Effects of multiple stressors on the stability of functional traits: examining individual variability in the green shore crab, Carcinus maenas, exposed to plastic odour and ocean acidification

Howard, Bethany Rose

Abstract

The development of anthropogenic activities during recent centuries has led to an increase in environmental pollutants such as greenhouse gases causing atmospheric changes, resulting in elevated atmospheric heat retention, triggering global and ocean warming. The excess atmospheric carbon dioxide (CO2) dissolved into the Earth’s oceans, reacts with water molecules in seawater, resulting in the ocean becoming more acidic and pH decreasing. This process, termed ocean acidification, threatens marine organisms alongside a multitude of other anthropogenic stressors, one of which being plastic pollution. Plastics enter the ocean at a rate of 8 to 10 million tonnes per year. The lethal and sub-lethal impacts of plastic on organisms have been described including ingestion and entanglement, through to wider population effects such as bioaccumulation of toxic compounds and info-disruption.
While global climate change and plastic pollution are acknowledged threats to marine life, the prospective interactions between changing environmental parameters and plastics remains unclear. There remain significant gaps in our knowledge as to how these two stressors interact and on their combined effects on ecosystems. Crustaceans serve a crucial part in the aquatic food chains and are fundamental within their ecosystems. In order to assess their future in an altered environment and assist management decisions, reliable knowledge and dependable data are critical. This research builds on previous knowledge, identifying the effects of low pH on olfactory abilities on Carcinus maenas (Linnaeus, 1758), and explores the effects of plastic odour in tandem with ocean acidification. This thesis evaluates the effect of three levels of pH (8.2, 7.6, 7.2) on chemical communication and fitness in the green shore crab C. maenas when also exposed to plastic odour cues. Individuality factors were also investigated, relating to body size and weight, sex, injury, and colour of the crabs.
The effects of synthetic and natural chemical cues were investigated at different test pH treatments for C. maenas for a range of behavioural responses including time taken for initial response (antennular flicking), time taken to reach the location of an odour cue, the cue that was contacted and behaviours elicited at the cue location. The results of this study show that C. maenas experienced significant olfactory disruption in response to both feeding, and reproductive cues when in a reduced pH environment. Overall initial reaction times in crabs tested in low pH treatments (7.6 and 7.2) were significantly slower than the initial reaction times for crabs tested at pH 8.2. When individuals were tested with the plastic derived odour cues, there was an overall reduced response to cues with slower initial reaction time displayed. Additionally, when polyethylene (PE) plastic odour was present and tested in low pH treatments, reaction times to food and pheromone cues were significantly slower than treatments with plastic odour tested at normal pH 8.2. The data also demonstrated that C. maenas exhibited significant variation in response to cues. With initial reaction times showing significant variation between crabs of different size and colour. Additionally, it was found that individual variation relating to factors size, sex and weight had a significant impact on the choice of odour cue. These results may potentially consider long-term adaptation via selection for less sensitive individuals as a plausible outcome.
The observed response to chemical cues under different pH treatments suggests that pH is likely to impact the behavioural response to C. maenas. However, it is unclear as to whether this response is exacerbated by the presence of plastic odour and the relationship between these two stressors and how they interact is still unclear. The effect of pH on decision-making in C. maenas is a recognised concern and further study is essential to investigate the impacts of such multiple stressors. There is potential for plastic odour to become a more potent attractant under low pH conditions as a result of altered chemical signalling, which could have detrimental impacts on this species longevity.
This thesis examines the behavioural changes of crustacean species C. maenas during exposure to acidified seawater, plastic odour, and the combination effects of exposure to these stressors simultaneously. Following an introductory chapter- Chapter 1-Chapter 2 describes the methodology used for the present study, results, discussion, and conclusions.

Citation

Howard, B. R. Effects of multiple stressors on the stability of functional traits: examining individual variability in the green shore crab, Carcinus maenas, exposed to plastic odour and ocean acidification. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4251453

• Thesis Type: Thesis
• Deposit Date: Mar 27, 2023
• Publicly Available Date: Mar 27, 2023
• Public URL: https://hull-repository.worktribe.com/output/4251453
• Additional Information: Department of Biological Sciences, The University of Hull
• Award Date: 2022-07