Antagonistic interplay between pH and food resources affects copepod traits and performance in a year-round upwelling system

Abstract

Linking pH/pco 2 natural variation to phenotypic traits and performance of foundational species provides essential information for assessing and predicting the impact of ocean acidification (OA) on marine ecosystems. Yet, evidence of such linkage for copepods, the most abundant metazoans in the oceans, remains scarce, particularly for naturally corrosive Eastern Boundary Upwelling systems (EBUs). This study assessed the relationship between pH levels and traits (body and egg size) and performance (ingestion rate (IR) and egg reproduction rate (EPR)) of the numerically dominant neritic copepod Acartia tonsa, in a year-round upwelling system of the northern (23° S) Humboldt EBUs. The study revealed decreases in chlorophyll (Chl) ingestion rate, egg production rate and egg size with decreasing pH as well as egg production efficiency, but the opposite for copepod body size. Further, ingestion rate increased hyperbolically with Chl, and saturated at ~1 µg chl. L −1. Food resources categorized as high (H, >1 µg L −1) and low (L, <1 µg L −1) levels, and pH-values categorized as equivalent to present day (≤400 µatm pco 2 , pH > 7.89) and future (>400 µatm pco 2, pH < 7.89) were used to compare our observations to values globally employed to experimentally test copepod sensitivity to OA. A comparison (PERMANOVA) test with Chl/pH (2*2) design showed that partially overlapping OA levels expected for the year 2100 in other ocean regions, low-pH conditions in this system negatively impacted traits and performance associated with copepod fitness. However, interacting antagonistically with pH, food resource (Chl) maintained copepod production in spite of low pH levels. Thus, the deleterious effects of ocean acidification are modulated by resource availability in this system.

Phenotypic Plasticity Drives Seasonal Thermal Tolerance in a Baltic Copepod

“…Three measurements were obtained per individual and averaged in the later analysis. While formalin is usually used to preserve plankton samples for length analysis (Connolly et al, 2017;Aguilera et al, 2020), previous work on zooplankton has shown no effect of ethanol preservation on body size (Black and Dodson, 2003) and any size effect would be consistent across the experiment. Further, ethanol preservation allows for downstream genetic analyses, which is essential when dealing with cryptic copepod species.…”

Local scale extreme low pH conditions and genetic differences shape phenotypic variation in a broad dispersal copepod species

“…However, Pearson's analysis indicated population-specific phenotypic responses to local pH variations (Figure 4) that might reflect physiological to local scale pH conditions (Fitzer et al, 2012;Aguilera and Bednarsěk, 2022). Contradictory results have been found with regards to pH effects (null, positive, and negative) on Acartia species through in situ (Hansen et al, 2019;Aguilera et al, 2020b) or laboratory observations by means of short (day-week) to long term (transgenerational) experiments (Langer et al, 2019;Dam et al, 2021). This emphasized that both approaches are needed to draw more comprehensive patterns in the response of copepod species and related biological communities to climate change (Reum et al, 2016).…”

“…This emphasized that both approaches are needed to draw more comprehensive patterns in the response of copepod species and related biological communities to climate change (Reum et al, 2016). In the case of copepod physiological responses to low pH, such interaction can be modulated if ample and nutritious food is available (Aguilera et al, 2020b;Cominassi et al, 2020), such as that observed in both coastal habitats. Significant correlations between EPR and field pH conditions might also correspond to the effect of other simultaneous environmental drivers affecting copepods physiology, including changes in temperature (Sasaki and Dam, 2019;Dam et al, 2021) and food spectra (Kleppel and Burkart, 1995;Jońasdottir et al, 2009).…”