Unraveling the influence of environmental variability and cryptic benthic assemblages on reef-scale primary production and calcification

Recovery of ecosystem function in the aftermath of climate extremes such as cyclones and marine heat waves occurs in contest of highly variable environmental conditions and more chronic disturbances such as ocean acidification, which can further alter community structure and function. The present study investigated short-term responses of reef-scale primary production (Net Ecosystem Production; NEP), calcification (Net Ecosystem Calcification; NEC) and community structure in 2018 and again five years later in 2022 on a coral reef flat in Lizard Island on Australia’s Great Barrier Reef, between and following multiple consecutive stressors, namely two cyclones (2014 and 2015) and back-to-back bleaching events (2016–2017 and 2020). NEC in 2022 was highly variable compared to what it was in 2018. Conversely, NEP was higher in 2022 even though light availability was often reduced by cloud cover. High variability in NEC indicated that environmental parameters may have immediate impacts on carbonate chemistry in seawater and may largely and quickly affect short-term recovery trajectories. Therefore, comparison of metabolic rates over short time scales across decades should be done with caution. We also found that cover of calcifiers and particularly algae were highest in coral rubble suggesting that typical benthic surveys in the open reef flat largely underestimate their abundance and possible contribution to NEP and NEC. This study adds to the evidence that NEC and NEP might not be exclusively related to coral cover and likely not tied to vertical reef accretion.