Coral Reefs 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

Coral Reefs Structure Coral abundance & diversity decrease with depth 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?)

Coral Reefs Structure Fig. 15-12

Coral Reefs Types Fringing Fig. 15-10 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

Coral Reefs Types 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

Coral Reefs Types 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

Coral Reefs Types Atolls How do atolls form? Why do they occur in rings?

Fig. 15-11

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? Trophic Structure Nutrient cycling Within corals, tight relationship between polyps and zooxanthellae

Coral Reef Ecology Trophic Structure 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

Coral Reef Ecology Trophic Structure Nitrogen fixation Food webs 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 Food webs Base formed by corals and algae (esp. turf algae) Complex feeding interactions Diversity from extensive resource partitioning More niches  More species

Coral Reef Ecology Competition Limited resources include space and light Fast-growing corals may overgrow or shade slower-growing species

Coral Reef Ecology Competition Limited resources include space and light 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

Coral Reef Ecology Competition Limited resources include space and light Soft corals may release toxins that harm hard corals Ecological role filled by sponges on Caribbean reefs (fewer species of corals than in Pacific)

Coral Reef Ecology 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

Coral Reef Ecology 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

Coral Reef Ecology Mutualism Numerous mutualistic interactions in reef community Ex: Corals & zooxanthellae Ex: Giant clams & zooxanthellae Ex: Anemones & anemone fishes, crabs, shrimps

Fig. 9-1

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

Annelida 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

Annelida Polychaeta Larva = Trochophore Diverse lifestyles 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 Haliotis asinina Wikipedia Pomatoceros lamarckii Fig. 9-10

Annelida Polychaeta Larva = Trochophore Diverse lifestyles 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 niwa.co.nz Fig. 9-23

Nematoda Free living and parasitic forms Cosmopolitan/Ubiquitous tolweb.org 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