The growth response of a calcifying marine bryozoan (Electra pilosa) to present-dayand future ocean warming and acidification

• Main Author: Johnson, Mildred Jessica
• Format: Thesis
• Language: English
• Published: 2018
• Subjects: Ocean acidification
• Online Access: https://oceanrep.geomar.de/id/eprint/59645/; https://oceanrep.geomar.de/id/eprint/59645/1/Msc_Johnson_Mildred_2018.pdf

Macroalgae can alter the physical state of surrounding seawater and resources available to organisms that live at the macroalgae-seawater interface, the so-called boundary layer (BL). As a result, these organisms are constantly exposed to varying degrees of pH and oxygen fluctuations, which act on a larger scale (bulk seawater or within a canopy) or smaller scale (BL), depending on hydrodynamic conditions. Previous studies have mostly focused on single stressors or constant conditions which produced valuable results but provide limited information on the important role of natural fluctuations within and on habitatforming organisms. This study investigated whether such diurnal variations would amplify or buffer the responses of benthic bryozoans particularly to ocean acidification (OA) and warming, in the Baltic Sea. Electra pilosa is a colonial calcifying bryozoan, living as an epibiont on Fucus species. It grows by asexual budding, adding new interconnected individuals called zooids. To determine the effect of the small and large-scale BL, the growth response of Electra pilosa was compared on 2 substrates, namely Fucus serratus and acrylic glass slides. This multifactorial 35-day experiment was conducted at the Kiel Indoor Mesocosms programmed to 4 different pCO2 (2 constant and 2 fluctuating) conditions and 2 temperature regimes which were crossed, each representing a present-day and future scenario. Temperature had a significant effect on the growth efficiency (GE) of E. pilosa with higher growth reported at all future mean temperatures, regardless of substrate type or pCO2 (elevated or low; constant or fluctuating) treatment. The pCO2 treatment did not significantly affect E. pilosa. Instead, low temperature and Fucus substrate were highly positively correlated to reduced growth (p<0.001). The fluctuating BL of Fucus indicated favourable GEs compared to the constant treatments within this substrate type. Conversely, the growth response and variability were significantly higher on the glass substrate at ...