Flow-through Mesocosms Research Articles

Detection, movement and persistence of invertebrate eDNA in groundwater

Sampling groundwater biodiversity is difficult because of limited access and issues with species identification. Environmental DNA (eDNA) provides a viable alternative to traditional sampling approaches, however limited knowledge of the abundance and fate of DNA in groundwater hinders the interpretation of data from these environments. Groundwater environments are dark and have lower oxygen concentrations and microbial activity than surface waters. Consequently, assumptions about DNA fate in surface ecosystems may not apply to groundwaters. Here, we test the longevity and transport of eDNA in groundwater within a static microcosm and a flow-through mesocosm. A variety of invertebrates were placed within a mesocosm and microcosm to enable DNA shedding, and then removed. DNA persisted for up to 5 weeks after their removal in the static experiment and was detected between 9 and 33 days in the flow-through experiment. Sediments and water both proved important for eDNA detection. Crustacean DNA was detected sporadically and unpredictably, whereas non-crustacean DNA was detected more frequently despite their lower densities. We suggest that detecting crustaceans poses a challenge to utilising eDNA approaches for stygofauna monitoring. This is confounded by the scarcity of sequences for stygofauna in reference databases. Further research is needed before eDNA alone can be routinely employed for stygofauna detection.

Marine degradation and ecotoxicity of conventional, recycled and compostable plastic bags

Plastic bags are currently a major component of marine litter, causing aesthetical nuisance, and undesirable effects on marine fauna that ingest them or are entangled. Plastic litter also rises concern on the ecotoxicological effects due to the potential toxicity of the chemical additives leached in aquatic environments. Conventional plastic bags are made of polyethylene, either from first use or recycled, but regulations restricting single-use plastics and limiting lightweight carrier bags (<50 μm thickness) have fostered the replacement of thin PE bags by compostable materials advertised as safer for the environment. In this study, we assess the degradation of commercially available plastic bags in marine conditions at two scales: aquariums (60 days) and outdoors flow-through mesocosm (120 days). Strength at break point and other tensile strength parameters were used as ecologically relevant endpoints to track mechanical degradation. Ecotoxicity has been assessed along the incubation period using the sensitive Paracentrotus lividus embryo test. Whereas PE bags did not substantially lose their mechanical properties within the 60 d aquarium exposures, compostable bags showed remarkable weight loss and tensile strength decay, some of them fragmenting in the aquarium after 3–4 weeks. Sediment pore water inoculum promoted a more rapid degradation of compostable bags, while nutrient addition pattern did not affect the degradation rate. Longer-term mesocosms exposures supported these findings, as well as pointed out the influence of the microbial processes on the degradation efficiency of compostable/bioplastic bags. Compostable materials, in contrast toPE, showed moderate toxicity on sea-urchin larvae, partially associated to degradation of these materials, but the environmental implications of these findings remain to be assessed. These methods proved to be useful to classify plastic materials, according to their degradability in marine conditions, in a remarkably shorter time than current standard tests and promote new materials safer for the marine fauna.

The role of calcium and alkalinity on phosphorus removal by submerged aquatic vegetation in hardwater wetlands

The Everglades Stormwater Treatment Areas (STAs) are a 25,000 ha (61,000 acre) complex of constructed wetlands built to remove phosphorus (P) from agricultural and urban runoff in support of Everglades restoration. These STAs treat inflow waters that contain P in concentrations from 100 to 200 μg L−1, average calcium (Ca) concentrations of 60–90 mg L−1, and alkalinity (Alk) in the range of 150–350 mg L−1 as calcium carbonate (CaCO3). Photosynthesis, primarily from submerged aquatic vegetation (SAV) within these STAs, increases water pH resulting in CaCO3 formation, which is thought to contribute to P removal through coprecipitation and other processes. Since 2002, the STA complex has removed over 3000 MT of P and over 400,000 MT of Ca. Because the STAs at times treat Lake Okeechobee waters that are lower in Ca and Alk (35–50 mg L−1 and 95–125 mg L−1 as CaCO3, respectively), we conducted two experiments to explore the role of Ca and Alk on wetland P removal.First, in outdoor flow-through microcosms (0.18 m2) containing Najas guadalupensis and treating artificial inflow solutions, Ca/Alk at typical STA inflow concentrations (77 mg Ca L−1/316 mg L−1 as CaCO3) resulted in significantly lower outflow P concentrations compared to lower Ca/Alk treatments (28 mg Ca L−1/67 mg L−1 as CaCO3). Based on sediment organic carbon to total P (TP) ratios, organic matter production and sedimentation was the P removal mechanism under low Ca/Alk levels, where CaCO3 precipitation did not occur, and also under high Ca/Alk, low P (31 μg L−1) conditions, despite CaCO3 formation. High Ca/Alk increased organic matter sedimentation and associated P burial at low and high (168 μg L−1) water P concentrations. Additional P removal associated with CaCO3 precipitation occurred only under high Ca/Alk, high P concentrations, and accounted for about 47% of P sedimentation in those microcosms.Second, in flow-through mesocosms (4.75 m2) containing STA muck soil and common STA SAV species, elevated Ca/Alk (94 mg Ca L−1/185 mg L−1 as CaCO3) produced significantly lower outflow TP concentrations than treatments receiving unamended Lake Okeechobee inflow water with lower Ca/Alk concentrations (44 mg Ca L−1/112 mg L−1 as CaCO3). In the same experiment, Ca/Alk levels had no effect on P removal in mesocosms containing Typha domingensis, a common STA emergent macrophyte species. SAV mesocosms produced lower outflow TP concentrations than Typha, regardless of Ca/Alk levels. In a follow-on laboratory incubation, low Ca/Alk concentrations in incubation waters did not increase P release from sediments formed under prior low or high inflow Ca/Alk concentrations in the SAV mesocosms, but anoxia sharply increased P release from both.These experiments suggest that coprecipitation with CaCO3 is a meaningful P removal process in hardwater wetlands where high P concentrations and SAV coincide. Conversely, in STA outflow regions, where surface water P has already been treated to a low level, coprecipitation with CaCO3 probably does not contribute to further P reductions. However, Ca/Alk also may contribute to inorganic-C availability which influences submerged aquatic productivity, so the role of inorganic C limitation on STA vegetation communities and P removal merits further study.

Multistressor global change drivers reduce hatch and viability of Lingcod embryos, a benthic egg layer in the California Current System

Early life history stages of marine fishes are often more susceptible to environmental stressors than adult stages. This vulnerability is likely exacerbated for species that lay benthic egg masses bound to substrate because the embryos cannot evade locally unfavorable environmental conditions. Lingcod (Ophiodon elongatus), a benthic egg layer, is an ecologically and economically significant predator in the highly-productive California Current System (CCS). We ran a flow-through mesocosm experiment that exposed Lingcod eggs collected from Monterey Bay, CA to conditions we expect to see in the central CCS by the year 2050 and 2100. Exposure to temperature, pH, and dissolved oxygen concentrations projected by the year 2050 halved the successful hatch of Lingcod embryos and significantly reduced the size of day-1 larvae. In the year 2100 treatment, viable hatch plummeted (3% of normal), larvae were undersized (83% of normal), yolk reserves were exhausted (38% of normal), and deformities were widespread (94% of individuals). This experiment is the first to expose marine benthic eggs to future temperature, pH, and dissolved oxygen conditions in concert. Lingcod are a potential indicator species for other benthic egg layers for which global change conditions may significantly diminish recruitment rates.

Use of a wastewater recovery product (struvite) to enhance subtropical seagrass restoration.

Seagrasses are in decline worldwide, and their restoration is relatively expensive and unsuccessful compared to other coastal systems. Fertilization can improve seagrass growth in restoration but can also release nutrients and pollute the surrounding ecosystem. A slow-release fertilizer may reduce excessive nutrient discharge while still providing resources to the seagrass's rhizosphere. In this study, struvite (magnesium ammonium phosphate), a relatively insoluble, sustainable compound harvested in wastewater treatment plants, was compared to Osmocote™(14:14:14 Nitrogen: Phosphorus: Potassium, N:P:K), a popular polymer coated controlled release fertilizer commonly used in seagrass restoration. Two experiments compared the effectiveness of both fertilizers in a subtropical flow-through mesocosm setup. In the first experiment, single 0.5 mg of P per g dry weight (DW) doses of Osmocote™and struvite fertilizers were added to seagrass plots. Seagrass shoot counts were significantly higher in plots fertilized with struvite than both the Osmocote™and unfertilized controls (p< 0.0001). A significant difference in total P concentration was observed in porewater samples of Osmocote™vs struvite and controls (p< 0.0001), with struvite fertilized plots emitting more than controls (p ≤ 0.0001), but less than 2% of the total dissolved P (TDP) of Osmocote™fertilized plots (100+ mg/L versus x > 5 mg/L). A subsequent experiment, using smaller doses (0.01 and 0.025 mg of P per gram DW added), also found that the struvite treatments performed better than Osmocote™, with 16-114% more aboveground biomass (10-60% higher total biomass) while releasing less N and P. These results indicate the relatively rapid dissolution of Osmocote™may pose problems to restoration efforts, especially in concentrated doses and possibly leading to seagrass stress. In contrast, struvite may function as a slow-release fertilizer applicable in seagrass and other coastal restoration efforts.

Production of dissolved carbon and alkalinity during macroalgal wrack degradation on beaches: a mesocosm experiment with implications for blue carbon

Marine macroalgae are a key primary producer in coastal ecosystems, but are often overlooked in blue carbon inventories. Large quantities of macroalgal detritus deposit on beaches, but the fate of wrack carbon (C) is little understood. If most of the wrack carbon is respired back to CO2, there would be no net carbon sequestration. However, if most of the wrack carbon is converted to bicarbonate (alkalinity) or refractory DOC, wrack deposition would represent net carbon sequestration if at least part of the metabolic products (e.g., reduced Fe and S) are permanently removed (i.e., long-term burial) and the DOC is not remineralised. To investigate the release of macroalgal C via porewater and its potential to contribute to C sequestration (blue carbon), we monitored the degradation of Ecklonia radiata in flow-through mesocosms simulating tidal flushing on sandy beaches. Over 60 days, 81% of added E. radiata organic matter (OM) decomposed. Per 1 mol of detritus C, the degradation produced 0.48 ± 0.34 mol C of dissolved organic carbon (DOC) (59%) and 0.25 ± 0.07 mol C of dissolved inorganic carbon (DIC) (31%) in porewater, and a small amount of CO2 (0.3 ± 0.0 mol C; ca. 3%) which was emitted to the atmosphere. A significant amount of carbonate alkalinity was found in porewater, equating to 33% (0.27 ± 0.05 mol C) of the total degraded C. The degradation occurred in two phases. In the first phase (days 0–3), 27% of the OM degraded, releasing highly reactive DOC. In the second phase (days 4–60), the labile DOC was converted to DIC. The mechanisms underlying E. radiata degradation were sulphate reduction and ammonification. It is likely that the carbonate alkalinity was primarily produced through sulphate reduction. The formation of carbonate alkalinity and semi-labile or refractory DOC from beach wrack has the potential to play an overlooked role in coastal carbon cycling and contribute to marine carbon sequestration.Graphical abstract

Influence of amino acid concentrations on foraging and feeding in the rusty crayfish Faxonius rusticus (Girard, 1852) (Decapoda: Astacidea: Cambaridae), assayed in flow-through mesocosms

Abstract Organisms use chemical cues in their environment to extract relevant information to perform a variety of tasks, including foraging, finding shelter, and locating mates, and must locate and assess the quality of food sources based on these chemical cues. Crayfishes use chemical cues in the form of amino acids to locate food and to regulate consumption when determining the quality of food sources. It is currently unknown, however, whether crayfish foraging and feeding behavior in experimental flow-through systems are altered by differing amino acid concentrations. We collected individuals of the rusty crayfish, Faxonius rusticus (Girard, 1852), from two different watershed locations in Michigan, USA and exposed them to fish gelatin containing increasing concentrations of the amino acids β-alanine (excitatory amino acid) and L-tyrosine (inhibitory amino acid). The gelatin was weighed before and after each 24-hour trial to determine consumption. The addition of an excitatory amino acid (β-alanine) caused a significant drop in consumption but only for crayfish collected from one of the locations (P = 0.04). The addition of an inhibitory amino acid (L-tyrosine) had no effect on consumption from either location. This study demonstrates that feeding behaviors of F. rusticus are influenced by the presence of amino acids (β-alanine) in food sources.

Natural inactivation of MS2, poliovirus type 1 and Cryptosporidium parvum in an anaerobic and reduced aquifer

The study of microbial inactivation rates in aquifer systems has most often been determined in aerobic and oxidized systems. This study examined the inactivation (i.e. loss of infectivity) of MS2, poliovirus type 1 (PV1) and Cryptosporidium parvum in an anaerobic and reduced groundwater system that has been identified as storage zones for aquifer storage and recovery (ASR) facilities. Anaerobic and reduced (ORP<- 250mV) groundwater from an artesian well was diverted to an above-ground, flow-through mesocosm that contained diffusion chambers filled with MS2, PV1 or Cryptosporidium parvum. The respective infectivity assays were performed on microorganisms recovered from the diffusion chambers during 30- to 58-day experiments. The net reduction in infectivity was 5.73log10 over 30days for MS2, 5.00log10 over 58days for PV1 and 4.07log10 over 37days for C. parvum. The best fit inactivation model for PV1 was the log-linear model and the Weibull model for MS2 and C. parvum, with respective inactivation rates (95% confidence interval) of 0.19 (0.17-0.21) log10 day-1 , 0.31 (0.19-0.89) log10 day-1 and 0.20 (0.14-0.37) log10 day-1 . The groundwater geochemical conditions in this aquifer enhanced the inactivation ofMS2, PV1, and C. parvum at rates approximately 2.0-5.3-fold, 1.2-17.0-fold, and 4.5-5.6-fold greater, respectively, than those from published studies that used diffusion chambers in aerobic-to-anoxic groundwater systems, with positive redox potentials. Geochemical conditions like those in the aquifer zone in this study can naturally and significantly reduce concentrations of microbial indicators and pathogens of human health concern in injected surface water. Appropriate storage times for injected surface water could complement above-ground engineered processes for microorganism removal and inactivation (e.g. filtration, disinfection) by naturally increasing overall microorganism log-inactivation rates of ASR facilities.

The impact of climate change and eutrophication on phosphorus forms in sediment: Results from a long-term lake mesocosm experiment

Characteristics of bottom sediments in lake mesocosms 11 years after starting the experiment were studied in order to determine the effects of nutrient loading, temperature increase and vegetation type on concentration and vertical distribution of phosphorus (P) forms. The experimental setup consisted of 24 outdoor flow-through mesocosms with two nutrient treatments – low (L) and high (H) and 3 temperature levels – ambient (T0), heated by 2–4 °C (T1) and 3–6 °C (T2) in four replicates. Thickness of the organic sediment was measured and the sediment analysed for dry weight, organic matter, and P fractions (according to a sequential extraction scheme) and organic P compounds (by 31P nuclear magnetic resonance spectroscopy). Higher nutrient loading led to increased sediment accumulation and higher concentration of total P and most P fractions, except P bound to aluminium and humic matter. The dominant vegetation type covaried with nutrient levels. Vertical gradients in Ca bound P and mobile P in low nutrient mesocosms was perhaps a result of P coprecipitation with calcite on macrophytes and P uptake by roots indicating that in macrophyte-rich lakes, plants can be important modifiers of early P diagenesis. Temperature alone did not significantly affect sediment accumulation rate but the interaction effect between nutrient and temperature treatments was significant. At high nutrient loading, sediment thickness decreased with increasing temperature, but at low nutrient loading, it increased with warming. The effect of warming on sediment composition became obvious only in nutrient enriched mesocosms showing that eutrophication makes shallow lake ecosystems more susceptible to climate change.

Impact of Nutrients, Temperatures, and a Heat Wave on Zooplankton Community Structure: An Experimental Approach

Shallow lakes are globally the most numerous water bodies and are sensitive to external perturbations, including eutrophication and climate change, which threaten their functioning. Extreme events, such as heat waves (HWs), are expected to become more frequent with global warming. To elucidate the effects of nutrients, warming, and HWs on zooplankton community structure, we conducted an experiment in 24 flow-through mesocosms (1.9 m in diameter, 1.0 m deep) imitating shallow lakes. The mesocosms have two nutrient levels (high (HN) and low (LN)) crossed with three temperature scenarios based on the Intergovernmental Panel on Climate Change (IPCC) projections of likely warming scenarios (unheated, A2, and A2 + 50%). The mesocosms had been running continuously with these treatments for 11 years prior to the HW simulation, which consisted of an additional 5 °C increase in temperature applied from 1 July to 1 August 2014. The results showed that nutrient effects on the zooplankton community composition and abundance were greater than temperature effects for the period before, during, and after the HW. Before the HW, taxon richness was higher, and functional group diversity and evenness were lower in HN than in LN. We also found a lower biomass of large Cladocera and a lower zooplankton: phytoplankton ratio, indicating higher fish predation in HN than in LN. Concerning the temperature treatment, we found some indication of higher fish predation with warming in LN, but no clear effects in HN. There was a positive nutrient and warming interaction for the biomass of total zooplankton, large and small Copepoda, and the zooplankton: phytoplankton ratio during the HW, which was attributed to recorded HW-induced fish kill. The pattern after the HW largely followed the HW response. Our results suggest a strong nutrient effect on zooplankton, while the effect of temperature treatment and the 5 °C HW was comparatively modest, and the changes likely largely reflected changes in predation.

Fine sediment and flow velocity impact bacterial community and functional profile more than nutrient enrichment.

Freshwater ecosystems face many simultaneous pressures due to human activities. Consequently, there has been a rapid loss of freshwater biodiversity and an increase in biomonitoring programs. Our study assessed the potential of benthic stream bacterial communities as indicators of multiple-stressor impacts associated with urbanization and agricultural intensification. We conducted a fully crossed four-factor experiment in 64 flow-through mesocosms fed by a pristine montane stream (21d of colonization, 21d of manipulations) and investigated the effects of nutrient enrichment, flow-velocity reduction and added fine sediment after 2 and 3weeks of stressor exposure. We used high-throughput sequencing and metabarcoding techniques (16S rRNA genes), as well as curated biological databases (METAGENassit, MetaCyc), to identify changes in bacterial relative abundances and predicted metabolic functional profile. Sediment addition and flow-velocity reduction were the most pervasive stressors. They both increased α-diversity and had strong taxon-specific effects on community composition and predicted functions. Sediment and flow velocity also interacted frequently, with 88% of all bacterial response variables showing two-way interactions and 33% showing three-way interactions including nutrient enrichment. Changes in relative abundances of common taxa were associated with shifts in dominant predicted functions, which can be extrapolated to underlaying stream-wide mechanisms such as carbon use and bacterial energy production pathways. Observed changes were largely stable over time and occurred after just 2weeks of exposure, demonstrating that bacterial communities can be well-suited for early detection of multiple stressors. Overall, added sediment and reduced flow velocity impacted both bacterial community structure and predicted function more than nutrient enrichment. In future research and stream management, a holistic approach to studying multiple-stressor impacts should include multiple trophic levels with their functional responses, to enhance our mechanistic understanding of complex stressor effects and promote establishment of more efficient biomonitoring programs.

Degradation of RDX (Hexahydro-1,3,5-trinitro-1,3,5-triazine) in contrasting coastal marine habitats: Subtidal non-vegetated (sand), subtidal vegetated (silt/eel grass), and intertidal marsh

Hundreds of explosive-contaminated marine sites exist globally, many of which contain the common munitions constituent hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Quantitative information about RDX transformation in coastal ecosystems is essential for management of many of these sites. Isotopically labelled RDX containing 15N in all 3 nitro groups was used to track the fate of RDX in three coastal ecosystem types. Flow-through mesocosms representing subtidal vegetated (silt/eel grass), subtidal non-vegetated (sand) and intertidal marsh ecosystems were continuously loaded with isotopically labelled RDX for 16–17 days. Sediment, pore-water and overlying surface water were analyzed to determine the distribution of RDX, nitroso-triazine transformation products (NXs) and nitrogen containing complete mineralization products, including ammonium, nitrate+nitrite, nitrous oxide and nitrogen gas. The marsh, silt, and sand ecotypes transformed 94%, 90% and 76% of supplied RDX, respectively. Total dissolved NXs accounted for 2%–4% of the transformed 15N-RDX. The majority of RDX transformation in the water column was by mineralization to inorganic N (dissolved and evaded; 64%–78% of transformed 15N-RDX). RDX was mineralized primarily to N2O (62–74% of transformed 15N-RDX) and secondarily to N2 (1–2% of transformed 15N-RDX) which exchanged with the atmosphere. Transformation of RDX was favored in carbon-rich lower redox potential sediments of the silt and marsh mesocosms where anaerobic processes of iron and sulfate reduction were most prevalent. RDX was most persistent in the carbon-poor sand mesocosm. Partitioning of 15N derived from RDX onto sediment and suspended particulates was negligible in the overall mass balance of RDX transformation (2%–3% of transformed 15N-RDX). The fraction of 15N derived from RDX that was sorbed or assimilated in sediment was largest in the marsh mesocosm (most organic carbon), and smallest in the sand mesocosm (largest grain size and least organic carbon). Sediment redox conditions and available organic carbon stores affect the fate of RDX in different coastal marine habitats.

Effect of species diversity on particle clearance and productivity in farmed bivalves

Most bivalve farms are designed as monocultures, yet diverse communities often outperform monocultures in various metrics of ecosystem functioning, including particle clearance and productivity. This study tested the feasibility of bivalve polyculture by examining particle clearance, growth, and survival of 4 species that are economically important to the northeastern USA. Three particle depletion experiments were conducted to determine if more diverse bivalve assemblages had greater clearance rates than those which were less diverse. Different assemblages of Crassostrea virginica, Spisula solidissima, Mercenaria mercenaria, and Mya arenaria were supplied with a single cultured algal species, a mix of 2 cultured algal species, or natural seston. To determine how species richness affects bivalve productivity, growth and survival were monitored in a flow-through mesocosm experiment, which simulated farm conditions. In the cultured algae experiments, more diverse assemblages did not exhibit significantly greater clearance rates than those that were less diverse. Instead, the clearance rates of each species were additive across assemblages. Surprisingly, most assemblages did not display a significant preference for the larger microalgae species, Pavlova lutheri (4.0-6.0 µm), over Nannochloropsis oculata (1.90-3.75 µm). Most notably, when supplied with natural seston, the 4-species polyculture demonstrated a significantly greater tank-level clearance rate for particles &lt;25 µm compared to most monocultures. However, nearly all productivity metrics were not significantly affected by species richness. This work suggests that some degree of complementarity exists among these bivalves, and that in non-food limited systems, these bivalves could be co-cultured without outcompeting one another.

Effect of filter-feeding mollusks on growth of green macroalgae and nutrient cycling in a heavily exploited coastal lagoon

An increasing number of coastal lagoons are being exploited for intensive farming of bivalve filter-feeders. One of the most important farming sites in Europe for the Manila clam (Ruditapes philippinarum) is the Sacca di Goro lagoon (Po River Delta, Italy). Here, while on the one hand river runoff enhances high clam productivity, on the other hand it stimulates extensive blooms of green seaweeds of the genus Ulva. The latter can affect clams when macroalgal biomass collapses and decomposes. We hypothesized that the filtration of suspended particulate matter by farmed clams could enhance inorganic nitrogen and phosphorus recycling and simultaneously reduce phytoplankton biomass, thus facilitating macroalgal growth. An experiment simulating the effects of clams on early Ulva development was conducted over 7 days in outdoor flow-through mesocosms containing lagoon sediments with and without clams. On day 1, 3 and 7, macroalgal biomass and thallus elemental composition, water-dissolved nutrients and chlorophyll-a concentrations were recorded. On day 7, sediment-water nutrient fluxes were also measured on sediment cores sampled from each mesocosm. The presence of clams clearly stimulated Ulva growth and enhanced nutrient recycling rates. Furthermore, Ulva grown with clams had higher chlorophyll-a, nitrogen and phosphorus content. While sediments showed a net release of both soluble reactive phosphorus and ammonium when clams were present, in mesocosms without clams sediments constituted a sink for both dissolved inorganic phosphorus and nitrogen. Based on this evidence we can conclude that intensive clam farming over wide lagoon areas could significantly affect nutrient cycling, thus facilitating macroalgal blooms, with serious consequences for farming sustainability and for the functioning of the whole lagoon ecosystem.

Abundance, size, and survival of recruits of the reef coral Pocillopora acuta under ocean warming and acidification.

Ocean warming and acidification are among the greatest threats to coral reefs. Massive coral bleaching events are becoming increasingly common and are predicted to be more severe and frequent in the near future, putting corals reefs in danger of ecological collapse. This study quantified the abundance, size, and survival of the coral Pocillopora acuta under future projections of ocean warming and acidification. Flow-through mesocosms were exposed to current and future projections of ocean warming and acidification in a factorial design for 22 months. Neither ocean warming or acidification, nor their combination, influenced the size or abundance of P. acuta recruits, but heating impacted subsequent health and survival of the recruits. During annual maximum temperatures, coral recruits in heated tanks experienced higher levels of bleaching and subsequent mortality. Results of this study indicate that P. acuta is able to recruit under projected levels of ocean warming and acidification but are susceptible to bleaching and mortality during the warmest months.

Anthropogenic stressors affect fungal more than bacterial communities in decaying leaf litter: A stream mesocosm experiment.

Despite the progress made in environmental microbiology techniques and knowledge, the succession and functional changes of the microbial community under multiple stressors are still poorly understood. This is a substantial knowledge gap as microbial communities regulate the biogeochemistry of stream ecosystems. Our study assessed the structural and temporal changes in stream fungal and bacterial communities associated with decomposing leaf litter under a multiple-stressor scenario. We conducted a fully crossed 4-factor experiment in 64 flow-through mesocosms fed by a pristine montane stream (21 days of colonisation, 21 days of manipulations) and investigated the effects of nutrient enrichment, flow velocity reduction and sedimentation after 2 and 3 weeks of stressor exposure. We used high-throughput sequencing and metabarcoding techniques (16S and 18S rRNA genes) to identify changes in microbial community composition. Our results indicate that (1) shifts in relative abundances of the pre-existing terrestrial microbial community, rather than changes in community identity, drove the observed responses to stressors; (2) changes in relative abundances within the microbial community paralleled decomposition rate patterns with time; (3) both fungal and bacterial communities had a certain resistance to stressors, as indicated by relatively minor changes in alpha diversity or multivariate community structure; (4) overall, stressor interactions were more common than stressor main effects when affecting microbial diversity metrics or abundant individual genera; and (5) stressor effects on microbes often changed from 2 weeks to 3 weeks of stressor exposure, with several response patterns being reversed. Our study suggests that future research should focus more on understanding the temporal dynamics of fungal and bacterial communities and how they relate to ecosystem processes to advance our understanding of the mechanisms associated with multiple-stressor interactions.

Restoring the flat oyster Ostrea angasi in the face of a changing climate

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 625:27-39 (2019) - DOI: https://doi.org/10.3354/meps13047 Restoring the flat oyster Ostrea angasi in the face of a changing climate Roberta R. C. Pereira1, Elliot Scanes1, Laura M. Parker1,3, Maria Byrne1,2, Victoria J. Cole1,4, Pauline M. Ross1,* 1School of Life and Environmental Science, The University of Sydney, Camperdown, NSW 2006, Australia 2School of Medical Sciences, The University of Sydney, Camperdown, NSW 2006, Australia 3Present address: The University of New South Wales, School of Biological Earth and Environmental Sciences, Kensington, NSW 2052, Australia 4Present address: Port Stephens Fisheries Institute, Department of Primary Industries, Taylors Beach, NSW 2316, Australia *Corresponding author: pauline.ross@sydney.edu.au ABSTRACT: Across the globe, restoration efforts are stemming the loss of native oyster reefs and the ecosystem services they provide, but these efforts will need to consider climate change in order to be sustainable. South-eastern Australia is the focus of restoring the once abundant oyster Ostrea angasi. This region is also a climate change ‘hot spot’ where the ocean is warming rapidly, with the potential to be exacerbated by marine heatwaves and coastal acidification. In this study, the impact of near-future (~2050) elevated temperature and pCO2 on O. angasi was determined and considered in context with concerns for the long-term sustainability of oyster reef restoration efforts. Oysters were exposed to ambient and elevated pCO2 concentrations (mean ± SE: 408 ± 19.8 and 1070 ± 53.4 µatm) and ambient and elevated temperatures (22.78 ± 0.17 and 25.73 ± 0.21°C) for 10 wk in outdoor flow-through mesocosms. Shell growth, condition index, standard metabolic rate (SMR), extracellular pH and survival were measured. Elevated temperature caused high mortality (36%) and decreased the condition of oysters (33%). Elevated pCO2 increased SMR almost 4-fold and lowered the extracellular pH of O. angasi by a mean 0.29 pH units. In combination, elevated pCO2 and temperature ameliorated effects on SMR and survivorship of oysters. O. angasi appears to be living near the limits of its thermal tolerance. Restoration projects will need to account for the temperature sensitivity of this species and its changing habitat to ‘climate proof’ long-term restoration efforts. KEY WORDS: Reef restoration · Ostrea angasi · Ocean warming · Ocean acidification · Climate change · Flat oysters · Aquaculture · Physiology Full text in pdf format PreviousNextCite this article as: Pereira RRC, Scanes E, Parker L, Byrne M, Cole VJ, Ross PM (2019) Restoring the flat oyster Ostrea angasi in the face of a changing climate. Mar Ecol Prog Ser 625:27-39. https://doi.org/10.3354/meps13047 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 625. Online publication date: August 29, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

An assessment of iron and calcium amendments for managing phosphorus release from impacted Everglades soils

The recent implementation of agricultural best management practices (BMPs) and treatment wetlands called stormwater treatment areas (STAs) have reduced phosphorus (P) concentrations and loadings to the Everglades Protection Area (EPA) in Florida (USA). There is a concern that despite reductions in external P loadings, internal loading from the legacy P enrichment of the EPA wetland soils will continue to elevate water column P concentrations, and may impede restoration outcomes. In an effort to explore ways to reduce soil P efflux, we retrieved intact, vegetated (cattail, Typha domingensis) soil monoliths from two P-enriched areas of the EPA and deployed them at a location where they received pre-treated (low P) surface water as ex situ flow-through mesocosms for 21 months with a mid-study 7-week dry down to mimic natural hydroperiod conditions. Two treatments were tested for soils from both sites, using triplicate mesocosms for each treatment. After applying a herbicide (glyphosate) to eliminate the cattail vegetation, iron (Fe as liquid FeCl3) amendments provided no P retention benefits in the organic soils from the two sites, and did not yield significantly (P > 0.05; n = 43) lower flux rates (6.1 and 3.5 mg Pm−2 d−1) than the herbicide/no soil amendment control (3.9 and 2.1 mg Pm−2 d−1), as was expected. A combination of low oxidation–reduction potential, heightened organic matter P mineralization, high pH, and sulfide production acted interactively to enhance Fe and P mobilization in the Fe-amended mesocosms. The herbicide/limerock (CaCO3)-amended soils exhibited significantly lower (P ≤ 0.05; n = 43) P flux (1.3 and 1.1 mg Pm−2 d−1) than the herbicide/no soil amendment control soils, but it remains unknown whether the observed reduction in P efflux (ranging from 48 to 67%) would justify the expense and potential environmental impacts of applying a surficial limerock amendment to large regions of the P-enriched wetlands.

Warming and nutrient enrichment in combination increase stochasticity and beta diversity of bacterioplankton assemblages across freshwater mesocosms.

The current climate warming and eutrophication are known to interactively threaten freshwater biodiversity; however, the interactive effects on lacustrine bacterioplankton diversity remain to be determined. Here, we analyzed the spring bacterioplankton community composition (BCC) in 24 outdoor, flow-through mesocosms (mimicking shallow lake environments) under 3 temperature scenarios and 2 nutrient regimes. Our results revealed that neither long-term warming (8.5 years) nor nutrient enrichment had significant effects on bacterioplankton alpha diversity, whereas long-term enhanced warming (elevated 50% above the IPCC A2 climate scenario) and nutrient enrichment in combination increased bacterioplankton beta diversity. We also found that BCC shifted significantly under enhanced warming and nutrient-enriched conditions towards decreased relative abundances of Actinobacteria, Bacteroidetes and Betaproteobacteria, whereas the percentages of Cyanobacteria, total rare phyla and unclassified phyla significantly increased. Null-model tests indicated that deterministic processes played a more important role than stochastic processes in determining BCC. However, the relative importance of stochasticity, primarily ecological drift, was enhanced and contributed to the increased beta diversity of BCC under enhanced warming and nutrient-enriched conditions. Overall, our study suggests that the synergetic effects of warming and nutrient enrichment may result in high variability in the composition of bacterioplankton communities in lacustrine water bodies.

Differential modification of seawater carbonate chemistry by major coral reef benthic communities

Ocean acidification (OA) resulting from uptake of anthropogenic CO2 may negatively affect coral reefs by causing decreased rates of biogenic calcification and increased rates of CaCO3 dissolution and bioerosion. However, in addition to the gradual decrease in seawater pH and Ωa resulting from anthropogenic activities, seawater carbonate chemistry in these coastal ecosystems is also strongly influenced by the benthic metabolism which can either exacerbate or alleviate OA through net community calcification (NCC = calcification – CaCO3 dissolution) and net community organic carbon production (NCP = primary production − respiration). Therefore, to project OA on coral reefs, it is necessary to understand how different benthic communities modify the reef seawater carbonate chemistry. In this study, we used flow-through mesocosms to investigate the modification of seawater carbonate chemistry by benthic metabolism of five distinct reef communities [carbonate sand, crustose coralline algae (CCA), corals, fleshy algae, and a mixed community] under ambient and acidified conditions during summer and winter. The results showed that different communities had distinct influences on carbonate chemistry related to the relative importance of NCC and NCP. Sand, CCA, and corals exerted relatively small influences on seawater pH and Ωa over diel cycles due to closely balanced NCC and NCP rates, whereas fleshy algae and mixed communities strongly elevated daytime pH and Ωa due to high NCP rates. Interestingly, the influence on seawater pH at night was relatively small and quite similar across communities. NCC and NCP rates were not significantly affected by short-term acidification, but larger diel variability in pH was observed due to decreased seawater buffering capacity. Except for corals, increased net dissolution was observed at night for all communities under OA, partially buffering against nighttime acidification. Thus, algal-dominated areas of coral reefs and increased net CaCO3 dissolution may partially counteract reductions in seawater pH associated with anthropogenic OA at the local scale.