title: Habitat and scale shape the demographic fate of the keystone sea urchin Paracentrotus lividus in Mediterranean macrophyte communities.
abstract: Demographic processes exert different degrees of control as individuals grow, and in species that span several habitats and spatial scales, this can influence our ability to predict their population at a particular life-history stage given the previous life stage. In particular, when keystone species are involved, this relative coupling between demographic stages can have significant implications for the functioning of ecosystems. We examined benthic and pelagic abundances of the sea urchin Paracentrotus lividus in order to: 1) understand the main life-history bottlenecks by observing the degree of coupling between demographic stages; and 2) explore the processes driving these linkages. P. lividus is the dominant invertebrate herbivore in the Mediterranean Sea, and has been repeatedly observed to overgraze shallow beds of the seagrass Posidonia oceanica and rocky macroalgal communities. We used a hierarchical sampling design at different spatial scales (100 s, 10 s and <1 km) and habitats (seagrass and rocky macroalgae) to describe the spatial patterns in the abundance of different demographic stages (larvae, settlers, recruits and adults). Our results indicate that large-scale factors (potentially currents, nutrients, temperature, etc.) determine larval availability and settlement in the pelagic stages of urchin life history. In rocky macroalgal habitats, benthic processes (like predation) acting at large or medium scales drive adult abundances. In contrast, adult numbers in seagrass meadows are most likely influenced by factors like local migration (from adjoining rocky habitats) functioning at much smaller scales. The complexity of spatial and habitat-dependent processes shaping urchin populations demands a multiplicity of approaches when addressing habitat conservation actions, yet such actions are currently mostly aimed at managing predation processes and fish numbers. We argue that a more holistic ecosystem management also needs to incorporate the landscape and habitat-quality level processes (eutrophication, fragmentation, etc.) that together regulate the populations of this keystone herbivore.
authors.affiliation: Institut de Recerca i Tecnología Agroalimentàries (IRTA), Aquatic Ecosystems, Tarragona, Spain. patricia.prado@irta.cat
authors.forename: Patricia
authors.initials: P
authors.lastname: Prado
authors.forename: Fiona
authors.initials: F
authors.lastname: Tomas
authors.forename: Stefania
authors.initials: S
authors.lastname: Pinna
authors.forename: Simone
authors.initials: S
authors.lastname: Farina
authors.forename: Guillem
authors.initials: G
authors.lastname: Roca
authors.forename: Giulia
authors.initials: G
authors.lastname: Ceccherelli
authors.forename: Javier
authors.initials: J
authors.lastname: Romero
authors.forename: Teresa
authors.initials: T
authors.lastname: Alcoverro
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D017753:Ecosystem; D007814:Larva / Q000254:growth & development; D008018:Life Cycle Stages; D008522:Mediterranean Sea; D047328:Paracentrotus / Q000254:growth & development*; D011156:Population Density; D011157:Population Dynamics; D012044:Regression Analysis