Monica Bressan

First evidence of immunomodulation in bivalves under seawater acidification and increased temperature

Water acidification, temperature increases and changes in seawater salinity are predicted to occur in the near future. In such a global climate change (GCC) scenario, there is growing concern for the health status of both wild and farmed organisms. Bivalve molluscs, an important component of coastal marine ecosystems, are at risk. At the immunological level, the ability of an organism to maintain its immunosurveillance unaltered under adverse environmental conditions may enhance its survival capability. To our knowledge, only a few studies have investigated the effects of changing environmental parameters (as predicted in a GCC scenario) on the immune responses of bivalves. In the present study, the effects of both decreased pH values and increased temperature on the important immune parameters of two bivalve species were evaluated for the first time. The clam Chamelea gallina and the mussel Mytilus galloprovincialis, widespread along the coast of the Northwestern Adriatic Sea, were chosen as model organisms. Bivalves were exposed for 7 days to three pH values (8.1, 7.7 and 7.4) at two temperatures (22 and 28°C). Three independent experiments were carried out at salinities of 28, 34 and 40 PSU. The total haemocyte count, Neutral Red uptake, haemolymph lysozyme activity and total protein levels were measured. The results obtained demonstrated that tested experimental conditions affected significantly most of the immune parameters measured in bivalves, even if the variation pattern of haemocyte responses was not always linear. Between the two species, C. gallina appeared more vulnerable to changing pH and temperature than M. galloprovincialis. Overall, this study demonstrated that climate changes can strongly affect haemocyte functionality in bivalves. However, further studies are needed to clarify better the mechanisms of action of changing environmental parameters, both individually and in combination, on bivalve haemocytes.

Can the combination of decreased pH and increased temperature values induce oxidative stress in the clam Chamelea gallina and the mussel Mytilus galloprovincialis

The combined effects of decreased pH and increased temperature values on antioxidant enzyme activities and lipid peroxidation were evaluated for the first time in the clam Chamelea gallina and the mussel Mytilus galloprovincialis, two bivalve species that are widespread along the northwestern coast of the Adriatic Sea. For 7 days, bivalves were exposed to three pH values (8.1, 7.7 and 7.4) at two temperatures (22 and 28 °C). Three independent experiments were carried out at salinity values of 28, 34 and 40 psu. Superoxide dismutase, catalase and glutathione S-transferase activities as well as lipid peroxidation were measured in the gills and digestive gland of the bivalves. The results demonstrated that the experimental conditions significantly influenced the biochemical parameters of the bivalves, although the variation pattern varied depending on the species and tissues analysed.

Seasonal variations in biochemical composition and condition index of cultured mussels (Mytilus galloprovincialis Lmk) in the Lagoon of Venice (North Adriatic)

Abstract Seasonal changes in the main biochemical components and in the condition index of cultured mussels (Mytilus galloprovincialis Lmk) from the Venice Lagoon have been followed during the period October 1979–August 1981. Carbohydrates (2–32%) show winter minima and summer maxima, while proteins (30–52%) have a rather irregular pattern. Lipids (2–13%) and condition index exhibit an annual cycle with two minima (late spring; autumn-winter) and two maxima (early spring; summer). Seasonal variations of biochemical composition and condition index are discussed in connection with the reproductive cycle and some environmental parameters such as temperature and phytoplankton availability. The comparison between the present data and those from other geographic areas confirms the peculiarity of the environment of the Venice Lagoon.

Does seawater acidification affect survival, growth and shell integrity in bivalve juveniles?

Anthropogenic emissions of carbon dioxide are leading to decreases in pH and changes in the carbonate chemistry of seawater. Ocean acidification may negatively affect the ability of marine organisms to produce calcareous structures while also influencing their physiological responses and growth. The aim of this study was to evaluate the effects of reduced pH on the survival, growth and shell integrity of juveniles of two marine bivalves from the Northern Adriatic sea: the Mediterranean mussel Mytilus galloprovincialis and the striped venus clam Chamelea gallina. An outdoor flow-through plant was set up and two pH levels (natural seawater pH as a control, pH 7.4 as the treatment) were tested in long-term experiments. Mortality was low throughout the first experiment for both mussels and clams, but a significant increase, which was sensibly higher in clams, was observed at the end of the experiment (6 months). Significant decreases in the live weight (-26%) and, surprisingly, in the shell length (-5%) were observed in treated clams, but not in mussels. In the controls of both species, no shell damage was ever recorded; in the treated mussels and clams, damage proceeded via different modes and to different extents. The severity of shell injuries was maximal in the mussels after just 3 months of exposure to a reduced pH, whereas it progressively increased in clams until the end of the experiment. In shells of both species, the damaged area increased throughout the experiment, peaking at 35% in mussels and 11% in clams. The shell thickness of the treated and control animals significantly decreased after 3 months in clams and after 6 months in mussels. In the second experiment (3 months), only juvenile mussels were exposed to a reduced pH. After 3 months, the mussels at a natural pH level or pH 7.4 did not differ in their survival, shell length or live weight. Conversely, shell damage was clearly visible in the treated mussels from the 1st month onward. Monitoring the chemistry of seawater carbonates always showed aragonite undersaturation at 7.4 pH, whereas calcite undersaturation occurred in only 37% of the measurements. The present study highlighted the contrasting effects of acidification in two bivalve species living in the same region, although not exactly in the same habitat.

Effects of linear alkylbenzene sulphonate (LAS) on two marine benthic organisms

Abstract The effects of dissolved linear alkylbenzene sulphonate (LAS) on two marine benthic filter-feeders, the sea-squirts Botryllus schlosseri and Botrylloides leachi, were tested. The survival and growth rates of both species were significantly affected at LAS concentrations ranging from 0.25 to 0.50 ppm. Larvae were apparently more resistant than adults. However, treatments beginning at the pelagic stage strongly affected the negative response of the next benthic phase, although the pelagic stage only lasted 1.5% of the total duration of the treatment, indicating that the effects of LAS are exerted mainly on this phase of the life cycle.

Influence of temperature and salinity on embryonic development ofParacentrotus lividus (Lmk, 1816)

The combined effects of temperature and salinity on early development of the sea urchinParacentrotus lividus (Lmk, 1816) are reported. The optimal temperature-salinity combinations for development are 18 °–20 °C and 34–35‰; there is a significant temperature-salinity interaction. The optimal conditions found in the experiments are above the mean yearly values for the sampled populations environment (North Adriatic Sea), being more similar to those of the Tyrrhenian Sea. These results suggest that embryonic tolerances to temperature and salinity are under genetic and not environmental control.

Reproductive cycle of the mussel (Mytilus galloprovincialis Lmk) in Venice Lagoon (North Adriatic)

Abstract The reproductive cycle of Mytilus galloprovincialis Lmk cultured in Venice Lagoon has been studied from 1979 to 1982. Histology of the gonads shows that the gametes are ripe from September to May, when several spawnings occur with a peak at the end of winter (January -February). Reproductive activity is quiescent between July and August but release of gametes is possible even in summer, if only to a limited extent.

Effects of linear alkylbenzene sulphonate (LAS) on skeletal development of sea urchin embryos (Paracentrotus lividus LMK)

Abstract Linear alkylbenzene sulphonate (LAS) acts on the zygotes of the sea urchin Paracentrotus lividus , inducing total inhibition of skeletal development at concentrations higher than 0.45 ppm and a significant decrease at concentrations of 0.30 ppm. The effect of the surfactant is maximum at the end of gastrulation, when calcium uptake is very high, presumably related to the beginning of skeletal growth. This suggests that, in the environment, the sequestering action of LAS on calcium may significantly affect the availability of this ion for morphogenesis. Nevertheless, the experimental data presented in this paper suggest that the toxic action of LAS is also exerted at levels other than those involved in calcium uptake.

Seasonal distribution of Oikopleura (Larvacea) in the lagoon of Venice

Abstract The appendicularian population in the ebb and flow of the lagoon of Venice was studied for two years. Only three species were found, Oikopleura dioica, O. longicauda and O. fusiformis, the former being the more abundant. The seasonal distribution of the species was correlated to the hydrological conditions of the upper Adriatic Sea. There was a dramatic decrease (about 802) in the biomass of these appendicularians inside the lagoon between flow and ebb tide.

Combined effects of temperature and salinity on sexual reproduction and colonial growth of Botryllus schlosseri (Tunicata)

Abstract Combined effects of temperature and salinity on sexual reproduction and colonial growth of Botryllus schlosseri have been studied in nine experimental samples at several combinations of temperature (from 13° to 25°C) and salinity (from 25% to 40% S). Within such bounds the two environmental parameters do not influence the initial growth (at least not up to the 5th blastogenetic generation) or the formation of gonads in buds. A marked effect of experimental conditions is noted, instead, on the subsequent colonial growth and gonad maturation. The two processes present opposite thermosaline optima. The high temperature and the intermediate salinity stimulate the maturation of gonads, the low temperature and extreme salinities stimulate colonial growth. The ecological meaning of such behaviour is discussed also in the light of previous work in the field.