High acclimation potential in floating Macrocystis pyrifera to abiotic conditions even under grazing pressure – a field study

Abstract

The persistence of floating seaweeds, which depends on abiotic conditions but also herbivory, had previously been mostly tested in outdoor mesocosm experiments. In order to investigate if the obtained mesocosm results of high seaweed persistence under natural environmental conditions and under grazing pressure can be extrapolated to field situations, we conducted in situ experiments. During two summers (2007 and 2008), Macrocystis pyrifera was tethered (for 14 d) to lines in the presence and absence of the amphipod Peramphithoe femorata at three sites (Iquique, Coquimbo, Calfuco). We hypothesized that grazing damage and seaweed persistence vary among sites due to different abiotic factors. By incubating the sporophytes in mesh bags, we were either able to isolate (grazing) or exclude (control) amphipods. To test for a mesh bag artifact, a set of sporophytes was incubated without mesh bags (natural). Mesh bags used to exclude herbivores influenced sporophyte growth and physiological performance. The chlorophyll a (Chl a) content depended largely on grazers and grazed sporophytes grew less than natural and control sporophytes within the two summers. A decrease in Chl a content was found for the sites with the highest prevailing irradiances and temperatures, suggesting an efficient acclimation to these sea surface conditions. Our field‐based results of sporophyte acclimation ability even under grazing pressure widely align with previous mesocosm results. We conclude that M. pyrifera and other temperate floating seaweeds can function as long‐distance dispersal vectors even with hitchhiking mesoherbivores.

Photosynthetic pigments of co-occurring Northeast Atlantic Laminaria spp. are unaffected by decomposition

“…Similarly, brown algal antenna size is larger in species that are distributed lower down on rocky shores and consequently receive less light (Caron et al 2001). Conversely, if kelps are exposed to higher natural (Rothäusler et al 2011a(Rothäusler et al , 2018 or artificial (Rothäusler et al 2011b) irradiance, they exhibit reduced pigmentation.…”

“…However, studies on pigment concentrations in macroalgal detritus have been restricted the southern hemisphere (Rothäusler et al 2018, Hees et al 2019, Tala et al 2019. With the exception of Hees et al (2019), past research has also focused solely on floating detritus which occupies a markedly different photoenvironment to benthic detritus of boreal kelps which lack pneumatocysts or buoyant porous tissues.…”

“…Sporophytes of the latter species can withstand temperatures up to 25°C (Franco et al 2018) and increasingly dominate temperate kelp forests in the face of climate change (Pessarrodona et al 2019). In addition to thermal tolerance, adaptability of the photosynthetic apparatus to prevailing light regimes may facilitate biogeographic shifts (Rothäusler et al 2018, Tala et al 2019. L. ochroleuca displays a characteristic light ochre colouration across its range (Franco et al 2018), begging the question whether or not L. ochroleuca has a lower photosynthetic pigmentation than its congeners, potentially constraining its distribution.…”

Cast adrift: Physiology and dispersal of benthic Sargassum spinuligerum in surface rafts

“…Quantum Yield measurements at each site were always made at the same time of day for week 0, 1, and 2, however, because of the logistical constraints of the experiment, the times were different among the three sites. The MQY of experimental individuals was therefore calculated as a proportion of the MQY values of benthic control seaweeds (Rothäusler et al ). This calculation allowed us to compare across treatments and among sites by removing potential variability in MQY that may exist throughout the daily photocycle period.…”

Comparison of the photo-acclimation potential of floating and benthic thalli of Sargassum horneri (Phaeophyta) during autumn and winter

“…Some seaweed produce UV-absorbing compounds, such as mycosporine-like amino acids (red and green seaweeds) and phlorotannins (brown seaweeds), to avoid damage caused by UVR (Quintano et al, 2019). To cope with high levels of PAR and UVR, fl oating seaweeds employ some photoprotective strategies; for example, accumulation of UV-absorbing compounds (van Hee et al, 2019), dissipation of excess light energy as heat (Rothäusler et al, 2018), and reducing the content of accumulated pigments (Zhao et al, 2016).…”