Conservation and Ecology of Marine Reptiles

MARE 490Dr. Turner

Summer 2011

Turtles in Marine EcosystemsSea 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

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

“You have an absolutely unique genetic condition known as "Homer Simpson" syndrome.” Dr. Julius Hibbert

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 – consumersFishing down marine foodwebsHistoric Overfishing/Recent collapse

Ecological Roles Important?2. Understanding of Environmental Effects

Past or present environmental changes effect populations of sea turtles

Temperature – hatchlingstiming of nesting

Currents – migrations, 1° production

Habitat loss – nesting beaches, foraging areas

Ecological Roles Important?3. Meaningful goals of conservation & management

From – single-species managementTo – Ecosystem-based fishery

management

Lack of information – how many sea turtles required for a population to be ecologically important

Return of the Chelonii

Difficult to conceive large numbers of sea turtles in past oceans

Estimates: 15-30 fold decrease in last 300-500 years

Would have had very significant effects/impacts upon marine ecosystems

"Oh Jar Jar, everyone hates you but me.“ – Comic Book Guy

Significant EffectsConsumers – crustaceans, jellyfish, seagrass, seaweedPrey – fish, sharks, birds, whalesCompetitors - fishHosts (parasites)Substrates (epibionts) – barnicles, algaeNutrient transporters – connectivityHabitat modifiers - seagrass

Case StudiesEcological role of sea turtles as consumers

Caribbean Green – herbivore (seagrass)

Caribbean Hawksbill – carnivore (sponges)

Caribbean Green Turtle1492-1734 Cayman Islands not inhabited by people but turtles exploited by visitors

1688-1730 – 13,000 turtles/yr1790 economically extinct

1830 – econ extinct off Cuba1890 – Miskito Cays1901 – urged rearing program

How high were pre-exploitation numbers?Past records say 33-39 million

Preexploitation PopulationsTypically 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 CommunitiesThalassia testudinum - Turtle grass

Typically long (30cm) and covered with epiphytes/bionts

Low grazer effects – few/no herbivorous consumers

Grazer EffectsReduced epibionts

Moderate disturbance – “Intermediate disturbance hypothesis”

Reduced sediment deposition – more aquatic habitat

Deposition could significantly change habitat structureMass mortality in 1980’s

Caribbean Hawksbill TurtlePreexploitation/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

SpongeworthyEstimates 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

Documented decline in last 100 yrs – 75-98%

Estimated preexploitation levels at 540,000conservative estimate – 95% decline

Levels high enough to have significant effect upon structuring of coral reef systems

Survey Says!

Hawksbills can effect space competition among sponges and Scleractinian corals

Sponges often superior competitor

Also competition among sponge species

Office Space

Why extensive coral populations in Caribbean as compared with sponges in postexploitation hawksbill ecosystems?

Shift in other species – redundancy in webCan mask the effect of species removal

Fishing effects on spongivorous fish species now becoming depleted

Caribbean Situation

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

Conclusions