Aquatic photobiology in Latin America: A global change perspective for phytoplankton organisms

HELBLING, E.W; VILLAFAÑE, V. E.

Florianópolis

Congreso; IV Congreso Latino Americano de Biotecnología de Algas & IV Redealgas Workshop; 2013

There are many challenges that phytoplankton face in order to cope with climate change, which includes changes in solar radiation, temperature, nutrients and pH.  Increasing temperatures brings about an intensification of the strength of the pycnocline, together with a shallowing of the upper mixed layer (UML), causing two opposite effects: It increases the mean irradiance received by phytoplankton cells within the UML, and it also tends to deplete nutrients and increase the CO2 concentration, as mixing with deeper waters is reduced.  Various studies have addressed the individual impact of variables associated to climate change on phytoplankton processes.  For example, UVR inhibits photosynthesis, damages the DNA molecule, decreases primary production (among other effects).  Comparatively, very little is known about the combined impacts of variables related to climate change.  While in temperate phytoplankton increased temperature can counteract the UVR impact (antagonistic effect), in tropical species it acts synergistically with UVR to further harm the cells and decreasing photosynthesis.  Likewise, nutrient-repleted cells can cope better with solar radiation than nutrient-depleted ones.  Therefore, the assessment of how multiple variables impact on phytoplankton might change our gathered view from previous studies that considered only the effects of individual variables.  Moreover, the extent of the effects of climate change variables, depends on the species composition, the previous light history of exposure as well as the transparency and the depth of the UML, among other factors.  Also, it is important to consider the time scales that allow phytoplankton cells to acclimate to any change.  While short-term impacts / acclimation involves a rapid metabolic response of cells to cope with such changes, long-term impact, however, affects species composition, size distribution, nutritional state, etc.  Across Latin America, diverse environments suppose different strategies for phytoplankton acclimation.  In a latitudinal sense, when going from South towards the Equator not only temperature increases, but also solar radiation does, this latter variable due to a combination of the solar zenith angle and a shallower UML.  In a longitudinal sense, East-to-West also present differences - with western upwelling and deep mixing areas, and eastern areas comparatively shallow mixed and with less nutrients.  Moreover, continental inputs of particulate and dissolved (organic and inorganic) matter, via weathering or rivers, further complicates the prediction of phytoplankton acclimation.  All together, variables associated to climate change will affect not only photosyntesis and primary production, but also the quantity and quality of food for consumers.  Overall, phytoplankton (as well as other plankton organisms) are ?living within a narrow margin?, and need to adjust their metabolic machinery to balance the different (known and unknown) environmental stressors.