Abstract
Cyclones have one of the greatest effects on the biodiversity of coral reefs and the associated species. But it is unknown how stochastic alterations in habitat structure influence metapopulation structure, connectivity and genetic diversity. From 1993 to 2018, the reefs of the Capricorn Bunker Reef group in the southern part of the Great Barrier Reef were impacted by three tropical cyclones including cyclone Hamish (2009, category 5). This resulted in substantial loss of live habitat-forming coral and coral reef fish communities. Within 6–8 years after cyclones had devastated, live hard corals recovered by 50–60%. We show the relationship between hard coral cover and the abundance of the neon damselfish (Pomacentrus coelestis), the first fish colonizing destroyed reefs. We present the first long-term (2008–2015 years corresponding to 16–24 generations of P. coelestis) population genetic study to understand the impact of cyclones on the meta-population structure, connectivity and genetic diversity of the neon damselfish. After the cyclone, we observed the largest change in the genetic structure at reef populations compared to other years. Simultaneously, allelic richness of genetic microsatellite markers dropped indicating a great loss of genetic diversity, which increased again in subsequent years. Over years, metapopulation dynamics were characterized by high connectivity among fish populations associated with the Capricorn Bunker reefs (2200 km2); however, despite high exchange, genetic patchiness was observed with annual strong genetic divergence between populations among reefs. Some broad similarities in the genetic structure in 2015 could be explained by dispersal from a source reef and the related expansion of local populations. This study has shown that alternating cyclone-driven changes and subsequent recovery phases of coral habitat can greatly influence patterns of reef fish connectivity. The frequency of disturbances determines abundance of fish and genetic diversity within species.
Highlights
Cyclones are one of the most important key drivers of ecological heterogeneity and ecosystem function (Halford et al 2004; Fabricius et al 2008; Halford and Perret 2009; Roff et al 2015; Puotinen et al 2016)
We present the first long-term (2008–2015 years corresponding to 16–24 generations of P. coelestis) population genetic study to understand the impact of cyclones on the meta-population structure, connectivity and genetic diversity of the neon damselfish
At One Tree Island, the seascape on the exposed side of the reef changed from 42% to 18–25% total coral cover after the cyclone (Fig. 2a— cover at OTI reef; Fig. 3) and the effect size was even greater at other reefs in the Capricorn Bunker Group along the route of tropical cyclone (TC) Hamish (Online Resource Fig. S1)
Summary
Cyclones are one of the most important key drivers of ecological heterogeneity and ecosystem function (Halford et al 2004; Fabricius et al 2008; Halford and Perret 2009; Roff et al 2015; Puotinen et al 2016). Storm-induced coral loss can have a devastating effect on coral species assemblages due to loss of shelter, habitat and food (Doherty et al 1997; Woolsey et al 2012). In contrast to these devastating effects, Connell (1978) predicted that intermediate disturbance such as storms might be beneficial to ecosystem functioning because disturbances create the highest diversity by maintaining coral reefs in a non-equilibrium state with newly appearing niches providing space and shelter to specialized species with high colonization potential. Soon after a severe disturbance, diversity is supposed to be low because the time for colonization is short; only those few species that can cope with reduced shelter, produce propagules fast and happen to be within dispersal range will colonize disturbed habitat after a cyclone
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