Andalusia has a high diversity of wetlands. These include intertidal shallow systems, which are important both ecologically and economically, given that the microalgae that grow at the sediment surface are an important source of food for higher-level organisms such as fish, oysters etc.
The microphytobenthos (MPB) is the photosynthetic community living on the sediment surface. They play an important role in shallow estuaries as they can be responsible for a large part of the primary production. This community is dominated by diatoms (algae covered in a silicate casing, called the frustule) and can achieve very high densities giving a golden colour at the sediment surface.
In order to deal with the highly fluctuating environments conditions that characterize the intertidal areas, such as light, temperature, tide cycle and seasonal variations, diatoms have developed several strategies. For example, they have the capacity to migrate vertically during the day to adapt to the light conditions and tidal variation.
Marika Mecca, one of our PhD students, is trying to understand the effects of climate change on the physiology and behavior of these benthic microalgae. Under normal conditions, the sediment surface undergoes large changes in temperature between night and day, under water (immersion) or exposed to the air (emersion), and between seasons. Thus, under a climate change scenario where heatwaves are more frequent, the shifts in temperature will be even larger and the effects on the physiology of the microalgae can be detrimental.
To study these effects, Marika uses various instruments and sensors in the lab, such as oxygen microsensors to measure the amount of oxygen produced, temperature sensors to measure the variations vertically, reflectance sensors to detect the migration rhythms etc.
Experimental setup 
PAM measurements 
Oxygen profiles measurements 
Oxygen microsensors 
Reflectance measurements 
Optical oxygen sensors
The principal area of study is the Guadalquivir River. Once the cores are collected in the field, back at the laboratory these sediments are subjected to different conditions simulating the changes observed in the field under normal and extreme weather conditions.
The results show an effect of prolonged high temperatures on the migration rhythm of the microalgae (avoidance of the sediment surface), although differences in total net metabolism are less probably due to a stimulation of rates by the higher temperature. These results were presented at the ASLO 2023 conference in Mallorca.
