Sea Grass CommunitiesSea Grass Communities

• Vegetated, sandy substratesVegetated, sandy substrates

• Shallow, clear waterShallow, clear water

• Tropical and subtropical habitatsTropical and subtropical habitats

• Food webs often include large Food webs often include large grazersgrazers– turtlesturtles– dugongs or manateesdugongs or manatees

• Coastal locations increase exposure Coastal locations increase exposure to impacts from terrestrial land useto impacts from terrestrial land use

Shark Bay, AustraliaShark Bay, Australia

• Western AustraliaWestern Australia

• IsolatedIsolated

• World Heritage AreaWorld Heritage Area

• Rare example of an “intact” seagrass Rare example of an “intact” seagrass ecosystemecosystem

Shark Bay overview: beds and Shark Bay overview: beds and channelschannels

Diverse algaeDiverse algae

Anemone in seagrassAnemone in seagrass

Mega GrazersMega Grazers

MesograzersMesograzers

Top PredatorTop Predator

Tiger Shark

Predator effectsPredator effects

What regulates sea grass?What regulates sea grass?

Contrast a Seagrass system near Contrast a Seagrass system near peoplepeople

• e.g., southern Floridae.g., southern Florida

• Near extinction of Near extinction of – manateesmanatees– large sharkslarge sharks– sea turtlessea turtles

• Addition of Addition of – coastal developmentcoastal development– altered hydrologyaltered hydrology– increased nutrient inputincreased nutrient input

Problems in Florida Bay seagrassProblems in Florida Bay seagrass

Changes in seagrass bedsChanges in seagrass beds

Complexity in habitats: e.g., Big Pine Complexity in habitats: e.g., Big Pine KeyKey

Complexity in distributions of Complexity in distributions of organismsorganisms

Heterogeneous communitiesHeterogeneous communities

Changes in Changes in local local developmentdevelopment

Regional Patterns: Sampling Regional Patterns: Sampling LevelsLevels

Fresh water & nutrient inputs Fresh water & nutrient inputs increase chlorophyll concentrations increase chlorophyll concentrations

in waterin water

P or N nutrient limitation variesP or N nutrient limitation varies

Dry season patterns of chlorophyllDry season patterns of chlorophyll

Wet season patterns of chlorophyllWet season patterns of chlorophyll

Larry Brand 2000 Larry Brand 2000 http://www.reefrelief.org/main.html: http://www.reefrelief.org/main.html:

• An Evaluation of the Scientific Basis for An Evaluation of the Scientific Basis for "Restoring" Florida Bay by Increasing "Restoring" Florida Bay by Increasing Freshwater Runoff from the EvergladesFreshwater Runoff from the Everglades• ““Taken together, these data suggest Taken together, these data suggest

that nutrients from Everglades-that nutrients from Everglades-agriculture runoff are being transported agriculture runoff are being transported to not just Florida Bay, but also the to not just Florida Bay, but also the Florida Keys and coral reefs, and Florida Keys and coral reefs, and contributing to their eutrophication.”contributing to their eutrophication.”