Blue and Yellow Light Induce Changes in Biochemical Composition and Ultrastructure of Limnospira fusiformis (Cyanoprokaryota).

Limnospira fusiformis (also known as Spirulina) is a cyanobacterium that is widely cultivated due to its economic importance. It has specific pigments such as phycocyanin that allow it to grow at different light wavelengths compared to other cultivated algae. Our study investigated the effect of yellow (590 nm) and blue (460 nm) light fields on various biochemical features, including the pigment concentration, protein content, dry weight, and cell ultrastructure of L. fusiformis. Our findings revealed that biomass growth was faster in yellow light compared to blue light, with a higher relative amount of proteins even after one day of exposure. However, after eight days, the relative protein content in yellow versus blue light was not statistically different. Furthermore, in yellow light, we observed a decrease in chlorophyll a, an increase in cyanophycin granules, and an increase in the amount of dilated thylakoids. On the other hand, in blue light, there was an increase in phycocyanin after one day, along with an increase in electron-dense bodies, which are attributable to carboxysomes. However, after eight days, the differences in pigment content compared to the control were not statistically significant. Our study showed that using specific wavelengths during the harvesting phase of spirulina growth can enhance phycocyanin content with blue light (after one day) and biomass, growth rates, and protein content with yellow light after six days. This highlights the biotechnological potential of this approach.

Biogenic aerosol in central East Antarctic Plateau as a proxy for the ocean-atmosphere interaction in the Southern Ocean.

Ten years of data of biogenic aerosol (methane sulfonic acid, MSA, and non-sea salt sulfate, nssSO42-) collected at Concordia Station in the East Antarctic plateau (75° 06' S, 123° 20' E) are interpreted as a function of the Southern Annular Mode (SAM), Chlorophyll-a concentration (Chl-a; a proxy for phytoplankton biomass), sea ice extent and area. It is possible to draw three different scenarios that link these parameters in early, middle, and late summer. In early summer, the biogenic aerosol is significantly correlated to sea ice retreats through the phytoplankton biomass increases. Chl-a shows a significant correlation with nssSO42- in the finest fraction (< 1 µm). In contrast, only Chl-a in West Pacific and Indian Ocean sectors correlates with MSA in the coarse fraction. The transport routes towards the inner Antarctic plateau and aerosol formation processes could explain the different correlation patterns of the two compounds both resulting from the DMS oxidation. In mid-summer, Chl-a concentrations are at the maximum and are not related to sea ice melting. Due to the complexity of transport processes of air masses towards the Antarctic plateau, the MSA concentrations are low and not related to Chl-a concentration. In late summer, MSA and nssSO42- present the highest concentrations in their submicrometric aerosol fraction, and both are significantly correlated with Chl-a but not with the sea ice. In early and mid-summer, the enhanced efficiency of transport processes from all the surrounding oceanic sectors with air masses traveling at low elevation can explain the highest concentrations of nssSO42- and especially MSA. Finally, considering the entire time series, MSA shows significant year-to-year variability. This variability is significantly correlated with SAM but with a different time lag in early (0-month lag) and late summer (4-months lag). This correlation likely occurs through the effect of the SAM on phytoplankton blooms.

Enhanced nutrient loading and herbivory do not depress the resilience of subtidal canopy forests in Mediterranean oligotrophic waters.

The interaction between top-down and bottom-up forces determines the recovery trajectory of macroalgal forests exposed to multiple stressors. In an oligotrophic system, we experimentally investigated how nutrient inputs affected the recovery of Cystoseira brachycarpa following physical disturbance of varying intensities, both inside forested areas and at the boundary with sea urchin barrens. Unexpectedly, Cystoseira forests were highly resilient to disturbance, as they were able to recover from any partial damage. In general, the addition of nutrients sped up the recovery of Cystoseira. Thus, only the total canopy removal, in combination with either low nutrient availability or intense grazing pressure, promoted the expansion of mat-forming algae or urchin barrens, respectively. Our study suggests that the effects of enhanced nutrient levels may vary according to the trophic characteristics of the waterbody, and hence, are likely to vary among regions of the Mediterranean basin.

Macro-grazer herbivory regulates seagrass response to pulse and press nutrient loading.

Coastal ecosystems are exposed to multiple stressors. Predicting their outcomes is complicated by variations in their temporal regimes. Here, by means of a 16-month experiment, we investigated tolerance and resistance traits of Posidonia oceanica to herbivore damage under different regimes of nutrient loading. Chronic and pulse nutrient supply were combined with simulated fish herbivory, treated as a pulse stressor. At ambient nutrient levels, P. oceanica could cope with severe herbivory, likely through an increase in photosynthetic activity. Elevated nutrient levels, regardless of the temporal regime, negatively affected plant growth and increased leaf nutritional quality. This ultimately resulted in a reduction of plant biomass that was particularly severe under chronic fertilization. Our results suggest that both chronic and pulse nutrient loadings increase plant palatability to macro-grazers. Strategies for seagrass management should not be exclusively applied in areas exposed to chronic fertilization since even short-term nutrient pulses could alter seagrass meadows.

Carry over effects of nutrient addition on the recovery of an invasive seaweed from the winter die-back.

Nutrient enrichment of coastal waters can enhance the invasibility and regrowth of non-native species. The invasive alga Caulerpa cylindracea has two distinct phases: a well-studied fast-growing summer phase, and a winter latent phase. To investigate the effects of nutrient enrichment on the regrowth of the seaweed after the winter resting-phase, a manipulative experiment was carried out in intertidal rockpools in the North-western Mediterranean. Nutrients were supplied under different temporal regimes: press (constant release from January to May), winter pulse (January to March) and spring pulse (March to May). Independently from the temporal characteristics of their addition, nutrients accelerated the re-growth of C. cylindracea after the winter die-back, resulting in increased percentage covers at the peak of the growing season. Nutrient addition did not influence the number and length of fronds and the biomass. Native components of the algal community did not respond to nutrient additions. Our results show that nutrient supply can favour the spread of C. cylindracea even when occurring at a time of the year at which the seaweed is not actively growing.