title: Marine fisheries declines viewed upside down: human impacts on consumer-driven nutrient recycling.
abstract: We quantified how two human impacts (overfishing and habitat fragmentation) in nearshore marine ecosystems may affect ecosystem function by altering the role of fish as nutrient vectors. We empirically quantified size-specific excretion rates of one of the most abundant fishes (gray snapper, Lutjanus griseus) in The Bahamas and combined these with surveys of fish abundance to estimate population-level excretion rates. The study was conducted across gradients of two human disturbances: overfishing and ecosystem fragmentation (estuaries bisected by roads), to evaluate how each could result in reduced population-level nutrient cycling by consumers. Mean estimated N and P excretion rates for gray snapper populations were on average 456% and 541% higher, respectively, in unfished sites. Ecosystem fragmentation resulted in significant reductions of recycling rates by snapper, with degree of creek fragmentation explaining 86% and 72% of the variance in estimated excretion for dissolved N and P, respectively. Additionally, we used nutrient limitation assays and primary producer nutrient content to provide a simple example of how marine fishery declines may affect primary production. This study provides an initial step toward integrating marine fishery declines and consumer-driven nutrient recycling to more fully understand the implications of human impacts in marine ecosystems.
authors.affiliation: Marine Sciences Program, Department of Biological Sciences, Florida International University, 3000 NE 151st Street, North Miami, Florida 33181, USA. cal1634@yahoo.com
authors.forename: Craig A
authors.initials: CA
authors.lastname: Layman
authors.forename: Jacob E
authors.initials: JE
authors.lastname: Allgeier
authors.forename: Amy D
authors.initials: AD
authors.lastname: Rosemond
authors.forename: Craig P
authors.initials: CP
authors.lastname: Dahlgren
authors.forename: Lauren A
authors.initials: LA
authors.lastname: Yeager
mesh_terms: D000818:Animals; D017753:Ecosystem; D004777:Environment; D004784:Environmental Monitoring; D005398:Fisheries; D006802:Human Activities; D009584:Nitrogen / Q000737:chemistry / Q000378:metabolism; D010473:Perciformes / Q000502:physiology*; D010758:Phosphorus / Q000737:chemistry / Q000378:metabolism
chemical_list: D010758:Phosphorus; D009584:Nitrogen