Spatial subsidies drive sweet spots of tropical marine biomass production

Abstract

Spatial subsidies increase local productivity and boost consumer abundance beyond the limits imposed by local resources. In marine ecosystems, deeper water and open ocean subsidies promote animal aggregations and enhance biomass that is critical for human harvesting. However, the scale of this phenomenon in tropical marine systems remains unknown. Here, we integrate a detailed assessment of biomass production in 3 key locations, spanning a major biodiversity and abundance gradient, with an ocean-scale dataset of fish counts to predict the extent and magnitude of plankton subsidies to fishes on coral reefs. We show that planktivorous fish-mediated spatial subsidies are widespread across the Indian and Pacific oceans and drive local spikes in biomass production that can lead to extreme productivity, up to 30 kg ha−1 day−1. Plankton subsidies form the basis of productivity “sweet spots” where planktivores provide more than 50% of the total fish production, more than all other trophic groups combined. These sweet spots operate at regional, site, and smaller local scales. By harvesting oceanic productivity, planktivores bypass spatial constraints imposed by local primary productivity, creating “oases” of tropical fish biomass that are accessible to humans.

The role of nocturnal fishes on coral reefs: A quantitative functional evaluation

“…Given their outstanding reported homing ability (Gardiner & Jones, 2016 ; Marnane, 2000 ), it is not impossible that these fishes could be traveling hundreds of metres to feed each night, as has been reported for pempherids, another family of small nocturnal reef fishes (Koeda et al, 2021 ). If this is the case, the high productivity of apogonids could represent a significant source of spatial subsidies underpinning energy and nutrient flows from off‐reef locations to coral reefs (Morais et al, 2021 ).…”

“…The nocturnal proportion of the cryptobenthic community (driven greatly by Apogonidae) is well retained in combined UVC strip censuses when compared with results from rotenone stations (the most effective way to sample cryptobenthic communities; Ackerman & Bellwood, 2000 , 2002). Biomass and its production is often dominated by planktivores, inconspicuous medium‐sized species or relatively small, but conspicuous, species (Brandl et al, 2019 ; Morais et al, 2021 ; Morais & Bellwood, 2019 ). Unlike almost all other UVCs, our methods include counts specifically aimed at these fishes.…”

“…Original data collected, also used in Morais and Bellwood et al ( 2019 ), Morais, Connolly, and Bellwood ( 2020 ), Morais, Depczynski, et al ( 2020 ), and Morais et al ( 2021 ). Trait data used in growth and mortality modeling compiled from multiple data sources, available in “Key Resources Table” in Morais and Bellwood ( 2019 ) and “Zenodo Repository” in Morais et al ( 2021 ).…”

“…for pempherids, another family of small nocturnal reef fishes (Koeda et al, 2021). If this is the case, the high productivity of apogonids could represent a significant source of spatial subsidies underpinning energy and nutrient flows from off-reef locations to coral reefs (Morais et al, 2021).…”

Hidden benefits and risks of partial protection for coral reef fisheries

“…Globally, there are also substantial differences in productivity estimates between reef fish functional groups, with most productivity in reef fish assemblages originating from planktivorous species and water column photosynthesis, rather than enclosed reef energetic pathways (Morais et al 2019(Morais et al , 2021.…”