Physiological thresholds through early ontogeny: the effects of temperature and hydrostatic pressure on the common whelk Buccinum undatum (Linnaeus 1758)

Abstract

The eco-physiological thresholds controlling the distribution of marine invertebrates are of significance in understanding the evolution of marine diversity. This includes the direction of species radiation throughout the oceans. Range expansions occur as a result of evolutionary adaptations, or through environmentally or anthropogenically driven shifts in distribution. The success of such events is centred around a species ability to adapt; in order for a migration to be successful, all life history stages must tolerate the conditions of the new habitat. This thesis examines the thermal and hyperbaric thresholds affecting range extension in the marine environment. It focuses on the larval development of the shallow-water North Atlantic gastropod Buccinum undatum (Linnaeus 1758). The Buccinidae family consists of a wide range of shallow and deepwater species distributed globally. Improved knowledge on this topic will contribute to our understanding of the adaptations influencing both historical and modern shifts in the distribution of species.

The thermal and hyperbaric ranges observed during development indicate B. undatum to have the capacity to develop at both temperatures and pressures outside its current distribution. Thermal acclimation to low temperature was also found to increase pressure tolerance during development. A shift in number of embryos developing and nurse egg partitioning per embryo indicate a decrease in developmental success at temperatures above those it is naturally exposed to. An increase in energetic expenditure, with both increasing temperature and pressure, relates to a rise in the metabolic cost associated with development under either condition. These results, combined with the known life history of B. undatum, suggest range expansion into deep water may be a plausible scenario, but tolerance of warmer conditions remains questionable due to the cold-induced spawning observed in this species. The results of this thesis support theories of high-latitude migrations into the deep sea via cold, isothermal waters, and indeed, suggest polar temperatures may promote the rate at which such range expansions occur. Additionally, the observed metabolic cost associated with development suggests hydrostatic pressure may induce bathymetric limits, which explain patterns observed in reproductive trends, eco-physiological adaptations, and faunal distribution in marine invertebrates throughout the oceans.

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