Estimating dispersal potential for marine larvae: dynamic models applied to scleractinian corals

Abstract

Dispersal influences ecological dynamics, evolution, biogeography, and biodiversity conservation, but models of larval dispersal in marine organisms make simplifying assumptions that are likely to approximate poorly the temporal dynamics of larval survival and capacity for settlement. In particular, larval mortality rates are typically assumed to be constant throughout larval life; and all larvae are frequently assumed to acquire and lose competence at the same time. To improve upon these assumptions, we here develop simple models of dispersal potential that incorporate rates of mortality, and acquisition and loss of settlement competence. We fit these models to empirical competence and survival data for five scleractinian coral species, to test the models' ability to characterize empirical survival and competence patterns, and to estimate the dispersal potential implied by those patterns. The models fit the data well, incorporating qualitative features of competence and survival that traditional approaches to modeling dispersal do not, with important implications for dispersal potential. Most notably, there was high within-cohort variation in the duration of the competent period in all species, and this variation increases both self-recruitment and long-distance dispersal compared with models assuming a fixed competent period. These findings help to explain the seeming paradox of high genetic population structure, coupled with large geographic range size, observed in many coral species. More broadly, our approach offers a way to parsimoniously account for variation in competence dynamics in dispersal models, a phenomenon that our results suggest has important effects on patterns of connectivity in marine metapopulations.

Coral reproduction on the world’s southernmost reef at Lord Howe Island, Australia

“…broadcast spawning) in the sub-tropical waters of Lord Howe Island. In 2 species of broadcast spawners, median larval lifespan was very low: < 24 h for both Paragoniastrea australensis and Cyphastrea micro phthalma (Woolsey et al 2014) compared to typical values of > 30 d among the larvae of broadcast-spawning species at tropical locations (Graham et al 2008, Connolly & Baird 2010. This suggests that gametes of these sub-tropical broadcast-spawning corals were either of poor quality or highly sensitive to handling.…”

Modeling Fine-Scale Coral Larval Dispersal and Interisland Connectivity to Help Designate Mutually-Supporting Coral Reef Marine Protected Areas: Insights from Maui Nui, Hawaii

“…In this study, the minimum planktonic period was set at 24 h (1 day) and maximum coral-larval dispersal competency was defined at 72 h (3 days) because larval density (Sammarco and Andrews, 1988;Connolly and Baird, 2010) and the competency to settle (Connolly and Baird, 2010) decreases exponentially with time; mortality was set to zero due to this short timescale. The timescale of modeled flow and pelagic larval duration used in this effort was relatively short in comparison to many other studies (Oliver et al, 1992;Vaz et al, 2013;Kool and Nichol, 2015), and it was selected not only because it minimizes the exponential decrease in competency and larval density (due to dilution) but also because the probability of effective connectivity of a substantial number of coral larvae that would need to successfully be transported from one reef to another to support normal mortality decreases exponentially with time and distance.…”

Ontogenetic change in the lipid and fatty acid composition of scleractinian coral larvae

“…Many coral larvae have an extraordinary capacity to delay metamorphosis; in the absence of suitable settlement cues, a proportion of larvae can remain alive and competent for months (Richmond 1987;Graham et al 2008;Connolly and Baird 2010). Coral propagules can be either symbiotic or aposymbiotic (symbiont-free), depending on whether or not the zooxanthellae are transmitted into the egg, prior to release.…”

“…Larvae dispersal distance depends on many factors, both physical, such as currents and winds (Siegel et al 2009), and biological, such as larval energy reserves (Burgess et al 2009), survival and settlement competence dynamics (Connolly and Baird 2010), buoyancy and swimming ability (Whalan et al 2008), and a full understanding of dispersal potential requires all these factors to be considered (Jones et al 2009). …”