No sex-related dispersal limitation in a dioecious, oceanic long-distance traveller: the bull kelp Durvillaea antarctica

Abstract

Dispersal of dioecious floating seaweeds could be limited due to biological constraints. This study examined for benthic and floating populations (stranded individuals) of the rafting kelp Durvillaea antarctica whether male and female individuals cohabit within one holdfast. As a previous study had indicated colour differences between sexes, we also examined whether these colour differences are consistent and possibly related to pigment and phlorotannin concentrations. Our large-scale survey of rafted holdfasts and a small-scale survey of benthic holdfasts at two sites found that reproductive males and females do travel together in coalesced holdfasts, although this proportion is relatively low (5-17%). There were no sex-specific differences in pigment and phlorotannin concentrations, but there were significant differences between the two benthic populations. There was no relationship between the colouration of thalli and the concentration of pigments but there was a slight colour difference between vegetative and reproductive sexual stages. Based on these results we conclude that biological conditions are not the cause for the lack of genetic connectivity between D. antarctica populations from central Chile. Instead, we suggest that ecological processes, such as density-blocking and physical factors (i.e. currents and winds), limit the potential for successful rafting dispersal.

Latitudinal and seasonal effects on short-term acclimation of floating kelp species from the South-East Pacific

“…At mid latitudes (Concepción), M. pyrifera showed high reproductive activity in both seasons indicating their perennial strategies and high potential for rafting dispersal under moderate environmental conditions. In contrast, Durvillaea antarctica showed a strong seasonal (fall-winter) reproductive pattern in benthic (Santelices et al, 1980;Collantes et al, 2002) as well as in floating conditions Lizée-Prynne et al, 2016) along the SE Pacific. The consistently seasonal reproductive phenology of D. antarctica (Santelices et al, 1980;Collantes et al, 2002;Tala et al, 2013), confirmed herein for all three study sites, suggests that successful gamete dispersal is restricted to the cold season throughout its distributional range.…”

The variable routes of rafting: stranding dynamics of floating bull kelp Durvillaea antarctica (Fucales, Phaeophyceae) on beaches in the SE Pacific

“…Lizée‐Prynne et al. () showed for stranded and benthic holdfasts of D. antarctica that between 5% and 17% of all plants contain both sexes in reproductive stage, although only 50% tended to have multiple stipes. Consequently, the probability of successful rafting dispersal is lower in areas with small plants, such as the MED.…”

“…Given the purpose of the study and to simplify subsequent analyses, herein we only distinguished two maturity stages of tissues, namely “vegetative” and “reproductive” (see also Lizée‐Prynne et al. ): Vegetative: absence of cellular differentiation or initial differentiation of immature conceptacle between the subcortex and the medulla. In some cases, there may be newly formed conceptacles but, as the gametes are undeveloped and the sex is unidentifiable, these samples were considered as vegetative.…”

“…In D. antarctica , each stipe within a coalesced holdfast represents a single individual (Lizée‐Prynne et al. ), and therefore the percentage was calculated based on the total number of stipes analyzed for each beach. Also, the number of plants that had stipes at least 50 cm long was quantified, because at this size the individuals start to become sexually mature (Collantes et al.…”

“…, ), although there is no evidence for functional differences (i.e., pigment and phlorotannin concentrations) between sexes (Lizée‐Prynne et al. ). Furthermore, there are abundant strandings of kelp rafts on rocky and sandy beaches of southern‐central Chile (~39°S, see also Duarte et al.…”