Strong top-down control in southern California kelp forest ecosystems.
ABSTRACT Global-scale changes in anthropogenic nutrient input into marine ecosystems via terrestrial runoff, coupled with widespread predator removal via fishing, have created greater urgency for understanding the relative role of top-down versus bottom-up control of food web dynamics. Yet recent large-scale studies of community regulation in marine ecosystems have shown dramatically different results that leave this issue largely unresolved. We combined a multiyear, large-scale data set of species abundances for 46 species in kelp forests from the California Channel Islands with satellite-derived primary production and found that top-down control explains 7- to 10-fold more of the variance in abundance of bottom and mid-trophic levels than does bottom-up control. This top-down control was propagated via a variety of species-level direct and indirect responses to predator abundance. Management of top-down influences such as fishing may be more important in coastal marine ecosystems, particularly in kelp forest systems, than is commonly thought.
Full-textDOI: · Available from: Bernardo R Broitman, Jun 21, 2015
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ABSTRACT: AimTo improve our understanding of how parasitism interacts with geographical range expansions by quantifying diversity and abundance of parasites in 25 populations of a large marine snail, Kellet's whelk (Kelletia kelletii), throughout its historical and recently expanded range, which are separated by a well-known biogeographical boundary.LocationCalifornia coast (western North America).Methods Parasitological examinations were conducted on 199 whelks from 25 subtidal reefs throughout its expanded and historical ranges. We calculated infection risk, parasite intensity, and parasite species diversity. Abiotic (temperature, latitude, distance from range limit) and biotic (host density) variables were analysed as potential drivers of differential parasitism between expanded- and historical-range populations.ResultsCompared with historical-range whelks, expanded-range whelks were 20% as likely to be infected by parasites, and those that were infected had 6% the number of individual parasites. On average, expanded-range whelks had 14% the number of parasite species than the historical-range whelks. The marked decrease in species richness of parasites infecting expanded-range whelks was only partly explained by the low numbers of parasites. The reduced parasite abundance and diversity in the expanded-range whelks was not explained by the examined abiotic factors or by whelk density.Main conclusionsExpanded-range populations of Kellet's whelk experience substantially lower parasite abundance and diversity than the historical-range populations, despite relatively poor demographic performance. The reduced parasitism observed resembles the enemy escape typically characterizing invasive species. A possible explanation for the observed ‘parasite escape’ is that the biogeographical boundary limits the movements or drives the low abundance of other host species (elasmobranchs) required to complete the life cycles of the ‘missing’ parasites. We suggest that parasite escape may generally characterize range-margin expansions and be important in permitting expansions into what may otherwise be marginal habitats. This parasite escape may directly counter the spread of infectious diseases associated with global warming-induced range shifts.Journal of Biogeography 05/2014; 41(9). DOI:10.1111/jbi.12329 · 4.97 Impact Factor
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ABSTRACT: This paper argues that European colonialism from AD 1500 to the early 1800s marked a fundamental transformation in human-environment interactions across much of the world. The rapid founding of various colonial enterprises, particularly mission and managerial colonies, unleashed mission agrarian systems, plantations, fur trade outposts, and commercial fishing and whaling ventures into various tropical and temperate ecosystems in the Americas, Oceania, India, Asia, and Africa, which had tremendous repercussions for indigenous faunal and floral populations. These colonial enterprises placed tremendous pressures on long-standing anthropogenic landscapes leading to significant modifications with the invasion of foreign species, the disruption of native habitats, the extermination of keystone species, and in some places, the loss of biodiversity. We conclude with a case study that considers how anthropogenic environments in Alta and Baja California created by native peoples over many centuries became entangled with mission ranching and commercial fur hunting. Our findings support a longer chronology for the Anthropocene than traditionally recognized.12/2013; 4:101-115. DOI:10.1016/j.ancene.2013.09.002
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ABSTRACT: Seaweed beds can serve as a significant carbon dioxide (CO2) sink while also satisfying global needs for food, fodder, fuel, and pharmaceutical products. The goal of our Korean Project has been to develop new baseline and monitoring methodologies for mitigation and adaptation within the context of climate change. Using innovative research approaches, we have established the Coastal CO2 Removal Belt (CCRB), which comprises both natural and man-made plant communities in the coastal region of southern Korea. Implemented on various spatial-temporal scales, this scheme promotes the removal of CO2 via marine forests. For example, when populated with the perennial brown alga Ecklonia, a pilot CCRB farm can draw down similar to 10 t of CO2 per ha per year. This success is manifested by an increment in biomass accumulations and a decrease in the amount of dissolved inorganic carbon in the water column.ICES Journal of Marine Science 08/2013; 70(5):1038-1044. DOI:10.1093/icesjms/fss206 · 2.53 Impact Factor