title: Seasonal changes in fish assemblage structure at a shallow seamount in the Gulf of California.
abstract: Seamounts have generally been identified as locations that can promote elevated productivity, biomass and predator biodiversity. These properties attract seamount-associated fisheries where elevated harvests can be obtained relative to surrounding areas. There exists large variation in the geological and oceanographic environment among the thousands of locations that fall within the broad definition of seamount. Global seamount surveys have revealed that not all seamounts are hotspots of biodiversity, and there remains a strong need to understand the mechanisms that underlie variation in species richness observed. We examined the process of fish species assembly at El Bajo Espiritu Santo (EBES) seamount in the Gulf of California over a five-year study period. To effectively quantify the relative abundance of fast-moving and schooling fishes in a 'blue water' habitat, we developed a simplified underwater visual census (UVC) methodology and analysis framework suitable for this setting and applicable to future studies in similar environments. We found correlations between seasonally changing community structure and variability in oceanographic conditions. Individual species responses to thermal habitat at EBES revealed three distinct assemblages, a 'fall assemblage' tracking warmer overall temperature, a 'spring assemblage' correlated with cooler temperature, and a 'year-round assemblage' with no significant response to temperature. Species richness was greatest in spring, when cool and warm water masses stratified the water column and a greater number of species from all three assemblages co-occurred. We discuss our findings in the context of potential mechanisms that could account for predator biodiversity at shallow seamounts.
authors.affiliation: Conservation Research Department, Monterey Bay Aquarium, Monterey, California, United States; Department of Wildlife, Fish, & Conservation Biology, University of California, Davis, California, United States.
authors.forename: Salvador J
authors.initials: SJ
authors.lastname: Jorgensen
authors.affiliation: Department of Wildlife, Fish, & Conservation Biology, University of California , Davis, California , United States.
authors.forename: A Peter
authors.initials: AP
authors.lastname: Klimley
authors.affiliation: Fisheries Ecology Program, Centro de Investigaciones Biológicas del Noroeste S. C. , La Paz, Baja California Sur , Mexico.
authors.forename: Arturo
authors.initials: A
authors.lastname: Muhlia-Melo
authors.affiliation: Bodega Marine Lab, University of California, Davis , Bodega Bay, California , United States.
authors.forename: Steven G
authors.initials: SG
authors.lastname: Morgan
keywords: Biodiversity; Community ecology; Fish assemblage; Gulf of California; Marine biology; Marine ecology; Oceanography; Sea of Cortez; Seamount; Underwater visual census