Climatic forcing and larval dispersal capabilities shape the replenishment of fishes and their habitat‐forming biota on a tropical coral reef

Abstract

Fluctuations in marine populations often relate to the supply of recruits by oceanic currents. Variation in these currents is typically driven by large‐scale changes in climate, in particular ENSO (El Nino Southern Oscillation). The dependence on large‐scale climatic changes may, however, be modified by early life history traits of marine taxa. Based on eight years of annual surveys, along 150 km of coastline, we examined how ENSO influenced abundance of juvenile fish, coral spat, and canopy‐forming macroalgae. We then investigated what traits make populations of some fish families more reliant on the ENSO relationship than others. Abundance of juvenile fish and coral recruits was generally positively correlated with the Southern Oscillation Index (SOI), higher densities recorded during La Niña years, when the ENSO‐influenced Leeuwin Current is stronger and sea surface temperature higher. The relationship is typically positive and stronger among fish families with shorter pelagic larval durations and stronger swimming abilities. The relationship is also stronger at sites on the coral back reef, although the strongest of all relationships were among the lethrinids (r = .9), siganids (r = .9), and mullids (r = .8), which recruit to macroalgal meadows in the lagoon. ENSO effects on habitat seem to moderate SOI–juvenile abundance relationship. Macroalgal canopies are higher during La Niña years, providing more favorable habitat for juvenile fish and strengthening the SOI effect on juvenile abundance. Conversely, loss of coral following a La Niña‐related heat wave may have compromised postsettlement survival of coral dependent species, weakening the influence of SOI on their abundance. This assessment of ENSO effects on tropical fish and habitat‐forming biota and how it is mediated by functional ecology improves our ability to predict and manage changes in the replenishment of marine populations.

Dietary generalism accelerates arrival and persistence of coral‐reef fishes in their novel ranges under climate change

“…interesting are the many deviations from the perfect correlation, which highlight (a) that each establishment metric encapsulates dif- La Niña event to intensified southward advection arising from natural climatic oscillations (Pearce, Hutchins, Hoschke, & Fearns, 2016;Wilson et al, 2018) rather than anthropogenic climate change per se. We also maintain that our proxies for persistence, prevalence, and patchiness were complementary, because patchiness provided a measure of the temporal heterogeneity in prevalence.…”

Form and function of tropical macroalgal reefs in the Anthropocene

“…The consequences of macroalgal habitat degradation could also be substantial for key biota such as fishes. This is because of the strong functional links between macroalgal habitat quality and reef fish abundance, particularly canopy height and density, which are sensitive to variations in sea temperature over annual and interannual (Fulton et al, ) and longer (Wilson et al, ) temporal cycles. In years of poor canopy growth, we tend to find a lower abundance and diversity of juvenile and adult fishes on macroalgal reefs (Aburto‐Oropeza et al, ; Wilson et al, ), which can translate to smaller future fish populations on both macroalgal and coral reefs (Wilson et al, ).…”

“…This is because of the strong functional links between macroalgal habitat quality and reef fish abundance, particularly canopy height and density, which are sensitive to variations in sea temperature over annual and interannual (Fulton et al, ) and longer (Wilson et al, ) temporal cycles. In years of poor canopy growth, we tend to find a lower abundance and diversity of juvenile and adult fishes on macroalgal reefs (Aburto‐Oropeza et al, ; Wilson et al, ), which can translate to smaller future fish populations on both macroalgal and coral reefs (Wilson et al, ). These effects are particularly severe for species that are macroalgal reef specialists (Lim et al, ; Wenger et al, ), but they can also impact the many species that predominantly settle into macroalgal reefs.…”

Opposing life stage‐specific effects of ocean warming at source and sink populations of range‐shifting coral‐reef fishes

“…We used data from the most intensively sampled site, Cabbage Tree Bay, Sydney (33°48′00″S, 151°17′50″E), from January 2004 to December 2017. Sampling was done across the year but more frequently during the first semester (Figure S1), when the arrival of vagrant fishes to temperate sites is strongest due to intensified ocean currents (Booth et al., 2018) and a seasonal reproduction (Wilson et al., 2018). Depending on the year, the sampling frequency varied between 0 and 5 surveys/month (Figure S1).…”