First photosynthetic characterization of the giant kelp Macrocystis pyrifera from the Comau Fjord, Northern Patagonia region

Giant kelp ( Macrocystis pyrifera ) covers large coastal areas along the Comau Fjord (Northern Patagonia), following different environmental gradients that determine its structural complexity. In the present study, we compared the morphological (thallus length and biomass, holdfast diameter, blade morphology, etc.) and photobiological characteristics based on fluorescence (Effective Quantum Yield and P-I Curve Parameters) of six populations along the coast of Comau Fjord in three areas: Lilihuapi Island, Cahuelmo sector and Comau Fjord interior. The main results show that along the Comau Fjord, we found different structural conformations of M. pyrifera populations, where only at the mouth of the fjord was it possible to record a well-established “kelp forest”, while in its interior the “cords” parallel to the coastline predominated. The major differences between these types of populations of M. pyrifera populations were related to the shape of the blades ( e.g. , > blade areas in 4-CF, 5-Cf, and 6-Cf), being this a photo-acclimation strategy that responds to a marked environmental gradient along the fjord, in addition to particular geomorphology, surrounded by mountain ranges, which limits the availability of light during the pre-winter period, which translates into a balance along the Comau Fjord in its photosynthetic efficiency (α = 0.41, p  < 0.05 between sites) of optimizing light absorption. These adaptations help the algae to resist local and seasonal changes in water column conditions, adjusting its light use to low levels, similar to Antarctic brown algae, and cope with low light conditions. This type of study corresponds to the first morphological and physiological characterization of natural populations of M. pyrifera in this area of Northern Patagonia and underlines the importance of continuing to collect information on a broader spatio-temporal scale to understand how stressors influence the morphology and physiology of these populations in a region that is suffering the consequences of global climate change, such as Northern Patagonia, and that is also intensely impacted by local anthropogenic activities.