Supply-Side Ecology Works Both Ways: The Link Between Benthic Adults, Fecundity, and Larval Recruits

Abstract

“Supply‐side” ecology recognizes the potential role that recruitment plays in the local population dynamics of open systems. Apart from the applied fisheries literature, the converse link between adults and the production of cohorts of recruits has received much less attention. We used a hierarchical sampling design to investigate the relationships between adult abundance, fecundity, and rates of larval recruitment by acroporid corals on 33 reefs in five sectors (250–400 km apart) stretching from north to south along the length of the Great Barrier Reef, Australia. Our goal was to quantify patterns of recruitment at multiple scales, and to explore the underlying mechanisms. Specifically, we predicted that large‐scale patterns of recruitment could be driven by changes in the abundance of adults and/or their fecundity, i.e., that corals exhibit a stock–recruitment relationship. The amount of recruitment by acroporids in each of two breeding seasons varied by more than 35‐fold among the five sectors. Adult density varied only twofold among sectors and was not correlated with recruitment at the sector or reef scale. In contrast, fecundity levels (the proportion of colonies on each reef that contained ripe eggs) varied from 15% to 100%, depending on sector, year, and species. Spatial and temporal variation in the fecundity of each of three common Acropora species explained most of the variation (72%) in recruitment by acroporids, indicating that the production of larvae is a major determinant of levels of recruitment at large scales. Once fecundity was accounted for, none of the other variables we examined (sector, reef area, abundance of adults, or year) contributed significantly to variation in recruitment. The relationship between fecundity and recruitment was nonlinear, i.e., rates of recruitment increased disproportionately when and where the proportion of gravid colonies approached 100%. This pattern is consistent with the hypothesis that enhanced fertilization success and/or predator satiation occurs during mass‐spawning events. Furthermore, it implies that small, sublethal changes in fecundity of corals could result in major reductions in recruitment.

Limited recruitment during relaxation events: Larval advection and behavior in an upwelling system

“…Tracking large fluctuations in the numbers of recruits at a focal study area cannot resolve whether most larvae died or were transported to neighboring locales beyond this area of inference (Morgan 1995). In contrast, sampling over large spatial and long temporal scales has demonstrated that larval production and recruitment can be coupled (Robertson et al 1988;Hughes et al 2000) and oceanographic patterns can result in predictable spatial changes in populations and communities (Yoshioka 1982;Broitman et al 2008;Shanks et al 2010).…”

Barnacle reproductive hotspots linked to nearshore ocean conditions

“…First principles suggest why organisms in some places should produce more offspring than those in other places, e.g., due to genetic or environmental variation. Yet few empirical examples (3)(4)(5)(6)(7)(8) exist from marine populations of spatial variation in reproductive output at scales relevant to management (10s to 100s of kilometers). Moreover, marine population models for reserve design often include the assumption that the coastal ocean is a wellmixed and fairly uniform environment, where potential recruits to the adult populations are part of a global ''pool'' (9).…”

Recruitment, abundance, and predation on the blue mussel (Mytilus edulis) on northeastern estuarine rocky shores

“…However, at some broader geographic scale (within or beyond Casco Bay), mussel recruit and adult abundances must be connected, as Hughes et al (2000) showed for corals on the Great Barrier Reef; this indeed is the basis of metapopulation theory and standard stock-recruitment models.…”