Assessment and prediction of the potential threats of temperature change and invasive species to the sustainability of Northern Irish sea fisheries

Abstract

Understanding and predicting the way in which species interactions may change under the uncertain climatic future is imperative if the management of important resources is to be successful. Consumer – resource interactions underlie population dynamics and distribution, yet there is little known about how these interactions will respond to increasing temperature. Temperature increase can facilitate the movement and settlement of alien species into new ranges. Introduced species can often be ecologically damaging and unpredictable due to novel predator-prey interactions. Comparative functional response analysis has been used to gain insight into resource dependent behaviour and population dynamics. This study is an assessment of the way in which predicted temperature changes can affect resource consumption in three predators. The red lionfish Pterois volitans (Linnaeus, 1758) is a successful and hugely damaging invader in the Western Atlantic and sources point to an ongoing Mediterranean invasion. Through a series of laboratory experiments I assessed how temperature, habitat complexity, and light wavelength affect the functional response of lionfish towards a crustacean prey. I establish that lionfish have a persistent Type II functional response and that lower temperature decreased the magnitude of the functional response, suggesting that movement into the comparatively colder waters of the Mediterranean and British Isles could reduce the per capita response. Further, I found that red light reduced the maximum feeding rate of lionfish, compared to blue and white light, by dampening the attack rate. I assessed how temperature increase affects the proportional consumption of an amphipod prey by an intertidal predator, the bleniid, Lipophrys pholis (Linnaeus, 1758). Functional response analysis revealed that the shanny has a hump shaped relationship with increasing temperature wherein maximum feeding rate decreased at the highest temperature. Two prey supply models, where prey density was allowed to deplete, and where prey were replaced after consumption were compared and found to have differential results due to model choice. I used gut content data to assess the abundance, prey selection, degree of dietary overlap, in a commercial predator, cod (Gadhus morhua; Linnaeus, 1758) and a non-commercial predator, dogfish (Sycliorhinus canicula; Linnaeus, 1758) with regards to substrate type. While there were no significant conclusions to be made about habitat use, I found significantly larger populations of S. canicula and higher consumption of commercial invertebrates by S. canicula. I vi used this field data to inform further experiments, having highlighted S. canicula as a potential threat to commercial fisheries. A two-by-two experimental design was used to understand how differential acclimation of predator (S. canicula) and amphipod prey species (Echinogammarus marinus; Leach, 1815) affects the functional response of the predator. Increasing temperature concomitantly increased the magnitude functional response of S. canicula, however raised temperature caused a shift in functional response type, from Type II to Type III, conferring low prey density protection. Handling time was shorter when both predator and prey were acclimated to the raised temperature and as a result there was a significant interaction effect where maximum feeding rate was significantly higher when both predator and prey were acclimated. This increase in predation impact by S. canicula has the potential to affect valuable fisheries stocks due to the increasing populations of Scyliorhinus canicula and the additive effects of acclimation to raised temperature. Having highlighted the differential ways in which temperature can affect the per capita response of consumers I postulate a new metric wherein “Relative Impact Potential” of a consumer can be predicted under a set of environmental variables. This metric takes into account the per capita response, numerical response, and the potential change in predator and prey populations under the proposed conditions. I suggest the use of this metric as a rapid way of assessing and predicting potential threats to sustainability of fisheries under predicted climatic change. Overall, this thesis identifies species and scenarios wherein sustainability of important fisheries could be threatened. While this work focuses mainly on thermal responses, it demonstrates: (i) the utility of functional response analysis in assessing relative change in ecological impact under climate change scenarios; (ii) the species specificity of thermal responses and provides empiricle evidence of a hump shaped thermal response; (iii) the importance of considering both predator and prey when assessing ecological change, with reference to acclimation and population dynamics; and (iv) a metric with which to assess potential threats and ecological impact in a way that is standardized and easily accessible by managers and stakeholders alike. 

Date of Award	03 Oct 2017
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Jaimie Thomas Allan Dick (Supervisor) & Julia Sigwart (Supervisor)