Phytoplankton community response to a drought‐to‐wet climate transition in a subtropical estuary

Abstract

Arid subtropical climates often oscillate between drought and wet conditions, leading to a “flood or famine” paradigm for estuarine freshwater inflow, in which sporadic storm events drive dynamic changes in salinity and nutrient availability. Transitioning from prolonged drought to wet conditions can impact phytoplankton communities. The Mission‐Aransas Estuary, located on the south Texas coast, transitioned from a 5‐yr drought (2010–2015) to wet conditions (2015–2020), punctuated by several large flood events and the direct impact of category 4 Hurricane Harvey. Using an 8‐yr bimonthly sample set (2012–2019), we evaluated particulate organic carbon, chlorophyll a, nutrient concentrations, and accessory pigments to characterize the response of the phytoplankton community to these climate events. We found that phytoplankton biomass was diminished during severe drought and increased during prolonged wet conditions. The phytoplankton community switched from being diatom‐dominated during drought to cyanobacteria‐dominated following estuarine freshening, driven by lower salinity and increased nutrient availability. Seasonal fluctuations between taxa persisted regardless of climate condition. The drought‐to‐wet transition prompted a regime shift of the estuarine phytoplankton community to a new quasi‐steady state in the studied estuary. Globally, changing climate regimes may cause longer periods of extreme drought or wet conditions for estuarine systems. Detailed, long‐term ecosystem monitoring is necessary to fully evaluate ecological responses to extreme weather events, especially links between biogeochemical cycling and ecosystem function. These results suggest that oscillations between distinct wet and dry periods have lasting effects on primary productivity, phytoplankton community composition, and organic matter cycling in subtropical estuaries with long residence times.

Cascading, interactive, and indirect effects of climate change on aquatic communities, habitats, and ecosystems

“…The observed interactive and indirect effects indicated the unique impact that recent changes in precipitation patterns had on primary production. This result from a wetland is not unlike the impacts of changes in precipitation on estuarine primary producers documented by Douglas et al (2023). Here, the transition from dry to wet precipitation patterns over a decade elicited an increase in primary production and a shift in the dominant phytoplankton.…”

“…In the northern Great Plains wetlands, a recent increase in production of the potent greenhouse gas methane was inferred from changes in benthic and pelagic communities and their trophic interactions (Hu et al 2023). The identification of the emergence of a new type of wetland habitat by Hu et al (2023) and the hypotheses generated by the repeat observations by Douglas et al (2023) highlight the opportunities continuous studies provide for understanding our biosphere, support discovery of new patterns and processes, and possibly help to develop safer and more powerful mitigation strategies.…”

“…It is a strength of this special issue to be representative of diverse habitats and scales, including alpine streams (Leathers et al 2023), wetlands of the North American Great Plains (Hu et al 2023), lakes (Hébert et al 2023;Katkov and Fussmann 2023;Su et al 2023), estuaries (Douglas et al 2023;Franzè et al 2023), tropical reefs (Lange et al 2023), and the arctic ocean (Ramondenc et al 2023), as well as diverse organisms, from single celled algal primary producers (Vrana et al 2023) to top consumers such as right whales (Meyer-Gutbrod et al 2023). Moreover, contributions cover ecologically and climate-relevant ranges of scales, including laboratory experimentation lasting days (Bomfim et al 2023;Carrier-Bellau et al 2023, Fields et al 2023, mesocosm experiments of 1-month duration (Katkov & Fussmann 2023;Wang et al 2023), as well as the paleorecord (Hu et al 2023).…”