Degradation, utilization and microbial settlement of shark carcasses

Coordination: Christian Lott, Miriam Weber

Whale falls and actually log or wood falls were recognized as important spot-habitats on deep sea plains, representing at least 50% of the earths surface. Bacteria, free living or symbiotic, are able to decompose organic material from fatty whale bones for many decades. Via the production of sulfide chemoautotrophic processes are enabled that provide the basics for the existence of symbiotic animals within these extreme habitats. For whale and wood falls the possible role as "stepping stones" for the dispersal of organisms into other deep sea areas are discussed. 

At the end of may 2007 to basking sharks (Cetorhinus maximus) were found dead in a fishing net near the coast of Elba Island. The animals are of no economic value and are nor eaten, so the fishermen cut off the net and let the carcasses sink to a depth of about 50 meters.

We took advantage of this unintended experiment to study the decay and possible settlement of the dead sharks. A first visit ten days after the death of the animals already revealed a dense turf of bacteria but only moderate traces of scavengers. After further 5 weeks one carcasse already showed clear feeding traces, both sharks where completely covered by bacteria. Signs of bigger scavengers like sharks, hagfishes or others known from whale falls could not be detected.

The exciting part began when six months later the bigger parts of the skeleton were lying free. Unfortunately the fishing net with the remains of the sharks had slid down the slope to a depth of almost 60 metres. Some of the vertebra were lying in about 15 meters distance of the main part of the carcasse. Possibly some larger scavenger had dispersed the parts of the dead basking sharks. The cartilaginous skeleton of sharks contains less fat than for example whale bones. Perhaps in several months nothing will be left, perhaps the vertebra of about 10 cm of diameter will survive for several years... 


About 7 centimeters in diameter, a "bone" of a basking shark after 6 months. Organic compounds dissolved except for the rests of the cartilaginous bases of the ribs.

Thiovulum sulfur bacteria, the fastest moving bacteria worldwide, are building a floating mucus sheath around the rests of cartilage.




Dr. Stefanie Grünke, Prof. Dr. Antje Boetius (Habitat Group, Max Planck Institute for Marine Microbiology, Bremen): Morphology und phylogeny of big sulfide bacteria


Thanks to local supporters:

Special thanks to Carlo Diatto of the TALAS dive centre who called our attention to the dead basking sharks and to Isabell and Jürg from Marelino Sub for their logistic support with our first dives. Thanks as well to our friend Daniele Fontana from the DIVING SERVICE CENTER Seccheto for his assistance with the TRIMIX dives.