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Fucales (Phaeophyceae) are ecosystem engineers and forest-forming macroalgae whose populations are declining dramatically. In the Mediterranean Sea, Cystoseira sensu lato (s.l.)—encompassing the genera Cystoseira sensu stricto, Ericaria, and Gongolaria—is the most diverse group, and many species have been shown to be locally extinct in many areas, resulting in a shift toward structurally less complex habitats with the consequent loss of ecosystem functions and services. In this study, we report on the extensive occurrence of healthy and dense marine forests formed by Fucales in the Santa Maria di Castellabate Marine Protected Area in Cilento, Italy (Tyrrhenian Sea, Mediterranean). On a total area of 129.45 ha, 10 Cystoseira s.l. taxa were detected using a combined morphological and molecular approach, with an average cover of more than 70%. One of these taxa has been sequenced for the first time. These findings underline the high ecological value of this area as a hotspot of benthic biodiversity and highlight the importance of marine protected area management and regional monitoring programs to ensure the conservation of these valuable yet fragile coastal ecosystems. info:eu-repo/semantics/publishedVersion

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.

Cystoseira sensu lato marine forests, which are among the most productive and diverse systems in rocky intertidal and subtidal habitats of the Mediterranean Sea, are experiencing a widespread decline throughout the basin due to increasing human pressures. Yet it is still unclear whether Marine Protected Areas (MPAs) may represent effective tools for conservation of these important habitat formers and their associated assemblages. Here, we compared the biomass of intertidal stands of Ericaria amentacea (C. Agardh) Molinari and Guiry and their understory assemblages between the no-take zone and control sites in two Mediterranean MPAs. We did not find evidence supporting a significant effect of full protection in increasing the biomass of E. amentacea stands and associated assemblages, except for macroalgae of the understory in one of the investigated MPAs, raising concerns on the potential effectiveness of MPAs in mitigating human impacts on these marine forests. Such findings call for major efforts to implement long-term monitoring programs of protected Cystoseira s.l. forests in order to inform an adaptive management of conservation measures within MPAs and eventually to set active interventions of restoration.

Restoration of foundation species in historical habitat may be difficult if adult facilitation is obligatory for survival of early life stages. 2. On intertidal Mediterranean coasts, large-scale loss of the dominant forest- forming macroalga Ericaria amentacea have prompted restoration efforts using recruits. Yet, early life stages may be more susceptible to the abiotic stress that characterizes their habitat. 3. We tested strategies to enhance resilience of lab-cultured juveniles of E. amen- tacea to environmental stress in historical habitat lacking conspecifics. Juveniles were exposed in culture to fluctuations of the dominant physical stressors, irra- diance and temperature, and then outplanted in upper and lower zones of their native intertidal range. 4. Without adult canopy, juvenile outplant survival was limited to the lower tidal range, with nearly complete mortality in the upper zone. Survival was also strongly determined by spatial clumping of recruits within the outplant sub- strate. Longer-term growth in the lower zone was enhanced by fluctuating mild stress in culture, with variable irradiance and concurrent heat pulses increas- ing post-outplant cover by 40%–60% after 4 months. Clumping also promoted growth across experimental treatments. 5. Synthesis and applications. Reliance on self-facilitation feedbacks is a common barrier to foundation species restoration in high-stress habitats. Our results sug- gest that without adult habitat amelioration, environmental stress limits recruit survival in intertidal algal forest. Yet, exposure to transient, low environmental stress in culture and outplanting of clumped individuals may confer resilience and allow successful establishment of early life stages in zones of reduced abi- otic stress, providing a source for gradual colonization of more high-stress areas.

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.

The global decline of brown algal forests along rocky coasts is causing an exceptional biodiversity loss. Regardless of conservation efforts, different techniques have been developed for large-scale restoration strategies in the Mediterranean Sea. In this study we tested ex situ pilot restoration of Gongolaria barbata (=Treptacantha barbata) for the first time in Slovenian coastal waters. Healthy apical fronds of the species were collected and the development of recruits on clay tiles was followed under laboratory conditions for 20 days. Despite the experimental difficulties experienced, especially due to the lack of antibiotics to prevent the growth of the biofilm, G. barbata recruits were outplanted in the sea on two concrete plates with 48 tiles each, protected by purpose-built cages to avoid grazing by herbivorous fish. The high survival rate of juveniles after four months in the field (89% of the tiles on the plate that was constantly protected) suggests that outplanting G. barbata is an operable approach for restoration efforts in the northern Adriatic Sea. Our first experiment in Slovenian coastal waters provides new information for the optimization of the best practices during the laboratory cultivation and addresses the early steps of restoration and introduction of young thalli in the natural environment.

Coralline algae are one of the most diversified groups of red algae and represent a major component of marine benthic habitats from the poles to the tropics. This group was believed to be exclusively marine until 2016, when the first freshwater coralline algae Pneophyllum cetinaensis was discovered in the Cetina River, southern Croatia. While several studies investigated the element compositions of marine coralline algal thalli, no information is yet available for the freshwater species. Using XRD, LA-ICP-MS and nano indentation, this study presents the first living low-Mg calcite coralline algae with Mg concentrations ten times lower than is common for the average marine species. Despite the lower Mg concentrations, hardness and elastic modulus (1.71 &plusmn, 1.58 GPa and 29.7 &plusmn, 18.0 GPa, respectively) are in the same range as other marine coralline algae, possibly due to other biogenic impurities. When compared to marine species, Ba/Ca values were unusually low, even though Ba concentrations are generally higher in rivers than in seawater. These low values might be linked to different physical and chemical characteristics of the Cetina River.

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.

Rhodolith beds (RBs) are bioconstructions characterized by coralline algae, which provide habitat for several associated species. Mediterranean RBs are usually located in the mesophotic zone (below 40 m), and thus are frequently remote and unexplored. Recently, the importance and vulnerability of these habitats have been recognized by the European Community and more attention has been drawn to their investigation and conservation. This study reports the results of an extensive monitoring program, carried out within the Marine Strategy Framework Directive (2008/56/EC), in six sites off the Campania coast (Italy, Mediterranean Sea). New insights were given into the distribution, cover, vitality (i.e., live/dead rhodolith ratio), structural complexity, and coralline algae composition of RBs. Remotely operated vehicles (ROV) investigations allowed the description of several RBs, and the discovery of a RB with rhodolith cover &gt, 65% offshore the Capri Island. Only two sites (Secchitiello and Punta Campanella) showed a very low mean cover of live rhodoliths (&lt, 10%), hence, not being classifiable as RBs. The collected rhodoliths were mostly small pralines (~2 cm), spheroidal to ellipsoidal, with growth-forms ranging from encrusting/warty to fruticose/lumpy. Coralline algae identification revealed a high diversity within each bed, with a total of 13 identified taxa. The genus Lithothamnion dominated all sites, and Phymatolithon calcareum and Lithothamnion corallioides, protected by the Habitats Directive (92/43/EEC), were detected in all RBs.

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.

The resilience of ecological communities is often defined by one or a few species that have disproportionately important roles influencing many other species in the community. This is true for some areas of the Mediterranean Sea that are characterized by large brown fucoid algae in the genus Cystoseira that form dense underwater forests structurally similar to the giant kelps of the Pacific. While shorter than the giant kelp, Cystoseira form dense underwater stands, contributing to the three‐dimensional complexity of the seascape (Fig. 1). These canopy‐forming seaweeds play a crucial role in primary production and nutrient cycling of temperate coastal ecosystems from the Mediterranean Sea to the Atlantic Ocean (Mineur et al., 2015) and act as ‘ecosystem engineers', providing food, nursery, and shelter for a rich associated biota. Our study highlighted potential disruptive effects of winter hot spells on reproductive timing, recruitment, and adult survival that could severely affect the persistence of Cystoseira populations. Because extreme climate episodes are increasing in intensity and frequency, implementing coordinated initiatives connecting centers for climate alerts and algologists may shed light on how these phenomena impact population dynamics of Cystoseira species, and help current attempts to restore algal forests.

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.

Carpodesmia barbatula (= Cystoseira barbatula) (Fucales, Phaeophyta) is a species endemic to the Southern Mediterranean Sea, which grows in clean waters on exposed sublittoral rocky shores. Together with other species of the genus Cystoseira sensu lato, it is an ecosystem engineer that forms dense canopy forests, sustaining biodiversity, productivity and nutrient cycling in temperate rocky reefs. Human impacts and climate stressors are seriously hampering these ecosystems and actual conservation efforts appear insufficient for their preservation. Restoration actions could be a solution for the loss of these habitats, but they require the deep knowledge of the target species. In the present study, we describe egg release, zygote development and germling growth of C. barbatula, poorly known, despite its importance in the upper sublittoral seaweed flora. The aim is to improve the knowledge on the early life stages of this rare and threatened species, towards its possible future restoration.

In the Mediterranean Sea, brown algae belonging to the Cystoseira genus play a valuable role as foundation species. Due to evidences of regression/loss of the habitats of these species caused by the interplay of human and climatic disturbances, active restoration measures have been encouraged by EU regulations. In particular, nondestructive restoration techniques, which avoid the depletion of threatened species in donor populations, are strongly recommended. In the framework of the EU project ROCPOP-Life, the first ex situ outplanting experience of Cystoseira amentacea var. stricta has been implemented in the Cinque Terre Marine Protected Area (northwestern Mediterranean). A total of 400 clay tiles, hosting approximately three mm-long germlings of C. amentacea, were fixed to the rocky shore with screws: the tiles were monitored for the next 2 months by photographic sampling, and survival (presence/absence of juveniles on the tiles), cover and growth were assessed. Additional sampling was performed 6 months after tile deployment, after which an unprecedented storm surge severely affected the restoration performance. After 2 months, over 40% of the tiles were covered with Cystoseira juveniles, which reached approximately eight mm in total length. The tiles that survived the storm hosted three to six cm-long juveniles. The high cover (≥25%), assuring moisture and shading, and the appropriate size of the juveniles, to avert micro-grazing, at time of deployment were key to the survival and growth of the outplanted juveniles, increasing the potential for restoration success. Our findings show that outplanting of midlittoral canopy-forming species is a feasible approach for restoration efforts, with particular attention given to the early phases: (i) laboratory culture, (ii) transport, and (iii) juvenile densities. These results are strongly encouraging for the implementation of restoration actions for C. amentacea on a large scale, in light of EU guidelines.

Marine bioconstructions are biodiversity-rich, three-dimensional biogenic structures, regulating key ecological functions of benthic ecosystems worldwide. Tropical coral reefs are outstanding for their beauty, diversity and complexity, but analogous types of bioconstructions are also present in temperate seas. The main bioconstructions in the Mediterranean Sea are represented by coralligenous formations, vermetid reefs, deep-sea cold-water corals, Lithophyllum byssoides trottoirs, coral banks formed by the shallow-water corals Cladocora caespitosa or Astroides calycularis, and sabellariid or serpulid worm reefs. Bioconstructions change the morphological and chemicophysical features of primary substrates and create new habitats for a large variety of organisms, playing pivotal roles in ecosystem functioning. In spite of their importance, Mediterranean bioconstructions have not received the same attention that tropical coral reefs have, and the knowledge of their biology, ecology and distribution is still fragmentary. All existing data about the spatial distribution of Italian bioconstructions have been collected, together with information about their growth patterns, dynamics and connectivity. The degradation of these habitats as a consequence of anthropogenic pressures (pollution, organic enrichment, fishery, coastal development, direct physical disturbance), climate change and the spread of invasive species was also investigated. The study of bioconstructions requires a holistic approach leading to a better understanding of their ecology and the application of more insightful management and conservation measures at basin scale, within ecologically coherent units based on connectivity: the cells of ecosystem functioning.

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.

This article gives an up-to-date review of the status of and main changes in benthic algal flora that have occurred in recent decades along the Italian Adriatic coastline. Common traits among the main structural/functional changes observed and their causes are discussed. A synthesis of the challenges to and prospects of filling gaps in the data, ecological knowledge and protection measures are also given.

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.

Coralline red algae are significant components of sea bottom and up to now considered as exclusively marine species. Here we present the first coralline alga from a freshwater environment, found in the Cetina River (Adriatic Sea watershed). The alga is fully adapted to freshwater, as attested by reproductive structures, sporelings and an inability to survive brackish conditions. Morphological and molecular phylogenetic analyses reveal the species belongs to Pneophyllum and is described as P. cetinaensis sp. nov. The marine-freshwater transition most probably occurred during the last glaciation. The brackish-water ancestor was preadapted to osmotic stress and rapid changes in water salinity and temperature. The particular characteristics of the karst Cetina River, such as hard water enriched with dissolved calcium carbonate and a pH similar to the marine environment, favoured colonization of the river by a marine species. The upstream advance and dispersal is facilitated by exceptionally pronounced zoochory by freshwater gastropods. Pneophyllum cetinaensis defies the paradigm of Corallinales as an exclusively marine group.

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.

21 páginas, 6 figuras, 4 tablas., Habitat classifications provide guidelines for mapping and comparing marine resources across geographic regions. Calcareous bio-concretions and their associated biota have not been exhaustively categorized. Furthermore, for management and conservation purposes, species and habitat mapping is critical. Recently, several developments have occurred in the field of predictive habitat modeling, and multiple methods are available. In this study, we defined the habitats constituting northern Adriatic biogenic reefs and created a predictive habitat distribution model. We used an updated dataset of the epibenthic assemblages to define the habitats, which we verified using the fuzzy k-means (FKM) clustering method. Redundancy analysis was employed to model the relationships between the environmental descriptors and the FKM membership grades. Predictive modelling was carried out to map habitats across the basin. Habitat A (opportunistic macroalgae, encrusting Porifera, bioeroders) characterizes reefs closest to the coastline, which are affected by coastal currents and river inputs. Habitat B is distinguished by massive Porifera, erect Tunicata, and noncalcareous encrusting algae (Peyssonnelia spp.). Habitat C (non-articulated coralline, Polycitor adriaticus) is predicted in deeper areas. The onshore-offshore gradient explains the variability of the assemblages because of the influence of coastal freshwater, which is the main driver of nutrient dynamics. This model supports the interpretation of Habitat A and C as the extremes of a gradient that characterizes the epibenthic assemblages, while Habitat B demonstrates intermediate characteristics. Areas of transition are a natural feature of the marine environment and may include a mixture of habitats and species. The habitats proposed are easy to identify in the field, are related to different environmental features, and may be suitable for application in studies focused on other geographic areas. The habitat model outputs provide insight into the environmental drivers that control the distribution of the habitat and can be used to guide future research efforts and cost-effective management and conservation plans., This study has been funded by the Italian Ministry of Education, Universities and Research within the scientific research program of national interest "Coastal bioconstructions: structures, functions, and management" (2010-11 PRIN prot. 2010Z8HJ5M_003) and by the INTERREG Ita-Slo 2007-2013 Program (Project TRECORALA - TREzze e CORalligeno dell'ALto Adriatico: valorizzazione e gestione sostenibile nel Golfo di Trieste.http://www. trecorala.eu/it-IT/7-avvio-del-progetto-trecorala).

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.

The genera Hydrolithon and Porolithon are the most discussed taxa of non-geniculate Corallinaceae, as well as the most poorly known. Anatomical observations based usually on thallus construction, number of epithallial cell layers, trichocyte arrangement, occurrence of vegetative filaments between the trichocytes, and presence/absence of cell fusions and secondary pit connections led to different interpretations mainly due to the lack of available reproductive material from type specimens. Recently molecular surveys on the phylogeny of the Corallinales supported the hypothesis of considering Hydrolithon and Porolithon as two distinct genera but, up to now, several taxonomic questions remain in part unanswered. For these reasons identification of species belonging to these genera is still very difficult and can often lead to misidentification of taxa. In this study we report the discovery of a species of the Hydrolithon group found along the coast of Vis Island, Croatia, Adriatic Sea. Samples were identified through morpho-anatomical examinations and the phylogenetic position of this species was investigated through molecular analyses based on the nuclear nSSU and the plastidial psbA markers. This finding represents the first report for the Mediterranean Sea of Hydrolithon rupestre, one of the few encrusting coralline algae reported to overgrow live corals. The species can represent a possible threat to populations of Adriatic scleractinian corals.

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.

When submerged in sea water, all objects, whether artificial or natural, are soon covered by fouling. Some workers consider sediment and silt deposited on substrata to be‘fouling’and use the term‘biofouling’for animal and plant aggregates. In terms of a biocenosis biofouling cannot be defined as a distinctive biological entity since it varies in accordance with a multitude of environmental factors (Relini, 1977).