Turtles

Sea Turtles

Evolution

1. Testudines order, all species except leatherback in Cheloniidae family.
2. Species distinguishable by prefrontal scales on the head, the number and shape of scutes on the carapace, and the type of inframarginal scutes on the plastron.
   • Leatherback is only one that does not have a hard shell
     • Only living species in genus Dermochelys
       • Bears a mosaic of bony plates beneath its leathery skin. Lack of bony carapace. Instead of scutes, has thick leathery skin with embedded miniscule osteoderms. Unique among reptiles that their scales lack beta keratin.
       • Largest, as long as 7 feet and over 1,000 pounds at maturity. They weigh 1.6 ox when freshly hatched.
     • Countershading (Thayer’s Law) – turtle’s underside is lightly colored, dorsal surface is dark grey and black. Pattern of animal coloration is a form of camouflage. Reduce the ease of detection of predators and prey by counterbalancing effects of self-shadowing, when light falls on an object and makes it appear solid, acting as visual cue which makes the object easier to detect. Evolutionary theories of countershading include self-shadow concealment which results in improved background matching when viewed from below. Countershading is observed in a wide range of marine animals other than sea turtles, like the grey reef shark.

Behavior and Ecology

Habitat

1. Fairly shallow waters inside reefs, bays, and inlets
2. Attracted to abundance of marine grass and algae
3. Nesting requires open beaches with minimal disturbance

Life Cycle

1. Nesting season varies, occurs nocturnally at 2,3,4 year intervals
2. May lay as many as 9 clutches in a nesting season
   • Clutches range from 75-200 eggs
   • Incubation ranges from 45-75 days
   • Temperature affects incubation range and sex of hatchlings
3. Strong nesting fidelity – green sea turtles
4. 3 types of Life Cycles
   • Entirely neritic
     • All stages of life from juvenile to adult occur near the shore
     • Only Australian flatback turtles
   • Neritic and oceanic
     • Hatchlingand transitional stages occur near shore
     • Early juvenile stage occurs in the open ocean
     • Return near the shore for late juvenile period and adult stage
     • Loggerhead Turtles, green sea turtles, and hawksbill
   • Entirely oceanic
     • Spend entire lifetime after hatching in open ocean
     • Except when leaving the shore after hatching and returning to share for nesting
     • Leatherback Turtles

Diet

1. Hatchlings eat a variety of plants and animals
2. Adults feed almost exclusively on sea-grasses and marine algae
3. Leatherback sea turtles get their nutrition from jellyfish

Relationships with Humans

1. Leatherback – Endangered
2. Loggerhead – threatened
3. Olive Ridley - endangered in Mexico, threatened everywhere else
4. Kemp’s Ridley – Endangered
5. Hawksbill – endangered
6. Green – endangered in FL and Mexico, threatened everywhere else

Importance in Ecosystems

1. Maintaining healthy seagrass beds and coral reefs
   • Increase productivity and nutrient content of seagrass bladeswhen grazing
   • Decreasing supply of nitrogen
   • Hawksbills especially play a key role in managing the diversity of coral reefs by limiting the growth of sponges
2. Balancing marine food webs
   • Carry barnacles, algae, and epibionts which provide food for shrimp and fish
     • Some fish species eat only epibionts from turtles
3. Facilitating nutrient cycling
   • Nutrient recycling from shelled marine life by speeding up disintegration
   • Affect aeration, compaction, and nutrient distribution of the sediment

Threats

1. Desired for flesh and shell
2. Fishing methods
   • Bycatch
   • Long-lining
   • Shrimp trawling
3. Oil spills and marine debris
   • Fibropapillomatosis – tumor causing disease that can inhibit the turtle’s ability to swim, eat, and potentially cause other dangerous health problems
     • Linked to environmentally disturbed ocean habitats
     • Heavy pollution and high human population density
4. Beach Development – decreases nesting beach availability
   • Turtles are habitual when it comes to nesting so removing their nesting locations is detrimental to reproduction
   • Lighting – discourages females from nesting on developed beaches
   • Erosion and armoring – these have affected the available space for nesting
   • Use of turtle nesting habitat for leisure – discourages females from using that area for a nest – beach driving, furniture on beaches
5. Climate change
   • Changes in sea level lead to less beach area for nesting – nest crowding
   • Nesting has started to move north due to temperature changes
   • Currently protected areas may not overlap with the changing location of nests
6. Predators
   • Nests – raccoons, ants, and crabs
   • Hatchlings – birds, crabs
   • Adults – occasional shark attacks

Conservation Efforts

1. Hard to monitor the effectiveness of conservation efforts because only nests are being observed – no idea of whole population status due to wide range and limited ability to track populations aside from nesting
2. US Endangered Species Act – prohibits hunting of sea turtles and reduces incidental losses from shrimp trawling and development
3. Turtle Excluder Devices – a grid of bars with an opening at either end of the net, catches larger animals and ejects them through the opening while still catching the smaller animals ie: shrimp