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Conservation and Ecology of Marine Reptiles MARE 490 Dr. Turner Summer 2011

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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”.

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Presentation Transcript
slide1

Conservation and Ecology of Marine Reptiles

MARE 490

Dr. Turner

Summer 2011

slide2

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”

slide3

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

slide4

Ecological Roles Important?

1. Ecosystem function

2. Understanding of environmental effects

3. Meaningful goals of conservation & management

slide5

Ecological Roles Important?

1. Ecosystem function

What has been lost – consumers

Fishing down marine foodwebs

Historic Overfishing/Recent collapse

slide6

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

slide7

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

slide8

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

slide9

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

slide10

Case Studies

Ecological role of sea turtles as consumers

Caribbean Green – herbivore (seagrass)

Caribbean Hawksbill – carnivore (sponges)

slide11

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

slide12

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

slide13

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

slide14

Seagrass Communities

Thalassia testudinum - Turtle grass

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

Low grazer effects – few/no herbivorous consumers

slide15

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

slide16

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

slide17

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

slide18

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

slide19

Office Space

Hawksbills can effect space competition among sponges and Scleractinian corals

Sponges often superior competitor

Also competition among sponge species

slide20

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

slide21

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