Journal
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
Volume 285, Issue 1886, Pages -Publisher
ROYAL SOC
DOI: 10.1098/rspb.2018.1583
Keywords
nutritional physiology; omnivory; digestive biochemistry; stable isotopes
Categories
Funding
- National Geographic Society Young Explorers Grant
- UCI OCEANS Graduate Research Fellowship
- UCI Newkirk Center Graduate Research Fellowship
- Grover C. Stephens Memorial Award
- Sigma XI GIAR
- Society for Integrative and Comparative Biology GIAR
- American Society of Ichthyologists and Herpetologists
- US Department of Education
- National Science Foundation Graduate Research Fellowship Program
- UCI Graduate Division
- University of California
- Irvine laboratory start-up funds
- Florida International University
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What an animal consumes and what an animal digests and assimilates for energetic demands are not always synonymous. Sharks, uniformly accepted as carnivores, have guts that are presumed to be well suited for a high-protein diet. However, the bonnethead shark (Sphyrna tiburo), which is abundant in critical seagrass habitats, has been previously shown to consume copious amounts of seagrass (up to 62.1% of gut content mass), although it is unknown if they can digest and assimilate seagrass nutrients. To determine if bonnetheads digest seagrass nutrients, captive sharks were fed a C-13-labelled seagrass diet. Digestibility analyses, digestive enzyme assays and stable isotope analyses were used to determine the bonnethead shark's capacity for digesting and assimilating seagrass material. Compound-specific stable isotope analysis showed that sharks assimilated seagrass carbon (13.6 +/- 6.77 parts per thousand delta C-13 mean +/- s.d. for all sharks and all amino acid types analysed) with 50 +/- 2% digestibility of seagrass organic matter. Additionally, cellulose-component-degrading enzyme activities were detected in shark hindguts. We show that a coastal shark is digesting seagrass with at least moderate efficiency, which has ecological implications due to the stabilizing role of omnivory and nutrient transport within fragile seagrass ecosystems.
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