Environmental change impacts on the shell characteristics of rhynchonelliform brachiopods

• Main Author: Cross, Emma L.
• Format: Thesis
• Language: English
• Published: 2016
• Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems; New Zealand; Ocean acidification
• Online Access: http://eprints.esc.cam.ac.uk/3860/; http://eprints.esc.cam.ac.uk/3860/1/Dr%20Emma%20Cross%27%20Beast%20of%20a%20Thesis.pdf; http://eprints.esc.cam.ac.uk/3860/2/E%20L%20Cross%20cover.png

Since the Industrial Revolution, anthropogenically-increased CO 2 has altered oceanic surface seawaters through warming and acidification. Previous ocean acidification research has mainly focussed on short-term laboratory manipulations of conditions. Incorporating different approaches investigating both the impacts of past and future environmental change provides a more complete understanding of organisms’ responses. Rhynchonelliform brachiopods inhabit all of the world’s oceans, have been important marine taxa for 550 million years and are potentially one of the most vulnerable phyla to ocean acidification because >90% of their dry mass resides in their skeleton. Little is known, however, about the effects of lowered pH and warming on these taxa. A polar (Liothyrella uva) and a temperate (Calloria inconspicua) brachiopod were cultured under predicted end-century environmental conditions in separate CO 2 perturbation experiments for 7 months and 3 months, respectively. Multiple shell characteristics were analysed to determine the effects of future ocean acidification and warming on shell production and maintenance. Impacts of past environmental change were also evaluated on shell characteristics of C. inconspicua using museum specimens collected from the same sampling site in New Zealand every decade since 1900 to the present day. In the experiments on live specimens, lowered pH did not affect shell growth rates, ability to repair shells, punctal densities, calcite fibre size or elemental composition in either species. Shell dissolution with decreasing pH will impose a threat to both species, with more extensive dissolution occurring in L. uva because of the lower temperatures in its habitat. This was correlated with a decrease in the thickness of the primary layer that was counteracted by an increase in secondary layer thickness and total shell thickness in L. uva. The less extensive dissolution in C. inconspicua was reflected in the unaffected inner shell layers thicknesses and total shell thickness with decreasing pH. Shell growth rate was only affected by temperature in L. uva, with a 2°C rise increasing growth. Similarly, calcification index, total shell thickness, primary and secondary layer thickness, punctal density and elemental composition of C. inconspicua have not changed over the last century. Shell density in C. inconspicua, however, increased from 1900 to 2014 as this species appeared to lay down more shell by constructing thinner punctae. The majority of shell characteristics have remained unchanged over the last 110 years and are likely to continue to be unaffected by environmental change over the next 84 years. This indicates that shell production and maintenance are robust in a polar and a temperate brachiopod to recent past and predicted end-century acidified and warming conditions. Long-term laboratory experiments and historical specimens in this study have produced insights into how these species can acclimate and their possible ability to adapt to future change.