Microbial and sponge loops modify fish production in phase‐shifting coral reefs

Abstract

Shifts from coral to algae dominance of corals reefs have been correlated to fish biomass loss and increased microbial metabolism. Here we investigated reef benthic and planktonic primary production, benthic dissolved organic carbon (DOC) release and bacterial growth efficiency in the Abrolhos Bank, South Atlantic. Benthic DOC release rates are higher while water column bacterial growth efficiency is lower at impacted reefs. A trophic model based on the benthic and planktonic primary production was able to predict the observed relative fish biomass in healthy reefs. In contrast, in impacted reefs, the observed omnivorous fish biomass is higher, while that of the herbivorous/coralivorous fish is lower than predicted by the primary production-based model. Incorporating recycling of benthic-derived carbon in the model through microbial and sponge loops explains the difference and predicts the relative fish biomass in both reef types. Increased benthic carbon release rates and bacterial carbon metabolism, but decreased bacterial growth efficiency could lead to carbon losses through respiration and account for the uncoupling of benthic and fish production in phase-shifting reefs. Carbon recycling by microbial and sponge loops seems to promote an increase of small-bodied fish productivity in phase-shifting coral reefs.

Bacterial Community Associated with the Reef Coral Mussismilia braziliensis's Momentum Boundary Layer over a Diel Cycle

“…Interestingly, pico- and nanoeukaryotes abundance were negatively correlated with total viral abundance ( r = −0.61 and −0.65, respectively). This suggests that a significant fraction of the active community might be comprised of eukaryotic viruses, despite the fact that these viruses comprise only about 10% of total the viral community (Brussaard et al, 2010; Silveira et al, 2015). It was not possible to differentiate groups V1, V2, and V3 in our samples, which correspond to bacteriophages or eukaryotic viruses, preventing to conclusively determine if the largest variance was indeed in the eukaryotic virus group (Brussaard, 2004; Brussaard et al, 2010).…”

“…Water column reef communities experience diurnal physiological changes in response to photosynthesis/respiration rates (Kayanne et al, 1995). Yet, these changes are thought to be a result of benthic respiration and calcification, as most reef production is of benthic origin (Kayanne et al, 1995; Silveira et al, 2015). The water column microbial communities in Heron Island, Great Barrier Reef, was significantly different between day and night (Sweet et al, 2010).…”

A test of the sponge-loop hypothesis for emergent Caribbean reef sponges

“…Therefore, the sponge-loop could be a dominant and previously unrealized component in the cycling of carbon for coral reef ecosystems. Indeed, it has already been invoked to explain phase shifts in fish biomass on impacted reefs (Silveira et al 2015). Moreover, DOM consumption by sponges may contribute to a reciprocal positive interaction with macroalgae, whereby remineralized nutrients fuel the growth of macroalgae that subsequently results in enhanced levels of macroalgalderived DOM; a process termed the 'vicious circle hypothesis' because of the detrimental effect that enhanced sponge and macroalgal growth has on the ability of reef-building corals to compete for space in benthic reef communities .…”

Living inside a sponge skeleton: the association of a sponge, a macroalga and a diatom

“…However, most of the studies refer to associations which occur in tropical reefs (Lemloh et al 2009;Steindler et al 2002). Due to their abundance and ubiquity, sponges play a role in the benthic-pelagic coupling by removing organic matter from the water column (Silveira et al 2015). Phototrophic symbionts may contribute up to 80 % of the carbon assimilated by the sponge (Maldonado et al 2012 and references therein), suggesting that even endozoic algae affect its nutrient intake.…”