interspecific synchrony of fluctuations in abundance of nine damselfish species (genus Pomacentrus) and assess whether environmental factors could have influenced population synchrony. All species showed intraspecific synchrony among populations on reefs separated by < or =100 km, and interspecific synchrony was also common at this scale. At greater spatial scales, only four species showed intraspecific synchrony, over distances ranging from 100-300 km to 500-800 km, and no cases of interspecific synchrony were recorded. The two mechanisms most likely to cause population synchrony are dispersal and environmental forcing through regionally correlated climate (the Moran effect). Dispersal may have influenced population synchrony over distances up to 100 km as this is the expected spatial range for ecologically significant reef fish dispersal. Environmental factors are also likely to have synchronized population fluctuations via the Moran effect for three reasons: (1) dispersal could not have caused interspecific synchrony that was common over distances < or =100 km because dispersal cannot link populations of different species, (2) variations in both sea surface temperature and wind speed were synchronized over greater spatial scales (>800 km) than fluctuations in damselfish abundance (< or =800 km) and were correlated with an index of global climate variability, the El Niño-Southern Oscillation (ENSO), and (3) synchronous population fluctuations of most damselfish species were correlated with ENSO; large population increases often followed ENSO events. We recorded regional variations in the strength of population synchrony that we suspect are due to spatial differences in geophysical, oceanographic, and population characteristics, which act to dilute or enhance the effects of synchronizing mechanisms. We conclude that synchrony is common among Pomacentrus populations separated by tens of kilometers but less prevalent at greater spatial scales, and that environmental variation linked to global climate is likely to be a driving force behind damselfish population synchrony at all spatial scales on the Great Barrier Reef.

Effects of climate change on fish reproduction and early life history stages

“…However, even among tropical fishes, PLD can decline by 4-8% per 8C (Munday et al 2009c), which could have a significant effect on survivorship. Within the temperature range currently experienced by reef fishes, warmer years generally appear to favour good recruitment events for a variety of species (Meekan et al 2001;Wilson and Meekan 2002;Cheal et al 2007), which is consistent with the hypothesis that reduced PLD tends to increase larval survivorship. Recruitment of the bluehead wrasse, Thalassoma bifasciatum, in the Florida Keys increases with temperature, but also becomes more variable at high temperatures (Sponaugle and Cowen 1996), possibly because of the increased risk of starvation in warm-water cohorts.…”

Responses of reef fish communities to coral declines on the Great Barrier Reef

“…For example, changes in broad-scale climate may alter physical conditions (i.e. water temperature and major ocean currents) that drive marine food webs and strongly influence reef fish population growth over large areas of the GBR (Cheal et al 2007), while elevated ocean temperatures could dramatically reduce survival of young reef fishes (Gagliano et al 2007). To better understand and manage the effects of future climate change on coral reefs, it is necessary to increase our knowledge of the links between reef organisms and ecosystem resilience, and to minimise anthropogenic stresses that so commonly contribute to coral reef degradation around the world.…”

Crucial knowledge gaps in current understanding of climate change impacts on coral reef fishes

“…but changes in the nature of irregular but dramatic climatic events such as El Niño/La Niña have the potential for rapid broad scale effects. For example, El Niño/La Niña events have been shown to synchronise reef fish population dynamics over large spatial scales (Cheal et al, 2007) but the synchronising mechanisms during these events are unclear. Which aspects of El Niño/La Niña cycles are capable of driving broad scale changes in fish communities?…”