Impacts of pH on the Fitness and Immune System of Pacific White Shrimp

Veran Weerathunga,Hsueh-Han Hsieh,Wei-Ming Chen,Sam Dupont,Nathangi Piyawardhana,Fei-Ling Yuan,Jhe-Syuan Liao,Chia-Yu Lai,Wei-Jen Huang,Chin-Chang Hung

doi:10.3389/fmars.2021.748837

Abstract

The atmospheric partial pressure of CO2 (pCO2) has been increasing dramatically since the beginning of the industrial revolution and about 30% of the CO2 produced by anthropogenic activities was absorbed by the ocean. This led to a perturbation of the seawater carbonate chemistry resulting in a decrease of the average surface ocean pH by 0.1 and termed ocean acidification (OA). Projections suggest that pCO2 may reach 900 μatm by the end of the twenty-first century lowering the average pH of the surface ocean by 0.4 units. The negative impacts of OA on many species of marine invertebrates such as mollusks, echinoderms, and crustaceans are well documented. However, less attention has been paid to the impacts of low pH on fitness and immune system in crustaceans. Here, we exposed Pacific white shrimps to 3 different pHs (nominal pH 8.0, 7.9, and 7.6) over a 100-days experiment. We found that, even though there were no significant effects on fitness parameters (survival, growth and allometries between length and weight), some immune markers were modified under low pH. A significant decrease in total hemocyte count and phenoloxidase activity was observed in shrimps exposed to pH 7.6 as compared to pH 8.0; and phagocytosis rate significantly decreased with decreasing pH. A significant increase in superoxide production was also observed at pH 7.6 as compared to pH 8.0. All these results suggest that a 100-days exposure to pH 7.6 did not have a direct effect on fitness but lead to a modulation of the immune response.

Highlights

The atmospheric CO2 partial pressure has been increasing dramatically since the beginning of the industrial revolution (Feely et al, 2004) and about 30% of the CO2 produced by anthropogenic activities was absorbed by the ocean (Sabine et al, 2004)
Target pHs were reached and significant differences (ANOVA 2; p < 0.0001; Table 1) between nominal pH were observed for pH on the NIST scale (pHNIST), dissolved inorganic carbon (DIC), and pressure of CO2 (pCO2) with no significant difference (p > 0.05; Table 1) between replicates
Our results show no direct impact of the exposure to lower pH (7.9 and 7.6) on fitness parameters

Summary

Introduction

The atmospheric CO2 partial pressure (pCO2) has been increasing dramatically since the beginning of the industrial revolution (Feely et al, 2004) and about 30% of the CO2 produced by anthropogenic activities was absorbed by the ocean (Sabine et al, 2004) This led to a drop of the average pH of the surface ocean by 0.1 units (Orr et al, 2005). Local adaptation to present natural variability in pH or pCO2 has been identified as a key predictor of species sensitivity to ocean acidification (Vargas et al, 2017) This highlighted the importance to consider environmental variability while designing and interpreting experimental work. Enhanced energetic costs or alterations in energy allocation to different metabolic functions with a consequence for the energy budget of marine invertebrates was observed (Bibby et al, 2008; Stumpp et al, 2011; Mackenzie et al, 2014; Liu et al, 2016; Meseck et al, 2016; Cao et al, 2018)

Methods

Results

Conclusion