Photosynthetic response of monospecific macroalgal stands to density

Abstract

Photosynthesis by benthic marine macroalgae makes an important contribution to the productivity of coastal seas. Quantification of photosynthesis and productivity of macroalgal assemblages is therefore important in understanding ecosystem functioning in coastal seas and providing realistic values for coastal productivity in global models. Estimates of macroalgal productivity are often based on the photosynthetic characteristics of thallus pieces or whole thalli, and not on those of communities. Such methods may overestimate rates of productivity as they do not account for neighborhood shading effects that may reduce photosynthetic rates in macroalgal stands that typically have high densities. In order to determine whether productivity estimates based on individuals differ from those based on communities, a controlled laboratory experiment was conducted with 3 dominant sub-canopy macroalgal species (Cystophora scalaris, Xiphophora gladiata and Undaria pinnatifida) from southern New Zealand. Photosynthetic parameters (initial slope of the photosynthesis vs. irradiance [P-E] curve α, saturation irradiance E k , maximum rate of photosynthesis P max and darkrespiration R d ) were obtained via P-E experiments using a custom-built respirometry chamber for a range of densities that corresponded to the minimum, average and maximum densities of these species in the field. A 5 to 7-fold decrease in P max was observed when the density of the algal stand was above 1 ind. m -2. R d and α were also lower in communities than for individuals. Results illustrate that estimates based on single specimens substantially overestimate productivity and we recommend that the densities used in experiments reflect those observed in the field.KEY WORDS: Density · Photosynthesis · Primary production · Respiration · Seaweed · New Zealand · Cystophora scalaris · Undaria pinnatifida · Xiphophora gladiata Resale or republication not permitted without written consent of the publisherAquat Biol 13: [41][42][43][44][45][46][47][48][49] 2011 P max is reached; R d ; and β, the level of photoinhibition at high irradiances (Falkowski & Raven 2007) (Table 1).The photosynthetic parameters derived from P-E curves can be used to predict rates of primary production at different irradiances (Falkowski & Raven 2007). The most accurate approach is to use whole seaweeds, so that they remain connected to their storage re serves, which, for large seaweeds such as species from the Orders Fucales and Laminariales, may be located in the holdfast and stipe, i.e. for entire individuals the carbon and nitrogen sinks are still accessible (Gevaert et al. 2008). Consequently, for structurally complex seaweeds, photosynthetic responses ob tained from thallus pieces versus intact individuals can be quite different (Bin zer & Middelboe 2005, Middelboe et al. 2006, Sand-Jensen et al. 2007. Similarly, for nutrient uptake by members of the Fucales, the rates of thallus sections can be up to 10 times higher than those of whole algae (Harrison & Druehl 1982, Hurd & ...

Shading by giant kelp canopy can restrict the invasiveness of Undaria pinnatifida (Laminariales, Phaeophyceae)

“…Respiration ( R ) did not change in juveniles of both species transplanted to the IN condition, which contrasts with some previous studies. For instance, Richards et al (2011) observed a substantial reduction in R when adult sporophytes were experimentally shaded by a simulated dense canopy composed of overlapping seaweeds. Other studies found R highly variable (Campbell et al, 1999; Dean & Hurd, 2007).…”

“…Some authors state the superior photosynthetic performance and light‐use efficiency exhibited by adult sporophytes of U . pinnatifida (Campbell et al, 1999; Richards et al, 2011; Tait et al, 2015), critically contributed to its invasion success (Dean & Hurd, 2007, Desmond et al, 2019). Our results revealed that this apparent photosynthetic superiority could be further extrapolated to juvenile sporophytes.…”

“…Therefore, seaweeds have photoacclimation strategies to improve the capture of light, such as the increment of photosynthetic efficiency, α, and the reduction of compensation irradiance, E c (Umanzor et al, 2000). The photoacclimation capabilities of U. pinnatifida adult sporophytes have been examined previously (Desmond et al, 2019;Richards et al, 2011;Tait et al, 2015). However, little is known about the photo-physiology of juvenile stages, which is critical during the recruitment stage (see Campbell et al, 1999;Morelissen et al, 2013).…”

“…The photoacclimation capabilities of U . pinnatifida adult sporophytes have been examined previously (Desmond et al, 2019; Richards et al, 2011; Tait et al, 2015). However, little is known about the photo‐physiology of juvenile stages, which is critical during the recruitment stage (see Campbell et al, 1999; Morelissen et al, 2013).…”

Effect of UVB and temperature on the invasive algae Undaria pinnatifida

“…The success of U. pinnatifida in colonizing new environments is associated not only with its high physiological and morphological plasticity ), but also with its fast growth, high reproductive rate, and rapid maturation ). Research on this species in New Zealand has focused mainly on its natural spread (Forrest et al 2000), its physiology , Richards et al 2011) and its colonisation patterns (Hay & Sanderson 1999, Raffo et al 2009. Prior to the present study, the tolerance of U. pinnatifida to environmental changes has been poorly explored, even though these may lead to further invasive success under climate change, as seen in other invasive species , Bellard et al 2013, Ware et al 2014.…”