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The scoop on pinniped poop

Pinniped poop is like a One A Day® multivitamin for our coastal environment. It acts as a supplement to enhance the health of our kelp beds and other marine algae and seagrasses. In a published study, scientists in Australia showed that the busy work of sea lion gut microbial flora is responsible for making various key nutrients available to needy coastal flora.

On land, plants and algae make up the foundation of the food web, and this is also true in the ocean. Besides seaweed and seagrasses, the world's ocean harbors single-celled photosynthesizers, collectively called phytoplankton. Together, all these plant and plantlike species replenish our atmosphere by generating half its oxygen and help to scrub away excess carbon dioxide.

As rare as rubies

It’s common knowledge that photosynthesis is the chemical reaction wherein plants use sunlight and carbon dioxide from the air to make their own food but did you know that this chemical reaction is a no-go without the addition of trace nutrients like iron, which are as rare as rubies in shallow waters? It’s a wonder, then, that there aren’t more of these essential nutrients dissolved in the ocean. Actually, in what would seem a cruel irony, these nutrients are abundant in the ocean but you have to go into the sea’s dark depths to find them, and that’s not where photosynthesis can take place. Sure there’s a natural vertical circulation to bring a bit of those nutrients to surface waters but because of the ocean’s depth and breadth, it’s an excruciatingly sluggish system. Enter marine mammal poop for continual enrichment.

The ocean’s Miracle-Gro®

The researchers studied the microbial genetic profile of sea lion feces, finding high numbers of bacteria that break down iron and phosphorus. The sequence of events in poop breakdown begins with gut bacteria also found in the poop. The microbes in the released poop furiously digest the poop particles, taking what they need for their own growth (the web of life is all about linking one critter’s output to another’s input) but they aren’t stingy with their digestive activities so there are plenty of leftover nutrients. These dissolved nutrients are jettisoned into the surrounding water where they are gobbled up by phytoplankton. Maybe it’s more accurate to describe pinniped poop as the nearshore fertilizer equivalent to a gardener’s Miracle-Gro because it promotes the well-being and lushness of phytoplankton populations, from giant kelp beds to microscopic marine algae.

Results of this work are significant because they show that regular shallow-water release of fecal matter (harboring its host microbial machinery) keeps these nutrients cycling exactly where they are needed: in sun-drenched, coastal waters where algae like our giant kelp spend their days growing, reproducing, acting as food for others, and providing substrate for all manner of marine life. And because pinniped poop positively contributes to the environment by this recycling, the marine mammals also offset their own carbon footprints. Polluted water, indeed!

The literal end is only a beginning

Previous studies with whales indicate similar results but not many such studies have been carried out, partly because of the challenges involved in scooping the poop.  Yet it is clear that more research must be done to understand how microbes in the marine mammal gut interact and function with coastal flora in the ocean's web of life. Sea lions, seals, and other warm-blooded marine mammals hold the key to understanding how such mammal-host relationships have evolved, which includes unraveling our own biological mysteries as fellow mammals.

That we don’t understand much about marine mammals and their connections to us is another reason to be concerned about their conservation. The traits they share with us (large body size, long gestation period, and low number of offspring) make them inherently vulnerable to extinction (unlike us!), no matter how robust their numbers appear to be in isolated areas. A population seems vigorous until the advent of a sudden contagious disease or environmental crisis, and the population collapses. Chronic or acute threats linked to their decline include habitat degradation, hunting, accidental mortality (vessel strikes and fisheries by-catch), and pollution (including chemical contaminants, marine debris, and noise).  And, again, because collecting data is so difficult, experts estimate that declining populations may go unnoticed at least 70 percent of the time.

Speaking of connections to us, there is another tantalizing reason to fund such studies. The researchers also discovered that sea lion poop has a proportion of critical bacteria similar to those in obese humans, meaning that these bacteria may predispose pinnipeds to having excess body fat that, for them anyway, is essential for survival in temperate to icy conditions. Here then may be a link between the microbial makeup of the pinniped gut and obesity in humans. 

— Judith Lea Garfield, naturalist and underwater photographer, has authored two natural history books about the underwater park off La Jolla Cove and La Jolla Shores. Send comments to