Abstract. Coral reefs are among the most diverse and productive ecosystems on our planet. Scleractinian corals function as the primary reef ecosystem engineers, constructing the framework that serves as a habitat for all other coral reefassociated organisms. However, the coral's engineering role is particularly susceptible to global climate change. Ocean warming can cause extensive mass coral bleaching, which triggers dysfunction of major engineering processes. Sub-lethal bleaching results in the reduction of both primary productivity and coral calcification. This may lead to changes in the release of organic and inorganic products, thereby altering critical biogeochemical and recycling processes in reef ecosystems. Thermal stress-induced bleaching and subsequent coral mortality, along with ocean acidification, further lead to long-term shifts in benthic community structure, changes in topographic reef complexity, and the modification of reef functioning. Such shifts may cause negative feedback loops and further modification of coral-derived inorganic and organic products. This review emphasises the critical role of scleractinian corals as reef ecosystem engineers and highlights the control of corals over key reef ecosystem goods and services, including high biodiversity, coastal protection, fishing, and tourism. Thus, climate change by impeding coral ecosystem engineers will impair the ecosystem functioning of entire reefs.

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Macrocystis pyrifera (L.) C. Agardh is a canopyforming species that occupies the entire water column. The photosynthetic tissue of this alga is exposed to a broad range of environmental factors, particularly related to light quantity and quality. In the present work, photosynthetic performance, light absorption, pigment composition, and thermal dissipation were measured in blades collected from different depths to characterize the photoacclimation and photoprotection responses of M. pyrifera according to the position of its photosynthetic tissue in the water column. The most important response of M. pyrifera was the enhancement of photoprotection in surface and near-surface blades. The size of the xanthophyll cycle pigment pool (XC) was correlated to the nonphotochemical quenching (NPQ) of chl a fluorescence capacity of the blades. In surface blades, we detected the highest accumulation of UV-absorbing compounds, photoprotective carotenoids, RXC, and NPQ. These characteristics were important responses that allowed surface blades to present the highest maximum photosynthetic rate and the highest PSII electron transport rate. Therefore, surface blades made the highest contribution to algae production. In contrast, basal blades presented the opposite trend. These blades do not to contribute significantly to photosynthetate production of the whole organism, but they might be important for other functions, like nutrient uptake.

Summary• Here the mechanisms involved in excitation energy dissipation of Macrocystis pyrifera were characterized to explain the high nonphotochemical quenching of chlorophyll a (Chl a ) fluorescence (NPQ) capacity of this alga.• We performed a comparative analysis of NPQ and xanthophyll cycle (XC) activity in blades collected at different depths. The responses of the blades to dithiothreitol (DTT) and to the uncoupler NH 4 Cl were also assayed.• The degree of NPQ induction was related to the amount of zeaxanthin synthesized in high light. The inhibition of zeaxanthin synthesis with DTT blocked NPQ induction. A slow NPQ relaxation upon the addition of NH 4 Cl, which disrupts the transthylakoid proton gradient, was detected. The slow NPQ relaxation took place only in the presence of de-epoxidated XC pigments and was related to the epoxidation of zeaxanthin.• These results indicate that in M. pyrifera , in contrast to higher plants, the transthylakoid proton gradient alone does not induce NPQ. The role of this gradient seems to be related only to the activation of the violaxanthin de-epoxidase enzyme.