Baleen whales have been found to excrete nutrients that increase primary productivity in the ocean by up to 10%.

Scientists have known for some time that whales contribute to marine ecosystems by “recycling” nutrients. However, the exact impact on ocean productivity is unclear and has not been studied quantitatively. A new study, published in the journal Proceedings of the National Academy of Sciencessolved this problem by directly measuring nutrients excreted by baleen whales. The results show that these whales significantly increase the primary productivity of the oceans.

Primary productivity and the ocean food web

Primary productivity is a measure of how certain organisms, in this case phytoplankton, convert energy into organic compounds through processes such as photosynthesis or chemosynthesis, which ultimately serve as the basis of the food web. When primary productivity is higher, organisms along the food chain have more sustainable food sources.

For phytoplankton to produce these organic compounds, they must receive a good dose of nutrients, such as nitrogen, phosphorus and iron, necessary for photosynthesis and other processes. Unfortunately, many parts of the upper layer of ocean water are devoid of these nutrients. Some of these nutrients are replenished by land runoff, mix with deeper ocean waters, and are recycled by zooplankton, bacteria, and marine life as a whole.

Don’t waste, don’t want

According to the new study, baleen whales – a group that includes minke whales, fin whales, blue whales, humpback whales and bowhead whales – provide a significant amount of these nutrients through their waste. To determine the actual contribution, the research team collected and analyzed feces and urine from minke and fin whales, testing for nutrient content of nitrogen, phosphorus, iron and 14 other trace elements.

Next, they estimated daily and annual nutrient release for six other baleen whale species and used an ecosystem model, called NORWECOM.E2E, to simulate the impacts of nutrient release by whales on primary production and zooplankton. The study focused on the seas of Greenland, Norway and Iceland, where baleen whales migrate in summer, before returning to their winter breeding grounds at lower latitudes.

The results showed that baleen whales release significant amounts of nitrogen, mainly via urine, and phosphorus and trace elements, mainly via feces. In total, these whales recycle more than 815 tonnes of nitrogen and 325 tonnes of phosphorus daily in the Nordic and Barents Seas during the feeding season. The contribution varies depending on the specific species.

“The amount of nutrients released by whale populations is expected to depend on prey consumption rates and population abundance. Given their large size, blue whales, sei whales, and fin whales are the species contributing the highest nutrient loads per individual. However, when population abundance is taken into account, minke whales are the species that contribute the most to nutrient pools in most regions, including the Sea of Barents, the Norwegian Sea and the Greenland Sea,” explain the authors of the study.

Seasonal and spatial fluctuations

As expected, nutrient content varies over time, with higher amounts in late summer, increasing from May onwards, when whales migrate to these areas. In some regions, primary production was 10% higher in August. This effect was observed more in nutrient-poor offshore regions.

“The variation in annual net primary production was relatively small in most regions, with a spatial average of 0.63%, but reached 2–4.5% in the Norwegian Sea basin and the northern Barents Sea, east of Svalbard. In the Barents Sea, the development of phytoplankton blooms in spring and summer is mainly governed by available light and the progression of sea ice melt.

“In general, the Arctic-influenced northern Barents Sea is less productive due to lower light availability and nutrient concentrations than the southern Barents Sea. Our models indicate that whale-derived nutrients have a more pronounced impact in these regions far from alternative nutrient sources,” the study authors write.

Cascading effects of increasing primary productivity

Increased primary production ripples through the food web, benefiting many organisms. Mesozooplankton (organisms that feed on phytoplankton and microzooplankton) have been found to increase their biomass by up to 10%. The team points out that declines in survival and growth of Norwegian smolts have been observed in other studies, as well as changes in herring feeding migration patterns. These have been attributed to changes in zooplankton biomass in the Nordic Seas.

“Thus, mesozooplankton appear to provide an important link between primary producers and higher trophic levels. Although not all nutrients released by whales are readily used by phytoplankton, our study highlights their potential to increase both primary production and secondary growth,” the authors say.

In addition to boosting the food web, increasing primary productivity contributes to carbon sequestration. This is due to the inherent processes involved, which use carbon dioxide from the atmosphere by transforming it into organic compounds.

The future of marine ecosystems

It is clear that the ocean ecosystem is subject to complex processes that support and nourish its inhabitants. The study shows that protecting whale populations not only benefits whales, but also entire ocean ecosystems and the global climate.

Future research could help refine these models with improved data on whale movement, excretion depth and nutrient dissolution and by incorporating other marine vertebrates and more trace elements into the models.

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