Biological Response of Planktic Foraminifera to Decline in Seawater pH.

Shuaishuai Dong,Yanli Lei,Zhimin Jian,Kuidong Xu,Hongsheng Bi,Tiegang Li

doi:10.3390/biology11010098

Abstract

Simple SummaryThe ocean absorbs large amounts of CO2 emitted by human activities, which leads to a decrease in seawater pH, and has the potential to cause damage to calcareous marine organisms. Planktic foraminifera are some of the most important calcareous marine organisms in the ocean, although the biological response of planktic foraminifera to the decline in seawater pH is still unknown. In this study, the biological response of planktic foraminifera to declining seawater pH was studied through a series of on-board experiments. The experimental results showed that the decrease in seawater pH adversely affected the biological processes of planktic foraminifera, resulting in weaker predation, slower growth, lighter shells, and more deformities. In addition, for the first time, we report that microalgae that live with planktic foraminifera were also killed under low-pH conditions. Several indices were established to quantify the relationships between the biological parameters of planktic foraminifera and seawater pH, which could be used to reconstruct the paleoceanographic seawater pH. This study provides experimental data to quantify the biological response of calcareous plankton to a decline in seawater pH.Understanding the way in which a decline in ocean pH can affect calcareous organisms could enhance our ability to predict the impacts of the potential decline in seawater pH on marine ecosystems, and could help to reconstruct the paleoceanographic events over a geological time scale. Planktic foraminifera are among the most important biological proxies for these studies; however, the existing research on planktic foraminifera is almost exclusively based on their geochemical indices, without the inclusion of information on their biological development. Through a series of on-board experiments in the western tropical Pacific (134°33′54″ E, 12°32′47″ N), the present study showed that the symbiont-bearing calcifier Trilobatus sacculifer—a planktic foraminifer—responded rapidly to a decline in seawater pH, including losing symbionts, bleaching, etc. Several indices were established to quantify the relationships between these biological parameters and seawater pH, which could be used to reconstruct the paleoceanographic seawater pH. We further postulated that the loss of symbionts in planktic foraminifera acts as an adaptive response to the stress of low pH. Our results indicate that an ongoing decline in seawater pH may hinder the growth and calcification of planktic foraminifera by altering their biological processes. A reduction in carbonate deposition and predation could have profound effects on the carbon cycle and energy flow in the marine food web.

Highlights

Symbiont-bearing calcifiers, including planktic foraminifera, are sensitive to a decline in seawater pH [1,2]
Our study provides the first results documented on the responses of planktic foraminiferal biological processes to seawater pH
We identified the biotic indices that are clearly affected by seawater pH based on the culture experiments (Table 1)

Summary

Introduction

Symbiont-bearing calcifiers, including planktic foraminifera, are sensitive to a decline in seawater pH [1,2]. Geochemical analysis often requires a large number of planktic foraminiferal samples [13], limiting its application in areas with low numbers of planktic foraminifera, such as oligotrophic regions [14,15]. The biological response of symbiont-bearing planktic foraminifera to a decline in seawater pH has rarely been studied, e.g., in terms of survival, growth, calcification, and symbiotic activity. The lack of information on the biological response of symbiotic plankton to a decline in seawater pH limits the application of biotic indices in reconstructing the pH of ancient oceans [10]

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