Historical comparisons reveal multiple drivers of decadal change of an ecosystem engineer at the range edge.

Biogenic reefs are important for habitat provision and coastal protection. Long-term datasets on the distribution and abundance of Sabellaria alveolata (L.) are available from Britain. The aim of this study was to combine historical records and contemporary data to (1) describe spatiotemporal variation in winter temperatures, (2) document short-term and long-term changes in the distribution and abundance of S. alveolata and discuss these changes in relation to extreme weather events and recent warming, and (3) assess the potential for artificial coastal defense structures to function as habitat for S. alveolata. A semi-quantitative abundance scale (ACFOR) was used to compare broadscale, long-term and interannual abundance of S. alveolata near its range edge in NW Britain. S. alveolata disappeared from the North Wales and Wirral coastlines where it had been abundant prior to the cold winter of 1962/1963. Population declines were also observed following the recent cold winters of 2009/2010 and 2010/2011. Extensive surveys in 2004 and 2012 revealed that S. alveolata had recolonized locations from which it had previously disappeared. Furthermore, it had increased in abundance at many locations, possibly in response to recent warming. S. alveolata was recorded on the majority of artificial coastal defense structures surveyed, suggesting that the proliferation of artificial coastal defense structures along this stretch of coastline may have enabled S. alveolata to spread across stretches of unsuitable natural habitat. Long-term and broadscale contextual monitoring is essential for monitoring responses of organisms to climate change. Historical data and gray literature can be invaluable sources of information. Our results support the theory that Lusitanian species are responding positively to climate warming but also that short-term extreme weather events can have potentially devastating widespread and lasting effects on organisms. Furthermore, the proliferation of coastal defense structures has implications for phylogeography, population genetics, and connectivity of coastal populations.

The influence of environmental factors on the abundance and recruitment of the sand crab Emerita analoga (Stimpson 1857): source-sink dynamics?

The sandcrab Emerita analoga is the dominant species inhabiting sandy beaches along the Pacific coast of the American continent. In our study, 10 sandy beaches were sampled seasonally from 2006 to 2011, including coastal planktonic sampling from 2006 to 2008. Two major population cores were detected, the first one in the northern part of the study area and the second in the area immediately to the south of the Itata River mouth. Zoeal stages were found along the entire coastal zone. Highest densities and recruitment were found during spring and summer of each year. PLS regression indicated that source-sink habitat proxies correlated positively with morphodynamic parameters; while beach slope and total organic matter were negatively correlated. These results agree with the source-sink hypothesis, finding higher densities of adults, recruits and cohort recurrence on open coast beaches with milder physical dynamics. Furthermore, a hypoxic event and a mega-earthquake/tsunami negatively affected recruitment at the inter-annual scale.

Spatial variation in concurrent settlement of three damselfishes: relationships with near-field current flow.

Replenishment of local populations of reef fishes typically occurs via settlement of planktonic larvae, a process that is variable in space and time. We examined spatial variation in settlement of three species of damselfishes (genus Dascyllus) in relation to variation in average near-field current speed. Although the larvae of these species colonized at the same times, they repeatedly exhibited qualitatively different spatial patterns of settlement in the lagoons of Moorea, French Polynesia. Each damselfish had a unique, temporally consistent pattern of variation in settlement relative to among-site variation in near-field flow speed. At the speeds encountered, settlement was related linearly to increasing average current flow for yellow-tail dascyllus (D. flavicaudus), was a positive but decelerating function for humbug dascyllus (D. aruanus) and was a hump-shaped function for three-spot dascyllus (D. trimaculatus). Such qualitatively different relationships could arise if variation in current speed affected an individual's probability of settling differently among the species. The generalized relationships between flow speed and settlement of these species predicted well the pattern of covariation in settlement of these species among new sites where the availability of suitable habitat was standardized. These findings imply that differences in larval abilities in the near-field can result in distinctly different patterns of larval colonization among species, even in the absence of any other source of variation.