Giacomo Zagami

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.

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.

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.

Short-term Variability of Mesozooplankton in a Mediterranean Coastal Sound (Stagnone di Marsala, Western Sicily)

Short-term variations in mesozooplankton were studied during four 24-h periods at one station in a Mediterranean coastal sound (Stagnone di Marsala, western Sicily) in May, July and October 1996 and March 1997. Zooplankton samples were collected every three or six hours with a plankton net (mesh size 125 µm) towed horizontally at the surface. Hydrometric data (height of tide, speed and direction of current) were also recorded to assess the influence of the hydrodynamic conditions on fluctuations in zooplankton abundance and changes in population structure. The zooplankton assemblages were markedly dominated by copepods and their naupliar stages, which consistently accounted for more than 95% of the total numbers. Peaks in abundance were always recorded at night, due to the increase in coastal forms (mainly of the genus Acartia) and to a lesser extent in autochthonous forms (harpacticoids).The short-term variability of zooplankton seemed to be related both to hydrodynamic factors (tidal and wind-driven currents) and to the nocturnal upward migration of organisms.

Short-term changes in zooplankton community in Paso Ancho basin (Strait of Magellan): functional trophic structure and diel vertical migration

Knowledge on community structure oriented to describe energy flow during late summer season in Paso Ancho basin (Strait of Magellan) is scarce and particularly affected by vertical diel migration (VDM). The main aim of this work is to identify the VDM patterns of selected species and functional feeding groups of mesozooplankton, collected by the electronic multinet BIONESS in 1995. Detailed studies were carried out on keystone components of the community: 7 species of copepods (Ctenocalanus citer, Drepanopus forcipatus, Metridia lucens, Clausocalanus brevipes, Scolecithricella minor, Paraeuchaeta antarctica, Calanus simillimus), one ostracod (Discoconchoecia elegans), one chaetognath (Sagitta tasmanica), one euphausiid (Euphausia vallentini), and two polychaetes (Pelagobia longicirrata, Tomopteris planktonis). Unexpected deviations from the classic pattern reported in literature were uncovered. The shallow layer mesozooplankton at night, although dominated by exclusively or preferentially herbivores, particularly by E. vallentini, was not represented by several species known as herbivores that remained in the deep layer throughout the day cycle. The deep-layer zooplankton throughout the day cycle was well represented by carnivores, detritivores, and omnivores. It is suggested that during low-chlorophyll summer conditions, the composition of functional groups and diet, and VDM patterns changed to take advantage of sinking phytoplankton and picoplankton in deep layers. Pelagic-benthic coupling would be strengthened due to animals that suppressed their vertical daily rise to the shallow layer at nights but remained in the deep layers to feed on a rain of particulate organic matter and other non-migrant zooplankton.

Postembryonic Development of Pseudocyclops Umbraticus Giesbrecht, 1893 (copepoda, Calanoida) from Coastal Waters of Sicily

The authors describe the six naupliar and five copepodid stages of Pseudocyclops umbraticus raised in the laboratory. These are the first data on the ontogenetic stages of a species of the genus Pseudocyclops. On the basis of these results and the adult morphology (Giesbrecht, 1893), the authors place P. umbraticus in an intermediate position between the lepidotus-kulai and crassiremismagnus groups of Ohtsuka et al. (1999).

Food type effects on reproduction of hyperbenthic calanoid species Pseudocyclops xiphophorus Wells, 1967, under laboratory conditions

Egg production, hatching success and naupliar survival were determined for Pseudocyclops xiphophorus pairs fed a Skeletonema marinoi, a flagellate (Tetraselmis suecica, Pavlova lutheri and Isochrysis galbana) and a mixed (Skeletonema and flagellates) diet. Pairs fed Skeletonema marinoi showed significantly lower egg production and naupliar survival than couples fed flagellates and mixed diet. But hatching success was more or less similar with the three food types. Furthermore, feeding experiments demonstrated a clear preference of P. xiphophorus for the flagellate food type.

Distribution and Ecology of Mesozooplankton in the Northern and Central Adriatic Sea

Within the framework of the Prisma 2 Project, four oceanographic cruises were carried out in the central and northern Adriatic Sea from June 1996 to March 1997. Samples were collected both by BIONESS electronic multinet (204 samples from 54 sites) and by WP2 (101 samples from 19 sites) along inshore-offshore sections. The spatial-temporal distribution of the zooplankton community was analysed in relation to the variability of physico-chemical and biological parameters. The seasonal succession of the zooplankton community was characterized by an inversion of the dominance ratio between copepods and cladocerans. In early June, copepods and cladocerans represent on average 52 and 20% of the zooplankton community, respectively, while in late summer they represent 17 and 66%. During late spring-summer, the cladoceran population was clearly dominated by Penilia avirotris, which in some coastal sites constituted more than 90% of the zooplankton. In the coastal zone, the copepod population was characterized by low species diversity and greater dominance of A. clausi, P. parvus and T. stylifera (73% of the population). In the offshore zone of the neritic system, there was instead a more homogeneous copepod species composition. Because of their spatial distribution patterns, P. elongatus and T. longicornis, typical of estuarine environments,can be considered as hydrological indicator species of different water masses of the Adriatic neritic system. In winter, the zooplankton community was characterized by strong dominance of copepods (31 species identified), on average constituting 75% of the zooplankton, followed by invertebrate larvae, appendicularians, cladocerans, siphonophores and chaetognaths. From our analysis of the spatial distribution of the zooplankton community, we have formulated a preliminary trophic model concerning the association of ecologically similar species in the water masses of the Adriatic neritic system.

Spring and autumn spatial distribution of zooplankton carbon requirement across the Mediterranean Sea

ABSTRACT Zooplankton represents a key contributor to the ocean biological pump through its consumption of sinking and suspended carbon. A specific and highly sensitive method to evaluate zooplankton carbon requirement from the sinking flux is through the estimation of the activity of the electron transport system. The present study was carried out from samplings in 2006, and it was focused on the spatial 200–0 m zooplankton carbon demand across 24 sampling stations, along the Mediterranean Sea, from the island of Crete to the Strait of Gibraltar. Its potential day/night variability was evaluated. The zooplankton composition, abundance and biomass were investigated. The carbon demand per unit zooplankton biomass indicates geographical and diel differences among the sampling stations. A higher mean carbon demand was seen for the western Mediterranean with respect to the eastern Mediterranean, which can be justified through the observed ratio of gelatinous:crustacean taxa and the water temperatures recorded. Higher carbon demand was measured in samples collected during the dark hours. The relation to the presence and abundance of actively migrating euphausiids and copepods was discussed. A comparison with data from another of our study carried out in the same study area but in another seasonal period was done.