Transcript Dr. Julius Hibbert

Conservation and
Ecology of Marine
Reptiles
MARE 490
Dr. Turner
Summer 2011
Turtles in Marine Ecosystems
Sea turtle populations severely declined
Many substantially harvested before
European contact with Caribbean
Difficult to determine past roles due to :
“Shifting Baseline Syndrome”
Shifting Baseline Syndrome
“You have an absolutely unique genetic condition known as
"Homer Simpson" syndrome.” Dr. Julius Hibbert
Use of inappropriate baselines to
assess population change
Usually based upon “recent levels” or
levels present at “British Invasion”
Example – hawksbills heavily taken for
shells long before they were recorded
Ecological Roles Important?
1. Ecosystem function
2. Understanding of environmental effects
3. Meaningful goals of conservation &
management
Ecological Roles Important?
1. Ecosystem function
What has been lost – consumers
Fishing down marine foodwebs
Historic Overfishing/Recent collapse
Ecological Roles Important?
2. Understanding of Environmental Effects
Past or present environmental changes
effect populations of sea turtles
Temperature – hatchlings
timing of nesting
Currents – migrations, 1° production
Habitat loss – nesting beaches,
foraging areas
Ecological Roles Important?
3. Meaningful goals of conservation &
management
From – single-species management
To – Ecosystem-based fishery
management
Lack of information – how many sea
turtles required for a population to be
ecologically important
Return of the Chelonii
"Oh Jar Jar, everyone hates you but me.“ – Comic Book Guy
Difficult to conceive large numbers of sea
turtles in past oceans
Estimates: 15-30 fold decrease in last 300500 years
Would have had very significant
effects/impacts upon marine ecosystems
Significant Effects
Consumers – crustaceans, jellyfish,
seagrass, seaweed
Prey – fish, sharks, birds, whales
Competitors - fish
Hosts (parasites)
Substrates (epibionts) – barnicles, algae
Nutrient transporters – connectivity
Habitat modifiers - seagrass
Case Studies
Ecological role of sea turtles as consumers
Caribbean Green – herbivore (seagrass)
Caribbean Hawksbill – carnivore (sponges)
Caribbean Green Turtle
1492-1734 Cayman Islands not inhabited
by people but turtles exploited by visitors
1688-1730 – 13,000 turtles/yr
1790 economically extinct
1830 – econ extinct off Cuba
1890 – Miskito Cays
1901 – urged rearing program
How high were pre-exploitation numbers?
Past records say 33-39 million
Preexploitation Populations
Typically regulated by food limitations
Carrying capacity (K) would be a maximum
estimate of population size
Could use seagrass beds (Thalassia) to
determine preexploitation carrying capacity
Green only significant sea grass consumer
since Dugongid extinct in Pleistocene
Survey Says!
Based upon estimates of intake and
productivity – 660 million green turtles
Dependent upon grazing variability
probably ranged from 33-660 million
Current estimates represent 3-7% of
preexploitation levels
Seagrass Communities
Thalassia testudinum - Turtle grass
Typically long (30cm) and covered with
epiphytes/bionts
Low grazer effects – few/no herbivorous
consumers
Grazer Effects
Reduced epibionts
Moderate disturbance – “Intermediate
disturbance hypothesis”
Reduced sediment deposition – more
aquatic habitat
Deposition could significantly change
habitat structure
Mass mortality in 1980’s
Caribbean Hawksbill Turtle
Preexploitation/expoitation records not as
well known
Estimated current population ≈ 27,000
Can use a similar model of food limitations
Use sponges (Chondrilla) to determine
preexploitation carrying capacity
Spongeworthy
Estimates of abundance, energy content,
& assimilation efficiency
Used intermediate models between green
(herbivore) & loggerhead (carnivore)
Sponge wet mass shows carrying capacity
for more than recorded decline
Survey Says!
Documented decline in last 100 yrs –
75-98%
Estimated preexploitation levels at 540,000
conservative estimate – 95% decline
Levels high enough to have significant
effect upon structuring of coral reef
systems
Office Space
Hawksbills can effect space competition
among sponges and Scleractinian corals
Sponges often superior competitor
Also competition among sponge species
Caribbean Situation
Why extensive coral populations in
Caribbean as compared with sponges in
postexploitation hawksbill ecosystems?
Shift in other species – redundancy in web
Can mask the effect of species removal
Fishing effects on spongivorous fish
species now becoming depleted
Conclusions
1. All species of sea turtle once extremely
abundant millions to tens of millions
2. Past populations consumed large
quantities of prey
3. Virtual ecological extinction of sea
turtles have resulted in significant changes
to structure & function of marine
ecosystems