Does resource availability influence the vital rates of the tropical copepod Apocyclops royi (Lindberg, 1940) under changing salinities?

Abstract

<jats:title>Abstract</jats:title> <jats:p>The physiology of invertebrates inhabiting many coastal ecosystems is challenged by strong temporal fluctuations in salinity. We investigated how food availability influences vital rates in the tropical cyclopoid copepod Apocyclops royi subjected to different salinities (5–32 PSU). We hypothesized that (i) mortality decreases and egg production rate increases with food availability; (ii) under suboptimal salinity, mortality increases and the egg production rate is reduced and (iii) the threshold concentration for egg production (the lowest food concentration where egg production is initiated) shifts to higher food concentrations when challenged by salinity. Surprisingly, A. royi survived, ingested food and produced eggs at all tested salinities. Mortality rate was, however, dependent on salinity level, but not on food availability. Mortality increased (~12% h−1) during short-term (1 h) salinity acclimatization to 5 PSU and during the following 24-h incubations (~5% d−1) compared with higher salinities. Feeding and egg production rates increased with food availability up to an optimum at all salinity levels, with no effect of salinity on the lowest food concentration initiating egg production. This reveals a high-salinity tolerance by A. royi and may partly explain why this particular copepod is so successful compared with its congeners in occupying extreme habitats.</jats:p>

Can we adjust a marine cyclopoid copepod to freshwater?—First step towards a ‘universal’ live feed product for fish and shrimp larvae

“…Adjusting the internal osmolarity to a lowered external salinity requires downregulation of the intracellular FAA pool (Farmer & Reeve, 1978). Therefore, we agree on the question recently formulated by van Someren Gréve et al (2020) stating ‘it would be interesting to investigate in future studies changes in FAA concentrations in A. royi as an effect of decreasing external salinity’. In the present study, however, we tentatively conducted NMR analysis to identify standout organic molecules that may contribute to osmoregulation.…”

“…During the past 15 years, the understanding of A. royi's (molecular) physiology and tolerance for environmental stressors has increased (Blanda et al, 2017; Jørgensen et al, 2019; Lee et al, 2005; Nielsen et al, 2019, 2020, 2021; Pan et al, 2016). This copepod has been shown to tolerate and reproduce over a wide range of salinities (Muthupriya & Altaff, 2009; Pan et al, 2016; van Someren Gréve et al, 2020). In the Taiwanese fishponds from where the species used in the present study were isolated, salinity is variable over the season, with short‐term drops in salinity of 6 observed due to heavy monsoon rain events (Blanda et al, 2015).…”

“…A. royi exhibit a broad salinity tolerance (Lee et al, 2005; Pan et al, 2016). One study revealed that A. royi exposed to a salinity range 5 to 32, both during short‐term (1 h) acclimatization and following 24 h of incubation, showed a significantly higher mortality at salinity 5 compared with at salinity 10, 20 and 32 (van Someren Gréve et al, 2020). However, the copepods were able to survive, feed and reproduce in the 24‐h incubations at all tested salinities.…”

“…Hence, they demonstrated a surprising robustness towards low salinity challenges. The study by van Someren Gréve et al (2020), however, emphasized the process of active ion regulation, which is energy demanding as proposed by Hand and Hardewig (1996) and Bradly (2009). This leaves less energy for other basic physiological functions in the copepod, that is reproduction (Chen et al, 2006) when kept at low saline conditions.…”

Environmental Regulation of the Nitrogen Supply, Mean Trophic Position, and Trophic Enrichment of Mesozooplankton in the Mekong River Plume and Southern South China Sea

“…This hypothesis is consistent with the observation that zooplankton acclimate to the mean environment, which means a better fit between organism and environment in homogeneous areas and a poorer fit in heterogeneous areas where the mean condition might actually occur rarely or not at all. The time scale of variation is likely a critical factor in determining whether animals can optimize their feeding and acclimate their digestive processes to the available food (Hassett & Landry, 1990; Mayzaud et al., 1998) or their metabolic processes to environmental stressors like periodic shifts in salinity (Dutz & Christensen, 2018; Goolish & Burton, 1988; Van Someren Gréve et al., 2020).…”