MEPS 575:81-93 (2017)  -  DOI: https://doi.org/10.3354/meps12222

ABSTRACT: Light availability is a central determinant of seagrass physiology and therefore distributional patterns. While climax species usually inhabit areas with favorable light conditions, poor competitors like Halophila decipiens Ostenf. are often marginalized into areas of low and high light levels. Thus, their ecological success relies on the ability to withstand and quickly acclimate to contrasting light conditions. Here we determined the acclimation of H. decipiens to different light availabilities and its capacity to rapidly adjust to changing light environments. Morphological and physiological traits differed among depths, with deeper plants having longer, wider leaves and higher photosynthetic performance. This agreed with the reported shade-adapted nature of this species and suggests that the wide tolerance to different light environments of H. decipiens is accompanied by costs resulting in an optimal phenotype for high-light environments, but occasioning a decrease in fitness, most likely related to higher investments in photoprotection and photodamage repair. This species exhibits efficient photoprotective mechanisms, related to energy dissipation, but we also detected chloroplast movement in response to light intensity, which most likely protects the photosynthetic apparatus under high-light stress through minimizing light absorption. H. decipiens also showed high plasticity through quick morphological and physiological adjustments upon transplantation, within days exhibiting characteristics consistent with plants that had originated from the transplant site. This rapidly responding plasticity, in addition to the high sexual reproduction of this species and the formation of extensive seed banks, is likely one of the key features to understanding this species’ broad distribution and persistence when outcompeted to the distributional limits of dominant climax species.

KEY WORDS: Chloroplast movement · Halophila · Light stress · Photoacclimation · Photoprotection · Phenotypic plasticity · Seagrass · Transplants