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The loss of Mediterranean macroalgal populations dominated by Cystoseira sensu lato is driven by a multitude of pressures. In the eastern Mediterranean Sea, climate change and the establishment of Lessepsian herbivore species have further intensified the ongoing decline of these canopy-forming algae. Knowledge of the reproductive phenology, embryology and growth of Cystoseira species is the first step towards successful reforestation measures. Gongolaria montagnei is one of the most common canopy-forming algal species with a wide horizontal and vertical distribution along the Greek coasts. Mature receptacles were collected from Saronikos Gulf (Aegean Sea), and germlings were cultured in mesocosms for 34 days, reaching up to 1.30 mm in length. Divisions and early developmental stages of G. montagnei are described and possible implications for future restoration efforts are discussed. A new approach to growth rate modeling, based on surface measurements of embryos and germlings is presented.

As a result of several anthropogenic factors, Cystoseira sensu lato forests have declined or become regionally extinct in many coastal regions of the Mediterranean. Given the low natural recovery of lost populations, research efforts have been encouraged to develop sustainable and efficient restoration of macroalgal forests on a large scale. By promoting growth and fertility of collected thallus branches under controlled laboratory conditions, the availability of seedlings for restoration could be ensured without jeopardizing natural populations. Here we investigated the effect of a commercial algal biostimulant (AlgatronCifo®) on the photophysiology, growth and fertility of Gongolaria barbata (Stackhouse) Kuntze (Fucales, Phaeophyceae). In a factorial laboratory experiment, two different temperatures (10 ºC and 14 °C) and two culture media [i.e. seawater (SW) and Algatron (AT)] were tested. The photosynthetic performance of G. barbata doubled after three weeks of culture with AT, while it decreased by 25% when cultivated in SW. The highest photosynthetic performance and growth were achieved at 14ºC with AT, where fertile receptacles also developed, followed by seedling settlements. The thalli cultured in AT had similar or better photosynthetic performance than the initial control thalli. AT-cultured thalli had a greater ability to quench energy via photochemical pathways (qP) than those from the SW, which on the contrary, had higher levels of non-photochemical responses (qN, NPQmax). This limited photosynthetic performance was probably linked to the higher P-limitation experienced under that treatment. The algal biostimulant enhanced the physiological performance and induced fertility of G. barbata, demonstrating its valorization potential and setting a new path for improved restoration applications.

1. The aim of the present study was to propose a biotic index (North Adriatic Mesophotic BiogEnic Reefs, NAMBER) suitable for assessing the ecological quality of the mesophotic biogenic reefs of the northern Adriatic continental shelf based on photographic sampling. 2. At each of the 20 study sites, the degree of bioconstruction (expressed as percentage cover of crustose coralline algae), the α-diversity (expressed as the mean number of taxa), and the degree of sensitivity to human disturbance and climate change (based on literature data and expert judgement) of the benthic assemblages were selected as descriptors and combined in the NAMBER index, using the best values that the three metrics can currently achieve in the studied region as a reference. 3. The study highlighted that there was large spatial heterogeneity among reefs and high variability in the ecological quality values obtained by NAMBER, ranging from bad to high. The index indicates that reefs lying furthest from the coast, under substantially lower anthropogenic pressure, have a generally higher status of environmental quality. However, a clear geographical pattern did not emerge, as reefs close together often had different ecological qualities. 4. The NAMBER index, which combines three ecological descriptors, in accordance with the requirements of the European Marine Strategy Framework Directive, represents a specific adaptation to the northern Adriatic Sea of a multimetric index previously developed for the north-western Mediterranean Sea, capitalizing on previous knowledge and research efforts. 5. This multimetric biotic index provides an effective standardized tool for monitoring programmes and environmental impact assessments in the northern Adriatic mesophotic biogenic reefs and lays the foundation for ecosystem-based management and conservation in this basin.

In the Mediterranean, Cystoseira sensu lato (s.l.) (Phaeophyceae) forests have sharply declined and restoration measures are needed to compensate for the loss. Assisted regeneration through the outplanting of seedlings grown ex-situ has proven to be a sustainable option. Optimizing mesocosm culture can maximize survival of the most critical embryonic stages and reduce long-term maintenance costs. Host-microbiome interactions could also play a crucial role in seedling development and welfare. In this context, we aimed to advance a cultivation protocol that stimulates the growth and fitness of Ericaria amentacea (Phaeophyceae) seedlings and identify the associated microbial biofilm communities. Seedlings were cultured in 6 treatments [i.e., filtered seawater (SW, C, Control), von Stoch-enriched SW (VS), VS + algal extract (VSA), algal extract-enriched SW: A1< A2< A3]. After the field, A2 seedlings had the highest cover (1372 ± 53.66 mm2), which was 1.8 and 1.9 times greater than in VS and VSA, respectively. The addition of the algal extract and nutrients significantly affected the structure and composition of the microbial community that shifted over time in each culture medium. We identified a treatment-specific microbial fingerprint. After the mesocosm phase, A2 was characterized by 4 unique taxa: Postechiella, Winogradskyella, Roseovarius and Arenibacter (Bacteria). Given the success of A2 seedlings, we propose the probiotic consortia candidates characterized by the unique treatment-taxa in conjunction with the shared taxon Psychroserpens (Bacteria, present in A1, A2, VSA, VS) and the reminder community. Within the holobiont concept, the effect of algal extract or nutrients on the algae and/or biofilm could have important consequences for tuning the overall interaction networks. Our study has shown that macroalgal restoration could benefit from both the use of commercial algal extract and tailored nutrient enrichment in ex-situ cultures and the identification of probiotic consortia candidates that promote seedling growth.

Several anthropogenic factors are responsible for the decline of Cystoseira sensu lato (hereafter Cystoseira) forests along Mediterranean coasts. Some Cystoseira species are already regionally extinct, and their decline has been widely recorded. Sustainable and efficient techniques for the restoration of Cystoseira are needed. In this context, the objectives of this study were i) to analyse the reproductive traits of three populations of Gongolaria barbata from three nearby donor sites in the northern Adriatic Sea, assessing the differences in their reproductive potential and reproductive success; and ii) to evaluate the outplanting success in terms of the effectiveness of G. barbata restoration, in relation to the different donor and receiving sites (Miramare MPA and in front of the Marine Biology Station Piran - MBSP) and implemented methods (ex situ and hybrid method combining a mesocosm cultivation and a suspended culture in the field). After 2 weeks of cultivation in mesocosms, half of the tiles with germlings were transported to the receiving sites and placed on suspended lantern nets (hybrid method), which were later (after 3 months) transferred to the seabed on concrete plates with protective cages. The remaining tiles were placed on the seabed on concrete plates with protective cages after a 4-week culture (ex situ method). At both sites, lantern nets and plates were randomly placed at 3 m depth. Thallus length was measured monthly in each treatment. Seedlings in suspended culture showed lower performance at the Miramare MPA, most likely due to the unfavourable environmental conditions. The satisfactory results obtained at MBSP demonstrate the efficiency of the hybrid method and confirm its potential to reduce the cost and time required for cultivation. Since unpredictable climatic events pose the greatest threat to restoration performance, these challenges must be considered when establishing new restoration practices. Moreover, herbivore regulation is extremely urgent and should be planned and implemented on a larger regional scale.

In the present study, alginate yield and composition were investigated during the seasonal life cycle of the alien brown alga Sargassum muticum harvested from the Atlantic coast of Morocco. Alginate yield ranged from 11.14% in winter to 25.62% in spring/early summer, coinciding with maximum vegetative growth. Monthly monitoring of the alginate block structure showed that the highest mannuronate (M)/guluronate (G) ratio was recorded during the maximum development of S. muticum, before sexual maturity and during resumption of vegetative growth, giving maximum flexibility to the alga. The unusually high molar monad fractions (FG) and dyad fractions (FGG) of guluronic acid in late summer/early autumn appeared to be related to stiffness of senescent thalli. Rheological characterisation showed that the alginate of S. muticum exhibited pseudoplastic behaviour, with the highest apparent viscosities measured in late summer/early autumn when the G blocks dominated the alginate structure. This study suggests that S. muticum could be exploited as an alginophyte for commercial applications. The best harvest time is May-June, which corresponds to the highest alginate yield, maximum thallus growth, and largely completed sexual reproduction, ensuring sustainable exploitation of the species.

Canopy-forming brown algae support highly productive ecosystems whose decline has been attributed to the interplay of several anthropogenic disturbances. Climate change could have disruptive effects on the biology of these species, but the role of temperature in the development of early life stages is poorly understood. The aim of this study was to assess the response of Ericaria giacconei, a winter-reproducing Southern–Mediterranean endemic species, to thermal stress by testing five temperatures (12, 15, 18, 24, and 28°C) on adults and early stages. Chlorophyll a fluorescence of adult plants was measured at 0, 24, 72, and 120 h on nine fronds in each of the three aquaria per treatment. To assess egg release, zygote settlement, and embryo growth rate, approximately 1,200 receptacles were cultured on six Petri dishes per temperature treatment, and 10 random subsections of 2 ×2 mm were examined in three Petri dishes at 0, 20, 44, and 92 h after fertilization. Adult plants showed a plastic physiological response, and thermal stress had no significant effect on PSII efficiency. Embryos fully developed only at 12 and 15°C. Mortality increased at 18 and 24°C, and no zygotes survived at 28°C. In a scenario of further increasing temperatures, the effects of warming could affect the recruitment of E. giacconei and increase its vulnerability to further stresses. These effects on the survival of early stages, which are the bottleneck for the long-term survival of the species, should be taken into account in conservation and restoration measures to maintain canopy-forming macroalgal populations and associated biodiversity and ecosystem services.

Marine Protected Areas (MPAs) are at the core of management and conservation plans aimed at counteracting the ongoing widespread degradation of marine ecosystems. Although the outcomes of protection in enhancing marine biodiversity and restoring populations of exploited species are widely recognized, the putative effect of MPAs in increasing the resilience of marine communities and ecosystems is still underexplored. In this study, long-term data from a no-take area of a Mediterranean MPA and unprotected locations were used to investigate the effects of full protection on the temporal stability of sessile assemblages on shallow subtidal rocky reefs. Results highlighted that assemblages within the no-take area exhibited a more consistent structure over 20 years of study, whereas a significantly larger temporal variability characterized assemblages at the unprotected locations. Reduced levels of human pressure and stabilizing processes related to the re-establishment of the integrity of trophic networks within the MPA could underlie the observed patterns. Assessing whether MPAs may improve the ability of marine communities to absorb disturbance, from local to large scale sources, is essential to ascertain their contribution to future adaptive conservation strategies in the face of global change. This study provided evidence that MPAs, if well managed, can represent an effective tool to smooth fluctuations in the structure of marine communities, thus potentially reducing their vulnerability to natural and human-driven environmental changes.

1. The worldwide decline of marine forests, due to human impacts and climate change, emphasizes the need to develop and implement effective and sustainable solutions to restore these endangered habitats and to re-establish the services they provide. 2. In this study, the ex situ restoration of Treptacantha barbata, a Mediterranean subtidal habitat-forming species of brown seaweed, was for the first time implemented in a marine protected area in the Adriatic Sea. Two restoration efforts were performed in 2019. The first one was started in winter, after a marine heatwave that triggered early fertility, the second one in spring, when the species usually reproduces. 3. This study aimed to evaluate: 1) the disruptive effects of a thermal anomaly on the reproductive biology and performance in culture of T. barbata; and 2) the impact of the grazing pressure on juveniles after the outplanting. 4. The first cultivation was more productive than the second one, in terms of zygote release and germling growth. To mitigate the low efficiency of the second culture and to avoid prolonged highly-demanding maintenance in the mesocosms, the cultivation period was extended outdoors using a structure suspended in the water column. 5. The modular frames conceived for outplanting T. barbata proved to be effective because of their easy operability and low cost. Controlling for herbivorous fish had significant positive effects on both juvenile survival and growth. 6. The outcomes highlighted that an unpredictable climatic event and fish grazing were major threats that impaired the restoration process of T. barbata. These stressors should be considered when developing plans to implement effective large-scale restoration of canopy-forming macroalgae.

High complexity habitat traits (i.e. high heterogeneity and/or size of discrete habitat units) often promote larger abundances of fauna. Sandy and rhodolith sea bottoms are typically interspersed as mosaics within coastal landscapes. The aim of this study was to experimentally assess the effect of two complexity attributes of rhodolith nodules (i.e. their heterogeneity and size) on the abundance and structure of vagile epibenthic assemblages. An early-colonization experiment was set up (July 2016), where experimental units containing rhodolith nodules of varying heterogeneity and size were deployed at two adjacent recipient habitats: a sandy bottom and a rhodolith seabed. After one month, the abundance of fauna colonizing the experimental units was similar in both habitats, but the assemblage structure (i.e. composition) notably differed. Importantly, the heterogeneity, rather than the size, of experimental rhodolith nodules influenced patterns of vagile macrofauna (>0.5 mm) colonization, despite the habitat type where these experimental units were deployed considerably influenced colonization patterns. This result reinforces the idea of the importance of rhodolith tri-dimensional structure, as key influencer on faunal communities of nearshore habitats.

International audience; Lithophyllum species in the Mediterranean Sea function as algal bioconstructors, contributing to the formation of biogenic habitats such as coralligenous concretions. In such habitats, thalli of Lithophyllum, consisting of crusts or lamellae with entire or lobed margins, have been variously referred to as either one species, L. stictiforme, or two species, L. stictiforme and L. cabiochiae, in the recent literature. We investigated species diversity and phylogenetic relationships in these algae by sequencing three markers (psbA and rbcL genes, cox2,3 spacer), in conjunction with methods for algorithmic delimitation of species (ABGD and GMYC). Mediterranean subtidal Lithophyllum belong to a well‐supported lineage, hereby called the L. stictiforme complex, which also includes two species described from the Atlantic, L. lobatum and L. searlesii. Our results indicate that the L. stictiforme complex consists of at least 13 species. Among the Mediterranean species, some are widely distributed and span most of the western and central Mediterranean, whereas others appear to be restricted to specific localities. These patterns are interpreted as possibly resulting from allopatric speciation events that took place during the Messinian Salinity Crisis and subsequent glacial periods. A partial rbcL sequence from the lectotype of L. stictiforme unambiguously indicates that this name applies to the most common subtidal Lithophyllum in the central Mediterranean. We agree with recent treatments that considered L. cabiochiae and L. stictiforme conspecific. The diversity of Lithophyllum in Mediterranean coralligenous habitats has been substantially underestimated, and future work on these and other Mediterranean corallines should use identifications based on DNA sequences.

Macroalgal forests are one of the most productive and valuable marine ecosystems, but yet strongly exposed to fragmentation and loss. Detailed large-scale information on their distribution is largely lacking, hindering conservation initiatives. In this study, a systematic effort to combine spatial data on Cystoseira C. Agardh canopies (Fucales, Phaeophyta) was carried out to develop a Habitat Suitability Model (HSM) at Mediterranean scale, providing critical tools to improve site prioritization for their management, restoration and protection. A georeferenced database on the occurrence of 20 Cystoseira species was produced collecting all the available information from published and grey literature, web data portals and co-authors personal data. Data were associated to 55 predictor variable layers in the (ASCII) raster format and were used in order to develop the HSM by means of a Random Forest, a very effective Machine Learning technique. Knowledge about the distribution of Cystoseira canopies was available for about the 14% of the Mediterranean coastline. Absence data were available only for the 2% of the basin. Despite these gaps, our HSM showed high accuracy levels in reproducing Cystoseira distribution so that the first continuous maps of the habitat across the entire basin was produced. Misclassification errors mainly occurred in the eastern and southern part of the basin, where large gaps of knowledge emerged. The most relevant drivers were the geomorphological ones, followed by anthropogenic variables proxies of pollution and urbanization. Our model shows the importance of data sharing to combine a large number of spatial and environmental data, allowing to individuate areas with high probability of Cystoseira occurrence as suitable for its presence. This approach encourages the use of this modelling tool for the prediction of Cystoseira distribution and for supporting and planning conservation and management initiatives. The step forward is to refine the spatial information of presence-absence data about Cystoseira canopies and of environmental predictors in order to address species-specific assessments.

Connectivity is a fundamental ecological property affecting stability, resilience and recovery of marine populations, in particular in networks of patchy habitats as the Mesophotic Biogenic Habitats of the Northern Adriatic Sea. Specific information on the dispersal behaviour of many species living in these habitats is lacking, thus the connectivity simulations were performed over different pelagic propagules duration and different reproductive seasons of six consecutive years, covering most of the possible dispersal behaviour variability. The connectivity simulations were analysed with graph analysis methods by characterizing each connectivity graph with several structural measures and by identifying sites with greatest individual and group centrality. We tested the hypothesis that geographic proximity of sites cannot be a proxy for the connectivity and that hydrodynamic connectivity is statistically significantly related to the observed beta diversity among the studied sites. Results showed that species with different pelagic propagules duration follow greatly different dispersal dynamics, and that the network of studied outcrops is only partially connected to coastal benthic populations. Our results also made possible a critical appraisal of the current conservation strategies, evidencing gaps in the existing network of protected Mesophotic Biogenic Habitats in the Northern Adriatic Sea. We suggest possible improvements for an efficient preservation strategy of these unique biodiversity hotspots by including a fundamental ecological process, the dispersal connectivity, into the process of decision making for conservation.

Structure and spatial variability of coralligenous assemblages of the Apulian continental shelf in the southern Adriatic Sea were investigated. The area consists of small coralligenous outcrops distributed between 30 and 100 m of depth on coarse detritic or muddy bottom. Photographic samples, obtained through a Remotely Operated Vehicle, were analyzed to evaluate the abundance of the main taxa or morphological groups of macroalgae and sessile invertebrates, and the deposited sediment. A multifactorial sampling design was used to compare assemblages at two depth ranges, the shallow outcrops (between 35 and 45 m) and the deep outcrops (between 60 and 70 m), and to determine the main scales of spatial variation. Assemblages were dominated by encrusting and erect sponges, encrusting and filamentous algae, scleractinians, encrusting and erect bryozoans and the Zoantharia Parazoanthus axinellae. Deep assemblages were characterized by lower alpha and beta diversity, and by the decrease or disappearance of sensitive organisms, such as coralline macroalgae, scleractinians and erect bryozoans, and by the dominance of encrusting sponges, P. axinellae and hydrozoans. Sedimentation was higher on deep outcrops and was suggested to be the main driver of differences between shallow and deep assemblages. The peculiar composition of assemblages found in the Apulian continental shelf provides evidence that these outcrops represent an uncommon coralligenous habitat.

One of the objectives of the BALMAS project was to conduct Port Baseline Biological Surveys of native and non-indigenous benthic flora in 12 Adriatic ports. Samples of macroalgae growing on vertical artificial substrates were collected in spring and autumn 2014 and/or 2015. A total number of 248 taxa, 152 Rhodophyta, 62 Chlorophyta, and 34 Ochrophyta, were identified. Of these, 13 were non-indigenous seaweeds, mainly filamentous macroalgae, that were probably introduced through hull fouling. Some of these taxa had already been described in the study areas, others were recorded for the first time, a few were no longer detected at sites where they had previously been recorded (e.g. Sargassum muticum). Some other NISS reported for the Adriatic Sea, were not collected at any sampling site (i.e. Caulerpa cylindracea, Codium fragile). Possible reasons for the absence of these species are discussed.

Phymatolithon lamii (Hapalidiaceae, Corallinales, Rhodophyta) is reported for the first time in the Mediterranean Sea. A morphological-anatomical account of Gulf of Trieste specimens is presented along with comparisons with P. lamii specimens from other regions, comparisons with other Mediterranean species of Phymatolithon and a dichotomous key to known Mediterranean species of Phymatolithon. Whether P. lamii occurs naturally in the Mediterranean Sea but was previously misidentified as P. lenormandii or is, alternatively, an alien species, or both, has not been resolved.

In the framework of the WFD 2000/60/EC intercalibration process the updated versions of the EEI and R-MaQI, proposed by Italy and Greece for the transitional waters, have been applied to the macrophytes of the Venice lagoon to test their comparability and relationships with the pressure gradients. Submerged macrophytes were collected during spring 2007 at 60 sites spread within the lagoon. At each site, five random samples were collected and the total coverage of benthic macrophytes in the field was estimated based on a number of tests of the bottom. To assess seagrass epiphytes, five shoots were collected for each replicate. Physico-chemical data were collected in the water column at 14 sites selected to reflect the main hydro-geomorphological and trophic gradients of the lagoon. The analyses performed indicated that the two metrics appeared to be weakly intercalibrated and only the 30% of the sampling sites displayed the same quality class. The main differences fell into the Moderate and Low classes and the two indices provided discordant results in the intermediate and confined areas of the lagoon. In contrast, the two indices showed good affinity in the marine areas of inlets, which are characterised by seagrass meadows and late-successional macroalgae. Similar results were evidenced also in a redundancy analysis by the different relationships between quality classes and the physico-chemical gradients. The main reason for this seems to be the heterogeneity of species–environment relationships inside the groups of species on which the indices are based. Critical aspects of methodological differences and applicability of the macrophyte indices proposed by Italy and Greece for the transitional waters of the Mediterranean eco-region are discussed.

The coralline red alga Mesophyllum (Hapalidiaceae) is recorded for the first time from the Gulf of Trieste (Northern Adriatic Sea) and gametangial plants of M. macroblastum are recorded for the first time from the Mediterranean Sea. A morphological-anatomical account is provided, including comparisons with specimens from the western coast of Italy and with published data. Distribution and habitat information, comparison with Mediterranean species of Mesophyllum, and a dichotomous key to Mediterranean species are included along with brief comments on other species in the genus known to produce volcano-like tetrasporangial conceptacles.

Lithophyllum byssoides is a comm on coralline alga in the intertidal zone of Mediterranean coasts, where it produces biogenic concretions housing a high algal and invertebrate biodiversity. This species is an ecosystem engineer and is considered a target for conservation efforts, but designing effective conservation strategies currently is impossible due to lack of information abo ut its population structure. The morphological and molecular variation of L. byssoides was investigated using morphoanatomy and DNA sequences (psbA and cox2,3) obtained from populations at 15 localities on the Italian and Croatian coasts. Lithophyllum byssoides exhibited a high number of haplotypes (31 psbA haplotypes and 24 cox2,3 haplotypes) in the central Mediterranean. The psbA and cox2,3 phylogenies were congruent and showed seven lineages. For most of these clades, the distribution was limited to one or a few localities, but one of them (clade 7) was widespread across the central Mediterranean, spanning the main biogeographic boundaries recognized in this area. The central Mediterranean populations formed a lineage separate from Atlantic samples; psbA pairwise divergences suggested that recognition of Atlantic and Mediterranean L. byssoides as different species may be appropriate. The central Mediterranean haplotype patterns of L. byssoides were interpreted as resulting from past climatic events in the hydrogeological history of the Mediterranean Sea. The high haplotype diversity and the restricted spatial distribution of the seven lineages suggest that individual populations should be managed as independent units.

The protocols available for sampling and monitoring shallow subtidal rhodolith beds (RBs) are inadequate for the deep Mediterranean analogues, and need calibration in order to attain comparable results. After reviewing the present knowledge of the specificities of Mediterranean RBs, and in the framework of the ongoing international effort for their conservation, a two-step approach is suggested for their definition, identification, delimitation, description, and monitoring. Regional mapping should be improved, and RBs should be identified and delimited as those areas of the sea floor with >10% cover of live rhodoliths over a minimum surface of 500 m2, on 1:10000 scale. More detailed scales (at least 1:1000) should be used for monitoring selected RBs, in order to detect significant changes through time. Beside location and areal extent, the description of RBs should include the occurrence of macroscopic sedimentary structures of the sea floor, thickness of live cover, mean percentage cover of live thalli and surface live/dead ratio, cover of dominant morphologies of rhodoliths (simplified on a ternary diagram), and volumetrically important calcareous algal species. For the purpose of assessment of the ecological status and the evaluation of human-induced impacts, quantitative data about community composition are required. The comparative assessment of ecological status and the identification of RBs of high conservation value for special protection should consider the natural geographic and seasonal/annual variability of RBs. Copyright © 2015 John Wiley & Sons, Ltd.

Phymatolithon calcareum is a species of non-geniculate coralline red algae that commonly forms maerl beds. Tetrasporangial thalli of this species are characterized by unattached growths (rhodoliths), which develop as a branched system without a central nodule, while the attached crustose forms are uncommon and are known only from Brittany (Atlantic coasts of France). In this study we confirm with molecular data the existence of attached crustose tetrasporangial thalli and describe for the first time epilithic, fruticose tetrasporangial specimens from the Mediterranean Sea (Vis Island, Croatia). Since the identification of coralline algal species is difficult due to the high morphological plasticity of the group, molecular analyses based on the nuclear nSSU and the plastidial psbA markers were necessary to correctly identify the specimens. Our study shows that P. calcareum tetrasporangial thalli have the ability to grow both unattached and attached, and we argue this to be in relation to the environmental conditions found at different depths. This ability permits the alga to colonize different habitats of the coastal environment.

In the Mediterranean region Cymodocea nodosa is widely distributed throughout shallow sites. Therefore, a correct assessment of the status of its meadows is of great importance for the implementation of the Water Framework Directive (WFD), the Marine Strategy Framework Directive (MSFD), and the Habitat Directive (HD), especially for areas where Posidonia oceanica meadows (the most frequently used indicator in the Mediterranean Sea) are rare or not present. The previously proposed index for the evaluation of the status of C. nodosa meadows (CymoSkew) is based on ln-transformed relative frequencies of photosynthetic leaf lengths, which we believe is statistically questionable. Therefore, we further improved the methodology and developed a new index named MediSkew, where ln-transformation is applied to raw data of leaf lengths. More specifically, the index is a combination of two metrics, both based on C. nodosa leaf length: deviation from the reference median length (Medi-) and skewness of the length frequency distribution (-Skew), though greater importance was assigned to the first. To develop the classification criteria for the assessment of the status, also a Pressure Index for Seagrass Meadows (PISM), for the evaluation of pressureeimpact relationships, was developed. The MediSkew is meant to be a rapid screening method for wide areas, therefore the index should be tested for the assessment of the status of C. nodosa meadows throughout Mediterranean coastal waters.

The practical assessment of the biogenic structural complexity poses some problems in non-symmetrical or three-dimensional macroalgae. This study represents the first attempt to measure quantitatively the phenology and the plasticity of Cystoseira barbata (Stackhouse) C. Agardh in the Mediterranean Sea. This canopy-forming brown alga is characterised by a ramified monopodial cauloid and a dendroid frond. To analyse the morphological-spatial changes in time and the plasticity of C. barbata an experiment was conducted in a protected sea area of the Northern Adriatic Sea on thalli taken from a natural population and a transplanted one, re-located in deeper water. The three-dimensional complexity of thalli and the frond architecture were analysed by means of quantitative structural (total area, perimeter) and spatial (intercepting area, volume and interstitial area) attributes. A preliminary assessment of the primary production of the basiphyite-epiphyte system was investigated by a volumetric analysis. The thalli showed a seasonal pattern characterised by a marked phenological variation of the fronds, both in size and in shape. The seasonal trend was comparable in the both populations studied, with fronds largest in spring–summer, whereas the fall of phylloids and branchelets occurs in autumn–winter. Also the abundance of algal epibionts on the host varied seasonably and depended mainly on the life-form of Cystoseira fronds, where complex fronds encouraged more abundant associated epibionts. The morphological variability of different individuals was also investigated using some bio-structural indices. These indices were proposed as useful for a more detailed description of the phenology of C. barbata and for a better evaluation of the potential micro-spatial and structural habitat available inside the fronds. The proposed protocol and the quantitative descriptors analysed may be employed in physiological or ecological studies, being useful for a standardisable classification of a habitat’s complexity. The analysed spatial and structural attributes, as well as the definition of the complexity of C. barbata, enable the evaluation of the area available for the attachment and shelter of epibionts together with the number and type of potential habitats.

To evaluate the effect of grazing by sea urchins on the development of vegetation, plastic netting (6545-mm mesh) was stretched over the horizontal surfaces of two out of four cubes of a Loano artificial reef pyramid and held slightly above the surface. The macroalgal population of the horizontal surfaces of the four cubes was seasonally sampled over one and a half years. A qualitative analysis based on a floristic survey of all species present did not reveal significant differences between treatments. However, the quantitative analysis of the algal community based on biomass samples revealed marked differences. Before starting the experiment, fresh and dry weights of the vegetation of all four cubes were of comparable magnitude, while after deployment of the netting, biomass on the two surfaces protected by the net was always significantly higher than in the controls throughout the sampling period. The relative increase seems related to the mechanical effect of the netting in reducing the predatory pressure caused by sea urchins. 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd.

The distribution of the endemic brown alga Fucus virsoides was assessed along the northern Adriatic coastline. A high-resolution geographic information system database was created using visual census methods to identify the presence and abundance of algae, including the geomorphology of the substrate. Samples of F. virsoides were collected for analysis of the quantitative spatial distribution. The abundance of F. virsoides was related to several environmental variables, including the relative exposure index (REI). The results support the hypothesis that the distribution of F. virsoides in the Gulf of Trieste is influenced mainly by the stability of mediolittoral substrata, wave exposure and the vicinity of freshwater inputs. Populations of this species are widespread in the Gulf of Trieste. Many of them were found growing inside small harbours or along a boatyard, where fluctuations in salinity and nutrient concentrations are frequent. Therefore, we conclude that F. virsoides cannot be considered an ecological indicator for seawater pollution nor for climate change, since it is subjected naturally to high pollution levels and environmental variability.