Ecologically relevant dispersal of corals on isolated reefs: implications for managing resilience

Abstract

Coral reefs are in decline worldwide, and marine reserve networks have been advocated as a powerful management tool for maximizing the resilience of coral communities to an increasing variety, number, and severity of disturbances. However, the effective design of reserves must account for the spatial scales of larval dispersal that affect the demography of communities over ecological time frames. Ecologically relevant distances of dispersal were inferred from DNA microsatellite data in a broadcast-spawning (Acropora tenuis) and a brooding (Seriatopora hystrix) coral at isolated reef systems off northwest Australia. Congruent with expectations based on life histories, levels of genetic subdivision among populations were markedly higher in the brooder than in the broadcast spawner. Additionally, significant subdivision for both species between systems (>100 km), and between (>10 km) or within reefs (<10 km) within systems, indicated that many reefs or reef patches are demographically independent. There was also a clear distinction in the scale of genetic structure between the different systems; at the more geographically complex of the systems, a much finer scale structure was detected in both species. This suggested that the hydrodynamics associated with these complex reefs restrict distances regularly traveled by larvae. The primary implication is that short-term recovery of these coral communities after severe disturbance requires the input of larvae from viable communities kilometers to a few tens of kilometers away. Therefore, to be self-sustaining, we suggest that coral reef protected areas need to be large enough to encompass these routine dispersal distances. Further, to facilitate recovery from severe disturbances, protected areas need to be replicated over these spatial scales. However, specific designs also need to account for size, complexity, and isolation of reefs, which will either restrict or enhance dispersal within this range.

Rapid in situ settlement following spawning by Acropora corals at Ishigaki, southern Japan

“…In addition, these results were consistent with the results of laboratory experiments, which showed that settlement competency peaked 1 wk after fertilization in Acropora corals (Harrison 2006, Nozawa & Harrison 2008. The results are also consistent with the results of field experiments in western Australia, which showed that A. tenuis larvae dispersed less than 10 to 20 km even in an isolated system of reefs , Underwood et al 2009). Because intensive larval recruitment over a short period may be a key factor in population maintenance and resilience in Acropora corals (i.e.…”

“…Several population genetics studies (Ayre & Hughes 2000, Nishikawa et al 2003, Baums et al 2005, Underwood et al 2009) have suggested that in many cases, gene flow between populations is limited in reef corals. For example, genetic subdivisions based on DNA microsatellite data in a spawner, Acropora tenuis, and a brooder, Seriatopora hystrix, between islands (>100 km), between reefs (>10 km) or between sites within reefs (<10 km) in western Australia, indicated that many reefs or reef patches are demographically independent (Underwood et al 2009).…”

“…For example, genetic subdivisions based on DNA microsatellite data in a spawner, Acropora tenuis, and a brooder, Seriatopora hystrix, between islands (>100 km), between reefs (>10 km) or between sites within reefs (<10 km) in western Australia, indicated that many reefs or reef patches are demographically independent (Underwood et al 2009). A genetic approach is suitable for assessing population dynamics in an evolutionary time scale, but is not reliable in an ecological time scale.…”

Genetic diversity and connectivity in a brooding reef coral at the limit of its distribution

“…Stochasticity of recruitment as well as differences in life history, larval competency periods, settlement and survival requirements (Harrison & Wallace 1990;Harrison & Booth 2007) mean that different species will have different levels of connectivity to, and genetic diversity at, isolated locations (e.g. Miller & Ayre 2008;Underwood et al 2009). Species with high population subdivision and limited dispersal are hypothesized to be more vulnerable to disturbances than populations with higher connectivity (e.g.…”

Clones in space—how sampling can bias genetic diversity estimates in corals: editorial comment on the feature article by Gorospe et al.

“…Genetic studies have consistently shown that asexual reproduction is very common; consequently, coral colonies from the same reef (or nearby reefs) often have identical genotypes. A growing number of studies have formally quantified the genetic similarity among proximate colonies (i.e., positive spatial autocorrelation, for example : Miller 1998;Costantini et al 2007;Underwood et al 2007;Miller and Ayre 2008;Underwood et al 2009;Gorospe and Karl 2013;Smilansky and Lasker 2014). Given that clonality appears to be ubiquitous for corals and that closely related colonies (including clonal copies) tend to be nearby, how does spatial genetic structure (especially small-scale positive spatial autocorrelation) affect common metrics of genetic diversity?…”