The biological response of foraminifera to ocean acidification
Abstract
Elevated atmospheric concentrations of carbon dioxide (CO₂), partly driven by
anthropogenic activity, are decreasing the pH of the oceans. This thesis aimed to
assess the biological response of foraminifera to ocean acidification. Foraminifera
are single-celled organisms that form the dominant component of many marine
communities. A series of laboratory experiments were carried out on benthic
intertidal foraminifera from the Eden and Ythan estuaries, NE Scotland, to assess
the impacts of ocean acidification.
The responses of two dominant intertidal species of foraminifera (Haynesina
germanica and Elphidium williamsoni) to ocean acidification were initially
investigated in a short-term (6 week) experiment. Multiple species and multiple
stressors (seasonal temperature regime and elevated CO₂) were then incorporated in a long-term (18 month) mesocosm study to investigate the physiological
consequences (e.g. survival, growth) of ocean acidification.
Survival of both Haynesina germanica and Elphidium williamsoni was significantly
reduced under low pH conditions. Live specimens of both these calcareous species
were however recorded at low pH, in reduced numbers. Following long-term
exposure to ocean acidification, foraminiferal populations were still dominated by
calcareous forms. Agglutinated foraminifera were recorded throughout the long-term
incubations but their numbers were not high enough in the initial sediment collections
to allow them to contribute significantly to the populations. Overall, survival of all
foraminifera was greatly reduced in elevated CO₂ treatments. Temperature effects
were observed on foraminiferal survival and diversity with the largest CO₂ effects
recorded under the seasonally varying temperature regime.
Foraminiferal test damage for all live species was also highest under elevated CO₂ conditions. Test dissolution was particularly evident in Haynesina germanica with
important morphological features, such as functional ornamentation, becoming
reduced or completely absent under elevated CO₂ conditions. A reduction in functionally important ornamentation could lead to a reduction in feeding efficiency
with consequent impacts on this organism’s survival and fitness. In addition, changes
in the relative abundance and activities of these important species could affect
biological interactions (e.g. food web function) and habitat quality.
Type
Thesis, PhD Doctor of Philosophy
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