An alga stressed by the light
During the summers of 2010 and 2011, the UPV/EHU's Bentos Marino group analysed samples of algae populations from five zones and measured the amount of light present in and the temperature of each zone over the summer. The research group observed that the algae that displayed the most signs of stress were from the zones exposed to the most solar radiation. The results of the research have been published in the Journal of Sea Research.
Gelidium corneum is a very common alga along the Basque coast. It grows at a depth of between 3 and 15 metres, and from September onwards can be seen out of the water. It gets broken up by storms and washed up on the beaches where it forms a red carpet. On some parts of the coast, above all in transparent water zones, the fronds of the algae have turned yellowish. The researchers have identified this change as a symptom of stress.
There are more sunny days during the summer which is when the algae are exposed to increased solar radiation. However, this is not necessarily harmful, since the more light there is, the more the algae will grow. But if the light exceeds the optimum average, the algae become inhibited. After choosing algae populations located at the same depth in five zones along the Biscay coast (Kobarón, Górliz, Ogoño, Ea and Lequeitio), it was possible to observe that the algae in transparent waters were suffering greater stress. The ones under the influence of an estuary, as in the case of Górliz, are in a better condition, since the turbid waters in the zone mean that they are exposed to less solar radiation.
A stressed alga is one that cannot carry out its functions properly. The UPV/EHU researchers used certain biochemical parameters to measure the stress of the alga, and, after examining the results, came across a direct relationship between the amount of solar radiation, antioxidant activity and the C:N ratio of the alga.
The increase in solar radiation increases the alga's photosynthesis, which happens in any plant. But above certain levels the researchers have been able to confirm that antioxidant activity decreases. In principle, the increase in solar radiation leads to greater antioxidant activity, because this is the mechanism the alga uses to manage the oxygen-free radicals generated when photosynthesis intensifies. But if solar radiation exceeds the limits, the alga suffers fatigue, cannot control the free radicals and goes into basal mode. It only carries out the functions needed to survive.
Yet there is another reason supporting the fact that the excess of solar radiation decreases antioxidant activity: ultraviolet solar radiation directly destroys the enzymes that have an antioxidant capability.
The researchers believe that the excess of solar radiation could lead to another problem. Normally, the more the amount of light increases, the greater the C:N ratio becomes, in other words, the interior percentage of nitrogen decreases. The fact is, the alga needs more nutrients (sources of nitrogen) to increase photosynthesis, and over the summer the quantity of nutrients in the sea tends to run low. So if the solar radiation is excessive, the alga will use the reserves it keeps inside it to survive. These reserves contain pigments that dye the alga red: phycolipoproteins:
If these red pigments are in short supply, the alga turns yellow. This process is similar to that which happens in deciduous trees in autumn: in order to get itself ready for the winter, the tree appropriates the reserves accumulated in the leaves and that is why the leaves turn yellow. In the case of algae, this is not adaptation that takes place on a yearly basis, but a means of protection that is activated at a given moment and could be one of the symptoms of a situation of stress. If the conditions were to deteriorate, the alga would turn white and brittle.
Transparent water is not better
Recent years have seen a fall in the amount of G. corneum algae in some spots along the Basque coast. As observed in another piece of research, the increase in the frequency of storms and big waves is linked to this loss. Likewise, the population displays a weaker appearance in areas of transparent waters, and even though the solar radiation does not directly reduce the amount of algae, it could render the algae more sensitive to possible threats and changes.
The result of the research has been published in the Journal of Sea Research. This research is part of a broader study and comes within the thesis submitted by Endika Quintano, a UPV/EHU Researcher.