Bonnethead Sharks Digest Seagrass Organic Matter at 50% Efficiency, Study Finds
Laboratory trials confirm the bonnethead shark assimilates plant nutrients, identifying the first known omnivorous shark species.
Bonnethead sharks (Sphyrna tiburo) can digest and assimilate nutrients from seagrass, according to an experimental study published in the journal Proceedings of the Royal Society B Biological Sciences. Researchers evaluated captive specimens to determine whether the consumption of aquatic vegetation—which can account for up to 62.1% of their gut content mass in coastal habitats—translates into metabolic nutrient uptake doi.org
Proceedings of the Royal Society B Biological Sciencesdoi.orgOpen source ↗.
Isotopic Tracking and Digestibility
To verify digestion, investigators fed captive sharks an experimental diet consisting of 90% seagrass enriched with carbon-13 (^13C) and 10% squid over controlled trials. Compound-specific stable isotope analysis revealed that the sharks successfully assimilated carbon from the plant material into their tissues, yielding a mean δ^13C value of 13.6 ± 6.77‰ across all individuals and analyzed amino acid types. Further digestive assays established that the animals processed seagrass organic matter with a digestibility efficiency of 50 ± 2%.
Hindgut Enzymatic Activity
Biochemical evaluations demonstrated that the gastrointestinal tract of Sphyrna tiburo possesses specialized digestive mechanisms to degrade fibrous material. The authors detected specific cellulose-component-degrading enzyme activities directly in the sharks' hindguts. These enzymatic pathways confirm that plant breakdown is not accidental but an active biochemical process, officially classifying the bonnethead shark as an omnivorous elasmobranch with direct energetic implications for coastal seagrass meadows.
