Victor Ugo Ceccherelli

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.

Nutrient regeneration processes in bottom sediments in a Po delta lagoon (Italy) and the role of bioturbation in determining the fluxes at the sediment-water interface

A study on nutrient regeneration processes and a measure of their fluxes at the sediment-water interface was carried out in two different stations of a shallow lagoon of the Po delta river (Italy). A few parameters on the solid fraction (grain-size, porosity, C, N) and pore water profiles of o-P, NH3, NOinf3sup−, SiO2, Tot-CO2, SOinf4sup2−, Fe, Mn, Ca, Mg, pH, Eh were determined. At both stations the results were typical for fine sediments rich in organic matter. The ratio of variations of sulphate (ΔSOinf4sup2−) to total carbonate demonstrates the main role sulphate reduction plays on the organic matter decay. The use of the ratios of variations of sulphate (ΔSOinf4sup2−) to ammonia (ΔNH3) and of sulphate (ΔSOinf4sup2−) to phosphate (Δo-P) in pore waters enabled us to calculate the C/N/P of the decomposing organic matter. Obtained C/N/P indicated an enrichment of N and P with regard to C/N/P ratios of the solid fraction, due to the selective stripping of N and P during organic matter mineralization. This phenomenon decreases with depth, where organic matter becomes more refractory. Calculations on saturation degrees have shown the possibility of authigenic calcite, apatite and rhodochrosite precipitation in sediments. Nutrient fluxes were estimated for SiO2, NH3 and o-P by means of benthic chambers and modelling the pore water profiles. The model used for the calculation of fluxes allowed us to account for the bioturbation-irrigation influence near the interface, by means of a cumulative diffusion coefficient. Directly measured fluxes proved to be always significantly greater than the theoretical ones. These differences seem to be due to surface processes which do not affect pore water concentrations (degradation of fresh materials at the interface; micro-bioturbation by small gasteropoda such as Hydrobia ventrosa) and/or to the different concept of the two methods in time and space. Number, size and biomass of macrobenthic species living in the sediment underneath the benthic chambers were determined. The comparison between data on macrobenthic populations and flux values showed a good relationship between the number of organisms and benthic fluxes within each station. However, flux variations between stations are to be attributed mainly to the different arrangement of the tubes of the polychaetes Polydora ciliata in the sediment.

Comparing efficacy of different taxonomic resolutions and surrogates in detecting changes in soft bottom assemblages due to coastal defence structures

Sandy shores on the West coast of the North Adriatic Sea are extensively protected by different types of defence structures to prevent coastal erosion. Coastal defence schemes modify the hydrodynamic regime, the sediment structure and composition thus affecting the benthic assemblages. This study examines the effectiveness in detecting changes in soft bottom assemblages caused by coastal defence structures by using different levels of taxonomic resolution, polychaetes and/or bivalves as surrogates and different data transformations. A synoptic analyses of three datasets of subtidal benthic macrofauna used in studies aimed at assessing the impact of breakwaters along the North Adriatic coast has been done. Analyses of similarities and correlations between distance matrices were done using matrices with different levels of taxonomic resolution, and with polychaetes or bivalves data alone. Lentidium mediterraneum was the most abundant species in all datasets. Its abundance was not consistently related to the presence of defence structures. Moreover, distribution patterns of L. mediterraneum were masking the structure of the whole macrofaunal assemblages. Removal of L. mediterraneum from the datasets allowed the detection of changes in benthic assemblages due to coastal defences. Analyses on different levels of taxonomic resolution showed that the level of family maintained sufficient information to detect the impacts of coastal defence structures on benthic assemblages. Moreover, the outcomes depended on the transformation used. Patterns of distribution of bivalves, used as surrogates, showed low correlations with the patterns of the total macrofaunal species assemblages. Patterns of polychaetes, if identified to the species or genus level showed higher correlations with the whole dataset. However, the identification of polychaetes to species and genus level is as costly as the identification of all macrobenthic taxa at family level. This study provided additional evidences that taxonomic sufficiency is a useful tool in environmental monitoring, also in investigations on the impacts of coastal defence structures on subtidal macrofauna. The use of coarser taxonomic level, being time-efficient, would allow improving sampling designs of monitoring programs by increasing replication in space and time and by allowing long term monitoring studies.

Effects of an artificial protection structure on the sandy shore macrofaunal community: the special case of Lido di Dante (Northern Adriatic Sea)

This study analysed the benthic compartment at Lido di Dante (Northern Adriatic Sea, Italy) within the frame of an integrated European project (DELOS), which aimed to identify, describe and quantify the effects of the Low Crested Structures (LCS) on the beach environment of many European coastlines. Both macrofaunal benthic communities and sediment characteristics were analysed in a sandy beach protected by a LCS parallel to the shoreline and laterally connected to land by two groynes, which have been responsible for changes of hydrodynamic patterns. A first survey (2001) focused on three exposure levels with respect to wave action. A higher species richness and a different community structure were found in the sheltered site as compared to the exposed and partially exposed sites. In addition, changes in sediment variables were found according to the exposure levels. A second survey (2002) assessed the combined effects of exposure and depth on both benthic communities and sediment variables. Our results suggest that both exposure and depth interact on measured biotic and abiotic variables. Species richness, community structure and size-classes distribution of the macrofauna, as well as the sediment composition, showed the greatest differences among the shallowest exposed zone and the deepest sheltered ones. On the contrary no difference at all occurred between the shallowest sheltered zone and the deepest exposed ones.

Effects of a mucilage event on the Mediterranean gorgonian Paramuricea clavata. I - Short term impacts at the population and colony levels

Abstract A Paramuricea clavata population thriving between 29 and 39 m depth on a shoal at the northern entrance to the Strait of Messina (Tyrrhenian Sea) was affected by mucilage coverage at the end of summer 1993. Mucilage became entangled in projecting branches and necrotized the coenenchyme below, leaving the axial skeleton bare. The entire population was heavily affected, extent of injuries being negatively correlated with size of colonies. Colony size, scale and location of damage were related to successful regeneration after six months. Smaller colonies showed a higher mortality, while colonies with over 50–60% of their total branch length damaged were overgrown by invaders and died. The extent of injuries in the central part of the colony was found to be a critical parameter in determining colony regrowth. A number of injured colonies grew during the six months following the disappearance of mucilage, which shows that their regrowth was apparently not influenced by stress due to mucilage.

Meiofaunal recolonization of azoic sediment in a Po Delta lagoon (Sacca di Goro)

Abstract A recolonization experiment of azoic sand by meiofauna was carried out in the Sacca di Goro, a brackish water environment of the Po Delta, in order to describe the recovery dynamics of meiobenthic communities after simulated small and large scale disturbance (defaunation). Two trays of azoic sand were placed in two different sites (Fig. 1). The first tray was laid directly on the bottom of a site (NS) close to the control (CR) from which the sand was originally drawn. The second tray was located at a site (FS) 2 km from CR and suspended 0.5 m above a mudflat zone. Recolonization was very fast at both experimental sites. At NS, average densities of major taxa became similar to those of CR after one day, with nematodes dominating as at CR. On the contrary, at FS, mean abundances were always lower than those both at CR and at NS and the dominant group was represented by harpacticoids and nauplii together, which showed themselves to be good wide range colonizers. Whereas the NS community seems to rea...

A field experiment on the effect of two types of sediment disturbance on the rate of recovery of a meiobenthic community in a eutrophicated lagoon

A recolonization field experiment of two different artificially disturbed sediments (both defaunated sand and defaunated/reduced sand through organic enrichment) was carried out in the Sacca di Goro (Adriatic sea, Po river Delta, Italy). Copepods showed themselves better colonizers than nematodes. In particular, copepods, in the defaunated sand, were able to reach the same densities as the control site after only seven days from the beginning of the experiment. In the reduced-sand, copepod recolonization occurred more slowly but reached the densities found in both azoic and control sediments at the end of the experiment (15 days), when the values of total carbon content decreased. The recovery evolution of the community structures was mostly dependent on the different behaviour of the active epibenthic species of the harpacticoids (e.g. Canuella perplexa T & A. Scott, 1893, Ameira parvula (Claus, 1866), Robertgurneya similis (A. Scott, 1896)) and of the passively transported endobenthic ones (e.g. Asellopsis sarmatica Jakubisiak, 1938, Ectinosoma dentatum Steuer, 1940).

Ecological research on the animal communities of the Po River Delta lagoons

Abstract The main results of research on invertebrate biology and ecology in the lagoons of the Po River Delta (Sacca del Canarin, Sacca di Scardovari, Sacca di Goro) are presented and related to the more significant approaches followed in ecological research during the last two decades. The lagoons, which are intrinsically eutrophic water bodies, have recently undergone intense eutrophication due to the dramatic increase in the Po river nutrient loading. A shift towards a dystrophic state was indicated by the appearance of large Ulva rigida beds in spring and by extensive anoxia during the summer due to the decomposition of the huge macroalgal biomass. Particularly severe dystrophic crises occurred in the Sacca di Goro. Zooplankton and zoobenthos changes were analyzed according to the variations in hydrographic features as well as those in the trophic state of the water. The significance of population dynamics studies in evaluating biological responses to environmental stresses is emphasized. Investigati...

Trade-off between conservation and exploitation of the transitional water ecosystems of the northern Adriatic Sea

Transitional waters (TWs) provide ecosystem goods and services that are essential for the well-being of human populations. These unpredictable aquatic systems, characterised by large environmental fluctuations, are under severe stress due to human activities. Increasing pressures (e.g. over-harvesting, eutrophication, habitat loss) inevitably lead to the degradation of these ecosystems. Analysis of the complexity of species distribution patterns within and among TW habitats is relevant to understanding the underlying processes and promoting appropriate management strategies. Assessment of the trophic status is one of the most critical aspects of TWs. Untangling the relevance of anthropogenic nutrient inputs from internal biogeochemical processes is of primary importance in defining appropriate restoration strategies. Biotic indices have been suggested as an operational tool to assess environmental quality in TWs. However, the application in TWs of indices developed for coastal waters can give distorted results (e.g. low species diversity and high abundance are natural features). The BITS approach provides a rapid assessment of ecological quality, although its sensitivity in reflecting field conditions remains to be assessed. The major challenge to TWs management is to couple long-term conservation with productive activities. This goal can be achieved using an integrated approach, forecasting conservation of TW ecosystem functioning together with sustainable economic development. North-western Adriatic TW habitats have been exploited for centuries and major shifts in ecological processes have occurred. In this study, knowledge of the ecological features of these habitats is summarised and analysed using recent ecological tools. Based on these findings, possible strategies for conservative management have been discussed.

Taxonomic distinctness and diversity measures: Responses in lagoonal macrobenthic communities

Abstract Sampling campaigns were carried out in 1976 and in 1989 in the Sacca degli Scardovari, a brackish lagoon in the Po Delta (upper Adriatic Sea). By means of different methods (i.e., average taxonomic distinctness index, conventional diversity measures, and non‐parametric multivariate analysis), changes in benthic community structure were investigated. In the 13‐year period, the southern area of the lagoon underwent a marinization process. A quite strong environmental gradient along its main N‐S axis was then found. Multivariate analysis was the most powerful tool for the assessment of benthic community changes, revealing community patterns that univariate measures of diversity were unable to detect. Relevant information on the taxonomic structure of the community was given by the distinctness index, but this did not prove sensitive to environmental changes, probably due to the characteristics of the studied environment.