title: Deep-water kelp refugia as potential hotspots of tropical marine diversity and productivity.
abstract: Classic marine ecological paradigms view kelp forests as inherently temperate-boreal phenomena replaced by coral reefs in tropical waters. These paradigms hinge on the notion that tropical surface waters are too warm and nutrient-depleted to support kelp productivity and survival. We present a synthetic oceanographic and ecophysiological model that accurately identifies all known kelp populations and, by using the same criteria, predicts the existence of >23,500 km(2) unexplored submerged (30- to 200-m depth) tropical kelp habitats. Predicted tropical kelp habitats were most probable in regions where bathymetry and upwelling resulted in mixed-layer shoaling above the depth of minimum annual irradiance dose for kelp survival. Using model predictions, we discovered extensive new deep-water Eisenia galapagensis populations in the Galápagos that increased in abundance with increasing depth to >60 m, complete with cold-water flora and fauna of temperate affinities. The predictability of deep-water kelp habitat and the discovery of expansive deep-water Galápagos kelp forests validate the extent of deep-water tropical kelp refugia, with potential implications for regional productivity and biodiversity, tropical food web ecology, and understanding of the resilience of tropical marine systems to climate change.
authors.affiliation: Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA. mgraham@mlml.calstate.edu
authors.forename: Michael H
authors.initials: MH
authors.lastname: Graham
authors.forename: Brian P
authors.initials: BP
authors.lastname: Kinlan
authors.forename: Louis D
authors.initials: LD
authors.lastname: Druehl
authors.forename: Lauren E
authors.initials: LE
authors.lastname: Garske
authors.forename: Stuart
authors.initials: S
authors.lastname: Banks
mesh_terms: D001267:Atlantic Ocean; D004463:Ecology; D044423:Kelp / Q000502:physiology*; D008386:Marine Biology; D010140:Pacific Ocean; D012623:Seawater