Iacopo Bertocci

Marine reserves: fish life history and ecological traits matter.

Marine reserves are assumed to protect a wide range of species from deleterious effects stemming from exploitation. However, some species, due to their ecological characteristics, may not respond positively to protection. Very little is known about the effects of life history and ecological traits (e.g., mobility, growth, and habitat) on responses of fish species to marine reserves. Using 40 data sets from 12 European marine reserves, we show that there is significant variation in the response of different species of fish to protection and that this heterogeneity can be explained, in part, by differences in their traits. Densities of targeted size-classes of commercial species were greater in protected than unprotected areas. This effect of protection increased as the maximum body size of the targeted species increased, and it was greater for species that were not obligate schoolers. However, contrary to previous theoretical findings, even mobile species with wide home ranges benefited from protection: the effect of protection was at least as strong for mobile species as it was for sedentary ones. Noncommercial bycatch and unexploited species rarely responded to protection, and when they did (in the case of unexploited bentho-pelagic species), they exhibited the opposite response: their densities were lower inside reserves. The use of marine reserves for marine conservation and fisheries management implies that they should ensure protection for a wide range of species with different life-history and ecological traits. Our results suggest this is not the case, and instead that effects vary with economic value, body size, habitat, depth range, and schooling behavior.

TEMPORAL VARIANCE REVERSES THE IMPACT OF HIGH MEAN INTENSITY OF STRESS IN CLIMATE CHANGE EXPERIMENTS

Extreme climate events produce simultaneous changes to the mean and to the variance of climatic variables over ecological time scales. While several studies have investigated how ecological systems respond to changes in mean values of climate variables, the combined effects of mean and variance are poorly understood. We examined the response of low-shore assemblages of algae and invertebrates of rocky seashores in the northwest Mediterranean to factorial manipulations of mean intensity and temporal variance of aerial exposure, a type of disturbance whose intensity and temporal patterning of occurrence are predicted to change with changing climate conditions. Effects of variance were often in the opposite direction of those elicited by changes in the mean. Increasing aerial exposure at regular intervals had negative effects both on diversity of assemblages and on percent cover of filamentous and coarsely branched algae, but greater temporal variance drastically reduced these effects. The opposite was observed for the abundance of barnacles and encrusting coralline algae, where high temporal variance of aerial exposure either reversed a positive effect of mean intensity (barnacles) or caused a negative effect that did not occur under low temporal variance (encrusting algae). These results provide the first experimental evidence that changes in mean intensity and temporal variance of climatic variables affect natural assemblages of species interactively, suggesting that high temporal variance may mitigate the ecological impacts of ongoing and predicted climate changes.

The seaweed Caulerpa racemosa on Mediterranean rocky reefs: from passenger to driver of ecological change

Disentangling the ecological effects of biological invasions from those of other human disturbances is crucial to understanding the mechanisms underlying ongoing biotic homogenization. We evaluated whether the exotic seaweed, Caulerpa racemosa, is the primary cause of degradation (i.e., responsible for the loss of canopy-formers and dominance by algal turfs) on Mediterranean rocky reefs, by experimentally removing the invader alone or the entire invaded assemblage. In addition, we assessed the effects of enhanced sedimentation on the survival and recovery of canopy-forming macroalgae at a relatively pristine location and how their loss affects the ability of C. racemosa to conquer space. C. racemosa did not invade dense canopy stands or influence their recovery in cleared plots. Competition with C. racemosa could not explain the rarity of canopy-forming species at degraded sites. Removing the assemblages invaded by C. racemosa and preventing reinvasion did not trigger the transition from algal turfs to canopies, but it enhanced the cover of morphologically complex erect macroalgae under some circumstances. Once established, C. racemosa, enhancing sediment accumulation, favors algal turfs over erect algal forms and enables them to monopolize space. Our results show that introduced species that rely on disturbance to establish can subsequently become the main drivers of ecological change.

Implications of spatial heterogeneity for management of marine protected areas (MPAs): examples from assemblages of rocky coasts in the northwest Mediterranean.

Marine protected areas (MPAs) are increasingly used as a management tool to preserve species and habitats. Testing hypotheses about the effectiveness of MPAs is important for their implementation and to identify informative criteria to support management decisions. This study tested the general proposition that MPAs affected assemblages of algae and invertebrates between 0.0 and 0.5 m above the mean low water level of rocky coasts on two islands in the Tuscan Archipelago (northwest Mediterranean). Protection was concentrated mainly on the west coasts of the islands, raising the possibility that neither the full range of assemblages nor the relevant scales of variation were properly represented within MPAs. This motivated the comparison of assemblages on opposite sides of islands (habitats). The effects of MPAs and habitat were assessed with a multifactorial sampling design; hypotheses were tested about differences in structure of assemblages, in mean abundance of common taxa and in univariate and multivariate measures of spatial variation. The design consisted of three replicate shores for each condition of protected and reference areas on the west side of each island and three unprotected shores on the eastern side. Assemblages were sampled independently four times on each island between June 1999 and January 2001. At each time of sampling two sites were selected randomly at each of two tidal heights to represent midshore and lowshore assemblages on each shore. Estimates of abundance were obtained using non-destructive sampling methods from five replicate 20x20 cm quadrats at each site. Results indicated differences among habitats in structure of assemblages, in mean abundance of common taxa and in univariate and multivariate measures of spatial variation at the scale of shores. Most of these patterns were inconsistent with the predicted effect of management through MPAs. The data suggest that designation of MPAs in the Tuscan Archipelago should proceed through management of multiple shores and types of habitat selected to guarantee protection to a representative sample of assemblages and to the processes responsible for maintenance of spatial patchiness at different scales. This study also shows that considerations of spatial heterogeneity are important to underpin management decisions about the number, size and location of MPAs.

Contrasting effects of mean intensity and temporal variation of disturbance on a rocky seashore

Understanding the extent to which natural assemblages withstand changes in the regime of disturbance has considerable practical and theoretical interest. In this paper we examine the separate and interactive effects of intensity, temporal variation, and spatial extent of disturbance on temporal variance in assemblages of algae and invertebrates of rocky shores in the northwest Mediterranean. Temporal variation of disturbance is a predictor variable in the experiment, while temporal variance in abundance and number of taxa and in structure of assemblages are response variables. Multivariate analyses detected a positive relationship between intensity of disturbance and temporal variance in the structure of assemblages, while temporal variation of disturbance elicited the opposite effect. Univariate analyses conducted on the most abundant taxa revealed idiosyncratic patterns, while temporal variance in mean number of taxa was greatly reduced by disturbance, with no distinction among levels of intensity, temporal variation, or spatial extent. These outcomes suggest caution in interpreting the results of experiments in which intensity and temporal variation of disturbance cannot be separated. Distinguishing between these traits of disturbance may be key to predicting the ecological consequence of environmental fluctuations, including those expected under modified climate scenarios.

Variation in rocky shore assemblages in the northwestern Mediterranean: contrasts between islands and the mainland

Insular assemblages of species are often considered unique because they are exposed to unpredictable patterns of colonization/extinction that depend on distance from other sources of colonists and on size of islands. An alternative explanation is that islands provide fundamentally different habitats of those of the mainland, regardless of any possible effect of size and isolation. These alternatives were examined by comparing assemblages of rocky shores on islands of the Tuscany Archipelago with those of the mainland in the same geographical region. Sandy beaches created a pattern of discrete areas of rock along the mainland with spatial discontinuities and extents comparable to those of the insular environment. Possible effects of isolation and size were therefore controlled in this study, so that one would expect no difference between islands and the mainland if only size and isolation matter. In contrast, differences are expected if historical events or other processes have distinct influences on assemblages in these environments. These hypotheses were tested by comparing assemblages of midshore and lowshore habitats of two islands with those of two similarly distributed locations on the mainland over a period of 2 years, using a hierarchical sampling design. Multivariate and univariate analyses revealed various patterns in the data. There were differences between islands and the mainland in structure of assemblages, in mean abundance of common taxa and in the magnitude of spatial and temporal variance in abundance in both habitats. Collectively, these findings support the model that islands in the Tuscany Archipelago have distinct assemblages from the mainland, thereby contributing to the

Spatial heterogeneity in the distribution of plants and benthic invertebrates in the lagoon of Orbetello (Italy)

Abstract Many studies in marine coastal lagoons have focused on the marine-to-terrestrial gradient as a main source of variation for the structure of assemblages. In this paper, the magnitude of differences among locations arranged along the marine-to-terrestrial gradient of the western lagoon of Orbetello (Grosseto, Italy) was contrasted with the amount of spatial variability occurring among sets of locations that were not positioned along this axis. We propose that if the most important processes influencing assemblages were those associated with the external–internal gradient of the lagoon, as usually supposed, then assemblages should differ more among these locations than among any other locations. To test the above proposition, four locations arranged along the two major axes of the lagoon were established in November 2000. Each location was sampled three times (November 2000, April 2001, August 2001) to test for temporal consistency in spatial patterns. At each time of sampling, three replicate sites were established in each location. This design enabled estimates of spatial variability to be obtained at three scales: among locations hundreds of meters apart, among sites tens of meters apart and among quadrats hundreds of centimeters apart. Non-metric multidimensional scaling (nMDS) ordination plots on abundance data revealed differences among assemblages hundreds of meters apart. Assemblages in the inner part of the lagoon were separated from those closer to the sea inlet, depending on the marine-to-terrestrial gradient. In addition to this pattern, differences also occurred among assemblages hundreds of meters apart, but positioned at a similar distance from the sea. Multifactorial Anovas on abundance of the most common taxa showed significant differences in mean values at the scales of location and site, with patterns changing over time. These results indicated that spatial structure in assemblages was not a distinctive feature of locations arranged along the marine-to-terrestrial gradient in the lagoon of Orbetello. Similar differences also occurred among other sets of locations at the scale of hundreds of meters, regardless of their position in the lagoon.

Data integration for European marine biodiversity research: creating a database on benthos and plankton to study large-scale patterns and long-term changes.

The general aim of setting up a central database on benthos and plankton was to integrate long-, medium- and short-term datasets on marine biodiversity. Such a database makes it possible to analyse species assemblages and their changes on spatial and temporal scales across Europe. Data collation lasted from early 2007 until August 2008, during which 67 datasets were collected covering three divergent habitats (rocky shores, soft bottoms and the pelagic environment). The database contains a total of 4,525 distinct taxa, 17,117 unique sampling locations and over 45,500 collected samples, representing almost 542,000 distribution records. The database geographically covers the North Sea (221,452 distribution records), the North-East Atlantic (98,796 distribution records) and furthermore the Baltic Sea, the Arctic and the Mediterranean. Data from 1858 to 2008 are presented in the database, with the longest time-series from the Baltic Sea soft bottom benthos. Each delivered dataset was subjected to certain quality control procedures, especially on the level of taxonomy. The standardisation procedure enables pan-European analyses without the hazard of taxonomic artefacts resulting from different determination skills. A case study on rocky shore and pelagic data in different geographical regions shows a general overestimation of biodiversity when making use of data before quality control compared to the same estimations after quality control. These results prove that the contribution of a misspelled name or the use of an obsolete synonym is comparable to the introduction of a rare species, having adverse effects on further diversity calculations. The quality checked data source is now ready to test geographical and temporal hypotheses on a large scale.

INTERACTIVE EFFECTS OF SPATIAL VARIANCE AND MEAN INTENSITY OF GRAZING ON ALGAL COVER IN ROCK POOLS

An increasing number of studies suggest that the variance around the mean of predictor variables is an important determinant of the structure of assemblages, but few have separated effects of mean from those of variance of predictor variables experimentally. We addressed these issues by examining the effects of limpets on algal recovery in littoral rock pools. An initial experiment indicated that algal cover was a negative accelerating function of density of limpets, although this effect was weak. Superimposed to this effect there was a clear trend of variability in algal cover among pools that decreased with increasing density of limpets. These results suggested that mean intensity and spatial variance of grazing could affect algal colonization both within and among pools. This proposition was tested with a novel experimental design in which the mean intensity and the spatial variance of grazing were manipulated in factorial combinations. The experiment was repeated twice to examine possible generalities of outcomes. In both runs spatial variance of grazing enhanced spatial variance in algal cover, although this effect occurred under weak intensity of grazing in the first run and in combination with strong intensity of grazing in the second run. In contrast, intensity and variability in grazing operated independently on mean algal cover, with strong intensity depressing colonization of algae and large variance increasing colonization consistently in time. By manipulating the mean intensity and the spatial variance of grazing simultaneously, we were able to explain spatial patterns in algal cover that would have been classified as unexplained variation otherwise. We suggest that this novel experimental design may be fruitful to understand spatially variable processes in a wide range of ecological systems.

Patterns of variation of intertidal species of commercial interest in the Parque Litoral Norte (north Portugal) MPA: Comparison with three reference shores

Marine Protected Areas (MPAs) are world-wide established with the aim of conserving biodiversity and preventing overexploitation of marine organisms. Evaluating the effectiveness of MPAs is needed in order to support and implement their management, but it is complicated by the large natural variability in space and time of distribution and abundance of natural populations. Here, we tested the hypothesis that patterns of total abundance and size-frequency distribution of two intensively harvested intertidal species (the sea urchin Paracentrotus lividus and the mussel Mytilus galloprovincialis) differed between a protected and three reference shores along the rocky coast of north Portugal. Response variables were in terms of mean values and measures of variance at different spatial scales (from centimetres to metres) and over time (along a period of about 12 months). A further comparison involved the estimation of the reproductive potential of sea urchins, quantified as variations of Gonad Index (GI = gonad dry weight/body dry weight × 100) at the scale of shore. Results did not generally support a predictable direct effect of protection, as the total abundance and the abundance of larger individuals of both species and GI did not differ between the MPA and reference shores. However, a considerable temporal and spatial variability at smaller scales was detected for several response variables. Such findings have implications for management of MPAs, highlighting the need for sampling designs properly replicated in space and time, in order to examine their effectiveness, and for considering spatial and temporal heterogeneity of target populations and driving processes as a criterion for their implementation and design.