Heterotrophic Bacteria Respond Differently to Increasing Temperature and Dissolved Organic Carbon Sources in Two Tropical Coastal Systems

Abstract

Around 10% of the world's coastal water lies within the tropics (Jahnke, 2010). Tropical coastal waters naturally have high temperatures and sunlight levels, and are amongst the most active biogeochemical zones in the ocean (Brunskill, 2010;Jennerjahn, 2012;Lønborg et al., 2021). Despite this importance, comparatively few studies in tropical coastal waters have investigated the role of microbes in biogeochemical cycling and which environmental factors impact their physiology. In polar and temperate coastal waters, given its large variability, temperature emerges as a key control variable (Huete-Stauffer et al., 2015;Pomeroy & Wiebe, 2001). On the contrary, in tropical coastal waters temperatures are more stable, but it is still uncertain whether temperature is a major controlling factor (Lønborg et al., 2021). Some studies suggest that in these waters microbial processes are already functioning close to their optima; therefore, increasing temperatures further should not have any large impact or a negative influence on biogeochemical process rates (Morán et al., 2017;Wiebe & Pomeroy, 1999). However, other studies suggest that tropical marine microbes actually increase their activity under warmer conditions (Lønborg et al., 2019;McKinnon et al., 2017).