Soft-bottom Communities Research Articles

Living under Arctic kelp forests: linking soft-bottom communities to kelp cover in the Canadian Arctic

Kelp forests are dominant habitats along Canadian Arctic coastlines. While their extent and productivity are expected to change dramatically due to global warming, their role in supporting Arctic coastal biodiversity remains poorly explored. Leveraging an extensive data set encompassing core samples, video transects, and environmental data, this study explores the patterns and drivers of benthic diversity, particularly focusing on kelp cover, across 4 Eastern Canadian Arctic regions. We show that the widespread soft bottoms in many subtidal coastal Arctic areas are associated with high densities of the kelp Saccharina latissima, often growing in mixed stands with Laminaria solidungula and Alaria esculenta. These kelps enhance the diversity of invertebrate communities thriving in the sediment below, increasing densities in specific groups and promoting subsurface feeding activity. Interregional comparisons indicate that high turbidity conditions typically lead to low macroalgal cover and low invertebrate richness, whereas extensive sea ice cover can favor high macroalgal abundance and unique diverse communities. Conditions of intermediate open-water duration and high water clarity support tall kelp forests, hosting approximately 70% of local rare taxa. Based on these surveys, we provide a list of Arctic invertebrate taxa according to their level of selectivity for kelp forests as habitats. Despite variation among regions, kelp forests enhance biodiversity and drive unique benthic communities in the Canadian Arctic. Due to their ecological significance and potential vulnerability, we recommend efforts to integrate kelp forests into marine protected areas and minimize human-induced damaging activities within or near these habitats.

Macrobenthic fauna and the ecological status of a shellfish farm in the Mediterranean Sea (Algeria)

A faunistic and ecological study on the benthic macrofauna was carried out in the shellfish farm in Ain Chorb (Ain Taya), central Algeria. This study aims to characterise the composition, structure, and functioning of the benthic community to establish the reference state and ecological quality of the shellfish farm and to monitor its evolution through an adapted sampling and observation methodology adapted and used by the scientific community at the international level. Benthic fauna samples were collected in two different periods (warm and cold season) between February 2020 and June 2021; six grab samples were carried out at three sampling stations. Different indices were evaluated based on the benthic community characteristics (species richness, abundance, density, ecological and trophic groups, and the biotic index) and indicator species. An inventory of the macrobenthic fauna of the farm allowed us to identify 6 phyla, 10 classes, 48 families, 106 genera, and 138 species, with a total of 45960 ind/m2. The benthic assemblage is characterised by the dominance of the species Abra alba, Salvatoria clavata, Caecum spp., and Bittium spp. The results of the four benthic indices (the Shannon-Weaver diversity index [H′], the AZTI Marine Biotic Index [AMBI], the multivariate AZTI Marine Biotic Index [M-AMBI], and the BENTIX) indicated that that the sampling stations have a moderate and good ecological status. These results were confirmed by the abundance/biomass comparison curves and geometric abundance class methods. This study provides the first inventory and represents the reference state of the soft-bottom communities of the aquaculture farm. The findings also indicate that the macrobenthic assemblage is excellent indicator of the ecological status.

Weakened pelagic-benthic coupling on an Arctic outflow shelf (Northeast Greenland) suggested by benthic ecosystem changes

Arctic marine ecosystems are becoming more boreal due to climate change. Predictions of ecosystem change focus mainly on Arctic inflow or interior shelves, with few comprehensive studies on Arctic outflow regions. During September–October 2017, soft-bottom communities were sampled and benthic ecosystem processes were quantified at 12 stations on the Northeast Greenland shelf (outflow shelf) and compared to the last regional ecosystem study, conducted in 1992 and 1993. The benthic habitat was characterized in terms of sediment granulometry, pigment concentrations, and porewater chemistry (dissolved inorganic carbon, nutrients). Total abundance and biomass of macrobenthos and meiobenthos, bacterial abundance, porewater dissolved inorganic carbon and ammonium concentrations were higher on the outer shelf compared to locations adjacent to the Nioghalvfjerdsfjorden glacier at 79°N and the inner shelf stations (e.g., macrofauna: 1,964–2,952 vs. 18–1,381 individuals m−2). These results suggest higher benthic production in the outer parts of the NEG shelf. This difference was also pronounced in macrobenthic and meiobenthic community structure, which was driven mainly by food availability (pigments with 1.3–4.3 vs. 0.3–0.9 µg g−1 sediment, higher total organic carbon content and bacterial abundance). Compared to the early 1990s, warmer bottom water temperatures, increased number of sea-ice-free days and lower sediment pigment concentrations in 2017 were accompanied by decreased polychaete and increased nematode abundance and diversity, and a different community structure of nematode genera. The present study confirms previous reports of strong pelagic-benthic coupling on the NEG shelf, but highlights a possible weakening since the early 1990s, with a potential shift in importance from macrofauna to meiofauna in the benthic community. Increasing inflow of Atlantic water and decreasing volume transport and thickness of sea ice through the Fram Strait, probably affecting the Northeast Water Polynya, may be responsible, suggesting ecosystem-wide consequences of continued changes in sea-ice patterns on Arctic shelves.

Three decades of change in the Skagerrak coastal ecosystem, shaped by eutrophication and coastal darkening

Global coastal ecosystems are under accelerating pressure from human activities and climate change. In this study we explore a long-term time series (mostly 1990–2016) from major Norwegian rivers, together with coastal time series from the Norwegian Skagerrak coast. The aims are to: 1) test long-term trends in riverine loadings to Skagerrak, changes in coastal water quality and pelagic and benthic species composition, and 2) to describe the relationships between human drivers (eutrophication and coastal darkening) and community structure of benthic communities. Riverine discharge and transport increased by 23–85% over the time period, corresponding to a 40–78% increase in concentrations of suspended particulate material in coastal waters and reduced surface salinity, connected to the reported coastal darkening of coastal waters. There was a worsening in ecological status for hard-bottom benthic communities (0–30 m) and a reduction in the lower growth depth limit of several macroalgae species. A structural shift in the community composition from macroalgae to increased abundance of animals was found to be related to increased coastal darkening and reduced eutrophication. The concentration of coastal inorganic nutrients (DIN, PO4) declined by 27–36%, in response to management efforts to reduce eutrophication in European regional seas. Results indicate that reduced eutrophication was related to increased ecological status of the deep soft-bottom community (350 m), with a reduction in opportunistic polychaetes and an increase in filter feeding bivalves. This work highlights how climate change and other human-induced changes in a boreal ecosystem intensifies land-ocean interactions, and calls for more adaptive monitoring, where traditional water quality programs and policies evolve iteratively as new information emerges and the major drivers of the systems change.

Biogeographic patterns in sea pens (Octocorallia: Pennatulacea)

Pennatulaceans (Octocorallia: Pennatulacea) are among the most dominant octocoral species living in soft bottom communities. Some of them are cosmopolitan and have been recorded in all seas and oceans of the world, from shallow waters up to about 6260 m deep. In the present study, we try to find answers to questions about the biogeographical distribution of sea pens including most recently described species. We also evaluate the diversity and faunistic affinities among pennatulaceans of the world’s oceans, and determine the degree of faunistic isolation of the Mediterranean Sea from the Atlantic. Finally, we return to the old debate about the hypothetical oldest diversification center of sea pen lineages.

First Application of the AMBI Index to the Macrobenthic Soft-Bottom Community of Terra Nova Bay (Ross Sea, Southern Ocean)

The assemblages of marine benthic organisms and sediment characteristics were investigated in the coastal area between the Mario Zucchelli Antarctic Research Station and Adelie Cove in Terra Nova Bay (Ross Sea, Southern Ocean) during the 2015 summer season. Sediment samples were taken from 11 stations at depths between 25 and 140 m. The dominance of sand characterised sites, and the biochemical composition of the sedimentary organic matter resulted in very variable between the different sites. A total of 142 taxa were identified, with Annelida (68 taxa) and Arthropoda (35 taxa) constituting the main macrobenthic groups. The benthic community at deeper stations showed higher species richness and lower dominance compared to the shallower stations. For the first time in Antarctica, we also investigated the response of the AZTI’s Marine Biotic Index (AMBI) to the organic gradient. Of the 142 taxa found, 97 were not listed in the AMBI library, and we were able to assign as many as 88 taxa to an ecological group. All of these new species were added to the new AMBI species list. AMBI showed a good response to the organic gradient.

Prey Selectivity in Juvenile Red King Crabs from the Coastal Barents Sea

The invasive red king crab, Paralithodes camtschaticus, has become an abundant and important component in the food web of the coastal Barents Sea and can affect the structure and functioning of the local benthic communities through competition and predation. Although dietary composition and feeding behavior of the crab have been intensively studied, prey selectivity in this species under natural conditions remains poorly defined. For this reason, juvenile red king crabs and benthic samples were collected simultaneously at five coastal sites in Kola Bay to reveal the species composition and structure of feeding habits and the diet of red king crabs. The results of stomach and gut content analyses coupled with calculated Ivlev’s indices indicated that 2–5-year-old crabs frequently consumed bivalve mollusks in relative proportions to prey field biomasses. At all sites, juveniles selectively rejected polychaetes. In soft-bottom communities, when the average density of Bivalvia decreased, the crabs showed increased preference for Gastropoda, Crustacea, and Echinodermata. As a result of selective feeding focused on infaunal suspension-feeding mollusks, juvenile red king crabs have altered the structure of benthic communities in the mouth of Kola Bay. Our results may have important implications for evaluating the consequences of the crab introduction and its population management.

Demersal and epibenthic communities of sedimentary habitats in the Avilés Canyon System, Cantabrian Sea (NE Atlantic)

The aim of this study was to describe the epibenthic and demersal communities of the Avilés Canyon System (ACS) in relation to the environmental variables that characterize their biotope. ACS (Cantabrian Sea, NE Atlantic) was recently included in the Natura 2000 network as a Site of Community Importance (SCI). Data of faunal biomass derived from 6 surveys carried out using beam trawl and otter trawls in 2009 and 2010 within INDEMARES and ERDEM projects. Data were divided into two groups to obtain information about the two ecological compartments: benthic and demersal. The total number of species used in this analysis ascended to 116 in the case of benthic organisms and 110 in the case of demersal. Hierarchical clustering analysis was applied to obtain groups of samples similar in terms of species composition for the two ecological components. Depth was the main discriminating factor for grouping hauls, showing high consistency of bathymetric range independently from the compartment examined. Six groups were identified by depth as follows: medium shelf (∼100–200 m), external shelf (∼150–300m), shelf break (∼300–400 m), upper-slope (∼500–700 m), upper middle-slope (∼700–1100 m), and lower-middle-slope (1200–1500 m). SIMPER analysis on biomass values was performed to determine the structure of the faunal assemblages observed for each group in both compartments. Using biomass values for the analysis allowed for the exploration of groups playing important roles in ecosystem functioning and energy fluxes taking place on the sedimentary bottom of this SCI. Finally, CCA analysis revealed that the main environmental drivers were depth, broad scale bathymetric position index (BPI), near-bottom salinity, sedimentary type, and dynamics related variables (Q50 phy and So). This study gives an inventory of the soft bottom assemblages along a very wide depth range (100–1500 m) inside a SCI, linking both epibenthic and demersal communities with the biotope preferences. This study contributes to fundamental knowledge on soft-bottom communities as a pre-requisite, necessary for the next steps in terms of management framework in the SCI.

Spatio-temporal variability of zooplankton and zoobenthos as the elements of integrated zoocenosis in a marine lake (Crimea, Black Sea): What is a general pattern?

The number of small lakes (<1 km2) on Earth is much greater than the total of all large lakes. Marine small saline lakes play an important environmental, social, and economic role but there is often a lack of studies within these environments. Changes are ongoing in many lakes due to natural and anthropogenic causes, and these changes can be dramatic in marine small saline lakes. The authors conducted a study of the spatio-temporal variability of zooplankton and zoobenthos in a small hypersaline Crimean lake of marine origin. The study was done at three lake sites during 3–5 periods in 2018. Animal composition and abundance were studied in plankton, floating filamentous green algae mats, and soft bottom. The temperature fluctuated between 10 and 28 °C, and salinity varied between 23 and 170 g L−1. 9 macrotaxa of animals were found in plankton, and 9 in the benthos. Harpacticoida dominated in 80% of cases, and Ostracoda in 20% of cases. The total abundance of zooplankton averaged 42.4 × 104 ind. m−3. The total abundance of zoobenthos was on average 9.2 × 105 ind. m−2 in mats, and in the soft bottom community on average 2.4 × 105 ind. m−2. There is a single differentiated integrated zoocenosis in the lake without division into separate zoocenoses of plankton, mat, and bottom. Comparison with data of 2004–2006 showed that despite the high level of variability of the components of the zoocenosis, there were no direct long-term changes within it.

Generalized changes of benthic communities after construction of wind farms in the southern North Sea

Over the last years, the development of offshore renewable energy installations such as offshore wind farms led to an increasing number of man-made structures in marine environments. Since 2009, benthic impact monitoring programs were carried out in wind farms installed in the southern North Sea. We collated and analyzed data sets from three major monitoring programs. Our analysis considered a total of 2849 sampling points converted to a set of biodiversity response metrics. We analyzed biodiversity changes related to the implementation of offshore wind farms and generalized the correlation of these changes with spatial and temporal patterns. Our results demonstrate that depth, season and distance to structure (soft-bottom community) consistently determined diversity indicators and abundance parameters, whereas the age and the country affiliation were significantly related to some but not all indices. The water depth was the most important structuring factor for fouling communities while seasonal effects were driving most of the observed changes in soft-sediment communities. We demonstrate that a meta-analysis can provide an improved level of understanding of ecological patterns on large-scale effects of anthropogenic structures on marine biodiversity, which were not visible in single monitoring studies. We believe that meta-analyses should become an indispensable tool for management of offshore wind farm effects in the future, particularly in the view of the foreseen development of offshore renewable energies. This might lead to a better picture and more comprehensive view on potential alterations. However, this requires a modern open-source data policy and data management, across institutions and across national borders.

Morphological analysis of Rhynchospio aff. asiatica (Annelida: Spionidae) and comments on the phylogeny and reproduction of the family Spionidae.

The genus Rhynchospio has fronto-lateral horns on prostomium, paired branchiae from chaetiger 2 to near the posterior end, capillary notochaetae only, and more than two pairs of pygidial cirri. Rhynchospio species are common in coastal soft bottom communities; nevertheless, many recorded Rhynchospio specimens around the world are currently undescribed. Here we described a Rhynchospio species based on specimens collected from Qingdao, China. Comparison with the reported DNA sequences of four gene markers (16S rRNA, 18S rRNA, 28S rRNA, and Histone H3) and brief morphological description of specimens collected from Jinhae Bay, South Korea, previously reported as Rhynchospio aff asiatica, indicated that they are conspecific. Morphologically, specimens of R. aff. asiatica from Qingdao are characterized by having neuropodial hooded hooks from chaetigers 14–17 (vs. 10–23 in R. asiatica) to near pygidial chaetigers, sperm from chaetiger 11 to 14 (vs. from chaetiger 11 to 21–22 in R. asiatica), oocytes from chaetigers 16–17 to 26–39 (vs. from 22–24 in R. asiatica), and 4–6 (vs. up to 6 in R. asiatica) pygidial cirri. Genetically, Rhynchospio aff. asiatica is most closely related to R. arenincola Hartman, 1936 from California, USA with the interspecific distances of 20.02% (16S rRNA), 4.50% (18S rRNA), 8.44% (28S rRNA), 2.74% (Histone H3), and 6.10% (concatenated sequences). Water flow across the dorsum created by ciliary beating of the branchiae and nototrochs, observed on live specimens, may help transport gametes from reproductive segments in anterior and middle parts to the posterior brooding segments. Phylogenetic trees based on concatenated sequences of four gene markers of 54 spioniform species in 25 genera revealed two clades, covering the two subfamilies Spioninae and Nerininae respectively. Two families (i.e., Poecilochaetidae and Trochochaetidae) in the order Spionida were clustered within Spionidae, supporting a morphology-based proposal that these families bearing a pair of prehensile, grooved palps should be grouped within a more broadly defined family Spionidae. Mapping morphological and reproductive characteristics to the phylogenetic trees indicated that the ancestor of spionids might lack branchiae, broadcast spawn thick-envelop oocytes and ect-aquasperm, and produce planktotrophic larvae.Electronic supplementary materialSupplementary material (Supplementary Table S1–S3, Supplementary Fig. S1, and Supplementary videos S1–S4) is available in the online version of this article at 10.1007/s00343-021-1068-z.

A Manipulative Field Experiment to Evaluate the Impact of Discarded Plastic Bags on Shallow Vegetated Benthic Communities

Coastal regions are biologically active areas with significant ecological and socioeconomic values. These regions are increasingly being affected by marine litter. The impact of macro-sized marine litter on biomass and net primary production of hard and soft bottom communities was investigated by using a manipulative field experiment. Plastic bags were used to mimic the disturbance caused by litter to benthic vegetation and fauna. The experiment was carried out on a soft substrate community dominated by sago pondweed Stuckenia pectinata (L.) Boerner and bladder wrack Fucus vesiculosus L. as a foundation species of a hard substrate. A rapid negative impact of the plastic bag cover on vegetation biomass of soft-bottom community was detected, while the impact on the biomass of hard bottom vegetation was non-significant. Plastic bag cover substantially reduced the net production rates of hard substrate species Fucus and the biomass of associated zoobenthos. The difference in net production rates of Stuckenia with and without plastic cover was negligible.

Deep-sea acorn worms (Enteropneusta) from the Bering Sea with the description of a new genus and a new species of Torquaratoridae dominating soft-bottom communities

Five species of deep-sea acorn worms (Enteropneusta) were found in the Bering Sea during cruises of the RV Akademik M.A. Lavrentyev in 2016, 2018, and 2021. The worms were recorded on slopes of the Volcanologists Massif and in the Komandorsky Graben at depths between 1830 and 4278 m and on the Koryak slope between 419 and 662 m. Four of the species were only photographed but not collected; these were an unidentified Torquaratoridae gen. sp. 1 and three harrimaniids: Saxipendium sp., Harrimaniidae gen. sp. 1 and Harrimaniidae gen. sp. 2. Harrimaniidae gen. sp. 1 and gen. sp. 2 were recorded on the Koryak slope in the vicinity of methane seeps. The fifth species was photographed in situ and collected. It has been examined using morphological and molecular methods. It is described in the present study as Quatuoralisia malakhovi n. gen. n. sp. Ezhova et Lukinykh (fam. Torquaratoridae). The abundance of this species in the soft-sediment community at the depth 1830–2290 m was up to 12 specimens per m2, the highest ever recorded for any deep-sea enteropneusts. Morphologically, Q. malakhovi n. gen. n. sp. is noteworthy for the mesocoel ducts, the heart-kidney complex with a pericardial coelom, the two-plated skeleton supporting the proboscis stalk, and conspicuously elongated lateral wings developed on either side of the trunk. The molecular analysis based on the mitochondrial 16S rRNA showed that Q. malakhovi n. gen. n. sp. is closest to several torquaratorid species that have yet to be formally described morphologically.

Spatial and temporal variability of microphytobenthos in a marine hypersaline lake (Crimea): Are there some general patterns?

The microphytobenthos is one of the key elements in the marine hypersaline water bodies. To find the general regularities of microphytobenthos distribution patterns in marine hypersaline lakes and lagoons, the accumulation of data on various cases is needed. Studies on species composition and abundance of microphytobenthos were conducted in a Crimean closed hypersaline lagoon at three stations from April to September 2018. Floating mats of the filamentous green algae Cladophora and the benthic community were investigated. Salinity varied from 23 to 170 g L−1. In total, 25 microalgal species were recorded in the mats and on the bottom, including Bacillariophyta – 19 species, Haptophyta – 2 species, Miozoa – 2 species, and Cyanobacteria – 2 species. 17 Bacillariophyta species were recorded in the mats, and 5 species at the bottom. In the mats, Bacillariophyta species contributed from 50 to 100% of the total species richness. The total microalgal abundance in the mats varied from 2.5 × 106 cells m−2 to 3.8 × 108 cells m−2 (on Cladophora filament area). In 43% of all bottom samples, there was no microphytobenthos at all or there were only single cells, due to hypoxic or even anoxic conditions under the floating mats. The average microalgal abundance in the soft-bottom community was very low, on average 4.1 × 108 cells m−2 of the bottom area. Data on fluctuations of the total microalgae abundance in mats showed that temporal variability is higher than spatial. The factor of chance is important in the determination of microphytobenthos structure variability.

Species diversity and status of key marine habitats in Cu Lao Cham Marine Protected Area, Quang Nam province

In recent years, several studies relating to assessments of marine biodiversity conducted in the Cu Lao Cham Marine Protected Area. However, the data and information from these studies have not been synthesized. This study was based on analyses of data and information from 22 sites of coral reefs, ten sites of rocky shores, five sites of seagrass beds, eight sites of Sargassum beds, and four sites on soft-bottom communities conducted in 1994, 2004, 2008, 2016 and 2017. A total of 976 species belonging to 223 families of 9 common groups (330 species corals, 277 species of fishes, 156 species mollusks, 91 species seaweeds, 71 species of polychaetes, 24 species crustaceans, 22 species of echinoderms and five species of seagrasses) were found. Coral reefs supported the highest number of species (779 species) compared to that of the soft- bottom (135 species), seagrass beds (124 species), and rocky shores (58 species). In general, most of the coral reefs and seagrass beds were not in good condition, with a low mean cover of hard corals (24,8 ± 15,7%) and of seagrasses (11,9 ± 11,6%). Densities of target macro-invertebrates and fishes with large sizes and high value were extremely low, giving exception of a high density of large fishes of fusiliers, snappers, emperors, rabbitfishes, queenfishes, barracuda) found at Bai Dau Tai, Bai Bac, Hon Mo, Hon Tai and the submerged reefs (Ran La, Ran Manh).

Ecological quality assessement of marinas: An integrative approach combining biological and environmental data

The importance of marinas as infrastructures for recreational boating is increasing substantially. However, information on their soft-bottom benthic communities, a key tool for managing programmes, is still scarce. We combined environment features with macro- and meiofaunal soft-bottom community information for assessing the ecological status of marinas with an integrative approach. To address this issue, we focused on eight marinas of the Southern Iberian Peninsula. Macro- and meiofauna data revealed high benthic heterogeneity at a spatial scale. The environmental variables which correlated best with macrofauna were mainly phosphorus, granulometry, and total organic carbon, and secondarily important variables were faecal coliforms, the biocide Irgarol, and heavy metals; total hydrocarbon concentration was also significant for meiofauna. Annelida was the dominant phylum in terms of number of species (37%) and abundance (66%) and were better descriptors of the environmental conditions than Arthropoda and Mollusca. Although identification to the species level is desirable and mandatory for assessing biological pollution, significant differences among marinas and correlations between fauna and abiotic variables were already detected at the level of family and order. This implies that biota assessment at higher levels may still be useful in monitoring programmes limited by time and budget constraints. The major novelty of this study lies in the development of an integrative assessment method based on the following selected ecological indicators: Marinas Environmental Pollution Index (MEPI), Biocontamination Index (BCI), macrofaunal biotic indices (AMBI, M-AMBI, BENTIX, MEDOCC and BENFES), macrofaunal taxa richness and Shannon-Wiener's diversity, and nematode:copepod index. This approach was able to discriminate marinas of the Southern Iberian Peninsula based on their ecological status, which ranged from poor to good. The method can be useful to design standards for assigning “sustainable quality seals” to those marinas with better values of ecological indicators.

Effects of Detached Seaweeds on Structure and Function of Arctic Intertidal Soft-Bottom Communities

Expected lower sea-ice cover and increased storm frequency have led to projections of an increase in seaweed detritus in Arctic marine systems in the near future. To assess whether detached seaweed affects structural and functional traits of species assemblages in soft-bottom habitats, comparable experiments were run in two intertidal sites (Longyearbyen and Thiisbukta) on Svalbard. At each site, we fixed nets containing the locally dominating seaweeds Saccharina latissima and Desmarestia aculeata (Thiisbukta) or Fucus sp. (Longyearbyen) to intertidal mud flats. Empty nets were fixed as procedural controls at both sites. After 2.5 months, one sediment core was taken from each manipulated plot and the number of individuals, dry mass, and average length of each encountered animal taxon were recorded. The same measurements were taken from cores collected from unmanipulated areas at each site, both at the start and end of the experiment. Abundance data were used to calculate estimates of diversity (Shannon-index, evenness, and taxon richness), while initial and final average length measurements were used to estimate taxon-specific growth. Log response ratios of initial and final abundance in unmanipulated areas were used to estimate magnitude and direction of the effect of change in community traits over time, serving as a reference to log response ratios estimating manipulated seaweed effects. In Longyearbyen, the presence of detached seaweeds reduced abundance and dry mass by, on average, 46 and 70%, respectively, compared to unmanipulated benthic communities. In Thiisbukta, the presence of seaweeds enhanced evenness, on average by 16%, but reduced abundance and growth of benthic fauna by, on average, 31 and 86%, respectively. Seaweed effects were generally smaller in Thiisbukta than in Longyearbyen. At both sites, time effects were generally opposite in direction to those caused by the seaweed treatments, yet of similar or larger magnitude. Through reversing temporal dynamics of several of the tested community traits, detached seaweeds strongly modified the structure and functioning of soft-bottom species assemblages at both intertidal sites. We suggest that the detected effects possibly result from seaweed-induced changes in environmental conditions and/or physical disturbance as underlying processes.

Population dynamics, growth, production, and reproduction of the purple clam Amiantispurpurata

AbstractAmiantis purpurata is the dominant clam of shallow subtidal soft bottom communities in Buenos Aires province where it is a major prey item of economically important fish and gastropods as well as anemones. Despite its significant role in the benthic food web, there are few studies dealing with the population biology of this species. Growth, age, mortality, and production along with reproductive patterns and size at first maturity of A. purpurata were investigated at Mar del Plata (38 ºS) area and compared with a population at the southernmost point of distribution, the only other studied population (42 ºS). Early growth was empirically documented for the first time for this species by following a newly recruited cohort throughout the first two years of growth. This allowed for the size and age at first maturity to be accurately determined and provided early growth data for models, which are often difficult to obtain. Larger asymptotic size and quicker rates were reached at lower latitudes. Reproduction followed patterns similar to other temperate venerid bivalve populations with a more extended period of spawning observed at Mar del Plata. The studied population shows relatively high growth rates, achieves sexual maturity at approximately two years of age, and successfully recruits in this area, which was not observed in the other studied population for over 15 years. The environmental conditions in this area are likely more favorable than that of the southernmost population which shows low growth rates and no successful recruitment.

Basin-wide infaunalisation of benthic soft-bottom communities driven by anthropogenic habitat degradation in the northern Adriatic Sea

Shallow coastal seas play an important role in the economy of many countries by sustaining fisheries, tourism, aquaculture and other economic activities. Their exploitation has large-scale ecosystem effects that are easily overlooked, as they often built up over decades or centuries, and historical ecological reference data are rarely available. Here, we assess these effects by comparing live and surface death assemblages (recording historical community states) of soft-bottom molluscs across a range of habitats in the northern Adriatic Sea, using the degree of mismatch between the 2 assemblages as a proxy for ecological change. We found a consistent live-dead mismatch at all stations. Although the degree of mismatch varied between stations with low and high time-averaging (i.e. the range of post-mortem shell ages), the community change followed the same trend over the entire Adriatic basin regardless of the type of sedimentary environment, with a loss of epifaunal species and the reduction of grazers, carnivores, and herbivores. In turn, the abundance of infaunal and opportunistic species feeding on plankton or detritus strongly increased in the living communities. Directionality and magnitude of these changes cannot be explained by time-averaging or by differences in species durability, but reflect a true ecological shift in response to multiple, long-lasting anthropogenic pressures, mainly bottom trawling, eutrophication and hypoxia. The original heterogeneous assemblages characteristic of different sedimentary habitats are thus replaced by a more infaunal, functionally impoverished and less diverse benthic community representing a new ecological baseline shaped by human impact.

Description of the sea pen Calibelemnon hinoenma sp. nov. from shallow waters in southern Japan

Sea pen species of the genus Calibelemnon are important components of soft bottom communities. Here, we formally describe Calibelemnon hinoenma sp. nov. from shallow waters in Amami Oshima, Kagoshima in the Ryukyu Islands, via molecular and morphological observations and analyses. This species can be distinguished from its congeners by the presence of paired autozooids, siphonozooids aligned irregularly in one to three rows at the side of the rachis between polyps, and the red-brown rufous color of the oral disks. Phylogenetically, the new species is located in an Anthoptilum–Umbellula–Calibelemnon clade. Ancestral state reconstruction analyses suggest that Calibelemnon species may have undergone at least two habitat changes, from shallow to deep waters, followed by a return to shallow waters. In the Ryukyu Islands, there have been many recent discoveries of unique marine species, with this sea pen species being the latest.