I. Coral Reefs

C. Components & Dynamics• Corals important components of reefs

• Other organisms also contribute

• Coralline red algae cement debris together• More important in Pacific than Atlantic• Part of bioerosion process

Fig. 15-8

I. Coral Reefs

D. Structure

Fig. 15-12• Coral abundance & diversity decrease with depth• Competition for light affects growth forms• Upper slope - doming corals• Mid slope - branching corals• Lower slope - plate-like corals (Why?)

I. Coral Reefs

D. Structure

Fig. 15-12

I. Coral Reefs

E. Types1. Fringing

• Simplest, most common type of reef• Occur near shore throughout tropics

• Form narrow band (fringe) along shoreline• Proximity to land vulnerability to sedimentation,

freshwater runoff, human influence

Fig. 15-10

I. Coral Reefs

E. Types2. Barrier

• Not always obviously distinct from fringing reefs• Often occur farther from shore (up to 100+ km)

• May be sand cays on back reef slope

Fig. 15-10

I. Coral Reefs

E. Types3. Atoll

• Most common in Indo-West Pacific• Rare in Caribbean, tropical Atlantic

• Usually far from land• Little influence from freshwater runoff,

sedimentation• Range in size from <1 to 20+ miles in diameter• Often influenced by trade winds

• Differences between windward and leeward sides• Windward: Spur-and-groove, distinct algal ridge

Fig. 15-10

I. Coral Reefs

E. Types3. Atolls

• How do atolls form?• Why do they occur in rings?

Fig. 15-11

II. Coral Reef Ecology

• Among most productive communities in ocean

• Generally occur in areas with low nutrient concentrations, low primary production

• How can coral reefs be so productive?

A. Trophic Structure1. Nutrient cycling

• Within corals, tight relationship between polyps and zooxanthellae

II. Coral Reef Ecology

A. Trophic Structure1. Nutrient cycling

• “Nutrient traps”• Other reef animals also contain symbionts and recycle

nutrients within their tissues• Sponges• Nudibranchs• Giant clams• Sea squirts

• Waste products also recycled• Some inputs still required

II. Coral Reef Ecology

A. Trophic Structure2. Nitrogen fixation

• Primarily by cyanobacteria• Some free living, some symbiotic in sponges

• Nitrogen may not limit productivity in coral reefs• Different from most other marine communities

• Nitrogen also acquired by• Absorption of dissolved organic matter (DOM)• Predation on zooplankton

3. Food webs• Base formed by corals and algae (esp. turf algae)• Complex feeding interactions• Diversity from extensive resource partitioning

• More niches More species

II. Coral Reef Ecology

B. Competition• Limited resources include space and light

1) Fast-growing corals may overgrow or shade slower-growing species

II. Coral Reef Ecology

B. Competition• Limited resources include space and light

2) More aggressive corals may attack other corals• Mesenterial filaments used to digest away tissue

from competitor/neighbor (video)• Special sweeper tentacles sting adjacent colonies• Slower growers tend to be most aggressive• Faster growers tend to be less aggressive

II. Coral Reef Ecology

B. Competition• Limited resources include space and light

3) Soft corals may release toxins that harm hard corals• Ecological role filled by sponges on Caribbean

reefs (fewer species of corals than in Pacific)

II. Coral Reef Ecology

C. Predation• Most coral predators eat portion of coral

• Ex: Butterflyfishes, parrotfishes• Doesn’t kill coral; permits regrowth• Predation may limit growth rates of certain fast-

growing species

• Other coral predators eat entire corals• Ex: Crown-of-Thorns Sea Star

• Extrudes stomach, digests coral tissue

II. Coral Reef Ecology

D. Grazing• Many fishes are herbivorous

• Ex: Surgeonfishes, parrotfishes, damselfishes

• Invertebrate grazers and microherbivores also important

• Ex: Sea urchins, gastropods, crustaceans

• Grazing controls populations of seaweeds• Could overgrow corals if not grazed by herbivores• Ex: Seaweeds protected from grazers grew much

faster than unprotected seaweeds• Removal of grazers proliferation of algae

II. Coral Reef Ecology

E. Mutualism• Numerous mutualistic interactions in reef

community• Ex: Corals & zooxanthellae• Ex: Giant clams & zooxanthellae• Ex: Anemones & anemone fishes, crabs, shrimps

Fig. 9-1

III. Annelida

• Mostly segmented worms• Body composed of repeated segments

• Gut runs through body cavity (coelom)• Coelom filled with fluid – hydrostatic skeleton• Longitudinal and radial muscles

• Efficient locomotion and burrowing

• More than 15,000 species• Cosmopolitan

III. Annelida

A. Polychaeta (class)• 10,000+ species (mostly marine)• Body segments bear pairs of parapodia

• Parapodia used for locomotion, feeding• Often tipped with setae

• Closed circulatory system**• Efficient transport of blood, gases

• Gas exchange• Small species exchange gases across body wall• Large species have gills for gas exchange

• Highly vascularized with capillaries and thin body walls

Fig. 9-21

III. Annelida

A. Polychaeta• Larva = Trochophore

• Band of cilia around body; tuft on apex• Same larval stage in Mollusca

• Diverse lifestyles• Errant vs. Sedentary• Free-living predators

• Often well-developed eyes, sense organs, jaws• Deposit feeders

• Nonselective• Selective

• Suspension feeders• Active• Passive

• Solitary• Colonial

• Reproduction Pomatoceros lamarckii

Haliotis asininaWikipedia

Fig. 9-10

III. Annelida

A. Polychaeta• Larva = Trochophore

• Band of cilia around body; tuft on apex• Same larval stage in Mollusca

• Diverse lifestyles• Errant vs. Sedentary• Errant: Free-living predators

• Often well-developed eyes and sense organs, jaws• Deposit feeders

• Nonselective• Selective

• Suspension feeders• Active• Passive

• Solitary• Colonial

• Reproduction

Fig. 9-23

niwa.co.nz

IV. Nematoda

• Free living and parasitic forms• Cosmopolitan/Ubiquitous

• Mostly in sediments (free living) or hosts (parasitic)

• Common in fine muds• Organic rich areas

• Described species: 28,000+ (>55% parasitic)• May be up to 500,000 species total!

• Extremely abundant!!• Up to hundreds of individuals per ml of sediment• 90,000 in one rotting apple (not marine)

• Hydrostatic skeleton• Longitudinal muscles only• Move by whipping back and forth

tolweb.org