Interactions between free-living nematodes and benthic diatoms: insights from the Gulf of Trieste (northern Adriatic Sea)

From July 2010 to July 2012, free-living nematodes were investigated in terms of abundance, genera and trophic composition at the long term St. C1 (depth 18 m), located in the Gulf of Trieste (northern Adriatic Sea). The integration of these results with environmental (e.g. sediment grain-size, Biopolymeric C and Chl a) and biological variables (benthic diatom biomass and composition) collected synoptically with nematodes, allowed to clarify the linkage between these organisms and another ecosystem component, i.e. benthic diatoms. The observed peaks of nematode abundance in summer samplings were ascribable almost exclusively to piercing nematodes that feed on microalgae (Chromadoridae and, among them, Ptycholaimellus) and were concomitant with the highest numbers of benthic diatoms. DISTLM outputs further corroborated this interaction by indicating Chl a, i.e. a proxy of benthic diatoms, as the only environmental variable that significantly shaped nematode assemblage over the 2-year period. This linkage was not explained only quantitatively (i.e. more diatoms supported more nematodes) but also qualitatively. During winter, in fact, the presence of heavily silicified diatoms co-occurred with nematode minima and the lowest percentage of piercing organisms, suggesting an overall minor ability of the assemblage in using this feeding strategy. In a benthic ecosystem functioning point of view, the observed seasonal pattern of variation in both nematodes and benthic diatoms suggests that more of the energy flowing to nematodes during the summer derives directly from benthic diatom primary production while in the winter this linkage is less important.</div

biodiversity feeding habits and reproductive strategies of benthic macrofauna in a protected area of the northern adriatic sea a three year study

The macrozoobenthic community at a sublittoral station located in the Marine Protected Area of Miramare, Gulf of Trieste (Italy) was investigated monthly from June 2002 to July 2005. Community variables were studied and related to food sources (particulate, total and biopolymeric carbon contents, benthic microalgae and meiofauna). In addition, the macrofaunal response to a heatwave that occurred in summer 2003 in the area was also explored. Univariate and multivariate analyses highlighted that the macrozoobenthic community structure shifted towards the end of the study. Diversity remained fairly stable throughout the study, despite the high turnover values. From a dominance of short-lived invertebrates related to irregular fresh organic matter inputs, the community shifted toward long-lived taxa, principally related to an increase of biopolymeric C and microalgal biomass. Semelparous invertebrates seem to be less resistant to high temperatures compared to iteroparous ones. The latter proved to be capable competitors since they prevailed over the semelparous species towards the end of the study.The community exhibited a certain degree of resistance to high temperature, due to the adaptation of the macrofaunal invertebrates to this particular stress, induced by the wide natural fluctuations in temperature that occur on a seasonal basis in the Gulf of Trieste. This study highlights the importance of long datasets to assess the state and ecological processes of the macrofaunal communities

Benthic foraminifera for the ecological status assessment of tourist marinas

Living benthic foraminifera were investigated in three tourist marinas of the Central Adriatic in order to test the suitability of these organisms for a quick and cost-effective assessment of the ecological quality status (EcoQS). Local high concentrations of biocidal metals (Cu, Zn, Cr, Sn, Ni and Pb) were measured in the sediments nearby the boathouse areas, i.e. where the careening activity takes place, suggesting that the accumulation of current and past antifouling residues is the main source of pollution in these particular maritime spaces. Factors such as the capacity of the marina, its shape as well as the location of the boathouse area concur to the degree of antifouling residues accumulation. Foraminifera responded to the different environmental conditions and to metal contamination in terms of abundance and species composition. At the boathouse stations these organisms were scarcely numerous and no living specimen was observed in the most polluted sediments. Three categories of indices were tested based on: (1) the percentages of abnormal tests, (2) biodiversity and (3) the sensitive-tolerant species occurrence (i.e. Foram-AMBI). The most diverse assemblage was observed at intermediate metal levels and seemed to be influenced by other environmental factors such as the presence of submerged vegetation that likely provides additional resources and increased heterogeneity. Unexpectedly, the station with the lowest metal levels was characterized by the least biodiverse assemblage. Notwithstanding, among the few species observed, at this site the dominant one was the sole species encountered in the present study that is recognized as sensitive, i.e. Ammonia parkinsoniana. Consequently, while the diversity indices provided very low values, Foram-AMBI outputs indicated the presence of an assemblage not exclusively dominated by opportunistic taxa. This result suggests a complementarity of these two categories of indices that should be taken into account for an accurate EcoQS assessment of tourist marinas