Sciencespeak: Whale Pump

Whales can poop almost anywhere they want. They have the entire ocean to relieve themselves in, so most of the planet can theoretically be their toilet. Yet, despite having a near-universal lavatory pass, cetaceans often relieve themselves near the surface. In the words of marine biologists Joe Roman and James McCarthy, many whales feed in the deeper tiers of the sea to then return to the surface and release “flocculent fecal plumes” – cetacean clouds that may create what Roman and McCarthy call a “whale pump“.

The researchers laid out their logic in a 2010 PLOS ONE paper. Our planet’s seas are constantly recycling themselves. Showers of marine snow send organic matter cascading down to the sea floor, and zooplankton excrete poop full of nitrogren, phosphorus, and iron in deep water as they go about their regular up-and-down migration through the water column. This is a downward “pump” of resources. But other organisms can also bring some of these elements back from the deep. Whales and other marine mammals, Roman and McCarthy hypothesized, replenish the surface waters with their excrement.

The researchers based their case on an array of cetacean observations. Whales must surface to breathe, the physiological consequences of diving and surfacing make it likely that marine mammals will let it all go near the surface, and observations of crappy clouds have shown that they dissipate through the water rather than sink. And even though whales sometimes feed in the upper portion of the sea, they often dive deeper to reach dense pockets of fish and invertebrates. These hard-to-reach resources are key to Roman and McCarthy’s proposal. Whales feed on deepwater prey that are taking up elements from far below. After a bit of digestion, the whales then jettison some of those elements in shallower waters and leave plankton to recycle the slightly-used nitrogen.

Seals and sea lions might do their share, too. If you’ve ever smelled a pinniped colony at the height of breeding season, you’ve probably cursed your sense of smell. What the blubbery mammals spill onto the shore can be washed back into the sea, emanating the ecological reek of seal-processed fish and squid returning nitrogen to the water.

It’s one thing to theorize from an armchair, though, and quite another to get out on a boat and collect some whale feces. That’s exactly what Roman and McCarthy did to further investigate their idea, taking 16 samples of billowy poops from the Gulf of Maine. All of the samples contained significantly more ammonium – a nitrogen-rich waste product – than the surrounding water. Based on these analyses, Roman and McCarthy suggested that whales could be responsible for dumping 2,3000 metric tons of nitrogen into the Gulf of Maine every year. The amount was probably even higher before commercial whaling tried to sate its hunger for the massive mammals.

And seagoing beasts may only be continuing a trend that was in place long before they took to the water. At this past weekend’s PaleoFest at the Burpee Museum of Natural History, paleontologist Ryosuke Motani pointed out that marine reptiles were doing the dive-and-surface shuffle hundreds of millions of years before the hoofed ancestors of whales were even a glimmer in natural selection’s eye. Some of these marine reptiles – such as the fish-like ichthyosaurs – were some of the first deep-divers, Motani pointed out, and they could have played an ecological role similar to what Roman and McCarthy have suggested for whales. So perhaps it’s too narrow to talk about “whale pumps” or “marine reptile pumps” feeding the seas. Those are just more academically-acceptable ways of talking about “poop pumps”.

Reference:

Roman, J., McCarthy, J. 2010. The whale pump: marine mammals enhance primary productivity in a coastal basin. PLOS ONE. doi: 10.1371/journal.pone.0013255