Federica Semprucci

Meiofauna of the Adriatic Sea: present knowledge and future perspectives

Owing to technical problems and difficult taxonomic identification, meiofauna have been generally less studied than macrofauna. However, the role of meiofauna in marine ecosystem functioning, and their effective and rapid response to anthropogenic alterations and climatic changes have recently been acknowledged, leading to increasing scientific and applied interest. At present, systematic and biogeographic knowledge of the meiofauna of the Adriatic Sea is extremely heterogeneous, because most of the data are limited to a few taxa and the sampled areas are scattered, being located mainly in the coastal areas of the northern basin. Analysis of the composition and distribution of meiobenthic groups in the Adriatic Sea highlights the presence of several endemisms. Meiofauna also include bioindicator taxa, which allow assessment of the quality of marine sediments; this is particularly useful in systems characterised by the synergistic effect of different forms of anthropogenic impact, such as the Adriatic basin. Current knowledge about the ecology of the meiofauna and use of this component in applied ecological studies, along with the availability of a standardised protocol for the analysis of meiofaunal assemblages, allows us to recommend formal acknowledgement of the need to integrate information derived from the analysis of macrofauna with information derived from the study of meiofauna. Future research based on the simultaneous use of both of these benthic components will allow faster and more accurate evaluation of the response of coastal marine ecosystems to anthropogenic disturbance.

Benthic communities along a littoral of the Central Adriatic Sea (Italy)

Bacteria, meio- and macrofauna were investigated at different depths in a coastal area of the Central Adriatic Sea, yielding information about the composition and abundance of the benthic community. In particular, 14 nematode genera were recorded for the first time in the Upper Adriatic Sea. All communities resulted as being significantly different between inshore and offshore stations, especially when the season interaction was considered. Sediment grain size seemed to be the main natural variable, along with trophic resources, affecting the distribution and composition of these benthic components, whilst there was no clear evidence of competition for food sources and predatory pressure between the communities. Meiofauna appeared the most useful community for detecting disturbances and river influences. In particular, the lowest copepod abundance in the shallow waters seemed to be related to a greater anthropogenic disturbance inshore, whilst meiofaunal abundance and diversity together with the nematode maturity index suggest the influence of the Foglia and Metauro rivers and the small stream Arzilla.

Meiofauna as a Tool for Marine Ecosystem Biomonitoring

Meiofauna are the metazoan component of the benthos, and also include large protozoans (e.g. foraminifera). They are defined by their body size (44-1000 μm) and are the most diversified element of the marine biota: as many as 24 of the 35 animal phyla have meiobenthic representatives which live in meiofauna, whether for all their life or just temporarily. It is the most abundant benthic group in the marine realm, and is thought to be closely connected to other faunal compartments of the benthic system. The function of meiofauna in marine benthic systems seems to be much more complex than previously supposed, and requires investigation to clarify their ecological importance in the benthic domain (see Balsamo et al., 2010 for review).

On the quantitative distribution and community structure of the meio and macrofaunal communities in the coastal area of the Central Adriatic Sea (Italy)

Many coastal areas have served as repositories of different anthropogenic and naturally induced organic material and nutrients. The major sources thereof are riverine inputs which strongly influence the spatial and temporal distribution of benthic communities. In this study, the benthic foraminiferal, meiofaunal, and macrofaunal colonies in front of three rivers in a poorly known, but environmentally valuable, area of the Central Adriatic Sea have been examined concurrently. The physico-chemical parameters of bottom water and sediment characteristics were determined in order to characterize both the sediment–water interface and the benthic environments. Although changes in the biota are neither univocal nor unidirectional, a moderate influence of riverine input on the different communities’ components can be inferred. The most affected taxa are foraminifera and copepods and, to a lesser extent, meiofaunal polychaetes and platyhelminthes. These results are also tested by the ABC curves, which reveal that the macrofaunal communities closest to the river mouths are moderately disturbed. This integrated investigation documents, for the first time, how benthic communities can be used as an early warning indicator with which to monitor the health quality of a coastal ecosystem.

Meiobenthos and free-living nematodes as tools for biomonitoring environments affected by riverine impact

The effects of the human impact on the coastal environments and relative biota can be different and even greater than those derived by natural fluctuations. The major disturbance causes in the coastal systems are rivers that may be important sources of nutrients and pollutants, particularly in a semi-closed basin such as the Adriatic Sea. In this context, we investigated the distribution of both meiobenthic and nematode assemblages in the Central Adriatic Sea to evaluate whether and how they are influenced by riverine discharges and which faunal descriptors are the most effective in detecting this type of stress. On the basis of our results, the disturbance effects in the studied area might be caused by both local streams and Po plume, and even if the latter might be considered of lesser extent, it is worthy to note its real impact at a short distance from the coastline. Meiobenthic assemblage structure appears as a good tool for detecting short-term responses of the benthic domain, whereas nematode assemblages seem more useful for defining long-term responses. Accordingly, the former highlighted from poor to sufficient ecological quality status (EQS) of this area, whereas the latter from moderate to bad EQS. Life strategy traits prove to be the most informative faunal descriptor due to their high correspondence with the environmental variables and particularly with this type of disturbance.

Meiofauna associated with coral sediments in the Maldivian subtidal habitats (Indian Ocean)

Coral reefs are important hot spots of biodiversity, but despite the problems related to their conservation, studies on meiobenthic biodiversity are scarce. This paper provides a preliminary overview of the meiofauna and nematodes inhabiting coral sediments in the outer reef and lagoon habitats of the Maldives, and investigates their relationships with micro-habitat type. The abundance and community structure of the meiofauna and nematodes reveal significant differences between stations. Coral fragments and rubble from the outer reefs seem to act as a trap for the finest sediment, which might contribute to creating a heterogeneous micro-habitat suitable for both epifaunal (Epsilonematidae and Draconematidae genera) and sediment-dwelling (Tricoma, Richtersia, Ptycholaimellus and Molgolaimus) taxa. On the other side, the lagoon’s sediments are mainly colonized by dwelling taxa, probably due to the low-flow regime that enhances the deposition of organic matter and pelite fractions. A high level of diversity was recorded in both the habitats studied. Among the factors that probably determine the high diversity in the lagoon is the presence of small biogenic structures. These are characterized by a high degree of angularity, which might add more complexity to the habitat. The nematodes reveal an overlap in the taxonomic composition between the Maldives and other geographically distant areas, possibly supporting the existence of iso-communities that are typical of the coral degradation zone. Nematode trophic composition reflects differences in availability of food resources; epigrowth and non-selective deposit feeders are dominant in the lagoon, while selective deposit and epistrate feeders are dominant in the outer reefs.

Spatial patterns of distribution of meiofaunal and nematode assemblages in the Huvadhoo lagoon (Maldives, Indian Ocean)

Huvadhoo Atoll is a little-known and generally uncontaminated atoll of the southern Maldives, although the human pressure is increasing. This study represents the first attempt to characterize the meiofaunal and nematode assemblages of its lagoon both from a taxonomic and functional point of view. The nematode assemblage was made up of a total of 131 genera in 33 families. Desmodoridae, Chromadoridae and Xyalidae represented the richest and most abundant families, followed in terms of abundance by Selachinematidae and Comesomatidae. The nematode richness was overall higher than that reported in the previous studies carried out in the Central part of the archipelago. The diversity patterns revealed higher values than those reported for the back-reefs platforms, so confirming the positive influence of the water depth on the biodiversity of the nematode assemblage. The statistical analysis highlighted a significant taxonomic difference of the assemblages between the stations characterized by fine and medium-coarse sands, respectively, in line with the auto-ecological preferences of the taxa detected. The use of some nematode descriptors for assessing the ecological quality status (EQS) of the lagoon has revealed a slight disturbance in the station close to Viligili, one of the most urbanized islands. However, the summarization of all the descriptors used allows the highlighting of the good EQS of the Huvadhoo lagoon. Thus, the results of this study may be taken as the starting point for the future monitoring of the potential and real impact of the anthropogenic activity on the area over time.

Temporal changes of the meiofaunal assemblage as a tool for the assessment of the ecological quality status

The Adriatic Sea, being a semi-closed and shallow basin, is more sensitive to anthropogenic impact than other areas of the Mediterranean Sea. Given the crucial role of meiofauna in the marine ecosystems, temporal series of data on this benthic assemblage are fundamental to give new insights into the health status of this basin. A data set (decade 2002–2012) on the meiofauna of two river mouths (Foglia and Metauro) close to a Natural Park (Monte San Bartolo, Central Adriatic Sea) has been analysed and related to several environmental parameters. In particular, changes in the meiofaunal structure, abundance and diversity have been investigated in order to evaluate possible variations of ecological quality status (EQS), in accordance with the Water Framework Directive. The structure of the meiofaunal assemblage appeared significantly different in the period studied, with a higher abundance of annelids in 2002 and an increase of nematodes in the following sampling campaigns. Among the faunal parameters, the Shannon and Pielou indices suggested a decline of the EQS over time, likely mainly due to the negative effect of chlorophyll- a peaks, which may highlight the influence of eutrophication phenomena and an enhancement of the organic matter supply. The lowering of the EQS of the study area suggests the need to intensify management and conservation efforts in the coastal systems, and supports the use of the meiofaunal assemblage as a useful bioindicator.

Biodiversity trends of the meiofaunal and foraminiferal assemblages of Lake Varano (southern Italy)

Abstract In this study, the meiofaunal diversity in Lake Varano (southern Italy) is investigated in detail. Using a statistical approach, these data were coupled with the physicochemical parameters of the bottom water and the sediment characteristics in order to understand the factors influencing meiofaunal biodiversity distribution. The lake is selectively influenced by different factors, namely: organic matter and grain-size, as well as water salinity. Although these assemblages appear to be poorly diversified, the diversity index values are similar to those generally reported in other transitional environments. Relatively higher values of both meiofaunal and benthic foraminiferal diversity were found in front of the Capoiale channel and in the inner part of the lake. The meiofaunal assemblages are mainly dominated by nematodes, copepods, and turbellarians. The benthic foraminiferal assemblages comprise 18 taxa and are mainly represented by calcareous forms, suggesting a relatively low degree of confinement and, consequently, moderately restricted conditions. These assemblages are comparable to the Ammonia assemblages with Haynesina germanica that are characteristic of lagoons along the Mediterranean coasts. On the basis of these findings, coupled with the biotic data, the lake can be regarded as an oligo-mesotrophic environment.

Taxonomic and functional biodiversity variations of meiobenthic and nematode assemblages across an extreme environment: a study case in a Blue Hole cave

Abstract In this paper we have explored for the first time the biodiversity pattern of the meiobenthic assemblage in a Blue Hole of the Maldivian Archipelago. The cave is characterised by a marked change of the chemical water parameters below 50 m of depth, with a relevant increase in hydrogen sulfide, carbon dioxide, and sulfates (H2S, CO2 and SO42–). Thus, three stations were selected above and two below the chemo-thermocline in order to test the possible effects of the chemical variations on the meiobenthos. The difficulty of adaptation to these environmental conditions is clearly suggested by the presence of only a few dominant meiobenthic taxa in the bottom of the cave. However, meiobenthic organisms seemed more resistant than macrobenthos, which disappeared completely below this depth. The nematode assemblage was mainly represented by Xyalidae, Desmodoridae, Comesomatidae and Linhomoeidae. A high level of confinement of nematode genera at the different depths has been documented. In the upper part, their structure and biodiversity were comparable to those of the Maldivian subtidal habitats characterised by fine coralline sediments, while a notable dominance was detected in the bottom. The Blue Hole features also influenced the functional traits of the nematode assemblage with a documented increasing number of general opportunists and decrease of Maturity Index. The dominance of non-selective deposit feeders supports the hypothesis of a high amount of organic matter accumulated on the sea bottom of the cave.