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Tropical CommunitiesTropical Communities

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Background

• Occupy less than 0.2% of planet, yet…• Have upwards of 5% of all species• Use 50% of CaCO3 and with it, CO2 to

build reefs; around 700 billion kg/year• Very productive areas in a desert, extremely

diverse

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Worldwide distributions4

Main Players• Hermatypic Corals- with zooxanthellae; these are

the reef building corals– Cnidaria, class Anthozoa, order Scleractinia

• Calcareous Algae- provide most of the “cement”that holds reefs together; also large producer of CaCO3 in their own right– Reds and Greens

• Others: Fish, inverts, fleshy algaes

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Coralline Algae

Halimeda sp.Produces most

of the sand in reef areas

Others cement the coral reefs together

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Types of Reefs

Chuck does it again-1953- 1,283 m- hit

volcanic rock~60 myo

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Major Physical Factors

1. Temperature- Limited to 20 C –coral or zooxanthellae?

2. Depth- Must be <70 m, most <25m

3. Light- Need adequate illumination for photosynthesis

4. Salinity- Need narrow range 32-35 ppt, absent in FW areas

5. Sedimentation- Decease light, cover coral

6. Wave action- Often in high energy areas, bring in O2and food, remove sediment

7. Emergence- Upper bound is air interface, no higher than low tide, can only handle a few hours

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Physical Factors10

Low tide exposure

11 Which is NOT a major factor for coral health and growth

A. Amount of SunlightB. Clarity of the waterC. Adequate food in the planktonD. SedimentationE. Proper temperature

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Types of Coral

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Day vs. Night

Contracted/relaxed

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Figure 14.02

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Anatomy of a polyp16

• Corals are Farmers

• Plankton can only account for 5-10% of total food requirements

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ZooxanthellaeAre nitrogen limited“Host Factor”

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Species Interactions• Competition

– Interspecific battles between corals for the sun

– Coral vs. Algae- mediated by herbivores– Coral vs. Cryptofauna

• Predation– Predators of coral- fish, sea stars,

mollusks, crabs, etc…• Grazing

– Short algal turf eaten by fish and urchins– Remove urchins = 10x increase in algae =

Coral kill

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• Over fishing on reefs removes herbivorous fish (and others)

• Diadema increase in number and control the algae

• But if you have die offs of the Diadema…algae takes overand corals die

Jamaica- Hurricane in 1980…still not recovered

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Figure 14.26

21 Fish can influence coral in many ways

• Predators• Herbivores that control the algae and other

inverts• Fertilizers

– Fish feed in one area, seek refuge in another and poop all day / night long

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Reef Fish

• Huge diversity• Large amount of habitat heterogeneity

– Within coral, overhangs, caves, sand, etc…• Day/ night differences in species

assemblages• Still not enough to account for diversity of

fish observed…might it be related to recruitment?

Why are there so many fish?

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Bioerosion• Cryptofauna destroys coral skeletons

– Sponges, echinoderms, mollusks, others.• Coral build 206 tons/ year; Bioerosion =

163 tons/year

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Threats to Coral Reefs• Storms, El Nino, industrialization• Coral Bleaching

– El Nino- water temps +2 to 4 C- some reefs >90% dead

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Palau26

Marine Lakes

• Land-locked marine ecosystems

• Greatly simplified flora and fauna

• H2S- Hydrogen Sulfide layer

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Core Points- Reefs

• What are the importance of reefs?• Where are they found and why?• What living things define them?• What physical factors influence them?• How are they formed?• What sorts of ecological interactions are

important for their health?

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Mangroves vs. Mangal

• Sheltered areas, no waves, high sediment, mud (anoxic)

Physiological ConvergenceSubtle physiological adjustments regulate responses to salinity, bright tropical sun, variable and often low nutrient availability, flooding, soil anoxia, and tidal action.

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Adaptations

• Ultrafiltration process, salt glands in leaves, cell expansion, and increased leaf succulence, thick cuticle, and differences in xylem anatomy

• Mangroves need fresh water and must maintain tissue water potential below the osmotic potential of the very salty substrate.Water-Use efficiency enables transpiration, withdrawing water slowly from the soil and slowing the buildup of salt around the roots

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Mangrove Lifecycle32

Aerial Roots• Support and Gas exchange in anoxic

sediments- shallow roots and Pneumatophores

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What is it like in the understory?What is it like in the understory?

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Mangrove Distribution36

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Mangroves and Costal Protection

39Mangroves and

Aquaculture

Honduras 40

Core Points- Mangroves

• What are mangrove communities?• Where are they found?• What special adaptations do the plants

have?• What are some of the ecological

interrelations in the mangal?• What are some human impacts on the

mangal?