首页|Fish grazing enhanced by nutrient enrichment may limit invasiveseagrass expansion
Fish grazing enhanced by nutrient enrichment may limit invasiveseagrass expansion
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NSTL
The success of invasive macrophytes can depend on local nutrient availability and consumer pressure, which mayinteract. We therefore experimentally investigated the interacting effects of nutrient (nitrogen and phosphorus)addition, the exclusion of large herbivorous fishes and mimicked grazing on the expansion rates of the invasiveseagrass Halophila stipulacea. The experiments were established on Bonaire and Aruba, two islands in thesouthern Caribbean, which differ in fish community structure. We observed that multiple Caribbean fish speciesfeed on H. stipulacea. At both study sites, nutrient enrichment decreased invasive leaf carbon:nitrogen ratios.However only on Bonaire, where herbivore fish abundance was 7 times higher and diversity was 4.5 timeshigher, did nutrient enrichment result in a significant reduction of H. stipulacea expansion into native Thalassiatestudinum meadows. This effect was likely due to increased herbivory on nutrient enriched seagrass leaves, as wefound that excluding large herbivorous fish (e.g. parrotfish) doubled invasive expansion rates in bare patches onBonaire. On Aruba, H. stipulacea expansion rates were higher overall, which coincided with lower abundancesand diversity of native fishes, and were limited by mimicked fish grazing. We suggest that top-down control bythe native fish community may counteract eutrophication effects by increased grazing pressure on nutrient-richinvasive seagrass leaves. We conclude that diverse and abundant herbivore communities likely play an importantrole in limiting invasion success and their conservation and restoration may serve as a tool to slow down seagrassinvasions.
NSTL
