Comments on: Eat fish and acidify the oceans http://masonposner.com/afisheyeview/2009/01/eat-fish-and-acidify-the-oceans/ blogging about comparative physiology with some marine and regional flavor Thu, 29 Jul 2010 18:39:12 -0600 hourly 1 http://wordpress.org/?v=3.0 By: Mason Posner http://masonposner.com/afisheyeview/2009/01/eat-fish-and-acidify-the-oceans/comment-page-1/#comment-53 Mason Posner Fri, 23 Jan 2009 04:04:14 +0000 http://masonposner.com/afisheyeview/?p=222#comment-53 Misha - thanks for pointing out some of the complexities of this paper. The authors do not clearly state how the production of carbonates by fishes would affect ocean pH other than hypothesizing that these carbonates lead to the higher than expected alkalinity found in the upper layers of the ocean (shallower than 1000 m). The patchy nature of fish biomass and their presence over continental shelves (where as you point out carbonates may become buried in sediment before dissolving) and the effect of upwelling zones on carbonate distribution seem to make generalizing about the effects of these carbonates difficult. So in that sense, I probably did put too much stress on the conclusion that fish reduce the acidity of the ocean. What is unclear to me is whether reduced fish biomass would lead to a decrease in overall ocean acidity. You point out that fish have a negative effect (increased acidity) in epipelagic waters. I suggested that the production of these carbonates would have an overall net effect of decreasing acidity in the ocean as a whole. These don't seem mutually exclusive. Of course any heterotroph is going to raise acidity by producing CO2 during its metabolism and releasing it into the environment. The activity of carbonic anhydrase will also promote the production of H+, also increasing acidity. Fish would produce bicarbonate ions even if they did not make carbonates in their gut. Does the increased carbonic anhydrase activity needed to make these gut carbonates so outweigh the buffering effects of the carbonates that the fish have a net acidifying effect? If it is true that all heterotrophs have a net acidifying effect, does gut carbonate production in fish mitigate this in surface waters, or make it worse? What about in the entire ocean? Misha – thanks for pointing out some of the complexities of this paper. The authors do not clearly state how the production of carbonates by fishes would affect ocean pH other than hypothesizing that these carbonates lead to the higher than expected alkalinity found in the upper layers of the ocean (shallower than 1000 m). The patchy nature of fish biomass and their presence over continental shelves (where as you point out carbonates may become buried in sediment before dissolving) and the effect of upwelling zones on carbonate distribution seem to make generalizing about the effects of these carbonates difficult. So in that sense, I probably did put too much stress on the conclusion that fish reduce the acidity of the ocean.

What is unclear to me is whether reduced fish biomass would lead to a decrease in overall ocean acidity. You point out that fish have a negative effect (increased acidity) in epipelagic waters. I suggested that the production of these carbonates would have an overall net effect of decreasing acidity in the ocean as a whole. These don’t seem mutually exclusive.

Of course any heterotroph is going to raise acidity by producing CO2 during its metabolism and releasing it into the environment. The activity of carbonic anhydrase will also promote the production of H+, also increasing acidity. Fish would produce bicarbonate ions even if they did not make carbonates in their gut. Does the increased carbonic anhydrase activity needed to make these gut carbonates so outweigh the buffering effects of the carbonates that the fish have a net acidifying effect? If it is true that all heterotrophs have a net acidifying effect, does gut carbonate production in fish mitigate this in surface waters, or make it worse? What about in the entire ocean?

]]> By: Misha Matz http://masonposner.com/afisheyeview/2009/01/eat-fish-and-acidify-the-oceans/comment-page-1/#comment-47 Misha Matz Tue, 20 Jan 2009 20:47:35 +0000 http://masonposner.com/afisheyeview/?p=222#comment-47 There seems to be misunderstanding going on concerning the implications of Wilson et al results. According to Wilson et al data, fish actually exacerbate (rather than mitigate) the problem of acidification of the surface waters. Fish essentially strip the protons off the bicarbonate and excrete them into the water through gills, while the generated calcium carbonate sinks and either dissolves in the deeper water or gets buried in the sediment if the fish are in the shallows. Wilson et al say that this process may lead to the previously unexplained alkalinization of waters at 500-1000 m - which implies that the surface waters must get correspondingly acidified, just like being titrated with HCl. Moreover, Wilson et al predict that this process will be intensified as global CO2 rises. Bad news for coral reefs. There seems to be misunderstanding going on concerning the implications of Wilson et al results. According to Wilson et al data, fish actually exacerbate (rather than mitigate) the problem of acidification of the surface waters. Fish essentially strip the protons off the bicarbonate and excrete them into the water through gills, while the generated calcium carbonate sinks and either dissolves in the deeper water or gets buried in the sediment if the fish are in the shallows. Wilson et al say that this process may lead to the previously unexplained alkalinization of waters at 500-1000 m – which implies that the surface waters must get correspondingly acidified, just like being titrated with HCl. Moreover, Wilson et al predict that this process will be intensified as global CO2 rises. Bad news for coral reefs.

]]> By: Douglas Watts http://masonposner.com/afisheyeview/2009/01/eat-fish-and-acidify-the-oceans/comment-page-1/#comment-45 Douglas Watts Mon, 19 Jan 2009 09:06:14 +0000 http://masonposner.com/afisheyeview/?p=222#comment-45 Interesting. There are many good reasons to consider curtailing fish consumption, including that many of the most highly sought after species are close to extinction because people are buying them in the supermarket. Interesting.

There are many good reasons to consider curtailing fish consumption, including that many of the most highly sought after species are close to extinction because people are buying them in the supermarket.

]]>