Contrasting effect of Saharan dust and UVR on autotrophic picoplankton in nearshore versus offshore waters of Mediterranean Sea

Abstract

Autotrophic picoplankton (APP) is responsible for the vast majority of primary production in oligotrophic marine areas, such as the Alboran Sea. The increase in atmospheric dust deposition (e.g., from Sahara Desert) associated with global warming, together with the high UV radiation (UVR) on these ecosystems, may generate effects on APP hitherto unknown. We performed an observational study across the Alboran Sea to establish which factors control the abundance and distribution of APP, and we made a microcosm experiment in two distinct areas, nearshore and offshore, to predict the joint UVR × dust impact on APP at midterm scales. Our observational study showed that temperature (T) was the main factor explaining the APP distribution whereas total dissolved nitrogen positively correlated with APP abundance. Our experimental study revealed that Saharan dust inputs reduced or inverted the UVR damage on the photosynthetic quantum yield (ΦPSII) and picoplanktonic primary production (PPP) in the nearshore area but accentuated it in the offshore. This contrasting effect is partially explained by the nonphotochemical quenching, acting as a photorepair mechanism. Picoeukaryotes reflected the observed effects on the physiological and metabolic variables, and Synechococcus was the only picoprokaryotic group that showed a positive response under UVR × dust conditions. Our study highlights a dual sensitivity of nearshore versus offshore picoplankton to dust inputs and UVR fluxes, just at the time in which these two global‐change factors show their highest intensities and may recreate a potential future response of the microbial food web under global‐change conditions.

Increased nutrients from aeolian‐dust and riverine origin decrease the CO2‐sink capacity of coastal South Atlantic waters under UVR exposure

“…Nevertheless, we can rule out that toxic elements and heavy metals (e.g., Pb, Cu) carried by the dust may have interfered with the planktonic metabolism and growth (e.g., HPP) (Paytan et al ; Jordi et al ) and, consequently, may have influenced the CO 2 ‐sink capacity of the ecosystem with respect to the riverine treatments. In fact, we found that the concentration of such elements were below the detection limits, in agreement with recent reports showing no significant amount of these elements after dust deposition (González‐Olalla et al ).…”

The interactive effects of stratospheric ozone depletion, UV radiation, and climate change on aquatic ecosystems

“…Deposition of wind-borne dust from the Sahara is an important source of phosphorus to nutrient-limited phytoplankton in the Mediterranean Sea that, depending on the composition of the community, can either augment or diminish the adverse effects of UV radiation. 85 In offshore waters, the adverse effects of UV radiation were accentuated by deposition of this dust, while in nearshore waters, deposition of dust counteracted the adverse effects of UV radiation. Similarly, the composition of species as well as the occurrence of deposition influences the interaction of dust-borne phosphorus and UV responses in lakes 35 and in oligotrophic coastal waters (see section 6.2.1 for southern ocean examples).…”

Dust storms increase the tolerance of phytoplankton to thermal and pH changes

“…The positive effect of dust on S. obliquus growth rate and abundance observed in our study (P‐limited environment; NP molar ratio = 75) is consistent with real world observational studies, and likely related to the alleviation of phosphorus (P) limitation (Camarero & Catalan, 2012), highlighting the potential of dust as a driver of primary production and phytoplankton growth (Ballantyne et al., 2011; Morales‐Baquero et al., 2006), particularly in freshwater ecosystems of the western United States (Brahney, Ballantyne, et al., 2015), southern Europe (Cabrerizo et al., 2017; González‐Olalla et al., 2018), as well as increasing phytoplankton biomass (Stockdale et al., 2016) and Chl a in marine areas of the Mediterranean sea (Gallisai et al., 2014; González‐Olalla et al., 2017) South China Sea (Chu et al., 2018), or Tropical Atlantic Ocean and Southern Ocean (Barkley et al., 2019).…”

“…Chl a in marine areas of the Mediterranean sea (Gallisai et al, 2014;González-Olalla et al, 2017) South China Sea (Chu et al, 2018), or…”