Soft-bottom Areas Research Articles

Ecological status of benthic communities associated to mussel farms in South of Chile: Can it be predicted using AMBI?

One hundred percent of the blue mussel farm production in 2021 took place in the administrative region of Los Lagos, Chile. Despite the spatial concentration of this activity, there are no studies evaluating the environmental impact where farms are operating. This study integrated various approaches to assess soft-bottom areas in which two farms with different productions, culture systems, and maintenance routine were operating in Reloncaví Sound during the period May 2012-May 2013. One of the approaches used was the AZTI’s Marine Biotic Index (AMBI). Modelled AMBI values, prior to the survey (in 2011), showed that the sites were moderately to heavily impacted. A reduction of the mussel biomass production allowed the sites to improve their ecological status, according to estimated AMBI values (slightly disturbed). The comparison of current and predicted AMBI values, under the mussel biomass existing during the survey, suggests the model could be used for further evaluations and environmental impact studies, prior to a larger validation. Shells, mussels, and farm structures on the bottom promoted sea urchin-dominated communities. Their absence or a reduced presence promoted the presence of scavengers.

Nursery habitat use patterns of the scalloped hammerhead shark, Sphyrna lewini, in coastal areas of the central Mexican Pacific.

This work aimed to characterize the nursery habitat use patterns of the scalloped hammerhead shark, Sphyrna lewini (SPL), in coastal areas of Jalisco and Colima, through the birth pattern, space-time distribution and relationship with environmental conditions. Information was combined from three sources: monitoring bycatch from the artisanal fishery, fishery-independent samplings, and acoustic tracking and monitoring. From September 2013 to May 2017, 408 juvenile SPL (41.6-100.1cm total length) were recorded. Births occurred between May and December (rainy-warmer season), within a radius of 2 km from river mouths in Marabasco, Navidad Bay, Rebalsito-Tecuan and Cuitzmala mainly in shallow (<20 m), turbid and soft-bottom areas. Some tagged SPL moved from Marabasco and Rebalsito to Navidad Bay. The peak of catch and births occurred in June-August. Tagged SPL remained near the river mouth in Rebalsito for up to 27 days, showing a mean residency index of 0.29, a home range of 5.55 km2 with a core area of 1.23 km2 located within a 1.5km radius from the river mouth. In December-January SPL left the river mouth areas and the catch was scarce until the following May-June, except in January 2016, when the catch was high due to El Niño 2015. SPL bycatch was significantly associated with temperature, precipitation and the Oceanic Niño Index.

Tidewater glacier retreat in Antarctica: The table is set for fast-growing opportunistic species, is it?

The rapid warming of the West Antarctic Peninsula (WAP) is causing an important expansion of marine coastal areas due to glacier retreat. These new ice-free areas offer additional habitats for the colonization of benthic species in areas formerly occupied by ice. The establishment of benthic species can represent important negative feedback to the warming process due to the new carbon fixed and stored. Opportunistic, fast-growing, and high turnover species are expected to colonize these new emerging areas. At Potter Cove, the glacier retreat has opened wide areas of soft bottoms, which provides an excellent study area to assess the colonization process and the success of opportunistic species. Here, we examined the population response of the opportunistic soft coral Malacobelemnon daytoni species in the soft bottom area of Potter Cove with different exposure times due to glacier retreat. Our results show a significant variation of M. daytoni population among the sampled areas in terms of presence, abundances, and distribution. In the long-term ice-free areas, opened for more than 60 years, we observed a ~20-fold increase of M. daytoni densities within just 15 years. However, this extraordinary population outburst was not observed in the newer ice-free areas (≤15 years). We registered very low densities in areas of 15 years and no colonies in areas with 10 years of open sea conditions. These were unexpected results based on colonization capabilities showed by the species and habitat suitability of the new areas. Indeed, using Species Distribution Models (SDMs) we also obtained contrasting outputs. SDMs based on long-term areas presence data predicted high habitat suitability and the potential presence of the species in the newer areas. However, when based on newer and older areas data, SDMs showed low habitat suitability and potential absence of the species in the newer areas. This work suggests that species that can be considered as fast and efficient colonizers, could not perform in that way under certain conditions. This deepens the current knowledge on species natural history and environmental relationships, especially to improve our prediction capabilities under changing environmental conditions.

Organic matter assimilation by hard substrate fauna in an offshore wind farm area: a pulse-chase study

AbstractThe installation of offshore wind farms (OWFs) adds artificial hard substrates into naturally soft-bottom areas, changing the local biodiversity. The turbine foundations are rapidly colonized by colonizing organisms, mainly consisting of suspension feeders that can potentially reduce the local primary producer standing stock. In this study, we estimated the amount of organic matter processed by colonizing assemblages of OWFs. We conducted a laboratory pulse-chase experiment, by offering 13C-labelled fragmented microalgae to PVC panels colonized by OWF colonizing fauna. The blue mussel Mytilus edulis showed the highest biomass-specific carbon assimilation, while the high densities of the amphipod Jassa herdmani resulted in the highest total carbon assimilation. By upscaling our results to the total number of the installed offshore wind turbines in the Belgian part of the North Sea, we estimate that these species can reduce the local primary producer standing stock in the area by ca. 1.3%. Mytilus edulis and J. herdmani communities colonizing offshore wind turbine foundations significantly increase carbon assimilation compared to natural soft sediment macrofauna inhabiting the same surface area (i.e. footprint of the turbines).

Diversity of decapod crabs (Crustacea: Brachyura) in two islands of Ubatuba, southeast of Brazil

This is the first comparative study of the alpha and beta diversity of crabs from soft bottom areas nearby two coastal islands (Couves and Mar Virado Islands). Crabs were captured monthly from January 1998 to December 1999. The samplings were carried out with a shrimp fishery boat provided with double-rig nets within a marine protected area in Ubatuba off the north coast of Sao Paulo. The ecological indexes of diversity (H′), equitability (J′) and β-diversity were used to compare the variation in diversity between islands and years. In total, we captured 2221 brachyurans (570 in Couves and 1651 in Mar Virado), belonging to 42 species, 28 genera, and 13 families. Twenty species occurred in both islands, ten occurred only in Couves, and 12 were exclusive of Mar Virado. The three most abundant species were Callinectes ornatus, Hexapanopeus paulensis, and Hepatus pudibundus. There were statistical differences in equitability (between islands in the year of 1998) and abundance (among seasons in the autumn of 1999) (p < 0.05). Although the two islands are geographically close to each other, they have distinct environmental features. Couves Island, for instance, is more affected by the water masses reaching Ubatuba than Mar Virado Island. These characteristics are probably driving the community composition of these islands.

Fukui foldable traps versus fyke nets as options for fishing European green crabs (Carcinus maenas) in soft-bottom habitats: Exploring efficiency and limiting bycatch

The European green crab (Carcinus maenas) continues to expand in Atlantic Canada and other coastal regions worldwide. Since most control measures for this species have failed, there is a need for innovative and ecologically responsible mitigation measures. One such measure is a green crab control harvesting wherein affected fishers could recoup some of their losses through value-added products. As with any new control initiative, gear choice must be carefully considered. This study assessed catch efficiency and bycatch of two common gear: Fukui foldable traps and fyke nets. Both types of gear were systematically compared in two soft-bottom areas with abundant green crab populations over the course of a field season (early May–late September). In this study, fyke nets were more efficient, catching roughly three times the number of green crabs caught by individual Fukui foldable traps. However, fyke nets also caught nearly ten times more bycatch and doubled the number of native species caught. Fyke net bycatch also included proportionally higher numbers of endangered and commercially important species, such as American eel (Anguilla rostrata) and winter flounder (Pleuronectes americanus). Although in principle Fukui foldable traps seem better suited for green crab control because of lesser bycatch impacts, further studies should find ways to increase Fukui foldable trap efficiency or test fyke nets with bycatch reduction devices.

Resource Niches of Co-occurring Invertebrate Species at an Offshore Wind Turbine Indicate a Substantial Degree of Trophic Plasticity

Offshore wind farms in the North Sea are proliferating, causing alterations in local ecosystems by adding artificial hard substrates into naturally soft-bottom areas. These substrates are densely colonized by fouling organisms, which may compete for the available resources. While the distribution of some species is restricted to specific parts of the turbine, others occur across depth zones and may therefore face different competitive environments. Here we investigate the trophic niches of seven invertebrate species: three sessile (Diadumene cincta, Metridium senile and Mytilus edulis), one hemi-sessile (Jassa herdmani) and three mobile species (Ophiothrix fragilis, Necora puber and Pisidia longicornis) that occur in multiple depth zones. We hypothesized that these species would be trophic generalists, exhibiting trophic plasticity by selecting different resources in different depth zones, to cope with the different competitive environments in which they occur. We analyzed δ13C and δ15N of these species and their potential resources across depth zones. Our results show that most of these invertebrates are indeed trophic generalists which display substantial trophic plasticity, selecting different resources in different zones. Degree of trophic plasticity was not related to mobility of the species. There are two possible explanations for these dietary changes with depth: either consumers switch diet to avoid competition with other (dominant) species, or they benefit from the consumption of a non-limiting resource. Only Diadumene cincta was a trophic specialist that consumed suspended particulate organic matter independent of its zone of occurrence. Altogether, trophic plasticity appears an important mechanism for the co-existence of invertebrate species along the depth gradient of an offshore wind turbine.

Coral carpets- a novel ecological engineering tool aimed at constructing coral communities on soft sand bottoms

Hard bottom substrates that are the hallmark property of the coral reefs can be expanded by transforming sedimentary areas into engineered reefs. Testing this rationale, we developed here two preset coral-carpet prototypes (‘coral sods’; 6 units, each 7.5 m2), one containing branching species and one with both coral forms (mixed-units) that were transplanted on a soft bottom area, containing 10 coral species (five branching, five massive; 354 ramets from 30 genotypes and 181 whole-colonies). Ramets from branching genotypes were distributed in central and peripheral coral-sod locations, whereas all massive colonies were put in central locations. The ‘coral sod’ carpets were set-up at the Eilat, Red Sea nursery, held in place for 2–8 months, then transplanted into a highly hostile soft-bottom area (15 m depth) and monitored for up to 17 months. Results revealed high survival rates for corals in the peripheral/center positions (80–100%; most combinations). A fast increase in ecological volume (EV) was recorded during 447 residency days, up to 112% in EV for Acropora variabilis mixed-units in the peripheral position. There was no statistically significant difference between treatments and sod's locations, except for the Pocillopora. damicornis branching/mixed treatment. At day 514, corals' aerial coverage has increased from 50% at onset to 67.3% for the branching units and to 61.5% in the mixed-units. Larvae released from transplanted Stylophora pistillata corals outperformed those of natal colonies in the two following reproductive seasons, significantly higher in the first reproductive season when compared to the second. Coral recruitment (day 485) was up to 4 times higher in the centers compared to the peripheries, in both coral-sod types. Using gypsum sticks dissipation, we recorded reduced water velocities at lateral and uppermost colonial architectures and in the coral sod centers as compared to peripheries. These results reveal the first steps for improved ‘coral sod’ units aiming to shape sandy tropical areas into flourishing coral reef sites.

Small-scale distribution modeling of benthic species in a protected natural hard ground area in the German North Sea (Helgoländer Steingrund)

Natural stony and coarse-grained habitats entail important ecological features for the marine environment. Due to the complexity of their bottom characteristics, they host a high biodiversity compared to surrounding soft bottom areas. The German nature conservation area “Helgolander Steingrund” (HSG; 54°14.00 N and 8°03.00 W) is subject to regular monitoring but lacks information on the spatial distribution of benthic species. Within this study, a new approach using species distribution models (SDM) was tested to fill these gaps of knowledge. Newly recorded environmental data (depth, sediments, current velocities) in the HSG and information on the presence and absences of nine benthic species (Echinus esculentus, Metridium senile, Cancer pagurus, Phymatolithon spp., Axinella polypoides, Homarus gammarus, Flustra foliacea, Alcyonidium diaphanum, Alcyonium digitatum), collected using video analysis of drop camera records, was used to perform SDMs. The models revealed good evaluation measures (true skill statistic > 0.7; area under the receiver operation characteristic curve > 0.90), implying that the model showed good predictive performance for the potential distribution of the tested species. The outcome of this study is a clear recommendation on SDM application in further environmental monitoring programs on the HSG and other protected hard ground areas.

Benthic colonization in newly ice-free soft-bottom areas in an Antarctic fjord.

Extended glacier retreat is among the main consequences of the rapid warming of the West Antarctic Peninsula. Particularly, in the inner part of Potter Cove (South Shetland Islands, Antarctica) large areas are now exposed to open sea conditions owing to the retreat of Fourcade glacier. During the 2010 austral summer, underwater photographic surveys were undertaken by SCUBA diving up to 30 m in these new ice-free areas 80 m from the glacier front. Our main aim was to investigate colonization and early succession of the benthic assemblages on soft-bottom areas. Here, we reported a total of 1,146 animals belonging to 13 taxa. Filter-feeders comprised the largest trophic group and sessile fauna showed much higher coverages and densities than mobile fauna at all depths. The most abundant groups were ascidians and bryozoans, which together comprised ~90% of all taxa documented. In a region where most of marine-terminating glaciers are in retreat, these results are an important contribution to improve our knowledge on colonization in the newly ice-free areas.

Selective byssus attachment behavior of mytilid mussels from hard- and soft-bottom coastal systems

In both sedimentary and rocky coastal habitats, epibenthic mytilid mussels use byssal threads for attachment to the substratum and to form beds with high densities of individuals. Number and attachment strength of byssal threads can be adjusted according to external factors such as hydrodynamic forces or predators, but it is unknown whether mytilid mussels distinguish between substrata of different quality for byssus attachment in different habitat types. In field studies, we examined the attachment strength of the mussel Perumytilus purpuratus growing on Pacific hard- and soft-bottom shores in Chile and of the blue mussel Mytilus edulis from an Atlantic rocky shore in France and a sedimentary shore in the North Sea (Germany), respectively. In additional laboratory experiments, we studied mussel substratum selectivity of both bivalve species from soft and hard bottoms by offering living versus dead, barnacle-fouled vs. unfouled, and firmly attached vs. loose conspecifics. In the field, attachment strength of P. purpuratus on hard bottoms was substantially higher than on soft bottoms even though mussels produced more byssus in the latter habitat. In contrast, blue mussels M. edulis showed only a slightly reduced attachment strength on soft compared to hard bottoms. In the soft-bottom habitat, fouled individuals from the edge of a blue mussel bed were especially strongly attached. In the byssus attachment behavior experiments, P. purpuratus from both habitats showed a significant preference for living conspecifics and those from soft bottoms preferred firmly attached conspecifics. Blue mussels had no preference for particular conspecifics except those from soft-bottom habitats, which preferred fouled over clean mussels. In general, in the choice experiments hard-bottom M. edulis produced more byssus. Our results confirmed that mytilid mussels may show active substratum choice for byssus attachment, which depends on mussel species and habitat type. The results suggest that mussels are adapted to a particular habitat type, with P. purpuratus showing lower adaptation to soft-bottom areas while M. edulis shows successful strategies for both environments.

Macrozoobenthic community structure in subtidal soft-bottom area along the coast of Lembeh Island -North Sulawesi

The present paper describes the soft-bottom macrozoobenthic community structure inhabiting Lembeh Island’s waters (North Sulawesi). Material for the study was collected from 5 stations in October 2013 using a La Motte grab (600 cm2) and subsequently sieved through a 1 mm square mesh sieve. A total of 1147 individuals belonging to 78 species (taxa) of macrozoobenthos and representative of higher taxonomic groups belonging to 12 phyla were recorded and identified. Univariate analysis showed low abundance of individuals and number of species in the Pintu Kota station which has a black sludge of sediment but Shannon index values at this station is the highest. Instead Motto station relatively far from anthropogenic disturbance showed a high abundance of individuals and number of species but Shannon index values at this station is the lowest. The station is dominated by Tanais sp at a density of 9533 individuals m-2. Shannon index is less sensitive to measure the effect of anthropogenic disturbances compared with the abundance of individuals and number of species. The multivariate analysis (Cluster Analysis and Correspondence Analysis) managed to separate the three groups (essemblage) makrozoobethos: Group A (Posokan), Group B (Motto) and Group C (Pancoran, Mawali and Pintu Kota). Abiotic factors such as granulometri, physicochemical, hydrodynamics and anthropogenic factors believed to be the factors controlling the formation of the ecological group.Keywords: macrozoobenthos, anthropogenic impact, multivariate analysis, Lembeh Island. ABSTRAKTulisan ini menggambarkan struktur komunitas makrozoobentos substrat lunak yang menghuni perairan Pulau Lembeh (Sulawesi Utara). Materi untuk studi ini dikumpulkan dari 5 stasiun pada Oktober 2013 dengan menggunakan grab La Motte (600 cm2) dan kemudian disaring dengan saringan berukuran 1 mm persegi mata saringan. Sebanyak 1147 individu yang termasuk dalam 78 spesies (taksa) makrozoobentos dan mewakili 12 fila atau grup taksonomi telah dicatat dan diidentifikasi. Analisis univariat menunjukkan rendahnya kelimpahan individu dan jumlah spesies di stasiun Pintu Kota yang memiliki sedimen lumpur berwarna hitam tetapi nilai indeks Shannon di stasiun ini adalah yang tertinggi. Sebaliknya di stasiun Motto yang relatif jauh dari gangguan antropogenik menunjukkan tingginya kelimpahan individu dan jumlah spesies tetapi nilai indeks Shannonnya adalah yang terendah. Stasiun ini didominasi oleh Tanais sp dengan kepadatan 9533 individual m-2. Indeks Shannon kurang peka mengukur pengaruh gangguan antropogenik dibandingkan dengan nilai kelimpahan individual dan jumlah spesies. Analisis multivariat (Analysis Kluster dan Analisis Korespondensi) berhasil memisahkan 3 grup (essemblage) makrozoobetos: Grup A (Posokan), Grup B (Motto) dan Grup C (Pancoran, Mawali dan Pintu Kota). Faktor abiotik seperti granulometri, hidrodinamika dan fisika-kimia perairan serta faktor antropogenik diduga merupakan faktor-faktor pengendali pembentukan grup ekologis tersebut.Kata kunci: makrozoobentos, dampak antropogenik, analisis multivariat, Pulau Lembeh.

Isotopic determination of the trophic ecology of a ubiquitous key species – The crab Liocarcinus depurator (Brachyura: Portunidae)

Knowledge of the trophic ecology of predators is key to understanding how they affect food web structure and ecosystem functioning. The harbour crab Liocarcinus depurator (L.) (Brachyura: Portunidae) is one of the most abundant decapod species in soft-bottom areas of the Mediterranean Sea and northeast Atlantic Ocean. It is both a common prey and predator of commercial and non-commercial marine species and its predation pressure appears to have little effect on the subtidal community assemblage. However, there are few studies of its diet and little is known about its role in mediating energy flows in marine ecosystems. In this study, carbon (δ13C) and nitrogen (δ15N) stable isotope analysis (SIA) and Bayesian analytical tools were used to characterise the trophic niche of L. depurator and to quantify the most important prey supporting this species under various environmental conditions. Specimens of L. depurator, their potential prey and basal resources were collected from two different subtidal areas of the Gulf of Gaeta, one affected by human activities (north side) and the other seasonally influenced by freshwater inputs originating from the River Garigliano (south side). While there were differences between the two sampling areas in terms of the abundance and δ15N and δ13C values of the macrobenthic prey community, no differences in the δ15N values and trophic position of L. depurator were observed. Specifically, Bayesian mixing models showed Polychaeta Errantia as the main source of crab diets in both areas. The observed differences in the δ13C values and the analysis of trophic pathways also indicate that the terrestrial organic matter originating from the discharge of the River Garigliano was integrated along the food web up to L. depurator. Although this species is usually considered an opportunistic feeder, it appears to be highly selective and its trophic habits did not influence food web topology, which in contrast was found to be strongly influenced by River Garigliano discharge.

Facilitation in the low intertidal: effects of an invasive species on the structure of an estuarine macrozoobenthic assemblage

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 522:157-167 (2015) - DOI: https://doi.org/10.3354/meps11168 Facilitation in the low intertidal: effects of an invasive species on the structure of an estuarine macrozoobenthic assemblage Adriana Novais1,*, Allan T. Souza2, Martina Ilarri3, Cláudia Pascoal1, Ronaldo Sousa1,2 1CBMA - Centre of Molecular and Environmental Biology, Department of Biology, University of Minho, Campos de Gualtar, 4710-057 Braga, Portugal 2Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), University of Porto, Rua dos Bragas 289, 4050-123 Porto, Portugal 3ICBAS-UP – Abel Salazar Biomedical Sciences Institute, University of Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313, Porto, Portugal *Corresponding author: adriana.novais1990@gmail.com ABSTRACT: The Asian clam Corbicula fluminea (Müller, 1774) has been recognized as one of the most important invasive alien species in aquatic ecosystems and may have significant ecological and economic impacts. Recently, the presence of C. fluminea was associated with changes in benthic and epibenthic fauna. In this study, we aimed to understand the mechanisms underlying the effects of C. fluminea on an estuarine macrozoobenthic assemblage using a manipulative experiment. We used 5 different treatments (control, rock, closed, live, open), which were placed in a low sandy intertidal soft bottom area in the Minho estuary (NW Iberian Peninsula) for 2 months. We found that the presence of live and open empty shells of C. fluminea had positive effects on the density, biomass and species richness of macrozoobenthos, specifically on species belonging to Annelida, Mollusca and Crustacea. Our results may be explained by 2 main mechanisms: (1) the production of feces and pseudofeces by C. fluminea, which increases organic matter content and food resources for some macrozoobenthic species; and (2) ecosystem engineering activities by C. fluminea, which can create conditions for the establishment of other species via shell production and bioturbation in the sediments. KEY WORDS: Corbicula fluminea · Alien species · Ecosystem engineering · Invertebrates · Minho estuary Full text in pdf format PreviousNextCite this article as: Novais A, Souza AT, Ilarri M, Pascoal C, Sousa R (2015) Facilitation in the low intertidal: effects of an invasive species on the structure of an estuarine macrozoobenthic assemblage. Mar Ecol Prog Ser 522:157-167. https://doi.org/10.3354/meps11168 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 522. Online publication date: March 02, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Soundscape variation from a larval perspective: the case for habitat-associated sound as a settlement cue for weakly swimming estuarine larvae

Settlement is a critical phase in the life history of most benthic marine organisms and has important implications for their survival and reproductive success, and ultimately for pop - ulation and community dynamics. Larval encounter with settlement habitats is likely facilitated through the use of habitat-specific physical and chemical cues, but the scales over which particular habitat-related environmental cues may operate are rarely measured. In Pamlico Sound, North Carolina, USA we used passively drifting acoustic recorders to measure the varia- tion in habitat-related underwater sound, a potential broad-scale settlement cue, at spatio - temporal scales relevant to dispersing bivalve larvae in the estuary. Sound levels increased by up to 30 dB during passage over oyster reefs compared to off-reef soft bottom areas, and sound level fluctuations in the 2000 to 23 000 Hz frequency range closely corresponded to the presence of oyster reef patches below drifters, indicating that sound characteristics could reliably provide a signal of benthic habitat type to planktonic larvae. Using these soundscape measurements and the known descent capabilities of oyster larvae, we demonstrate with a conceptual model that response to habitat-related sound cues is a feasible mechanism for enhanced larval encounter with settlement substrate.

Applying macrophyte community indicators to assess anthropogenic pressures on shallow soft bottoms

Vegetated soft bottoms are under pressure due to a number of anthropogenic stressors, such as coastal exploitation and eutrophication. The ecological value of these biotopes has gained recognition through international conventions and the EU directives, which request methods for assessment of the environmental status of coastal areas. However, currently there is no appropriate method for assessing the status of shallow vegetated soft bottoms in the northern Baltic Sea. Therefore, we developed a macrophyte community index and tested its response in relation to important pressures (eutrophication and boating activity) and natural gradients (topographic openness, depth and salinity) on shallow bays in the northern Baltic Sea. The macrophyte index, and hence the proportion of sensitive to tolerant species, decreased with increasing phosphorus concentration, turbidity and level of boating activity, while the cumulative cover of macrophytes only showed a negative trend in response to increasing turbidity. Juvenile fish abundance was positively related to the index, indicating importance of sensitive macrophyte species for ecosystem functioning. As the index was tested in a wide geographic area, and showed a uniform response across natural gradients, it is a promising tool for assessment of environmental status that may be applied also in other vegetated soft-bottom areas.

Estuarine soundscapes: distinct acoustic characteristics of oyster reefs compared to soft-bottom habitats

Different types of benthic habitats likely produce distinct soundscapes due to differences in the physical and biological contributors to ambient sound. Despite their potential importance to ecologi- cal processes such as larval settlement, the sound- scapes of most coastal and estuarine habitats have not been characterized. We investigated whether an es- tuarine soundscape is a reliable indicator of habitat type by measuring the sounds of oyster reefs and nearby off-reef soft-bottom areas in Pamlico Sound, North Carolina, USA. Acoustic sampling in 3 areas across the estuary revealed distinct acoustic patterns in oyster reef habitats compared to surrounding off- reef areas, with reef soundscapes dominated by snap- ping shrimp sounds and the vocalizations of reef- dwelling fish species. Compared to soft-bottom habitat, oyster reefs had significantly higher sound pressure levels in the 2−23 kHz frequency band and higher acoustic diversity index values at each concurrent sampling event. Spectral differences between adja- cent reef/off-reef habitats were present throughout the summer and fall sampling season and across 2 sampling years, but the acoustic signal strength dif- fered between reef sites. Passive sound propagation surveys found that the distinct acoustic characteristics of oyster reefs within the 2−23 kHz frequency band were highly localized, with effective source levels of 108.8 to 120.0 dB re 1 μPa @ 1 m and transmission loss approximating a cylindrical geometric spreading model. This soundscape characterization study sug- gests that spatial heterogeneity in ambient sound could serve as a reliable indicator of habitat type and potentially convey habitat quality information to dis- persing organisms.

Reducing the impact of blue mussel (Mytilus edulis) dredging on the ecosystem in shallow water soft bottom areas

Abstract Dredging blue mussels (Mytilus edulis) and thus removing structural elements, inducing resuspension of sediment as well as reducing filtration capacity, will inevitably affect the ecosystem. The study demonstrates that the impacts of fishing can be reduced through gear developments. A new light dredge was tested on commercial vessels using two different experimental setups. First, a twin haul experiment tested the standard gear (i.e., a Dutch dredge) against the light dredge by fishing the two gears side by side onboard the same vessel. Second, a single dredge experiment tested the absolute performance of the two gears by fishing in areas with a known blue mussel density. Results from the twin haul experiment demonstrate that the weight of sediment retained in the gear per square metre fished is 49% less in the light dredge compared with the Dutch dredge which will reduce resuspension of sediment at the surface. Also, the drag resistance of the light dredge was significantly less (177.1 vs. 202.7 kg m‐1). In the twin haul experiment no significant difference was found in the catch per unit effort (CPUE) of the two gears. The single dredge experiment, on the other hand, demonstrated a significant increase in CPUE exceeding 200% when using the light dredge. Seafloor tracks made by the two dredges could not be distinguished by use of side‐scan sonar and the tracks were still detectable 2 months after fishing. It was concluded that replacement of the Dutch dredge with the light dredge would reduce the impact of the fishery on the ecosystem by (i) reducing resuspension of sediment, (ii) reducing fuel consumption, and (iii) potentially reducing energy transfer to the sediment through a reduced gear drag resistance. A potential increase in catch efficiency may reduce the area affected. Fishing with the light dredge is discussed in relation to management of Natura 2000 sites. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Effects of two antagonistic ecosystem engineers on infaunal diversity

The role of ecosystem engineers has been highlighted in recent decades because of their importance for ecosystem functioning, although the interaction between different antagonistic engineer species and their effects on ecosystems have been so far poorly investigated. Coastal areas are good natural laboratories to explore such interactions, since they are often inhabited by macrophyte beds (autogenic engineers) and bioturbator species (allogenic engineers) with antagonistic effects on ecosystem properties and processes (e.g. species diversity, nutrient fluxes, etc.). The main goal of this study was to determine how coexisting antagonistic ecosystem engineers could influence benthic diversity and available resources in soft-bottom areas. To achieve this goal, a two-month experiment was carried out in situ by introducing artificial seagrass patches in a soft-bottom area inhabited by the fiddler crab Uca tangeri. Both the experimental exclusion of burrows as well as the presence of artificial seagrass-like structures (mimics) resulted in higher macrobenthic density and species richness in the benthic community. Resource availability for organisms (sediment chlorophyll a and epiphytes) was also favoured by the presence of mimics. Therefore, the higher structural complexity (above- and below-ground) associated with seagrass mimics promoted positive effects for infauna such as creation of a new habitat ready to colonize, reduction of the crab burrowing activity and the enhancement of resource availability, which resulted in increased diversity in the benthic community.

A quantitative estimate of the function of soft-bottom sheltered coastal areas as essential flatfish nursery habitat

Essential fish habitat suitability (EFHS) models and geographic information system (GIS) were combined to describe nursery habitats for three flatfish species (Solea solea, Pleuronectes platessa, Dicologlossa cuneata) in the Bay of Biscay (Western Europe), using physical parameters known or suspected to influence juvenile flatfish spatial distribution and density (i.e. bathymetry, sediment, estuarine influence and wave exposure). The effects of habitat features on juvenile distribution were first calculated from EFHS models, used to identify the habitats in which juvenile are concentrated. The EFHS model for S. solea confirmed previous findings regarding its preference for shallow soft bottom areas and provided new insights relating to the significant effect of wave exposure on nursery habitat suitability. The two other models extended these conclusions with some discrepancies among species related to their respective niches. Using a GIS, quantitative density maps were produced from EFHS models predictions. The respective areas of the different habitats were determined and their relative contributions (density × area) to the total amount of juveniles were calculated at the scale of stock management, in the Bay of Biscay. Shallow and muddy areas contributed to 70% of total juvenile relative abundance whereas only representing 16% of the coastal area, suggesting that they should be considered as essential habitats for these three flatfish species. For S. solea and P. platessa, wave exposure explained the propensity for sheltered areas, where concentration of juveniles was higher. Distribution maps of P. platessa and D. cuneata juveniles also revealed opposite spatial and temporal trends which were explained by the respective biogeographical distributions of these two species, close to their southern and northern limit respectively, and by their responses to hydroclimatic trends.