Disturbance frequency influences patch dynamics in stream benthic algal communities

Disturbance is integral to the organisation of riverine ecosystems. Fluctuating low flows caused by supra-seasonal drought and water management periodically dewater habitat patches, potentially creating heterogeneity in the taxonomic composition and successional dynamics of benthic communities. The frequency of disturbance induced by low flows is contingent upon the topography of the river bed and thus varies among patches. We investigated whether the frequency of patch dewatering influenced the structure and temporal dynamics of benthic algal communities attached to the upper surfaces of stones in stream mesocosms (4 m²). In a 693-day disturbance experiment, we applied short dewatering disturbances (6 days) at high (33-day cycles) and low frequencies (99-day cycles) and compared algal assemblages with undisturbed controls at 21 endpoints. In the absence of disturbance, epilithic space was dominated by the green encrusting alga Gongrosira incrustans. However, drying disturbances consistently reduced the dominance of the green alga, and crust abundance decreased with increasing disturbance frequency, thereby opening space for a diversity of mat-forming diatoms. The response of mat diatoms to disturbance varied markedly during the experiment, from strong reductions in the abundance of loosely attached mats in mid-late 2000 to the exploitation of open space by closely adhering mats in 2001. Contrary responses were attributed to changes in the species composition of mat diatoms, which influenced the physiognomy and hence stress-resistance and resilience of the assemblage. Our results indicate that patchy dewatering of habitat patches during periods of low flow influences the successional dynamics of algae, thereby creating distinctive mosaics on the stream bed. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Response of Antarctic benthic communities to disturbance: first results from the artificial Benthic Disturbance Experiment on the eastern Weddell Sea Shelf, Antarctica

The long-term benthic disturbance experiment (BENDEX) was started on the eastern Weddell Sea shelf off Austasen (Antarctica) during ‘Polarstern’ cruise ANT XXI/2 in December 2003 to simulate the impact of grounding icebergs on the seabed and follow the steps and timescales of recovery of disturbed benthos and demersal fish communities. Here, we report the basic approach and first results for this experimental field study. By means of 11 densely-placed hauls with a modified bottom trawl, a seabed area of approximately 100 × 1000 m was artificially scoured to inflict a similar damage to the benthic habitats as a grounding iceberg. Before the disturbance event and 11 days after it, the seafloor communities were sampled (invertebrate assemblages by multibox corers, the fish fauna by trawl hauls) and comparatively analyzed. Sediment texture and chemistry was not significantly altered by the heavy disturbance inflicted by repeated trawling, whereas the fauna was negatively affected. Invertebrate benthic biomass was drastically reduced by a factor of 10, while mean abundances were only slightly reduced. Demersal fish biomass and abundance were slightly but not significantly smaller after the disturbance. Effects of disturbance became more evident in the composition of the fish fauna, with Trematomus pennelli and T. hansoni being dominant at disturbed sites, whereas Chionodraco myersi was the dominant species in trawl catches from undisturbed stations.     

Legacies of recent environmental change in the benthic communities of Lake Joyce, a perennially ice-covered Antarctic lake

Many Antarctic lakes provide habitat for extensive microbial mats that respond on various timescales to environmental change. Lake Joyce contains calcifying microbialites and provides a natural laboratory to constrain how environmental changes influence microbialite development. In Lake Joyce, depth-specific distributions of calcitic microbialites, organic carbon, photosynthetic pigments and photosynthetic potential cannot be explained by current growth conditions, but are a legacy of a 7-m lake level rise between 1973 and 2009. In the well-illuminated margins of the lake, photosynthetically active benthic communities colonised surfaces submerged for just a few years. However, observed increases in accumulated organic material with depth from 5 to 20 m (2-40 mg ash-free dry weight cm(-2)) and the presence of decimetre-scale calcite microbialites at 20-22 m depth, apparently related to in situ photosynthetic growth, are inconsistent with the current distributions of irradiance, photosynthetic pigments and mat photosynthetic potential (as revealed by pulse-amplitude-modulated fluorometry). The microbialites appeared photosynthetically active in 1986 and 1997, but were outside the depth zone where significant phototrophic growth was possible and were weakly photosynthetically competent in 2009. These complex microbial structures have persisted after growth has ceased, demonstrating how fluctuating environmental conditions and the hysteresis between environmental change, biological response and microbialite development can be important factors to consider when interpreting modern, and by inference ancient, microbially mediated structures.     

Evidence for successional development in Antarctic hypolithic bacterial communities

Hypoliths (cryptic microbial assemblages that develop on the undersides of translucent rocks) are significant contributors to regional C and N budgets in both hot and cold deserts. Previous studies in the Dry Valleys of Eastern Antarctica have reported three morphologically distinct hypolithic community types: cyanobacteria dominated (type I), fungus dominated (type II) and moss dominated (type III). Here we present terminal-restriction fragment length polymorphism analyses to elucidate the bacterial community structure in hypolithons and the surrounding soils. We show clear and robust distinction in bacterial composition between bulk surface soils and hypolithons. Moreover, the bacterial assemblages were similar in types II and III hypolithons and clearly distinct from those found in type I. Through 16S rRNA gene 454 pyrosequencing, we show that Proteobacteria dominated all three types of hypolithic communities. As expected, Cyanobacteria were more abundant in type I hypolithons, whereas Actinobacteria were relatively more abundant in types II and III hypolithons, and were the dominant group in soils. Using a probabilistic dissimilarity metric and random sampling, we demonstrate that deterministic processes are more important in shaping the structure of the bacterial community found in types II and III hypolithons. Most notably, the data presented in this study suggest that hypolithic bacterial communities establish via a successional model, with the type I hypolithons acting as the basal development state.     

Reproductive adaptations of Antarctic benthic invertebrates

The majority of Antarctic benthic invertebrates so far studied do not produce pelagic larvae, but develop non-pelagically by means of egg capsules, brooding or viviparity. The predominance of protected development in the Antarctic benthos is primarily due to the short period of summer phytoplankton abundance and the low sea temperature. Such conditions make it difficult for a larva to complete pelagic development before food becomes scarce in the surface waters. Prosobranch gastropods illustrate some important aspects of Antarctic benthic invertebrate reproduction. Species which develop non-pelagically have an aseasonal or prolonged spawning period. They produce a small number of large yolky eggs which remain in the benthos and develop slowly, giving rise to large, fully competent juveniles. Conversely, one species with free development has a short, synchronous spawning period during early summer, producing larvae which can benefit from the phytoplankton bloom. Protected development by means of brooding will limit dispersion, but transport on floating algae and by anchor ice may partially compensate for this in the Antarctic.     

A comparison of the short term effects of diesel fuel and lubricant oils on Antarctic benthic microbial communities

The effects of diesel fuel and three lubricating oils on microbial communities in marine sediment were investigated in a field experiment at Casey Station, Antarctica. Sediment from a pristine site in Antarctica was treated with either Special Antarctic Blend (SAB) diesel, a synthetic lubricant (Mobil 0W-40), the same lubricant after use in a vehicle or an equivalent unused biodegradable lubricant (Titan GT1). The sediment was re-deployed in trays on the seabed for 5 weeks during the austral summer. The microbial community structure in the sediment upon collection, deployment and retrieval was investigated using denaturing gradient gel electrophoresis (DGGE), most probable number (MPN) counts and direct microscopic counting. It was found that only minor changes occurred in the microbial communities due to the experimental protocol. After 5 weeks however, there were significant differences between the communities in the SAB and clean and used lubricant (Mobil 0W-40) as compared to the control treatment. There was no significant difference between the control and biodegradable oil (Titan GT1) treatment. These results indicate that SAB and synthetic lubricants have a measurable effect on sediment microbial communities in the short-term. The biodegradable oil did not produce such an effect and we conclude that the use of such an oil could reduce the risks associated with oil spills in the Antarctic environment.     

Disturbance,coral reef communities,and changing ecological paradigms

We examine changing ecological theory regarding the role of disturbance in natural communities and relate past and emerging paradigms to coral reefs. We explore the elements of this theory, including patterns (diversity, distribution, and abundance) and processes (competition, succession, and disturbance), using currently evolving notions concerning matters of scale (temporal and spatial), local versus regional species richness, and the equilibrium versus nonequilibrium controversy. We conclude that any attempt to categorize coral reef communities with respect to disturbance regimes will depend on the question being asked and the desired level of resolution: local assemblage versus regional species pool, successional versus geological time, and on the taxonomic and tropic affinities of species included in the study. As with many communities in nature, coral reefs will prove to be mosaics of species assemblages with equilibrial and nonequilibrial dynamics.     

Colonization by lichens and the development of lichen-dominated communities in the maritime Antarctic

Three long-term studies of lichen growth and colonization have been undertaken at Signy Island, South Orkney Islands, in the maritime Antarctic. Small individual thalli of several crustose species and uncolonized plots on 12 fresh rock surfaces were photographically monitored at intervals of 3–4 years over a period of up to 20 years. The development of Ochrolechia frigida colonies on a regenerating moss bank, recently uncovered by a receding glacier, was similarly monitored. The results indicate that many lichens growing in sites enriched by nitrogenous compounds derived from populations of sea birds, have relatively rapid colonization and growth rates. Mean percentage increase in thallus area can be as high as 15–32% per annum in some nitrophilous saxicolous species (e.g. Acarospora macrocyclos, Xanthoria elegans and species of Buellia and Caloplaca), but as low as 0·4–4% in nitrophobous species (Lecanora physciella, Lecidea sp., Rhizocarpon geographicum). Umbilicaria antarctica and Usnea antarctica also yielded data indicating high growth rates, with colonist plants reaching several centimetres after 20 years. Colonization by mixed assemblages of lichens of new rock surfaces can attain 40→90% cover after 20 years in nutrient-enriched sites, and even 20–25% in non-biotically influenced sites. Colonization by or increase in extant O. frigida on the regenerating moribund moss bank was also quite rapid. It is suggested that the ~exceptionally large thalli of several lichen species and the locally extensive dense lichen fellfield communities in the maritime Antarctic may be much younger than previously supposed.     

Paleodepth determination from Antarctic benthic diatom assemblages

Analysis of modern surface sediments from fjords in the Vestfold Hills (Antarctica) indicates that 58% of the variation in benthic diatom assemblages can be attributed to changes in environmental parameters with water depth. Attenuation of light through the water column is suggested to account for 45% of the variation, and the decrease in substrate grain size with depth possibly accounts for a further 13%. Cluster analysis and principal component analysis were used to objectively circumscribe five floral zones between the surface and 35 m depth. The depth distribution of the benthic diatoms was then used to interpret the paleodepth of relict fjord (Holocene) sediments exposed around Deep Lake in the Death Valley (Vestfold Hills). Paleodepths measured from the sea-ice bench around Deep Lake combined with data from grain size analysis indicate that the relict fjord sediments have no analogue amongst the modern fjord sediments sampled in the Vestfold Hills. Without a comparable modern habitat on which to model the diatom depth zones, however, this study was unable to accurately determine the paleowater depth at Deep Lake using diatoms. Paleodepth determination will be possible using grain size analysis and diatom data when the substrate and light requirements of benthic diatoms are understood.     

System concepts and the evolution of benthic communities

Hoffman, Antoni 197804 IS: System concepts and the evolution of benthic communities.
Benthic communities can be regarded as open systems. Then, both the ecological and evolutionary behavior of a benthic community must be made clearly distinct from those of its constituent populations. Longevity of community structures through geological (or evolutionary) time appears to be related to both virtual eurytopy of the constituent species populations and elasticity of the Structures themselves. There is no single, major controlling factor to be found in characteristics of ecological communities, responsible for the ability of their structures to resist long-term environmental changes in geological time.     

Contribution of sea ice microbial production to Antarctic benthic communities is driven by sea ice dynamics and composition of functional guilds

Organic matter produced by the sea ice microbial community (SIMCo) is an important link between sea ice dynamics and secondary production in near‐shore food webs of Antarctica. Sea ice conditions in McMurdo Sound were quantified from time series of MODIS satellite images for Sept. 1 through Feb. 28 of 2007–2015. A predictable sea ice persistence gradient along the length of the Sound and evidence for a distinct change in sea ice dynamics in 2011 were observed. We used stable isotope analysis (δ¹³C and δ¹⁵N) of SIMCo, suspended particulate organic matter (SPOM) and shallow water (10–20 m) macroinvertebrates to reveal patterns in trophic structure of, and incorporation of organic matter from SIMCo into, benthic communities at eight sites distributed along the sea ice persistence gradient. Mass‐balance analysis revealed distinct trophic architecture among communities and large fluxes of SIMCo into the near‐shore food web, with the estimates ranging from 2 to 84% of organic matter derived from SIMCo for individual species. Analysis of patterns in density, and biomass of macroinvertebrate communities among sites allowed us to model net incorporation of organic matter from SIMCo, in terms of biomass per unit area (g/m²), into benthic communities. Here, organic matter derived from SIMCo supported 39 to 71 per cent of total biomass. Furthermore, for six species, we observed declines in contribution of SIMCo between years with persistent sea ice (2008–2009) and years with extensive sea ice breakout (2012–2015). Our data demonstrate the vital role of SIMCo in ecosystem function in Antarctica and strong linkages between sea ice dynamics and near‐shore secondary productivity. These results have important implications for our understanding of how benthic communities will respond to changes in sea ice dynamics associated with climate change and highlight the important role of shallow water macroinvertebrate communities as sentinels of change for the Antarctic marine ecosystem.     

Pollution and tidal benthic communities of the James River Estuary,Virginia

Distribution of benthic communities in the estuarine portion of the James River was controlled mainly by salinity. Pollution effects were localized and difficult to assess because of a rigorous physical environment. Mesohaline and oligohaline communities were very similar to those in other estuaries of the eastern United States. Macrobenthic densities were most severely depressed in tidal freshwater habitats near Richmond & Hopewell, where the major portion of the pollution load enters the river. Cluster analysis of species distributional patterns and ordination of pollution and physical parameters produced similar results, dividing the river into mesohaline, oligohaline, and upper and lower tidal freshwater zones. Further analysis of only the tidal freshwater portion indicated the distribution of benthic communities reflected the location and concentration of pollution sources along the river. Tidal freshwater communities were dominated by the Asiatic clam, Corbicula fluminea, tubificid oligochaetes of the genus Limnodrilus and the chironomid insect larva Coelotanypus scapularis. The fauna of the freshwater zones was very eurytopic with respect to sediment type and has a great resemblance to the fauna of eutrophic lakes. The classical concept of a sharp increase in number of species occurring from oligohaline to freshwater zones was found to be misleading. This increase does not occur until free flowing (or lotic) freshwater areas of greater habitat diversity are reached.     

Antarctic Porifera database from the Spanish benthic expeditions

The information about the sponges in this dataset is derived from the samples collected during five Spanish Antarctic expeditions: Bentart 94, Bentart 95, Gebrap 96, Ciemar 99/00 and Bentart 2003. Samples were collected in the Antarctic Peninsula and Bellingshausen Sea at depths ranging from 4 to 2044 m using various sampling gears.The Antarctic Porifera database from the Spanish benthic expeditions is unique as it provides information for an under-explored region of the Southern Ocean (Bellingshausen Sea). It fills an information gap on Antarctic deep-sea sponges, for which there were previously very few data.This phylum is an important part of the Antarctic biota and plays a key role in the structure of the Antarctic marine benthic community due to its considerable diversity and predominance in different areas. It is often a dominant component of Southern Ocean benthic communities.The quality of the data was controlled very thoroughly with GPS systems onboard the R/V Hesperides and by checking the data against the World Porifera Database (which is part of the World Register of Marine Species, WoRMS). The data are therefore fit for completing checklists, inclusion in biodiversity pattern analysis and niche modelling. The authors can be contacted if any additional information is needed before carrying out detailed biodiversity or biogeographic studies.The dataset currently contains 767 occurrence data items that have been checked for systematic reliability. This database is not yet complete and the collection is growing. Specimens are stored in the author’s collection at the Spanish Institute of Oceanography (IEO) in the city of Gijón (Spain). The data are available in GBIF.     

Disturbance,neutral theory,and patterns of beta diversity in soil communities

Beta diversity describes how local communities within an area or region differ in species composition/abundance. There have been attempts to use changes in beta diversity as a biotic indicator of disturbance, but lack of theory and methodological caveats have hampered progress. We here propose that the neutral theory of biodiversity plus the definition of beta diversity as the total variance of a community matrix provide a suitable, novel, starting point for ecological applications. Observed levels of beta diversity (BD) can be compared to neutral predictions with three possible outcomes: Observed BD equals neutral prediction or is larger (divergence) or smaller (convergence) than the neutral prediction. Disturbance might lead to either divergence or convergence, depending on type and strength. We here apply these ideas to datasets collected on oribatid mites (a key, very diverse soil taxon) under several regimes of disturbances. When disturbance is expected to increase the heterogeneity of soil spatial properties or the sampling strategy encompassed a range of diverging environmental conditions, we observed diverging assemblages. On the contrary, we observed patterns consistent with neutrality when disturbance could determine homogenization of soil properties in space or the sampling strategy encompassed fairly homogeneous areas. With our method, spatial and temporal changes in beta diversity can be directly and easily monitored to detect significant changes in community dynamics, although the method itself cannot inform on underlying mechanisms. However, human‐driven disturbances and the spatial scales at which they operate are usually known. In this case, our approach allows the formulation of testable predictions in terms of expected changes in beta diversity, thereby offering a promising monitoring tool.     

Competitive hierarchies in marine benthic communities

Summary Patterns of competitive displacement by over-growth were examined in communities of sessile organisms in the low intertidal zone at three sites in Washington state and Alaska. Cruotose invertebrates and algae can be arranged into a hierarchy such that species of lower competitive rank rarely overgrow any higher ranking species. Erect and solitary species show a wide range of competitive abilities, but whether they fall into a strict hierarchy is unknown. Few of the solitary or erect species occupy substantial amounts of space in the communities examined.An approximate competitive hierarchy is well established in middle to high intertidal areas dominated by mussels, fleshy algae, and barncles, and has been an important concept in developing both an intuitive understanding and specific mathematical models of the dynamics of benthic marine communities. In particular, lower ranking species in such communities are thought to depend upon predation or chronic disturbance to the dominants to avoid competitive displacement. An alternative viewpoint, proposed on the basis of nonstransitive competitive relationships observed in cryptic encrusting communities on the undersides of coral plates, is that specific competitive loops or networks allow the coexistence of a number of competitors. Although the growth forms and higher taxa represented in the low intertidal bear some similarity to those in the cryptic coral reef community, there is little evidence of ecologically important competitive loops in the intertidal. A reanalysis of data from cryptic reef communities suggests that they also do not depart substantially from a competitive hierarchy, although there appear to be many more cases of local reversals in the outcome of competition. It is suggested that the ecological importance of departures from a strict hierarchy depends upon the competitive rankings of the participants, with departures involving competitively dominant species likely to contribute much more to community structure than those involving opportunistic species.     

In the mood for wood-habitat specific colonization patterns of benthic invertebrate communities along the longitudinal gradient of an Austrian river

Instream large wood (LW) constitutes an indispensable element of natural river ecosystems. It affects local hydraulics, morphology, nutrient budget, overall habitat complexity, and dynamics. Despite numerous studies about LW as a habitat for benthic communities, information on the varying importance along the longitudinal gradient of a river is lacking. The focus of this study is therefore to investigate general differences between lithal and xylal colonizers and to further investigate trends along the river course. We analyzed lithal and xylal communities at ten sites along the medium-sized Lafnitz River in Southeast Austria. Our results significantly show (1) a general differentiation between lithal and xylal communities, (2) an increasing distinction of the lithal and xylal fauna along the longitudinal gradient of the river, and (3) a distinct correlation between the distance from source and the number of exclusive xylal and nowadays predominantly rare taxa. The presence of LW is therefore directly linked to higher aquatic biodiversity compared to rocky substrates and presents a unique element for river restoration, especially in lower river sections.     

On the origin of Antarctic marine benthic community structure

Environmental conditions fostering marine communities around Antarctica differ fundamentally from those in the rest of the world's oceans, particularly in terms of pronounced climatic fluctuations and extreme cold. Here, we argue that the rarity of pelagic larval stages in Antarctic marine benthic invertebrate species is a consequence of evolutionary temperature adaptation and that this has greatly contributed to the current structure of the Antarctic benthic community. In arguing this position, we challenge the likelihood of previously suggested survival strategies of benthic communities on the Antarctic continental shelf and slope during Cenozoic glacial periods. By integrating evidence from marine geology and geophysics, we suggest that the Antarctic continental shelf and slope were both unfavourable environments for benthic communities during glacial periods and that community survival was only possible in the deep sea or in shelters on the continental shelf as a result of the diachronism in maximum ice extent.