Browsing by Author "Wieters, EA"

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    Alongshore and temporal variability in chlorophyll a concentration in Chilean nearshore waters
    (2003) Wieters, EA; Kaplan, DM; Navarrete, SA; Sotomayor, A; Largier, J; Nielsen, KJ; Véliz, F
    Phytoplankton and particulate organic matter constitute the primary food source for adult filter-feeders, as well as for larval stages of many benthic and pelagic organisms. The structure and dynamics of nearshore benthic communities may be associated with variation in nearshore primary production. However, we know little about the scales of variability in phytoplankton in nearshore waters along open coasts, or about their causes. To characterize spatial and temporal patterns of chl a concentration, we conducted 2.5 yr of daily, shore-based monitoring at 3 sites separated by 10s of km within an upwelling region in central Chile. We found that: (1) peaks in chl a concentration were typically short-lived, persisting no longer than 4 d, (2) blooms occurred in spring to early summer months at all sites, but also during autumn months at 1 site (Las Cruces), and (3) the intensity and frequency of blooms were consistently different among sites; highest concentrations were at Las Cruces, lower at El Quisco, and the lowest at Quintay. Analyses of wind data and surface temperature, and inspection of Advanced Very High Resolution Radiometer (AVHRR) satellite images, suggested that among-site differences were due, at least in part, to alongshore variation in upwelling intensity and the formation of warm-water pockets or upwelling shadows in sections of the coast, such as Las Cruces. In contrast to the spatial pattern described offshore and over larger spatial scales, chl a concentrations were significantly lower at the coldest site, Quintay, located at the core of an upwelling center (Pta. Curaumilla), than at the warmer site of Las Cruces, which lies downstream from upwelling. Day-to-day variation in chl a levels during spring at Las Cruces seems related to the alongshore intrusion of waters upwelled upstream. Overall, the pattern observed at our 3 sites, together with previous studies at other upwelling systems, suggests that sections of the coast around 15 to 20 km downstream (equatorward) from upwelling centers could exhibit consistently higher phytoplankton concentrations than sites located in front of upwelling centers, generating a source-sink type of geographic pattern of nearshore nutrients and phytoplankton along the coast.
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    Scales of benthic-pelagic and the intensity of species interactions: From recruitment limitation to top-down control
    (2005) Navarrete, SA; Wieters, EA; Broitman, BR; Castilla, JC
    Large and usually unpredictable variation in species interaction strength has been a major roadblock to applying local experimental results to large-scale management and conservation issues. Recent studies explicitly considering benthic-pelagic coupling are starting to shed light on,and find regularities in, the causes of such large-scale variation in coastal ecosystems. Here, we evaluate the effects of variation in wind-driven upwelling on community regulation along 900 km of coastline of the southeastern Pacific, between 29 degrees S and 35 degrees S during 72 months. Variability in the intensity of upwelling occurring over tens of km produced predictable variation in recruitment of intertidal mussels, but not barnacles, and did not affect patterns of community structure. In contrast, sharp discontinuities in upwelling regimes produced abrupt and persistent breaks in the dynamics of benthic and pelagic communities over hundreds of km (regional) scales. Rates of mussel and barnacle recruitment changed sharply at approximate to 32 degrees-33 degrees S, determining a geographic break in adult abundance of these competitively dominant species. Analysis of satellite images demonstrates that regional-scale discontinuities in oceanographic regimes can couple benthic and pelagic systems, as evidenced by coincident breaks in dynamics and concentration of offshore surface chlorophyll-a. Field experiments showed that the paradigm of top-down control of intertidal benthic communities holds only south of the discontinuity. To the north, populations seem recruitment-limited, and predators have negligible effects, despite attaining similarly high abundances and potential predation effects across the region. Thus, geographically discontinuous oceanographic regimes set bounds to the strength of species interactions and define distinct regions for the design and implementation of sustainable management and conservation policies.
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    Upwelling control of positive interactions over mesoscales: a new link between bottom-up and top-down processes on rocky shores
    (2005) Wieters, EA
    The dependence of positive species interactions on the traits of individuals has rarely been explored, particularly in marine communities. Therefore, we have little idea about their generality, scales of variability, or reliance on local conditions. Transplant experiments and surveys conducted at 14 sites spanning across similar to 900 km of the central Chilean coast demonstrate that alongshore variation in upwelling, occurring over 10s to 100s of kilometers, explains among-site differences in growth rates of the turf-forming alga Gelidium chilense, which drives predictable landscape patterns in turf height. At upwelling centers, turf algae grew faster and attained taller heights than at warmer downstream locations, where the algal turf remained short because it grew slower and was pruned-back in winter. Replicated, reciprocal transplants of tall and short algal turf, combined with manipulations that controlled predator access to turf, revealed that recruitment of the mussel Perumytilus purpuratus was differentially enhanced by the turf; benefits were strong when the turf was short, but disappeared when the turf was tall. By determining mussel prey supply to higher trophic levels, upwelling-controlled facilitation has important consequences for community regulation. This is the first study to identify upwelling as a physical mechanism generating environmental conditions that (1) control trait-dependent habitat modification and (2) regulate the relative importance of facilitation in marine rocky intertidal communities.