# Contrasting responses of Thermocyclops crassus and T. oithonoides (Crustacea, Copepoda) to thermal stress

## TL;DR

This study compares how two copepod species respond to heat stress, finding that one survives better and adapts by dropping eggs quickly.

## Contribution

The study reveals new insights into thermal tolerance and adaptive strategies of copepod species under heat stress.

## Key findings

- Thermocyclops crassus shows higher thermal tolerance than T. oithonoides.
- T. crassus drops egg sacs faster under thermal stress, possibly as an adaptive mechanism.
- The findings suggest implications for copepod survival in changing thermal environments.

## Abstract

Thermal tolerance is a critical factor influencing the survival of living organisms. This study focuses on the thermal resistance of copepod species, Thermocyclops crassus (Fischer, 1853) and T. oithonoides (Sars G.O., 1863), with overlapping distribution ranges in Europe. Short-term heat shock experiments were conducted to assess the thermal resistance of these copepods, considering various temperature increments and exposure durations. Additionally, the study explored the influence of heat shock on egg sac shedding, a vital indicator of population dynamics. Results indicate that widely distributed T. crassus exhibits higher thermal tolerance compared to narrowly distributed T. oithonoides, with survival rates varying under different heat shock conditions. Furthermore, T. crassus demonstrated a quicker response in dropping egg sacs in response to thermal stress, suggesting a potential adaptive mechanism for the survival of adults. However, rapid egg sac droppings pose high risks for eggs facing unfavorable conditions. T. crassus, inhabiting environments with greater temperature fluctuations such as the littoral and pelagial zones, exhibited better survival mechanisms compared to T. oithonoides, which predominantly resides in the pelagic zone. The findings have implications for understanding copepod responses to global warming and thermal pollution. This research contributes insights into the adaptive strategies of thermophilic copepod species and their ecological consequences.