Fish Feces Sequester Carbon, Rogue Millionaire Poisons Pacific Ocean
Does fish fecal matter fight global warming by carrying organic carbon to the bottom of the ocean where it is sequestered in sediment? A new study claims that fish poo is under appreciated as a part of the natural carbon cycle and that it carries carbon to the ocean bottom much faster than dead zooplankton sink on their own. “Measurements of in situ abundance of fish fecal pellets or their flux are lacking, likely due to the difficulty of adequately sampling these particles,” the study's authors state, “to our knowledge, this is the first study to present estimates of fish fecal pellet abundance.” This study indicates that fish poo is an under appreciated component of both the carbon and nitrogen cycles. Surprisingly, waste from marine mammals, including whales, breaks up and degrades as it sinks, returning its carbon, nitrogen and other elements back to the environment.
It is not a subject that many people, even marine biologists, dwell on—just what sort of contribution does the excrement of marine animals make to nature's recycling of carbon? Some answers to this question are presented in “Abundance, Composition, and Sinking Rates of Fish Fecal Pellets in the Santa Barbara Channel,” a report in the journal Nature by Grace K. Saba and Deborah K. Steinberg, both researchers at the Virginia Institute of Marine Science. They studied the coastal waters of the Santa Barbara Channel, in California, and found it was not just the amount of poo but how fast it sinks that makes a difference. Here is the author's overview:
Rapidly sinking fecal pellets are a major contributor to the ‘biological pump’, the vertical transport of biologically generated particulate organic matter (POM) from the surface to the ocean's interior. Sinking rates of small or low mass fecal pellets of some zooplankton (i.e., copepods, euphausiids, doliolids, appendicularians, heteropods), as well as phytodetritus and marine snow, range from <10 to hundreds of meters per day, while very large or high mass fecal pellets of other zooplankton (i.e., salps, pteropods, chaetognaths) tend to sink faster (tens to thousands of meters per day). Sinking rates of fecal pellets produced by fish, of which only a few have been reported in the literature, reach well over thousands of meters per day. Fast-sinking fish feces could therefore contribute substantially to export of organic matter; fecal matter of anchovies in the Peru upwelling system (Engraulis ringens) contained high amounts of organic carbon and nitrogen, and represented up to 17% of total carbon flux in sediment traps.
It is no secret that there are a lot of critters in the ocean. They all eat and they all excrete, and that material has no place to go but down. But up until now, no comprehensive study of how fast the stuff sinks has been performed. “Measurements of fish fecal pellet sinking rates and the vertical flux of particulate carbon are very limited, and no previous study has measured the abundance of fish fecal pellets in situ,” the authors state, explaining the motivation for their study.
“Feces produced by the fish in our study were long cylinders, that likely broke across the length axis into pellet fragments of varying length,” write Saba and Steinberg, preferring to call the material under study pellets. The pellets were similar in width, ranging between 0.6 and 1.5 mm and averaging 1.0 ± 0.2 mm. The length was more variable ranging between 1.0–6.0 mm while averaging 2.1 ± 1.0 mm.
The amount of particulate organic carbon (POC) and nitrogen (PON) in each pellet was carefully measured. Carbon weighed in at an average 21.7 μg per pellet, nitrogen around 2.7 μg. That does not seem like a lot but there are a lot of small fish and they are pooping all the time. See the report for other characteristics of the pellets in question.
Just what is in these fishy fecal pellets? Prey items were identified using epifluorescence microscopy and a wide range of zooplankton were found: dinoflagellates, various diatoms, silicoflagellates, ciliates, and copepods were common components of fecal pellets. It seems that small fish like the northern anchovy have a varried diet and are opportunistic feeders. Some of the items on their oceanic menu can be seen in the pictures below.
Dominant prey items found within fish fecal pellets.
The upshot of this is that fish feces contains both organic and inorganic carbon, which it can rapidly transport to the sea floor, at least when compared with the slow descent of dead diatoms and marine snow. Could this mechanisim be an underestimated pathway to carbon sequestration? The authors summarized their findings this way:
Northern anchovy contributed a large proportion to total commercial fish landings in the Santa Barbara Channel during the last decade; thus, their fecal matter likely contributes a significant component of the vertical flux of organic carbon and nitrogen. Our estimates suggest that anchovy pellets produced near the surface would reach the benthos (512 m) in < 1 day. Additionally, anchovies may transport particulate carbon spatially along the coast as they exhibit both vertical and onshore-offshore diel migrations to mimic prey movements. It is unknown if all bony fish form similar cohesive, rapidly sinking fecal pellets or if some fish form loose, porous pellets which will break up and degrade easily in the upper water column as reported for marine mammals such as whales. However, all reports on fish fecal pellets thus far (northern anchovy [present study], seven midwater fish species, the Peruvian anchovy, and the blacksmith reef fish) have demonstrated the formation of cohesive, rapidly sinking pellets. Finally, recent studies revealed that fish contribute up to 15% of total oceanic carbonate production (inorganic C) via the formation and excretion of various forms of precipitated (non-skeletal) calcium carbonate from their guts. Thus, the downward transport of particulate matter produced by fish could be a significant, but underappreciated, component of both organic and inorganic carbon flux in coastal environments.
“Fecal matter produced by the Peruvian anchovy is hypothesized to play an important role in carbon and nitrogen flux in highly productive, upwelling systems,” Saba and Steinberg conclude. “Our study demonstrates that fecal matter likely produced by the northern anchovy may also export significant amounts of repackaged surface material to depth in the California coastal system.”
This blog has reported on newly discovered carbon transport mechanisms in the past, specifically on salps (see “New "Jelly Pump" Rewrites Carbon Cycle”). Fish feces seems to be another mechanism whose part in the overall carbon cycle is underestimated. With every new discovery science shows how ignorant we are of nature. Meanwhile, a rogue businessman has taken it on himself to alter the ocean off the coast of western Canada.
In July, controversial Californian businessman Russ George dumped around 100 tons of iron sulphate into the Pacific Ocean off the west coast of Canada as part of a geoengineering scheme. The intention was that the iron would create an algal bloom. Most of the time, oceanic algal growth is limited by lack of iron. Adding even a relatively small amount of iron to ocean waters can cause explosive growth creating an algal bloom. In this case, it would seem that the seripticious dumping did result in a large algal bloom, shown in the NASA picture below.
This scheme—a geoengineering technique known as ocean fertilization—was sold to the native American inhabitants of the Village of Old Massett as a way to increase food for young salmon. The “experiment” was supposed pay for itself through the selling of carbon credits. Needless to say, there are a lot of people upset with this intentional polluting of the waters of the Pacific Northwest.
Now, the Guardian is reporting that the Canadian government knew of the iron dumping plan. Regardless of government approval, Tom Pedersen, from the Pacific Institute for Climate Solutions, believes that the $2.5 million in carbon credits will not be marketable to any reputable agency. Ecologists everywhere are rightfully upset about this, but that is what you get when you try to bribe people to do what you want by letting them sell carbon credits.
The problem is, algal blooms can deplete ocean waters of oxygen leading to massive die-offs of higher marine life. Given the fish feces report cited above, rather than increasing carbon sequestration the iron fertilization could decrease carbon capture over the long run. Trouble is that there is little reliable data on how such draconian measures affect the environment over time. It would appear that a group of mad scientists and a megalomaniac millionaire sold a desperate tribe of native Americans on a dangerous and unproven scheme to mess with nature.
Can I interest you in some carbon credits?
“It is difficult if not impossible to detect and describe important effects that we know might occur months or years later,” said John Cullen, an oceanographer at Dalhousie University. “Some possible effects, such as deep-water oxygen depletion and alteration of distant food webs, should rule out ocean manipulation. History is full of examples of ecological manipulations that backfired.”
There are two main lessons here. First, as the fish feces study shows, science really does not understand how the environment works in detail, and not having detailed understanding means recommendations based on current knowledge can go horribly wrong. Second, byzantine schemes, created by collusion between climate scientists, ecologists and governments, intended to coerce people into supposedly eco-friendly actions are a truly horrid idea.
Be safe, enjoy the interglacial and stay skeptical.