Swimming behaviour and prey perception in the calanoid copepod Clausocalanus furcatus.

Small planktonic copepods (The aim of this PhD thesis was to investigate some aspects of the swimming behaviour of C. furcatus adult female that could shed light on its small-scale interactions with the surrounding environment. In particular, the work was focused on the mechanisms regulating the perception and capture of prey items, in order to understand the success of this species in oligotrophic regions. To this purpose, four different approaches have been utilised: - the numerical characterization of the trajectories performed by freely swimming C. furcatus adult females in presence of dinoflagellate cells and in association with capture events; - the reconstruction of the perception area and of the mechanisms involved in the capture of prey items; - the morphological investigation of the sensory structures present on the first antennae, which bear mechano- and chemo-sensors involved in the perception of external cues; - the evaluation of the sensory performance of the mechanoreceptors on the first antennae by means of electrophysiological experiments. The results of these investigations concur in depicting a coherent scenario. In C. furcatus, the modalities of detecting and capturing prey seem to be forged to efficiently exploit food particles when they are grouped in small patches, and are aimed at maximising the success of C. furcatus in oligotrophic environments

Distinctive diffusive properties of swimming planktonic copepods in different environmental conditions

Suspensions of small planktonic copepods represent a special category in the realm of active matter, as their size falls within the range of colloids, while their motion is so complex that it cannot be rationalized according to basic models of self-propelled particles. Indeed, the wide range of individual variability and swimming patterns resemble the behaviour of much larger animals. By analysing hundreds of three-dimensional trajectories of the planktonic copepod Clausocalanus furcatus, we investigate the possibility of detecting how the motion of this species is affected by different external conditions, such as the presence of food and the effect of gravity. While this goal is hardly achievable by direct inspection of single organism trajectories, we show that this is possible by focussing on simple average metrics commonly used to characterize colloidal suspensions, such as the mean square displacement and the dynamic correlation functions. We find that the presence of food leads to the onset of a clear localization that separates a short-time ballistic from a long-time diffusive regime. Such a benchmark reflects the tendency of C. furcatus to remain temporally feeding in a limited space and disappears when food is absent. Localization is clearly evident in the horizontal plane, but is negligible in the vertical direction, due to the effect of gravity. Our results suggest that simple average descriptors may provide concise and useful information on the swimming properties of planktonic copepods, even though single organism behaviour is strongly heterogeneous

Behaviour-dependent predation risk in swimming zooplankters

Background: The survival of zooplanktonic organisms is determined by their capability of moving in a fluid environment, trading off between the necessities of finding prey and avoiding predators. In previous numerical experiments, we concentrated on the relationship between natatorial modality and encounter success of a virtual copepod swimming in the presence of prey distributed either in patches or uniformly in the environment. Results: In this contribution, we extend this simulation framework to the encounter with chaetognaths, the primary copepod predators, considering different motion rules as a proxy of different swimming strategies and looking at the influence of the concentration of predators and the size of their detection radius in posing a risk on copepod survival. The outcomes of our simulations indicate that more convoluted trajectories are more vulnerable to predator encounter while straighter motions reduce predation risk. Conclusions: Our results are then complemented with those obtained in our previous studies to perform a general cost-benefit analysis of zooplankton motion

Ecophysiological and behavioural responses to salinity and temperature stress in cyclopoid copepod Oithona davisae with comments on gender differences

The gender differences in reaction to salinity (3-50) and temperature (6-26°C) stress were studied in the thermophilic cyclopoid copepod Oithona davisae, introduced in the brackish temperate Black Sea since 2001. Both females and males possessed similar salinity tolerance ranges (6–40) irrespective of the salinity change rate, and females displayed a striking osmotic control upon sharp (18-40 and 40-18) salinity shocks. By contrast, the temperature response of males and females were different. Torpidity was recorded at a temperature below 10°C in males collected both in warm and cold seasons, as well as in summer-autumn females whilst in females grown up at the beginning of winter the locomotor parameters were high even at 6°С. The total metabolic rate of summer-autumn and winter females was determined by the level of basal metabolic rate and energy expenditures due to motor activity. In winter females that maintained high activity at low temperature, the total and basal metabolic rates, differing by 2.3 times at all temperatures within the range of 8–28°C, varied in accordance with the temperature coefficient Q10 of about 2, whereas in summer-autumn females at low temperatures total metabolic rate decreased to the basal level. The plasticity of both males and female to wide ranges in abiotic conditions provide an adaptive strategy to sustain the spreading of O. davisae in diverse environments

Wintertime transport processes in the Gulf of Naples investigated by HF radar measurements of surface currents

Transport processes play a fundamental role in regulating the water renewal in coastal systems. The Gulf of Naples (Southern Tyrrhenian Sea) is a highly urbanised area, receiving pollutant discharges and terrestrial inputs that may reside inside the basin. For this reason, understanding the processes governing coast-offshore transport is of paramount importance for the welfare of the ecosystem and the sustainable exploitation of environmental resources. In this work, we analyse the wind-driven transport over lags of three days in winter reconstructing the basin scale surface circulation by means of High-Frequency radars and evaluating its dependence on wind circulation. Simulations of particle exchange between a coastal and an offshore area have been carried out, outlining the strong relationship between particle fate and circulation structures. Results are interpreted in terms of residence times and possible aggregative areas in the Gulf of Naples

HF Radar Measurements of Surface Waves in the Gulf of Naples (Southeastern Tyrrhenian Sea): Comparison With Hindcast Results at Different Scales

HF radar systems wave measurements are evaluated against numerical simulations in the Gulf of Naples (Southeastern Tyrrhenian Sea). Wave measurements are obtained from three CODAR SeaSonde HF radars installed along the coast of the Gulf of Naples. The numerical models employed are WavewatchIII, implemented on a regional scale with a resolution of about 10 km in longitude and latitude in the whole Mediterranean Sea, and SWAN, implemented with a 200 m resolution in the area of interest. Numerical simulations are also validated against experimental data acquired by a buoy installed offshore the Gulf of Naples. The agreement between HF radar measurements and model hindcasts is evaluated through the estimate of statistical error indices for the main wave characteristics (significant wave height, mean period, and mean direction). The consistency between wave parameters retrieved by HF radars and hindcasted by the models opens the way to future integration of the two systems as well as to the utilization of HF radar wave parameters that could be envisaged for data assimilation in wave models

An integrated reconstruction of the multiannual wave pattern in the gulf of naples (South-Eastern Tyrrhenian Sea, Western Mediterranean Sea)

Surface gravity waves retrieved by a network of HF (High Frequency) radars and measured in situ by an ADCP (Acoustic Doppler Current Profiler) current meter connected to an elastic beacon were used to carry out a multiple-year characterization of the wave field of the Gulf of Naples (south-eastern Tyrrhenian Sea, western Mediterranean). The aim of the work was to create a climatology of the study area and to demonstrate the potential of an integrated platform for coastal studies. The patterns recorded by the different instruments were in agreement with the wave climatology of the southern Tyrrhenian Sea as well as with previous scores for the same area. The results presented in this work also highlight seasonal and interannual consistency in the wave patterns for each site. In a wider context, this study demonstrates the potential of HF radars as long-term monitoring tools of the wave field in coastal basins, and supports the development of integrated observatories to address large-scale scientific challenges such as coastal ocean dynamics and the impact of global change on the local dynamics

Spreading factors of a globally invading coastal copepod

The Mediterranean Sea is one of the areas most affected by alien invasions, which are continuously increasing also due to intense human activities and environmental changes that favor the introduction of species previously unable to colonize the basin. This is the case of the copepods of the genus Pseudodiaptomus, first described in the Indian Ocean and considered one of the most resistant to unfavorable conditions but never recorded in the Mediterranean until 2011 though present in adjacent seas. Pseudodiaptomus marinus, in particular, is common in shallow marine-brackish waters and is one of the species often found in ballast waters and in aquaculture plants. Native of Japan, it has started spreading since 1950s and its populations have established in several harbours, eutrophic inlets and lagoons along the coasts of the Pacific and Indian Oceans. In the last few years, P. marinus has been increasingly reported in European Seas (Mediterranean Sea and North Sea). In this paper, we review the invasion history of this species with a special emphasis on its records in the Mediterranean Sea, and its occurrence and establishment in Sicilian waters. We also compare the biological traits and population dynamics of P. marinus with those of other representative of the genus and discuss about the possible mechanisms of introduction in new environments. Aim of our work is to understand the reasons of successful invasion of P. marinus and the environmental and biological factors that may lead to its further biogeographic expansion

ITS2 in calanoid copepods: reconstructing phylogenetic relationships and identifying a newly introduced species in the Mediterranean

Phylogenetic inference and molecular taxonomy are becoming increasingly important approaches to classical morphological systematics and marine ecology. The number of molecular markers suitable for such goals is quite high, but general use restricts the list to a few of them, mainly mitochondrial (namely cytochrome c oxidase subunit I, COI and Cytochrome b), especially in copepods. The ribosomal cistronic regions have been widely used for broad phylogenetic analyses in different taxa. Among them, the internal transcribed spacers (ITS rDNA) are powerful tools for phylogenetic reconstructions at the different taxonomic levels, although not yet extensively used for copepods. In the present work, we tested the suitability of ITS2 rDNA marker to reconstruct the phylogenetic relationships of calanoid copepods using sequences retrieved from GenBank, complementing the phylogenetic positions of the species studied with their morphological and ecological traits. Through ITS2 rDNA we provided the first molecular evidence for the invasive calanoid Pseudodiaptomus marinus from the Mediterranean Sea (Lake Faro, Sicily, Italy), and compared it with the GenBank ITS2 sequences for P. marinus from Korea and other calanoid species. The divergence of the sequences of our P. marinus from those of Korean specimens was quite prominent (4.4%) and allowed us to hypothesise either a new forma living in the Mediterranean or a cryptic species. This study highlights the appropriateness of ITS2 for phylogenetic reconstructions and species identification, as well as for barcoding, meta-barcoding and phylogeographic approaches, and evidences the need for a more thorough knowledge of ribosomal regions in copepods from different sites