Abstract
Arthrocardia corymbosa is an important articulate coralline algae species in rocky reef ecosystems around New Zealand. A. corymbosa is an crucial component in these ecosystems, as it provides key ecosystem functions such as aiding juvenile recruitment of species, such as Haliotis iris (pāua). The aim of this thesis is to gain an understanding of the effects of light, orientation and Marine Heat Wave (MHW) conditions on the physiological responses of A. corymbosa: photosynthetic health (Fv/fm), pigment concentrations (chlorophyll a and phycoerythrin) and visual bleaching.
An experimental set up was developed to provide controlled conditions with one or more factors (e.g. light, temperature. pH, water motion) and that could be manipulated to investigate mechanisms related to an organisms response to stress. This experiment was developed by utilising previously recorded light data from the study site of interest. Butterfly Bay, Karitāne, Otago, New Zealand. It included six light treatments and allowed for a total of 24 individuals, whilst still ensuring independence of replicates. It was found that light treatment (ranging from 30µ mol d-1 m-2 to >250µ mol d-1 m-2) over 5 days had no strong effect on the physiological responses of A. corymbosa
In the natural environment A. corymbosa is found growing at a range of orientations on rock substrata in relation to the water surface and light direction. When testing the effect of orientation and light on A. corymbosa it was found that orientation and light treatment had no influence on pigment concentration or photosynthetic health. However, the pigment concentrations (both chlorophyll-a and phycoerythrin) decreased over a five-day experimental period.
Over the summer of 2016-2017 the Otago region was subjected to an unprecedented MHW with sea temperatures reaching above 20°C. Based on this, an experiment was run over a month period with periodical testing to investigate the effect of duration and the MHW under three light treatments (<5µ mol d-1 m2, 30µ mol d-1 m-2, >210µ mol d-1 m-2). It was found that longer exposure to a MHW caused more bleaching and greater decrease of photosynthetic health and pigment concentration in A. corymbosa. In low (<5µ mol d-1 m-2) and high light (>210µ mol d-1 m-2), there was increased bleaching due to light conditions reducing individuals photosynthetic health, perhaps a result of additional stress in high light and lack of energy in low light.
The results of this thesis demonstrate how light and MHW influence the physiology of A. corymbosa. Whilst this thesis focused on one species, MHW are becoming more frequent yet little is understood about the effect these events have on cold-temperate marine ecosystems.