On the relevance of freshwater nematodes for ecological assessment in transitional waters

Nematoda is the most common group of organisms in the meiobenthic assemblages of freshwater and marine systems and, in Portugal, its distribution has been studied along the estuarine gradient of two estuaries. Nematodes are recognized as good indicators of anthropogenic impacts in aquatic ecosystems and, together with the taxonomic data, the inclusion of functional diversity can create a powerful tool, providing information on the functioning of ecosystems. Most estuarine studies do not encompass information to genus/species level of freshwater nematodes or reduce the information to family level, impoverishing thus information on diversity. The main aim of this study is to evaluate the information loss effect on the assessment of the ecological quality status of the upstream area of the Mondego estuary, caused by the non identification of freshwater nematodes– both taxonomic and functional approaches of nematode estuarine communities. Results show that nematodes assemblages reflected the salinity gradient, with increasing densities and diversity from oligohaline to euhaline areas. Freshwater nematodes contributed with a small percentage (3.5% of total density), but were very abundant in the upstream areas (0.5 – 47.4%). Without freshwater nematodes, the separation of salinity stretches was maintained (with lower distinction of the stretches) and the performance of the Index of Trophic Diversity and the Maturity Index revealed a worse condition of the ecological status of oligohaline and mesohaline stretches. This study shows that taxonomic and biologic characteristics of freshwater nematodes should be evaluated when assessing the ecological status of an estuary in order to correctly classify the uppermost sections of estuaries. Keywords: estuarine gradient, Mondego estuary, Portugal, subtidal meiobenthi

Meiofauna in a changing world

This special issue emerged under the umbrella of the 17th International Meiofauna Conference (SeventIMCO), which celebrated the 50th anniversary (1969–2019) of the International Association of Meiobenthologists under the general theme “Meiofauna in a changing world”. Traditionally, the triannual IMCO is the major assembly for scientists who are active in very divergent disciplines such as taxonomy, phylogeny, ecology, ecotoxicology, impact assessment, … using a wide array of methods, but who converge on the use of meiofauna as model organisms to address their scientific questions

Benthic meiofauna as indicator of ecological changes in estuarine ecosystems: The use of nematodes in ecological quality assessment

a b s t r a c t Estuarine meiofauna communities have been only recently considered to be good indicators of ecological quality, exhibiting several advantages over macrofauna, such as their small size, high abundance, rapid generation times and absence of a planktonic phase. In estuaries we must account not only for a great natural variability along the estuarine gradient (e.g. sediment type and dynamics, oxygen availability, temperature and flow speed) but also for the existence of anthropogenic pressures (e.g. high local population density, presence of harbors and dredging activities). Spatial and temporal biodiversity patterns of meiofauna and freeliving marine nematodes were studied in the Mondego estuary (Portugal). Both taxonomic and functional approaches were applied to nematode communities in order to describe the community structure and to relate it with the environmental parameters along the estuary. At all sampling events, nematode assemblages reflected the estuarine gradient, and salinity and grain size composition were confirmed to be the main abiotic factors controlling the distribution of the assemblages. Moreover, the low temporal variability may indicate that natural variability is superimposed by the anthropogenic pressures present in some areas of the estuary. The characterization of both meiofauna and nematode assemblages highlighted the usefulness of the integration of both taxonomic and functional attributes, which must be taken into consideration when assessing the ecological status of estuaries

Temporal and spatial meiofauna patterns in the Nazaré Submarine Canyon, Northeast Atlantic.

Submarine canyons are characterized by highly heterogeneous habitats, topography and hydrography with enhanced organic matter input. These factors have a profound effect on canyon faunal communities in time and space. As part of the HERMES project, one of the largest European canyons, the Nazaré canyon was sampled in spring-summer in three consecutive years (2005, 2006, 2007), permitting the study of inter-annual patterns in meiofaunal communities at two contrasting habitats at 3500 and 4300 m water depth. Meiofauna standing stocks and structural and functional diversity were investigated in relation to biogeochemical sediment data. Substantially increased sediment sand content in 2006 and consistent phytodetritus levels indicated the occurrence of one or more deposition events between the 2005 and 2006 sampling events. Nematode standing stocks and trophic diversity decreased in the 2006 samples, seemingly followed by a recovery period as observed by community patterns in 2007, when communities were strongly correlated with the increase of quality and bioavailability of the organic matter supplied. Nevertheless, inter-annual variations were not the main driver for the faunal communities; the depth effect on the faunal communities was greater. The community differences between the sampled habitats were markedly greater than what was caused by inter-annual variation, likely because of the contrasting hydrodynamic and food supply conditions. The higher meiofauna/nematode abundances, biomass, and trophic complexity at the 3500 m station, compared to the 4300 m station, was related to the higher food supply, and greater quality and bioavailability at the 3500 m site

How nematode morphometric attributes integrate with taxonomy-based measures along an estuarine gradient

Nematodes are highly susceptible to environmental change and possess a wide array of morphological and functional characteristics for the assessment of the “Good Environmental Status”, within Marine Strategy Framework Directive. However, while the taxonomic sufficiency of nematodes in detecting spatial gradients and related ecological niche conditions is well recognized, very little is known about nematodes functional morphometric attributes in response to environmental drivers. To explore this knowledge gap, we aimed to assess the efficacy and efficiency of nematode morphometric attributes (length, width, length/width ratio, biomass) in detecting spatial patterns along a Portuguese estuarine gradient, and compare it with the taxonomic approach. We hypothesized that abundance data weighted by the morphometric attributes will have a higher explanatory power in detecting spatial patterns than using abundance of morphometric data alone. Based on the recent recommendations regarding the time and cost related efficacy of methods in biomonitoring and ecological assessments we also hypothesized that a reduced dataset based on the most common genera will suffice to capture the same distributional patterns displayed by the whole assemblage. Our results demonstrated that dataset solely based on genera abundances had consistently better explanatory power than combined datasets or morphometric datasets alone, however, combined dataset provided different spatial patterns and performed better at discriminating estuary areas. The main gradients described by the taxonomy-based dataset were related to the sediment particle size and water depth. Considering combined datasets, spatial discrimination was mainly driven by the variation in dissolved oxygen % saturation, pointing out to the importance of this variable in determining estuarine conditions substantial for nematodes morphometric distributional patterns. The same analysis repeated for the most frequent genera resulted in similar distributional patterns as for the whole assemblage dataset, clearly demonstrating that spatial estuarine gradients can be sufficiently described by using only the most frequent genera. Such information may substantially increase the efficiency of bioassessment surveys by reducing the cost and work associated with identification and measurements of all of the individual nematode genera.info:eu-repo/semantics/publishedVersio

Benthic Nematode assemblages response to seagrass beds spatial heterogeneity in natural recovery process of Zostera Noltii after major colapse

After a seagrass beds (Zostera noltii) colapse in 2008 of the Mira estuary (SW coast of Portugal) symptoms of early recovery were observed. The principal goal of this study is to assess the evolution and resilience of the benthic nematodes assemblages during the natural recovery of the seagrass beds through analysis of the spatial and temporal differences in structural and functional characteristics of the communities. The horizontal macroscale (km) and small scale (m) variability was evaluate. We hypothesize that the new environmental conditions of the early recovery, with sparsely distributed and small-sized seagrass patches, will increase the spatial heterogeneity of nematode communities and significantly affect community diversity, both taxonomic and functional. The sampling design was follows: Samples were collected in five “occasions”, (February, June, September, December 2010 and February 2011), at randomly “stations” located over a distance 50 m, at two “sites”, 2km distance. To test the hypothesis that the composition of nematodes assemblages changes spatially and seasonally a two–way PERMANOVA analysis was performed. Mean nematode densities varied between 1416 ± 107 ind. 10 cm-2 (Site A) and 2611 ± 230 ind. 10 cm-2 (Site B) , and a total of 89 species were identified. The PCO ordination based on abundance and composition of nematode genera do not shown the discrimination of the two sampling sites. However densities and trophic groups showed significant differences across macroscale (sites A and B), the increase of spatial heterogeneity was clear identified in small scale. No significant differences was observed between the temporal variation. The response of the nematode assemblages after the collapse, both in terms of density and diversity, showed a substantial potential of resilience and recovery

Sample acidification effects on carbon and nitrogen stable isotope ratios of macrofauna from a Zostera noltii bed

Acidification treatment has been used in most stable isotope studies to eliminate inorganic non-dietary carbon, allowing d13C measurement of organic carbon needed for trophic studies. Because only limited information about the acidification effects on isotopic ratios exists in the literature, we provide an assessment of such effects for a wide range of benthic macroinvertebrates from estuarine intertidal sediments with sparse Zostera noltii Hornem. vegetation. Our results revealed only few significant d13C shifts for macrobenthos; however, d13C decrease after acidification was substantial for several species. We conclude that acidification is not necessary for removing calcium carbonate in a majority of macrobenthos, but we also suggest preliminary testing before deciding it can be omitted. The magnitude of the d15N shifts was substantial for some species and variability in d15N values of replicate acidified samples exceeded that of nonacidified samples. Therefore, sample acidification should be avoided for d15N determination. Moreover, acidification effects vary considerably among species belonging to a single class, rendering generalisations from single-species information potentially spurious

POPULATION DYNAMICS OF PLANT PARASITIC NEMATODES AND THEIR RELATIONSHIPS WITH SOIL PHYSICO-CHEMICAL PARAMETERS DURING THE FALLOW PERIOD AFTER SUGARBEET AND LEADING INTO TOMATO CULTIVATION

The main objective of this research was the study of the soil nematode community, and in particular plant parasitic nematodes (PPN), from a field located in Portugal’s southern region, used for sugarbeet production. The study was performed from February to July 2003, covering part of the fallow period previous to tomato cultivation, the alternative crop in the rotation. The end of the fallow period in March and the soil preparation period in May were marked by a significant reduction in the numbers of PPN, whereas their numbers increased on the following tomato crop. The genus Helicotylenchus stood out as the most representative group, forming 90% of all PPN counted each month. The genus Heterodera was relatively abundant in the months following the previous sugarbeet crop, and numbers of the genus Meloidogyne increased during the tomato crop. The correlations between these group and environmental parameters show that, apart from the direct influence of the host, pH, organic matter, temperature and soil moisture significantly influenced nematode abundance and community composition

Recovery of benthic nematode assemblages after a major collapse of Zostera noltii seagrass beds.

During 2008, Zostera noltii seagrass beds of the Mira estuary (SW coast of Portugal) suffered a total collapse, though during 2009 slight symptoms of their recovery were already observed. This association of events, in a short period of time, creates a rare opportunity for obtaining new knowledge concerning natural recovery of ecosystems and habitats. The principal goal is to analyse nematode community responses to the collapse of seagrass beds. Through a comparison of pre- and post-impact data, nematode assemblage recovery and resilience will be assessed. Additionally, the carbon resources utilized by nematodes will be examined, in order to better understand the importance of seagrass detritus as a potential resource for meiobenthic organisms. Significant differences were observed in the community patterns and trophic composition of nematode assemblages before and after the Zostera collapse. The dominant genera of the precollapse community were Terschellingia, Odontophora and Linhomoeus, generally considered microbivorous and/or deposit-feeding nematodes. Immediately after the collapse, they were replaced by Ptycholaimus, Paracomesoma and Metachromodora, all of which are herbivores feeding on diatoms and other microalgae

Multi-element profiles as a fingerprint to discriminate estuarine R. philippinarum populations.

Filter-feeder bivalves such as non-indigenous Ruditapes philippinarum absorb and accumulate metals, resulting in multi-element signatures. The goal of this study was to analyse if multi-element profiles of R. philippinarum can discriminate between spatial and temporal patterns of estuarine bivalves’ populations. Spatial and temporal variability patterns of chemical profiles were assessed by collecting samples of R. philippinarum and sediment at i) three sites with different environmental and physiological conditions of clams, ii) located within two Portuguese estuaries (Tagus and Sado estuaries) and iii) sampled at three different occasions (May 2018, January 2019, May 2019). This sampling design hypothesized that there are significant differences in the bivalves’ chemical profiles between estuaries, among sampling sites and among sampling occasions. The chemical elements were categorized according to the estuarine geomorphology sources (Se,Co, Ni and Cu), elements with function in metabolic processes of the clams (Mn, Fe, Zn and Cr) and elements derived from the anthropogenic inputs (As, Pb and Cd). The multielement concentrations of clams’ soft tissues and sediments were obtained using a powerful analytical technique, ICP-MS (inductively coupled plasma mass spectrometry). Multivariate differences were tested in multi-element concentrations of bivalves’ soft tissues and sediments. Results revealed that Zn, Co, Ni and Pb were the main contributors for the chemical signatures of Tagus estuary populations, whilst for the Sado estuary populations were Cu, Fe, Cr, As and Cd. These elements were representative of all elemental categories and proved to be spatial and temporal habitat discriminators of bivalves’ estuarine populations. The multi-element signatures of R. philippinarum as a natural tag derived from the physical and chemical conditions of its habitat can be considered as a potential rapid tool for ecological biomonitoring and habitat assessment, accounting for spatial and temporal habitat differences of estuarine populations