Genetic and experimental evidence for a mixed‐age, mixed‐origin bank of kelp microscopic stages in southern California

Abstract

Laboratory studies have demonstrated that the microscopic stages of kelps can rapidly resume development from a delayed state. Like terrestrial seeds or aquatic resting eggs, banks of delayed kelp stages may supplement population recovery after periods of stress, playing an important role for kelp populations that experience adult sporophyte absences due to seasonal or interannual disturbances. We found that removing the microscopic stages from natural rock substratum could prevent the appearance of juvenile kelp sporophytes for three months and the establishment of a diverse kelp assemblage for over four months within a southern California kelp forest. Juveniles were observed within one month in plots where microscopic stages were left intact, which may confer an advantage for the resulting sporophytes as they attain larger sizes before later recruiting neighbors. Microsatellite diversity was high (expected heterozygosity HE approximately 0.9) for juveniles and adults within our sites. Using a microsatellite-based parentage analysis for the dominant kelp, Macrocystis pyrifera, we estimated that a portion of the new M. pyrifera sporophyte recruits had originated from their parents at least seven months after their parents had disappeared. Similar delay durations have been demonstrated in recent laboratory studies. Additionally, our results suggest that zoospore dispersal distances > 50 m may be supported by including additional microsatellite loci in the analysis. We propose a mixed-age and, potentially, a mixed-origin bank of M. pyrifera gametophytes promotes maximal genetic diversity in recovering populations and reduces population genetic subdivision and self-fertilization rates for intact populations by promoting the survival of zoospores dispersed > 10 m and during inhospitable environmental conditions.

Deep reefs are climatic refugia for genetic diversity of marine forests

“…One hypothesis for this pattern is related to subpopulation structure. If arrested, development of microscopic stages (Carney et al ., ) is more common towards the warmer and nutrient‐poorer south (one of the hypotheses in Assis et al ., ), it could generate co‐existence of multiple subpopulations thereby promoting departures from random mating (temporal Wahlund effect; Morand et al ., ). A second and non‐exclusive hypothesis is supported by the lower sporophyte densities at most southern sites (Assis et al ., ).…”

Connectivity structures local population dynamics: a long‐term empirical test in a large metapopulation system

“…Additionally, male and female giant kelp spores must settle at high densities to ensure fertilization (.1 spore/mm 2 ; Reed 1990). However, additional research is needed to evaluate the survival and demographic importance of latent early life-history stages (Carney et al 2013). Lastly, early life-history stages of giant kelp (gametophytes and microscopic sporophytes) are capable of arrested development (up to a few months; Edwards and Herna´ndez-Carmona 2005) and this could further disrupt the relationship between connectivity and colonization.…”

“…Lastly, early life-history stages of giant kelp (gametophytes and microscopic sporophytes) are capable of arrested development (up to a few months; Edwards and Herna´ndez-Carmona 2005) and this could further disrupt the relationship between connectivity and colonization. However, additional research is needed to evaluate the survival and demographic importance of latent early life-history stages (Carney et al 2013).…”

A COMPARISON OF DRAGON KELP, EUALARIA FISTULOSA, (PHAEOPHYCEAE) FECUNDITY IN URCHIN BARRENS AND NEARBY KELP BEDS THROUGHOUT THE ALEUTIAN ARCHIPELAGO1

“…2004), it is likely that the Eualaria fistulosa sporophytes occurring in the urchin barrens play an important role in any subsequent recruitment within that habitat as most macroalgal recruitment is supported by the recent settlement of zoospores (e.g., Hoffman 1987, Reed 1990, Santelices 1990, Norton 1992). However, recent studies have also shown that at least some kelps can rely on long‐lived banks of dormant microscopic stages of mixed origins that accrue over time on the seafloor, ultimately reducing inbreeding and increasing their effective dispersal distances (Carney et al. in press).…”