# Antioxidant and Antimicrobial Properties of Selected Red Seaweeds from Central Portugal
## 4 Discussion
### Species-Specific Notes  
Algae can occur in complex habitats and sometimes in extreme environmental conditions, which play a role in shaping the development of defense strategies, such as metabolite production [63]. All species considered in the present study were harvested in the intertidal region, which, over the course of a single day, can suffer from a range of environmental shifts in temperature, light, salinity, air desiccation and water motion, depending on tidal \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Species Code**} & \multicolumn{2}{c}{**B. subtilis**} & \multicolumn{2}{c}{_S. cerevisiae_} \\ \cline{2-5}  & **MIC (mg\(\cdot\)mL\({}^{-1}\))** & **Growth (\%)** & **MIC (mg\(\cdot\)mL\({}^{-1}\))** & **Growth (\%)** \\ \hline PoUm & 3.13 & 86.60 \(\pm\) 2.12 ** & - & - \\ CeCi & 6.25 & 65.29 \(\pm\) 8.56 & - & - \\ OsPi & 1.56 & 80.80 \(\pm\) 2.69 ** & 12.5 & 81.98 \(\pm\) 0.23 \\ ChCr & 12.5 & 73.35 \(\pm\) 2.12 & - & - \\ SpCo & 0.02 & 80.82 \(\pm\) 3.63 ** & - & - \\ PlCa & 3.13 & 84.03 \(\pm\) 4.13 ** & - & - \\ CoOf & 6.25 & 83.14 \(\pm\) 3.49 ** & - & - \\ ElEl & - & - & - & - \\ AmRi & 6.25 & 83.17 \(\pm\) 1.48 ** & - & - \\ J4 Ru & 6.25 & 67.59 \(\pm\) 1.42 & - & - \\ MeLi & 12.5 & 18.02 \(\pm\) 2.49 & 1.56 & 11.91 \(\pm\) 2.97 \\ LiVi & 6.25 & 73.31 \(\pm\) 5.33 & 12.5 & 82.79 \(\pm\) 3.60 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Minimum Inhibitory Concentration (MIC) and respective extract concentrations for twelve red seaweed species, assessed against _Bacillus subtilis_ and _Saccharomyces cerevisiae_. PoUm: _Porphyra umbilicalis_, CeCi: _Ceranium cilatum_, OsPi: _Osmundea pinnatifida_, ChCr: _Chondrus crispus_, SpCo: _Sphaerococcus coronopifolius_, PlCa: _Ploanim carilagineum_, CoOf: _Cornulina officinalis_, EIE: _Ellisolandia elongata_, AmRi: _Amphiroa rigida_, JaRu: _Jania rubens_, McLei: _Mesophyllum lichenoides_, LiVi: _Liagora viscosita_. Values are presented as means \(\pm\) SD (\(n=4\)), or (-) whenever all the concentrations tested yielded more than 100% bacterial growth. Asterisks (**) indicate statistically highly significant differences between the species with the lowest bacterial growth (MeLi) and all other remaining species (_B. subtilis_: Kruskal–Wallis test (\(\chi^{2}(10)=31.670\); \(p=0.000\))). influence at any given time [71]. Especially near the upper limits of the intertidal area and during the low tide, seaweeds are exposed to drought, solar radiation, extreme salinities and temperature shifts [71; 72; 73]. For example, species such as _P. umbilicalis_, _C. crispus_ and _O. pinnatifida_ were collected in the upper intertidal region where they are out of water during low tide, exposed to air, and are, thus, fully exposed to all of the extreme conditions mentioned above. This scenario is, therefore, highly oxidative and both physically and physiologically stressful for most of the other algal species considered, which were collected in the lower portion of the intertidal region and have been mostly, if not at all times, fully submerged. _P. umbilicalis_ present, by far, the highest phenol content when compared to the other studied algae, as well as a high scavenging ability. These results likely indicate strong antioxidant activity, as it is known that seaweeds are able to develop antioxidant shielding mechanisms and strategies to withstand highly oxidative environments [36; 74]. Indeed, _P. umbilicalis_ is a seaweed that stood out from the other red seaweed species in most analyses performed in the present study. In the ABTS assay, _P. umbilicalis_ is able to scavenge ABTS+ with a lower extract concentration when compared to the majority of the species analyzed. Regarding antimicrobial activity, _P. umbilicalis_ shows activity against _Bacillus subtilis_, but no activity recorded for _Escherichia coli_ or _Sachromyces cerevisiae_.