Salinity-controlled benthic associations from the Upper Jurassic of Portugal

The Upper Kimmeridgian—basal Tithonian clastic sequence at Santa Cruz, Estremadura, represents environments ranging from river channels and flood plains to lagoons and protected bays showing a deltaic influence. Within the marginal marine environments, five benthic macroinvertebrate associations are recognized and analysed in terms of diversity and species composition. All five are thought to be controlled largely by salinity and to represent lowered and/or fluctuating salinity regimes. They can be grouped along a salinity gradient in which the Mesosaccella dammariensis—Corbulomima suprajurensis association, occurring in prodelta silts and marls, represents the closest approach to fully marine conditions and in which the Eomiodon securiformis association, typical of delta front sands, extends into the oligohaline regime. Banks of the Isognomon lusitanicum association and patch reefs of the Praeexogyra pustulosa—Nanogyra nana association are thought to be typical of brachy-to mesohaline conditions occurring in brackish bays and lagoons. Characteristic of the latter salinity regimes is also the Jurassicorbula edwardi association. The integrated approach, using benthic faunas, trace fossils and sedimentological data, leads to a detailed interpretation of the sedimentary sequences and the construction of a biofacies model which can also be used for other parts of the Lusitanian Basin.     

Biostratinomy and palaeoecology of the cassian formation (Triassic) of the Southern Alps

The sediments forming the Cassian Formation (Middle—Upper Triassic) of the Central Dolomites represent the following environments: back-reef areas, shallow marginal basins, slope, and central basin. In each of these major environments faunal assemblages were found whose composition, mode of preservation and occurrence proved to be characteristics. In the back-reef areas, algal/foraminifera- and calcareous sponge/coral-patch reefs with a highly diverse fauna of frame-builders and reef-dwellers, in some localities excellently preserved, form the most conspicuous feature. In the shallow marginal basins autochthonous algal meadow/soft-bottom associations dominated by gastropods and deposit-feeding bivalves prevail. Slope deposits do not contain any autochthonous associations but either remains of pelagic faunas or transported faunal elements of shallow-water origin in the form of Cipit boulders (subaerially cemented parts from the outer edge of the carbonate platforms), worn Pachycardia rugosa-dominated, or echinoderm debris-dominated assemblages. Sediments of the central basin lack benthic faunas but contains pelagic assemblages of low diversity dominated by Daonella, Posidonia, and some ammonites.     

Invasive bivalves increase benthic communities complexity in neotropical reservoirs

Invasive bivalves often act as ecosystem engineers, generally causing physical alterations in the ecosystems in which they establish themselves. However, the effects of these physical alterations over benthic macroinvertebrate communities’ structure are less clear. The objective of this study was to characterize the ecological effects of the invasive bivalves Corbicula fluminea and Limnoperna fortunei on the structure of benthic macroinvertebrate communities in neo-tropical reservoirs. Three hypotheses were tested: (1) invasive bivalves act as facilitator species to other benthic macroinvertebrates, resulting in communities with higher number of species, abundance and diversity; (2) invasive bivalves change the taxonomic composition of benthic macroinvertebrate communities; (3) invasive bivalves increase the complexity of benthic macroinvertebrate communities. For that it was used data from 160 sampling sites from four reservoirs. We sampled sites once in each area, during the dry season from 2009 to 2012. The first hypothesis was rejected, as the presence of invasive bivalves significantly decreased the host benthic communities’ number of species and abundance. The second hypothesis was corroborated, as the composition of other benthic macroinvertebrates was shown to be significantly different between sites with and without invasive bivalves. We observed a shift from communities dominated by common soft substrate taxa, such as Chironomidae and Oligochaeta, to communities dominated by the invasive Gastropoda Melanoides tuberculata. The biomass data corroborated that, showing significantly higher biomass of M. tuberculata in sites with invasive bivalves, but significantly lower biomass of native species. Benthic macroinvertebrate communities presenting invasive bivalves showed significantly higher eco-exergy and specific eco-exergy, which corroborate the third hypothesis. These results suggest that while the presence of invasive bivalves limits the abundance of soft bottom taxa such as Chironomidae and Oligochaeta, it enhances benthic communities’ complexity and provide new energetic pathways to benthic communities in reservoirs. This study also suggests a scenario of invasion meltdown, as M. tuberculata was facilitated by the invasive bivalves.     

Facies distribution patterns of some marine benthic faunas in early paleozoic platform environments

Worldwide Late Cambrian—Silurian lithofacies patterns indicate that the platforms of that time were sites of accumulation of two essentially different rocks suites: the platform carbonate rocks and the platform terrigenous rocks. Most of the platform rocks accumulated as sediments in shallow marine environments similar to those of the present but far more widely spread.Present-day marine benthic faunas are distributed in depth zones which are primarily controlled by temperature. Faunas tend to occur in substrate-related discrete clusters (communities) within each life zone; similar substrates in different depth zones commonly have different faunal associations. Individual phyletic stocks may encounter environmental optimum or near-optimum conditions in certain areas, that commonly are revealed by an abundance of species and individuals within species in each stock. Environmental optimum conditions depend upon availability of food that may be utilized, modes of feeding of the animals present, water motion, and substrate, among other factors. Organisms in past seas were distributed in patterns similar to those of the present.Carbonate platforms were particularly widespread during the latest Cambrian—Early Ordovician. Intertidal environments spread widely across those platforms during that time and characteristic faunal associations developed in them. Saukiid and related tribolites dominated latest Cambrian carbonate platform intertidal faunas. The Early Ordovician carbonate platform intertidal was dominated by archeogastropod-nautiloid cephalopod faunas. These animals were joined by tabulate corals and certain brachiopods during the latter part of the Ordovician and Silurian as prominent faunal elements in the carbonate platform intertidal—shallow subtidal. Cruziana and related trace fossils, bivalves, and certain tribolites (notably homalonotids and dalmanitids) dominated most terrigenous platform intertidal—shallow subtidal faunas of the Ordovician and Silurian.Articulate brachiopods (primarily orthoids, strophomenoids, and rhynchonelloids) appear to have been relatively prominent during the Early Ordovician in shallow subtidal environments on both carbonate and terrigenous platforms and to have spread down the bathymetric gradient into increasingly deeper subtidal areas of both platforms during the latter part of the Ordovician. Tribolites dominated faunas in relatively moderate to deep subtidal environments on both platforms during the early part of the Ordovician. They were gradually replaced by brachiopods in first the shallower, and later the deeper subtidal as dominant members of the faunas. Brachiopods (primarily pentameroids and spiriferoids) dominated nearly all Silurian warm-water subtidal environments from the shallow subtidal to the edges of the platforms.Platform uplifts in the Middle Ordovician and glacio-eustatic sea-level fluctuations in the Late Ordovician caused environmental changes across the platforms that were accompanied by marked replacements among marine benthic faunas in all environments. The distribution of Ordovician carbonate platforms and glacial deposits suggests that an Ordovician polar region may have been close to present-day equatorial Africa and that Ordovician warm temperate-tropical regions lay close to the present-day North Pole.     

Effects of different management regimes on aquatic macroinvertebrate diversity in Australian rice fields

The maintenance of invertebrate diversity within agricultural environments can enhance a number of agronomically important processes, such as nutrient cycling and biological pest control. However, few Australian studies have been undertaken which specifically address the effects of commercial management regimes on rice field biodiversity. In this study, we compared aquatic macroinvertebrate communities within Australian rice fields cultivated under three commercial management regimes: conventional-aerial (agrochemicals applied, aerially sown), conventional-drill (agrochemicals applied, directly drill-sown) and organic-drill (agrochemical-free, directly drill-sown). These comparisons were undertaken using a combination of community assessment approaches, including morphospecies richness, abundance, diversity and community composition. In general, greater biodiversity existed within macroinvertebrate communities that developed under organic management regimes than under conventional regimes (i.e., higher morphospecies richness and Shannon diversity). Although there were significant differences in several parameters across management regimes early in the rice-growing season, as the growing season progressed the invertebrate communities that developed in the different management regimes became more similar. Only community composition analyses showed significant differences late in the growing season, with functional differences across aquatic faunal assemblages suggested by increased predator abundance in communities sampled from the organic management regime. In order to improve biodiversity within these aquatic environments, management techniques need to be examined individually and the most disruptive processes identified. Alternative management procedures can then be developed that minimise biodiversity loss whilst still delivering required agronomic outcomes.     

Nearshore subtidal community structure compared between inner coast and outer coast sites in Southeast Alaska

Processes that structure subarctic marine communities, particularly in glaciated regions, are not well understood. This understanding is needed as a baseline and to manage these communities in the face of future climate-driven changes. This study investigates two coastal regions of Southeast Alaska with the goals to (a) identify and compare patterns of subtidal community structure for macroalgal, fish, macroinvertebrate (>5?cm), and small epibenthic invertebrate (<5?cm) communities between inner coast and outer coast sites and (b) link patterns of community structure to habitat and environmental parameters. Species assemblage and benthic habitat data were used to compare species diversity and community composition at 6?m and 12?m depths at nine inner coast and nine outer coast sites. Multivariate analysis was applied to reduce environmental variables to major gradients, to resolve community structure, and to relate community structure to habitat and environmental variables. Increased salinity and decreased temperature at outer coast sites compared with inner coast sites were associated with community structure, with greater species diversity at outer coast sites at 6?m depth. Invertebrate community composition was associated with benthic habitat, including crust and coralline algae for macroinvertebrates, and algal cover and substrate for small epibenthic invertebrates. This research suggests that marine communities in glaciated regions are strongly influenced by freshwater input and that future climate-driven changes in freshwater input will likely result in marine community composition changes.     

Comparative ecological analysis of Toarcian (Lower Jurassic) benthic faunas from southern France and east-central Spain

Toarcian (Lower Jurassic) argillaceous-marly sediments of southern France (Causses) and east-central Spain (Barranco de la Puta section) were deposited in mid to lower shelf settings. They contain a low to moderately diverse, autochthonous fauna of benthic macroinvertebrates dominated by bivalves and gastropods, in the case of the Causses, and by bivalves and brachiopods in the Barranco de la Puta section. Five benthic associations are recognized at the latter locality and four at the former. In the Causses, low species diversity, evidence of seasonal mass mortality, presence of the opportunistic bivalve Parvamussium pumilum, local dominance of the soft bottom coral Thecocyathus mactrus and the dark-grey, fine-grained sediment point to high rates of sedimentation, high turbidity, intermittently lowered oxygen values and soft to soupy substrate conditions. These factors, together with eutrophic water masses, were the main environmental parameters governing faunal distribution. Soupy substrate conditions are thought to be largely biologically produced by the activity of infaunal depositfeeders, chiefly nuculoid bivalves. In the Barranco de la Puta section, abundant brachiopods, higher carbonate content of the sediment, and evidence of intermittent in-situ reworking and winnowing point to an influence of storm-induced currents, a shallower depositional depth, lower turbidity, a lower rate of sedimentation, and a somewhat firmer substrate. As a consequence, the fauna is largely dominated by epifaunal suspension-feeders. Compared with maximum and average sizes from elsewhere in the Jurassic, most bivalve species are distinctly smaller, a feature interpreted as stunting. Brachiopods, in contrast, reach normal size. The lack of nuculids, scarcity of deposit-feeders in general, and stunting are interpreted as evidence of an oligotrophic environment. Lowered oxygen conditions appear to have played only a very limited role in shaping the distribution pattern. Many of the differences between both areas can be explained by the different trophic regimes that reflect considerably higher run-off and consequently higher input of terrigenous sediment and dissolved nutrients to the basin in the case of the Causses. This in turn is thought to possibly reflect differences in regional climate; humid in southern France and more arid in eastcentral Spain.     

Early Jurassic shell beds from marginal marine environments in southern Mendoza, Argentina

External estuarine facies in Late Sinemurian beds from the base of the Puesto Araya Formation in the Atuel river region, Mendoza Province, Argentina, contain concentrations of a new species of Cardinioides (a shallow burrowing suspension-feeding Pachycardiidae bivalve) and a low diversity benthic fauna. These bivalves appear in tidal inlet facies of a wave-dominated estuary (environment similar to lagoon-barrier island systems), forming bioclastic lags at the channel bases. The taphonomic attributes (such as shell articulation, degree of fragmentation and abrasion, bioclast size, orientation) change from North to South, from monospecific concentrations of nearly complete large Cardinioides shells with low degree of fragmentation and abrasion, through beds with smaller Cardinioides shells associated with a few bivalves from marine environments, to only isolated fragmented specimens associated with a fully marine biota including not only other bivalves but also brachiopods and ammonoids. This, together with different palaeoecologic, sedimentologic and stratigraphic attributes at the studied localities are evidence of southwards changing environmental conditions from marginal marine (brackish) to fully marine on the eastern margin of the Neuquén basin at that time. From detailed analysis of taphonomic features, size distribution of shells, and the associated fauna at the different localities, the new species is regarded as a brackish water endemic, possibly a low salinity euryhaline species, which inhabited well oxygenated waters. Salinity, turbulence levels and food supply were the main limiting factors in the distribution of the species.     

Evolutionary rates of the Triassic marine macrofauna and sea-level changes: Evidences from the Northwestern Caucasus,Northern Neotethys (Russia)

A diverse Triassic marine macrofauna from the Northwestern Caucasus sheds new light on the biotic evolution after the end-Permian mass extinction. In the early Mesozoic, the study area was located on the northern margin of the Neotethys Ocean. Data on stratigraphic ranges of 130 genera of brachiopods, bivalves, ammonoids, corals, and sponges have been used to calculate the changes in two evolutionary rates, namely faunal transformation rate (FTR) and rate of transformation of the taxonomic diversity structure (TTDSR). The FTR demonstrates the changes in the generic composition of assemblages through geologic time, whereas the TTDSR indicates changes in the generic control of the species diversity. The Triassic marine macrofauna of the Northwestern Caucasus was characterized by very high FTR and TTDSR during the Early Triassic through early Late Triassic. The FTR slowed in the Middle Triassic, and accelerated again in the Carnian–Norian. In contrast, the FTR was abnormally slow in the Norian–Rhaetian. A remarkable turnover among macrofauna occurred at the Carnian–Norian transition. Regional sea-level changes were similar to the global eustatic fluctuations. It is difficult to establish their direct connections with changes in the evolutionary rates, although the turnover at the Carnian–Norian boundary coincided with a prominent regressive episode. In general, high evolutionary rates reported for the Triassic marine macrofauna of the Northwestern Caucasus may be explained as a consequence of the devastating end-Permian mass extinction.     

Biodiversity gradient in the Baltic Sea: a comprehensive inventory of macrozoobenthos data

In the Helsinki Commission Red List project 2009–2012, taxonomic and distributional data of benthic (macro) invertebrates were compiled by the present authors in a comprehensive checklist of the Baltic Sea fauna. Based on the most recent and comprehensive data, this paper presents the diversity patterns observed among benthic invertebrates in the Baltic Sea. As expected, the total number of species per sub-region generally declined along the salinity gradient from the Danish Straits to the northern Baltic Sea. This relationship is well known from the Baltic Sea and has resulted in a general assumption of an exponentially positive relationship between species richness and salinity for marine species, and a negative relationship for freshwater species. In 1934, Remane produced a diagram to describe the hypothetical distribution of benthic invertebrate diversity along a marine–freshwater salinity gradient. Our results clearly indicated the validity of this theory for the macrozoobenthic diversity pattern within the Baltic Sea. Categorisation of sub-regions according to species composition showed both separation and grouping of some sub-regions and a strong alignment of similarity patterns of zoobenthic species composition along the salinity gradient.     

Late quaternary variations in oxygen and carbon isotopic compositions in Canadian Arctic marine bivalves

The oxygen and carbon isotopic composition of arctic marine bivalves Mya truncata, Hiatella arctica, and Mytilus edulis are reported on samples from raised marine deposits in Hudson Bay and eastern Baffin Island. The shells range in age from modern, through the Holocene, to “old” marine units. During the Holocene the ¹⁸O/¹⁶O ratio in shells rose to a maximum about 3,500 B.P. which coincides in time with the period of maximum growth rates of bivalves, maximum size and maximum faunal diversity. The change is interpreted to indicate that about 3,500 years ago arctic waters may have reached a salinity ≈ 1–2% greater than present. Comparison of Holocene shell-carbonate isotopic compositions with those from the “old” marine shells (that are characteristically extremely thick) suggests that during the early Wisconsin advance on eastern Baffin Island, surface and near-surface waters were more saline than at present. This may have been related to low meltwater discharge. Paradoxically, positive values of ¹⁸O/¹⁶O and ¹³O/¹²C in marine shells occurred during the Holocene marine optimum and during the early Wisconsin ice advance.     

Paläobiogeographie jurassischer Muschelfaunen: Beziehung zwischen Süd- und Nordrand der Tethys

Similarities of mid-Jurassic bivalve faunas between the European and the Ethiopian faunal province are very high at the genus-level. At the species-level, however, it is shown that during the Bathonian and Callovian 35% of the bivalves occurring in the Ethiopian faunal province are restricted to this province. In the region of Kachchh (W-India) in the same time-interval 25% of all bivalves are endemic. In the Ethiopian faunal province a clear tendency of increasing endemism from the Bathonian to the Tithonian/Lower Cretaceous at the genus-level and, even more obviously, at the species-level exists. Endemism and provincialism are most marked within the orders Arcoida, Trigonioida, and Nuculoida. The degree of endemism is lower within the Veneroida, but still very high. The orders Mytiloida, Pterioida, and Pholadomyoida hold the largest portion of cosmopolitan species. The rise of endemism and provincialism in Kachchh and m the Ethiopian faunal province from the Bathonian onwards can be explained only partly by the increasing broadening of the Tethys and its effect as an oceanic barrier. The steep increase of endemism in the Upper Jurassic of Kachchh is essentially caused by a radiation within the astartids and trigoniids, accompanied by a reduction of facies-types, due to a regional regression. The very southerly palaeogeographic position of India, the opening of the ‘South African Seaway’, and a change in the marine current system in the uppermost Jurassic led to an increasing differentiation of the Ethiopian faunal province in an ‘Ethiopian-Tethyan’ subprovince to the north and an ‘Ethiopian-Austral’ subprovince to the south. A migration of bivalves in mid-Jurassic times can be reconstructed along the southern margin of the Tethys mainly from east to west. On the other hand, an easternward migration of bivalves along the northern margin of the Tethys from Europe to China and Japan can be documented especially in the Upper Jurassic. This corroberates the existence of a clock-wise marine current system in the northern hemisphere in the Jurassic. The distribution patterns of bivalves in Kachchh and the Ethiopian faunal province are essentially characterized by ‘migration’ of bivalves. The opening of the ‘Hispanic Corridor’ in the Pliensbachian gave way to the immigration of East Pacific bivalves via the western Tethys as far as Kachchh and Madagascar. The dispersal ofPisotrigonia, Seebachia, Tendagurium, andMegacucullaea in the uppermost Jurassic/lowermost Cretaceous from Kachchh and East-Africa respectively to South-Africa and South-America documents the establishment of a ‘South-African Seaway’ and favours migration. However, ‘migration’ and ‘vicariance’ do not exclude each other. On the contrary, both are important mechanisms for creating distributional patterns of bivalves, although within different geological dimensions. Vicariance events produce faunal provinces which last for a long time and within this time-interval, migration seems to be the more important mechanism affecting palaeobiogeographic distribution of bivalves. There is no evidence that the distribution patterns of bivalves in Kachchh and in the Ethiopian faunal province are governed by eustatic sea-level changes. The dominating factors have been a change of the palaeogeographic constellation as a consequence of the break-up of Gondwana, and the local facies distribution. The number of bivalve species known from Europe is much larger than the number of species of the Ethiopian faunal province. A comparison of rarefaction curves of associations, however, shows that this is not a primary feature, but is a consequence of a greater number of different facies types and is due to a far more intense collecting activity in Europe. The bivalves of the Spiti Shales are unequivocal Ethiopian-Tethyan in character. The composition of the fauna indicates the deposition on the deeper shelf of the southern margin of the Tethys. All occurring ‘European’ faunal elements are not significant because of their more or less cosmopolitan distribution.     

Effects of land cover type on community structure and functional traits of alpine stream benthic macroinvertebrates

1. In the European Alps, due to the current changes in land use driven by different social and economic factors, grasslands and pastures are being increasingly replaced by forests. Whereas many studies have focused on the impacts of urbanisation and intensive agricultural activities, no study has evaluated the effects of changes among types of natural to semi-natural land cover in the Alps with a focus on lotic environments.
2. Here, combining taxonomic and functional approaches, we show the effects of four different alpine land cover types (rocks, grasslands, coniferous forests, valley bottom pastures) on stream benthic macroinvertebrate communities. Irrespective of elevation, grasslands and pastures exhibited unpredicted similarity in terms of the composition of the macroinvertebrate assemblages and hosted the highest diversity of benthic organisms, whereas in each of the other land cover types, the density and diversity of the faunal assemblages showed distinct and characteristic values.
3. When analysing the functional diversity decomposed to richness, evenness, and divergence components, grasslands and pastures again showed a similar trend, being characterised by high levels of resource exploitation and niche differentiation, with the potential to host additional organisms. However, as expected, differences driven by land cover type and elevation emerged when examining the single functional traits, since elevation played a major role in terms of the distribution of traits conferring resistance and resilience.
4. Our results demonstrate that land cover type is a prominent factor influencing the taxonomic and functional variety of stream benthic macroinvertebrate communities. Moreover, alpine grasslands contained an unexpected diversity of aquatic insects, as previously assessed for other organisms (e.g. plants and snails). Overall, our study highlights the importance of the preservation of the diversity of habitats in the alpine region, with a special focus needed for valuable semi-natural landscapes, such as grasslands and pastures, particularly in a time of increasing intensification and abandonment of lands in the alpine context.

     

Ecophysiological adaptability of tropical water organisms to salinity changes]

Physiological response of tropical organisms to salinity changes was studied for some marine, estuarine and freshwater fishes (Astyanax bimaculatus, Petenia karussii, Cyprinodon dearborni, and Oreochromis mossambicus), marine and freshwater crustaceans (Penaeus brasiliensis, Penaeus schmitti and Macrobrachium carcinus), and marine bivalves (Perna perna, Crassostrea rhizophorae, and Arca zebra) collected from Northeast Venezuela. They were acclimated for four weeks at various salinities, and (1) placed at high salinities to determine mean lethal salinity, (2) tested by increasing salinity 5@1000 per day to define upper lethal salinity tolerance limit, or (3) observed in a saline gradient tank to determine salinity preference. Acclimation level was the most significant factor. This phenomenon is important for tropical aquatic organisms in shallow waters, where they can adapt to high salinity during the dry season and cannot lose their acclimation level at low salinity during abrupt rain. For saline adaptation of tropical organisms, this behavior will contribute to their proliferation and distribution in fluctuating salinity environments.     

Community replacement of a Pleistocene Crepidula biostrome

A sequence of fossil associations preserved in early Pleistocene mudstone, exposed on the Neuse River, eastern North Carolina, illustrates community replacement by species turnover, in this case involving addition of new species with rank demotions of formerly important community members. Here, a Crepidula biostrome is replaced by more diverse fossil associations dominated by oysters and infaunal bivalves. Biostrome deposits represent an extensive Crepidula snail bank that occupied a subtropical bay environment with low turbidity, near-normal marine salinity, and temporally stable water currents and food supplies. Because of local shoaling, extensive substrate coverage by these sessile epifaunal gastropods was gradually disrupted. A patchier subtidal environment, with more varied habitats for benthic organisms, succeeded the snail bank, thus giving rise to species-rich Oslrea clump and Anadara-Noetia associations containing only a few remaining Crepidula aggregations. Community replacement, species turnover, addition with rank demotions, autochthonous fossils, subtropical marine bay .     

Foraminifera diversity changes and paleoenvironmental analysis: the Lower Cretaceous shallow-water carbonates of San Lorenzello, Campanian Apennines, southern Italy

A high-resolution stratigraphic study, carried out on the carbonate platform strata of the San Lorenzello section (Matese Mountains, southern Italy), Valanginian–Hauterivian in age, has allowed to: recognise lithofacies and their associations; assign the lithofacies associations to specific environments and individuate early meteoric diagenetic modifications, recurring at specific horizons. In this frame the vertical variation of benthic foram diversity has been analysed. On the whole, foraminiferal genera diversity decreases from open to restricted marine environments. Moreover, a climatic control on carbonate sedimentation is suggested by a Milankovitch cyclicity organised in elementary cycles, bundles and superbundles as well as by diagenetic characteristics testifying that humid and arid conditions alternated during the Early Cretaceous times. The orbital cyclicity is also documented by foraminiferal diversity changes, even if some discrepancies between the lithofacies and the diversity locally occur. Therefore, the above diversity changes do not appear to provide sufficient information for the sequence-stratigraphic interpretation of shallow-water carbonates.     

Salinity drives meiofaunal community structure dynamics across the Baltic ecosystem

Coastal benthic biodiversity is under increased pressure from climate change, eutrophication, hypoxia, and changes in salinity due to increase in river runoff. The Baltic Sea is a large brackish system characterized by steep environmental gradients that experiences all of the mentioned stressors. As such it provides an ideal model system for studying the impact of on‐going and future climate change on biodiversity and function of benthic ecosystems. Meiofauna (animals < 1 mm) are abundant in sediment and are still largely unexplored even though they are known to regulate organic matter degradation and nutrient cycling. In this study, benthic meiofaunal community structure was analysed along a salinity gradient in the Baltic Sea proper using high‐throughput sequencing. Our results demonstrate that areas with higher salinity have a higher biodiversity, and salinity is probably the main driver influencing meiofauna diversity and community composition. Furthermore, in the more diverse and saline environments a larger amount of nematode genera classified as predators prevailed, and meiofauna‐macrofauna associations were more prominent. These findings show that in the Baltic Sea, a decrease in salinity resulting from accelerated climate change will probably lead to decreased benthic biodiversity, and cause profound changes in benthic communities, with potential consequences for ecosystem stability, functions and services.     

Microscopic species make the diversity: a checklist of marine flora and fauna around the Island of Sylt in the North Sea

Based on the past 150 years of research and ongoing time-series observations we give a comprehensive overview of marine species composition around the island of Sylt in the eastern North Sea. A total of 2758 species is listed according to the categories microplankton (591 species), zooplankton (137), nekton (118), benthic microflora (158), benthic macroflora (125), benthic micro-and meiofauna (1204), benthic macrofauna (509), birds and mammals (91), and neobiota (39). Plants account for a third of the species, most (85%) of them are microscopic Chromista. Among animals, 60% of the species are micro- and meiofauna though this faunal component is still insufficiently known. These figures are similar to records from the southern North Sea and therefore may by typical for temperate climate sedimentary coastal areas. A comparison with the total of marine species suggests that the small benthic fauna may be severely understudied over most of the world. Analysis of global change depends on sound baseline data and species inventories like this can assist in the detection of biodiversity changes. They emphasise rare species and the full range of local habitats while time-series measurements usually rely on a few selected habitats and biotic components to generate a very general picture of the state of an ecosystem.     

VARIATION IN GROWTH-RATE AND FORM OF A BATHONIAN (MIDDLE JURASSIC) OYSTER IN ENGLAND, AND ITS ENVIRONMENTAL IMPLICATIONS

Abstract:  We review controls on extensional growth rate and shell thickness in the extant oyster Crassostrea . Data on these shell parameters for the ecologically similar Bathonian oyster Praeexogyra hebridica , sampled at carefully selected sites, are then used to test a hypothesis that small size in contemporaneous marine bivalves of north-west Europe was the product of reduced salinity. The hypothesis is refuted, at least to the extent that some additional factor must be involved. The relatively low extensional growth rate and shell thickness at the highest-salinity site, together with the elongate ('etiolated') shape there and the low extensional growth rate at all sites in comparison with Crassostrea , suggests that this factor is reduced primary productivity. Other faunal, sedimentological and diagenetic evidence is consistent with low productivity. We point to other possible instances of reduced productivity during the Middle Jurassic and discuss the possible role of this factor in encouraging the widespread colonization of brackish-water environments by bivalves in the Bathonian Stage.