Understanding the relationship between biodiversity and stability is a central issue in ecology. This is particularly needed under current scenarios of biodiversity loss due to multiple anthropogenic stressors. In this study, we experimentally examined the combined effects of the loss of key functional species (canopy-forming macroalgae) and mechanical disturbance on macroalgal intertidal assemblages at 2 sites along the rocky coast of northern Portugal. We tested the model that the canopy may buffer the effects of disturbance on associated organisms, leading to the logical hypothesis that effects of mechanical disturbance would be lower where the canopy was left intact compared to patches where it was experimentally removed. The proposed model was supported by multivariate and univariate results, as both differences in the structure of whole assemblages and in the abundance of individual taxa between disturbed and undisturbed assemblages were reduced or prevented by the presence of the canopy, independently of the examined site. Specifically, only in the absence of the canopy did disturbance determine a decrease in the abundance of the red alga Ahnfeltiopsis devoniensis and an increase in articulated coralline algae of the genus Corallina. Present findings have relevant implications for understanding and predicting the consequences of multiple factors responsible for the erosion of biodiversity occurring globally in coastal areas, as current rates of loss of canopy-forming species in urban areas may be expected to exacerbate the effects of predicted climate change, including modifications in intensity and temporal patterns of storms. KEY WORDS: Biodiversity · Multiple stressors · Canopy algae · Disturbance · Rocky intertidal Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 414: [107][108][109][110][111][112][113][114][115][116] 2010 ability of communities to resist perturbations. These include specific studies on macroalgal beds and thermal stress (Allison 2004), eelgrass meadows and grazing by geese (Hughes & Stachowicz 2004) or disturbance (Williams 2001, Reusch et al. 2005, and microalgal biomass and combinations of sediment types and varying temperatures (Worm et al. 2006). The ability of systems dominated by canopy-forming algae to resist disturbance needs further experimental evaluation. Moreover, changes in patterns of biodiversity, and their functional consequences, are affected by multiple biological and abiotic drivers (Paine et al. 1998), leading to the need for examining how the effects of one stressor are modulated by those of concomitant others (Folt et al. 1999, Crain et al. 2008.Species with particular morphological or physiological traits, whose extinction may have drastic consequences for relevant ecological processes, are of overwhelming importance for the study of the relationship between biodiversity and ecosystem functioning (Schwartz et al. 2000, Geider et al. 2001, Loreau et al. 2002, Smith & Knapp 2003. Such species include key...

Reproductive cycles of marine invertebrates with complex life histories are considered to be synchronized by water temperature and feeding conditions, which vary with season and latitude. This study analyses seasonal variation in the occurrence of oyster (Crassostrea gigas) and mussel (Mytilus edulis/galloprovincialis) larvae across European coastal waters at a synoptic scale (1000s of km) using standardised methods for sampling and molecular analyses.We tested a series of hypotheses to explain the observed seasonal patterns of occurrence of bivalve larvae at 12 European stations (located between 37°N to 60°N and 27°W to 18°E). These hypotheses included a model that stated that there was no synchronisation in seasonality of larval presence at all between the locations (null hypothesis), a model that assumed that there was one common seasonality pattern for all stations within Europe, and various models that supposed that the variation in seasonality could be grouped according to specific spatial scales (i.e., latitude, large marine ecosystems and ecoregions), taxonomic groups, or several combinations of these factors.For oysters, the best models explaining the presence/absence of larvae in European coastal waters were (1) the model that assumed one common seasonal pattern, and (2) the one that, in addition to this common pattern, assumed an enhanced probability of occurrence from south to north. The third best model for oysters, with less empirical support than the first two, stated that oysters reproduced later in the south than in the north. For mussels, the best models explaining the seasonality in occurrence of larvae were (1) the model that assumed four underlying trends related to large marine ecosystems, and (2) the one that assumed one common seasonal pattern for larvae occurrence throughout Europe.Such synchronies in larval occurrences suggest that environmental conditions relevant to bivalve larval survival are more or less similar at large spatial scales from 100s to 1000s of km. To unravel the underlying mechanisms for this synchronisation is of particular interest in the light of changing environmental conditions as the result of global climate change and the possible consequences for marine food webs and ecosystem services.

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Natural assemblages are variable in space and time; therefore, quantification of their variability is imperative to identify relevant scales for investigating natural or anthropogenic processes shaping these assemblages. We studied the variability of intertidal macroalgal assemblages on the North Portuguese coast, considering three spatial scales (from metres to 10 s of kilometres) following a hierarchical design. We tested the hypotheses that (1) spatial pattern will be invariant at all the studied scales and (2) spatial variability of macroalgal assemblages obtained by using species will be consistent with that obtained using functional groups. This was done considering as univariate variables: total biomass and number of taxa as well as biomass of the most important species and functional groups and as multivariate variables the structure of macroalgal assemblages, both considering species and functional groups. Most of the univariate results confirmed the first hypothesis except for the total number of taxa and foliose macroalgae that showed significant variability at the scale of site and area, respectively. In contrast, when multivariate patterns were examined, the first hypothesis was rejected except at the scale of 10 s of kilometres. Both uni-and multivariate results indicated that variation was larger at the smallest scale, and thus, smallscale processes seem to have more effect on spatial variability patterns. Macroalgal assemblages, both considering species and functional groups as surrogate, showed consistent spatial patterns, and therefore, the second hypothesis was confirmed. Consequently, functional groups may be considered a reliable biological surrogate to study changes on macroalgal assemblages at least along the investigated Portuguese coastline.

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Kelp communities are in decline in many regions. Detecting and addressing population declines require knowledge of patterns of spatial and temporal variation in the distribution and abundance of kelps and their associated organisms. We quantified kelp and associated macroalgal assemblages three times over a period of 2 years, at three regions along a natural gradient in temperature and nutrient availability across the Portuguese coast. Kelps were mostly found at the northern cool region (Viana do Castelo), which was also clearly separated from the two more southerly regions (Peniche, Sines) in terms of algal assemblage structure. This pattern was consistent, although varying in intensity, through time, providing support for this general spatial configuration. The overall richness of taxa increased towards lower latitudes. These findings indicated that kelp beds in southern Europe are currently restricted to northern Portugal, though supporting less diverse macroalgal assemblages compared with those located in central and southern Portugal.

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