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

Conservation and Ecology of Marine Reptiles

MARE 494Dr. Turner

Summer 2007

Foraging Ecology & NutritionRole of sea turtles in marine ecosystems

Understanding of quantitative aspects of:diet selectiondigestive processingnutrition

Coordinate population structure & food web analysis

Biomass Pyramids:Transfer of energy

Food chain efficiency (gross ecological efficiency)

Energy to next trophic levelEnergy received from lower trophic level

~2% of light E-> organic substance (autotrophs)~80-95% lost at each transfer (trophic level)

=

“Whoa, slow down there maestro. There's a New Mexico?” – C. Montgomery Burns

500,000units of solar E

10,000 units

1,000 units100 units

10 units

1 unit of humanE converted to

human mass

Ecosystem Energy Flow

≈ 10% transfer

≈ 2% transfer

1) Not eaten (evades or dies) 2) Inefficient conversion

E = P + R + W

E!

E = ingested energyP = secondary productionR = respirationW = waste

Loss due to incomplete transfer among trophic levels

Where did the E go?Why is transfer efficiency so low?

Assimilation efficiency: the percentage of what is initially consumed that becomes incorporated into the consumer

E = P + R + W“Quit your Jibba Jabba fools!”– Mr. T

Assimilation efficiency (A) = (P + R)P = Secondary Production = growth, fat storage, birthR = Respiration = energy lost through respiration

First name Mr, middle name period, last name E

“As a kid, I got three meals a day. Oatmeal, miss-a-meal and no meal”– Mr. T

Gonna' teach this sucka a lesson!

Therefore…assimilation is opposite of excretion (waste)

E = A + W

Assimilation efficiency affected by:1) Food quality2) Amount of food3) Age of consumer

Energy available to the consumer is 1° a function of assimilation

efficiency

Foraging EcologyTremendous gaps in knowledge

Foraging habitat typically separate from nesting & juvenile habitats

How do we determine diet in protected species?

Feces – pelletsStomach lavageBiochemical techniques

Stable isotopesFatty acids

Foraging EcologySome sea turtles have a crop (Pacific Green)

sac-like structure between esophagus & stomach

Allow for collection of relatively undigested prey

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

How Do We Track Diet?

Alternative approaches sought to overcome the limitations of past studies

Stable Isotopes and Fatty AcidsRequire small tissue amounts

- approximately 1 gramUse extensively in other fieldsOvercome biasesLonger foraging window – weeks to months

Can be used to retrospectively determine

diet

Stable IsotopesCarbon and nitrogen generally used (sulfur recently)

- Both abundant throughout natureValues expressed as ratios of two isotopes

- 13C/12C or 15N/14N = δCan determine: primary producer (C&S) - Organic material has “isotopic signature” trophic level of feeding (N)

Stable IsotopesBased upon principle of “Fractionation”

Each time stable isotope is metabolized there is “Fractionation” (do not participate equally – bias toward lighter)

15N15N

Fractionation

-20 ‰

12C

13C 13C 13C

12C 12C

+1 ‰ +1 ‰ +1 ‰

+7 ‰ +10 ‰ +13 ‰ +16 ‰+3 ‰ +3 ‰ +3 ‰

15N

14N 14N14N

C

N

-19 ‰ -18 ‰ -17 ‰Est. Value

Est. Value

Seagrass

-10

13C…origin of organic matter

-22

-9 -21

-8 -20 Fractionation ofCarbon 1 ppt perTrophic level

Phytoplankton

15N…Trophic position of consumer Fractionation ofNitrogen 3-4 ppt Per Trophic level

6

18

15

12

9

15N

14

12

10

8

6diatoms

13C-22 -20 -18 -16

Shrimp

Crabs

Turtles

SHARKS!

What are Fatty Acids

Largest components of lipids (fat molecules)

Three fatty acids + glycerol backbone = triacylglyceride (TAG)Saturated – no double bondsMonounsaturated – one double bondPolyunsaturated – more than one double bondPUFAs – Polyunsaturated Fatty Acids

“Whoo Hoo, look at that blubber fly” – Homer Simpson

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

PUFAs

Stable Isotope & Fatty Acid Analyses

“You Are What You Eat”

=+

Prey is consumed by the

predator

Prey is incorporated into

the predator

Predator reflects “signature” of the

prey

Green Feeding EcologyJuveniles in pelagic stage – thought to be omnivorous to carnivorous

Associated with Sargassum mats?

Known to feed on jellies

Green Sea TurtlesEmpirical evidence of difference in pelagic vs. neretic feeding ecology?

Seaborn et al. 2005

RS1 – smallerRS3 – larger

Green Sea TurtlesEnter neretic habitat and shift to herbivorous diet 20-25 cm (Atl) 35 (Hawaii)

Why herbivorous? Lower trophic level; higher energyNicheLow assimilation efficiency

Either seagrasses (Caribbean) or seaweeds (Hawaii)

Hawaiian Green Sea TurtlesFeed 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)

Hawaiian Green Sea TurtlesLow/no growth in several regions

Poor food quality?Assimilation efficiency?

Loggerhead Feeding EcologyJuveniles – associated with Sargassum

Current fronts – mixture of drift material; algae, detritus, insects, crustaceans

Rely upon jellies

Loggerhead Sea TurtlesAdults – feed in benthos

Primarily sea pens & crustaceans

Hawksbill Sea TurtlesJuveniles – again with the Sargassum

Carnivorous pelagic life history

Recruit to neretic habitat 20-25cm; 35cmsimilar to greens

Hawksbill Sea TurtlesAdults – >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

Kemp’s RidleyJuveniles – Sargassum, Yes Sargassum

Recruits/adults – primarily crabsalso molluscs, fish, shrimp

Thought to scavenge shrimp trawling bycatch*

* not thought to include dead-turtle bycatch

Olive RidleyJuveniles – Sarg..No, really? Are you sure?

Not known

Recruits/adults – primarily salps & fish - also molluscs & crustaceansLittle known

FlatbackJuveniles – planktonic (larvae) & benthic (corals, molluscs, bryozoans)

Recruits/adults – jellyfish & soft-bodied invertebrates (sea pens & soft corals)

Leather Back KotterMost pelagic of sea turtles

Foraging patterns dependent upon distribution of prey

jellies, ctenophores, salpsaccumulate along convergent zones

Feeding not size dependent – jelliesnot ontogenetic feeding shift

Leather Back KotterAlso known to feed on squid

Interact with long-line fisheries using squid as bait