The El Niño Southern Oscillation drives multidirectional inter-reef larval connectivity in the Great Barrier Reef

Abstract

The El Niño Southern Oscillation (ENSO) is the strongest source of interannual global climate variability, and extreme ENSO events are projected to increase in frequency under climate change. Interannual variability in the Coral Sea circulation has been associated with ENSO, although uncertainty remains regarding ENSO's influence on hydrodynamics and larval dispersal in the adjacent Great Barrier Reef (GBR). We investigated larval connectivity during ENSO events from 2010 to 2017 throughout the GBR, based on biophysical modelling of a widespread predatory reef fish, Lutjanus carponotatus. Our results indicate a well-connected system over the study period with high interannual variability in inter-reef connectivity associated with ENSO. Larval connectivity patterns were highly correlated to variations in the Southern Oscillation Index (SOI). During El Niño conditions and periods of weak SOI, larval dispersal patterns were predominantly poleward in the central and southern regions, reversing to a predominant equatorward flow during very strong SOI and extreme La Niña conditions. These ENSO-linked connectivity patterns were associated with positive connectivity anomalies among reefs. Our findings identify ENSO as an important source of variation in larval dispersal and connectivity patterns in the GBR, which can influence the stability of population dynamics and patterns of biodiversity in the region.

Reproducing within-reef variability in coral dynamics with a metacommunity modelling framework

“…It may be reasonable to assume that a cluster of reefs being modelled is a closed system, but this depends on the spatial context. In our case study, the Great Barrier Reef is a well- connected system [5, 6, 93, 94] and there are generally other reefs surrounding potential reef clusters of interest, which likely contribute coral larvae to the reefs inside a chosen cluster. Therefore, for the simulations presented here, the ReefMod-GBR model [5] was also run, for the whole of the Great Barrier Reef, with the same environmental forcings.…”

Connectivity modelling identifies sources and sinks of coral recruitment within reef clusters

“…All of these methods have limitations, either logistically or in the capacity to detect patterns of connectivity over demographic, ecological or evolutionary time steps. Of all the methods, biophysical models are most commonly used to assess demographic connectivity, by exploring dispersal among populations within reef clusters over years to decades 11,20,[22][23][24][25][26] . Biophysical models explicitly simulate the hydrodynamics in the region of interest, larval production, dispersal and behaviour prior to settlement.…”

“…Several studies have investigated GBR connectivity using low resolution biophysical models. eReefs hydrodynamic model configured at 4 km resolution and the Lagrangian particle tracking simulator, CONNIE (web interface available at https://connie.csiro.au/) 34 , was used to infer a high degree of mixing across the GBR in certain reef fish 26 .…”

A Larval “Recruitment Kernel” to Predict Hatching Locations and Quantify Recruitment Patterns

“…Unsuccessful dispersal is inevitable in the simulation, as many larval particles are transported to unsuitable settlement areas. By choosing only the successful trajectories, forward Lagrangian particle tracking models can be used to also study successful larval dispersal (Chaput et al., 2022; Gurdek‐Bas et al., 2022).…”