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The response of algae to stressors that affect their survival and growth appears to be strictly related to their dimension and shape. Coralline algae (Corallinophycidae, Rhodophyta) show a variety of morphological types that may play a role in their tolerance to stressful conditions. Nevertheless, only a few studies have investigated their response to multiple stressors when grouped by morphology. The aim of this work was to investigate the performance of the 2 main morpho-functional groups of coralline algae (nongeniculate and geniculate) in response to different stressors acting simultaneously (presence of fleshy macroalgae and/or benthic mucilage and sediment deposition). For this purpose, a manipulative field experiment was conducted on superficial rocky substrata (subtidal, 0.5 m depth) in the Tavolara Punta Coda Cavallo Marine Protected Area, Sardinia, in 2016-2018. The effect of each stressor, alone and in combination, was tested on the 2 groups of algae (4 treatments applied in triplicate), with the percent substratum covered by living coralline algae and the net primary production as response variables. Results showed that although some common trends were evident, different effects were observed for each morpho-functional group in relation to the considered response variable. These results highlight the importance of considering morpho-functional classification when predicting the response of coralline algae to disturbance and identifying their main threats.

The aim of this study was to define the simplest and least expensive protocol for total protein extraction for three different macroalgae of the genus Caulerpa (the invasive C. taxifolia and C. cylindracea and the autochthonous C. prolifera). Five multi-step protein extraction procedures, set up for other macroalgal species, were tested. For each of them, different pre-treatment and extraction conditions were simultaneously examined, according to a factorial design, considering the starting material, the solvent-to-biomass ratio, and the incubation temperature. Protein yield in the obtained extracts was estimated with the Bradford method. Further, polyacrylamide gel electrophoresis (SDS-PAGE) was used to resolve proteins, assessing their quality and integrity. Significant differences in protein yield were observed among the extraction protocols and the conditions tested, also in relation to the considered species. Profiles having an acceptable quality were obtained for C. prolifera and C. cylindracea, and from the obtained results, the best method to obtain high yield and quality protein extracts for the two above-mentioned species appears to require the use of a primary TCA/acetone extraction buffer followed by a lysis buffer with NaCl, KCl, urea, Triton, SDS and a protease inhibitor. The best results, in particular, were obtained starting from fresh pulped material with a buffer-to-biomass ratio of 10:1 and an incubation temperature of 4°C. For C. taxifolia, instead, none of the tested protocols produced satisfactory results and further studies will be required.

This paper focuses on the interactive short and long-term effect of three different stressors on a macroalgal assemblage. Three stressors are considered: herbivory, nutrients and mucilage. The experiment was conducted in Tavolara Punta Coda Cavallo Marine Protected Area (Mediterranean Sea) during a bloom of the benthic mucilage-producing microalga Chrysophaeum taylorii (Pelagophyceae); this microalga is recently spreading in the Mediterranean Sea. On a rocky substratum, 36 plots 20 x 20 cm in size were prepared. Factorial combinations of three experimental treatments were applied in triplicate, including three grazing levels crossed with two nutrient enrichment and two mucilage removal treatments. Significant differences were observed among treatments 8 weeks later, at the end of summer. In particular, dark filamentous algae were more abundant in all enriched plots, especially where mucilage and macroalgae had been removed; a higher percent cover of crustose coralline algae was instead observed where nutrients had been increased and no grazing pressure acted. Furthermore, the abundance of Dictyota spp. and Laurencia spp. was significantly higher in enriched mucilage-free plots where the grazing pressure was null or low. However, the effects of the treatments on the overall assemblage of the macroalgal community were not long persistent (36 weeks later). These results illustrate the capacity of a shallow-water macroalgal community to quickly recover from the simultaneous impacts of herbivory, nutrient enrichment, and mucilage.

In this study, gamete release by Caulerpa cylindracea was investigated for the first time in the Tyrrhenian Sea (Sardinia, Western Mediterranean), focusing on the main environmental factors triggering gametogenesis and spawning of the species. For this purpose, a combination of field and laboratory experiments was conducted. First, a 2-year mensurative experiment was performed in the field during summer to individuate and quantify the occurrence of C. cylindracea gametogenesis and spawning events, linking them to environmental conditions. Then, based on the results of the field work, a laboratory experiment was performed to directly test, under controlled conditions, the effect on the above-mentioned processes of two abiotic factors that appeared to play a key role in species gamete release processes in the area: sea water temperature and water movement. During the 2 years of field research, several gametogenesis events were recorded in the study area and two spawning events also occurred. Significant differences were observed between the ratio of fertile and total thalli and between releasing thalli (RT) and fertile thalli (FT), among sites with different hydrodynamic conditions and sampling periods with different sea water temperatures. Overall, these results suggest that C. cylindracea sexual reproduction also occurs in the Tyrrhenian Sea, and that, therefore, new genotypes that favor the invasive profile of the species could be produced in the basin, where both its gametogenesis and spawning seem to be mainly regulated by water movement and sea water temperature.

The benthic mucilage producing microalga Chrysophaeum taylorii Lewis and Bryan (Pelagophyceae) has recently received attention for its rapid spread in the Mediterranean Sea, where its blooms have remarkable detrimental effects. So far no information on C. taylorii response to multiple stressors, especially in terms of mucilage hyperproduction, is available in the literature yet, and a manipulative field experiment in this topic was designed in Tavolara Punta Coda Cavallo Marine Protected Area. The aim of the study was to test the effects of nutrient enrichment (addition of nutrients), mechanical disturbance (partial and total benthic organisms removal) and hydrodynamics (increased water turbulence) on C. taylorii cell density and mucilage abundance. To the purpose, the three above mentioned stressors were simulated and the three treatments were assigned to 20 × 20 cm plots following a full-factorial design (n = 3). Interactive effects of the three stressors affected significantly both benthic C. taylorii cell density and mucilage cover although differently. Mechanical disturbance and high hydrodynamics produced consistent effects on cell density and mucilage production (i.e. the former factor enhancing and the latter decreasing). Nutrient enrichment on the contrary led to contrasting effects, promoting cell abundance and inhibiting mucilage production. Therefore, important mucilage blooms are expected in oligotrophic sheltered coastal locations where barren areas are present.

Chrysophaeum taylorii Lewis & Bryan (Pelagophyceae) is a mucilage-producing benthic microalga that has recently begun to spread in the Mediterranean Sea, where a range expansion is occurring. This paper presents the results of three field experiments that aimed to increase the knowledge on mucilage provision mechanisms for this benthic microalga and to evaluate the importance of mucilage in its range expansion. By means of two correlative field experiments (several years of data were considered to encompass the variability of mucilage cover) we found that, on the sea bottom, mucilage cover does not depend on epilithic cell density and that both its cover and settling are affected by water flow. We also tested the hypothesis that cells embedded in floating mucilage fall on the underlying substratum, where their abundance depends on water flow. To this aim, in the field we manipulated the presence of floating mucilaginous aggregates in cages with different levels of exposure to winds. The abundance of C. taylorii cells on the substratum under cages with mucilage was compared with that of two control treatments: cages without mucilage and mucilage in still water, in the field and lab, respectively. The results suggested that mucilage can represent an excellent strategy for the species to disperse, as C. taylorii cells fall from the floating mucilage and, if the water flow is unimportant, settle on hard substrata just underneath the cage. This study enriches the portfolio of knowledge of the dispersal strategies of microalgae and contributes to the understanding of the spread of invasive species.

Few field studies have investigated how changes at one trophic level can affect the invasibility of other trophic levels. We examined the hypothesis that the spread of an introduced alga in disturbed seagrass beds with degraded canopies depends on the depletion of large consumers. We mimicked the degradation of seagrass canopies by clipping shoot density and reducing leaf length, simulating natural and anthropogenic stressors such as fish overgrazing and water quality. Caulerpa racemosa was transplanted into each plot and large consumers were excluded from half of them using cages. Potential cage artifacts were assessed by measuring irradiance, scouring by leaf movement, water flow, and sedimentation. Algal invasion of the seagrass bed differed based on the size of consumers. The alga had higher cover and size under the cages, where the seagrass was characterized by reduced shoot density and canopy height. Furthermore, canopy height had a significant effect depending on canopy density. The alteration of seagrass canopies increased the spread of C. racemosa only when large consumers were absent. Our results suggest that protecting declining habitats and/or restoring fish populations will limit the expansion of C. racemosa. Because MPAs also enhance the abundance and size of fish consuming seagrass they can indirectly promote algal invasion. The effects of MPAs on invasive species are context dependent and require balancing opposing forces, such as the conservation of seagrass canopy structure and the protection of fish grazing the seagrass.

Chrysophaeum taylorii Lewis and Bryan (Pelagophyceae) is an allochthonous benthic microalga recently recorded in the Mediterranean Sea where it is spreading quickly. Although this species secretes mucilage which is seriously affecting marine communities, it has been scarcely studied and no information on its ecology is available yet. We present the results of a five year study aimed to increase knowledge on substratum and depth preferences of this bloom-forming microalga with special emphasis on its colonisation efficiency.Three separate field experiments established that cell abundances of Chrysophaeum taylorii were significantly lower on macroalgae, mollusc shells and sand than on hard granitic substrata, where the microalga settled efficiently and proliferated immediately independently of the colonisation level of the substratum (bare vs colonised) and the substratum stability (mobility) (cobbles vs rocks). Furthermore, C. taylorii abundance (density) decreased with depth >2m, showing it prefers shallow waters in which it is able to resist to high light intensities.These results offer some important insights into the ecology of this bloom-forming microalga that will contribute to the planning of future research and strategies for management of bloom events.

Nowadays harmful algal blooms (HABs) represent a serious problem for the conservation of the biodiversity in the Mediterranean Sea. Nevertheless the knowledge on the presence of potentially toxic benthic microalgae in particular habitats, such as tide pools, is still scarce. In order to detect HAB-producing benthic microalgae in tide pools of the rocky intertidal zone, a pilot study was conducted in Tavolara Punta Coda Cavallo Marine Protected Area (MPA) during the late spring of 2016. Three different pools were sampled in two study sites (six pools were sampled in total) and the cell density of toxic species was estimated in each. In all the collected samples, the two potentially toxic dinoflagellates, Prorocentrum lima (Ehrenberg) F. Stein and Coolia monotis Meunier, were recorded and significant differences in their density were observed, in relation to both sites and pools.