Increasing evidence indicates that spatial and temporal pattern in ecological systems are not independent from the scale of measurement. In this study we used a hierarchical sampling design to examine spatial pattern in assemblages of algae and invertebrates in midshore and lowshore habitats of rocky coasts in the Mediterranean Sea, increasing the range of scales usually covered by this type of study in marine habitats. To put our results in a broader context, we also conducted a review of the literature targeting studies that explicitly investigated spatial patterns with hierarchical designs. We addressed two main questions: 1- how does small-scale variability compare to large-scale patterns of variation? 2- is there any pattern of variability that can be generalized across species and habitats? The review of the literature indicated that hierarchical analyses of spatial pattern have been limited to a narrow range of habitats and taxa and that very few studies have addressed regional scales of variation (1000s of km). The available data, however, did identify a general pattern: variability was larger at small spatial scales (meters) in almost all habitats, whereas variation over larger spatial scales (10s to 100s of km) depended on the specific habitat and taxa examined. In our case study, we obtained measures of spatial variability through the use of two alternative methods: hierarchical nested design and independent estimate of spatial variance between pairs of quadrats. Both approaches provided further support to the patterns displayed by the analysis of the literature. Most response variables exhibited large variation over small spatial scales, while the significance of mid- to large-scale variability differed between midshore and lowshore habitats and among taxa. Though a proper understanding of large-scale patterns will require additional comparisons across wide geographical areas, small-scale variability emerges as a general property of benthic assemblages in marine coastal habitats. We suggest that this pattern is common to a wide range of natural systems where assemblages are influenced by complex sets of physical and biological processes like those operating in the marine environment

Characterizing the potential effects of human activities on natural systems is a central problem in applied ecology. This requires the development of analytical procedures able to separate human perturbation from natural spatio-temporal variability displayed by most populations. Beyond-BACI experimental designs provide a framework to address these issues but, to date, their use is limited to the analysis of human impacts on the abundance of single species or other univariate measures. Here, we describe in detail an asymmetrical design that included 1 impact location (I) and a set of 3 controls (Cs), sampled at a hierarchy of spatial scales 4 times over a period of 15 mo. We focused on shallow subtidal assemblages of sessile organisms exposed to sewage discharge along a stretch of coast in southern Italy. The purpose of this paper is to illustrate (1) the comparison of variance components for the assessment of impacts and (2) the use of recently developed multivariate methods (distance-based premutational MANOVA) in the analysis of multivariate species data in response to a complex asymmetrical design. Results indicated that temporal changes in the whole assemblage at I were distinct from those occurring at Cs, and that the nature of this difference (although not its size) was fairly consistent through time. A suite of taxa was identified as important in characterizing the differences found between I and Cs. Some algae (e.g. Colpomenia sinuosa, Gelidium sp. and Pterocladiella sp.), in particular, occurred uniquely at I. Univariate analyses indicated significant Time × I-v-Cs interactions for several taxa, and significantly smaller spatial variation at the scale of quadrats at I compared to Cs. In contrast, the small-scale spatial variation in the number of taxa was significantly greater at I than at Cs. The findings of this study have important implications for future multivariate and univariate analyses in environmental impact assessment.

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An annual study on hard-substrate meiofaunal assemblages was carried out at 2 depths (2.5 and 8 m) along a vertical cliff of the Middle Adriatic (Mediterranean Sea) characterised by different macroalgal canopies and structural substrate complexities. The upper sampling area of the rocky cliff was covered by macroalgae, and its upper limit was characterised by the presence of a dense belt of Mytilus galloprovincialis. At 8 m depth, mussels were not present, the algal assemblage was less diversified, and phytal coverage decreased. Dynamics and community structure of meiofauna-inhabiting hard substrates were compared with those of meiofauna collected from soft sediments at the cliff base (9 m depth). Meiofauna of hard and soft substrates displayed significant differences both in terms of density (7-fold higher in soft substrates) and assemblage structure. Meiofauna from rocky substrates were dominated by crustaceans (copepods, nauplii and amphipods), while soft sediments were largely dominated by nematodes (ca 90%). Significant temporal changes of meiofaunal density were observed on both hard and soft substrates, with higher densities in spring to summer and lowest abundance in winter. Despite a completely different algal assemblage and coverage at 2.5 and 8 m depths, hard substrates displayed very similar meiofaunal densities and community structure. Crustacean taxa were correlated with algal coverage. Polychaetes inhabiting hard substrates increased their relevance with depth, whilst amphipods, being significantly correlated with algal biomass, decreased. Nematodes were related with the structural complexity index, calculated on the basis of macroalgal geometric complexity and biomass, whereas copepod and nauplius densities were related with the total structural complexity (as a sum of the algal complexity). The results of the present study indicate that the nature of the substrate (hard vs soft) is the main factor responsible for the differences observed between hard-and soft-bottom meiofauna assemblages, whereas phytal coverage and substrate complexity influenced the structure of hard bottom meiofaunal assemblages. Finally, the analysis of spatial variability of meiofaunal assemblages indicates that hydrodynamic stress also played an important role in meiofaunal structure and distribution on hard substrates, especially at shallow depths.

Like most ocean regions today, the European and contiguous seas experience cumulative impacts from local human activities and global pressures. They are largely in poor environmental condition with deteriorating trends. Despite several success stories, European policies for marine conservation fall short of being effective. Acknowledging the challenges for marine conservation, a 4-year multinational network, MarCons, supported collaborative marine conservation efforts to bridge the gap between science, management and policy, aiming to contribute in reversing present negative trends. By consolidating a large network of more than 100 scientists from 26 countries, and conducting a series of workshops over 4 years (2016-2020), MarCons analyzed challenges, opportunities and obstacles for advancing marine conservation in the European and contiguous seas. Here, we synthesize the major issues that emerged from this analysis and make 12 key recommendations for policy makers, marine managers, and researchers. To increase the effectiveness of marine conservation planning, we recommend (1) designing coherent networks of marine protected areas (MPAs) in the framework of marine spatial planning (MSP) and applying systematic conservation planning principles, including re-evaluation of existing management zones, (2) designing MPA networks within a broader transboundary planning framework, and (3) implementing integrated land-freshwater-sea approaches. To address inadequate or poorly informed management, we recommend (4) developing and implementing