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Conservation and Ecology of Marine Reptiles MARE 494 Dr. Turner Summer 2007

Conservation and Ecology of Marine Reptiles MARE 494 Dr. Turner Summer 2007. Foraging Ecology & Nutrition. Role of sea turtles in marine ecosystems Understanding of quantitative aspects of: diet selection digestive processing nutrition

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Conservation and Ecology of Marine Reptiles MARE 494 Dr. Turner Summer 2007

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  1. Conservation and Ecology of Marine Reptiles MARE 494 Dr. Turner Summer 2007

  2. Foraging Ecology & Nutrition Role of sea turtles in marine ecosystems Understanding of quantitative aspects of: diet selection digestive processing nutrition Coordinate population structure & food web analysis

  3. Biomass Pyramids: Transfer of energy “Whoa, slow down there maestro. There's a New Mexico?” – C. Montgomery Burns Food chain efficiency (gross ecological efficiency) Energy to next trophic level Energy received from lower trophic level = ~2% of light E-> organic substance (autotrophs) ~80-95% lost at each transfer (trophic level)

  4. Ecosystem Energy Flow 500,000 units of solar E ≈ 2% transfer 1 unit of human E converted to human mass ≈ 10% transfer 10,000 units 10 units 1,000 units 100 units

  5. E! Where did the E go?Why is transfer efficiency so low? Loss due to incomplete transfer among trophic levels 1) Not eaten (evades or dies) 2) Inefficient conversion E= P + R + W E= ingested energy P = secondary production R = respiration W = waste

  6. First name Mr, middle name period, last name E “Quit your Jibba Jabba fools!”– Mr. T E= P + R + W Assimilation efficiency (A)= (P + R) P = Secondary Production = growth, fat storage, birth R = Respiration = energy lost through respiration Assimilation efficiency:the percentage of what is initially consumed that becomes incorporated into the consumer

  7. Gonna' teach this sucka a lesson! “As a kid, I got three meals a day. Oatmeal, miss-a-meal and no meal”– Mr. T Assimilation efficiency affected by: 1)Food quality 2)Amount of food 3)Age of consumer Therefore…assimilation is opposite of excretion (waste) E = A + W Energy available to the consumer is 1° a function of assimilation efficiency

  8. Foraging Ecology Tremendous gaps in knowledge Foraging habitat typically separate from nesting & juvenile habitats How do we determine diet in protected species? Feces – pellets Stomach lavage Biochemical techniques Stable isotopes Fatty acids

  9. Foraging Ecology Some sea turtles have a crop (Pacific Green) sac-like structure between esophagus & stomach Allow for collection of relatively undigested prey

  10. How Do We Track Diet? In past studies, foraging ecology measured with - Direct observation - Stomach contents - Scat analysis Each have inherent difficulties/biases - often biased by large, hard components - underestimates small, soft prey Alternative approaches sought to overcome the limitations of past studies

  11. Stable Isotopes and Fatty Acids Require small tissue amounts - approximately 1 gram Use extensively in other fields Overcome biases Longer foraging window – weeks to months Can be used to retrospectively determine diet

  12. Stable Isotopes Carbon and nitrogen generally used (sulfur recently) - Both abundant throughout nature Values expressed as ratios of two isotopes - 13C/12C or 15N/14N = δ Can determine: primary producer (C&S) - Organic material has “isotopic signature” trophic level of feeding (N)

  13. Stable Isotopes Based upon principle of “Fractionation” Each time stable isotope is metabolized there is “Fractionation” (do not participate equally – bias toward lighter)

  14. Fractionation 12C 12C 12C C 13C 13C 13C -20 ‰ -19 ‰ -18 ‰ -17 ‰ Est. Value +1 ‰ +1 ‰ +1 ‰ 14N 14N 14N N 15N 15N 15N +10 ‰ +7 ‰ +13 ‰ +16 ‰ Est. Value +3 ‰ +3 ‰ +3 ‰

  15. 13C…origin of organic matter -8 -20 Fractionation of Carbon 1 ppt per Trophic level -9 -21 -10 -22 Phytoplankton Seagrass

  16. 15N…Trophic position of consumer Fractionation of Nitrogen 3-4 ppt Per Trophic level 18 SHARKS! 14 12 10 8 6 15 Turtles 12 Crabs 15N Shrimp 9 diatoms 6 -22 -20 -18 -16 13C

  17. What are Fatty Acids “Whoo Hoo, look at that blubber fly” – Homer Simpson Largest components of lipids (fat molecules) Three fatty acids + glycerol backbone = triacylglyceride (TAG) Saturated – no double bonds Monounsaturated – one double bond Polyunsaturated – more than one double bond PUFAs – Polyunsaturated Fatty Acids

  18. PUFAs Prevalent in most marine organisms Highly conserved and abundant Cannot be synthesized de novo in consumers Essential for life processes Must be obtained exclusively from dietary sources Represent natural dietary tracers in marine organisms

  19. + = Prey is consumed by the predator Prey is incorporated into the predator Predator reflects “signature” of the prey Stable Isotope & Fatty Acid Analyses “You Are What You Eat”

  20. Movie Green Feeding Ecology Juveniles in pelagic stage – thought to be omnivorous to carnivorous Associated with Sargassum mats? Known to feed on jellies

  21. Green Sea Turtles Empirical evidence of difference in pelagic vs. neretic feeding ecology? RS1 – smaller RS3 – larger Seaborn et al. 2005

  22. Green Sea Turtles Enter neretic habitat and shift to herbivorous diet 20-25 cm (Atl) 35 (Hawaii) Why herbivorous? Lower trophic level; higher energy Niche Low assimilation efficiency Either seagrasses (Caribbean) or seaweeds (Hawaii)

  23. Movie Hawaiian Green Sea Turtles Feed on up to 56 species of algae; typically 9 Green, red, & Brown Feed on several introduced species Minimal feeding on seagrass (Halophila) & invertebrates (jellies & sponges)

  24. Hawaiian Green Sea Turtles Low/no growth in several regions Poor food quality? Assimilation efficiency?

  25. Movie Loggerhead Feeding Ecology Juveniles – associated with Sargassum Current fronts – mixture of drift material; algae, detritus, insects, crustaceans Rely upon jellies

  26. Loggerhead Sea Turtles Adults – feed in benthos Primarily sea pens & crustaceans

  27. Hawksbill Sea Turtles Juveniles – again with the Sargassum Carnivorous pelagic life history Recruit to neretic habitat 20-25cm; 35cm similar to greens

  28. Hawksbill Sea Turtles Adults – >95% of diet urchins, crabs, jellies - rare Some soft coral feeding Sponge nutrition thought to be low but contain high number of endosymbiotic algae Produce chemical toxins

  29. Kemp’s Ridley Juveniles – Sargassum, Yes Sargassum Recruits/adults – primarily crabs also molluscs, fish, shrimp Thought to scavenge shrimp trawling bycatch* * not thought to include dead-turtle bycatch

  30. Olive Ridley Juveniles – Sarg..No, really? Are you sure? Not known Recruits/adults – primarily salps & fish - also molluscs & crustaceans Little known

  31. Flatback Juveniles – planktonic (larvae) & benthic (corals, molluscs, bryozoans) Recruits/adults – jellyfish & soft-bodied invertebrates (sea pens & soft corals)

  32. Leather Back Kotter Most pelagic of sea turtles Foraging patterns dependent upon distribution of prey jellies, ctenophores, salps accumulate along convergent zones Feeding not size dependent – jellies not ontogenetic feeding shift

  33. Leather Back Kotter Also known to feed on squid Interact with long-line fisheries using squid as bait

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