Trophic status and meiofauna biodiversity in the Northern Adriatic Sea: Insights for the assessment of good environmental status

Effects of acidification on the biogeochemistry of unvegetated and seagrass marine sediments

Many studies addressed ocean acidification (OA) effects on marine life, whereas its effects on sedimentary organic matter (OM) have received less attention. We investigated differences in OM features in sediments from unvegetated and seagrass (Posidonia oceanica) beds in a shallow hydrothermal area (Aeolian Archipelago, Mediterranean Sea), under natural (8.1-8.0) and acidified (7.8-7.9) conditions. We show that a pH difference of -0.3 units have minor effects on OM features in unvegetated sediments, but relevant consequences within acidified seagrass meadows, where OM quantity and nutritional quality are lower than those under natural pH conditions. Effects of acidified conditions on OM biogeochemistry vary between unvegetated and seagrass sediments, with lower C degradation rates and longer C turnover time in the former than in the latter. We conclude that OA, although with effects not consistent between unvegetated and vegetated sediments, can affect OM quantity, composition, and degradation, thus having possible far-reaching consequences for benthic trophic webs.

Keep It Simple: Improving the Ex Situ Culture of Cystoseira s.l. to Restore Macroalgal Forests

Brown algae from genus Cystoseira s.l. form dense underwater forests that represent the most productive areas in the Mediterranean Sea. Due to the combined effects of global and local stressors such as climate change, urbanization, and herbivore outbreaks, there has been a severe decline in brown algal forests in the Mediterranean Sea. Natural recovery of depleted sites is unlikely due to the low dispersal capacity of these species, and efficient techniques to restore such habitats are needed. In this context, the aims of our study were (1) to improve and simplify the current ex situ laboratory protocol for the cultivation of Gongolaria barbata by testing the feasibility of some cost-effective and time-efficient techniques on two donor sites of G. barbata and (2) to evaluate the survival and growth of young thalli during the laboratory phase and during the most critical five months after out-planting. Specifically, the following ex situ cultivation methods were tested: (A) cultivation on clay tiles in mesocosms with culture water prepared by three different procedures (a) filtered seawater with a 0.22 μm filter membrane, (b) filtered seawater with a 0.7 μm filter membrane (GF), and (c) UV-sterilized water, and (B) cultivation on clay tiles in open laboratory systems. After two weeks, all thalli were fixed to plastic lantern net baskets suspended at a depth of 2 m in the coastal sea (hybrid method), and the algal success was monitored in relation to the different donor sites and cultivation protocol. The satisfactory results of this study indicate that UV-sterilized water is suitable for the cultivation of G. barbata in mesocosm, which significantly reduces the cost of the laboratory phase. This opens the possibility of numerous and frequent algal cultures during the reproductive period of the species. Additionally, if the young thalli remain in the lantern net baskets for an extended period of several months, they can grow significantly in the marine environment without being exposed to pressure from herbivorous fish.

Multi-benthic size approach to unveil different environmental conditions in a Mediterranean harbor area (Ancona, Adriatic Sea, Italy)

Harbors are hubs of human activity and are subject to the continuous discharge and release of industrial, agricultural, and municipal waste and contaminants. Benthic organisms are largely known to reflect environmental conditions they live in. Despite meio- and macrofauna interacting within the benthic system, they are ecologically distinct components of the benthos and as such may not necessarily respond to environmental conditions and/or disturbances in the same way. However, in a few field studies the spatial patterns of meio- and macrofauna have been simultaneously compared. In the present study, we assess the response and patterns in the abundance, diversity, and distribution of the two benthic size classes to the different environmental conditions they live in (i.e., sediment concentrations of selected trace metals and polycyclic aromatic hydrocarbons (PAHs); organic matter contents and grain size) characterizing the Ancona Harbor (Adriatic Sea). Meio- and macrofauna provided partially similar types of information depending on the indices used (univariate measures or community structure/species composition) and the different 'response-to-stress'. The community structure (i.e., taxa composition) of both benthic size components clearly showed differences among sampling stations located from inside to outside the harbor, reflecting the marked environmental heterogeneity and disturbance typically characterizing these systems. Notwithstanding, the univariate measures (i.e., meio- and macrofauna total abundance, diversity indices and equitability) didn't show similar spatial patterns. Meiofauna were likely to be more sensitive to the effects of environmental features and contaminants than macrofauna. Overall, trace metals and PAHs affected the community composition of the two benthic components, but only the meiofauna abundance and diversity were related to the environmental variables considered (i.e., quantity and quality of organic matter). Our results pinpoint the importance of studying both meio- and macrofauna communities, which could provide greater insight into the processes affecting the investigated area and reveal different aspects of the benthic ecosystems in response to harbor conditions.

Effects of Field Simulated Marine Heatwaves on Sedimentary Organic Matter Quantity, Biochemical Composition, and Degradation Rates

Simple Summary

Marine heatwaves (MHWs) are intensifying due to global warming. Based on their effects on biochemical reactions, they are also likely to affect coastal biogeochemistry. We investigated organic matter quantity, composition and degradation rates in nearshore sediments affected by simulated MHWs, with 1.5 and 5.0 °C anomalies, before and after 3 and 11 weeks from the release of an artificial warm water plume. MHWs enhanced organic loads (by >100%), with larger effects in the short-term under the highest temperature anomaly. Phytopigment contents increased (by 50–90%) in the short term but decreased to initial values in the longer one. The autotrophic and lipid contents decreased with time (by 15–50% 53–79%, respectively), suggesting a drop in the nutritional quality of organic matter, along with a slowdown of its turnover. We contend that MHWs’ intensification will affect not only species and communities but will also alter sediment biogeochemistry and, possibly, the energy transfer towards higher trophic levels.

Abstract

Since rising temperature (T) will enhance biochemical reactions and coastal marine sediments are hotspots of carbon cycling, marine heatwaves’ (MHWs’) intensification caused by climate change will affect coastal biogeochemistry. We investigated the effects of MHWs on sediment organic matter (OM) in a nearshore locality (NW Sardinia, Mediterranean Sea) receiving an artificial warm water plume generating T anomalies of 1.5–5.0 °C. Sediments were collected before and after 3 and 11 weeks from the initial plume release. Both MHWs influenced sedimentary OM quantity, composition, and degradation rates, with major effects associated with the highest T anomaly after 3 weeks. Both MHWs enhanced sedimentary OM contents, with larger effects associated with the highest T anomaly. Phytopigment contents increased in the short term but dropped to initial levels after 11 weeks, suggesting the occurrence of thermal adaptation or stress of microphytobenthos. In the longer term we observed a decrease in the nutritional quality of OM and a slowdown of its turnover mediated by extracellular enzymes, suggestive of a decreased ecosystem functioning. We anticipate that intensification of MHWs will affect benthic communities not only through direct effects on species tolerance but also by altering benthic biogeochemistry and the efficiency of energy transfer towards higher trophic levels.

Relationships Between Annual and Perennial Seagrass (Ruppia sinensis) Populations and Their Sediment Geochemical Characteristics in the Yellow River Delta

Annual and perennial populations commonly occur for the same submerged aquatic angiosperm species, yet relationships between population types and sediment characteristics are poorly understood. In the current study two Ruppia sinensis habitats with annual and perennial populations were surveyed in the Yellow River Delta (YRD). Biomass and seasonal seed bank size were used to evaluate population status and potential recruitment capacity. Sediment geochemical parameters including moisture, sulfide, Chl a, carbohydrate, OM, TOC, TN, and TP were measured to compare sediment nutrient composition and variability. The results revealed a higher biomass and larger seed bank in the annual R. sinensis population compared with the perennial population. The P levels in sediments between the two R. sinensis populations were similar; while the N level in the sediment of the annual population was significantly higher than the perennial population, which might support the recruitment of vegetative shoots when a large amount of seeds germinated during wet periods. The annual population exhibited greater resilience after habitat desiccation, with the population recovering rapidly once water appeared. The results of this study add to the knowledge of R. sinensis populations and their sediment geochemical characteristics, and can be used as a reference for Ruppia population conservation and management.

Environmental DNA metabarcoding reveals estuarine benthic community response to nutrient enrichment - Evidence from an in-situ experiment

Nutrient loading is a major threat to estuaries and coastal environments worldwide, therefore, it is critical that we have good monitoring tools to detect early signs of degradation in these ecologically important and vulnerable ecosystems. Traditionally, bottom-dwelling macroinvertebrates have been used for ecological health assessment but recent advances in environmental genomics mean we can now characterize less visible forms of biodiversity, offering a more holistic view of the ecosystem and potentially providing early warning signals of disturbance. We carried out a manipulative nutrient enrichment experiment (0, 150 and 600 g N fertilizer m^-2) in two estuaries in New Zealand to assess the effects of nutrient loading on benthic communities. After seven months of enrichment, environmental DNA (eDNA) metabarcoding was used to examine the response of eukaryotic (18S rRNA), diatom only (rbcL) and bacterial (16S rRNA) communities. Multivariate analyses demonstrated changes in eukaryotic, diatom and bacterial communities in response to nutrient enrichment at both sites, despite differing environmental conditions. These patterns aligned with changes in macrofaunal communities identified using traditional morphological techniques, confirming concordance between disturbance indicators detected by eDNA and current monitoring approaches. Clear shifts in eukaryotic and bacterial indicator taxa were seen in response to nutrient loading while changes in diatom only communities were more subtle. Community changes were discernible between 0 and 150 g N m^-2 treatments, suggesting that estuary health assessment tools could be developed to detect early signs of degradation. Increasing variation in community structure associated with nutrient loading could also be used as an indicator of stress or approaching tipping points. This work represents a first step towards the development of molecular-based estuary monitoring tools, which could provide a more holistic and standardized approach to ecosystem health assessment with faster turn-around times and lower costs.

Sedimentary Organic Matter, Prokaryotes, and Meiofauna across a River-Lagoon-Sea Gradient

In benthic ecosystems, organic matter (OM), prokaryotes, and meiofauna represent a functional bottleneck in the energy transfer towards higher trophic levels and all respond to a variety of natural and anthropogenic disturbances. The relationships between OM and the different components of benthic communities are influenced by multiple environmental variables, which can vary across different habitats. However, analyses of these relationships have mostly been conducted by considering the different habitats separately, even though freshwater, transitional, and marine ecosystems, physically linked to each other, are not worlds apart. Here, we investigated the quantity and nutritional quality of sedimentary OM, along with the prokaryotic and meiofauna abundance, biomass, and biodiversity, in two sampling periods, corresponding to high vs. low freshwater inputs to the sea, along a river-to-sea transect. The highest values of sedimentary organic loads and their nutritional quality, prokaryotic and meiofaunal abundance, and biomass were consistently observed in lagoon systems. Differences in the prokaryotic Operational Taxonomic Units (OTUs) and meiofaunal taxonomic composition, rather than changes in the richness of taxa, were observed among the three habitats and, in each habitat, between sampling periods. Such differences were driven by either physical or trophic variables, though with differences between seasons. Overall, our results indicate that the apparent positive relationship between sedimentary OM, prokaryote and meiofaunal abundance, and biomass across the river-lagoon-sea transect under scrutiny is more the result of a pattern of specifically adapted prokaryotic and meiofaunal communities to different habitats, rather than an actually positive ‘response’ to OM enrichment. We conclude that the synoptic analysis of prokaryotes and meiofauna can provide useful information on the relative effect of organic enrichment and environmental settings across gradients of environmental continuums, including rivers, lagoons, and marine coastal ecosystems.

Meiobenthic nematodes in the assessment of the relative impact of human activities on coastal marine ecosystem

Ecological quality (EcoQ) status of the Southwest and West coasts of South Korea was evaluated within the "National Investigation of Marine Ecosystems in Korea" in the 2015. In particular, the study dealt to assess the ecological quality of the sediments using free-living nematode communities. A total of 149 species were found in the study area, and Daptonema, Sabatieria, Parodontophora, Sphaerolaimus, and Viscosia were found as dominant genera. Statistical analysis of both environmental and faunal parameters showed an increasing human pressure from Western to Southern coasts. The community structure changed with the environmental features of the study area and allowed the detection of a suite of possible nematode indicators that might be used in monitoring studies. In particular, Dorylaimopsis spp. appeared heavy metal and organic matter resistant taxa, Sabatieria an eutrophication resistant genus, while Paracanthonchus and Neotonchus as heavy metal and organic matter sensitive genera. The principal component analysis (PCA) results showed a clear negative correlation between maturity index and both heavy metal and organic matter increasing, while diversity indices did not appear to be significantly influenced by them. Appling the thresholds of the synthetic nematode indices, the EcoQ of the study area was assessed as poor to moderate.

Meiofaunal communities in four Adriatic ports: Baseline data for risk assessment in ballast water management

Ports receive a variety of contaminants related to a wide range of anthropogenic activities - including ship ballast water (BW) - that ultimately find their way to sediments. Benthic meiofauna from four Adriatic ports (Ancona, Trieste, Koper, and Split) was assessed for the main environmental pollutants, to evaluate the effects of human activities on meiobenthos and identify the most appropriate descriptor to assess the ecological quality of marine ecosystems. Sediment analysis demonstrated that Trieste and Split were the most contaminated ports, followed by Koper and Ancona. All meiofaunal parameters showed high spatial and temporal variability, in line with the marked heterogeneity of the four ports. Sand, total organic carbon, and pollutants seemed to be the variables that best explained meiofaunal patterns. Community structure and rare taxa were the meiofaunal descriptors that reflected the environmental status and biological response most accurately. The present data suggest that meiofauna can be used to assess the biological impact of BW.

Multiple human pressures in coastal habitats: variation of meiofaunal assemblages associated with sewage discharge in a post-industrial area

Marine ecosystems are globally threatened by human activities, but some areas, such as those affected by abandoned industrial plants, show an overlap of acute and chronic impacts, which determine a considerable deterioration of their health status. Here we report the results of a research conducted on coastal sewers that discharge their loads in the highly contaminated area of Bagnoli-Coroglio (Tyrrhenian Sea, Western Mediterranean). The sampling area is characterized by heavy industrial activities (a steel plant using coal, iron and limestone) started in 1905 and ceased in 1990, which left widespread heavy metals and hydrocarbon contamination. After taking into account the potential influence of sediment grain size ranges through their inclusion as covariates in the analysis, we tested the potential impact of sewage discharge on the total abundance and multivariate structure of meiofaunal assemblages, as well as on the abundance of single taxa. The organic matter was analysed in terms of total phytopigment and biopolymeric carbon concentrations. Nematoda, Copepoda (including their nauplii), and Tardigrada were the most abundant meiofaunal taxa at all sites, but nematodes did not show a consistent pattern relative to the sewage outfalls. However, the sewer located in the historically most contaminated area showed a minimal abundance of all taxa, including nematodes, while copepods were relatively less abundant at the two southernmost sewers. Comparing the north vs. south site of the sewers, higher meiofaunal abundances were observed in the southward part, likely as a result of the local circulation. The results of this study indicate the general adaptation of meiofauna to multiple stressors (sewage discharge, superimposed to chronic industrial contamination) and its likely modulation by other local processes. They also provide relevant baseline information for future restoration interventions that would take into account the spatial variation of target organisms as needed.

The response of cultured meiofaunal and benthic foraminiferal communities to lead exposure: Results from mesocosm experiments

Lead (Pb) is regarded as a highly toxic element that poses a serious threat to biota. A mesocosm experiment was performed to assess the influence of Pb on meiofaunal (metazoans within 45-500 μm) and benthic foraminiferal (protozoan) communities. To this end, sediments bearing such communities were incubated in mesocosms, exposed to different levels of Pb in seawater, and monitored for up to 8 wk. Concentrations of Pb <1 ppm in water did not promote a significant increase of this metal in sediments. Relatively high concentrations of Pb seemed to affect meiofaunal and benthic foraminiferal communities by reducing their richness or diversity, and the abundance of the most sensitive taxa. The mesocosm approach can be considered an effective method to document the responses of meiofaunal and benthic foraminiferal communities to various kinds and concentrations of pollutants over time. This approach allows the evaluation of dose-response relationships, validates the outcomes of field studies, and possibly confirms the sediment quality guidelines and thresholds. Environ Toxicol Chem 2018;37:2439-2447. © 2018 SETAC.

Biodiversity loss and turnover in alternative states in the Mediterranean Sea: a case study on meiofauna

In the Mediterranean Sea hard-bottom macroalgal meadows may switch to alternative and less-productive barrens grounds, as a result of sea urchins overgrazing. Meiofauna (and especially nematodes) represent key components of benthic ecosystems, are highly-diversified, sensitive to environmental change and anthropogenic impacts, but, so-far, have been neglected in studies on regime shifts. We report here that sedimentary organic matter contents, meiofaunal taxa richness and community composition, nematode α- and β-biodiversity vary significantly between alternative macroalgal and barren states. The observed differences are consistent in six areas spread across the Mediterranean Sea, irrespective of barren extent. Our results suggest also that the low biodiversity levels in barren states are the result of habitat loss/fragmentation, which is associated also with a lower availability of trophic resources. Furthermore, differences in meiofaunal and nematode abundance, biomass and diversity between macroalgal meadow and barren states persist when the latter is not fully formed, or consists of patches interspersed in macroalgal meadows. Since barren grounds are expanding rapidly along the Mediterranean Sea and meiofauna are a key trophic component in marine ecosystems, we suggest that the extension and persistence of barrens at the expenses of macroalgal meadows could also affect resilience of higher trophic level.

Meiofauna distribution in a mangrove forest exposed to shrimp farm effluents (New Caledonia)

Meiofauna abundance, biomass and individual size were studied in mangrove sediments subjected to shrimp farm effluents in New Caledonia. Two strategies were developed: i) meiofauna examination during the active (AP) and the non-active (NAP) periods of the farm in five mangrove stands characteristics of the mangrove zonation along this coastline, ii) meiofauna examination every two months during one year in the stand the closest to the pond (i.e. Avicennia marina). Thirteen taxonomic groups of meiofauna were identified, with nematodes and copepods being the most abundant ones. Meiofauna abundance and biomass increased from the land side to the sea side of the mangrove probably as a result of the increased length of tidal immersion. Abundance of total meiofauna was not significantly different before and after the rearing period. However, the effluent-receiving mangrove presented twice the meiofauna abundance and biomass than the control one. Among rare taxa, mites appeared extremely sensitive to this perturbation.