Cristina Misic

Characteristics of the mesophotic megabenthic assemblages of the Vercelli Seamount (North Tyrrhenian Sea)

The biodiversity of the megabenthic assemblages of the mesophotic zone of a Tyrrhenian seamount (Vercelli Seamount) is described using Remotely Operated Vehicle (ROV) video imaging from 100 m depth to the top of the mount around 61 m depth. This pinnacle hosts a rich coralligenous community characterized by three different assemblages: (i) the top shows a dense covering of the kelp Laminaria rodriguezii; (ii) the southern side biocoenosis is mainly dominated by the octocorals Paramuricea clavata and Eunicella cavolinii; while (iii) the northern side of the seamount assemblage is colonized by active filter-feeding organisms such as sponges (sometimes covering 100% of the surface) with numerous colonies of the ascidian Diazona violacea, and the polychaete Sabella pavonina. This study highlights, also for a Mediterranean seamount, the potential role of an isolated rocky peak penetrating the euphotic zone, to work as an aggregating structure, hosting abundant benthic communities dominated by suspension feeders, whose distribution may vary in accordance to the geomorphology of the area and the different local hydrodynamic conditions.

Short-term variations in particulate matter flux in Terra Nova Bay, Ross Sea

As part of the Ross Sea Marginal Ice Zone Ecology Project (ROSSMIZE) the summer organic matter flux through the water column was measured at 40 m depth in Terra Nova Bay. Water samples and material from a sediment trap on the sea-bottom were analysed for their biochemical composition. A close coupling between biochemical composition of the organic matter in the water column and the material collected in the sediment trap was found, resulting from complex interactions between physical and biological processes. The physical processes are related to break-up and melting of the ice cover and occur mainly in the early summer season, whilst biological processes play a key role in mid summer and, from the evidence from faecal pellets, are related to the primary production and consumption processes.

Vibrios in association with sedimentary crustaceans in three beaches of the northern Adriatic Sea (Italy)

In the marine environment, vibrios adhere to a number of substrates including chitin-rich organisms such as crustaceans. Their wide diffusion in coastal waters and pathogenic potential require knowledge of the lifestyle and environmental reservoirs of these bacteria. To test the presence of culturable vibrios in coastal areas and their association with benthic crustaceans, vibrios were isolated from water, sediments and crustaceans (copepods and anphipods) at three stations placed in front of heavily used tourist beaches of the Adriatic Sea. We observed significant correlations between vibrios and temperature. Benthic and planktonic copepods harboured vibrios in summer, while benthic amphipods harboured these bacteria in spring and autumn. Vibrio alginolyticus and Vibrio parahaemolyticus strains gave positive results using primers for Vibrio cholerae toxR and toxS. Sedimentary crustaceans may extend Vibrio persistence in seawater and may represent an additional aquatic reservoir of these bacteria.

Bacteria and organic matter dynamics during a bioremediation treatment of organic-rich harbour sediments.

We studied the dynamics of bacteria and organic matter in the Ancient Port of Genoa (Italy) during a bioremediation treatment of sediment (during summer-autumn 1998) in an area characterised by continuous sewage discharge. A strong increase in total benthic bacterial density (TBN) was recorded at the end of the study, from 14 x 10(8) to 58-172 x 10(8) cell g(-1) in different parts of the treated area. The TBN increase was linked to organic matter depletion, from more than 40 to less than 20 mg x g(-1). In order to highlight the main ecological mechanisms involved in bioremediation, a laboratory experiment based on both water and sediment from the basin studied was carried out. We observed an increase in TBN during the first 20 days and a decrease in sediment organic matter (up to about 20%). Increases of organic matter (about 2-fold) and TBN (from 21 to 33 x 10(9) cell l(-1)) occurred in the overlying water, suggesting a strong association between the sediments and water column processes. Hydrolytic activities, which double in the sediment and increase up to a 300-fold in the water, are consistent with the decrease in sediment organic matter and with the water fraction dynamics.

Sedimentary organic matter and bacterial community in microtidal mixed beaches of the Ligurian Sea (NW Mediterranean)

The quantity and quality of organic matter, and bacterial density and frequency of dividing cells were investigated in six microtidal mixed beaches of the Ligurian Sea (NW Mediterranean) to evaluate their main trophodynamic features. Concentrations of biopolymeric carbon (average 88.5 ± 89.0 µgC/g) and the protein:carbohydrate ratio (on average lower than 1) were very low and classified these beaches as highly oligotrophic. The study of biochemical composition highlighted the nature of organic matter as being mainly refractory; furthermore, the quantitative differences observed along the across-beach gradient together with the unchanged pattern in qualitative features suggest that the organic matter in Ligurian beaches is prevalently of marine origin. This implies a negligible contribution of allochtonous and anthropogenic terrestrial input or in situ autochthonous production. Bacterial density displayed values ranging from 0.1–9.0 cell × 108/g DW in the top 2 cm layer and showed a significant correlation with the quantity of organic matter. In addition, the frequency of dividing cells showed a positive correlation with the protein:carbohydrate ratio, suggesting that the biochemical composition of organic matter also has an influence on the active bacterial fraction. Because of the exposed nature, a strong coupling was found between the beach and the marine systems, and this seems to be of fundamental importance in terms of material and energy supply for the beach ecosystem. A shortage within this linkage was observed in summer owing to the strong environmental constrains leading to a sort of “beach desertification” and to a marked oligotrophy. Summer also has an effect of smoothing for spatial variability occurring within the biochemical and microbiological variables among the different beaches. The linkage observed between the sea and the land is the main factor controlling the origin and nature of sediment organic matter in these beaches also regulating bacterial abundances and the frequency of dividing cells.

Organic matter features, degradation and remineralisation at two coastal sites in the Ligurian Sea (NW Mediterranean) differently influenced by anthropogenic forcing

Organic matter (OM) features, degradation and remineralisation were studied in the seawater of a natural coastal site (Marine Protected Area of Portofino) and at an urbanised coastal site (Quarto, Genoa city) of the Ligurian Sea. The accumulation of low trophic value OM and the persistence of phytoplanktonic biomass throughout the year were observed only at the urbanised site. Efficient OM degradation and remineralisation via high-activity (two times higher than at the Portofino site) hydrolytic enzymatic activities (alkaline phosphatase and leucine aminopeptidase) were recorded. This active degradation indicated a generally good resistance of the Quarto system to environmental pressures (coastal inputs and anthropogenic influence). However, the high potential release of recycled inorganic nutrients and the favourable environmental conditions (i.e. higher seawater temperature at the Quarto site and allochthonous inputs), could encourage unpredictable development of the autotrophic fraction, including an already observed dystrophic blooming of toxic microalgae.

Land forcing controls pelagic-benthic coupling in Adelie Cove (Terra Nova Bay, Ross Sea)

Benthic-pelagic coupling processes were studied in Adelie Cove, a small 70-m deep V-shaped bay, located on the coast of Terra Nova Bay (Ross Sea). This cove is set apart from the open sea by a 12- to 15-m deep sill. Samplings were carried out over 20 days in summer 1997/1998 in the water column, in the sediment and in material collected from the sea-bottom interface by means of a sediment trap. Benthic communities were studied mainly using ROV video tapes. The complex and peculiar interactions between physical, chemical and biological processes, both in the water column and in the sediments, were tightly linked to a katabatic wind pattern, which is the main constraint in water mass circulation. A clear evolution in organic matter distribution and composition was observed. These processes led to a high build-up of materials in the sediments in the deepest part of the cove, which favoured deposit-feeding species and largely contributed to the organic enrichment of the sediments.

Biogeochemistry and algal communities in the annual sea ice at Terra Nova Bay (Ross Sea, Antarctica)

During the fifteenth Italian Antarctic expedition, in the framework of the Pack Ice Ecosystem Dynamics programme, we investigated structure and functioning of the sympagic communities in the annual pack ice at Terra Nova Bay (74 °41.72′ S, 164 °11.63′ E). From November 1 to November 30 1999, we collected intact sea ice cores and platelet ice samples at an interval of 3 days. Ice samples were analysed for inorganic nutrients concentrations, algal biomass and productivity, pigment spectra, extracellular enzymatic activities and bacterial carbon production, micro-algal and metazoan community structure. Autotrophic biomass in the bottom ice increased more than two orders of magnitude from the beginning to the end of November 1999 (i.e. from c. 1–400 mg chlorophyll a m−3). In the same temporal interval, inorganic nutrients concentrations as well as dissolved organic matter sharply increased. Pigment spectra and microscopic analyses revealed that bottom ice communities were different from those of the platelet ice. The bottom-ice sympagic flora was represented almost exclusively by cryobenthic species, whereas platelet ice was characterised by the presence of both cryopelagic and cryobenthic species. Metazoan community in the bottom sea ice was largely dominated by copepods. In particular, the calanoiod Stephos longipes and the harpacticoid Harpacticus furcifer accounted for more than 90% of the sympagic fauna. In the bottom sea ice concentrations of phaeophorbides and other degraded phytopigments were low indicating that most of the sympagic flora was active. These findings suggest that grazing pressure might be only a minor factor controlling or regulating inorganic nutrient concentrations. Conversely, potential degradation rates of organic carbon mediated by extracellular enzymatic activity were very high and largely exceeded organic matter production by photosynthesis.

Meio- and macrofauna communities in three sandy beaches of the northern Adriatic Sea protected by artificial reefs

Interactions between meio- and macrofaunal assemblages and food availability were investigated in relation to tourism pressures on three beaches of the northern Adriatic Sea. All beaches were characterised by the presence of artificial reefs, freshwater inputs and tourism pressures. Beach sediments displayed high organic loads and low protein and chlorophyll a contributions to the bulk of the organic matter. Consequently, the organic matter was of mostly refractory composition and, thus, of scarce nutritional quality. Macrofaunal community structure and biomass were related to the quantity and nutritional quality of sedimentary organic matter, whereas meiofauna was apparently not. No relationships were found between physical variables and the metazoan communities. Most likely, the presence of artificial reefs reduced the physical impact of waves on the beach assemblages, whereas the presence of synergistic human impacts, including freshwater inputs and the tourism pressure, negatively influenced both the meio- and the macrofaunal assemblages.

Relationship between ectoenzymatic activity and availability of organic substrates (Ross Sea, Antarctica): an experimental approach

Abstract Organic matter consumption and decomposition were studied in four experimental systems, having collected different organic substrates in the Ross Sea in December 1994. For the experimental approach selected, processes normally acting on a mixed pool of substances could be separated and the main features of each phenomenon could be focused on. Through the strict relationship between each experimental system and natural conditions shown by organic matter assessment, ectoenzymatic activity trends and their relation with Antarctic water substrates could be described. Through ice melting the water column becomes rich in large pools of substrates, as well as enzyme-producing micro-organisms, capable of quick development. The quantitative predominance of leucine-aminopeptidase throughout the year is well known, but its relative importance seems to decrease when, owing to production events, the environment is enriched with autotrophic- and heterotrophic-derived substances, leading to glycolytic enzymes expression. Thus, ectoenzymatic activity is supposed to be one of the factors responsible for organic matter variations, showing quantitative and qualitative changes depending on substrate availability.