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 300-500 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