Question

What have scientists and researchers found out about the effects of ocean acidification on shark physiology (4-5 paragraphs)?

Answer 1

Sharks play a key role in the structure of marine food webs, but are facing major threats due to overfishing and habitat degradation.The increasing amount of carbon dioxide (CO2) in the atmosphere due to climate change as well as from the contribution of pollution have also led to a higher concentration of CO2 in the oceans. The CO2 dissolves in the seawater to create carbonic acid that acidifies the oceans.

This higher acidity has already been found to damage the calcium carbonate in corals and other animals with calcium-based structures. While regular fish have flat scales, shark 'scales' look more like teeth. But their denticles also cover their body and in particular influence their ability to swim. The denticles are made up of a compounds containing calcium.The research team from three South African research institutions, from the University of Duisburg-Essen and HHU has now examined whether the more acidic seawater is also affecting sharks.

The study was performed on puffadder shysharks, which live in the Atlantic Ocean off the coast of Cape Town and are also kept in aquariums in the DAFF Research Aquarium in Cape Town. A number of sharks were exposed to more acidic water over a period of several weeks and compared with control sharks in normal seawater. After that time, the researchers found that an average of around 25 percent of the denticles had been damaged compared to a figure of less than ten percent for sharks in a benchmark group living in normal water. The harm to the group exposed to acid can be so great that it limits their ability to swim. Because the sharks' teeth are made from a similar material, they can also be negatively affected, which can in turn have an impact on their food intake.

In a further series of studies, the researchers analysed the blood of the animals kept in both acidic and normal seawater. They found that both CO2 and bi-carbonate concentrations were higher in the exposed group, with bi-carbonate preventing the blood itself from becoming more acidic. This means that sharks have acid-base regulatory mechanism for adapting to the environmental conditions.

While embryo survival and development time are mostly unaffected by elevated CO2, there are clear effects on body condition, growth, aerobic potential and behaviour (e.g. lateralization, hunting and prey detection). Furthermore, studies to date suggest that the effects of OA could be as substantial as those due to warming in some species. A major limitation is that all past studies have involved relatively sedentary, benthic sharks that are capable of buccal ventilation—no studies have investigated pelagic sharks that depend on ram ventilation. Future research should focus on species with different life strategies (e.g. pelagic, ram ventilators), climate zones (e.g. polar regions), habitats (e.g. open ocean), and distinct phases of ontogeny in order to fully predict how OA and climate change will impact higher-order predators and therefore marine ecosystem dynamics.