Abstract
A widespread mass mortality event of the sea urchin Diadema africanum was detected in the subtropical eastern Atlantic, extending from Madeira to the Canary Islands, covering a straight- line distance of >400 km. This is the first disease- related die-off of a diadematid documented in the eastern Atlantic Ocean. Diseased individuals showed deterioration of the epidermis and water-vascular system, resulting in epidermal necrosis and release of spines. Despite some spatial heterogeneity in disease incidence at the study sites, there was a 65% overall reduction in urchin abundance after the mortality event compared to numbers pre-mortality. However, the reduction in urchin numbers did not compromise the species' reproductive success; the settlement peak following the mortality event was of a similar magnitude to that in prior years. Bacterial isolation and cul ture techniques, and subsequent laboratory in fection experiments, strongly suggested that Vibrio alginolyticus was involved in the disease. We hypo thesize that the mass mortality event devel- oped due to anomalously high seawater tempera- tures recorded in the 2 studied archipelagos and that warmer temperatures enabled infection of D. africa - num by waterborne pathogenic bacteria. Fluctua- tions in urchin populations are key in de termining the structure and functioning of benthic ecosystems: under the current seawater warming scenario, dis- ease may result in more frequent phase shifts, aiding the persistence of macroalgae.
Highlights
In recent decades, mass mortality events resulting from disease have been widely described in the marine environment (e.g. Goreau et al 1998, HoeghGuldberg 1999, Porter et al 2001) and the prevalence or severity of these disease outbreaks in marine organisms appears to be increasing (Epstein 1996, Harvell et al 1999, Hayes et al 2001, Lafferty et al 2004)
Benthic communities in the eastern Atlantic Archipelagos, including Madeira and the Canary Islands during the months of February to (Island), similar to other temperate and subtropical regions, are often characterized by 1 of 2 alternative community states: productive macroalgal beds or barren grounds dominated by sea urchins and encrusting coralline algae (Hernández et al 2008a)
Each artificial collector consisted of 100 moulded 3.9 cm diameter plastic balls placed into a mesh bag (Hernández et al 2006), which provided a large surface area favourable for larval settlement (Harrold et al 1991, Hernández et al 2010). These collectors were used at 2 urchinbarren sites off Tenerife, Canary Islands (Abades and Boca Cangrejo) (Fig. 1), where long-term settlement data were available for the sea urchin before the occurrence of the mortality event (2003 to 2008)
Summary
Mass mortality events resulting from disease have been widely described in the marine environment (e.g. Goreau et al 1998, HoeghGuldberg 1999, Porter et al 2001) and the prevalence or severity of these disease outbreaks in marine organisms appears to be increasing (Epstein 1996, Harvell et al 1999, Hayes et al 2001, Lafferty et al 2004). In this location, the mortality events were associated with increases in SST and an increase in the incidence of tropical storms (Scheibling & Hennigar 1997, Scheibling et al 2010, Feehan et al 2012). Benthic communities in the eastern Atlantic Archipelagos, including Madeira and the Canary Islands, similar to other temperate and subtropical regions, are often characterized by 1 of 2 alternative community states: productive macroalgal beds or barren grounds dominated by sea urchins and encrusting coralline algae (Hernández et al 2008a). The comprehensive study of this phenomenon aids our understanding of mechanisms that mediate transitions between alternate
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