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Coralligène formations in the eastern Mediterranean Sea: Morphology, distribution, mapping and relation to fisheries in the southern Aegean Sea (Greece) based on high-resolution acoustics
Abstract
Coralline algae are one of the most important constructors of biogenic habitats. In the Mediterranean Sea, the dominant coralline algae species form crusts comprising formations known as coralligène, considered as very important fishing grounds by fishermen. Due to the destructive effect of fishing gear activities over coralligène, these formations were recently protected from the use of active benthic gears by the EU 1967/2006 Mediterranean fisheries management Regulation. However, the lack of maps and information on their distribution makes the effective application of these measures impossible. The present publication contributes to the mapping of coralligène in the southern Aegean Sea (eastern Mediterranean), and to the study of coralline algae formation morphology, distribution, development conditions and relation to fisheries using a combination of single-beam echo sounder, sidescan sonar, sub-bottom profiler recordings and biological and sedimentological ground-truthing techniques. The coralligène formations were recognized as two distinct acoustic signatures of localized backscatter facies distinguishable from other hard substrate reflectors at depths ranging from 55.9 to 114.0 m, but mainly between 70 and 90 m. Two types of formations were identified: minute reefs 0.5-2.5 m in height and superficial layer formations no more than 0.2 m thick over the substrate. The seismic profiles revealed a cavernous internal structure of the minute reefs and recorded their development on both hard and soft substrates. The distribution of formations was contagious, creating aggregations. The finding of superficial layer formations and coralline shreds around minute coralligène reefs indicated that the former could be an intermediate development type between isolated small coralline pebbles, rhodoliths, and minute reefs. Regarding the development conditions, sidescan sonar imagery indicated that the optimal conditions for the establishment and development of coralligène formations are medium intensity currents. Concerning human activity over coralligène, trawl traces were recorded near but not over minute reefs and both near and crossing superficial layer type aggregations, while a submarine cable was also recorded among minute reefs. The mapping of coralligène aggregation areas is essential for the application of the EU Regulation and the protection of this important marine habitat.
... These habitats are critical for the health of the sea bottom by serving as excellent feeding grounds for many fish and crustaceans as well as by regulating carbon production (Martin et al., 2013). While there is sufficient research on species of coralligenous formations around the Mediterranean (Ballesteros, 2006;Blondel et al., 2006;Bartlett et al., 2009;Bonacorsi et al., 2012;Giakoumi et al., 2013;Martin et al., 2014;Ingrassia et al., 2019;Pierdomenico et al., 2021;Romagnoli et al., 2021;De Falco et al., 2022), only one systematic study (Georgiadis et al., 2009) refers to the Eastern Mediterranean region. Coralligenous formations are under heavy stress due to human activities such as fishing, anchoring, invasion of alien species, and environmental pollution (Georgiadis et al., 2009;Coll et al., 2012;Giakoumi et al., 2013). ...
... While there is sufficient research on species of coralligenous formations around the Mediterranean (Ballesteros, 2006;Blondel et al., 2006;Bartlett et al., 2009;Bonacorsi et al., 2012;Giakoumi et al., 2013;Martin et al., 2014;Ingrassia et al., 2019;Pierdomenico et al., 2021;Romagnoli et al., 2021;De Falco et al., 2022), only one systematic study (Georgiadis et al., 2009) refers to the Eastern Mediterranean region. Coralligenous formations are under heavy stress due to human activities such as fishing, anchoring, invasion of alien species, and environmental pollution (Georgiadis et al., 2009;Coll et al., 2012;Giakoumi et al., 2013). The European Union has taken protection measures over the last four decades in order to minimize the impact and raise public awareness. ...
... While the coralligenous formations of the Greek Seas, especially those in the Aegean Sea, are considered the most well-formed assemblages of the Mediterranean Sea (Ballesteros, 2006), they are also the ones that are the least researched. Even though many studies in the area that used marine remote sensing and ground-truthing techniques for other purposes (e.g., marine geoarchaeology and habitat mapping) (Geraga et al., 2017;Fakiris et al., 2018) refer to these habitats, the only study dedicated to mapping and investigating them using marine geo-acoustics was by Georgiadis et al. in 2009. This study took place between six islands of the Cyclades Plateau mapping an area equal to 184 km 2 , mainly using an SSS and a sub-bottom profiler (SBP) while the ground truthing was performed using both sediment sampling and remotely operated vehicles (ROVs). ...
Our understanding of the distribution of coralligenous formations, throughout but mostly on the Eastern Mediterranean seafloor, is still poor and mostly relies on presence-only opportunistic trawling and fishermen reports. Previous efforts to gather this information created relevant geodatabases that led to a first draft predictive spatial distribution of coralligenous formations in the Mediterranean Sea using habitat suitability modelling techniques. In the last few decades, the use of hydroacoustics to map the seafloor for various geotechnical and habitat mapping projects accumulated high amounts of detailed spatial information about these formations, which remains majorly unexploited. Repurposing these datasets towards mapping key habitats is a valuable stepping stone to implementing the EU Habitat Directive. In Greece, a unique volume of seafloor mapping data has been gathered by the Laboratory of Marine Geology and Physical Oceanography, Geology Department, University of Patras. It accounts for more than 33 marine geophysical expeditions during the last three decades, having collected hydroacoustic data for a total seafloor area of 3,197.68 km². In the present work, this information has been curated, re-evaluated, and archived to create the most complete, until now, atlas of coralligenous formations in the Greek Seas and the only integrating presence–absence data. This atlas has been used to train and validate a predictive distribution model, incorporating environmental variables derived from open data repositories, whose importance has been assessed and discussed. The final output is an improved probability map of coralligenous formation occurrence in the Greek Seas, which shall be the basis for effective spatial planning, gap detection, and design of future mapping and monitoring activities on this priority habitat.
... While many studies are dedicated to different species of corals found around the Mediterranean (Ballesteros, 2006;Blondel et al., 2006;Bartlett et al., 2009;Bonacorsi et al., 2012;Giakoumi et al., 2013;Martin et al., 2014;Ingrassia et al., 2019;Romagnoli et al., 2021;Pierdomenico et al., 2021;De Falco et al., 2022), only a few take note of the unique coralligenous formations found throughout the Aegean Sea, especially in the Cyclades archipelago. There is only one systematic study (Georgiadis et al., 2009) dedicated to the research and mapping of this unique east Mediterranean habitat. ...
... While many studies have been conducted in order to map these two habitats around the Aegean part of the Mediterranean Sea, these are either too broad scaled and the results are based on probability models and different levels of data quality and source (Giakoumi et al., 2013;Martin et al., 2014;Sini et al., 2017) or they are using only a limited set of data or techniques (Georgiadis et al., 2009). The aim of this study is to present the results of mapping the sea bottom of Gyaros Island, a remote island in the Cyclades archipelago with a great historical and ecological value, through the combined application of a wide range of acoustic (SBES, MBES, SBP, SSS), visual [underwater towed camera (UTC) footage] and sampling (sediment and biota samples) techniques. ...
... While SSS and MBES are the most widespread methods to detect and map coralligenous reefs through this survey, SBP proved to be an extremely accurate method for the detection of reefs. The detection of coralligenous reefs through SBP has also been mentioned before (Georgiadis et al., 2009;Fakiris et al., 2018;Fakiris et al., 2019). The SBP lines were appropriately processed, applying TVG and amplitude signal enhancements in order to better highlight the area between 40 and 110 m of water depth. ...
The aim of this study is to present the results of the first complete marine habitat mapping through marine remote sensing techniques in Gyaros Island, a remote island in the Cyclades archipelago with a great historical and ecological value. Gyaros Island is of great biological importance and, for this reason, since 2011, is part of the NATURA 2000 network and, by 2019, is characterised as a marine protected area (MPA). More than 80 km² of seafloor area were inspected through a multi-platform marine remote sensing technique survey through two individual expeditions in 2014 and 2017. The remote sensing survey was conducted utilising side scan sonar, sub bottom profiler and multi- and single-beam echosounders. In addition to the remote sensing survey, an extensive ground truth network was established utilising a underwater towed camera and VanVeen sediment grabber. These resulted in the area being fully covered with high-quality data. Through these, a classification of the area was performed based on three distinct seafloor habitat mapping schemes (Expert, European Nature Information System and NATURA HD). The survey and the classification revealed that over 50% of the seafloor is covered by Posidonia oceanica meadows and coralligenous and other calcareous bio-concretion priority habitats. Based on the results of this work, Gyaros MPA was also established and different protections and conservation zones were set.
... Small sponges, polychaetes and soft-tissue corals cover the top of the mounds (Figure 7c-f). These biogenic mounds are quite similar to the coralline algae reefs that have been reported in the Eastern Mediterranean Sea (Aegean Sea) by [29]. Coralline algae are one of the most important constructors of biogenic habitats and form crusts comprising formations known as coralligène. ...
... Coralline algae are one of the most important constructors of biogenic habitats and form crusts comprising formations known as coralligène. So far, two types of coralligène formations have been recognized: minute reefs (0.5-2.5 min height) and superficial layer formations (less than 0.2 m thick [29]). Coralligène formations have been observed at depths ranging from 56 to 114 m, but they are more often observed between 70 and 90 m [29]. ...
... So far, two types of coralligène formations have been recognized: minute reefs (0.5-2.5 min height) and superficial layer formations (less than 0.2 m thick [29]). Coralligène formations have been observed at depths ranging from 56 to 114 m, but they are more often observed between 70 and 90 m [29]. The biogenic mounds found in the present survey area are quite similar to the minute reefs of the Aegean Sea, but they are not as well developed as those. ...
A series of marine remote sensing and ground-truth surveys were carried out at NW Gulf of Patras (W. Greece). The same area was surveyed in 1971 by Throckmorton, Edgerton and Yalouris, who are among the pioneers in the application of remote sensing techniques to underwater archaeology. The researchers conducted a surface reconnaissance survey to locate the site where the Battle of Lepanto took place on 7 October 1571. Their remote sensing surveying resulted in a map of two "target" areas that showed promise as possible remnants of wrecks from that battle and proposed a ground truth survey for their identification and in the detection of two modern shipwrecks. The ground truth survey was never fulfilled. The objectives of our repeat surveys, which were completed 50 years later, were to relocate the findings of this pioneer survey with higher spatial and vertical resolution, to ground-truth the targets, fulfilling their investigation, and to interpret the newly collected data in the light of modern developments in marine geosciences. Our repeat surveys detected mound clusters and individual mounds referred to "target" areas. These mounds could be interpreted as the surface expression of mud and fluid expulsion from the underlying deformed soft sediments. The ground truth survey demonstrated that the tops of mounds represent biogenic mounds. The ROV survey did not show any indication of wreck remnants of the Battle of Lepanto within the two survey areas. The site formation processes of the two modern shipwrecks were also studied in detail. Two noticeable seafloor morphological features were detected around the wreck sites; field of small-sized pockmarks and seafloor depressions. We would like to dedicate this work to the memory of Peter Throckmorton and Harold E. Edgerton, who are among the pioneers in the formative years of underwater archaeology in Greece.
... Direct contact of trawling nets and trawl doors with the seafloor scraps the seafloor and leaves scars in pairs, causing sediment suspension [10,11]. Bottom trawling has destructive effects on priority habitats (e.g., coral community, coralligenous formations, seagrass beds) which are targets for conservation actions [12][13][14]. In addition, marine geoarchaeological sites have also been heavily impacted by trawl-fishing [15,16]. ...
... Ground truthing survey showed that those mounds are biogenic mounds (Figure 2). These biogenic mounds are quite similar to the coralline algae reefs that have been reported in the Eastern Mediterranean Sea (Aegean Sea) by the authors of [13]. The linear features of the third acoustic pattern are interpreted as marks produced by bottom-fishing gear (TMs) (Figure 2). ...
... The SSS mosaic also depicts complex areas that represent scattered biogenic mounds. A growing body of literature pays particular attention to the extent and the acoustic pattern of coralligenous formations [13,71,86,87]. Despite the fact that the EU 1967/2006 Mediterranean fisheries management Regulation protects the biogenic habitats, they are commonly impacted by fishing activities [13,88]. ...
Bottom trawl footprints are a prominent environmental impact of deep-sea fishery that was revealed through the evolution of underwater remote sensing technologies. Image processing techniques have been widely applied in acoustic remote sensing, but accurate trawl-mark (TM) detection is underdeveloped. The paper presents a new algorithm for the automatic detection and spatial quantification of TMs that is implemented on sidescan sonar (SSS) images of a fishing ground from the Gulf of Patras in the Eastern Mediterranean Sea. This method inspects any structure of the local seafloor in an environmentally adaptive procedure, in order to overcome the predicament of analyzing noisy and complex SSS images of the seafloor. The initial preprocessing stage deals with radiometric inconsistencies. Then, multiplex filters in the spatial domain are performed with multiscale rotated Haar-like features through integral images that locate the TM-like forms and additionally discriminate the textural characteristics of the seafloor. The final TMs are selected according to their geometric and background environment features, and the algorithm successfully produces a set of trawling-ground quantification values that could be established as a baseline measure for the status assessment of a fishing ground.
... Mediterranean coralligenous formations refer to biogenic structures made up of encrusting coralline algae and calcareous animal material. They typically develop under dim light conditions at depths ranging from 20 to 120 m, either (a) as outcrops of rocky substrates (i.e., coralligenous of the littoral rock), or (b) as banks/platforms/minute reefs (sensu Georgiadis et al., 2009) surrounded by sedimentary substrates or even sandy bottoms (Ballesteros, 2006;Georgiadis et al., 2009). The geographic distribution of coralligenous formations in the Aegean Sea was mainly based on data provided by previous mapping efforts of variable spatial resolution (e.g., Georgiadis et al., 2009;Fakiris, 2012;Giakoumi et al., 2013;Martin et al., 2014;Papatheodorou et al., 2014;Dimas et al., 2015;Geraga et al., 2016), and ecological assessments (e.g., Sini et al., 2015;Supplementary File 4). ...
... Mediterranean coralligenous formations refer to biogenic structures made up of encrusting coralline algae and calcareous animal material. They typically develop under dim light conditions at depths ranging from 20 to 120 m, either (a) as outcrops of rocky substrates (i.e., coralligenous of the littoral rock), or (b) as banks/platforms/minute reefs (sensu Georgiadis et al., 2009) surrounded by sedimentary substrates or even sandy bottoms (Ballesteros, 2006;Georgiadis et al., 2009). The geographic distribution of coralligenous formations in the Aegean Sea was mainly based on data provided by previous mapping efforts of variable spatial resolution (e.g., Georgiadis et al., 2009;Fakiris, 2012;Giakoumi et al., 2013;Martin et al., 2014;Papatheodorou et al., 2014;Dimas et al., 2015;Geraga et al., 2016), and ecological assessments (e.g., Sini et al., 2015;Supplementary File 4). ...
... They typically develop under dim light conditions at depths ranging from 20 to 120 m, either (a) as outcrops of rocky substrates (i.e., coralligenous of the littoral rock), or (b) as banks/platforms/minute reefs (sensu Georgiadis et al., 2009) surrounded by sedimentary substrates or even sandy bottoms (Ballesteros, 2006;Georgiadis et al., 2009). The geographic distribution of coralligenous formations in the Aegean Sea was mainly based on data provided by previous mapping efforts of variable spatial resolution (e.g., Georgiadis et al., 2009;Fakiris, 2012;Giakoumi et al., 2013;Martin et al., 2014;Papatheodorou et al., 2014;Dimas et al., 2015;Geraga et al., 2016), and ecological assessments (e.g., Sini et al., 2015;Supplementary File 4). New information on coralligenous formations of the littoral rock found at depths shallower than 40 m was acquired through interviews and questionnaires with divers, and during the SCUBA diving surveys of the present study. ...
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.
... However, the exact functional role of coralligenous habitats in the Mediterranean basin has not yet been clarified (Georgiadis et al., 2009). Previous studies indicated that coralligenous species strongly structure their environment by capturing particulate organic matter sedimentation, creating niches and improving the food availability for a number of species, such queen scallops, soft clams, sea urchins, starfish and gadoids (Kamenos et al., 2004;Lloret et al., 2007). ...
... However, human activities and in particular commercial fishing interests are in conflict with conservation goals. Since coralligenous communities compose the habitat of several species of fish, mechanistic destruction due to fishing remains one of the main threats for coralligenous habitats in the Mediterranean region (Georgiadis et al., 2009). The efficacy of future conservation measures will thus largely depend on the selection of regions and depth belts to preserve. ...
... Given the important ecological role of coralligenous habitats, providing habitat and filter functions for several microorganisms and fish species, and their low resilience to disturbance (Georgiadis et al., 2009), Mediterranean marine conservation needs to be designed and implemented on the basis of spatially adaptive methods able to monitor the three-dimensional spatial variability of diversity. We suggest that using taxonomic diversity alone may be misleading, and that additional information, at least on phylogenetic diversity, is required to properly set future conservation goals and enable conservationists to apprehend the spatial variations of community composition (Mouquet et al., 2012). ...
... Although researchers have paid attention to the distribution and the typology of the deep sea cold corals in Mediterranean Sea and worldwide (Taviani et al. 2005;Roberts et al. 2006;Hovland 2008), the information regarding of algae coralline formations is very limited. A recent side scan sonar survey which took place in the Cyclades Islands (Aegean Sea, Eastern Mediterranean Sea) showed that algae coralline formations form aggregations on the seabed (Georgiadis et al. 2009). The algae aggregations appeared in most cases as minute reef aggregations, with the majority of minute reefs occurred in clusters of up to 30 individual reefs (Georgiadis et al. 2009). ...
... A recent side scan sonar survey which took place in the Cyclades Islands (Aegean Sea, Eastern Mediterranean Sea) showed that algae coralline formations form aggregations on the seabed (Georgiadis et al. 2009). The algae aggregations appeared in most cases as minute reef aggregations, with the majority of minute reefs occurred in clusters of up to 30 individual reefs (Georgiadis et al. 2009). In rare cases, superficial layer (less than 0.5 m in height) type aggregations were observed (Georgiadis et al. 2009). ...
... The algae aggregations appeared in most cases as minute reef aggregations, with the majority of minute reefs occurred in clusters of up to 30 individual reefs (Georgiadis et al. 2009). In rare cases, superficial layer (less than 0.5 m in height) type aggregations were observed (Georgiadis et al. 2009). ...
In this paper, the TargAn software package that is dedicated to parameterizing regions of interest (ROIs) in greyscale images that reflect backscatter information derived by marine geo-acoustical instrumentation (e.g. Side Scan Sonar and Multi-Beam Echo-Sounder) is presented. The ROIs, whose boundaries are marked out either manually or via simple segmentation techniques, are analyzed for as many as 37 features. The adopted and developed methodologies lead to the extraction of: (1) grey-level intensity (1st order) and texture analysis statistics estimated from the inner ROI, (2) descriptors that measure the separation of the ROI in comparison to the intensity characteristics of the peripheral seabed, (3) shape geometry descriptors of the ROI’s boundary itself and (4) regional statistics of distinct (segmented) objects possibly included in the ROI. TargAn is implemented in Matlab with a graphical user interface that helps the user to have control over the digitization, segmentation and feature extraction processes involved. It also provides tools for the construction of compact geo-databases, suitable for geostatistical analysis and visualization in popular Geographical Information Systems, concerning the extracted descriptors and the geographic features (e.g. ROIs’ boundaries, skeletons, segmented objects) that have been considered for ROIs’ analyses. The TargAn software is particularly useful when large amounts of image ROIs need to be objectively quantified and is demonstrated through two case studies regarding Side Scan Sonar imageries. The first one concerns the quantification of marine biohabitats (coralline formations) while the second exhibits the geometrical analysis of pockmarks.
... C morphotypes have been categorized mainly in two groups, banks and rims [4,15,16] that is based upon the nature of the substrate. Among banks, several different terms have been used to distinguish diverse local morphotypes (heads, blocks, patches, or banks [17]; vertical pillar, [18]; algal reefs, [19,20]; mound-shaped algal banks, [21]; minute reef aggregation and superficial layer formations, [22]; columns and ridges, [14]). A first attempt to use shape geometry descriptor to extract C from backscatter data was proposed by [23], but only recently a new categorization of C morphotypes, based on such a quantitative technique, has been proposed [11]. ...
... When associated with the occurrence of C build-ups, the first return from the seafloor is imaged by an indistinct, low-amplitude, and highly transparent reflector, whereas lateral continuity and overall amplitude increase crossing the surrounding seafloor. A similar seismic structure for algal reefs was described in [22], where the underlying acoustic basement was also visible. Interestingly, in our surveyed area, C build-ups are in contact with an erosional truncation that marks the top of the underneath sequence ( Figure 6). ...
In the Mediterranean Sea, crustose coralline algae form endemic algal reefs known as Coralligenous (C) build-ups. The high degree of complexity that C can reach through time creates notable environmental heterogeneity making C a major hotspot of biodiversity for the Mediterranean basin. C build-up can variably modify the submarine environment by affecting the evolution of submerged landforms, although its role is still far from being systematically defined. Our work proposes a new, ad-hoc semi-automated, GIS-based methodology to map the distribution of C build-ups in shallow coastal waters using high-resolution bathymetric data, collected on a sector of the southern Apulian continental shelf (Southern Adriatic Sea, Italy). Our results quantitatively define the 3D distribution of C in terms of area and volume, estimating more than 103,000 build-ups, covering an area of roughly 305,200 m2, for a total volume of 315,700 m3. Our work firstly combines acoustic survey techniques and geomorphometric analysis to develop innovative approaches for eco-geomorphological studies. The obtained results can contribute to a better definition of the ocean carbon budget, and to the monitoring of local anthropogenic impacts (e.g., bottom trawling damage) and global changes, like ocean warming and acidification. These can affect the structural complexity and total volume of carbonate deposits characterizing the Mediterranean benthic environment.
... Our results strengthen this evidence, since we showed the development of peculiar CAAs. In the Mediterranean Sea, CAAs have been only reported along the Apulian continental shelf (Bracchi et al., 2015), off Cap Corse (Pergent-Martini et al., 2014), off Columbretes Islands (Linares et al., 2015), off Balearic Islands (Aguilar et al., 2009), and in the southern Aegean Sea (Georgiadis et al., 2009;Sini et al., 2017). This typology of coralline algae formations are generally observed in seafloor areas characterized by high backscatter signatures associated with local small bioconstructions. ...
... The finding of this rare type of CAAs strengthens the ecologically valuable of the Zannone area. In addition, the large variety of the coralline algae formations detected in the study area, coupled with the widespread co-occurrence of coralligenous assemblages and rhodolith beds, led us to support the hypothesis that free coralline algae are capable to create biogenic structures from the coalescence of free thalli or rhodoliths that are not located on a hard substrate (Pérès and Picard, 1952;Georgiadis et al., 2009;Bracchi et al., 2015). Another ecological relevant aspect of the Zannone coralline algae formations is the presence of black coral colonies (i.e. ...
In the Mediterranean Sea, coralline algae assemblages (i.e. rhodolith beds and coralligenous assemblages) are considered biodiversity hotspots comparable to tropical reefs. However, information regarding their environmental distribution is still poor. In this view, relevant international actions have been adopted by the European Union to fill this gap. This work represents one of a few cases of predictive (fine-scale) habitats distribution map obtained through an integrated semi-automatic approach based on bathymetry, backscatter, seismic profiles, video, and sampling data. The used method has permitted the identification of nine morphological zones, four backscatter facies, and four benthic habitats distributed on the Zannone seafloor (western Pontine Archipelago; Tyrrhenian Sea). In particular, the finding of widespread sensitive habitats (i.e. coralligenous assemblages and rhodolith beds) reveals as the marine area off the western Pontine Archipelago (Tyrrhenian Sea) is highly suitable for their development (distance from the mainland, lack of river mouths), confirming the relevant ecological value of the Zannone area. Therefore, such information constitutes an update to the Mediterranean habitats distribution inventory, highlighting the need for the application of protection actions possibly targeted in the establishment of a Marine Protected Area.
... The Mediterranean rhodolith beds are mostly located around islands and capes (among others : Jacquotte 1962 ;García-Carrascosa 1987 ;Ballesteros et al. 1993 ;Atabey 1998 ;Schembri 1998 ;Bordehore et al. 2002a ;Piazzi et al. 2002 ;Salomidi et al. 2009 ); on top of submarine plateaux, like the top of seamounts (Aktan 2012 ;Aguilar et al. 2009 ), marine terraces (Damiani et al. 1988 ;Savini et al. 2012 ), interisland or island-mainland channels (Barberá et al. 2012 ;Bakir and Katağan 2005 ;Bracchi and Basso 2012 ;Sezgin et al. 2009 ;Georgiadis et al. 2009 ;Papakosta et al. 2012 ), and banks (Parenzan 1960 ;Cecere and Perrone 1987 ). ...
... Nevertheless, the protection of a specifi c habitat type cannot be effectively gained without access to sound geospatial data and monitoring plans (Salomidi et al. 2012 ). To this purpose, modern advances in remote sensing and acoustic habitat mapping (Georgiadis et al. 2009 ;Savini et al. 2012 ;Barbera et al. 2012) can provide an effective tool to assessing the distribution, extent and state of the rhodolith beds, thus easing management and conservation actions. ...
The available references to rhodolith beds have been analysed for a totl of 125 locations in the Mediterranean Sea, equally distributed in the eastern and western sub-basins. Mediterranean rhodoliths beds occur from 9 to 150m of water depth, with a mean depth about 55m in both sub-basins. Most rhodolits beds lay within the depth range 30-75m, while those extending deeper than 77m are about 18% of the total, and those shallower than about 25m are uncommon. The deepest and the largest Mediterranean rhodolith beds are both located in the Balearic Sea. Water motion from bottom currents, waves, and tides is needed to keep rhodoliths unburied, with mesotrophic to oligotrophic water conditions. Rhodolith bed are common small (<0.01km2) and multispecific, showing growth-form mixing and a much higher coralline diversity than Atlantic beds. They are vulnerable to physical disturbance by fishing gears and smothering, and to water pollution by organic enrichment and sewage. The existing instruments of legal protection appear il defined, since these are based on scientific literature mostly derived from northern Europe, where specific and different environmental setting, species composition, depth distribution, and anthropogenic pressures occur. The protection of a specific habitat type cannot be effectively gained without access to geospatial and compositional data and an increased research effort is needed to improve taxonomic inventories, habitat mapping, and monitoring activities on a basin scale.
... Even if we have an overall knowledge about the composition and distribution of coralligenous and marl populations in the Mediterranean (Ballesteros, 2006;Georgiadis et al., 2009; UNEP-MAP-RAC/SPA, 2009), the absence of cartographical data on the overall distribution of these populations is one of the greatest lacunae from the conservation point of view (Agnesi et al., 2008). The summary crafted by these authors confirms the scarcity of available data, with less than 50 cartographies listed for the Mediterranean basin. ...
... transects, quadrates), this method of investigation quickly shows its limits when the area of study and the depth increase significantly, even if the technique can be optimised for a general description of the site (dragged diver, video transects; Cinelli, 2009). Having recourse to acoustic methods of investigation (side sweep sonar, multi-bundle sounder; Georgiadis et al., 2009) or submerged observation systems (Remote Operating Vehicle; dragged cameras) is found to be necessary. However, acoustic techniques must be supplemented by a great deal of 'field data', for the answers obtained usually concern the substratum rather than the population that develops there, and submerged observation systems require a very long acquisition time given their limited speed and range. ...
In the framework of the Action Plan for the Conservation of Coralligenous and other Mediterranean bio-constructions adopted by Contracting Parties to Barcelona Convention Barcelona in 2008, several priority actions are identified which relate in particular to (i) The strengthening the knowledge on the distribution and composition of these population, (ii) The compiling a database of specialists and (iii) The establishment of a spatio-temporal monitoring of coralligenous and maërl populations. However, inventory and monitoring of coralligenous and maërl raise several problems, related to the accessibility of these populations, their heterogeneity and lack of standardized protocol used by different teams working in this field. The aim of this document is to make a census of the main methods used in the Mediterranean for inventory and monitoring of coralligenous and maërl populations, , and to better understand their benefits, limitations and conditions of use.
... In the Mediterranean Sea, the benthic habitats characterized by the highest biodiversity are represented by coralligenous beds, Posidonia oceanica meadows [14,55], and rhodolith/maerl beds [10,11,56,57]. ...
Coralline algal beds are comprised of biogenic calcareous formations considered a habitat of high conservation interest, hosting a high great biodiversity. To assess the status of this habitat in the Italian seas, we report results from a systematic analysis of the available scientific literature. Italian rhodolith/maerl beds are reported on 31 Italian sites mostly located around islands, shoals, banks, terraces, and gentley sloping shelves, from 9 m to 130 m water depth (with a mean depth of about 56 m). The dominant species occurring in the Italian submarine sites are Phymatolithon calcareum and Lithothamnion corallioides, with a rich associated fauna including sponges, bryozoans, hydrozoans, polichaetes, molluscs, amphipods, gastropods, echinoderms. Despite the high biodiversity characterizing the Italian rhodolith/maerl beds, only seven submarine sites hosting this sensitive habitat are part of Marine Protected Areas (MPAs). This evidence highlights the need for actions focused on the implementation of effective management and proper conservation measures to preserve such precious habitats. Protection of this habitat cannot be effectively provided without access to multidisciplinary data (e.g., geospatial, biological, geophysical, geomorphological data) capable of assessing its spatial distribution and biological characteristics over wide areas. An increased research effort to improve the production of fine-scale distribution maps and monitoring activities is therefore needed.
... An important finding of this study was that local fishers could quite accurately characterize substrate types, since in our hauls C. caespitosa was mostly prevalent over the so-called coral beds. Fishing with static nets may cause direct damage to biogenic builders, such as corals, by detaching, fragmenting and extracting pieces during hauling (Georgiadis et al., 2009). Given that coral colonies are quite fragile, they are usually returned fragmented back to the sea. ...
While hanging nets may have fewer overall environmental impacts than towed gears, they still catch unwanted species and sizes, which are then discarded. Gillnets are one of the most common types of nets used in Mediterranean small-scale fisheries,
with commercial catches and discards containing a diverse range of fish and invertebrate species. In this study, the catch profile of gillnets in the Thermaikos Gulf (NE Mediterranean) was analyzed with a focus on the discarding of species with unfavorable conservation status, such as the Mediterranean-endemic scleractinian coral Cladocora caespitosa, which is listed as endangered due to
declining population sizes. Our survey was conducted over two seasons (May to October in 2020 and 2021) and included 69 fishing trials under realistic fishing conditions. In general, gillnets exhibited a relatively low discards ratio (17.2%; 7.1% when only fish were considered) and a low prevalence and capture intensity of endangered or threatened species; during the entire survey, only one chondrichthyan was captured (1 specimen of Raja radula), while only two out of 54 fish species were of vulnerable IUCN status. These advantages were offset in part by the high catchability of C. caespitosa colonies, which occurred in 61% of hauls and accounted for 53% of total invertebrate biomass and 30% of total discarded biomass. The likelihood of hauling living colonies of C. caespitosa was higher when fishing over known coral beds (81% vs. 43%), and the overall probability of hauling C. caespitosa in any state was 18% higher over coral beds, suggesting that gillnets frequently detach colonies from the seafloor, which are then dispersed over a larger area as fragments with probably low survival potential. Our findings highlight the importance of identifying C. caespitosa beds so that fishermen avoid setting their nets in these areas, provided that they are well-informed and educated
about the ecological significance of this endemic, threatened, and ecologically important species.
... Although new data of seabed mapping of the circalittoral zone have been locally produced (e.g. Bracchi et al., 2015;Bracchi et al., 2017;Cánovas Molina et al., 2016;De Luca et al., 2018;Georgiadis et al., 2009), the knowledge of coralligenous habitatsin the Mediterranean distribution is largely incomplete. ...
Mapping of coralligenous banks was carried out along the continental shelf of the northern and western margin of Sardinia Island (Italy, western Mediterranean Sea) in the context of the European Marine Strategy Framework Directive (MSFD, 2008/56/EC). Coralligenous banks are bioconstructions produced by calcareous coralline algae. Seafloor mapping was carried out through multibeam echosounder surveys and video transects, using a Remote Operating Vehicles (ROV), in areas not formerly explored. A high-resolution digital model of the seabed (DTM) was obtained from multibeam data. A total surface of 436 km2 of sparse patches of coralligenous banks was mapped in the depth range ~40-160 m. A final map of coralligenous habitat distributions along the western and northern continental shelf of Sardinia (scale 1:250,000) was produced. The base-map is formed by the shaded DTM of the seabed. Other mapped features include the edge of the continental shelf and the distribution of rocky seabed.
... P. oceanica meadow is a habitat that has been thoroughly investigated through SSS [75][76][77][78] for mapping its extent or evaluating its ecological status. SSS is even more important for the mapping of coralligenous formation due to the depth that most of these formations are found [17,26,34,[79][80][81]. Modern-day remote sensing surveying considers the simultaneous use of both MBES and SSS a must, and this is why integrated systems that are able to supply bathymetric and backscatter intensity data simultaneously have been developed. ...
The rising human activities and resource exploitation have increased pressure in the coastal zone and the marine environment, risking the very existence of Marine Priority Habitats (MPH) and Underwater Cultural Heritage (UCH). The delimitation of these two priority areas in a time-and cost-effective way is essential for the sustainable management and exploitation of sea resources and natural-cultural heritage preservation. We propose an Integrated Methodological Approach for the Detection and Mapping of MPH and UCH. To achieve this, we used a downscale methodological approach of increasing spatial resolution based on three main methodological axes: (i) desk-based research, (ii) marine geophysics/seafloor classification, and (iii) in-depth visual inspection/3D mapping. This methodological scheme was implemented at the Saronic Gulf and focused on Aegina island. The methodology proposed, which combines existing and new techniques, proved successful in detecting and mapping the MPH and UCH in detail, while it compiled the information necessary for the establishment of Marine Spatial Planning (MSP) maps. Finally, the MSP map constructed for the Saronic Gulf demonstrated the lack of holistic coastal zone management plans due to impacts on UCH linked to anthropogenic intervention and the sparsity of marine habitats owing to marine pollution.
... Coralligène is mainly a trammel net and longline fishing ground; trammel nets (e.g. targeting spiny lobster) can remove parts of the substrate (Georgiadis et al. 2009), but no specific study exists on the effects of this gear use. ...
Small-scale fisheries in Greece are characterised by a large number of fishers and vessels scattered along an extensive coastline, a variety of fishing gears and target species, and intense heterogeneity. There are various definitions of small-scale fisheries; in general, they comprise all gears except for trawls and purse seines. Despite having little direct economic value, small-scale fisheries do have significant social importance, especially for remote rural and insular areas. Small-scale fisheries are structured around the family; contemporary fishers are relatively old, tend to inhabit their place of birth, have a low educational level and diverse levels of dependence on the profession. The fisheries are mainly located in the coastal zone and managed through control measures regulating effort, gear types, and gear use in terms of space and time. In general, small-scale fisheries have characteristics associated with sustainability, although there are cases with adverse effects on the marine ecosystem. In past decades, due to a number of management practices (e.g. vessel modernisation and replacement), Greek small-scale fisheries have, however, lost their traditional advantages of “cost-effect” relationship and morphed into “small-becoming-big-scale fisheries” with high costs, low profits, increased fishing effort and pressure on fish resources. In addition, the complex and outdated legal framework regarding professional fisheries and the individualistic character of the profession act as obstacles to collective action and complicate management.
... Moreover, since the rise in sea-level aforementioned (Benjamin et al. 2017), this zone hosts biogenic buildings made by coralline algae (i.e. coralligenous; Ballesteros 2006;Ingrosso et al. 2018) developed thousands of years ago at shallower depths (e.g. from 3000 to 7000 years BP in the Western Mediterranean, Bertolino et al. 2014 andSartoretto et al. 1996 respectively; 12,-000-14,000 years BP in the Eastern Mediterranean, Georgiadis et al. 2009). Stability and longevity can allow to some organisms living in this zone, such as gorgonian (e.g. ...
Mesophotic habitats, hosting benthic assemblages totally unknown and unexpected in the early 2000s, are attracting an increasing interest from scientists. Realizing that many long living and habitat forming species are playing a unique pocket of biodiversity in the frame of climate crisis, it is important to recognize the potential of the mesophotic zone in conservation strategies. The mesophotic zone is characterized by environmental factors generally more stable than the shallow counterpart; therefore, it represents a refuge habitat to preserve species that, in shallow waters, may be involved in bleaching events, massive mortalities or other pathologies generally triggered by thermal anomalies. The definition of the mesophotic zone in the temperate seas is confused, creating possible misunderstandings and problems not only from a scientific point of view but also in communication and outreach strategies. Here, we review the scientific literature to build the best definition possible based on the maximum consensus coming from papers analysis. Moreover, the key roles of mesophotic habitats, including ecosystem engineers as animal forests, have been schematized to enhance the perception of the potential risks we are running in case of damage or loss of these habitats.
... Destructive methods have been used for a long time because of excellent results for studying sessile organisms, particularly suitable for studies with strong taxonomical components, but not suitable for studies on assemblages and long-time monitoring, leading to the necessity to use alternative nondestructive methods of investigation, such as transects or quadrats. The study of bioconstructions, such as coralligenous accretions in the Mediterranean Sea, provided up to today important general knowledge concerning the composition of benthic communities (Ballesteros, 2006;Georgiadis et al., 2009;Casas-Güell et al., 2015). ...
Thanks to several European directives and conventions there is a general increase of awareness regarding the key ecological role of coralligenous habitats in the Mediterranean Sea, addressing several research projects to standardize protocols for the description of its integrity. Here we surveyed 13 stations along the Italian coasts of the Western Mediterranean Sea, using video-transects technique, comparing the biological structure of coralligenous assemblages and testing the importance of their three-dimensional complexity as a proxy to define their health conditions. We considered the diversity of taxa, fishing impacts and the entity of damage on gorgonian's choenenchyme due to thermal stress, to evidence a gradient in the coralligenous health conditions. Here we developed a method to evaluate coralligenous complexity, selecting categories of taxa particularly sensitive to multiple stressors, named Structural Descriptors to describe the three-dimensional structure of the bioconcretions and to assess a unique Index of 3D - Structural Complexity.
... In these early expeditions, scientists reported on the occurrence of coralligenous formations in this ecoregion (sensu Spalding et al., 2007), either as outcrops of the littoral rock developing in the lower infralittoral and circalittoral zones, or as biogenic banks surrounded by detritic substrates (also known as coralligène de plateau) found at depths of up to 120 m. Recent mapping efforts have validated the presence of numerous coralligenous formations in most parts of the Aegean Sea (Georgiadis et al., 2009;Giakoumi et al., 2013;Sini et al., 2017). However, the community structure, biodiversity and ecology of these formations remain largely underexplored, while their conservation status is effectively unknown. ...
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.
... Acoustic techniques (i.e. multibeam, multibeam backscattering and side scan sonar) allow obtaining wide scale mapping of rocky reefs topography, with some details on the fine threedimensional structure of substrate and the rough distribution of benthic assemblages (Georgiadis et al., 2009;Rattray et al., 2009;Lucieer et al., 2013). Anyway, visual direct observation or photo/video surveys are necessary to validate any acoustic data. ...
... Coralline algae can also densely occur in coastal to deep-subtidal settings but originating bioconstructions: algal ridges, algal frameworks, coralligènes, trottoirs, and corniches Picard 1958 , 1964 ;Blanc 1968 ;Adey 1978 ;Bosence 1985a ;Freiwald and Henrich 1994 ;Freiwald 1998 ;Macintyre et al. 2001 ;Nalin et al. 2006 ;Ballesteros 2006 ;Georgiadis et al. 2009 ;Aguirre et al. 2014 ). In all these cases, encrusting coralline algae form a rigid structure. ...
Calcareous coralline algae (Rhodophyta; Corallinales, Hapalidiales, and Sporolithales; corallines hereafter) constitute one of the most widespread and successful groups of marine macrophytes. They occur as crusts partially coating hard or soft substrates, as laminar thalli growing directly on the seabed, or forming structures rolling freely on the substrate with an inner nucleus or without it. These latter structures are called rhodoliths. They can be one of the most abundant components in carbonate platform deposits, forming the so-called rhodalgal facies. In assessments of the rhodoliths, internal and external algal growth morphology, rhodolith external form, rhodolith inner arrangement, and assemblages of organisms forming the rhodoliths can provide valuable information for reconstructing palaeoenvironmental and palaeoclimatic conditions. Rhodoliths can occur massively concentrated in beds several meters thick. These concentrations are referred as rhodolith beds. These rhodolith beds may be the result of biotic (autochthonous rhodolith beds), abiotic (allochthonous rhodolith beds) concentrations or due to a mixture of processes (paraautochthonous rhodolith beds). Taphonomic and facies analyses, as well as faunal assemblages, can provide the information needed to confidently differentiate among them. The rock record offers unique information to envisage the founding conditions and the long-term maintenance of the rhodolith beds. In this chapter, we review and update the information on fossil rhodoliths and rhodolith beds, and discuss their value for palaeoenvironmental and palaeoclimatic reconstructions. Also, we discuss the sedimentary and the sequence stratigraphy contexts in which rhodolith beds are preferentially formed and developed.
... However, in the Mediterranean Sea S. fruticulosus thrives on mobile substrates shallower than 30 m water depth (e.g., Braga et al., 2009). In coastal to deep-subtidal settings encrusting corallines form rigid bioconstructions named algal ridges, algal frameworks, coralligènes, trottoirs, and corniches (e.g., Pérès and Picard, 1964;Blanc, 1968;Bosence, 1985b;Freiwald and Henrich, 1994;Freiwald, 1998;Macintyre et al., 2001;Ballesteros, 2006;Georgiadis et al., 2009). None of these bioconstructions were identified in the studied area, rather the microfacies VCP and CAB represent fine soft substrates consisting in a quartz-silty packstone with thin-shelled bivalves and peloids. ...
... This type corresponds to a seafloor where coralligène formations have been built up. These benthic organisms form colonies, like small reefs, by hard, usually calcified, casings producing localized strong backscatter facies and hyperbolic echoes on seismic profiles (Georgiadis et al., 2009). Due to their nature, the acoustic signature of these biogenic reefs on side scan sonar and profiling records can be misinterpreted as rocky formations if the reefs are developed on hard substrates; or as artificial sites (i.e. ...
A marine geoarcheological survey was conducted at the southwestern end of the Argosaronic gulf in Greece, an area of archaeological importance. The survey was initiated by the discovery of a Late Bronze Age (LBA) shipwreck off Modi Islet. The survey which employed echo-sounding, sub-bottom profiling, side scan sonar systems and sediment coring extended to the area between Poros Island, Modi Islet and Argolid peninsula, aiming to evaluate the changes of the coastal zone extent in the past. The evolution of the palaeo-shoreline over the last 20 ka is proposed based on the interpretation of the acquired bathymetric and seismic records, the estimation of the thickness of the marine sediments and the examination of existing datasets of the relative sea level changes in the area.
... Only one European law (Council Regulation (EC) Nº 1967/2006 prohibits destructive fishing over Mediterranean coralligenous and mäerl communities but it remains ineffective in the current scenario of a lack of relevant geospatial data (UNEP-MAP-RAC/SPA 2008, Salomidi et al. 2012). Although some efforts have been made to increase information on the distribution of this sensitive habitat (Georgiadis et al. 2009, Giakoumi et al. 2013, Martin et al. 2014, knowledge of the geographical and depth distribution of coralligenous assemblages as well as their biodiversity and its relation to their functioning is still needed for their conservation and sustainable use (UNEP-MAP-RAC/SPA 2009, European Commission 2011, Pergent 2011. The current situation is not helped by the fragmented geopolitical scenario characterizing the Mediterranean basin, with weak, uncoordinated, conflicting approaches or non-existent regulatory frameworks, policy mechanisms and enforcement (Fraschetti et al. 2011). ...
A review and update of the existing knowledge on the coralligenous assemblages of Liguria (NW Italy) was conducted as an essential step towards management measures for their conservation according to the EU Marine Strategy Framework Directive. By combining a literature review, acoustic mapping and in situ observations on a geographic information systems platform, we were able to assess the distribution and heterogeneity of coralligenous assemblages and the main pressures affecting them. The reliability of the literature was previously estimated using a dependability index. The coralligenous assemblages cover an area of 130.9 ha and range from 10 to 113 m depth. Twelve different biological facies (five of them not included in the EUNIS list) were identified and four main geomorphotypes (plungingcliffs, paleocliffs, rockfalls and shoals) were recognized. Incident light values influenced the distribution of four facies in Portofino promontory. Pressures were found on 33% of the coralligenous assemblages investigated, mainly due to fishing activities, mass mortality events, invasive species and occasional mucilaginous events. Our results showed a high spatial, geomorphological and biological heterogeneity of coralligenous assemblages in Liguria.
... Coralline algae can also densely occur in coastal to deep-subtidal settings but originating bioconstructions: algal ridges, algal frameworks, coralligènes, trottoirs, and corniches Picard 1958 , 1964 ;Blanc 1968 ;Adey 1978 ;Bosence 1985a ;Freiwald and Henrich 1994 ;Freiwald 1998 ;Macintyre et al. 2001 ;Nalin et al. 2006 ;Ballesteros 2006 ;Georgiadis et al. 2009 ;Aguirre et al. 2014 ). In all these cases, encrusting coralline algae form a rigid structure. ...
... The protection of a specific habitat type cannot be achieved effectively without access to sound geospatial data and monitoring plans (Salomidi et al., 2012). To this purpose, modern advances in remote sensing and acoustic habitat-mapping provide effective tools for assessing the distribution, extent and state of the RBs (Georgiadis et al., 2009;Barberá et al., 2012;Savini et al., 2012). Beside mapping, evaluation of the GES of the RBs should include: (1) characterization of the 3-D structure of the bed and identification of the main habitat-forming red calcareous algae; (2) measurement of the physical-chemical variables correlated with the RBs occurrence and status (PAR, temperature, salinity, pH, nutrient concentration, suspended matter, hydrodynamics, sediment grain-size and composition, bed sedimentary structures, pollutants in the water column and in the sediment) (Sciberras et al., 2009;Barberá et al., 2012); (3) comparative assessment of the natural intra-bed and inter-bed variability in pristine conditions, in order to set limits outside of which management action is needed; and (4) identification of possible pressures and impacts, with emphasis on the pressures to which RBs have been proven to be vulnerable. ...
1. 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.
2. 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.
3. 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. 4. 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. 5. 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.
... have an overall knowledge about the composition of the Mediterranean coralligenous assemblages [1,24,26], the absence of cartographical data and associated species on the overall distribution, of these assemblages is one of the greatest lacunae from the conservation point of view [23,27]. Most of the cartographic information is based on surveys carried out in the north-western Mediterranean Sea [e.g. ...
Coralligenous habitats are of special interest in the Mediterranean Sea because they represent one of the most important biodiversity ‘hot-spots’ and are considered of great relevance for fisheries activities in the region. Despite their importance, however, there are missing consensual methodologies for their monitoring and, despite some attempts, no environmental or ecological quality indices have been established yet. This situation could be related to the difficulties associated with their exploration and their spatial heterogeneity. These habitats are in urgent need of efficient standard monitoring and management protocols programmes to develop an effective network for their conservation. Here we reviewed the available methodologies and robotics tools used to evaluate and monitor benthic habitats, highlighting the importance of defining rapid cost-effective sampling and analyses approaches and architectures for future monitoring of changes in coralligenous habitats based on current technological developments. We identified still images acquisitions as the most effective data gathering system. Stereo photogrammetry, photomosaic elaboration and three-dimensional (3D) modelling may largely improve the data analysis and therefore the quality status assessment of the coralligenous habitats. The advantage and efficiency of different approaches and methods, and whether they should be applied and standardised for further monitoring activities, were discussed.
... They can develop on hard and soft seafloor substrates. Due to their nature these reefs area easily recognizable on the sonographs by localized strong backscatter facies (Georgiadis et al., 2009) (Fig. 14). On the seismic profiles they are presented by a lowamplitude reflector on the top which it might include hyperbolic and single domeshaped almost acoustically transparent structures due the cavernous internal structure of the reefs (Fig. 14). ...
In the present paper we present the marine remote surveying conducted aiming to investigate an ancient shipwreck offshore Kefalonia island, in Ionian Sea, Greece. Within the framework of the survey efforts were given to examine the site formation of the wreck and to define the best practices for the detection and mapping of similar potential archaeological targets located on the shelf zone, where the geological and biological regime of the seafloor complicates the detection.
... In order to fill this gap, fine-scale mapping efforts are multiplying in Europe especially in France [13][14][15], Spain [16][17][18], Italy [12,[19][20][21] or Greece [22,23] or along the Baltic sea [24]. Because of the high costs to acquire such data, these fine-scale maps are generally funded in order to respond to specific and local objectives (the study of protected areas, a specific habitat [25] or particular features [26], environmental impact assessment [27]). ...
Ecosystem services provided by oceans and seas support most human needs but are threatened by human activities. Despite existing maps illustrating human impacts on marine ecosystems, information remains either large-scale but rough and insufficient for stakeholders (1 km² grid, lack of data along the coast) or fine-scale but fragmentary and heterogeneous in methodology. The objectives of this study are to map and quantify the main pressures exerted on near-coast marine ecosystems, at a large spatial scale though in fine and relevant resolution for managers (one pixel = 20 x 20 m). It focuses on the French Mediterranean coast (1,700 km of coastline including Corsica) at a depth of 0 to 80 m. After completing and homogenizing data presently available under GIS on the bathymetry and anthropogenic pressures but also on the seabed nature and ecosystem vulnerability, we provide a fine modeling of the extent and impacts of 10 anthropogenic pressures on marine habitats. The considered pressures are man-made coastline, boat anchoring, aquaculture, urban effluents, industrial effluents, urbanization, agriculture, coastline erosion, coastal population and fishing. A 1:10 000 continuous habitat map is provided considering 11 habitat classes. The marine bottom is mostly covered by three habitats: infralittoral soft bottom, Posidonia oceanica meadows and circalittoral soft bottom. Around two thirds of the bottoms are found within medium and medium high cumulative impact categories. Seagrass meadows are the most impacted habitats. The most important pressures (in area and intensity) are urbanization, coastal population, coastal erosion and man-made coastline. We also identified areas in need of a special management interest. This work should contribute to prioritize environmental needs, as well as enhance the development of indicators for the assessment of the ecological status of coastal systems. It
... Μεταξύ των μεγα-ρυτιδώσεων και των ακτών της Άνδρου, σε βάθη ~70 m, εντοπίστηκε μια ζώνη με λοφοειδές μικροανάγλυφο που αποδόθηκε στην ύπαρξη βιογενών σχηματισμών (Εικ. 4), βάσει της παρόμοιας μορφής που έχουν με σχηματισμούς σε άλλες θέσεις των Κυκλάδων (Georgiadis et al., 2009). Οι βιογενείς σχηματισμοί δρουν ως «εμπόδιο» και συγκρατούν ιζήματα που κινούνται με τη δράση μικρής-μέσης έντασης ρευμάτων με συνέπεια τη διατήρηση/αύξηση του μεγέθους τους. ...
A geophysical survey and sediment sampling were conducted at Kafireas Strait (Cavo-Doro) to discover geomorphological evidence indicative of bottom current activity in the absence of current-meter measurements. The results revealed sand waves, megaripples and biogenic mounds in Andros shelf, ambiguous bedforms in Evia-Andros valley, extended anomalous rocky relief almost all over the surveyed zone and recent sediments of small thickness. The bottom current velocities responsible for the bedform generation might reach 100 cm/s.
... (Abella et al., 2005;Gouraguine et al., 2011;Tserpes et al., 2008)) and some localized efforts have also been made for mapping sensitive and essential fish habitats that are important for the management of fishery resources (e.g. (de Juan and Lleonart, 2010;Georgiadis et al., 2009;Peña and Barbara, 2008;Sciberras et al., 2009;Barberá et al., 2012;Ardizzone, 2006)). A large quantity of the existing scientific data, including results from marine biodiversity surveys, are very fragmented and scattered, and frequently they are available only on paper or in old electronic format. ...
... Furthermore, the interplay of bacterial and algal communities found in proximity to (e.g., in ambient seawater) and within rhodoliths (i.e., as endoliths) and their function for higher trophic levels in the northwestern Gulf of Mexico is currently unknown. Because crustose corallines are generally known to release chemosensory compounds that have been implicated in the larval settlement and morphogenesis of a range of invertebrates, especially reef-building corals (e.g., Hadfield and Paul 2001), mollusks (Roberts 2001), cnidarians, crustaceans, echinoderms (Riosmena-Rodríguez andMedina-Lopez 2011), sponges (Ávila and Riosmena-Rodríguez 2011), and gorgonians (Georgiadis et al. 2009), we hypothesize that corallinedominated rhodoliths in the northwestern Gulf of Mexico may likewise be implicated in controlling the dynamics of their microbionts as well (i.e., through cryptobiosis or seedbank dormancy during environmental stress). ...
The diversity of seaweeds and decapod crustaceans associated with rhodoliths on deep offshore banks in the northwestern Gulf
of Mexico decreased dramatically after the Macondo blowout. Decapod crustacean communities declined in both abundance and
diversity and exhibited major shifts in species dominance. Rhodoliths appear to serve as seedbanks for biological diversity
because dead rhodolith rubble became covered by epi- and endolithic algae and microbes in laboratory microcosms. Decreased
seaweed abundance in the field may relate to nutrient availability and microbial interactions. We hypothesize that declines
of deep bank decapods largely reflect the loss of seaweed cover, which may have led to cascading effects on direct consumers
and higher trophic levels. However, negative impacts of postspill increases in lipoclastic and chitinoclastic bacteria cannot
be ruled out as possible contributors to overall decapod declines, although the evidence implicating these factors was limited
only to decapod samples from nearby deeper soft substrates.
... The acquisition software of 4100 P topside recording unit applied the geocoding of SSS digital records, using navigation and vessel speed data supplied from the GPS system model MAGELAN NAV 6500. The 100 kHz signal was considered as an effective frequency for the selection of a wide spectrum of acoustic faces indicative of a variety of seafloor texture, bed forms and particularly biological formations (Georgiadis et al. 2009). ...
Temporal and spatial variations of environmental and water quality parameters and their relations with macrobenthic flora were investigated in an eastern Mediterranean lagoon. Kaiafas is a mesohaline lagoon, which is influenced by point and diffused sources from the adjacent agricultural land and the nearby city. Water samples were analyzed for physicochemical parameters, microbial load and primary production, on a seasonal and spatial scale, while heavy metal concentrations were measured into two different sediment cores. An overall analysis of seasonal dynamics of water parameters and Chl-a based on trophic index TSI pointed out the lagoon as eutrophic. According to water quality parameters the lagoon was separated into two parts. The southern sector of the lagoon which was more affected by human activities showed higher nutrients, Chl-a, heavy metals and total Coliforms concentrations. Sediment texture and distribution of macrophytes were detected through the acoustic side scan sonar method, which proved to be a promising tool for defining and monitoring vegetation coverage of shallow lagoons. A number of distinct echo types and three different sediment types were revealed on the basis of the backscatter level and the variability of low and high backscatter areas. Furthermore, the extension and the coverage of Potamogeton pectinatus and Chara hispida f. corfuensis were successively depicted by combining the data of SSS and ground truthing samples. Meadows of P. pectinatus were established to the lagoon limits where high turbidity and silty substrate occurred, while C. hispida f. corfuensis was limited in deep and high transparent waters with sandy substrate.
... Extensive aggregations of coralligene formations with similar acoustic characteristics have been detected elsewhere in the Aegean Sea (Georgiadis et al., 2009). ...
The present study presents the results of the preliminary marine geophysical survey conducted in 2006 at the gulf of Sounion, southern Attica, Greece. The site is of great archaeological importance since cape Sounion served as a navigational landmark and a naval fortress protecting the sea-lanes towards the metropolis of Athens and the silver mines of Lavreotiki during the Classical and Hellenistic periods. Parts of the coastal ancient installations are now submerged. The results of the collected geophysical data include the examination of the seafloor texture and stratigraphy. Therefore a geomorphological map of the gulf was constructed based on the configuration of the substrate and the seafloor stratigraphy. Archaeological remains lying on the seafloor have been detected on the sonographs and have been correlated with the results of previous studies. The development and the evolution of the gulf during the prehistoric period were evaluated via the sea floor stratigraphy and the prediction of sea level change in the area based on the eustatic and glacio-hydro-isostatic response. The sea level change during the historic period was examined and a relative sea level rise of at least 2,5-3,0 m was suggested for the last 2500 years based on the marine geophysical survey results.
... Relatively high damage to organisms or alteration of the fishing ground (e.g. see effects of trawling in the vicinity of coralligenous formations in Georgiadis et al., 2009) could have direct effects on the biological community and the fisheries resources. B10-Certainty: The type of study that provided the relevant data was used as an indication of certainty. ...
The present work presents an integrated comparative assessment of the sustainability of fishing tactics or metiers (combinations of area, season, fishing gear, and target species). An index, which includes biological, conservation, socioeconomic, and management criteria, was created for this purpose: the “Metier Sustainability Index” (MSI25). It was designed using the traffic lights approach and comprises 25 indicators that refer to the “health” of the fisheries. Additionally, the MSI25 provides an indication of the “certainty”
of that information with regard to the data type/heterogeneity. Subsequently, the index was tested using data from six case studies (81 metiers) from the Mediterranean and the Atlantic. The index showed that 63.0% of the metiers were “sustainable”, 21.0% were “unsustainable” and 16.0% were “under pressure”; 59.3% of characterizations were considered as “certain”. The index evaluation showed significant differences between areas and gears. This paper considers the characteristics of the datasets used, the case
management status, and the applicability of the index in improving the management of specific fisheries. Overall, the MSI25 was found to be a useful tool for the evaluation and management of highly heterogeneous fisheries and data from various sources and types.
... A barrier to development of management plans in coralligenous habitats is that their distribution remains poorly characterised because they have not been mapped with sufficient accuracy and with spatial resolutions high enough to support their efficient management and conservation [23][24][25]. Even if we have an overall knowledge about the composition of the Mediterranean coralligenous assemblages [1,24,26], the absence of cartographical data and associated species on the overall distribution of these assemblages is one of the greatest lacunae from the conservation point of view [23,27]. Most of the cartographic information is based on surveys carried out in the north-western Mediterranean Sea [e.g. ...
Coralligenous habitats are of special interest in the Mediterranean Sea because they
represent one of the most important biodiversity ‘hot-spots’ and are considered of
great relevance for fisheries activities in the region. Despite their importance,
however, there are missing consensual methodologies for their monitoring and,
despite some attempts, no environmental or ecological quality indices have been
established yet. This situation could be related to the difficulties associated with their
exploration and their spatial heterogeneity. These habitats are in urgent need
of efficient standard monitoring and management protocols programmes to develop an
effective network for their conservation. Here we reviewed the available
methodologies and robotics tools used to evaluate and monitor benthic habitats,
highlighting the importance of defining rapid cost-effective sampling and analyses
approaches and architectures for future monitoring of changes in coralligenous
habitats based on current technological developments. We identified still images
acquisitions as the most effective data gathering system. Stereo photogrammetry,
photomosaic elaboration and three-dimensional (3D) modelling may largely improve
the data analysis and therefore the quality status assessment of the coralligenous
habitats. The advantage and efficiency of different approaches and methods, and
whether they should be applied and standardised for further monitoring activities,
were discussed.
... The acquisition software of 4100 P topside recording unit applied the geocoding of SSS digital records, using navigation and vessel speed data supplied from the GPS system model MAGELAN NAV 6500. The 100 kHz signal was considered as an effective frequency for the selection of a wide spectrum of acoustic faces indicative of a variety of seafloor texture, bed forms and particularly biological formations (Georgiadis et al. 2009). In the Kaiafas lagoon survey, high backscatter was represented by light tones and low backscatter by dark tones, on the sonographs. ...
Temporal and spatial variations of environ-mental and water quality parameters and their relations with macrobenthic flora were investigated in an eastern Mediterranean lagoon. Kaiafas is a mesohaline lagoon, which is influenced by point and diffused sources from the adjacent agricultural land and the nearby city. Water samples were analyzed for physicochemical parameters, microbial load and primary production, on a seasonal and spatial scale, while heavy metal concentrations were measured into two different sediment cores. An overall analysis of seasonal dynamics of water parameters and Chl-a based on trophic index TSI pointed out the lagoon as eutrophic. According to water quality parameters the lagoon was separated into two parts. The southern sector of the lagoon which was more affected by human activities showed higher nutrients, Chl-a, heavy metals and total Coliforms concentrations. Sediment texture and distribu-tion of macrophytes were detected through the acoustic side scan sonar method, which proved to be a promising tool for defining and monitoring vegetation coverage of shallow lagoons. A number of distinct echo types and three different sediment types were revealed on the basis of the backscatter level and the variability of low and high backscatter areas. Furthermore, the extension and the coverage of Potamogeton pectinatus and Chara hispida f. corfuensis were successively depicted by combining the data of SSS and ground truthing samples. Meadows of P. pectinatus were established to the lagoon limits where high turbidity and silty substrate occurred, while C. hispida f. corfuensis was limited in deep and high transparent waters with sandy substrate.
... (Abella et al., 2005;Gouraguine et al., 2011;Tserpes et al., 2008)) and some localized efforts have also been made for mapping sensitive and essential fish habitats that are important for the management of fishery resources (e.g. (de Juan and Lleonart, 2010;Georgiadis et al., 2009;Peña and Barbara, 2008;Sciberras et al., 2009;Barberá et al., 2012;Ardizzone, 2006)). A large quantity of the existing scientific data, including results from marine biodiversity surveys, are very fragmented and scattered, and frequently they are available only on paper or in old electronic format. ...
... The graph of the cumulative number of species did not show a tendency to stabilise in an asymptotic curve and highlights the heterogeneity of habitat distribution in Menorca Channel (Clarke and Warwick 2001; Gray 2002). There is little information in this article on the deep coralligenous habitats in the Mediterranean, which are considered to be amongst the most diverse (Batala et al. 2005; Ballesteros 2006; Georgiadis et al. 2009), and no data on other components of the benthos, such as the supra-and infauna, in the area. However, our results confirm the assumption that although soft-sediments are not generally considered highly structured, some habitats within these bottoms, such as maërl beds, can support high biodiversity (Birkett et al. 1998; Foster 2001; BIOMAE¨RLBIOMAE¨BIOMAE¨RL Team 1999; Bordehore et al. 2003). ...
Menorca Channel (Balearic Islands, western Mediterranean) comprises 98,700 Ha of continental shelf. It has been proposed to include this area in the Natura 2000 network due to the wide range of species and habitats of high conservation value found here, such as Posidonia oceanica meadows and maA << rl and coralligenous beds. This study aimed to establish a scientific basis for managing and protecting the continental shelf bottoms in Menorca Channel. Sampling was carried out with side-scan sonar, beam trawls, box corers, a remote-operated vehicle and an underwater drop camera. The information collected was used to map the habitat distribution between 50 and 100 m depth, as well as make an inventory and describe the spatial patterns of both the specific and functional diversity. A total of 636 species was recorded in a mosaic of habitats in which Corallinacea calcareous algae and other soft red algae (Osmundaria volubilis and Peyssonnelia spp.) were the most abundant groups. Hotspots of specific and functional diversity were located in areas with high habitat heterogeneity and complexity. Protection of Menorca Channel should not only include the habitats and species in the European directives, but also the habitats that are not currently protected, such as O. volubilis and Peyssonnelia beds, due to their biogeographical and ecological interest and their contribution to the biodiversity of shelf bottoms in the Mediterranean Sea
... Although rapid on a geological time-scale, these accumulation rates are far too low for the maerl to be regarded as a sustainable resource for extraction for agricultural and industrial use. In a recent study by Georgiadis et al. (2009) undertaken in the Aegean Sea (Eastern Mediterranean), coralligène formations were recorded at water depths ranging from 60 m to 114.0 m, with 81% of the total surface being restricted to water depths between 70 m and 90 m. Within 50 m -120 m depth range, maerl habitats occupied 4.3% of the seabed area. ...
... Maerl beds have a low growth rate, approximately 0.1-1 mm per year, and these production and accumulation rates are similar to the lower end of such rates from tropical coral reef environments (Bosence and Wilson, 2003). In a recent study in the Aegean Sea of the E. Mediterranean (Georgiadis et al. 2009), coralline formations were recorded at depths ranging from 60 to 114.0 m, with 81% of the formations restricted to depths from 70 to 90 m. In the depth range of 50-120m, maerl habitats occupied 4.3% of the seabed surface. ...
Aquaculture has increased substantially in the Mediterranean during the past 30 years and has become an important industry for rural and island communities. However, this rapid expansion of the industry has not been without environmental impact at various spatial and temporal scales. The most widely studied impacts are those on macrofaunal benthic communities, but recent research projects have also addressed the effects on nutrients and plankton, on seagrass meadows (particularly Posidonia oceanica) and wild fish assemblages. Due to its role in the global food production system and the expected increase of the global human population, it is very likely that aquaculture will further increase to a much larger scale than the present. Consequently, the associated environmental issues need to be considered by taking into account the potential changes in the marine environment.
Citation: Pérez-Peris, I.; Navarro-Mayoral, S.; de Esteban, M.C.; Tuya, F.; Peña, V.; Barbara, I.; Neves, P.; Ribeiro, C.; Abreu, A.; Grall, J.; et al. Effect of Depth across a Latitudinal Gradient in the Structure of Rhodolith Seabeds and Associated Biota across the Eastern Atlantic Ocean. Diversity 2023, 15, 103. Abstract: Rhodolith seabeds are 'ecosystem engineers' composed of free-living calcareous red macroalgae, which create extensive marine habitats. This study addressed how depth influenced the structure (size and morphology) of rhodoliths and the abundance of associated floral and faunal epibionts across the Eastern Atlantic Ocean. Sampling was carried out at two sites within five regions (Brittany, Galicia, Madeira, Gran Canaria, and Principe Island), from temperate to tropical, covering a latitudinal gradient of 47 • , in three depth strata (shallow, intermediate and deep), according to the rhodolith bathymetrical range in each region. Depth typically affected the rhodolith size at all regions; the largest nodules were found in the intermediate and deep strata, while rhodolith sphericity was larger at the shallow depth strata. Higher biomasses of attached macroalgae (epiphytes) were observed at depths where rhodoliths were larger. The abundance of epifauna was variable across regions and depth strata. In general, the occurrence, structure, and abundance of the associated biota across rhodolith habitats were affected by depth, with local variability (i.e., sites within regions) often displaying a more significant influence than the regional (large-scale) variation. Overall, this study showed that the rhodolith morphology and associated epibionts (flora and fauna) were mostly affected by depth, irrespective of latitude.
Rhodoliths (nodular calcareous red algae) are considered one of the most important bioengineers in the Mediterranean Sea, making rhodolith beds ecologically relevant ecosystems. On the insular shelf surrounding the western Pontine Archipelago (depth from 43 to 112 m), rhodolith beds were identified through the analysis of an extensive dataset of grab samples and videos to ground-truth the backscatter acoustic facies. Six acoustic facies (low backscatter, dishomogeneous low-backscatter, dishomogeneous high-backscatter, high-backscatter, rocks and high backscatter, and rocks and medium backscatter) were recognized. We studied how rhodoliths characteristics (density, morphotype, size and structure) differently influence the backscatter signature. At the western Pontine Archipelago, rhodolith beds are mainly represented by facies dishomogeneous high backscatter, high backscatter, high backscatter with rocks, and medium backscatter with rocks. The obtained results increase both the knowledge on the heterogeneous structure of such ecologically relevant benthic habitat and highlight the use of distinctive acoustic facies for their identification. Finally, the used approach could be considered a useful method for indirect detection and mapping of rhodolith beds.
Coralligenous has a relevant role in submarine landscape formation and demise through geological times, producing various morphotypes on the seafloor. Several terms are used to define coralligenous morphotypes, but their application through different geological and environmental settings still remains inconsistent. Through a systematic analysis of seafloor acoustic remote data (multibeam, side scan sonar and subbottom profiler) along Apulia continental shelf, ground-truthed by video observations and direct sampling, we detected a number of coralligenous morpho-acoustic facies as 0.2 up to 4 m topographic reliefs with steep flanks and a rigid inhomogeneous biogenic framework, characterized by medium to strong SSS backscatter and a variable plan-view geometry. The observed pattern led to the identification of coralligenous meso- and macrohabitat in which the biogenic frameworks (i.e. coralligenous) prevail as sole biocommunity on the seafloor or are associated with other type of habitats: (i) coralligenous sensu stricto, (ii) coralligenous and detritic bottom, (iii) coralligenous and muddy bottom, (iv) coralligenous and Posidonia meadow. Finally we improve the geomorphological definition of bank, proposing this new descriptive rigorous categorization for coralligenous morphotypes on sub-horizontal substrate: 1) tabular bank, 2) discrete relief, and 3) hybrid bank.
The available references to rhodolith beds have been analyzed for a total of 125 locations in the Mediterranean Sea, equally distributed in the eastern and western sub-basins. Mediterranean rhodolith beds occur from 9 to 150 m of water depth, with a mean depth of about 55 m in both sub-basins. Most rhodolith beds lay within the depth range 30–75 m, while those extending deeper than 75 m are about 18 % of the total, and those shallower than about 25 m are uncommon. The deepest and the largest Mediterranean rhodolith beds are both located in the Balearic Sea. Water motion from bottom currents, waves, and tides is needed to keep rhodoliths unburied, within mesotrophic to oligotrophic water conditions. Rhodolith beds are commonly small (<0.01 km2) and multispecific, showing growth-form mixing and a much higher coralline biodiversity than Atlantic beds. They are vulnerable to physical disturbance by fishing gears and smothering, and to water pollution by organic enrichment and sewage. The existing instruments of legal protection appear ill defined, since these are based on scientific literature mostly derived from northern Europe, where specific and different environmental settings, species composition, depth distribution, and anthropogenic pressures occur. The protection of a specific habitat type cannot be effectively gained without access to geospatial and compositional data and an increased research effort is needed to improve taxonomic inventories, habitat mapping, and monitoring activities on a basin scale.
The Hellenic shelf lies within and around the Aegean microplate, which is one of the world's most seismically active areas, and has experienced extreme tectonism throughout Quaternary time. This activity, together with eustatic sea-level changes and watercirculation patterns over the same time period, controls the overall configuration of the Hellenic shelf, the rates of uplift and subsidence, and determines the sediment supply and depot centre, as well as the sediment-transfer processes. The above-mentioned geological processes are the causative factors for the frequent occurrence of a variety of geological hazards, such as active faults, submarine gravitational mass movements, tsunami and active gas seeping from the seabed.
The Menorca channel (Balearic Islands, NW Mediterranean Sea) is one of the high priority areas to be included as MPA in the EU nature 2000 Network, being studied by the LIFE+ INDEMARES Project. Recent studies provide information on the shallow littoral habitats and the shelf on this area (Ballesteros 1994; 2006; Canals and Ballesteros 1997; Massutí and Reñones 2005; Coma et al. 2006; Cardona et al. 2007; Deudero et al 2008; Ordines y Massutí 2009). However, to make an effective application of conservation measueres, it is necessary to obtain maps and information on the areal distribution of these communities. Barberá et al. (2012) made the first biogenic habitat mapping on the Menorca channel, including coralligène formations and maërl beds, basing their cartography on biological sampling and, locally, side scan sonar data. Coralline algae are one of the most important constructors of biogenic habitats in the Mediterranean. Coralligène formations can appear on rocky outcrops, ranging from a thin film to extensive formations (Bosence, 1985; Georgiadis et al., 2009). Over flat seabed, the coraligène may form minute reefs 0.5-4 m high (Laborel, 1987; Georgiadis et al., 2009), but also surface films associated to rodoliths and maërl beds that have been found at depths up to 160 m (Peres, 1967; Bosence, 1985; Laborel, 1987). Reports about the acoustic characterization of these formations are scarce, especially in the Mediterranean Sea (Georgiadis et al., 2009). In this work, we use an integrated geophysical dataset and seafloor groundtruthing, in addition to biological sampling, with the aim to describe the main geomorphologic and acoustic characteristics of coralline algae communities.
In the northwestern Gulf of Mexico, beds of rhodoliths and unconsolidated rubble at 55-70 m depth are associated with unique offshore deep bank habitats known as salt domes or diapirs. Prior to the 2010 BP Deepwater Horizon oil spill these harbored the highest known seaweed diversity in the northern Gulf of Mexico. Six post-spill cruises led offshore Louisiana to two sites previously documented with rich algal assemblages (i.e. pre-spill) revealed a dramatic post-spill die-off of seaweeds at both sites, with dredged rhodoliths appearing bleached and mostly denuded of fleshy algae, or "bare" (with a few crustose genera only, e.g. Corallinales and Peyssonneliales). This rubble, brought to the laboratory and maintained in a series of ~75 liter microcosm tanks, gradually became covered by a suite of red, green and brown seaweed germlings that to this day continue to grow to adult size, reproduce, disappear and re-emerge, and whose species composition reflects pre-spill assemblages. These experiments revealed the expression of biodiversity from alternative life stages or resting stages apparently repressed in the Gulf at the time of sampling, including new, previously overlooked diversity. The rate of algal succession was documented by biweekly photography, and species taxonomic identity is being confirmed by ongoing molecular and morphological evidence. The implications of these exciting results, namely that undetected propagules, spores and endolithic filaments collected along with the "bare" substrata and in situ seawater have been triggered to germinate, grow, and reproduce under laboratory conditions are far-reaching. We hypothesize the function of rhodoliths and rubble as marine seedbanks for biological diversity and explore the role of this ecosystem for community resilience following a major anthropogenic disaster. This is a speculative paper since we currently lack many rigorous, quantitative data. The paper is envisioned as a "first step" in approaching the dynamics of rhodoliths and associated diversity following a catastrophic anthropogenic event, from which the algal and invertebrate diversity has not recovered, as of October 2013, our last collecting expedition to Ewing Bank in the NW Gulf of Mexico.
Abstract
1.
Maerl beds occur worldwide and are formed by an accumulation of unattached calcareous red algae (Rhodophyta).
2.
Maerl‐forming algae grow in a superficial living layer on sediments within the photic zone.
3.
Maerl beds are spatially complex habitats with a high degree of species and trophic group diversity.
4.
The European Commission's ‘Habitats Directive’ mandates the conservation management of two of the main European maerl‐forming species, Phymatolithon calcareum and Lithothamnion corallioides.
5.
Mediterranean maerl beds are to be considered for inclusion in national inventories of sites of conservation interest, as required by the SPABIM Protocol of the Barcelona Convention.
6.
In spite of their importance, and the requirement for their conservation management, European maerl grounds suffer a variety of anthropogenic perturbations including direct exploitation through extraction, fishing impacts and chemical pollution by organic matter and excess nutrients.
7.
The ecology of northeast Atlantic and Mediterranean maerl beds has received little attention, in contrast to other marine communities (e.g. kelp forests, sea‐grass meadows).
8.
Key conservation and management measures proposed include: the recognition that maerl beds are non‐renewable resources and cannot sustain direct exploitation; prohibitions on the use of towed gear on maerl grounds; moratoria on the issue of further permits for the siting of aquaculture units above maerl grounds; monitoring of existing exploited or impacted maerl beds; the designation of ‘no‐take’ reserves; measures to limit the impacts that might affect water quality above maerl beds; a programme of monitoring of the ‘health’ of European maerl beds; an awareness campaign on the biological importance of maerl beds; a higher conservation status for maerl habitats and maerl‐forming species in European legislation; and further research on maerl ecosystems.
Seabed fluid flow involves the flow of gases and liquids through the seabed. Such fluids have been found to leak through the seabed into the marine environment in seas and oceans around the world - from the coasts to deep ocean trenches. This geological phenomenon has widespread implications for the sub-seabed, seabed, and marine environments. Seabed fluid flow affects seabed morphology, mineralization, and benthic ecology. Natural fluid emissions also have a significant impact on the composition of the oceans and atmosphere; and gas hydrates and hydrothermal minerals are potential future resources. This book describes seabed fluid flow features and processes, and demonstrates their importance to human activities and natural environments. It is targeted at research scientists and professionals with interests in the marine environment. Colour versions of many of the illustrations, and additional material - most notably feature location maps - can be found at www.cambridge.org/9780521819503.
Deep-water coral reefs are found along large sections of the outer continental shelves and slopes of Europe, from North Cape to the Gulf of Cadiz, and because they also occur along the Atlantic seaboard of USA, the Gulf of Mexico, off Brazil, in the Mediterranean, and off New Zealand, they are currently being targeted by international groups of marine scientists. They have become popular and opportune deep-water research targets because they offer exciting frontier exploration, combined with a whole plethora of modern scientific methods, such as deep-sea drilling, sampling, remote control surveying and documentation. Furthermore they represent timely opportunities for further developments within the application of geochemistry, stable isotope research, bacterial sciences, including DNA-sequestering, and medical research (search for bioactive compounds).
The Integrated Ocean Drilling Program (IODP) has arranged a deep-sea scientific drilling campaign on giant carbonate banks off Ireland. Because the reefs currently defy traditional marine-ecological theories, they represent future research opportunities and will enjoy scientific scrutiny for many years to come.
Ecosystem engineers are organisms that directly or indirectly modulate the availability of resources to other species, by causing physical state changes in biotic or abiotic materials. In so doing they modify, maintain and create habitats. Autogenic engineers (e.g. corals, or trees) change the environment via their own physical structures (i.e. their living and dead tissues). Allogenic engineers (e.g. woodpeckers, beavers) change the environment by transforming living or non-living materials from one physical state to another, via mechanical or other means. The direct provision of resources to other species, in the form of living or dead tissues is not engineering. Organisms act as engineers when they modulate the supply of a resource or resources other than themselves. We recognise and define five types of engineering and provide examples. Humans are allogenic engineers par excellence, and also mimic the behaviour of autogenic engineers, for example by constructing glasshouses. We explore related concepts including the notions of extended phenotypes and keystone species. Some (but not all) products of ecosystem engineering are extended phenotypes. Many (perhaps most) impacts of keystone species include not only trophic effects, but also engineers and engineering. Engineers differ in their impacts. The biggest effects are attributable to species with large per capita impacts, living at high densities, over large areas for a long time, giving rise to structures that persist for millennia and that modulate many resource flows (e.g. mima mounds created by fossorial rodents). The ephemeral nests constructed by small, passerine birds lie at the opposite end of this continuum. We provide a tentative research agenda for an exploration of the phenomenon of organisms as ecosystem engineers, and suggest that all habitats on earth support, and are influenced by, ecosystem engineers.
A 200-km2 area in the Bay of Concarneau on the South Brittany coast was surveyed acoustically using different sidescan sonars (a 100-kHz
EdgeTech DF1000, and a 240-kHz Reson SeaBat 8101). The area corresponds to a sector of the REBENT network. It was selected
for its physical and biological characteristics, reflecting the sedimentary heterogeneity and biological diversity of Brittany's
coastal seafloors. The work presented here illustrates the methodology for mapping subtidal seabed habitats in the context
of the network. Backscatter mosaics were produced covering 100% of the survey area. Extensive ground-truthing was carried
out involving 93 Shipek grab samples and 25 drop-down video profiles. From interpretation of the acoustic facies, 40 biological
soft-bottom stations were sampled using a Hamon grab to characterize macrobenthic communities (>2 mm). The results indicated
considerable variation in backscatter responses in relation to high densities of macrobenthic species (Lithothamnion, Asterias, Haploops, Maldane, Ophiocomina), and a wide variety of substratum types present within a relatively small area. Dense biocenoses of maerl were accurately
surveyed from 20-m to <5-m depth (Lower Astronomical Tide; LAT). Boundaries of Haploops communities are associated with dense small pockmarks in the centre of the bay. The relationships between sediment sometimes
colonized by macrobenthic species and backscatter responses are discussed.
A Symposium entitled "Classification of Large-Scale Flow-Transverse Bedforms" was convened at the 1987 Mid-Year Meeting of SEPM in Austin, Texas with the purpose of examining the problems involved in classifying large subaqueous flow-transverse bedforms developed in fluvial, intertidal, and marine environments, and recommending changes in nomenclature. The consensus of the participants is that despite the wide spectrum of morphologies of large-scale flow-transverse bedforms (excluding antidunes), they all occupy a similar position in the lower-flow-regime sequence between ripples and upper plane bed. The wide variety of forms is a reflection of secondary effects such as channelization, fluctuating water levels, and unsteady and reversing flows. The bedforms appear not to fall into size classes with naturally occurring boundaries but rather form a continuum with spacing from just under 1 m to over 1,000 m. The symposium panel proposes, therefore, that they should have only one name, DUNE. Dune is preferred as it has historical precedence over other terms in use, such as megaripple and sand wave. The term "dune" should be modified by primary descriptors of shape (i.e., 2-D or 3-D) and size based on spacing (small (0.6-5 m), medium (5-10 m), large (10-100 m) or very large (> 100 m) and the adjective subaqueous when it is important to distinguish them from eolian dunes. The panel recommends a morphologically based classification that is descriptive, with an underlying genetic rationale. Second order descriptors such a sediment size and bedform superposition may be used to describe more thoroughly the variety of subaqueous dunes in nature.
1.A comparative study of the characteristics of sediment structure and associated assemblages was conducted in two areas with different trawling histories, one with low trawling pressure and protected since 1989 (Marine Reserve of Tabarca), and another with a high frequency of trawling (Benidorm).2.The study was based on seasonal quantitative and qualitative sampling of macrofauna, megafauna and algae, over a period of 1 year, using scuba diving and dredging.3.Sediment composition differed between sites. Overall Tabarca had a coarser sediment than Benidorm where there was a higher mud content and no vertical stratification. At Tabarca there was a differential vertical profile, with a higher percentage of coarse sediment in the surficial horizon, which corresponded mostly to rhodoliths. Benidorm had more mineral gravel, and Tabarca a higher percentage of biogenic gravel.4.There were no differences between sites in the percentages of live and dead rhodoliths in the sediment. Cover of rhodoliths, however, was four times greater at Tabarca. Maximum size of rhodoliths was greater at Tabarca ( mean 16.18 mm S.D. 5.73) than at Benidorm (mean 7.64 mm S.D. 2.16).5.The number of species of algae did not differ significantly between sites: 155 species were found at Tabarca, and 153 at Benidorm, with 13 and 10 exclusive species respectively. Although both algal assemblages were qualitatively similar, there were significant differences in the cover of the main species. At Tabarca, the cover of Corallinales was around 50% of total algal cover, while at Benidorm approximately 90% of the cover was due to non-Corallinales algae, mainly species from the genus Peysonnelia.6.The number of macrofaunal species at Tabarca was greater than at Benidorm, with 293 (144 exclusive spp.) and 204 (53 exclusive spp.) species, respectively. Density and biomass of macrofauna was also greater at Tabarca.7.Based on our observations, well preserved Mediterranean maerl grounds are sites with a high diversity and also support a high macrobenthic secondary production which may be important for species of commercial interest. High trawling pressure on maerl areas may affect assemblages negatively by breaking up rhodoliths, diminishing their cover and hence affecting the associated biota. Copyright © 2003 John Wiley & Sons, Ltd.
Hundreds of large coral reefs up to 45 m high exist (A) on the continental shelf and (B) on morainic threshold ridges in fjords of northern, mid-, and southwest Norway. They occur in water depths between 400 and 40 m, and contain a large variety of megafauna. The most common frame-building coral is Lophelia pertusa (L.). The oldest reef found to date is 8600 calendar years old, determined by radiocarbon dating of buried Lophelia skeleton. Even though many of these reefs have been known to science for over 200 years, there is as yet no viable and unifying hypothesis to explain their existence in deep, cool waters, other than perhaps the ‘hydraulic theory’, presented by the author in 1990. It states that primary producers (mainly bacteria) are locally formed and concentrated at reef locations due to seepage of light hydrocarbons (mainly methane) on the continental shelf, and nutrient-rich groundwater in the fjords. The hydraulic theory is supported by the following topographic, reflection seismic, and geochemical indicators; for the continental shelf reefs (A): seaward-dipping sedimentary permeable strata, enhanced acoustic seismic reflectors, adjacent pockmark craters, locally elevated light hydrocarbon sediment content, locally elevated seawater methane content; for the fjord reefs (B): threshold morainic substratum rather than adjacent hardrock substratum, sub-surface dipping sedimentary layers, H2S smell of near-surface sediment samples. These indicators, or reef-associated observations, have been documented by German, British, and Norwegian researchers over the last 10–15 years. However, all the listed indicators do not necessarily occur at each of the respective shelf and fjord reef locations simultaneously.
1.Maerl beds occur worldwide and are formed by an accumulation of unattached calcareous red algae (Rhodophyta).2.Maerl-forming algae grow in a superficial living layer on sediments within the photic zone.3.Maerl beds are spatially complex habitats with a high degree of species and trophic group diversity.4.The European Commission's ‘Habitats Directive’ mandates the conservation management of two of the main European maerl-forming species, Phymatolithon calcareum and Lithothamnion corallioides.5.Mediterranean maerl beds are to be considered for inclusion in national inventories of sites of conservation interest, as required by the SPABIM Protocol of the Barcelona Convention.6.In spite of their importance, and the requirement for their conservation management, European maerl grounds suffer a variety of anthropogenic perturbations including direct exploitation through extraction, fishing impacts and chemical pollution by organic matter and excess nutrients.7.The ecology of northeast Atlantic and Mediterranean maerl beds has received little attention, in contrast to other marine communities (e.g. kelp forests, sea-grass meadows).8.Key conservation and management measures proposed include: the recognition that maerl beds are non-renewable resources and cannot sustain direct exploitation; prohibitions on the use of towed gear on maerl grounds; moratoria on the issue of further permits for the siting of aquaculture units above maerl grounds; monitoring of existing exploited or impacted maerl beds; the designation of ‘no-take’ reserves; measures to limit the impacts that might affect water quality above maerl beds; a programme of monitoring of the ‘health’ of European maerl beds; an awareness campaign on the biological importance of maerl beds; a higher conservation status for maerl habitats and maerl-forming species in European legislation; and further research on maerl ecosystems. Copyright © 2003 John Wiley & Sons, Ltd.
The surface sediments of the Kafireas Strait and Petalion Gulf, the area between the islands of Evvoia, Andros, Gyaros and Kea in the Aegean Sea, were examined for grain size, mineralogical composition and geotechnical properties. Contents of sand, silt, clay and carbonates as well as porosity, absolute and relative water contents, grain density and bulk mineralogy were determined in samples collected at 35 localities during two oceanographic cruises in April 1986 and July 1991. In addition, current measurements were carried out at three localities in the periods May-June 1988 and July 1991. Muddy sand and sand (52-96% sand) cover the continental shelf, whereas sandy mud (3-49% sand) predominates in deeper areas. Absolute water content varied between 22 and 42%, whereas the values for relative water content were 28-73%. Porosity showed a moderate range of values (36-62%), whereas grain density varied between 2.52 and 2.77 g/cm3. Carbonate content showed a wide range of values (30-72%). Mica and kaolinite are the dominant minerals (average contents 32 and 16.6%, respectively), and quartz, plagioclase, calcite and aragonite showed lower contents of 12.9, 9.8, 13.5 and 9.6%, respectively. Higher mica, kaolinite, chlorite and plagioclase contents closer to Evvoia Island may be related to local mica-amphibolitic-chloritic schists and cipollin outcrops, whereas higher percentages of mica, calcite and aragonite probably relate to the mica schists and marbles of Andros Island. Strong currents were recorded near the seabed in the vicinity of the Kafireas Strait (24 and 38 cm/s maximum velocity on the continental shelf off Evvoia and Andros islands, respectively). The regional geomorphology and bathymetry, the texture and mineralogical composition of terrigenous material, and the particular meteorological and hydrodynamic conditions in the area are the main factors which control the texture, mineralogy and distribution of seabed sediments in the vicinity of the Kafireas Strait.
In Scotland, Atlantic salmon Salmo salar cages are being moved out of areas with slow water movements, to disperse wastes and reduce impacts on benthic communities. This first study of the effects of fish farms on maerl beds (red algal coralline gravels of high conservation importance) demonstrated major impacts on the benthos, even in strongly tidal areas. SCUBA surveys of 3 fish farms located over maerl revealed a build-up of waste organic matter and 10 to 100-fold higher abundances of scavenging fauna (e.g. Necora puber, Pagurus bernhardus) than on 6 reference maerl beds. Visible waste was noted up to 100 m from cage edges, and all 3 farms caused significant reductions in live maerl cover, upon which this habitat depends. Near-cage infaunal samples showed significant reductions in biodiversity, with small Crustacea (ostracods, isopods, tanaids and cumaceans) being particularly impoverished in the vicinity of cages, and significant increases in the abundance of species tolerant of organic enrichment (e.g. Capitella spp. complex, Ophryotrocha hartmanni). Relocation of fish farms to areas with strong currents is unlikely to prevent detrimental effects to the structure and organisation of the benthos, and `fallowing' (whereby sites are left unstocked for a period of time to allow benthic recovery) is inadvisable where slow-growing biogenic habitats such as maerl are concerned, as this may expand the area impacted.
Overfishing is a major environmental problem in the oceans. In addition to the direct loss of the exploited species, the very act of fishing, particularly with mobile bottom gear, destroys habitat and ultimately results in the loss of biodiversity. Furthermore, overfishing can create trophic cascades in marine communities that cause similar declines in species richness. These effects are compounded by indirect effects on habitat that occur through removal of ecological or ecosystem engineers. Mass removal of species that restructure the architecture of habitat and thus increase its complexity or influence the biogeochemistry of sediments could have devastating effects on local biodiversity and important water–sediment processes. The possible overexploitation of engineering species requires more attention because the consequences extend beyond their own decline to affect the rest of the ecosystem. This is particularly problematic in the deep ocean, where oil and gas exploration and fishing pressure are likely to increase.
In maerl beds, architectural complexity is a physical factor which can explain the high specific diversity, and these habitats are moreover characterized by a high functional diversity. The physical structure of this habitat consists in providing refuges for a lot of predators and biotic interactions founded on predation, disturbance, competition... prevent any ressources monopolisation by only a few dominating species. Comparison of macrobenthic structures on homogeneous muddy bottoms and maerl beds in the Bay of Brest gives a first explanation to this high diversity. A second comparison between Control and Impacted maerl beds stations (eutrophication in the northern basin of the Bay of Brest, turbidity by direct exploitation of coralline algae in Glenan) suggests the existing links between specific and functional diversities.
The East and West Flower Garden Banks are located on the outer continental shelf in the northwestern Gulf of Mexico, approximately 190 km south-southeast of Galveston, Texas, at 27°55′N, 93°36′W and 27°52′N, 93°49′W, respectively (Fig. 1). These bathymetric highs are surface expressions of salt domes, with the seafloor elevated to approximately 20 m of the surface by the upward movement of the Jurassic Louann Salt. These two banks are similar in origin and each is presently capped by living coral reefs at its crest.
Middle Eocene sedimentation on the southeastern margin of the Catalan Basin (northeast Spain) is characterized by alluvial fan and deltaic sedimentation. Northwards these clastic sediments pass into a carbonate ramp, with nummulitid mounds in shallower areas. Coralgal reefs develop in an arcuate band on preexisting delta lobes. The small patch reefs are constructed by an intergrowth of corals (Caulastrea, Porites, Astreopora and Acropora) and coralline algae. The coralline algae overgrow the corals with up to 30 cm densely superposed crusts of Mesophyllum, Archaeolithothamnium and Lithoporella. Some crusts are built laterally around coral heads and others are eroded and redeposited. Abundant previous submarine cements are now present in the form of calcite micrite and spar botryoids. The association of corallines within the crusts is typical of relatively deep tropical waters, which contrasts with the shallow marine corals and surrounding fan delta and beach sediments. The coralline crusts are thought to represent a shallow shaded flora growing over and between corals, in relatively turbid waters. -Authors
Coralline algal buildups (coralligene) occur in the intertidal zone (trottoir) and at depths of 20-40 m (Coralligene de Plateau) off the rocky Albere coastline of southern France. The deep water examples from areas of small reefs with a relief of 1-4 m and diameters of 10 s of meters. The reefs are surrounded by basement rocks, locally derived carbonate gravels, rhodoliths, and terrigenous muds and sands. Reef frameworks are constructed by foliaceous crusts of the coralline algae Mesophyllum, Lithothamnium, Pseudolithophyllum, Neogoniolithon, and Tenarea. Lightly calcified Peyssonnelia and Halimeda also occur as epiphytes. Bioerosion by sponges, bivalves, polychaetes and algae is common. The many cavities are usually infilled with sediment. Patches of the reef interior are cemented by void-filling, blade-shaped crystals of aragonite. The recent reefs have many features in common with Miocene coralline limestones from Tethyan areas. They are considered to be the best known Recent analogs for these limestones. -Author
Interactions between organisms are a major determinant of the distribution and abundance of species. Ecology textbooks (e.g., Ricklefs 1984, Krebs 1985, Begon et al. 1990) summarise these important interactions as intra- and interspecific competition for abiotic and biotic resources, predation, parasitism and mutualism. Conspicuously lacking from the list of key processes in most text books is the role that many organisms play in the creation, modification and maintenance of habitats. These activities do not involve direct trophic interactions between species, but they are nevertheless important and common. The ecological literature is rich in examples of habitat modification by organisms, some of which have been extensively studied (e.g. Thayer 1979, Naiman et al. 1988).
Coralligenous concretions, the unique calcareous formations of biogenic origin in Mediterranean benthic environments, are produced by the accumulation of encrusting algae growing in dim light conditions. This review provides an overview of the results obtained by the main studies dealing with these formations, including the environmental factors which influence the development of coralligenous communities, their distribution, types, assemblages, builders and eroders, the biotic relationships and processes that create and destroy coralligenous assemblages, their dynamics and seasonality, and the functioning of several outstanding and key species. Special attention is devoted to the biodiversity of coralligenous communities and a first estimation of the number of species reported for this habitat is provided. Major disturbances affecting coralligenous communities are discussed, ranging from large-scale events that are probably related to global environmental changes to degradation by waste water or invasive species. Degradation by fishing activities and by divers is also considered. Finally, the main gaps in current scientific knowledge of coralligenous communities are listed and some recommendations are made regarding their protection. © R. N. Gibson, R. J. A. Atkinson, and J. D. M. Gordon, Editors Taylor & Francis.
A Symposium entitled "Classification of Large-Scale Flow-Transverse Bedforms' was convened at the 1987 Mid-Year Meeting of SEPM in Austin, Texas. The consensus of the participants is that despite the wide spectrum of morphologies of large-scale flow-transverse bedforms (excluding antidunes), they all occupy a similar position in the lower-flow-regime sequence between ripples and upper plane bed. The wide variety of forms is a reflection of secondary effects such as channelization, fluctuating water levels, and unsteady and reversing flows. The bedforms appear not to fall into size classes with naturally occurring boundaries but rather form a continuum with spacing from just under 1m to over 1000m. -from Author
The indirect effects of demersal fisheries, such as habitat degradation, are currently thought to be impacting gadoid stocks. Maerl fulfils nursery area prerequisites for several invertebrate species, so its role in similar ecosystem service provision for gadoids has been addressed. Juvenile cod (Gadus morhua), saithe (Pollachius virens), and pollack (Pollachius pollachius) in shallow (<7 m) inshore waters were surveyed with fykenets and scuba off western Scotland over a period of 12 months. Juvenile densities were highest from September to November, and at that time, significantly more were present during the day and associated with maerl (that lacked macroalgal cover) than with heavily vegetated rocky and gravel substrata. Juvenile cod were present throughout the year, whereas saithe appeared in July, and pollack from September to January. With its abundance of food, maerl probably has a high holding capacity for juvenile gadoids, and thus is an important part of the inshore nursery system.