Ecological characterization of intertidal rockpools: Seasonal and diurnal monitoring of physico-chemical parameters

Diurnal and seasonal variations in temperature, salinity, oxygen concentration, carbonate chemistry parameters and nutrient concentration were monitored within mid-tidal rockpools on the north-western coast of Brittany, France. We also examined the importance of rockpool physical characteristics (e.g. shore height, surface, volume and depth) on the physico-chemical variability. Rockpool shore height and depth appeared as the main physical factors driving physico-chemical variations. Shallow upper shore rockpools exhibited the largest diurnal and seasonal fluctuations of temperature, oxygen concentration and pH T T . Conversely, deeper and lower shore rockpools experienced weaker variations, excepted for salinity and nutrient concentrations. The physico-chemical environment was likely to be strongly influenced by rockpool community composition, especially in summer when rockpools were colonized by dense canopy-forming algae. During the day-time emersion, photosynthesis increased oxygen concentration and pH T T but decreased nutrient concentrations in upper shore rockpools. The increase in rockpool pH T T provided an alkaline environment conducive to coralline algal calcification. Conversely, at night, upper shore rockpools presented a strong decrease in oxygen concentration and pH T T due to the high community respiration, increasing the dissolution in coralline algae. Therefore, rockpools are characterized by complex interactions between physical and chemical parameters and biological processes. Rockpools appear as suitable environments to examine the physiological processes set up by species to face natural variability, especially in a context of climate change.