Two centuries of whaling had an unforeseen side effect: a disruption in ocean nutrient cycling. Why? The diminishing global whale population has had an interesting side effect: less whale feces. This is important because the feces introduce leftover nutrients, which are then taken up by fish or birds. These organisms distribute the nutrients across the globe, even to land (e.g., a fish swims upriver and is consumed by a bear). The dramatic decline in whales means less poop. Unfortunately, the process also works in reverse.
A 1995 paper by Chery Butman and colleagues was one of the first to note how whaling might have impacted the transfer of nutrients from the surface to the deep sea. A whale’s large carcass sinks rapidly and lands on the ocean floor intact, a windfall in a low-nutrient area. Detritus and other sinking organic matter may be sources of nutrients, but none so large and concentrated as a whale carcass (known as whale-falls).
Whale-falls are so special that entire ecosystems spring up around them within a short period of time. The scavengers that feed on the carcass become the prey of other predators. Worms or other organisms take up residence in old skeletons, attracted by shelter and the high oil content of the whale bones. After a time, the bones decompose, use up the surrounding oxygen, and allow colonization by chemosynthetic bacteria that process sulfur compounds in the bones. Clams and tube worms follow, just like a deep sea vent community. These carcasses attract such a wide variety of life that many researchers see them as vital for deep sea biodiversity, especially on a local scale.
Whaling, of course, impacted the availability of whales. As whale populations dropped, there were fewer whale carcasses available to support deep sea communities. Whaling also tended to shift whale-falls around. During the heyday of whaling, the mammals were killed in areas where they hunted, which differed in location from where pods of whales would gather. Thus, many whale-falls were displaced from their naturally occurring region. The result was a geographic distribution of nutrients from one area to another, with unknown results.
Whale populations have not fully rebounded, and likely never will. As a result, the historical cycle of whale-falls and the distribution of nutrient-rich whale poop can never be completely restored. Can the system balance itself out?