PRESENCE OF SPOROPHYLLS IN FLOATING KELP RAFTS OF MACROCYSTIS SPP. (PHAEOPHYCEAE) ALONG THE CHILEAN PACIFIC COAST¹

Abstract

Some species of macroalgae continue to live for extended periods of time after detachment and may even maintain reproductive structures, yet very little is known about this process. Here, we describe the presence of sporophylls (with sporogenous tissues) on floating kelp rafts of Macrocystis spp. along the coast of Chile. Surveys were conducted at nine sites (18-501 S) during austral summer 2002, and floating kelp rafts were seen and collected at seven of these nine sites (between 22 and 501 S). Fifteen (26.8%) of the 56 samples had sporophylls, indicating maintenance of sporophylls after detachment. Some of the kelp sporophytes with reproductive blades showed signs of having been afloat for long periods (indicated by the large size of attached stalked barnacles). Additionally, experiments showed that floating kelps released viable zoospores. To understand the reproductive dynamics of floating kelps, we compared these results with information from attached populations of Macrocystis spp. at nearby coastal sites. In general, attached kelp had higher proportions of sporophylls than floating rafts, suggesting that detachment may negatively affect reproductive status. Nevertheless, floating kelps remained functionally reproductive, suggesting that zoospores may be dispersed via floating rafts. Published reports on other macroalgae indicate that some species (Lessoniaceae, Fucaceae, and Sargassaceae) are fertile and probably release zoospores or zygotes while floating or drifting in ocean currents. Because dispersal distances achieved by spores of most macroalgae are relatively short, release of spores from floating algae may be an alternative mechanism of long-distance dispersal.

Kelps’ Long-Distance Dispersal: Role of Ecological/Oceanographic Processes and Implications to Marine Forest Conservation

“…It is essential to recognize that these species are known for their ability to travel long distances due to morphological structures, such as aerocysts, which provide buoyancy [39,45,94,95]. Studies involving passive dispersion of these species recorded distances of tens of kilometers [46,96].…”

Oceanic rafting by a coastal community

“…Weekly inspection of beach-cast bull kelp (wrack) at St Clair Beach, South Island (New Zealand), typically reveals D. antarctica plants completely lacking or bearing only small goose barnacles (C. I. Fraser 2006 -2010, personal observation; figure 1a), indicating a short duration at sea following local detachment [19]. By contrast, five complete specimens of beach-cast D. antarctica covered in notably large Lepas australis (figure 1b) were found at St Clair Beach on 26 February 2009, and a sixth such specimen was collected on 30 May 2010.…”

“…that rapidly colonize flotsam in the marine environment [19,31,32,37]. For each bull kelp specimen, the 10 largest Lepas barnacles were removed and preserved in 95 per cent ethanol.…”

Kelp rafts in the Humboldt Current: Interplay of abiotic and biotic factors limit their floating persistence and dispersal potential

“…Assuming that these epibionts colonize floating algae shortly after they become detached, their growth rates serve as good approximations of minimum algal floating duration (Macaya et al 2005). Thus, the approximate growth rate of bryozoans and stalked barnacles was used to evaluate whether the distance from source populations is related to floating time.…”