Lucia Mazzella

PRODUCTION OF MUCILAGE BY THE ADRIATIC EPIPELIC DIATOM CYLINDROTHECA CLOSTERIUM (BACILLARIOPHYCEAE) UNDER NUTRIENT LIMITATION

The carbon partitioning of the epipelic diatom Cylindrotheca closterium (Ehrenberg) Reiman and Lewin isolated from the Adriatic Sea was studied in the laboratory under varying scenarios of nutrient limitation. Total number of cells, photosynthesis measured at 695 μmol photons·m−2·s−1 irradiance (P695‐μmol), chlorophyll (a+c) content, respiration, extracellular polymeric substances (EPS), total particulate carbohydrate (TPC), and dissolved carbohydrate were evaluated under nitrogen and phosphorus deficiencies in culture. The highest total number of cells was found in the control, whereas the nitrogen‐limited treatment showed the lowest value. During the transition phase of growth, photosynthesis in the nitrogen‐limited treatment was 3‐fold lower than in the phosphorus‐limited treatment and 4‐fold lower than in the control. Differences in respiration rates and chlorophyll (a+c) content were even more marked. Dissolved carbohydrate remained the same in all the treatments, whereas during the transition and stationary phase, EPS presented the highest values under phosphorus limitation and the lowest in the control treatment. The production of EPS was closely linked to the periods of carbon assimilation (transition phase) in the nutrient depleted treatments, especially in the phosphorus‐limited treatment. These results point out the relevance of the nutrient imbalance (nitrogen or phosphorus) in the production of EPS by the benthic or resuspended diatoms and suggest that these diatoms play an important role in nutrient‐unbalanced systems like sediments or marine snow.

Grazing effect of two Gibbula species (Mollusca, Archaeogastropoda) on the epiphytic community of Posidonia oceanica leaves

Abstract The temporal and spatial patterns of the molluscs Gibbula ardens (L., 1758) and G. umbilicaris (Von Salis, 1793), which inhabit beds of Posidonia oceanica (L.) Delile indicated that these species occupy well-differentiated niches. To understand better this niche differentiation, the effect of the grazing activity of the two Gibbula species (Mollusca, Archaeogastropoda) on the epiphytic community (micro- and macroglora) of P. oceanica leaves was studied by scanning electron microscopy (SEM). The epiphytic community differs along the leaf axis according to leaf age: the basal (youngest) part is colonized by bacteria and diatoms, ageing tissues by encrusting soft and calcareous algae, and the tips (oldest part) by an upright layer on the encrusting layer. The large variety of periphyton components growing on the leaves represents a diversified food source for the herbivorous molluscs. G. ardens seems to prefer bacteria and diatoms, and seldom feeds on calcareous encrusting algae; G. umbilicaris seems to feed preferentially on erect macroalgae and seldom on soft encrusting species. Feeding habits are in accordance with species spatial arrangement along the leaves and the spatio-temporal distribution in the meadow.

Biological succession on silicone fouling‐release surfaces: Long‐term exposure tests in the harbour of ischia, Italy

A static test site was set up in the Harbour of Ischia (Gulf of Naples, Italy) to investigate the antifouling effectiveness of newly developed non‐polluting coatings. Two‐year exposure experiments were performed on sets of panels coated with silicone‐based coatings, and results were compared both to sets of panels coated with toxic agents, and non‐toxic epoxydic compounds. Abiotic factors, strength of adhesion of the temporal dynamics of succession of foulers were analyzed throughout the period of immersion. Brown algae constantly represented the “border point”; between the early community, dominated by sume, micro‐ and macroalgae, and the late community, mainly represented by bryozoans and molluscs, as well as polychaetes, sponges and tunicates. Brown algae, such as Ectocarpus siliculosus, tunicates (mainly Botryllus schlossen) and polychaetes (Hydroides elegans, Pileolaria pseudomilitaris) were demonstrated to be key species, triggering the community and influencing its development. Light was the main abiotic factor discriminating the community on the two sides of panels exposed to different irradiances. The best performing coatings (silicone easy release coatings without additives) substantially influenced community structure, shifting it to the earliest stages of colonization. Silicone coatings proved to be unsuitable for colonization by organisms typical of mature communities, due to their low energy surfaces. The results of the present paper demonstrate that silicone coatings technology represents an alternative to the use of biocidal antifouling paints.

Biofouling and barnacle adhesion data for fouling-release coatings subjected to static immersion at seven marine sites

Little is known about the performance of fouling‐release coatings at different geographical locations. An investigation was designed to measure the differences in biofouling and biofouling adhesion strength on three known silicone formulations and an epoxy control at seven static immersion sites located in California, Florida, Hawaii, Hong Kong, India, Italy and Singapore. The study found that whilst the relative performance of the coatings was similar at each site, there were statistically significant differences in the type and intensity of fouling that developed on the coatings and in barnacle adhesion strength among sites. The results emphasize the importance of evaluating potential coatings at more than one static immersion site.

Chloroplast tRNALeu (UAA) intron sequences provide phylogenetic resolution of seagrass relationships

Abstract Recent molecular studies have indicated that seagrasses comprise three convergent angiosperm clades. Although seagrass polyphyly has been demonstrated persuasively, other details of their phylogenetic relationships remain uncertain or weakly supported. To further assess seagrass relationships, we explored the potential of chloroplast trnL (UAA) intron sequences for phylogenetic reconstruction in the Alismatidae. Sequence analysis revealed considerable length variation of the trnL intron among the eight species of the subclass Alismatidae examined. These regions (representing large insertions/deletions in loops) were difficult to align and too variable to use reliably in phylogenetic analysis. However, conserved regions of the intron were readily aligned and were characterized by levels of divergence comparable to coding rbcL sequences. When analyzed phylogenetically, conserved trnL intron sequences recovered the same phylogenetic relationships among seagrass clades that were obtained using rbcL data. Combined analysis of trnL intron and rbcL coding sequences yielded a single most parsimonious tree with levels of nodal support higher than those obtained independently for either of the datasets. Analyses of conserved intron and coding chloroplast DNA sequences provide continued support for the polyphyly of seagrasses, the monophyly of Zosteraceae and a clade comprising Ruppiaceae, Posidoniaceae and Cymodoceaceae. Conserved trnL intron should be useful for evaluating other phylogenetic relationships in subclass Alismatidae.

Feeding ecology of platynereis dumerilii (audouin & milne-edwards) in the seagrass posidonia oceanica system: The role of the epiphytic flora (Polychaeta, nereididae)

Abstract The feeding ecology and the ecological role of the herbivorous polychaete Platynereis dumerilii (Audouin & Milne-Edwards) (Nereididae) in the epiphytic community of the Mediterranean seagrass Posidonia oceanica (L.) Delile was investigated under natural and laboratory conditions. Experiments were devised to define the preferred items, their consumption rate and degree of assimilation of chlorophylls. Results of faecal pellets analyses, food-choice experiments and photosynthetic pigment analyses demonstrated that P. dumerilii feeds preferentially on erect filamentous algae. Worms of length above 10 mm may graze also on living tissue of Posidonia leaves, when starved. This behaviour has rarely been reported for invertebrates, and especially for poly-chaetes in Posidonia ecosystems. Small individuals had a lower feeding rate on large macroalgae (e.g., Cystoseira), but higher digestive efficiency. Platynereis dumerilii thus feeds preferentially on erect micro- and macroalgae which are more easily cut by the jaws of its eversible pharynx. This selective herbivore thus has a special microniche, with respect to other mesograzers inhabiting the Posidonia meadows.

Reti trofiche e flussi di energia nei sistemi a fanerogame marine

Abstract Food webs and energy flow in seagrass ecosystems. A review on the pathways in the food webs of seagrass ecosystems, both tropical and temperate, with a particular emphasis to Mediterranean Posidonia oceanica meadows is given. Three main pathways of energy transfer from primary producers (host plant and algal epiphytes) were identified: i) the plant itself through photosynthetic tissue; ii) the leaf detritus which in some species forms a litter compartment; iii) the algal epiphytes of leaf blades. The detritus and epiphyte ways are the most common, but they can be differently important according to the season and the spatial patterns of the meadows.