Antagonistic and synergistic responses to solar ultraviolet radiation and increased temperature of phytoplankton from cenotes (sink holes) of the Yucatán Peninsula, México

Abstract

Cenotes (sink holes) are karstic formations characteristic of the Yucatán Peninsula and are the main source of fresh water in the region. Because of their tropical location, they receive high levels of solar radiation and are exposed to high temperatures. However, the effect of these global-change-related variables on phytoplankton in cenotes is unknown. We carried out experiments with phytoplankton communities collected from 2 cenotes differing in their penetration of solar radiation (Leona Vicario [LV]: turbid, Las Mojarras [LM]: clear) to assess the combined effect of solar ultraviolet radiation (UVR; 280-400 nm) and increased temperature on their photosystem (PS) II photochemistry. We exposed samples in microcosms to solar radiation (with and without UVR) and 2 temperatures (ambient = 25°C and increased by 3°C) and analyzed photochemical performance over daily cycles. A significant antagonistic interaction between UVR and temperature in LV caused a combined inhibition of the effective photochemical quantum yield (Φ PSII) that was smaller (63%) than the sum of the 2 individual effects of UVR and temperature (116%). In contrast, a significant synergistic interaction between UVR and temperature in LM caused the combined inhibition of Φ PSII (172%) to be higher than the sum of the individual effects of the 2 variables (134%). Differences in the size distribution and taxonomic composition of the phytoplankton communities, with smaller cells in LV than in LM, seem to account for much of the variability in responses to UVR and increased temperature between the 2 communities. Our results suggest that phytoplankton communities from clear cenotes will be more affected by the combined effects of solar UVR and increased temperature that those from turbid cenotes.

Microorganisms and spatial distribution of the sinkholes of the Yucatan Peninsula, underestimated biotechnological potential?

“…Though the biodiversity in the SYP is known, with the presence of phytoplankton, rotifers, cladocerans, copepods, macroscopic invertebrates (Iliffe, 1993), more than 45 species of crustaceans (Alvarez et al , 2015) and almost 40 species of fish (Schmitter‐Soto and Gamboa‐Pérez, 1996), in the present decade new taxa continue to be registered. However, research carried out on microorganisms living in these environments is scarce, without taking into account the reports due to anthropogenic contamination, they are found in plankton and phytoplankton (Sánchez et al , 2002; Aké‐Castillo, 2014; Irola‐Sansores et al , 2014; Szeroczyńska and Zawisza, 2015; Villafañe et al , 2015); fungal biomass (Gómez‐Reyes et al , 2017); tropical microscopic fungi (Gamboa‐Angulo et al , 2012; Moreno‐Pérez et al , 2014; Moreno‐Pérez et al , 2016); sediments from anchialine caves (Van Hengstum et al , 2009); and moderately halotolerant bacteria (De La Rosa‐García et al , 2007). In comparison with the bacterioplankton estimations of 5.8 × 10 2 –8.0 × 10 3 cells/mL in some sinkholes and their associated caves (Alcocer et al , 1999), the proportion of microorganisms identified is scarce; however, they have given notoriously relevant evidence of their biotechnological potential as mentioned below.…”

Global change effects on plankton community structure and trophic interactions in a Patagonian freshwater eutrophic system

“…Previous studies on the global change impact have mainly focused on the responses of individual variables on aquatic communities (e.g., eutrophication: Smith et al, 1999, ultraviolet radiation: Williamson et al, 1999; more recently, however, several studies have highlighted the importance of considering multivariables approaches to better understand and predict how communities will respond to complex future environmental conditions (Garcia et al, 2013;Boyd et al, 2016). This is because in Nature, ecosystems are simultaneously subjected to the action of multiple variables which may act in a synergistic or antagonistic manner (Crain et al, 2008;Dunne, 2010); thus the observed responses do not necessarily represent the sum of the individual effects of each variable (Villafan ˜e et al, 2015a). For example, previous studies showed that high nutrient availability reduces the negative effects of UVR by improving the phytoplankton's photosynthetic performance (Heraud et al, 2005;Marcoval et al, 2007;Cabrerizo et al, 2014).…”

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

“…This can promote greater heterotrophy by increased community respiration (Martínez‐García et al ), thus altering the energy transfer to higher trophic levels (Tsagaraki et al ). On the other hand, it is known that current or enhanced levels of UVR inhibits the PP (Helbling et al ; Villafañe et al ), nutrient uptake (Hessen et al ), Φ PSII or DNA repair (Jeffrey et al ; Harrison et al ; Villafañe et al ); however, although the combined impact of both global change drivers is generally considered antagonistic (e.g., nutrients attenuate the harmful effect of UVR), recent results by Carrillo et al () and Harrison et al () evidence that nutrient inputs can also unmask the harmful UVR effects on planktonic responses.…”