Whales could be a valuable carbon sink, say scientists

Nature-based solutions to fight climate change take a holistic approach that promotes biodiversity and ecosystem preservation. While many efforts have focused on planting trees or restoring wetlands, researchers publishing in Trends in Ecology and Evolution on December 15 advocate for the importance of understanding the carbon sequestration potential of the planet's largest animals -- whales. In their paper, the researchers explore how these marine giants can influence the amount of carbon in our air and waters and potentially contribute to the overall reduction of atmospheric carbon dioxide.

"Understanding the role of whales in the carbon cycle is a dynamic and emerging field that may benefit both marine conservation and climate-change strategies," write the authors, led by Heidi Pearson, a biologist from the University of Alaska Southeast. "This will require interdisciplinary collaboration between marine ecologists, oceanographers, biogeochemists, carbon-cycle modelers, and economists."

Whales can weigh up to 150 tons, live over 100 years, and be the size of large airplanes. Like all living things, their hefty biomass is composed largely of carbon and they make up one of the largest living carbon pools in the pelagic ocean, part of the marine system that is responsible for storing 22% of Earth's total carbon.

"Their size and longevity allow whales to exert strong effects on the carbon cycle by storing carbon more effectively than small animals, ingesting extreme quantities of prey, and producing large volumes of waste products," write the authors. "Considering that baleen whales have some of the longest migrations on the planet, they potentially influence nutrient dynamics and carbon cycling over ocean-basin scales."

Whales consume up to 4% of their massive body weight in krill and photosynthetic plankton every day. For the blue whale, this equates to nearly 8,000 pounds. When they finish digesting their food, their excrement is rich in important nutrients that help these krill and plankton flourish, aiding in increased photosynthesis and carbon storage from the atmosphere.

A blue whale can live up to 90 years. When they die and their bodies fall to the seafloor, the carbon they contain is transferred to the deep sea as they decay. This supplements the biological carbon pump, where nutrients and chemicals are exchanged between the ocean and the atmosphere through complex biogeochemical pathways. Commercial hunting, the largest source of population decline, has decreased whale populations by 81%, with unknown effects on biological carbon pump.

Read more at Science Daily

Animals are key to restoring the world's forests

As UN climate talks close in Egypt and biodiversity talks begin in Montreal, attention is on forest restoration as a solution to the twin evils roiling our planet. Forests soak up atmospheric carbon dioxide and simultaneously create habitat for organisms. So far, efforts to help forests bounce back from deforestation have typically focused on increasing one thing -- trees -- over anything else. But a new report uncovers a powerful, yet largely overlooked, driver of forest recovery: animals. The study by an international team from the Max Planck Institute of Animal Behavior, Yale School of the Environment, the New York Botanical Garden, and the Smithsonian Tropical Research Institute examined a series of regenerating forests in central Panama spanning 20 to 100 years post-abandonment. The unique long-term data set revealed that animals, by carrying a wide variety of seeds into deforested areas, are key to the recovery of tree species richness and abundance to old-growth levels after only 40-70 years of regrowth. The article, published in Philosophical Transactions of the Royal Society B, is part of a theme issue focused on forest landscape restoration as part of the UN Decade on Ecosystem Restoration.

"Animals are our greatest allies in reforestation," says Daisy Dent, a tropical ecologist from MPI-AB and the study's senior author. "Our study prompts a rethink of reforestation efforts to be about more than just establishing plant communities."

The report also notes that situating regenerating forests near patches of old growth, and reducing hunting, encourages animals to colonize and establish. "We show that considering the wider ecosystem, as well as features of the landscape, improves restoration efforts," says Sergio Estrada-Villegas, a biologist now at Universidad del Rosario (Bogotá, Colombia) and the study's first author.

Seed dispersal by animals is key to forest expansion. In the tropics, over 80% of tree species can be dispersed by animals, which transport seeds throughout the landscape. Despite this, forest restoration efforts continue to focus on increasing tree cover rather than reestablishing the animal-plant interactions that underpin ecosystem function. "Figuring out how animals contribute to reforestation is prohibitively hard because you need detailed information about which animals eat which plants," says Estrada-Villegas.

The forest at the Barro Colorado Nature Monument (BCNM), in the Panama Canal, offers a unique solution to this problem. In one of the best studied tropical forests in the world, generations of scientists at have documented frugivore interactions to understand which groups of animals disperse which tree species.

In the present study, the team led by Estrada-Villegas and Dent examined this unique long-term dataset to determine the proportion of plants dispersed by four groups of animals -- flightless mammals, large birds, small birds, and bats -- and how this proportion changed over a century of natural restoration.

Their results offer the most detailed data of animal seed dispersal recovery across the longest timeframe of natural restoration. "Most studies examine the first 30 years of succession, but our data spanning 100 years gives us a rare glimpse into what happens in the late phase of restoration," says Dent.

The study found that young regenerating forests were made up mostly of trees dispersed by small birds. But as the forest aged, trees dispersed by larger birds increased. Surprisingly, however, the majority of plants were dispersed by terrestrial mammals across all forest ages -- from 20 years old to old growth. "This result is quite unusual for post-agricultural regenerating forests," says Dent. "It is likely that the presence of large tracts of preserved forests near our secondary stands, coupled with low hunting, has allowed the mammal populations to thrive and to bring an influx of seeds from neighboring patches."

Read more at Science Daily