Abstract
Greenhouse gas concentrations have reached unprecedented levels, driving significant climatic shifts worldwide. One of the most notable changes is the rise in sea surface temperatures, which threatens a diverse range of species and ecosystems. These shifts lead to alterations in species distribution, physiology, and behaviour, with the species in intertidal ecosystems being particularly vulnerable. Intertidal zones are not only rich in biodiversity but also serve as a foundational component of broader oceanographic ecosystems. As a model ecosystem for climate-related studies, the species that inhabit these zones act as ecological indicators, reflecting broader changes in oceanic and coastal ecosystems. The intertidal zone play’s a critical role as an early warning system for the assessment of the ecological impacts of climate change. Among the primary inhabitants of these intertidal zones are the numerous fish species that contribute to maintaining ecological balance and structural integrity. Disruptions to these species can set off cascading effects throughout marine communities leading to widespread disruptions in ecosystem stability.
This study focuses on some of the intertidal triplefins endemic to New Zealand, with a focus on the generalist Forsterygion lapillum. While previous research has highlighted the significant influence of temperature on the physiological function of this family, affecting both metabolism and enzymatic activity, this thesis shifts the focus to how temperature affects the behaviour of triplefins. By exploring these behavioural changes, this thesis seeks to establish a foundation for long-term intertidal monitoring at two key ecological sites north of Dunedin, serving as proactive measures for conservation management in the face of global climate change.
Chapter 2 provides environmental relevance to the study and serves as a foundation for long term environmental monitoring. This chapter aims to investigate how temperature and dissolved oxygen levels influence triplefin abundance and behaviour within the intertidal zone. To achieve this, monthly field surveys were conducted from March to November 2024 at two contrasting study sites – Warrington and Moeraki. Data on triplefin abundance and behaviour were collected using underwater cameras and visual surveys. In addition, environmental parameters, temperature, and dissolved oxygen were also recorded to complement the behavioural data. I predicted that higher temperatures would positively impact triplefin abundance, while reducing latency to emerge and time to first feed due to an increase in activity. I also anticipated that dissolved oxygen concentrations would not affect triplefin abundance or behaviour, given their physiological adaptations for efficient oxygen uptake in variable conditions. I found both supporting and conflicting evidence for these predictions. At Warrington, higher temperatures did indeed have a positive influence on triplefin abundance, increasing activity and reducing latency to emerge. Additionally, seasonal abundance patterns revealed lower abundance counts during winter with an increase in abundance and temperature during spring aligning with my predictions. However, no significant effect of temperature was observed at Moeraki, nor did temperature influence time to first feed at either site. Regarding dissolved oxygen concentrations, no significant impact was observed on triplefin abundance or feeding behaviour, consistent with predictions.
Chapter 3 centres on the behavioural assays of Forsterygion lapillum, to examine how temperature influences key behavioural responses: activity, emergence, feeding, predation response, and aggression. To conduct this, adult F. lapillum were acclimated to either a 10°C or 20°C for six weeks prior to the behavioural assays. I predicted that triplefins acclimated to higher temperatures would be more active, show higher levels of predator avoidance, consume larger amounts of food, display a decrease in emergence latency and exhibit increased aggression. The results largely support these predictions. During the acclimation phase, the 20°C treatment group consumed larger amounts of food while spending less time hidden within refuges. Additionally, in the behavioural assays, the 20°C acclimated group was more behaviourally active, showing greater total movement, increased aggression and a reduced latency to move. However, no differences were observed in evasive actions in response to the bird strike simulation.
In conclusion, this thesis provides compelling evidence that temperature significantly affects both the abundance and behaviour of intertidal triplefins. Considering the ongoing and intensifying impacts of global climate change, these findings highlight the critical need to understand how species will respond to changing environmental conditions. Additionally, this research establishes a foundation for long-term environmental monitoring within intertidal ecosystems, which will be essential for detecting and responding to potential future ecological shifts.