Coralligenous formations dominated by Eunicella cavolini (Koch, 1887) in the NE Mediterranean: biodiversity and structure

Coralligenous formations are biogenic structures typical of the underwater Mediterranean seascape. Their intricate, multi-layered species assemblages are composed of perennial, long-lived organisms, particularly vulnerable to natural or human-induced disturbances. Despite their high ecological role and conservation value, few studies have addressed the assemblages outside the NW Mediterranean. This is the first quantitative assessment of coralligenous in the N Aegean Sea (NE Mediterranean), specifically focusing at the upper bathymetric limit of assemblages that are dominated by the yellow gorgonian Eunicella cavolini. The number and percent cover of macrobenthic species were studied at depths of 18 to 35 m, using a photoquadrat method. A total of 99 benthic taxa were identified, out of which 89 perennial ones were used to investigate spatial patterns in assemblage structure, composition, and biodiversity. A mean number of 47 perennial taxa were recorded per site, with encrusting coralline algae and sponges being the dominant groups in percent cover and species number, respectively. Across the studied localities, structural complexity and community composition were overall similar, but assemblages presented distinctive differences at the level of sites highlighting the role of local abiotic and anthropogenic factors in the shaping of the coralligenous. Compared to the rest of the Mediterranean, assemblages hosted a similar number of taxa. However, the number and percent cover of erect bryozoans were generally low, while, apart from E. cavolini, other erect anthozoan species were absent. This work provides an important baseline for comparisons and monitoring at a local or Mediterranean scale level.

Medium range omnidirectional multibeam sonar observation of fish schools around drifting FADs

International audienc

Medium range omnidirectional multibeam sonar observation of fish schools around drifting FADs

International audienc

Spatiotemporal distribution of fish schools around drifting fish aggregating devices

International audienceOmnidirectional sonar surveys were conducted in close proximity to drifting fish aggregating devices (FADs) offshore Seychelles, western Indian Ocean, to investigate the number, size, and distribution of FAD-associated fish schools. Echotrace detection techniques applied on the raw multibeam data enabled the extraction of empirical statistics regarding inter-school distances, and allowed the visualization of the temporal evolution of the pelagic aggregation on a FAD-centered coordinate system. The sonar recordings revealed the concurrent existence of multiple fish schools that were spatially clustered and exhibited low permanence in size and structure. Schools were predominantly detected within a radius of 500 m from the FADs, although 15% of detections occurred between 500 to 1500 m from the floating devices. Fish school biomass detected with the sonar was aggregated into a few, large schools during daytime, and dispersed into a larger number of small schools during nighttime. Compared to daytime observations, nighttime schools maintained smaller inter-school distances and were located closer to the drifting FADs. The study demonstrates that horizontal sonars are powerful tools for studying the spatiotemproral distribution of large pelagic schools in the vicinity of drifting FADs

Adaptation of fisheries sonar for monitoring schools of large pelagic fish: dependence of schooling behaviour on fish finding efficiency

Multibeam omnidirectional sonars are tools currently used by fishers, but also allow the monitoring of pelagic fish schools surrounding a platform. Multibeam processing methods now offer improved capacities for raw data storage. The Simrad SP90 sonar was used for the detection of fish schools associated with drifting fish aggregating devices (FADs), and digital systems developed for the acquisition and processing of volume backscattering echoes and position data. Data sampling methods were defined based on two modes: one for periods searching for FADs and associated schools, and one for school monitoring in drifting mode. Validation of the detection of several FAD-associated schooling species was made by simultaneous visual observations or/and cross-checking with echosounder recordings. The characteristics of schooling behaviour in the targeted fish species are fundamental for the correct interpretation of acoustic data. Sonar detection threshold is the result of a compromise between fish number, size, species and the nearest neighbour distance (NND) of individuals per dynamic structure (school or shoal). Tuna schooling dynamics mean that NND can sometimes be too large to allow the presence of these fish to be detected, despite their number. Sonar data should be analysed and interpreted in a holistic manner, in combination with behaviour pattern and dynamics of all species around the drifting FADs. An autonomous sonar buoy prototype equipped with 360° scanning sonar coupled to video cameras will increase our understanding of tuna behaviour around drifting or anchored objects. A similar methodology can be applied to different kinds of platforms, either anchored or in permanent positions. This would improve the monitoring of fish schools around artificial reefs, open sea aquaculture farms, and across estuaries, channels or straits; applications which are undoubtedly essential for progressive fisheries management

Optimizing biodiversity prediction from abiotic parameters

An integrated methodology is proposed for the effective prediction of biodiversity exclusively from abiotic parameters. Phytoplankton biodiversity was expressed as richness, evenness and dominance indices and abiotic parameters included temperature, salinity, dissolved inorganic nitrogen and phosphates. Prediction was based on three machine learning techniques: model trees, multilayer perceptron and instance based learning. To optimize diversity prediction, indices were calculated on a large number of phytoplankton field assemblages, but also on corresponding noise-free simulated assemblages. Biodiversity was most accurately predicted by the instance based learning algorithm and the efficiency was doubled with simulated assemblages. Based on the optimal algorithm, indices, and dataset, a software package was developed for phytoplankton diversity prediction for Eastern Mediterranean waters. The proposed methodology can be adapted to any group of organisms in marine and terrestrial ecosystems whereas important applications are the integration of community structure in ecological models and in assessments of global change scenarios

Towards an Autonomous Pelagic Observatory: Experiences from Monitoring Fish Communities around Drifting FADs

This work presents a methodological synthesis for the in situ monitoring of fish aggregating devices (FADs) using a combination of optical, echosounder and SCUBA observations conducted in the vicinity of drifting FADs. The acoustic methods allowed, according to the devices used, the description of the spatial organisation and dynamics of biotic scattering layers, individual fishes, schools, shoals and mammals, while visual, photographic and video observations permitted species identification within a range of 0 to ~ 25 m. Based on these results, we elaborate on the interest to combine acoustic and visual methods, and present an autonomous instrumented drifting buoy for remotely monitoring fish diversity and abundance in the pelagic ecosystems. The perspective of autonomously collecting large amounts of basic information useful for ecological and fisheries studies in an ecosystem approach for open sea, as well as coastal pelagic environment, is also emphasized. As perspective we present “Seaorbiter” a futuristic large drifting platform which will allow performing innovative ecosystemic studies taking into account simultaneously all macro components of the pelagic ecosystem

Assembling Ecological Pieces to Reconstruct the Conservation Puzzle of the Aegean Sea

The effective conservation of marine biodiversity through an integrated ecosystem-based management approach requires a sound knowledge of the spatial distribution of habitats and species. Although costly in terms of time and resources, acquiring such information is essential for the development of rigorous management plans and the meaningful prioritization of conservation actions. Located in the northeastern part of the Mediterranean, the Aegean Sea represents a stronghold for marine biodiversity. However, conservation efforts are hampered by the apparent lack of spatial information regarding marine habitats and species. This work is the first to address this knowledge gap by assembling, updating, and mapping information on the distribution of key ecological components. A range of data sources and methodological approaches was utilized to compile and complement the available data on 68 ecological features of conservation interest (58 animal species, six habitat categories, and four other vulnerable ecological features). A standardized data evaluation procedure was applied, based on five semi-quantitative data quality indicators in the form of a pedigree matrix. This approach assessed the sufficiency of the datasets and allowed the identification of the main sources of uncertainty, highlighting aspects that require further investigation. The overall dataset was found to be sufficient in terms of reliability and spatiotemporal relevance. However, it lacked in completeness, showing that there are still large areas of the Aegean that remain understudied, while further research is needed to elucidate the distribution patterns and conservation status of several ecological features; especially the less charismatic ones and those found in waters deeper than 40 m. Moreover, existing conservation measures appear to be inadequate to safeguard biodiversity. Only 2.3% of the study area corresponds to designated areas for conservation, while 41 of the ecological features are underrepresented in these areas. Considering the high geomorphological complexity and transnational character of the Aegean Sea, this study does not offer a complete account of the multifaceted diversity of this ecoregion. Instead, it represents a significant starting point and a solid basis for the development of systematic conservation plans that will allow the effective protection of biodiversity within an adaptive management framework

Biological Invasions in Conservation Planning: A Global Systematic Review

International audienceBiological invasions threaten biodiversity in terrestrial, freshwater and marine ecosystems, requiring substantial conservation and management efforts. To examine how the conservation planning literature addresses biological invasions and if planning in the marine environment could benefit from experiences in the freshwater and terrestrial systems, we conducted a global systematic review. Out of 1,149 scientific articles mentioning both “conservation planning” and “alien” or any of its alternative terms, 70 articles met our selection criteria. Most of the studies were related to the terrestrial environment, while only 10% focused on the marine environment. The main conservation targets were species (mostly vertebrates) rather than habitats or ecosystems. Apart from being mentioned, alien species were considered of concern for conservation in only 46% of the cases, while mitigation measures were proposed in only 13% of the cases. The vast majority of the studies (73%) ignored alien species in conservation planning even if their negative impacts were recognized. In 20% of the studies, highly invaded areas were avoided in the planning, while in 6% of the cases such areas were prioritized for conservation. In the latter case, two opposing approaches led to the selection of invaded areas: either alien and native biodiversity were treated equally in setting conservation targets, i.e., alien species were also considered as ecological features requiring protection, or more commonly invaded sites were prioritized for the implementation of management actions to control or eradicate invasive alien species. When the “avoid” approach was followed, in most of the cases highly impacted areas were either excluded or invasive alien species were included in the estimation of a cost function to be minimized. Most of the studies that followed a “protect” or “avoid” approach dealt with terrestrial or freshwater features but in most cases the followed approach could be transferred to the marine environment. Gaps and needs for further research are discussed and we propose an 11-step framework to account for biological invasions into the systematic conservation planning design