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.
Highlights
Ecosystems are frequently connected by flows of energy and material [1,2,3]
What are the energetic implications of these high abundances of planktivorous fishes for tropical coral reefs?
We searched for potential predictors of the proportional productivity of planktivores in these 3 locations. We found that this was predicted with high precision by planktivore species abundance and maximum size, current velocity, and pelagic net primary productivity (NPP) (Bayesian R2 = 0.80; are likely to be optimal (HPD) = 0.77 to 0.82)
Summary
Ecosystems are frequently connected by flows of energy and material [1,2,3]. These flows occur via the movement of resources (i.e., nutrients, detritus, or prey) or consumers across ecosystem boundaries, characterising spatial subsidies [2,3]. Contributed to funding: James Cook University (Postgraduate Research Scholarship to RAM, ACS and PSW, and HDR Competitive Research Training Grant to RAM), the Lizard Island Reef Research Foundation and plankton from a myriad of oceanographic mechanisms [14], and interhabitat consumer mobility, connect reefs to adjacent ecosystems across seascapes (e.g., mangroves, seagrass beds, open ocean) [15,16,17,18,19] These processes provide energy and nutrient subsidies and channel the productivity from large unconstrained areas to the strongly delineated coral reef structure. Sweet spots with extreme fish productivities (15 to 30 kg ha−1 day−1) were exclusively associated with dominance by planktivorous fishes, and no other guild
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