Benthic Community Dynamics Research Articles

27 years of benthic and coral community dynamics on turbid, highly urbanised reefs off Singapore.

Coral cover on reefs is declining globally due to coastal development, overfishing and climate change. Reefs isolated from direct human influence can recover from natural acute disturbances, but little is known about long term recovery of reefs experiencing chronic human disturbances. Here we investigate responses to acute bleaching disturbances on turbid reefs off Singapore, at two depths over a period of 27 years. Coral cover declined and there were marked changes in coral and benthic community structure during the first decade of monitoring at both depths. At shallower reef crest sites (3–4 m), benthic community structure recovered towards pre-disturbance states within a decade. In contrast, there was a net decline in coral cover and continuing shifts in community structure at deeper reef slope sites (6–7 m). There was no evidence of phase shifts to macroalgal dominance but coral habitats at deeper sites were replaced by unstable substrata such as fine sediments and rubble. The persistence of coral dominance at chronically disturbed shallow sites is likely due to an abundance of coral taxa which are tolerant to environmental stress. In addition, high turbidity may interact antagonistically with other disturbances to reduce the impact of thermal stress and limit macroalgal growth rates.

Spatial and temporal patterns of benthic polychaete communities on the northern Gulf of Mexico continental slope

Community structure and abundance of benthic polychaetes along a transect on the central northern Gulf of Mexico continental slope were examined. Spatial, seasonal, short- (~1 year), and long-term (~16–17 years) temporal comparisons of assemblages were conducted with samples collected in 1983–1984 and 2000–2001. Polychaete abundance did not consistently decrease between 325 and 1500 m, but sharply decreased between 1500 and 2100 m. On the upper slope (325–1500 m) polychaete abundance approximately doubled between fall 1983 and spring 1984, but had returned to initial levels by fall 1984. On the lower slope (2500 m) seasonal variations in abundance were less pronounced. The taxonomic composition of the polychaete assemblages changed continuously along a depth gradient; however, temporal variations of the assemblages at all water depths were generally minor. This study provides a baseline for naturally occurring spatial and temporal dynamics of benthic polychaete communities on the northern Gulf of Mexico continental slope.

Mechanisms of resilience: empirically quantified positive feedbacks produce alternate stable states dynamics in a model of a tropical reef

Summary Alternate stable states (ASS) theory is a dominant conceptual framework for understanding processes that support resilience of ecological communities in the face of multiple anthropogenic disturbances. For decades, coral reefs have been cited as a classic example of ASS, yet this position remains highly controversial, largely because convincing empirical evaluations have been elusive. Using a combination of empirical measurements of positive feedback processes and simulation modelling, we assessed ASS in coral reefs of the Eastern Tropical Pacific (ETP) by identifying the potential for multiple basins of attraction from a mechanistic perspective. Using bioassays of algal growth and consumption, we quantified two spatially localized positive feedback mechanisms on coral reefs: increasing herbivore activity associated with higher coral abundances and amelioration of nutrient limitation leading to higher algal growth in areas with higher algal abundance. Analysis of a model of benthic community dynamics incorporating these feedbacks showed they were central to producing hysteresis and bistability in the model, two hallmarks of ASS. Further, reefs simulated with conditions matching those measured at Isla Contadora, Panamá, displayed ASS dynamics while producing spatial patterns matching field observations. This provides model‐derived support, based on empirically measured conditions of ETP reefs, for the presence of ASS. Synthesis. The combination of experimental bioassays to measure feedback strengths and simulation models to evaluate the influence of those feedbacks provides a novel, non‐destructive approach to evaluating ASS dynamics that can be applied in threatened ecosystems where classic approaches are not viable.

The Structure and Dynamics of Macrozoobenthic Communities of the Bega River Water

The benthic macro invertebrates are good indicators of localized conditions, as many of the benthic macro invertebrates have limited migration patterns or a sessile mode of life. Most species have a complex life cycle of one year or more. Sensitive life stages will respond quickly to stress; the overall community will respond more slowly. The structure and distribution of the different benthonic macro-invertebrates communities is considered to be one of the important indicators of the surface waters’ quality . In November 2014, were collected 20 quantitative samples of benthic zones, in the Bega River in order to highlight the links between pollution degree and the saprobionte organisms community. The aim of this paper is to show the effects of human impact (Ghiroda village, potable water treatment station, sewage water treatment station of Timisoara, SA¢nmihaiu Roman village) on benthic community structure and dynamics of different ecosystems from Bega River water. After the laboratory work was carried out, it was identified ten groups of benthic macro invertebrates: Oligochaeta subclass Hirudin class, Lamelibranchiata class, Gastropoda class, Nematoda phylum, Diptera order (larvae of the families Chironomidae, Ceratopogonidae and Tipulidae ), Isopoda order, Trichoptera order, Odonata order, Coleoptera order).

Temporal dynamics of benthic macroinvertebrate communities and their response to elevated specific conductance in Appalachian coalfield headwater streams

Coal mining in central Appalachia USA causes increased specific conductance in receiving streams. Researchers have examined benthic macroinvertebrate community structure in such streams using temporally discrete measurements of SC and benthic macroinvertebrates; however, both SC and benthic macroinvertebrate communities exhibit intra-annual variation. Twelve central Appalachian headwater streams with reference quality physical habitat and physicochemical conditions (except for elevated SC in eight streams) were sampled ≤fourteen times each between June 2011 and November 2012 to evaluate benthic macroinvertebrate community structure. Specific conductance was recorded at each sampling event and by in situ data loggers. Streams were classified by mean SC Level (Reference, 17–142μS/cm; Medium, 262–648μS/cm; and High, 756–1535μS/cm). Benthic macroinvertebrate community structure was quantified using fifteen metrics selected to characterize community composition and presence of taxa from orders Ephemeroptera, Plecoptera, and Trichoptera. Metrics were analyzed for differences among SC Levels and months of sampling. Reference streams differed significantly from Medium-SC and High-SC streams for 11 metrics. Medium-SC streams had the most metrics exhibiting significant differences among months. Relative abundances of Plecoptera and Trichoptera were not sensitive to SC, as the families Leuctridae and Hydropsychidae exhibited increased relative abundance (vs. reference) in streams with elevated SC. In contrast, Ephemeroptera richness and relative abundance were lower, relative to reference, in elevated-SC streams despite increased relative abundance of Baetidae. Temporal variability was evident in several metrics due to influence by taxa with seasonal life cycles. These results demonstrate that benthic macroinvertebrate communities in elevated-SC streams are altered from reference condition, and that metrics differ in SC sensitivity. The time of year when samples are taken influenced measured levels and differences from reference condition for most metrics.

Spatial distribution of nominally herbivorous fishes across environmental gradients on Brazilian rocky reefs.

Assemblages of roving herbivores were consistently different between eastern, warmer, sheltered sites and western, colder, more wave-exposed sites. At eastern sites, detritivorous-herbivorous species dominated while omnivores had the highest biomass and were dominant at western sites. Macroalgivores did not show any trends related to location. These distributional patterns, at relatively small spatial scales of a few kilometres, mirror large-scale latitudinal patterns observed for the studied species along the entire Brazilian coast, where cold water associated species are abundant on south-eastern rocky reefs (analogous to the western sites of this study), and tropical species are dominant on north-eastern coral reefs (analogous to the eastern sites). Species-level analyses demonstrated that depth was an important factor correlated with biomasses of Diplodus argenteus, Sparisoma axillare and Sparisoma tuiupiranga, probably due to resource availability and interspecific competition. Herbivorous fish assemblages in the study area have been historically affected by fishing, and combined with the variation in assemblage structure, this is likely to have important, spatially variable effects on the dynamics of benthic communities.

Low temperature tolerance of a sea urchin pathogen: Implications for benthic community dynamics in a warming ocean

Disease outbreaks in the sea urchin Strongylocentrotus droebachiensis on the Atlantic coast of Nova Scotia have increased in frequency over the last 35years, in association with increasing sea temperatures and strong storm events. Previous studies suggest that the causative agent of disease, the pathogenic amoeba Paramoeba invadens, cannot withstand winter sea temperatures on this coast, and may be an alien species. Consequently, recurrent epizootics result from repeated introductions of this pathogen, possibly due to advection or vertical mixing associated with storm events. Here we test an alternative hypothesis that P. invadens has established resident populations, either through physiological adaptation to low winter temperatures, or because winter minima have increased since 1980. To test this hypothesis, we manipulated culture temperatures of P. invadens isolated from moribund sea urchins during a disease outbreak in 2012. Specific growth rates of P. invadens in culture at 0.5 to 18.0°C were similar to those observed in the early 1980s, providing no evidence of physiological adaptation. P. invadens declined to extinction in culture after ~1month at 0.5°C and 2.0°C, but survived for 3months at 3.5°C, as indicated by recovery of cultures following transfer to optimal temperature. These results indicate a lower temperature tolerance threshold around 2–3°C, which is consistent with observational data of recurrent mass mortalities of sea urchins in 1983 and 2012 in the absence of a storm but following relatively warm winters. A trend of increasing minimum temperatures in winter indicates that P. invadens could undergo a range expansion to establish a resident population in Nova Scotia within 1–2 decades. This is expected to increase the resilience of the kelp-bed state of the benthic ecosystem but result in the complete collapse of the sea urchin fishery.

Sessile and mobile components of a benthic ecosystem display mixed trends within a temperate marine reserve

Despite recent efforts to increase the global coverage of marine protected areas (MPAs), studies investigating the effectiveness of marine protected areas within temperate waters remain scarce. Furthermore, out of the few studies published on MPAs in temperate waters, the majority focus on specific ecological or fishery components rather than investigating the ecosystem as a whole. This study therefore investigated the dynamics of both benthic communities and fish populations within a recently established, fully protected marine reserve in Lamlash Bay, Isle of Arran, United Kingdom, over a four year period. A combination of photo and diver surveys revealed live maerl (Phymatolithon calcareum), macroalgae, sponges, hydroids, feather stars and eyelash worms (Myxicola infundibulum) to be significantly more abundant within the marine reserve than on surrounding fishing grounds. Likewise, the overall composition of epifaunal communities in and outside the reserve was significantly different. Both results are consistent with the hypothesis that protecting areas from fishing can encourage seafloor habitats to recover. In addition, the greater abundance of complex habitats within the reserve appeared to providing nursery habitat for juvenile cod (Gadus morhua) and scallops (Pecten maximus and Aequipecten opercularis). In contrast, there was little difference in the abundance of mobile benthic fauna, such as crabs and starfish, between the reserve and outside. Similarly, the use of baited underwater video cameras revealed no difference in the abundance and size of fish between the reserve and outside. Limited recovery of these ecosystem components may be due to the relatively small size (2.67 km2) and young age of the reserve (<5 years), both of which might have limited the extent of any benefits afforded to mobile fauna and fish communities. Overall, this study provides evidence that fully protected marine reserves can encourage seafloor habitats to recover, which in turn, can create a number of benefits that flow back to other species, including those of commercial importance.

Peculiarities of macrozoobenthos structure formation in riffles of the Karelian coast of the White sea

Species composition, abundance and biomass of macrozoobenthos were investigated in the riffles of the Karelian coast of the White Sea. The longitudinal dynamics of benthic communities’ structure is weak due to the stony-bottomed riffles almost throughout the rivers. Local factors can cause significant changes in the structure of macrozoobenthos. Thus, the communities with high level of filter-feeders biomass (net-weaving caddis fly larvae, the midge larvae, bivalves) are formed in the river sites downstream from the drainage lakes. In the areas affected by salty sea waters (parts of the river mouth), macrozoobenthos structure is significantly depleted. Local landscape features should be considered when describing the longitudinal changes in macrozoobenthos structure of rivers.

Benthic diatoms and phytoplankton to assess nutrients in a large lake: Complementarity of their use in Lake Geneva (France–Switzerland)

Lakes can be monitored using different bioindicators, among which phytoplankton and benthic diatoms. We compared these two indicators in Lake Geneva for nutrient assessment. Bimonthly samplings were carried out during one year in the euphotic layer of a pelagic site. In the same time four littoral sites were sampled at 40–50cm depth. Species compositions and abundances of both bioindicators were analyzed following European standards. Water physico-chemical composition was analyzed at the same time. Seasonal succession of benthic diatom guilds was observed. The dynamics of benthic diatom communities were better correlated to the pelagic chemistry than to the local littoral chemistry. We also observed that in the sampling sites frequently exposed to winds and waves, benthic diatoms showed lower correlations to physico-chemical dynamics, because of an increase of pioneer diatoms abundance adapted to turbulent environment, such sites must be avoided for lake monitoring. Finally, biotic indices calculated with benthic diatoms in wind protected sites showed higher correlations with pelagic nutrient concentration (PO43−) than indices calculated with phytoplankton. This unexpected situation can be explained by differences of temporal variability of chemical and biological compartments. Littoral chemistry changed faster than pelagic chemistry because of rains, diffuse flow from watershed and rivers flowing in the littoral zone whereas pelagic chemistry has a much smoother evolution because it is situated 10km from the coast. But phytoplankton showed a high temporal variability because of wind influence, which explained the low correlation with the smooth evolution of pelagic chemistry. On the other hand, benthic diatoms from sites protected from the dominant wind, showed a lower temporal variability and were more in synchrony with the smooth evolution of pelagic chemistry.Even if we show that diatom seem to be promising indicator of nutrient level of the lake, we also underline the complementarity of using both indicators: benthic diatom and phytoplankton. Each of them brings different information about temporal variability of the lake and about the functioning of different habitats. Comparing these two bioindicators only on the basis of nutrient correlation ability would be an over-simplification whom managers must be warned.

Recovery dynamics of benthic marine communities from the Lower Triassic Werfen Formation, northern Italy

The Lower Triassic Werfen Formation of northern Italy represents an important archive for Early Triassic ecosystems. Based on quantitative community analysis using species level identifications, we reconstruct the recovery of benthic ecosystems after the end-Permian mass extinction throughout this unit. The analysis of benthic macrofossil communities shows that incipient recovery has taken place during the Griesbachian and the Griesbachian–Dienerian transition. A probable deterioration in environmental conditions is observed towards the end of the Dienerian. The Smithian part of the Werfen Formation is characterized by high siliciclastic input, which ceases around the Smithian-Spathian boundary. The Spathian marks the definitive phase of recovery in the Werfen Formation. The comparison of this pattern with other palaoegeographical regions suggests that both the Griesbachian recovery and the Dienerian decline were of inter-regional if not global extent, whereas the Smithian diversity low in the Werfen Formation is a local signal. In contrast to the recovery dynamics of ammonoids and conodonts, the Smithian–Spathian boundary interval was no caesura for benthic ecosystems. The Spathian recovery pulse is possibly also an inter-regional event, at least in the palaeotropics. These results are in contrast with the previously proposed scenario of persistent hostile conditions during the Griesbachian time interval and highlight an initial recovery phase restricted to Griesbachian times. Instead, the apparently sluggish recovery of benthic ecosystems was at least partly shaped by set-backs due to short-term environmental perturbations during the Dienerian.

Rhythmic behaviour of marine benthopelagic species and the synchronous dynamics of benthic communities

Light-intensity cycles drive the relentless motion of species in the oceans, and water column migrants may cyclically make contact with the seabed, hence influencing the temporal dynamism of benthic ecosystems. The influence of light on this process remains largely unknown to date. In this study, we focus on the occurrence of day–night changes in benthic communities on the western Mediterranean continental shelf (100m depth) and slope (400m depth) as a potential result of a behaviourally sustained benthopelagic coupling. We analysed fluctuations in species abundance based on trawling at hourly intervals over a 4-day period as a proxy of activity rhythms at the seabed. We also measured light in situ to assess how the depth-related decrease of its intensity influences species rhythms and the occurrence of the putative benthopelagic synchronisation. Temporal similarities in the catch patterns for different species were screened by dendrogram analysis. On the continental shelf, species performing diel migrations (i.e., over a 24h period) that were either vertical (i.e., benthopelagic) or horizontal across depths (i.e., nektobenthic) clustered together separately from the more sedentary endobenthic and epibenthic species. At the same depth, waveform analysis showed a significant diurnal increase in the catch of water column species and benthic species at night. Such coupling was absent on the continental slope, where light intensity was several orders of magnitude lower than that on the shelf. Our data indicate that diel activity rhythms, which are well known for vertical pelagic migrators, are also evident in the benthos. We discuss the role of light as a major evolutionary driver shaping the composition and biodiversity of benthic communities via visual predation.

Spatio-temporal pattern of community development in dredged material used for habitat enhancement: A study case in a brackish lagoon

Dredged material is a potential resource for beneficial use for create/improve subtidal habitats. In a northwestern Adriatic lagoon, dredged sand was placed in inner areas with the management objective of improving the characteristics of the muddy areas being recharged. With this study we investigated the recolonization dynamics of benthic communities following the placement of dredged sand in a microtidal lagoon. The disposal of dredged sand had an immediate and negative effect on resident fauna. After an initial reduction, benthic communities followed different recovery pathways. One year after disposal, we recorded an almost complete recovery of the benthic invertebrates in terms of univariate parameters. Despite multivariate analyses still showed significantly different community structures, the trajectories of recovery for disposal areas converged towards the same basin of attraction of control areas. The ecological quality of sites, assessed with benthic indices, did not improve, thus no new beneficial habitat was created for macrobenthos.

Canopy-forming seaweeds in urchin-dominated systems in eastern Canada: structuring forces or simple prey for keystone grazers?

Models of benthic community dynamics for the extensively studied, shallow rocky ecosystems in eastern Canada emphasize kelp-urchin interactions. These models may bias the perception of factors and processes that structure communities, for they largely overlook the possible contribution of other seaweeds to ecosystem resilience. We examined the persistence of the annual, acidic (H2SO4), brown seaweed Desmarestia viridis in urchin barrens at two sites in Newfoundland (Canada) throughout an entire growth season (February to October). We also compared changes in epifaunal assemblages in D. viridis and other conspicuous canopy-forming seaweeds, the non-acidic conspecific Desmarestia aculeata and kelp Agarum clathratum. We show that D. viridis can form large canopies within the 2-to-8 m depth range that represent a transient community state termed “Desmarestia bed”. The annual resurgence of Desmarestia beds and continuous occurrence of D. aculeata and A. clathratum, create biological structure for major recruitment pulses in invertebrate and fish assemblages (e.g. from quasi-absent gastropods to >150 000 recruits kg−1 D. viridis). Many of these pulses phase with temperature-driven mass release of acid to the environment and die-off in D. viridis. We demonstrate experimentally that the chemical makeup of D. viridis and A. clathratum helps retard urchin grazing compared to D. aculeata and the highly consumed kelp Alaria esculenta. In light of our findings and related studies, we propose fundamental changes to the study of community shifts in shallow, rocky ecosystems in eastern Canada. In particular, we advocate the need to regard certain canopy-forming seaweeds as structuring forces interfering with top-down processes, rather than simple prey for keystone grazers. We also propose a novel, empirical model of ecological interactions for D. viridis. Overall, our study underscores the importance of studying organisms together with cross-scale environmental variability to better understand the factors and processes that shape marine communities.

Habitat dynamics, marine reserve status, and the decline and recovery of coral reef fish communities

Severe climatic disturbance events often have major impacts on coral reef communities, generating cycles of decline and recovery, and in some extreme cases, community-level phase shifts from coral-to algal-dominated states. Benthic habitat changes directly affect reef fish communities, with low coral cover usually associated with low fish diversity and abundance. No-take marine reserves (NTRs) are widely advocated for conserving biodiversity and enhancing the sustainability of exploited fish populations. Numerous studies have documented positive ecological and socio-economic benefits of NTRs; however, the ability of NTRs to ameliorate the effects of acute disturbances on coral reefs has seldom been investigated. Here, we test these factors by tracking the dynamics of benthic and fish communities, including the important fishery species, coral trout (Plectropomus spp.), over 8 years in both NTRs and fished areas in the Keppel Island group, Great Barrier Reef, Australia. Two major disturbances impacted the reefs during the monitoring period, a coral bleaching event in 2006 and a freshwater flood plume in 2011. Both disturbances generated significant declines in coral cover and habitat complexity, with subsequent declines in fish abundance and diversity, and pronounced shifts in fish assemblage structure. Coral trout density also declined in response to the loss of live coral, however, the approximately 2:1 density ratio between NTRs and fished zones was maintained over time. The only post-disturbance refuges for coral trout spawning stocks were within the NTRs that escaped the worst effects of the disturbances. Although NTRs had little discernible effect on the temporal dynamics of benthic or fish communities, it was evident that the post-disturbance refuges for coral trout spawning stocks within some NTRs may be critically important to regional-scale population persistence and recovery.

High frequency variability of environmental drivers determining benthic community dynamics in headwater streams

Headwater streams are an important feature of the landscape, with their diversity in structure and associated ecological function providing a potential natural buffer against downstream nutrient export. Phytobenthic communities, dominated in many headwaters by diatoms, must respond to physical and chemical parameters that can vary in magnitude within hours, whereas the ecological regeneration times are much longer. How diatom communities develop in the fluctuating, dynamic environments characteristic of headwaters is poorly understood. Deployment of near-continuous monitoring technology in sub-catchments of the River Eden, NW England, provides the opportunity for measurement of temporal variability in stream discharge and nutrient resource supply to benthic communities, as represented by monthly diatom samples collected over two years. Our data suggest that the diatom communities and the derived Trophic Diatom Index, best reflect stream discharge conditions over the preceding 18-21 days and Total Phosphorus concentrations over a wider antecedent window of 7-21 days. This is one of the first quantitative assessments of long-term diatom community development in response to continuously-measured stream nutrient concentration and discharge fluctuations. The data reveal the sensitivity of these headwater communities to mean conditions prior to sampling, with flow as the dominant variable. With sufficient understanding of the role of antecedent conditions, these methods can be used to inform interpretation of monitoring data, including those collected under the European Water Framework Directive and related mitigation efforts.

Micro-topography mediates interactions between corals, algae, and herbivorous fishes on coral reefs

Processes occurring during the early life stages of corals are important for the replenishment of coral assemblages and the resilience of coral reefs. However, the factors influencing early life stages of corals are not well understood, and the role of micro-topographic complexity for habitat associations of juvenile corals is largely unexplored. This study investigated the microhabitat distribution patterns of early life stages of corals and a potential macroalgal competitor (Turbinaria ornata) across two reef zones (reef crest and outer reef flat) on Lizard Island, Great Barrier Reef. In both reef zones, both corals and T. ornata were significantly more abundant in concealed microhabitats than in semi-concealed or open microhabitats (GLMM: P < 0.001). The prevalence of juvenile corals and T. ornata within concealed environments suggests that they might be effective refuges from grazing by herbivorous fishes. The density of juvenile corals was positively related, and density of T. ornata negatively related to the abundance of two groups of herbivorous fishes, pairing rabbitfishes, and surgeonfishes in the genus Zebrasoma (BEST ENV-BIO: r s = 0.72, P < 0.01), which feed in concealed microhabitats. This correlative evidence suggests that crevices may be important for early life stages of both coral and macroalgae, and that a specific suite of crevice-feeding fishes may influence benthic community dynamics in these microhabitats.

Environmental drivers of macroinvertebrate communities in high Arctic rivers (Svalbard)

Summary The impacts of climate‐induced environmental changes on freshwater biodiversity are not well understood in Arctic regions. We quantified water source contributions (meltwater, ground water), environmental habitat conditions and benthic macroinvertebrate community dynamics in north‐west Svalbard. The aim was to use contemporary findings to infer how future environmental change may affect these Arctic river ecosystems. Water source dynamics played an important role in influencing environmental habitat conditions; meltwater contributions to flow were related significantly to discharge, channel stability, electrical conductivity and pH. Low regional benthic macroinvertebrate diversity relative to other Arctic regions was attributed to harsh winter conditions and biogeographical dispersal constraints associated with the Svalbard archipelago. Generalised estimating equations and multivariate ordination models showed benthic macroinvertebrate diversity and abundance were influenced significantly by several environmental habitat variables. Rivers in non‐glacierised basins typically supported more diverse and abundant communities than those in glacierised basins, most likely as a consequence of the warmer water temperature and less‐disturbed habitat conditions associated with these systems. Consequently, shifts in water source contributions driven by changes in climate may alter environmental habitat conditions in Svalbard rivers and could lead to an increase in abundance and diversity among some freshwater macroinvertebrate communities.

Seasonal dynamics of molluscan assemblages associated with littoral soft bottoms of the NW Alboran Sea (Western Mediterranean Sea)

Molluscan assemblages inhabiting subtidal soft bottoms in the northwestern Alboran Sea were studied to analyse temporal changes in structure and composition. A total of 117 samples were collected seasonally using a small rock dredge at 10 sampling stations, yielding 210 mollucan species. The assemblages occurring on the different soft bottoms were well-sorted fine sands assemblage (SFBC), mixed coarse sands assemblage (MX), muddy bioclastic sands assemblage (DE) and coastal bioclastic sands assemblage (DC), and all displayed high species richness values throughout the year. Different seasonal dynamics were observed and ecological indices were influenced by dominant species, especially the bivalve Spisula subtruncata at the shallow stations and the gastropods Calyptraea chinensis and Nassarius reticulatus at the deeper stations. SFBC displayed maximum abundance (N), species richness (S) and Shannon–Wiener diversity (H′) in autumn, DE and MX displayed maximum N and S in spring but maximum H′ in autumn (DE) and winter (MX), and finally DC displayed stable values of ecological indices throughout the year with minima in spring. Seasonal changes in the deep assemblages (25 m) were not significant and therefore less acute than those of shallower ones (5, 15 m), probably due to a lower influence of the environmental conditions and a higher habitat complexity. Seasonal patterns were somewhat different from those observed in more northern areas of Europe, where maximum abundance and species richness is usually concentrated at the end of summer. This original information will provide a baseline to understand the dynamics of benthic communities in this area.

Aluminum sulfate (alum) application interactions with coupled metal and nutrient cycling in a hypereutrophic lake ecosystem

Many lake ecosystems worldwide experience severe eutrophication and associated harmful blooms of cyanobacteria due to high loadings of phosphorus (P). While aluminum sulfate (alum) has been used for decades as chemical treatment of eutrophic waters, the ecological effects of alum on coupled metal and nutrient cycling are not well known. The objective of our study was to investigate the effects of an in-situ alum treatment on aluminum and nutrient (P, N, and S) cycling in a hypereutrophic lake ecosystem. Our results indicate that the addition of alum along with sodium aluminate (as a buffer) increased dissolved aluminum and sulfate in the surface and pore waters, and altered nitrogen cycling by increasing nitrous oxide (N2O) concentrations in the surface water. The increase of aluminum and sulfate may potentially feedback to alter benthic community dynamics. These results enhance our understanding of the unintended ecological consequences of alum treatments in hypereutrophic freshwater ecosystems.