In a possible solution to a marine chemistry mystery that has puzzled scientists for several decades, researchers have now calculated the contribution of teleost fish (bony fish) to marine carbonate (CO3) concentrations. They estimate that such fish secrete up to 15% of the ocean’s carbonate production, through their intestines, or guts (these are conservative estimates; the more liberal estimates show up to 45%).
This is important because sea water is saturated with calcium ions (Ca+2), which must be combined with carbonates to form the shells (as in bi-valves like clams and scallops) and habitat structures (as in gastropods, like conchs, and coral communities) made of Calcium carbonate (CaCO3). CaCO3 is a “neutral” (non ionic/reactive) and stable compound (within normal ocean ph ranges), and, with its plentiful constituent ions (Ca2+ and CO3-), it is an ideal material for marine creatures to utilize in constructing their shells and skeletons.
Teleosts, or bony fish, are referred to as Osteichthyes in taxonomy, and include ray-finned and lobe-finned fishes (most are ray-finned, lobe-finned fish species are fewer). Most fish are bony fish, which are considered to be vertebrates, and as such, are the largest taxa of vertebrates (29, 000 species) on the planet. With this recent research, their role in the ocean’s chemical and ecological health is now becoming more significant
It is known that most of the ocean’s carbonate production comes from zooplanktons such as the coccolithophores and foraminifera. However, most of this carbonate ends up on the ocean floor, as these creatures die and sink to the bottom. To understand how carbonates are produced, used, recycled and dissolved , scientists must estimate the “carbonate budget” (the metabolic needs and functions) of all marine life forms (total biomass). But their estimates came up short of their actual findings from samples in marine creatures and sediments. In previous global carbonate budget estimates, the contribution from these types of fish was not included, although it was suggested earlier that this might be a source of the ocean’s “missing carbonate”.
Much current marine research has focused on the “acidification” of the oceans–especially the shallower seas and sea beds where corals thrive. Too much acid (or a surplus of H+ ions) in the water makes for fewer carbonate ions available to build shells and coral structures (Hydrogen bonds with carbonate, forming bicarbonate, not CaCO3). This is part of the complex, acid-base reaction dynamics that go on continuously in the world’s oceans. It is believed that the recent decline in some coral species is the result of this acidification (see my earlier post : One Third of Reef-Building Corals Face Extinction Risk ).
However, this generally accepted fact stands in contrast to recent findings that show an increase in carbonate secretions–resulting in a higher ph (or more basic, or alkyline, outcome)–especially in shallower seas (100 to 300 meters depth). Further, as reported in Science (Contribution of Fish to the Marine Inorganic Carbon Cycle, January 19, 2009), by researchers R.W. Wilson et al, several studies indicate major contributions to the carbonate budget by teleost fish species, which secret carbonates at exceedingly high rates. This is even more pronounced as temperatures increase, due to the fact that this speeds up the fish’s metabolism.
Calculating the impact of acid increases (from excess CO2 in the atmosphere) and carbonate increases is highly intricate ecological work. Reaction chemistry between inorganic molecules is complex and difficult to capture completely (there are so many variables, like Magnesium, Mg+, content, which is also highly present in seawater). The simple fact that scientists, up until recently, have been ignoring teleost fish carbonate contributions in their calculations shows that more work, and better estimation formulas, are needed.
Will the carbonate contribution of bony fish (and other marine species) to the oceans balance out the contribution of CO2 emissions to ocean acidification? The answer may lie in the long-term health of teleost fish populations world wide. Many recent studies show numerous fish species in dramatic decline (due to heat stresses, over-fishing, loss of reef habitat, reproductive damage, etc.). For a recent fish come-back success story, see my recent post on this blog: Fish Species Rebounds After Years of Decline – Scientists Puzzled
photo credit: Diliff on wikipedia.org
About Michael Ricciardi
