Abstract
Ecosystem services provided by coral reefs may be susceptible to the combined effects of benthic species shifts and anthropogenic nutrient pollution, but related field studies are scarce. We thus investigated in situ how dissolved inorganic nutrient enrichment, maintained for two months, affected community-wide biogeochemical functions of intact coral- and degraded algae-dominated reef patches in the central Red Sea. Results from benthic chamber incubations revealed 87% increased gross productivity and a shift from net calcification to dissolution in algae-dominated communities after nutrient enrichment, but the same processes were unaffected by nutrients in neighboring coral communities. Both community types changed from net dissolved organic nitrogen sinks to sources, but the increase in net release was 56% higher in algae-dominated communities. Nutrient pollution may, thus, amplify the effects of community shifts on key ecosystem services of coral reefs, possibly leading to a loss of structurally complex habitats with carbonate dissolution and altered nutrient recycling.
Highlights
Coral reefs are among the most productive and biologically diverse ecosystems on Earth, despite generally growing in oligotrophic tropical waters (Hatcher, 1990)
The present study suggests similar directions and magnitudes of major biogeochemical processes of coral- and algae-dominated com munities at Abu Shosha reef in January 2018
The rates are in line with the literature (Albright et al, 2015, 2013; Roth et al, 2020), they are in contrast with some studies reporting significantly higher organic C turnover with a greater potential for autotrophic biomass accumulation per planar square meter of the reef for algae- compared to coraldominated communities (Fong and Paul, 2011; Kelly et al, 2017)
Summary
Coral reefs are among the most productive and biologically diverse ecosystems on Earth, despite generally growing in oligotrophic tropical waters (Hatcher, 1990). Under these conditions, the photo-symbiotic association of corals with dinoflagellate algae (LaJeunesse et al, 2018; Muscatine and Porter, 1977) and the efficient retention and recycling of carbon (C) and nitrogen (N) are critical to maintaining ecosystem functioning and support growth (De Goeij et al, 2013; Odum and Odum, 1955; Wild et al, 2004). Many extant coral reefs are characterized by a mosaic of co-occurring species (Lin and Denis, 2019; Ninio and Meekan, 2002; Tkachenko et al, 2007), a state with a lower coral cover that may evolve into a stable state supported by coral degradation events worldwide (Bellwood et al, 2019; Birkeland et al, 2017)
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