Propagule dispersal and the scales of marine community process

Abstract

Benthic marine organisms are characterized by a bipartite life history in which populations of sedentary adults are connected by oceanic transport of planktonic propagules. In contrast with the terrestrial case, where 'long distance dispersal' (LDD) has traditionally been viewed as a process involving rare events, this creates the possibility for large numbers of offspring to travel far relative to the spatial scale of adult populations. As a result, the concept of LDD must be examined carefully when applied in a marine context. Any measure of LDD requires reference to an explicit 'local' scale, often defined in terms of adult population demography, habitat patchiness, or the average dispersal distance. Terms such as 'open' and 'closed' are relative, and should be used with caution, especially when compared across different taxa and systems. We use recently synthesized data on marine propagule dispersal potential and the spread of marine invasive species to draw inferences about average and maximum effective dispersal distances for marine taxa. Foremost, our results indicate that dispersal occurs at a wide range of scales in marine communities. The nonrandom distribution of these scales among community members has implications for marine community dynamics, and for the implementation of marine conservation efforts. Second, in agreement with theoretical results, our data illustrate that average and extreme dispersal scales do not necessarily covary. This further confounds simple classifications of 'short' and 'long' dispersers, because different ecological processes (e.g. range expansion vs. population replenishment) depend on different aspects of the dispersal pattern (e.g. extremes vs. average). Our findings argue for a more rigorous quantitative view of scale in the study of marine dispersal processes, where relative terms such as 'short ' and 'long', 'open' and 'closed', 'retained' and 'exported' are defined only in conjunction with explicit definitions of the scale and process of interest. This shift in perspective represents an important step towards unifying theoretical and empirical studies of dispersal processes in marine and terrestrial systems.

Investigating the origin of vagrant dusky groupers, Epinephelus marginatus (Lowe, 1834), in coastal waters of Réunion Island

“…The adults are considered sedentary and aggregate to spawn but are not known to undertake long spawning migrations. This indicates that larval movement is the most obvious dispersal mechanism in this species as observed in other marine species with a bentho-pelagic life cycle (Kinlan et al, 2005).…”

A multi-locus assessment of connectivity and historical demography in the bluehead wrasse (Thalassoma bifasciatum)

“…In addition, levels of self-recruitment on small spatial scales, although substantial by ecological standards, may simply not be large enough in magnitude to affect genetic structure, as even small numbers of migrants between populations are sufficient to homogenize haplotype or allele frequencies (Wright, 1931). Even comparatively rare dispersal events could easily lead to panmixis as assayed by molecular markers (Palumbi, 2003;Kinlan et al, 2005). Second, it is also possible that molecular markers may not be neutral or that the species gene pool may represent a nonequilibrium system owing to historical demographic events such as population expansion.…”

“…In marine environments, multiple dispersal mechanisms operate, on varying spatio-temporal scales. In particular, the role of rare long-distance dispersal events may be of great importance over the longer timescales on which population connectivity is assessed by molecular markers, yet have little impact on demography measured over the short term (Kinlan et al, 2005).…”

Pelagic Larval Duration and Dispersal Distance Revisited

“…Our observations of the importance of behavior in determining dispersal distance have largely been ignored. Since Shanks et al (2003a) was published, a number of papers have presented models of larval dispersal that have attempted to estimate dispersal distance using PD coupled with oceanographic models with various degrees of sophistication (Siegel et al, 2003(Siegel et al, , 2008Kinlan et al, 2005;Edwards et al, 2007). Many of these models have assumed that larvae are passive; they present the null hypothesis of passive dispersal.…”