Abstract
Marine macrophytes are vertically distributed according to their ability to optimize their photosynthetic performance. We assessed the photo-physiological performance of the seagrass Cymodocea nodosa and the green seaweed Caulerpa prolifera at varying depth at Gran Canaria Island (Canary Islands, eastern Atlantic). The biomass of C. nodosa decreases with depth, while the opposite occurs for C. prolifera . Photochemical responses of both macrophytes were measured in shallow (5 m) and deep (20 m) waters at two times via chlorophyll a fluorescence and internal content of photoprotective pigments and antioxidant activity. We additionally carried out a reciprocal transplant experiment by relocating shallow and deep vegetative fragments of both macrophytes to assess their short-term photo-physiological acclimation. Overall, C. nodosa behaves as a ‘light-plant’, including a larger optimum quantum yield and ETR max under scenarios of high photosynthetically active radiation and a larger antioxidant activity. In contrast, C. prolifera is a ‘shade-adapted’ plant, showing a larger carotene content, particularly in shallow water. Deep-water C. nodosa and C. prolifera are more photochemically efficient than in shallow water. The alga C. prolifera shows a rapid, short-term acclimation to altered light regimes in terms of photosynthetic efficiency. In conclusion, decreased light regimes favour the photosynthetic performance of the green alga when both species coexist.
Highlights
A variety of marine macrophytes typically coexist in the same habitat; their distribution, may fluctuate under varying environmental conditions, operating at a range of spatial and temporal scales (Lüning 1990)
C. nodosa behaves as a ‘light-plant’, including a larger optimum quantum yield and ETRmax under scenarios of high photosynthetically active radiation and a larger antioxidant activity
Increasing turbidity in coastal areas alters the dominance and functioning of seascapes dominated by submersed vegetation, those constituted by marine angiosperms (Duarte et al 2008, Silva et al 2013)
Summary
A variety of marine macrophytes (e.g. seagrasses and macroalgae) typically coexist in the same habitat; their distribution, may fluctuate under varying environmental conditions (e.g. light, nutrients), operating at a range of spatial and temporal scales (Lüning 1990). Zonation patterns (or vertical distribution) of marine macrophytes are often related to their ability to resist high radiation stress (Hanelt 1998), e.g. uppershore species are more resistant to elevated solar UV In addition to their physiological responses, marine macrophytes show a certain degree of morphological flexibility that reflect long-term adaptations to varying environmental scenarios, including decreased light with depth in subtidal habitats (Olesen et al 2002). Ecophysiological approaches that integrate estimates of light absorption efficiency, pigment contents and mechanisms to dissipate excess energy (Hanelt 1998) provide useful insight to assess changes in the distribution of marine macrophytes This is pertinent under scenarios of global change, in which the intensity and frequency of anthropogenic perturbations are increasing. Understanding the physiological response of seagrasses and accompanying seaweeds to altered light regimes is important (Collier et al 2012)
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