A natural whale trap
The Baía de Todos os Santos, or Bay of All Saints, is the largest bay in Brazil, covering 1,223 square kilometers. Its unique geography and proximity to a major whale migration route create the conditions for a natural underwater graveyard. The bay has an average depth of 9.8 meters, but some areas plunge to 70 meters. This complex bathymetry, combined with the large number of islands, can disorient marine mammals that wander inside.
This region is adjacent to the Abrolhos Bank, the primary breeding and calving ground for humpback whales (Megaptera novaeangliae) in the western South Atlantic. Every year between July and November, thousands of humpbacks migrate from their Antarctic feeding grounds to these warmer waters. Whales that are old, sick, or young and separated from their mothers may enter the bay and find it difficult to navigate back to the open ocean. Over centuries, the remains of these animals have settled on the seafloor, creating a site for paleontological study.
Life after death: The whale fall ecosystem
When a 40-ton whale dies and sinks to the seafloor, it delivers a massive pulse of nutrients to the deep. This event, known as a "whale fall," triggers a long and complex ecological succession. The process unfolds in distinct phases. First is the mobile scavenger stage, where animals like sleeper sharks and hagfish strip the carcass of its soft tissue over a period of months to years.
Next, the enrichment-opportunist stage begins. Mollusks, crustaceans, and polychaete worms colonize the surrounding sediment and remaining flesh. This leads to the most enduring phase: the sulphophilic stage, which can last for 50 years or more. During this stage, anaerobic bacteria inside the bones break down the lipid-rich marrow, releasing hydrogen sulfide as a byproduct.
This chemical release supports a chemosynthetic community. Bacteria form thick mats on the bones, and these microbes, in turn, nourish other organisms. The inhabitants are bone-eating worms of the genus Osedax, sometimes called "zombie worms." First described in 2004, these bizarre annelids have no mouth or stomach. Instead, they secrete acid from a root-like structure that bores into the bone. Symbiotic bacteria within these roots digest the fats and oils, providing nourishment for the worm. A single large whale skeleton can support a diverse community of over 185 different species, is a hotspot of biodiversity on the otherwise sparse seafloor.