Muddy Bottoms Research Articles

Contribution of the development of the stratification of water to the expansion of dead zone: A sedimentological approach

To test a hypothesis that the development of the stratification of water enhances the phytoplankton blooming and hypoxia without any increase in the nutrient loading in an enclosed bay, the present study examines the spatial relationship among the hydrographic structures, physico-chemical conditions of the sediments, and macrobenthic communities at 21 stations in the inner part of Ariake Bay, Kyushu, Japan in August 2010, and compares the distribution of the mud content of the sediment in 2014 with those of last few decades focusing on the succession of sedimentary environment. The stratification of water developed in the innermost part of Ariake Bay, and hypoxia occurred below the well-stratified water. The distribution of the muddy bottom with high content of organic matter derived from phytoplankton almost overlapped with the stratified water. Cluster analysis concerning the grain size composition of the sediment corresponded greatly to that of the macrobenthic communities. These results indicate that the development of the stratification of water strongly influences the sedimentary environments and the community structure of macrobenthic animals in the inner part of Ariake Bay. Comparison with the past distribution of mud content revealed eastward expansion of the muddy sediment, and it suggests the distribution of the well-stratified water has expanded recently. The results of the present study show the possibility that the development of the stratified water causes a series of phenomena, which closely resemble ones following the development of the eutrophication of the water, without any increase in the nutrient loading in an enclosed bay or estuary.

Meiobenthos and nematode assemblages from different deep-sea habitats of the Strait of Sicily (Central Mediterranean Sea)

Much attention is currently devoted at upgrading our knowledge on biodiversity and functioning of deep water ecosystems. Information is constantly enriched by researchers, even from basins as the long-studied Mediterranean Sea. In such a perspective, we studied meiobenthic and nematode communities inhabiting muddy sediments from three different habitats at bathyal depths in the Strait of Sicily: a cold-water coral site (CS) in the Maltese Coral Province, a muddy bottom in the same area (MS), and a hydrocarbon imprinted pockmark site (PS) in the Gela Basin. The average meiofauna density at CS (1343 ind/10 cm2) and MS (1804 ind/10 cm2) is much higher than that reported in literature for similar habitats; it is also markedly more elevated than that recorded at PS (224 ind/10 cm2). Although nematodes of the three sites show different abundances, they share similar assemblage structure. Nematodes (avg. 86%) and copepods (avg. 9.3%) were the most abundant meiofaunal taxa at all sites followed by annelids, kinorhynchs and turbellarians. Nematodes were composed by 21 families and 46 genera, with Terschellingia, as most abundant genus (12.4%), followed by Microlaimus (11%), Daptonema (11%), Thalassomonhystera (10.8%), Acantholaimus (9.5%) and Sabatieria (8.7%). The genera Thalassomonhystera, Terschellingia, Microlaimus, Daptonema, Chromadorita, Sabatieria, and Anticoma display a dominance in at least one station. The taxonomic structure of meiofaunal communities of the studied sites is rather similar but differences in relative abundance are evident.

지속가능한 해삼 양식장 조성을 위한 생태적합 서식처 모형 개발

본 연구는 우리나라 생태환경에 맞는 해삼(Holothuroidea, de Blainville, 1834)의 생태적합서식 모형을 개발하고자 해삼의 주요 서식지인 백령도, 진도, 울진 해역의 수치조류도, 해황 및 저서환경을 조사하였다. 조사결과, 수온은 <TEX>$12{\sim}18^{\circ}C$</TEX>정도로 모두 냉수대 지역이며 표층과 저층 사이의 해수 순환이 활발하였다. 백령도와 진도의 수치조류도 분석 결과, 해수 흐름이 <TEX>$100{\sim}120cm\;s^{-1}$</TEX> 정도로 강한 유속장이 형성되는 특징을 보였다. 또한 세 지역 모두 저서에는 은신처 역할을 하는 암반과 전석 등이 고루 분포하며 다양한 해조류 군락 및 저서생물이 해삼과 함께 서식하였다. 이와 같이 해삼 서식처의 공통적인 특징을 바탕으로 사니질 저질, 다양한 해조류 군락, 저서동물 그리고 암반과 전석 등이 고루 분포하는 형태의 해삼생태적합서식처 모형을 개발하였다. 본 모형의 치삼 서식지는 조간대 지역으로 암초 및 해조류가 분포하며, 퇴적물의 구성은 펄질로 나타내었으며 성삼 서식지는 사질과 니질이 만나는 곳에서 가장 많은 해삼 분포와 수심이 깊어질수록 큰 개체를 나타내었다. 또한, 조간대보다 큰 전석과 해조류가 다수 분포하는 형태로 나타내었다. We investigated the tidal current, hydrographic data, and benthic environment of major sea cucumber (Holothuroidea, de Blainville, 1834) habitats in Baengnyeongdo, Jindo and Uljin to understand the optimal environmental or ecological habitat for sea cucumbers. The three study areas were characterized by a cold-water mass of temperatures ranging <TEX>$12{\sim}18^{\circ}C$</TEX>, with an active circulation between the surface and deep waters. According to an analysis of the tidal current map, a strong flow velocity of <TEX>$100{\sim}120cm\;s^{-1}$</TEX> appeared in Baengnyeongdo and Jindo. The three sea cucumber habitats showed the common characters of a bottom sediment composed of sand-silt, a diverse seaweed colony and benthic organisms, and boulders and rocks which provide a hideout for the organisms. We aimed to draw the optimal habitat condition for sea cucumbers in Korea, and the result showed that the low water temperature, rapid water flow, active vertical mixing between surface and deep waters, bottom composed by sand-silt, large rocks, and diverse seaweed colony and benthic organism were important factors. The optimal habitat for Juvenile sea cucumbers was the intertidal areas characterized by a muddy bottom, reef, and seaweed. The optimal habitat for adult sea cucumbers was characterized by a place where sand and mud are mixed, and the body size of the sea cucumber was proportional to water depth, and the relatively large boulders and rocks compared to the intertidal area.

Sublittoral soft bottom assemblages within a Marine Protected Area of the northern Alboran Sea

The composition and structure of sublittoral faunal assemblages inhabiting soft bottoms (15–72 m depth) within the Marine Protected Area ‘Acantilados y Fondos Marinos de Calahonda-Castell de Ferro’ in southern Spain (North Alboran Sea, Mediterranean) have been studied in relation to sediment and water column variables. Three assemblages were identified and corresponded to mixed bottom, unstable bottom and coastal detritic bottom assemblages, based on Pérès &amp; Picard's (1964) benthic classification. A total of 14,318 individuals were collected and 218 species identified, molluscs being the best represented group (141 species). Species richness displayed significant differences with depth and transect, with the highest values observed in the medium to very fine sand and muddy bottoms with bioclasts located at the shallowest sampling stations. The presence of some rare and poorly known invertebrates that are scarce in other areas of the Mediterranean Sea is remarkable, such as the crustacean decapods Bythocaris cosmetops and Pagurus mbizi, Atlantic species with no records in the Mediterranean Sea, and the bathyal molluscs Poromya granulata and Alvania testae, collected at shallow depths. The spatial distribution of faunal assemblages was mainly related to depth and percentage of gravel and clay according to the canonical correspondence analysis. The geographic location of the area, the heterogeneity of soft bottoms and the presence of upwellings in the area may favour the high biodiversity found in the studied soft bottoms. This study increases the scarce knowledge of the circalittoral fauna of sedimentary habitats of the Alboran Sea, providing a baseline for the management of this interesting SCI and for the EU Marine Strategy Framework Directive.

Ischnomesus harrietae sp. nov., a new benthic asellote (Crustacea: Isopoda: Ischnomesidae) from bathyal bottoms of the southern Bay of Biscay.

A new species of Ischnomesidae (Crustacea: Isopoda: Asellota), Ischnomesus harrietae sp. nov. is described from the southern Bay of Biscay. This new species is distinctive due to the presence of numerous pedestal setae arranged in longitudinal rows on pereonite 5. Because of this morphological peculiarity, it can be easily distinguished from the four other Ischnomesus species previously reported from bathyal/abyssal bottoms of the European continental margin. Within its known distributional area, the new species inhabits sandy and muddy bottoms between 619 and 1099 m, with a maximum abundance of 41.8 individuals per 100 m2 recorded at approximately 700 m on the Arcachon Plateau. Another new species is also reported, Ischnomesus sp.1, represented by one specimen only and briefly described. An identification key to European species of Ischnomesus is provided.

Multivariate paleoecological analyses of Badenian and Sarmatian molluscan assemblages from the NW Vienna Basin (Rohožník-Konopiská, Slovakia)

Middle Miocene marine sediments in the Vienna Basin provide opportunities for analyses of spatial and temporal variation in the composition of molluscan communities, especially across the Badenian/Sarmatian boundary. In this study, we describe variation in composition of molluscan assemblages with multivariate analyses (cluster and ordination analyses). In ongoing analyses, we test whether Badenian and Sarmatian assemblages (distinguished on the basis of foraminiferal assemblages) significantly differ in their taxonomic and life habit composition. We focus on a unique set of samples recovered by 80 closely-located borehole cores in 1963 near Rohoznik-Konopiska (Rohalova and Hash 2000), penetrating to ~30-100 m depth in the western part of Slovakia. These cores capture sediments of the Studienka (Badenian) and Halic (Sarmatian) formations that consist of clays, sands and silts. Cierna (1974) studied foraminiferal assemblages in these cores and found that they correspond mainly to the Upper Badenian and Sarmatian. The boundary between the Badenian and Sarmatian sediments is located at ~~206 m.a.s.l. in the SW part and at ~~180 m.a.s.l. in the NE part of the study area. Diverse molluscan assemblages in this area were described by Svagrovský (1971, 1981), Mesaros (1986) and Hladilova (1991). A well preserved shelly material from 80 borehole cores of Rohožnik contains presently more than 6000 individuals (mainly of Badenian age), with ongoing screening of additional samples. They correspond to 156 gastropod, bivalve, and scaphopod taxa at species and genus-level resolution. 72 samples were subjected to preliminary multivariate analyses. A cluster analysis is based on a Bray-Curtis distance and square-root transformed proportional abundances. Ordination analyses are represented by non-metric multidimensional scaling and by principal coordinate analysis. The cluster analysis discriminated five major sample groups with a recurrent taxonomic composition, although ordination analyses show that some of these groups do not form discrete clusters in a multivariate space but rather continuously grade into each other. Mohrensternia sp and Bittium reticulatum are dominant in the first group. These taxa represent herbivorous euryhaline gastropods, who preferred muddy bottoms (Svagrovský, 1971; Kowalke and Harzhauser, 2004). Nassarius illovensis , Acteocina lojankeriana , Nuculana fragilis and Clithon pictus dominate in the second group. N. fragilis represents an infaunal, mobile, asiphonate deposit-feeder, gastropods are represented by mobile taxa with different food requirements that lived in photic zone (Leonard-Pingel et al., 2012). The third group is dominated by Corbula gibba and Nucula nucleus . C. gibba and N. nucleus represented opportunistic bivalve species that indicate unstable habitats with muddy bottoms, frequently characterized by low-oxygen concentrations and by organic enrichment (Holmes 2002; Hrs-Brenko 2006; N´Siala et al. 2008). The fourt h group is dominated by Alvania curta , accompanied with Amalda gladiformis , Cerithium europaeum, and by Aporrhais pespelecani and Acanthocardia turonica that occur exclusively in the Badenian (Harzhauser et Piller 2007; Studencka et Popov 1996). A. turonica prefers sandy bottom, gastropods are represented by herbivore taxa (Svagrovský 1981, Studencka 1986). The fifth group can be characterized as Diloma and Cerithium -dominated association. It mainly consists of gastropods. Diloma occurs in sandy littoral environments (Kroh and Harzhauser, 1999). This discrimination of samples fits with the result of principal coordinate analysis where these taxa group similarly. Associations of molluscs indicate that sedimentation occurred in the photic zone because the determined molluscs predominantly occupied to shallow subtidal environments. The high abundance of Corbula gibba and Nucula nucleus shows a possibility of stratification of water column, with low content of O 2 on the bottom. Some samples in the uppermost parts of cores imply brachyhaline conditions.

New records of Chara connivens P. Salzmann ex A. Braun 1835 – an extremely rare and protected species in Polish brackish waters

The stonewort &lt;em&gt;Chara connivens&lt;/em&gt; was rediscovered in the Vistula Lagoon in 2011, almost 35 years after its last record. In 2012, the species was recorded for the first time in the Szczecin Lagoon. &lt;em&gt;Chara connivens&lt;/em&gt; occurred at shallow (0.5–1.2 m) sandy-muddy and muddy bottoms of small embayments. In the Vistula Lagoon, the stonewort was represented by single small specimens, while in the Szczecin Lagoon, it formed dense and extensive patches.

Sessile macro-epibiotic community of solitary ascidians, ecosystem engineers in soft substrates of Potter Cove, Antarctica

The muddy bottoms of inner Potter Cove, King George Island (Isla 25 de Mayo), South Shetlands, Antarctica, show a high density and richness of macrobenthic species, particularly ascidians. In other areas, ascidians have been reported to play the role of ecosystem engineers, as they support a significant number of epibionts, increasing benthic diversity. In this study, a total of 21 sessile macro-epibiotic taxa present on the ascidian species Corella antarctica Sluiter, 1905, Cnemidocarpa verrucosa (Lesson, 1830) and Molgula pedunculata Herdman, 1881 were identified, with Bryozoa being the most diverse. There were differences between the three ascidian species in terms of richness, percent cover and diversity of sessile macro-epibionts. The morphological characteristics of the tunic surface, the available area for colonization (and its relation with the age of the basibiont individuals) and the pH of the ascidian tunic seem to explain the observed differences. Recent environmental changes in the study area (increase of suspended particulate matter caused by glaciers retreat) have been related to observed shifts in the benthic community structure, negatively affecting the abundance and distribution of the studied ascidian species. Considering the diversity of sessile macro-epibionts found on these species, the impact of environmental shifts may be greater than that estimated so far.Keywords: Sessile macro-epibiont; ascidian; Antarctica; ecosystem- engineer.(Published: 27 January 2015)Citation: Polar Research 2015, 34, 24338, http://dx.doi.org/10.3402/polar.v34.24338

On the brink of the Arctic: Unusual intertidal sub-Arctic kelp associations in the Porsangerfjord, North Norway

The kelps Laminaria digitata and Saccharina latissima are typically sub-littoral species. It is therefore surprising to find large intertidal kelp beds dominated by these two species in the inner Porsangerfjord, North Norway. The areas of the nine intertidal kelp beds ranged from 0.01 to 3 km2 and covered a total area of 8.3 km2. Both species had a prostrate growth form with short stipes, usually less than 10 cm long, independent of the length of the lamina. The laminae of L. digitata and S. latissima measured 77.0 ± 35.2 cm and 99.4 ± 41.0 cm (mean ± 1 SD), respectively. The associations occurred in sheltered areas with a muddy bottom on wide, flat areas of moraine. The areas are completely drained at low tide. The holdfasts were attached to small pebbles sunk in the mud. The mean biomass density of the two dominant kelp species was 4.1 ± 1.8 kg m−2. The mean biomass of all the algal species in the association was 6.1 ± 2.2 kg m−2. A total of 32 species were identified in the association, of which 16 species were annuals and 16 were perennials. All the species found in the kelp associations are also found in the Arctic. The prostrate growth form of L. digitata and S. latissima, the topography and substrate of the intertidal zone, low summer temperatures, low desiccation and protective sea ice during winter are possible factors contributing to the formation of these unusual intertidal kelp associations.

First discovery of Armina babai (Gastropoda, Nudibranchia, Arminoidea) from southeast coast of India

In this study, Armina babai (Tchang-Si, 1934) belonging to the family Arminidae collected off the Southeast coast of India at depths of 180–250 m in the muddy bottom is reported for the first time in India. The number of notal ridges, the position of the genital papilla, the size and the shape of radular teeth, and the features of the masticatory process are the main differences to the congeneric species occurring in the South Indian coast.

Benthic Habitats Around Iceland Investigated During the IceAGE Expeditions

Abstract During the IceAGE (Icelandic marine Animals – Genetics and Ecology) expeditions in waters around Iceland and the Faroe Islands in 2011 and 2013, visual assessments of habitats and the study of surface sediment characteristics were undertaken in 119–2750 m water depth. Visual inspection was realized by means of an epibenthic sled equipped with a digital underwater video camcorder and a still camera. For determination of surface sediment characteristics a subsample of sediment from box corer samples or different grabs was collected and analyzed in the lab. Muddy bottoms predominated in the deep basins (Iceland Basin, Irminger Basin, deep Norwegian and Iceland Seas), while sand and gravel dominated on the shelves and the ridges, and in areas with high currents. Organic contents were highest in the deep Norwegian and Iceland Seas and in the Iceland Basin, and at these sites dense aggregations of mobile epibenthic organisms were observed. Large dropstones were abundant in the Iceland Sea near the shelf and in the Denmark Strait. The dropstones carried diverse, sessile epibenthic fauna, which may be underestimated using traditional sampling gear. The paper supplies new background information for studies based on IceAGE material, especially studies related to ecology and taxonomy.

Structuring Factors Of The Cumacean Communities Of The Continental Shelf Of Southeastern Brazil

Cumaceans are benthic crustaceans distributed worldwide, from intertidal to abyssal plains. They live in sandy and muddy bottoms and can sometimes be found in the water column. Despite their ecological importance as food items for fishes and other organisms and their usefulness as environmental indicators, very few studies have investigated their biodiversity and distribution in Brazil. The present paper reports an ecological study of the cumacean species found on the continental shelf off Santos, southeastern Brazil. It investigates the composition and spatio-temporal structure of the communities, the main environmental factors responsible for the maintenance of that structure and analyzes the effects of the seasonal oceanographic changes on the community descriptors. A grid of 21 stations located between 10 and 100 m depth was created in winter 2005 and summer 2006 and the sediment samples collected with a 0.1 m2 box corer. Twenty four species were obtained, five of them being the most numerous: Diastylis sexpectinata, D. sympterygiae, Eudorella sp., Oxyurostylis salinoi and Anchistylis notus, the latter highly dominant in summer. Diastylis sympterygiae was characteristic of the shallowest and least saline stations (&lt; 16 m depth; S = 33.07 - 34.2) in both seasons. Of the total of 919 individuals, nearly 70% occurred in summer. The area was divided into four depth bands and no significant temporal difference was found as regards the density distribution of cumaceans in those bands as between the samples of the two campaigns. There were, however, spatial differences within bands in the summer campaign: the higher values of density, diversity and richness were close to the 50 m isobath in both campaigns, a fact that could well be attributed to the ongoing effect of the South Atlantic Central Water in this area. The results showed also that depth and the sediment particle size were the main structural factors determining the composition and distribution of the cumacean species.

Trawling exerts big impacts on small beasts

Throughout the world, there is concern about the impact of trawling on deep-sea bottom communities (1). For the most part, this concern has been directed toward deep-sea coral reefs and sponge beds (2, 3). Reef structures, formed by the scleractinian coral, Lophelia pertusa, for example, can be up to 8,000 y old and can provide habitat for more than 700 smaller species (2). In contrast, there has been the sense that trawling on open mud bottoms has little or no impact on the resident species or at least that, because the smaller species have higher turnover rates, the recovery from trawling will be rapid (4). In PNAS, however, Pusceddu et al. show that trawling on deep-sea muddy bottoms strongly alters the biochemical nature of the sediment and reduces the species diversity and abundance of meiofaunal organisms (animals ∼40–500 µm in size), and, in particular, the nematodes (5).

The efficiency of tubular netting method of cultivation for Kappaphycus alvarezii (Rhodophyta, Gigartinales) on the southeastern Brazilian coast

Kappaphycus alvarezii must be adapted to different environmental conditions when introduced to other countries. In Brazilian commercial cultivations with muddy bottoms and increased seawater movement, the floating rafts system using tubular net technique was superior to the tie-tie technique. However, since this result was from only one cultivation cycle, the efficiency of the tubular net technique in other environments and in different periods of the year was analyzed to verify which K. alvarezii farming technique (tubular net or tie-tie) was more efficient with respect to cost, daily growth rate, and carrageenan yield. The results indicated that the efficiency of the tubular net technique in the farming of K. alvarezii yielded higher daily growth rates and lower farming costs as well as retaining more seedlings on the floating raft that is better for the environment preventing invasiveness.

Can small MPAs protect local populations of a coastal flatfish, Solea senegalensis?

AbstractThe benefits of protection of a small (4.3 km2) marine protected area (MPA) for Senegalese sole, Solea senegalensis, were investigated through experimental fishing trials and long‐term (up to 293 days) passive acoustic telemetry. A total of 106 trammel net sets were carried out between 2007 and 2011. Significant differences in abundance and biomass of sole between bottom types/depths (sandy bottoms between 12 and 20 m deep vs muddy bottoms between 35 and 45 m deep) were found, but no significant differences were attributable to the implementation of the no‐take area. Passive acoustic telemetry revealed that most Senegalese sole spent a large part of their time between first and last detections (average residency index = 69%) inside a relatively small area (average 95% = 1.2 km2), during which they preferred sandy bottoms, the most common habitat inside the MPA. Results also demonstrated that Senegalese sole do regular excursions beyond reserve boundaries, eventually emigrating from the MPA. The results suggest that small coastal MPAs providing adequate habitat may protect individuals of this species while allowing for moderate levels of adult spillover to neighbouring areas.

A new species of Paracrenhydrosoma (Copepoda: Harpacticoida: Cletodidae) from a subtidal muddy bottom of southern Korea, with a key to the species of Acrenhydrosoma-complex

A new species of Paracrenhydrosoma (Copepoda: Harpacticoida: Cletodidae) is described from samples taken from muddy bottoms in Jangmok, Geoje Island, Korea. The genus Paracrenhydrosoma is distinguished from other genera of the Acrenhydrosoma-complex (Acrenhydrosoma, Dyacrenhydrosoma and Neoacrenhydrosoma) by carrying an antennal exopod with two setae, P1 endopod with three setae, P3 endopod with two setae and P5 exopod with two setae. The new species differs from its congeners as follows: bifid rostrum on anterior margin, long caudal ramus, exceedingly long baseoendopodal mucroniform process of female P5 that reaches the end of the second free abdominal segment, and modified P3 endopod of male. A tabular key to aid in the identification of the Acrenhydrosoma-complex is provided. The worldwide distribution of the Acrenhydrosoma-complex is summarized and discussed.

Boring Polychaetes Associated withPycnodonte(Phygraea)Vesicularis(Lamarck) from the Upper Cretaceous of Patagonia. A Case of Commensalism?

The presence of the oyster Pycnodonte (Phygraea) vesicularis (Lamarck) is recorded in the Maastrichtian mudstones of the Jagüel Formation. This species was free-lying and inhabited muddy bottoms in a shallow marine shelf with a low sedimentation rate. Their shells supported a diverse community including fungi, algae, sponges, cirripedes, bryozoans, phoronids, polychaetes and mollusks. The most conspicuous components of this community are the boring polychaetes. The aim of this work is to assess possible paleoecological relationships between the oysters and polychaetes. Eighty-nine specimens of P. (Ph.) vesicularis were studied and presence/absence data were recorded. Most of the boring openings are located on the ventral margins and are perpendicular to the growth lines. Preferential distribution of borings on the external surface of valves and on the ventral margins suggests a syn-vivo colonization. The high density of polychaete traces on the valves is an evidence of aggregative behavior of these worms. Although the borings weakened the valve and reduced shell strength, this does not seem to have been lethal for the oysters because there is no evidence of borings opening on the external surface reaching the internal surface of the valve. This suggests that a symbiotic relationship probably existed between P. (Ph.) vesicularis and polychaetes and that this relationship could be classified as commensalism.

Early Permian post-glacial bivalve faunas of the Itararé Group, Paraná Basin, Brazil: Paleoecology and biocorrelations with South American intraplate basins

The uppermost portion of the Taciba Formation, Itararé Group, Paraná Basin, Brazil, records a succession of depositional environments tied to the demise of late Paleozoic glaciation. In the study area, Teixeira Soares county, state of Paraná, the unit is dominated by massive to laminated diamictites with inclusions of sandstones and other coarse-grained lithotypes, representing re-sedimented material in proximal areas. These are succeeded by fine to medium-grained sandstones with tabular cross-stratification and pectinid-rich shell pavements, interpreted as nearshore deposits. Above this, laminated and intensely bioturbated siltstones with closed articulated bivalve shells are recorded, probably deposited in inner shelf settings. Fine to very fine sandstones/siltstones with hummocky cross-stratification and intercalated mudstones, including infaunal in situ shells, are interpreted as stacked storm deposits, generated in distal shoreface environments. These are succeeded by fossil-poor, massive to laminated siltstones/mudstones or gray shales (=Passinho shale) that are inferred to be outer shelf deposits, generated in organic-rich, oxygen-deficient muddy bottoms. In this sedimentary succession dropstones or ice-rafted debris are missing and locally the Passinho shale marks the maximum flooding surface of the Itararé succession. These are capped by the fluvio-deltaic deposits of the Rio Bonito Formation (Sakmarian–Artinskian). Six facies-controlled, bivalve-dominated assemblages are recognized, representing faunal associations that thrived in aerobic to extreme dysaerobic bottoms along a nearshore–offshore trend. Within these assemblages, nineteen bivalve species (three of them new) were recorded and described in detail. The presence of Myonia argentinensis (Harrington), Atomodesma (Aphanaia) orbirugata (Harrington) and Heteropecten paranaensis Neves et al. suggests correlation with bivalve assemblages of the Eurydesma-bearing Bonete Formation, Pillahuincó Group, Sauce Grande-Colorado Basin (Buenos Aires Province), Argentina, indicating a possible Asselian age for this diverse post-glacial bivalve fauna. Despite that, typical members of the icehouse-style Eurydesma–Trigonotreta biota (stricto sensu) have not yet been found in the studied bivalve assemblages.

Dual-frequency ADCPs measuring turbidity

A pair of self-contained acoustic Doppler current profilers (SC-ADCPs) operating with different frequencies were moored on a muddy sea bottom at about 20 m depth in the Bay of Vilaine off the French Atlantic coast. With their acoustic beams oriented upwards, the SC-ADCPs ensonified most of the water column. The results of several months of in situ recorded echo intensity data spanning 2 years (2003 to 2004) from the dual-frequency ADCPs are presented in this paper. The aim was to estimate suspended particle mass concentration and mean size. A concentration index CI is proposed for the estimation of particle concentration. Based on theory the CI—unlike the volume backscatter strength—does not depend on particle size. Compared with in situ optical data, the CI shows reasonable precision but not increased with respect to that of the highest-frequency backscatter strength. Concerning the mean particle size, despite a lack of quantitative validation with optical particle-size measurements, the method yielded a qualitative discrimination of mineral (small) and organic (large) particles. This supports the potential of dual-frequency ADCPs to quantitatively determine particle size. A cross-calibration of the transducers of each ADCP shows that a specific component of the precision of the backscatter strength measured by ADCP depends on the acoustic frequency, the cell thickness and the ensemble integration time. Based on these results, the use of two ADCPs operating with distinctly different frequencies (two octaves apart) or a single dual-frequency ADCP is recommended.

Cumaceans as a food source for the benthic cnidarian Halcampoides purpurea

Cumaceans are peracarid crustaceans living in the sediment-water interface in all oceans and at all depths and they have been considered to be a permanent component of the suprabenthic communities. They can burrow into the sediment, thus obtaining protection from possible predators (Fig. 1a), but some littoral species also perform circadian migrations to the sea surface at night (Macquardt-Moulin 1991). Such migrations are undertaken mainly by males, which in most of the species have pleopods and a higher number of exopods that help them to swim better. The role of cumaceans in the marine food webs is poorly understood. They feed on epilithic diatoms by manipulating sand grains, on detritus by filtering water currents with plumose setae, or on benthic foraminifers that are captured by the piercing appendages present in some genera such as Campylaspis, which could be considered scavengers or even predators. In turn, these crustaceans seem to be the food source for a wide pool of predators (chaetognaths, cephalopod molluscs, decapod crustaceans, echinoderms, fishes, birds and even whales; information compiled from more than 140 papers). Within the cnidarians, cumaceans have only been reported as prey for the pelagic hydrozoan Velella velella and the benthic anthozoan Actinia equina. We offer here direct evidence of the capture of a cumacean (a male of the genus Iphinoe) by the anthozoan Halcampoides purpurea at night (Fig. 1b). This anemone inhabits sandy and muddy bottoms all around the world down to 1,000 m depth. It can alternate periods of activity and complete disappearance into the sediment. In marine caves this alternation could