Have you wandered to the California coast lately? Have you witnessed the up-close encounters with marine life, especially humpback whales? More importantly, have you pondered the ecologic benefits of what these and other visiting marine creatures leave behind? During these fall months, you have the opportunity to do all these things, and can reflect on the role of, yes, poop, in the connectivity of the web of life.
The population of humpbacks that visit the California coast are following food as they move between their summer homes offshore of Canada and their wintering grounds in the tropics (up to 10,000 miles, round-trip). These 40 ton Mysticedes eat mostly krill and small fish, such as anchovies and sardines, which generally amass in unpredictable patches in our nearshore and offshore seas. But in fall, this food source concentrates right next to the shoreline and humpback whales put on a spectacular foraging show lunging and jumping for their meals (Figure 1). Not surprisingly, whales return to the ocean what they have taken out, this time in the form of feces that are chock-full of recycled nitrogen once stored in their food. This nitrogen source replenishes the surface of the ocean, where whales spend much of their time, enhancing nutrient availability for primary production by phytoplankton, which is then eaten by zooplankton (such as krill), thus continuing the cycling of a marine food web.
The next time you see these insatiable humpback whales, you may think a bit differently about them and their role in the oceans. But they are not the only ones making connections with the food web.
Just past the coastline we find a different feat of nature: thousands to millions of dark-colored Sooty Shearwaters. They, too, are following the food, but their migration is a bit longer than other summer visitors. These seabirds clock a 40,000 mile round trip commute from their breeding grounds in New Zealand into eyesight just off the California coast. It is one of the longest documented migrations of any wild animal, and the longest daily transit of “Sooties” can reach just over 300 miles.
In addition to bringing astonishment to local communities who observe these dense flocks of birds that stretch for miles paralleling the shore, shearwaters also bring a connection with a foreign land. Sooty shearwaters, like most seabirds, spend the majority of their life at sea eating mostly fish and krill, just like whales. But each year they will return to the islands in New Zealand from which they were born. Here they rebuild nests (dug-out underground burrows), reunite with their partners, and rear the next generation of seabirds. At the end of the breeding season, typically in May, Sooty Shearwaters make their long distance migration again, back to their foraging grounds in the northern hemisphere. During this process, these birds leave a lot behind: feathers, abandoned eggs, themselves (if they die), and lots of stinky white guano chock full of the nutrients from the food they ate at sea. Studies have shown that these “subsidies” fertilize soils, impact plant communities and foster island food webs. Amazingly, Sooty Shearwaters, like many seabirds, fertilize islands like whales fertilize the oceans and link together land and sea ecosystems.
One more thing to ponder: While studies have yet to show the exact geographic source of nutrients in the subsidies left on islands from shearwater inhabitants, whatever they eat in places like California will likely end up, in one of many forms, far away on an island in New Zealand. Current research will soon address this question, but for now we are left to wonder and think about how our own backyard may be influencing someone else’s coastal playground far off in a different hemisphere.
Next up from this author: More global connections made by seabird survivors - The epic story of Pink Footed Shearwaters
Want to Learn More? Check out these resources:
Croll, D. A., Maron, J. L., Estes, J. A. Danner, E. M., & Byrd, G. V. (2005). Introduced predators transform subarctic islands from grassland to tundra. Science, 307 (57170), 1959-1961
National Audbon Society. Birds of North America Online Sooty Shearwater
NOAA Fisheries. Humpback Whale (Megaptera novaeangliae).
Roman, J., & McCarthy, J. J. (2010). The whale pump: marine mammals enhance primary productivity in a coastal basin.
Shaffer, Scott A., et al. "Migratory shearwaters integrate oceanic resources across the Pacific Ocean in an endless summer." Proceedings of the National Academy of Sciences 103.34 (2006): 12799-12802.
Stewart, R. (2005). Our Ocean Planet: Oceanography in the 21st Century. Marine Fisheries Food Webs.
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