Short-term effects of pCO2 (700 – 380 ppm; HC-LC) and nitrate content (50-5 βM; HN-LC) on photosynthesis, estimated by different pulse amplitude modulated (PAMs) fluorometers and by oxygen evolution, were investigated in Ulva rigida (Chlorophyta) under solar radiation (ex-situ) and in the laboratory under artificial light (in-situ). After 6-days of incubation at ambient temperature (AT), algae were subjected to a 4 oC-temperature increase (AT+4oC) for 3 d. Both in-situ and ex-situ, maximal electron transport rate (ETRmax) and in situ gross photosynthesis (GP) measured by O2 evolution presented the highest values under HCHN, and the lowest under HCLN, across all measuring systems. Maximal quantum yield (Fv/Fm), and ETRmax of PSII (ETR(II)max) and of PSI (ETR(I)max), decreased under HCLN under AT+4°C. Ex situ ETR was higher than in situ ETR. At noon, Fv/Fm decreased (indicating photoinhibition), whereas ETR(II)max and maximal non-photochemical quenching (NPQmax) increased. ETR(II)max decreased under AT+4oC in contrast to Fv/Fm, photosynthetic efficiency (αETR) and saturated irradiance (EK). Thus, U. rigida exhibited a decrease in photosynthetic production under acidification, LN levels and AT+4oC. These results emphasize the importance of studying the interactive effects between environmental parameters using in-situ vs. ex-situ conditions when aiming to evaluate the impact of global change on marine macroalgae.

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Microalgae are a relatively underutilised source of valuable nutritional compounds and biochemicals. Their high protein contents make them an interesting target for the generation of bioactive peptides for the functional food industry. Here, the nitrogenous components of the red microalga Porphyridium purpureum and the diatom- Phaeodactylum tricornutum were quantified, and their SDS-PAGE profiles analysed. Proteinswere isolated from these species by solubilisation at alkaline pH followed by precipitation at acidic pH. The protein extracts were hydrolysed with the food-grade proteolytic preparations Alcalase 2.4 L and Flavourzyme 500 L. The P. purpureum and P. tricornutum hydrolysates were examined for their in vitroanti-diabetic and antioxidant properties. The microalgal-derived protein hydrolysates had dipeptidyl peptidase (DPP) IV inhibitory activity, with IC50 values of 2.28 ± 0.36 and 2.68 ± 0.19 mg/mL for P. purpureum and P. tricornutum, respectively. The oxygen radical absorbance capacity (ORAC) and ferric reducing power (FRAP) values were, respectively, 13.98 ± 0.97 and 478.94 ± 34.43 for P. purpureum, and 15.04 ± 0.54 and 155.74 ± 38.30 for P. tricornutum expressed in μmol Trolox Equivalent (TE) per gram of dry matter.The results suggest that protein hydrolysates from these microalgae have potential use as functional food ingredients.

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The biodiversity associated with subtidal Irish kelp forests dominated by Laminaria hyperborea has never been described. To enumerate species assemblages in these ecosystems, subtidal surveys were done throughout the calendar year to investigate species assemblages within kelp forests, composition of benthic communities, species colonizing kelp thalli, recruitment to kelp forests, and habitat recovery processes after canopy clearances. Surveys were further undertaken in maërl beds, sediment‐bottom bays, Serpula vermicularis reefs, and bedrock habitats for comparison. Across all four seasons, kelp forests harbor the richest species assemblages, second only S. vermicularis reefs in diversity, with a total of 313 unique species in the habitat (from juvenile recruits to mature macrofauna). Peak diversity in kelp forests occurred in summer and echinoderms were one of the most abundant groups, though urchins never reach densities that would threaten over‐grazing. The thalli of L. hyperborea are diverse habitats harboring many deposit feeders, filter feeders, and marine macroalgae. Epibiotic communities become more diverse with age of kelp, culminating in a maximum of 1660 individuals on stipes and 949 on holdfasts. Recruitment of crustaceans, echinoderms, and worms was high in kelp forests, but recruitment of common Irish fish could not be monitored because of unique life history stage. Habitat establishment took over a year on artificial substrata which were colonized by macroalgae and dense canopy cover inhibited growth of juvenile sporophytes. This descriptive study represents an essential baseline for kelp forest biodiversity in Ireland.

As the commercial use of seaweed for natural product extraction calls for abundant, uniform biomass, this study focused on the production and the variability of the harvested biomass of valuable compounds produced by a commercially relevant red algal species, Asparagopsis armata. Its tetrasporophyte stage was retrieved from two Irish localities and grown for over 2 years in indoor cultures at 13 °C and 17 °C, and bromoform, mycosporine-like amino acids and phycobiliprotein contents were monitored over time. Growth rates at different temperatures were specific to isolates, and one isolate failed to grow at 17 °C. All compounds of interest were detected by the end of the 2-year cultivation period, and most of them were produced at an exponential rate at 13 °C but not at the higher temperature. At 13 °C, bromoform reached concentrations of 10.00 ± 0.55 mg g−1, total mycosporine-like amino acids of 2.65 ± 0.10 mg g−1, phycoerythrin of 11.46 ± 0.35 mg g−1 and phycocyanin of 72.13 ± 1.74 mg g−1 in Irish isolates. The observed variability in compound content was statistically significant but not large enough to impede commercial utilization. Bromoform content in cultivated samples was almost 6-fold higher than in field-collected samples though natural bromoform variability remains to be elucidated. Our findings suggest that the tetrasporophytic phase of A. armata is a suitable candidate for indoor cultivation; abundant and homogeneous biomass composition can be obtained which can be further optimized by growth temperature.