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Cross-ecosystem nutrient transfer can enhance coral reef functioning in an otherwise oligotrophic environment. While the influence of seabird-derived nutrients on coral reef organisms is increasingly recognized, how they are integrated into reef food webs remains unclear. Cryptobenthic reef fishes are crucial for energy transfer on coral reefs, and their fast life histories imply that they respond strongly to seabird-derived nutrients. Here, we investigate how variation in nearshore seabird nutrient subsidies affects coral reef fish communities. By comparing fish communities across locations differing in seabird nutrient inputs and using stable isotope analysis, we explore nutrient integration across depth, their influence on cryptobenthic and associated larger reef fishes and investigated the relative reliance of cryptobenthic fishes on seabird-enriched benthic and non-enriched pelagic pathways. We find that, near seabird colonies, cryptobenthic fishes’ diets can transition from pelagic to benthic dominance; cryptobenthic fish communities are larger; herbivores and all feeding groups comprising potential cryptobenthic fish predators have higher biomass. Collectively, our results stress the importance of seabirds in shaping energy pathways and suggest that, even in dynamic, ocean-swept reef systems, cryptobenthic fishes can mobilize seabird subsidies and potentially act as a nutritional bridge to higher trophic levels.
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Freshwater mussels alter fish distributions through habitat modifications at fine spatial scales
Aggregations of freshwater mussels create patches that can benefit other organisms through direct habitat alterations or indirect stimulation of trophic resources via nutrient excretion and biodeposition. Spent shells and the shells of living mussels add complexity to benthic environments by providing shelter from predators and increasing habitat heterogeneity. Combined, these factors can increase primary productivity and macroinvertebrate abundance in patches where mussel biomass is high, providing valuable subsidies for some fishes and influencing their distributions. We performed a 12-wk field experiment to test whether fish distributions within mussel beds were most influenced by the presence of subsidies associated with live mussels or the biogenic habitat of shells. We used remote underwater video recordings to quantify fish occurrences at fifty 0.25-m2 experimental enclosures stocked with either live mussels (2-species assemblages), sham mussels (shells filled with sand), or sediment only. The biomass of algae and benthic macroinvertebrates increased over time but were uninfluenced by treatment. We detected more fish in live mussel and sham treatments than in the sediment-only treatment but found no difference between live mussel and sham treatments. Thus, habitat provided by mussel shells may be the primary benefit to fishes that co-occur with mussels. Increased spatiotemporal overlap between fish and mussels might strengthen ecosystem effects, such as nutrient cycling, and the role of both fish and mussels in freshwater ecosystems
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- Award ID(s):
- 1457542
- PAR ID:
- 10107381
- Date Published:
- Journal Name:
- Freshwater science
- ISSN:
- 2161-9565
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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