Before we get into just how ocean warming and ocean acidification physically affect krill, let me explain just exactly what these two things are. Ocean warming is pretty self-explanatory, it is the ocean physically getting warmer. Ocean acidification is a little trickier. It pertains to the increased carbon dioxide in the atmosphere due to anthropological (human) influences. The ocean is a gigantic carbon sink and readily absorbs carbon dioxide. To make up for the chemical imbalance in the water due to all the extra carbon dioxide, some of the carbon dioxide is converted to carbonic acid and carbonic acid is not necessarily conducive to living things. Coral bleaching is one of the better known consequences of ocean acidification because the carbon stays in the bicarbonate form instead of continuing to decompose into carbonate. The bicarbonate does not break down the calcium surrounding the coral, but the coral is unable to create new growth through calcification, killing it. Now let's get to krill.
Ocean Warming
According to Flores et. al., 2012, the waters that make up the Antarctic Circumpolar Current, the largest ocean current on Earth, have warmed faster than anywhere else. The water temperature has gone up by at least 1 degree Celsius. Now, 1 degree may not sound like much, but Antarctic krill evolved in a very temperature specific area of the world and are as much a thermal specialist as species that live in tropical area, so one degree could be the difference between peak metabolic performance and the beginning of a decline. Flores et. al., 2012, speculates that as the water temperature rises, the krill's performance will rise as well, and metabolic rates will reach their peak performance levels. But as the water continues to warm, it will soon become too hot for krill. They will either need to modify their behavior and travel towards cooler water or krill that are better adapted for warmer conditions will become the prevalent species in the area. These are all just predictions for now, but ocean warming is occurring as you read this and will continue to happen long after you have signed off. Through ocean warming, the krill are losing their home. As the ocean warms and sea surface temperatures increase, the ice around Antarctica is retreating. Spots that have been a haven for krill in the past are now exposed, exposing the krill to more predation and driving them to deeper waters. The other important aspect of ice is the ice algae. Ice algae is one of the primary food sources for krill and when the ice melts in the summer and the algae goes into the water, it is also a key element in phytoplankton blooms. Less ice per year means less ice algae which also result in less phytoplankton blooms. Ice algae is also a key food source for developing krill that aren't strong enough to swim out and look for food. The juvenile krill can get the food they need without worrying about competition. The figure to the right shows how the sea ice distribution has changed and where majority of the krill can be found. where there is less ice, there is less krill.
Ocean Acidification
The other event we will discuss on this page is ocean acidification. Scientists have discovered at high enough levels of carbon dioxide in the water, krill embryo development will halt. The development of young krill also depends on carbon dioxide levels because increased carbon dioxide levels may affect the flow of carbon dioxide over the gills, effectively acidifying the haemolymph, the fluid of the circulatory system, and causing a physiological defect in the krill. No studies have been performed on Antarctic krill yet demonstrating their decreased function under high carbon dioxide levels, but the have been performed on a similar species called penaeid shrimp and their aerobic scope and their swimming ability was affected (Dissanayake & Ishimatsu, 2011, Synergistic effects of elevated CO2). The same effect can be expected for Antarctic Krill. Ocean acidification is only going to get worse as time goes by, and the krill will not be able to maintain a high fitness or abundance in challenging conditions like this. Phytoplankton, the krill's food source is also affected by ocean acidification. Coccolithophores, one form of phytoplankton, is predicted to do better as ocean acidification increases, meaning there could potentially be more food available for krill as the pH continues to decrease. However, this is all speculation, because again, we do not know yet how the krill is affected by decreasing pH. It is all still up in the air (Flores et. al., 2012, Impact of Climate Change).
Ocean Warming
According to Flores et. al., 2012, the waters that make up the Antarctic Circumpolar Current, the largest ocean current on Earth, have warmed faster than anywhere else. The water temperature has gone up by at least 1 degree Celsius. Now, 1 degree may not sound like much, but Antarctic krill evolved in a very temperature specific area of the world and are as much a thermal specialist as species that live in tropical area, so one degree could be the difference between peak metabolic performance and the beginning of a decline. Flores et. al., 2012, speculates that as the water temperature rises, the krill's performance will rise as well, and metabolic rates will reach their peak performance levels. But as the water continues to warm, it will soon become too hot for krill. They will either need to modify their behavior and travel towards cooler water or krill that are better adapted for warmer conditions will become the prevalent species in the area. These are all just predictions for now, but ocean warming is occurring as you read this and will continue to happen long after you have signed off. Through ocean warming, the krill are losing their home. As the ocean warms and sea surface temperatures increase, the ice around Antarctica is retreating. Spots that have been a haven for krill in the past are now exposed, exposing the krill to more predation and driving them to deeper waters. The other important aspect of ice is the ice algae. Ice algae is one of the primary food sources for krill and when the ice melts in the summer and the algae goes into the water, it is also a key element in phytoplankton blooms. Less ice per year means less ice algae which also result in less phytoplankton blooms. Ice algae is also a key food source for developing krill that aren't strong enough to swim out and look for food. The juvenile krill can get the food they need without worrying about competition. The figure to the right shows how the sea ice distribution has changed and where majority of the krill can be found. where there is less ice, there is less krill.
Ocean Acidification
The other event we will discuss on this page is ocean acidification. Scientists have discovered at high enough levels of carbon dioxide in the water, krill embryo development will halt. The development of young krill also depends on carbon dioxide levels because increased carbon dioxide levels may affect the flow of carbon dioxide over the gills, effectively acidifying the haemolymph, the fluid of the circulatory system, and causing a physiological defect in the krill. No studies have been performed on Antarctic krill yet demonstrating their decreased function under high carbon dioxide levels, but the have been performed on a similar species called penaeid shrimp and their aerobic scope and their swimming ability was affected (Dissanayake & Ishimatsu, 2011, Synergistic effects of elevated CO2). The same effect can be expected for Antarctic Krill. Ocean acidification is only going to get worse as time goes by, and the krill will not be able to maintain a high fitness or abundance in challenging conditions like this. Phytoplankton, the krill's food source is also affected by ocean acidification. Coccolithophores, one form of phytoplankton, is predicted to do better as ocean acidification increases, meaning there could potentially be more food available for krill as the pH continues to decrease. However, this is all speculation, because again, we do not know yet how the krill is affected by decreasing pH. It is all still up in the air (Flores et. al., 2012, Impact of Climate Change).
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Great explanations
ReplyDeleteI like how you separate the categories based on oceans and food supply - it really defines the scope of the problem well.
ReplyDeleteI would make subheading for the different topics you talk here, so it is easier to negative through the blog.
ReplyDelete