Daniela Prevedelli

Long term eutrophication effects on macrofaunal communities in northern Adriatic Sea

Abstract The macrozoobenthic community in the northern Adriatic Sea, south of the Po river, along the Emilia-Romagna region coast, was sampled in 1985. Sampling site was central to a highly eutrophicated area with greatly increased intensity and frequency of dystrophic events over recent decades. The sampled community differs from all those described in the same area in a period (1934–1936) previous to the actual degree of eutrophication. Large abundances of species indicative of unstable bottoms, such as the bivalve Corbula gibba and the polychaete Lumbrineris latreilli were recorded. Moreover, the community structural features indicate a state of immaturity, such as in early successional stage communities. The increased frequency of acute dystrophic events and consequent shortening of the time between successive disturbances is proposed as the cause of biocenosis modification and its current structure and composition.

Effects of temperature on two Mediterranean populations of Dinophilus gyrociliatus (Polychaeta: Dinophilidae): I. Effects on life history and sex ratio

Abstract The effects of temperature on the life history characteristics of two populations of the polychaete Dinophilus gyrociliatus , one from Ravenna (northern Adriatic Sea) and the other from Genoa (Ligurian Sea), were investigated. The temperatures tested (6, 12, 18, 24 and 30 °C) cover a wider range than those prevailing in the natural environment. In the populations studied there are broad differences in timing of development and reproduction. At 6 °C, the adults of both populations survive for a long time but they are unable to reproduce. At 12 °C, only the animals from Ravenna manage to reproduce. At the higher temperatures (18, 24 and 30 °C), the development of the animals belonging to the Genoa strain is faster than that of the Ravenna strain. The duration of the various phases of the biological cycle is very similar in both populations, but that from Ravenna exhibits greater tolerance of low temperatures, slower development rate and lower development threshold temperature than does the Genoa population. Temperature and geographical origin also have strong effects on reproductive characteristics. The highest fecundity values were observed at 12 °C in the Ravenna strain, the lowest at 30 °C in both groups. At 18 °C, the Genoa population is more fecund than the Ravenna one, while the situation is reversed at 12 °C. The smallest ovigerous capsules are produced at 30 °C, the biggest at 12 °C, and the Genoa females produce larger capsules than do the females from Ravenna, except at 12 °C. The size of both male and female eggs varies in relation to temperature, the smallest female eggs generally being laid at the higher temperatures. At all the temperatures tested, the sex ratio of the Ravenna population is higher than that of the Genoa population. In the Ravenna strain, temperature has no effect on the sex ratio, while in the Genoa strain the sex ratio at 24 °C is lower than at 18 and 30 °C. Comparison of the two populations at the same temperature reveals considerable differences in the characteristics of their respective life histories and sex ratios. It is very likely that the extreme selectivity of the harbor environments has favored the fragmentation of the species into differentiated populations that have adapted to the conditions prevailing in the different localities.

Responses of a Northern Adriatic Ampelisca–Corbula community to seasonality and short-term hydrological changes in the Po river

During the 20th century, increased nutrient inflow has increased the frequency and intensity of eutrophication events in the North-western Adriatic Sea. More recently, evidence of a reduction in the Po river flow and a recovery of the benthic environment were reported. We examined the role played by Po river regime and seasonality in determining the temporal pattern of macrozoobenthos variation: samples were collected from a site located 10-12km off Cesenatico during two years from October 2004 to September 2006, when the mean Po discharge remained exceptionally low. 88 taxa were found, and the community was dominated by few species: Ampelisca diadema, Lumbrineris latreillii, Corbula gibba, Aricidea claudiae, Levinsenia gracilis and Nucula nucleus account for about 80% of total abundances. The density of these species exhibited a marked seasonal variability. Moreover, the total abundance and the density of the sensitive species, A. diadema, were negatively affected by several disturbance events (hypoxic conditions, frequent storms and an anomalous winter flood) that occurred between November 2005 and March 2006. The reduction of C. gibba and the increase of A. diadema densities observed in the investigated period, and verified recently by other authors could be related to the reduction in river inputs as a consequence of climatic changes.

Trans-generational plasticity in physiological thermal tolerance is modulated by maternal pre-reproductive environment in the polychaete Ophryotrocha labronica

Maternal temperature is known to affect many aspects of offspring phenotype, but its effect on offspring physiological thermal tolerance has received less attention, despite the importance of physiological traits in defining organismal ability to cope with temperature changes. To fill this gap, we used the marine polychaete Ophryotrocha labronica to investigate the influence of maternal temperature on offspring upper and lower thermal tolerance limits, and assess whether maternal influence changed according to the stage of offspring pre-zygotic development at which a thermal cue was provided. Measurements were taken on adult offspring acclimated to 18 or 30°C, produced by mothers previously reared at 24°C and then exposed to 18 or 30°C at an early and late stage of oogenesis. When the shift from 24°C was provided early during oogenesis, mothers produced offspring with greater cold and heat tolerance whenever mother–offspring temperatures did not match, with respect to when they matched, suggesting the presence of an anticipatory maternal effect triggered by the thermal variation. Conversely, when the cue was provided later during oogenesis, more tolerant offspring were observed when temperatures persisted across generations. In this case, maternal exposure to 18 or 30°C may have benefited offspring performance, while limitations in the transmission of the thermal cue may account for the lack of correlation between maternal experiences and offspring performance when mother–offspring environments did not match. Our results provided evidence for a trans-generational effect of temperature on physiological performance characterised by a high context dependency, and are discussed in the light of maternal pre-reproductive experiences.

Effects of temperature on two Mediterranean population of Dinophilus gyrociliatus (Polychaeta: Dinophilidae): II. Effects on demographic parameters

Abstract The effects of temperature on demographic characteristics of two populations from Ravenna and Genoa of the polychaete Dinophilus gyrociliatus were investigated. Temperature affects age-specific survival and fecundity and all the demographic parameters often to a different degree in the two populations. Individuals from Ravenna survive longer than those from Genoa. The most evident differences in the age-specific fecundity curves of the experimental groups are related to age at maturity and the duration of the reproductive period that are in inverse proportion to temperature. In both populations of D. gyrociliatus , the maximum daily fecundity is observed at intermediate temperatures. In all cases, the Genoa females mature earlier, attain their maximum fecundity more quickly and have a shorter reproductive period than their Ravenna counterparts. Age at maturity, fecundity during the first reproductive events and juvenile survival are by far the most important characteristics in determining the fitness of the two populations at the tested temperatures. Even though the greatest net growth rates and highest expectation of life were recorded at 12 °C in the Ravenna population, the delay in the attainment of sexual maturity means that, at this temperature, the population growth rate is lowest. The higher juvenile survivorship and the greater fecundity observed at 24 °C is counter-balanced by the early attainment of sexual maturity induced at 30 °C. The comparison of the population growth rate calculated in laboratory with field data suggests that temperature is one of the main environmental parameters determining the fitness of D. gyrociliatus .

Relationship of non-specific commensalism in the colonization of the deep layers of sediment

The macrofauna of samples collected with a box-corer from northern Adriatic Sea muddy bottoms in five survey campaigns from 1985 to 1993 has been analysed separately in sediment strata of varying depth. Samples were collected before, during and after the dumping of large amounts of inert particulate material that covered the seabed and caused an almost total defaunation. After this disturbance the seabed was recolonized by a new community This new community differed from the original one mainly on account of the abundance of Mysella bidentata, a small bivalve filter or surface deposit-feeder. In the original community Al. bidentata was confined to the more superficial sediment layers (0-5 cm) at low population density. In the new community it was very abundant and evenly distributed even in the deep layers (5-20 cm). Analysis of species association performed on data from each of the 54 corer samples collected in the last sampling period, points to a marked association between M. bidentata and Nephtys incisa in deeper sediment layers. Deep layer colonization by Mysella in association with the burrowing polychaete N. incisa suggests a case of commensalism between these two species.

Recovery of the macrozoobenthic community of the Comacchio Lagoon System (Northern Adriatic Sea)

Abstract From 1976 to 1992 the Comacchio lagoon system (a polyhaline lagoon on the northern Adriatic Sea coast) was exploited for intensive farming of eels and other fish. This activity, and its consequent increased release of organic matter, has led to hypereutrophication of the lagoon, resulting in a bloom of cyanobacteria and an almost total elimination of eukaryotes at both the planktonic and benthic level. After farming stopped, the ecological conditions tended to improve and the macrozoobenthic community underwent a spectacular recovery. The current communities do not differ substantially from those present before this ecological catastrophe, with the exception of a low level of internal differentiation not only among different lagoon sites but also different substrates.

Reproductive effort, fecundity and energy allocation in two species of the genus Perinereis (Polychaeta: Nereididae)

Summary The reproductive effort in terms of fecundity and energy allocation was studied in two species of semelparous polychaetes belonging to the genus Perinereis, living in the same environment, with different reproductive modalities. There is a great individual variability both in terms of reproductive effort and fecundity. Fecundity varied from 4080 to 15000 oocytes in P. rullieri and from 7000 to 26000 in P. cultrifera; no linear relationship was found between oocyte number and total jaw length utilised as size index. The energy content of germinal and somatic tissues was determined by Differential Scanning Calorimeter (DSC). The reproductive effort was calculated as RE = EG/(EG + ES) where EG is the total energy in germinal tissues and ES is the total energy in somatic tissues. Reproductive effort is very high with mean values of 0.62 for P. rullieri and 0.79 for P. cultrifera. The different amounts of energy allocated in germinal tissues can be attributed to the different reproductive modalities—P....

Reproduction and larval development of Perinereis rullieri Pilato in the Mediterranean Sea (Polychaeta: Nereididae)

Abstract The reproductive biology and larval development of a brackish water population of the nereidid polychaete Perinereis rullieri Pilato was investigated. About 100 specimens were collected monthly over the course of a year from the Venice Lagoon. Observation on gametogenesis indicates that oogenesis takes about 12 months while spermatogenesis is faster and takes about 6 months. The study showed that reproduction occurs once a year with a good synchronization between individuals and that spawning occurs without epitokal metamorphosis. Larval development was studied under laboratory conditions; the stages of trochophora and metatrochophora developed within the periovular jelly matrix and the first free living stage was the 3-setigers nectochaeta. In this species many life history traits can be interpreted as an adaptation to the brackish environments. In particular the adaptive significance of the variable age at maturity and the enclosing of the fertilized eggs in a jelly matrix are discussed.

Survival and growth rate of Perinereis rullieri (Polychaeta, Nereididae) under different salinities and diets

Abstract The effects of salinity and diet on survival and growth rate of the nereidid polychaete Perinereis rullieri have been investigated under controlled laboratory conditions. The experiment began from nectochaetes at 5–6 setigerous segments to exclude the high mortality occurring immediately after hatching. The tested salinities were 10 ‐20 ‐ 30 and 40%o that slightly exceed those recorded in the natural environment during larval emergence. The larvae were fed with Tetramin MicroMin dry fish food and Tetramin MicroMin added with freeze‐dried lyophilised Ulva rigida to test the possible antistress effect of vitamins C and E, in which the alga is rich. The experimental results highlight the influence of salinity on survival and growth rate of P. rullieri. Enrichment with alga does not significantly affect survivorship and growth rates under all experimental conditions.