Invasive rats reshape reef food webs by altering seabird nutrient flows
A new study shows that rats on tropical islands suppress seabird colonies, which in turn changes the balance between tiny reef fish and invertebrates on nearby coral reefs.
A team led by Lancaster University and the University of Texas investigated how invasive rats affect coral-reef communities around remote Indian Ocean islands. Rats, introduced centuries ago, have devastated seabird colonies, reducing guano-derived nutrient inputs to the sea by up to 760-fold. On rat-free islands, nutrient-rich runoff supports large populations of cryptobenthic fish, whose biomass exceeds that of small invertebrates by more than five times.
Conversely, rat-infested islands show higher numbers of coral crabs, porcelain crabs and snapping shrimp, while fish numbers fall, equalising the biomass of fish and invertebrates. The researchers suggest that lower nutrient levels favor invertebrates with slower metabolisms, while fish lose their competitive edge. This reconfiguration influences higher-trophic predators, which rely more on fish where seabirds thrive and shift toward invertebrate-based pathways where they do not. The findings highlight the broader ecological impact of invasive mammals on marine food webs.
Why it matters
The research reveals how land-based invasive species can restructure marine ecosystems, informing conservation strategies for both islands and reefs.
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