THE EFFECT OF CLIMATE CHANGE ON DEVELOPMENT, GROWTH AND METABOLISM OF EMBRYONIC ELASMOBRANCHS, Scyliorhinus sp.

Abstract

Commonly addressed as the apex predator in the oceans, elasmobranchs play an important role in keeping the balance of a healthy marine ecosystem. About a quarter of all elasmobranchs are threatened by extinction mainly due to human activities, such as overfishing, destructive fisheries and shark finning. Elasmobranchs are vulnerable to extinction due to their slow growth, late sexual maturity, and low offspring production. Some oviparous elasmobranch species lay their sessile egg cases around shallow waters of the intertidal zone, where they are exposed to extreme environments, e.g. high temperatures and low dissolved oxygen levels. Climate models predict that CO2 levels will increase to 1100 ppm by 2100, which leads to ocean warming, as well as the extent and frequency of low dissolved oxygen zones. However, only few studies have considered the effect of elevated temperatures and low dissolved oxygen levels on biological fitness and physiological performances of elasmobranchs, especially during crucial embryonic stage. We developed an alternative scale for staging embryonic development non-invasively in living embryos (Chapter III), and then used this scale in later work to determine biological fitness, physiological performances and survival at specific developmental stages. This PhD research is therefore aimed to investigate the effect of both current extreme environments and predicted future climatic conditions, specifically ocean warming and hypoxia, on growth and survival (in Chapter IV), and metabolism (in Chapter V) of small-spotted catshark, Scyliorhinus canicula during early ontogeny. Our results revealed that exposure to elevated temperatures increase the embryonic growth, yolk consumption and metabolic rates of S. canicula, while shrinking the hatchling size. Under hypoxic conditions, S. canicula embryos showing a steady growth, but metabolic rates were significantly reduced, suggesting that S. canicula may have incorporated anaerobic metabolism during this period. As the incubation period was longer in hypoxic treatments, embryonic survival was negatively affected as the animals trapped longer inside the sessile egg cases under low dissolved oxygen conditions. The synergistic effects of both ocean warming and hypoxia increased mortality rate of S. canicula during early embryonic stages. To mimic the free-living hatchling stage that are free to swim in a preferred environment, S. canicula hatchlings were then transferred into a common environment (normoxia, 15 °C), where metabolic performances were re-measured after 1-week. Our results revealed that developmental environment does not have a lasting impact on metabolism of S. canicula hatchlings. Understanding the impacts of future predicted climate change on ecological and physiological aspects of elasmobranchs is essential from a conservation standpoint in order to accurately determine, predict and eventually reduce the consequences of human activity on marine habitats as well as the species within them.

Date of Award	31 Dec 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Holly Shiels (Supervisor) & John Fitzpatrick (Supervisor)