High-frequency sampling and piecewise models reshape dispersal kernels of a common reef coral

Larval and Adult Traits Coevolve in Response to Asymmetric Coastal Currents to Shape Marine Dispersal Kernels

AbstractDispersal emerges as an outcome of organismal traits and external forcings. However, it remains unclear how the emergent dispersal kernel evolves as a by-product of selection on the underlying traits. This question is particularly compelling in coastal marine systems, where dispersal is tied to development and reproduction and where directional currents bias larval dispersal downstream, causing selection for retention. We modeled the dynamics of a metapopulation along a finite coastline using an integral projection model and adaptive dynamics to understand how asymmetric coastal currents influence the evolution of larval (pelagic larval duration) and adult (spawning frequency) life history traits, which indirectly shape the evolution of marine dispersal kernels. Selection induced by alongshore currents favors the release of larvae over multiple time periods, allowing long pelagic larval durations and long-distance dispersal to be maintained in marine life cycles in situations where they were previously predicted to be selected against. Two evolutionarily stable strategies emerged: one with a long pelagic larval duration and many spawning events, resulting in a dispersal kernel with a larger mean and variance, and another with a short pelagic larval duration and few spawning events, resulting in a dispersal kernel with a smaller mean and variance. Our theory shows how coastal ocean flows are important agents of selection that can generate multiple, often co-occurring evolutionary outcomes for marine life history traits that affect dispersal.

Larval longevity and competency patterns of Caribbean reef-building corals

The potential for long-distance larval dispersal depends on the longevity of planktonic, free-swimming larvae and their capacity to successfully recruit to reef habitat. We present multi-year laboratory observations of the persistence of planular larvae and settlement competency over time for cohorts derived from the same parental populations of the most important Caribbean reef building coral species, Orbicella faveolata and Acropora spp. Despite variability among years/cohorts, larvae of both species display capacity for extended longevity (up to 83 d) and competency (demonstrated at up to 48 d). Both species also displayed significantly reduced survivorship and lower realized settlement under elevated temperatures. Although the observed levels of settlement in 24 h competency assays was extremely variable, the timing of onset of competence were highly consistent among years/cohorts but distinct between species. Orbicella faveolata displayed onset of competence during day 3–5 or 4–7 (with or without exposure to positive settlement cue) after spawning; whereas, onset for Acropora spp. was day 7–8 or day 10–11 (with or without cue, respectively). This longer pre-competency period for Acropora spp. nonetheless corresponded to a greater persistence of A. palmata larvae to this age of competence (71–83% of initial cohort compared to 54–55% for O. faveolata). Such life history variation implies meaningful differences in likely dispersal potential between these imperiled reef-building species.