Biologically active substances from microalgae can exhibit antioxidant, immunostimulating, antibacterial, antiviral, antitumor, antihypertensive, regenerative, and neuroprotective effects. Lipid complexes of microalgae Chlorella vulgaris and Arthrospira platensis exhibit antibacterial activity and inhibit the growth of the Gram-positive strain Bacillus subtilis; the maximum zone of inhibition is 0.7 ± 0.03 cm at all concentrations. The carbohydrate-containing complex of C. vulgaris exhibits antibacterial activity, inhibits the growth of the Gram-positive strain B. subtilis, Bacillus pumilus; the maximum zone of inhibition is 3.5 ± 0.17 cm at all concentrations considered. The carbohydrate complex of A. platensis has antimicrobial activity against the Gram-negative strain of Escherichia coli at all concentrations, and the zone of inhibition is 2.0–3.0 cm. The presence of mythelenic, carbonyl groups, ester bonds between fatty acids and glycerol in lipid molecules, the stretching vibration of the phosphate group PO2, neutral lipids, glyco- and phospholipids, and unsaturated fatty acids, such as γ-linolenic, was revealed using FTIR spectra. Spectral peaks characteristic of saccharides were found, and there were cellulose and starch absorption bands, pyranose rings, and phenolic compounds. Both algae in this study had phenolic and alcohol components, which had high antibacterial activity. Microalgae can be used as biologically active food additives and/or as an alternative to antibiotic feed in animal husbandry due to their antibacterial properties.

/pdf/identification-of-metabolites-with-antibacterial-activities-rhqtpzdi.pdf

Identification of Metabolites with Antibacterial Activities by Analyzing the FTIR Spectra of Microalgae

The response of Posidonia oceanica meadows to global warming of the Eastern Mediterranean Sea, where the increase in sea surface temperature (SST) is particularly severe, is poorly investigated. Here, we reconstructed the long-term P. oceanica production in 60 meadows along the Greek Seas over two decades (1997-2018), using lepidochronology. We determined the effect of warming on production by reconstructing the annual and maximum (i.e. August) SST, considering the role of other production drivers related to water quality (i.e. Chla, suspended particulate matter, Secchi depth). Grand mean (±SE) production across all sites and the study period was 48 ± 1.1 mg DW per shoot yr-1 . Production over the last two decades followed a trajectory of decrease, which was related to the concurrent increase in annual SST and SSTaug . Annual SST > 20°C and SSTaug  > 26.5°C was related to production decline (GAMM, P < 0.05), while the rest of the tested factors did not help explain the production pattern. Our results indicate a persistent and increasing threat for Eastern Mediterranean meadows, drawing attention to management authorities, highlighting the necessity of reducing local impacts to enhance the resilience of seagrass meadows to global change threats.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/nph.19084

Decline of seagrass (Posidonia oceanica) production over two decades in the face of warming of the Eastern Mediterranean Sea.

The Mediterranean Sea has been experiencing rapid increases in temperature and salinity triggering its tropicalization. Additionally, its connection with the Red Sea has been favouring the establishment of non-native species. In this study, we investigated the effects of predicted climate change and the introduction of invasive seagrass species (Halophila stipulacea) on the native Mediterranean seagrass community (Posidonia oceanica and Cymodocea nodosa) by applying a novel ecological and spatial model with different configurations and parameter settings based on a Cellular Automata (CA). The proposed models use a discrete (stepwise) representation of space and time by executing deterministic and probabilistic rules that develop complex dynamic processes. Model applications were run under two climate scenarios (RCP 2.6 and RCP 8.5) projected from 2020 to 2100 in four different regions within the Mediterranean. Results indicate that the slow-growing P. oceanica will be highly vulnerable to climate change, suffering vast declines in its abundance. However, the results also show that western and colder areas of the Mediterranean Sea might represent refuge areas for this species. Cymodocea nodosa has been reported to exhibit resilience to predicted climate scenarios; however, it has shown habitat regression in the warmest predicted regions in the easternmost part of the basin. Our models indicate that H. stipulacea will thrive under projected climate scenarios, facilitating its spread across the basin. Also, H. stipulacea grew at the expense of C. nodosa, limiting the distribution of the latter, and eventually displacing this native species. Additionally, simulations demonstrated that areas from which P. oceanica meadows disappear would be partially covered by C. nodosa and H. stipulacea. These outcomes project that the Mediterranean seagrass community will experience a transition from long-lived, large and slow-growing species to small and fast-growing species as climate change progresses. 

Climate change and the presence of invasive species will threaten the persistence of the Mediterranean seagrass community.

Seagrasses harbour bacterial communities with which they constitute a functional unit called holobiont that responds as a whole to environmental changes. Epiphytic bacterial communities rapidly respond to both biotic and abiotic factors, potentially contributing to the host fitness. The Lessepsian migrant Halophila stipulacea has a high phenotypical plasticity and harbours a highly diverse epiphytic bacterial community, which could support its invasiveness in the Mediterranean Sea. The current study aimed to evaluate the Halophila/Cymodocea competition in the Aegean Sea by analysing each of the two seagrasses in a meadow zone where these intermingled, as well as in their monospecific zones, at two depths. Differences in holobionts were evaluated using seagrass descriptors (morphometric, biochemical, elemental, and isotopic composition) to assess host changes, and 16S rRNA gene to identify bacterial community structure and composition. An Indicator Species Index was used to identify bacteria significantly associated with each host. In mixed meadows, native C. nodosa was shown to be affected by the presence of exotic H. stipulacea, in terms of both plant descriptors and bacterial communities, while H. stipulacea responded only to environmental factors rather than C. nodosa proximity. This study provided evidence of the competitive advantage of H. stipulacea on C. nodosa in the Aegean Sea and suggests the possible use of associated bacterial communities as an ecological seagrass descriptor.

/pdf/a-tight-interaction-between-the-native-seagrass-cymodocea-1ezwtu3f.pdf

A Tight Interaction between the Native Seagrass Cymodocea nodosa and the Exotic Halophila stipulacea in the Aegean Sea Highlights Seagrass Holobiont Variations

Predicted warming intensifies the negative effects of nutrient increase on tropical seagrass: A physiological and fatty acid approach

Distribution of the seagrass Halophila stipulacea: A big jump to the northwestern Mediterranean Sea

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Distribution of the seagrass Halophila stipulacea: A big jump to the northwestern Mediterranean Sea