A. Granata

Distribution and abundance of postlarval and juvenile Pleuragramma antarcticum (Pisces, Nototheniidae) off Terra Nova Bay (Ross Sea, Antarctica)

Abstract During the Italian Antarctic Expedition of 1987–1988 zooplankton was collected in Terra Nova Bay (Ross Sea) by a multinet BIONESS (250-μm or 500-μm net mesh size). The early life history of Pleuragramma antarcticum was described from 268 samples. More than 98% of a total of 34,436 fish larvae belonged to P. antarcticum. The mean relative abundance in the whole area for positive 0 to 150-m hauls was 434 ind./100 m3 (±720 SD). Postlarvae were most abundant and frequent in the samples (99.8%) while low concentrations of juveniles were found (n=67). Length of age group 0 ranged from 8 to 20 mm and age group 1+ were from 36 to 53 mm. Average growth rate over a period of 1 year was 0.08 mm per day. Based on modal values, the mean daily increment of P. antarcticum postlarvae in the period 5 January to 2 February (29 days) was about 0.21 mm. Highest abundances occurred near Cape Washington (mean: 2,108 ind./100 m3) while lower densities were recorded in the northern basin of the self (31 ind./100 m3). Horizontal and vertical distribution patterns in Terra Nova Bay seem to be strictly correlated to hydrographic features and different water masses with highest densities associated with the westward flowing current of the limb of the Antarctic coastal current and southern limb of the Ross Sea Gyre. These currents become part of the clockwise gyre in Terra Nova Bay. More than 62% of the postlarvae were collected in well-stratified warm surface water (0–50 m) near the summertime thermocline (20–70 m). The northern part of Terra Nova Bay seems to represent nursery ground of early stages of P. antarcticum and the presence of permanent polynya could provide favourable food conditions for development of the first stages of life. Differing distribution patterns probably reflect an interaction of various parameters including bathymetry, floating ice shelf, hydrographic features such as currents, local eddies and frontal systems, with P. antarcticum postlarval biology (spawning) and ecology (feeding, horizontal and vertical distribution patterns).

Ichthyoplankton abundance and distribution in the Ross Sea during 1987–1996

Abstract. During Italian expeditions, ichthyoplankton was collected in the Ross Sea and Terra Nova Bay, by BIONESS and Hamburg Plankton Net (250-µm and 500-µm mesh, respectively). A total of 394,453 fish larvae representing 46 species, 27 genera and 9 families were collected. Pleuragramma antarcticum dominated during three of the four cruises, whilst in 1994/1995 Trematomus lepidorhinus was also abundant. The most abundant icefish was Chionodraco myersi, which co-occurred with P. antarcticum. Macrouridae, Myctophidae and Bathylagidae were oceanic. Paralepididae occurred in all areas. Notothenioids, nearly 100% of the catch, occurred close to the coast and dominated the shelf ichthyoplankton community.

Copepods in spring annual sea ice at Terra Nova Bay (Ross Sea, Antarctica)

The aim of this study was to investigate patterns of abundance, distribution, temporal changes and species composition of the dominant ice-associated copepods in the spring annual pack ice, platelet ice and water column at Terra Nova Bay, Ross Sea, during late spring 1997. Ice cores were drilled for temporal and spatial scales. Stephos longipes and Harpacticus furcifer dominated the sea ice meiofauna in terms of numbers in the lower few centimeters of the bottom ice associated with high chlorophyll a and phaeopigment levels. Nauplii dominated the S. longipes population (91.6%) and occurred in extremely high concentrations. In contrast, copepodids were the dominant stages in H. furcifer. How H. furcifer carries out its entire life cycle and how it differs from ecologically similar species such as Drescheriella glacialis should be examined in more detail.

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.

Distribution, biomass and ecology of meso-zooplankton in the Northern Adriatic Sea

Two oceanographic cruises were carried out in the northern Adriatic Sea, from June, 1996 to February, 1997. Samples were collected using a BIONESS electronic multinet (204 samples on 54 stations) along inshore-offshore sections. Zooplankton abundance and biomass were estimated in relation to the variability of temperature, salinity and fluorescence. Spatial and vertical distribution patterns of the most important zooplankton groups were studied. During June, in the northern area, abundance and biomass of 2787 - 1735 r ind m and 29.3 - 26.7 r mg r m, respectively, were reported. The zooplankton community was constituted essentially by copepods and cladocerans. In the southern area, instead, an abundance of 4698 - 5978 r ind r m and a dry weight of 25.4 - 15.3 r mg r m were observed, with a reverse dominance ratio between these groups. In February, in the northern area the zooplankton community (1380 - 595 r ind r m and 19.6 - 9.9 r mg r m) was mainly constituted by copepods, larvae of invertebrates, appendicularians and cladocerans; in the southern area zooplankton average abundance was 969 - 493 r ind r m and 9.9 - 3.2 r mg r m being copepods, cladocerans, appendicularians and larvae of invertebrates. The zooplankton spatial distribution, in this period, did not show the classic inshore-offshore gradient. Spatial distribution and biomass values of zooplankton, in the northern Adriatic Sea, were strongly influenced by hydrological characteristics, allowed up to formulate a preliminary model about distribution, along the water column, of the different associations of species assemblages with regard to different water masses in the neritic system.

Diversity and Vertical Migration of Euphausiids Across the Straits of Messina Area

Samples used for this research were collected during the oceanographic cruises POP — EOCUMM ′95 (15 to 30 July 1995, N/O Italica) and carried out by a BIONESS multinet. Samples were taken on 8 stations, in lonian and in South Tyrrhenian Seas, across the Straits of Messina. All stations have been sampled at regular intervals of six hours (6.00 h; 12.00 h; 18.00 h; 24.00 h). The maximum sampled depth was 2030 m. A total of 5801 specimens of juvenile and adult euphausiids, belonging to 11 species (Thysanopoda aequalis, Meganyctiphanes norvegica, Euphausia krohni, E. brevis, E. hemigibba, Nematoscelis megalops, N. atlantica, Stylocheiron suhmi, S. longicorne, S. abbreviatum and S. maximum) were found and species composition of the two basins was related. N. megalops and E. krohni were the most common in the lonian Sea-Straits of Messina area, while in South Tyrrhenian Sea, T. aequalis, E. hemigibba and S. abbreviatum were the dominant species. Different abundance values and occurrence mean depths for juveniles and adults were underlined in the two areas just for the most important species. Day/night vertical distributions of the most representative species, in both areas, were studied.

Spatial Distribution and Feeding Habits of Larval and Juvenile Pleuragramma Antarcticum in the Western Ross Sea (Antarctica)

During four spring-summer Italian Antarctic expeditions to Terra Nova Bay and the Western Ross Sea in 1988, 1989–90, 1994–95 and 1996, zooplankton and ichtyoplankton were collected by a multinet BIONESS (250 μm and 500 μm) and PHN (500 μm), respectively. Nototheniids were predominant in the whole study area, representing 97.3% of all larvae. Pleuragramma antarcticum was the dominant species sampled in the spring-summer cruises of 1987–88 (98.6%), 1989–90 (95.9%) and 1995–96 (99.8%), while it predominated in association with Trematomus lepidorhinus in 1994–95. The early life history of Pleuragramma antarcticum was described from 891 samples. Maximum abundances of P. antarcticum postlarvae were confined to Terra Nova Bay. The mean relative abundance in the whole area in summer 1988, for positive 0- to 150-m hauls, was 434 (±720 SD) specimens 100 m−3 and 158 (±212 SD) specimens per 100 m3 in January 1990 for positive 0-140-m hauls. Off Terra Nova Bay, postlarval abundance did not exceed 5-86 individuals 100 m−3. Juvenile Pleuragramma antarcticum showed a more oceanic occurrence than postlarvae of the same species. Low concentrations between 0.1 and 12.5 ind 100 m−3 (mean 1.66 ± 2.88 SD) were recorded in offshore waters between 170° and 175°E and in the southern part of Terra Nova Bay. Postlarvae (n = 4385) ranged between 7 and 23 mm SL (mean 13.9 ± 1.62 SD) and juveniles (n = 388) were between 28 and 53 mm SL (mean 40.0 ± 4.78 SD). A growth rate of 0.08 mm day−1 was confirmed for the first year. The daily increments of Pleuragramma antarcticum postlarvae estimated from sequential sampling in 1987–88 from Terra Nova Bay and in 1995–96 from the southern western Ross Sea were about 0.21–0.25 mm. The co-occurrence of different postlarval size classes during the investigations confirm that two hatching periods occurred in Terra Nova Bay between early and late December. The presence of early stages in January 1988, 1990 and 1996 (7–9 mm SL) confirms that Pleuragramma antarcticum spawn in Terra Nova Bay. Highest concentrations of postlarvae occurred at the edge near Cape Washington and in the inshore waters of Drygalski Ice Tongue. These areas seem to represent a nursery ground of early stages, where the presence of permanent polynyas could provide favourable food conditions for the development of the first stages of life. More than 62% of the postlarvae were collected in well-stratified Antarctic Surface Waters (AASW) with temperature values that exceed 0°C and vertical distribution appears to be related to the summertime thermocline. From these sites, early stages were drifted by a westward-flowing current of the limb of the Antarctic coastal current and the southern limb of the Ross Sea Gyre. These large gyres favoured postlarval retention mostly in northern and southern areas of Terra Nova Bay, preventing the drift north of Cape Washington, south of Drygalski Ice Tongue and in offshore waters beyond 170°E. Thus, the youngest planktonic stages of Pleuragramma antarcticum concentrate in the surface mixed layer of Terra Nova Bay where feeding conditions are favourable. In the size classes 8-17 mm the diet was dominated by calanoid eggs (35.5%), Limacina (32.1%) and tintinnids (17.6%). The cyclopoid copepod Oncaea curvata contributed to 7.1% of the diet.

Zooplankton responses to hydrological and trophic variability in a Mediterranean coastal ecosystem (Lesina Lagoon, South Adriatic Sea)

Spatial and temporal variability in zooplankton was studied at eight stations located in the Lesina Lagoon (South Adriatic Sea) Salinity, temperature, dissolved oxygen and chlorophyll a (in the lagoon) at these stations were also assessed. The zooplankton community was characterised by clear seasonal oscillations and mostly represented by copepods and their larvae. The dominant copepod species were Calanipeda aquaedulcis and Acartia tonsa, which exhibited spatial–temporal segregation in the lagoon. C. aquaedulcis copepodites seemed to be better adapted to oligotrophic and oligohaline conditions compared with the A. tonsa population. The invasive species A. tonsa has completely replaced the formerly abundant Acartia margalefi. A positive correlation was found between abundances, total species numbers and trophic state. An increasing abundance trend was shown from the lagoon towards the sea. The highest diversity indices were recorded at the two channel inlets, during high tide due to the absence of a clear dominance of one or more coastal species and the co-occurrence of species of lagoon and marine origin.

Preliminary data on egg production rates of Pseudocyclops xiphophorus Wells, 1967 from the brackish lake Faro (north-eastern Sicily)

Field and laboratory studies were carried out on the bentho-planktonic species P. xiphophorus Wells, 1967. This species was found in the Mediterranean Sea, in the brackish Lake Faro (north-eastern Sicily) for the first time. Specimens of P. xiphophorus were collected from November 2003 to September 2004. Immediately after sampling, all adult females were sorted and pipetted individually into 50 ml crystallizing dishes containing lake water and incubated at the same enviromental temperature, measured at the sampling time. After 24 h, the number of eggs produced by each female was counted to estimate in situ egg production rate. In the laboratory, groups of five couples of males and females were placed individually into 50 ml crystallizing dishes containing filtered sea water enriched with three phytoplankton species, Tetraselmis suecica, Pavlova lutheri, and Isochrysis galbana, given in excess concentrations. Groups of five replicates were incubated at three different temperatures, 16, 24, and 28 °C, for each replicate. Every couple was monitored daily during the entire life cycle to estimate egg production rate in relation to temperatures. In the laboratory, mean egg production rates per female per day for each group of couples exhibited a positive correlation with temperature that was recorded in in situ experiments as well.

Use of biomarkers in zooplankton for assessment of the ‘health status’ of marine and brackish environments: a short overview

The biomarker approach has been used for 25 years to study the environmental quality of marine, brackish and freshwater ecosystems. Biomarkers may indicate health status and can be applied to organisms of all zoological phyla by destructive or non destructive methods. For 5 years we have been using this approach in zooplankton to detect ecotoxicological alterations at low levels of the food chain due to contaminants. Here we review our approach to validate and apply biomarker techniques in zooplankton. We discuss advantages, limitations, some results and future research. We indicate that biomarkers in zooplankton can be used as new indices of trophic status and ecological integrity of Italian marine coastal and lagoon environments, to be included among the tools specified by Italian law D.Lgs. 152/2006.