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

Abstract

During summer 2009, we conducted a field experiment and a field survey at 30uS in the coastal Humboldt Current to determine how floating time affects the physiological performance of kelp rafts. For the field experiment kelp rafts were tethered in coastal waters and the field survey was specifically designed to collect freefloating Macrocystis pyrifera across a latitudinal temperature gradient that reflects natural floating time. Experimental kelps were kept under photosynthetic active radiation (PAR) and PAR + ultraviolet (UV; PAR + UV) using filter foils, and tethered at the sea surface in their natural habitat. Ultraviolet radiation (UVR) did not affect kelp physiology, but caused a decrease in kelp biomass. The field survey confirmed that sea-surface temperature increased with distance from upstream source populations of M. pyrifera. Rafts sampled at increasing distance from sources showed high epibiont cover and reduced blade lengths. Physiological performance declined with increasing size of algal epibionts, which are indicators of floating time. Rafts that were farthest from the southern source populations had lost their sporophylls, suggesting that dispersal potential decreases with increasing floating time. The combined effects of abiotic (UVR and temperature) and biotic factors accelerate degradation of M. pyrifera and, thus, can impede successful dispersal in the Humboldt Current at 30uS. This suggests that floating macroalgae can be important dispersal vectors in areas with moderate environmental stress (i.e., in temperate oceans).

Gall-forming protistan parasites infect southern bull kelp across the Southern Ocean, with prevalence increasing to the south

“…The Chilean coast is affected by a number of oceanic current systems, in particular the Humboldt Current, which transports cool water towards the equator, and the Peru Countercurrent, which transports warmer subtropical water to the south (Silva et al 2009). These currents affect a range of organisms along the Chilean coast (Peters & Breeman 1993), including kelp rafts (Rothäusler et al 2011), with similar currents affecting organismal larval stages (Gaylord & Gaines 2000). As such, the lack of strong phylogeographic structure in Chile across more than 1000 km of coastline (Fig.…”

Implications of climate change for macrophytic rafts and their hitchhikers

“…grazing) factors influence raft longevity (e.g. Vandendries sche et al 2007b, 2011a. Nevertheless, with most studies on this topic coming from a few prolific researchers, conclusions are for the most part confined to a small number of raft identities (e.g.…”

“…Second, increasing temperatures are likely to accelerate raft decay by influencing the interaction strength between herbivores and primary producers (Rothäusler et al , 2011b, and by increasing the rate of decay of rafting materials (Rothäusler et al 2011a). Metabolic theory predicts that as the temperature of an organism approaches its thermal optimum, metabolic rate will increase (Brown et al 2004).…”

“…Levels of herbivore pressure (Rothäusler & Thiel 2006, Vandendriessche et al 2007b, Rothäusler et al 2011d) and flow conditions (e.g. water temperature and ultraviolet radiation; Rothäusler et al 2011a) influence raft longevity. Thus, relative to other raft materials (e.g.…”

“…1). The quality of macrophytic rafts as dispersal vectors is influenced by physical and biological factors that influence their resource provision and longevity (Thiel 2003, Rothäusler et al 2011a. Traits of the macrophytic material influence breeding opportunities for rafting organisms (e.g.…”