Newly published work in the prestigious science journal PLoS ONE confirms the vital role fish play in recycling iron that sustains their ocean pastures.
Or at least they used to, the shocking news is that depletion of ‘fish iron’ is destroying ocean pasture productivity.
Although iron is the fourth most abundant element in the Earth’s crust, bio-available iron which is vital to photosynthesis limits marine primary production in a large part of the ocean, the ocean pastures. The author/professors point out that the growing scarcity of vital iron availability that is the result of the diminishment of ocean fish has dramatic implications in the world of climate change because the removal of carbon dioxide from the atmosphere by phytoplankton requires that increasingly scarce iron.
This new paper using meta-analysis and literature values for global fish biomass estimates show just how vital fish are in the scheme of ocean ecology. Fish are not mere consumers on their ocean pastures they are actively engaged as the stewards and farmers of those very pastures. It’s their job.
Just this summer another paper reported on the potent role that the great whales play in also recycling iron that sustains their ocean pastures and the whales themselves. So it seems both fish and whales are vital ocean engineers or farmers depending on your preference for anthropomorpic vernacular.
Using a large array of published iron in fish data the authors show that fish biota store between 0.7–7 x 10^11 g of iron, that’s 70-700 thousand tonnes of elemental iron. Additionally, the global fish population recycles through excretion between 400,000–1.5 million tonnes of iron per year, which is approaching a similar magnitude as major recognized sources of iron (e.g. dust, sediments, ice sheet melting).
Keep in mind that iron driven ocean pasture productivity results in each tonne of iron fixing upward of one million tonnes of CO2 into ocean life. Thus the 1.5 million tonnes of fish iron is theoretically capable of sustaining the production of much more than 1.5 trillion tonnes of fish food!
In terms of biological effect this fish iron is very likely superior to dust inputs due to the targeted deposition, fish leave their manure in their ocean pastures. The much superior form of iron in biological excreta compared to iron found in inorganic minerals such as what arrives as dust in the wind also lends greatly to the role of fish iron. That biologically active iron is best at nurturing both nitrogen-fixing cyanobacteria (blue-green algae) and green plankton.
We know that each tonne of iron stimulates growth of tens of millions of tonnes of ocean pasture phyto-plankton. Even more the recycling of that iron by fish and other mechanisms greatly multiplies the beneficial effect sustaining ocean pasture blooms for periods far in excess of the time simple ocean physical chemistry models predict based on simple once through iron chemistry.
To estimate a loss term due to human harvesting activity the authors of this paper, led by professors Allison R. Moreno and Arlene L. M. Haffa of USC, referred to the total commercial catch for 1950 to 2010 which was obtained from the Food and Agriculture Organization of the United Nations. Marine catch data were separated by taxa. High and low-end values for elemental composition were obtained for each taxonomic category from the literature and used to calculate iron per mass of total harvest over time.
The marine commercial removal of fish is estimated to have removed 1–6 x 10^9 g of iron in 1950, the lowest values on record. There is an annual increase to 0.7–3 x 10^10 g in 1996, which declines slightly to 0.6–2 x 10^10 g in 2010. These storage, recycling, and export aspects of biotic ‘fish iron’ are not currently included in ocean iron and carbon mass balance calculations. These data suggest that fish and their depletion should be included in global oceanic iron and carbon cycles.
More Importantly The World Needs To Act Now To Restore And Revive Ocean Pastures.
So before we all just ignore the inevitable and go about our ocean-ignoring ways, there is a workable solution that is immediate, effective, and affordable. It is to take on the stewardship of our ocean pastures and to replenish, restore, and sustain those pastures so that they might return to a condition of abundance and bring the fish back.
This has now been demonstrated in what the world has called the largest ocean plankton pasture restoration project in history. And IT JUST WORKS!
In a project with more than 6 years in planning and execution a large ocean plankton pasture in the NE Pacific was replenished with an infinitesimal amount of mineral micro-nutrient iron. The amount used in the experiment was 120 tonnes of the raw product. Much of it was simple iron ore rock dust. Painstakingly administered into what became more than 30,000 square kilometres of ocean the vital and missing minerals brought an ocean desert back to life.
Intensive at-sea studies over months from the ocean pasture research ship have been followed up with months of analysis of the more than 168 million measurements made of the pasture and surrounding environment. Spectacular results were measured in growth of all forms of ocean life on the restored pasture.
Reference: Paper The Impact of Fish and the Commercial Marine Harvest
on the Ocean Iron Cycle is available for free online.