E. Crisafi

Particulate matter composition and bacterial distribution in Terra Nova Bay (Antarctica) during summer 1989–1990

Spatial distributions of particulate organic matter (POM) and microbes were investigated during the summer of 1989–1990 in the coastal waters of Terra Nova Bay (Antarctica). The elemental (organic carbon and nitrogen) and biochemical (lipids, proteins, carbohydrates, DNA and RNA) composition of organic matter was related to bacterioplankton abundance, and pico-phytoplankton density. The ATP concentrations were also measured to gather information about the relationships between particulate matter composition and microbial distribution in Antarctic waters. Total seston was characterized by little spatial variation and was unrelated to the distance from the coast. Suspended particulate matter included some terrestrial components but was mostly composed of autochthonous material. POM was characterized by a uniform distribution and homogeneous composition (mostly of phytoplanktonic origin), and was associated with a relatively scarce microbial community characterized at the surface by high picophytoplankton density. The increase with depth of the living carbon fraction suggested an increase in the microheterotrophic community in the deeper water layers. A significant positive relationship between total bacterioplankton density, and carbohydrate and RNA concentrations was found. Similar significant relationships between pico-phytoplankton abundance and lipids, proteins, carbohydrates and nucleic acids were observed. On the basis of the close coupling found between microbiological and chemical compartments, it seems that, in Terra Nova Bay, bacterial distribution depends on suspended matter and in particular to the labile fraction of the organic detritus.

Assessment of the ecological status of transitional waters in Sicily (Italy): First characterisation and classification according to a multiparametric approach

A 1-year cycle of observations was performed in four Sicilian transitional water systems (Oliveri-Tindari, Cape Peloro, Vendicari and Marsala) to characterise their ecological status. A panel of variables among which trophic and microbial (enzyme activities, abundance of hetetrophic bacteria and of bacterial pollution indicators) parameters, were selected. Particulate organic carbon (POC) and nitrogen (PON) and chlorophyll-a (Chl-a) contents defined the trophic state, while microbial hydrolysis rates and abundance gave insights on microbial community efficiency in organic matter transformation and on allochthonous inputs. To classify the trophic state of examined waters, the synthetic trophic state index (TRIX) was calculated. Microbial hydrolysis rates correlated positively with POC and Chl-a, which increased along the eutrophication gradient. The significant relationships among TRIX, trophic and microbial parameters suggested the use of leucine aminopeptidase, alkaline phosphatase and POC as suitable parameters to implement the Water Framework Directive when assessing the ecological status of transitional water systems.

Prokaryotic activities and abundance in pelagic areas of the Ionian Sea

The Ionian Sea represents a suitable basin for studying the biogeochemical processes mediated by microbial activities. Because of its characteristics as a crossing region between the western and eastern Mediterranean Sea, it is one of the sites most affected by changes in water mass composition and dynamics, caused by the Eastern Mediterranean Transient (EMT). To date, relatively few data exist on microbial activities in pelagic areas of the Ionian Sea. From 1998 to 2004, during different research cruises, prokaryotic parameters (abundance, extracellular enzyme activities leucine aminopeptidase, β-glucosidase, alkaline phosphatase, bacterial production and respiration) were measured together with culturable bacteria and the main physical, chemical and trophic parameters (temperature, salinity, nutrients, particulated organic matter). The aim of the study was to describe the spatial and temporal variability in microbial activities involved in the carbon and phosphorus cycles, in different layers. Results showed that organic matter transformation mediated by the microbial community displayed a significant increase in autumn, highlighting the occurrence of significant changes at meso- and bathypelagic depths. Unlike the dark ocean, bacterial growth efficiency in the Ionian Sea, which increased with depth, seemed to vary from being a source of carbon in the epipelagic layer to a sink in the meso- and bathypelagic layers. The mechanism of phosphatase regulation showed a weak inverse correlation between specific phosphatase and inorganic P in all seasons except autumn. It is worth mentioning that the reported results constitute, to the best of our knowledge, one of the available datasets giving information about microbial activities in the Ionian Sea.

Microbial Biomass and Respiratory Activity Related to the Ice-Melting Upper Layers in the Ross Sea (Antarctica)

In late austral spring 1994, a study was carried out in the Ross Sea, with sampling in the ice-free, ice-covered and marginal ice zones. Samples were taken along two transverse transects, to determine spatial variations in some microbiological parameters. Some stations were repeatedly sampled to study the temporal development of microbial components. Microbial biomass was measured as fractionated ATP in the following size categories: micro- (250–10µm), nano- (10–2µm) and picoplankton (2–0.2µm); bacterial biomass was estimated on the basis of lipopolisac-charide concentration and microbial respiratory rate was estimated by the Electron Transport System activity of organisms <200 µm.

Detection of Photobacterium damselae Subsp. piscicida in Seawaters by Fluorescent Antibody

A fluorescent antibody (FA) technique specific for Photobacterium damselae subsp. piscicida was tested via challenge experiments performed in microcosms. In the challenge tank, the pathogen concentration trended from 1.71 × 106 to 0 cell/100 ml, respectively, on the first and last days of the experiment. In the control tank, the pathogen was never detected. Results showed that the FA protocol could be used as a rapid and specific method allowing the early detection of Photobacterium damselae subsp. piscicida in fish farm waters. FA enables early detection of photobacteriosis in the environment, as bacteria can be detected even in absence of clinical sign of disease.

Microbiological characterization of a semi-enclosed sub-Antarctic environment: the Straits of Magellan

Among sub-Antarctic ecosystems, the microbiology of the Straits of Magellan has been poorly documented due to the scarcity of observations. In this context, the spatial distribution of microbiological parameters, both in terms of abundance (total picoplankton and picophytoplankton, cultivable heterotrophic bacteria) and biochemical assays (adenosine triphosphate and lipolysaccharide estimations, as well as electron transport system activity), was investigated in the epipelagic layer along the Straits during late summer 1991 and early autumn 1995. The microbial dynamics showed significant variations along the Straits, with increasing values generally determined eastward both in 1991 and 1995. Microbiological results were additionally correlated with available data on the physico-chemical and biological properties of the analyzed water masses. Taking into consideration the whole dataset, the principal component analysis led to the identification of three main macro-areas along the Straits of Magellan (Paso Largo, Paso Ancho and Angostura/Isla Isabel) with different trophic features. This held true when the two cruises were individually considered, as well as when comparing each macro-area between the two cruises. Additionally, a first attempt to quantify the carbon flux through the microbial compartment within the main identified macro-areas was made. The present work will allow the gaining of further understanding of the microbiology of this under-investigated sub-Antarctic marine ecosystem.