Abstract
Coral growth is an important component of reef health and resilience. However, few studies have investigated temporal and/or spatial variation in growth of branching corals, which are important contributors to the structure and function of reef habitats. This study assessed growth (linear extension, density, and calcification) of three branching coral species (Acropora muricata, Pocillopora damicornis and Isopora palifera) at three distinct locations (Lizard Island, Davies/Trunk Reef, and Heron Island) along Australia’s Great Barrier Reef (GBR). Annual growth rates of all species were highest at Lizard Island and declined with increasing latitude, corresponding with differences in temperature. Within locations, however, seasonal variation in growth did not directly correlate with temperature. Between October 2012 and October 2014, the highest growth of A. muricata was in the 2013–14 summer at Lizard Island, which was unusually cool and ~0.5 °C less than the long-term summer average temperature. At locations where temperatures reached or exceeded the long-term summer maxima, coral growth during summer periods was equal to, if not lower than, winter periods. This study shows that temperature has a significant influence on spatiotemporal patterns of branching coral growth, and high summer temperatures in the northern GBR may already be constraining coral growth and reef resilience.
Highlights
Coral reefs are important ecosystems, providing invaluable goods and services to tropical nations[1] as well as supporting a great diversity of reef-associated organisms[2,3,4]
This study showed that growth rates of three common coral species (A. muricata, P. damicornis and I. palifera) were highest at Lizard Island, in the northern Great Barrier Reef (GBR) (14.7 °S), and declined at higher latitude
Spatial variation in coral growth was largely consistent with variation in observed temperatures; average annual sea surface temperature (SST) at the two most northern reefs were similar (26.8 °C and 26.1 °C, at Lizard Island and Davies Reef, respectively), sea temperature at Heron Island was ~2 °C less (24.1 °C)
Summary
Coral reefs are important ecosystems, providing invaluable goods and services to tropical nations[1] as well as supporting a great diversity of reef-associated organisms[2,3,4]. Widespread declines in coral cover and structural complexity, as reported in a number of locations[6, 7] directly effect local diversity and productivity[8, 9], thereby undermining the ecological and economic value of reef ecosystems. The optimum temperature for coral calcification is typically 1–3 °C below the local summer maximum[19, 20], such that ocean warming will constrain coral growth by reducing the time that environmental conditions are conducive to maximum rates of calcification[12]. Ocean warming is purported to be key factor contributing to observed declines in growth of massive corals across many reef locations (Australia[21], Thailand[22], Red Sea[23], Florida[24]). Investigating variability in growth of branching corals over large temporal and spatial scales, where there are substantial differences in environmental conditions may provide insight into how these corals will respond to changing environmental conditions
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