marine ecology coral reefs

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CORALS Coral reefs: wave-resistant structures notable for their great species richness and topographic complexity Great Barrier Reef – 1,950 km long, northeastern Australia worlds corals divided into Atlantic and Indo-Pacific biogeographical provinces; probably different in the mid-Miocene

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Indo-Pacific different from Atlantic in: 1) higher diversity 2) atolls and rings of island capping submarine volcanoes (rare in Atlantic) 3) extensive development of rich coral population on intertidal flats - poor intertidal development in Atlantic province 4) difference in dominance of species

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Formal definition of Coral Reef: Compacted and cemented assemblages of skeletons and skeletal sediment of sedentary organisms living in warm waters with strong illumination

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Physiographic Features: reef-building corals - hermatypic corals combined with coralline algae (Order Scleractinia) zooxanthellae - endosymbiotic algae 25ºN and 25ºS latitudes, 23-25ºC (Florida Keys - 18ºC) Astrangia danae (not reef-building) in Long Island Sound - temps as low as 5ºC

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After temperature, light is the next important limiting factor Derived from dinoflagellates, zooxanthellae live within the gastrodermal tissues and are essential for rapid calcification Reef-building diminishes below 25m and is rare below 75m (Wells, 1957; Goreau, 1959) Montastrea and Agaricia can exist; calcification can be cut in half on a cloudy day

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Salinity: Hermatypic - require high salinity However, hypersaline conditions diminish growth Persian Gulf reefs develop in salinities greater than 40 ppt Turbidity: High rain runoff – Fiji, north Jamaica and Venezuela results in high particle loading – inhibits coral growth Lower coral species richness Corals do show differential adaptation for turbidity

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Platygyra and Acropora palmata produce large amounts of mucous when sediment is high Mucous can remove particles

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Wave Energy: Acropora palmata, Caribbean - live in reef crest zones, must withstand shock Coral can establish damaged structures within a few years from storms Hurricanes remove large coral heads (Sammarco, 1971)

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Reef Types and Depth Zonation: 2 types: 1) Atolls - horseshoe or ring-shaped arrays of islands, volcanic origin 2) Coastal - border coasts of islands or continents - Great Barrier , Australia to Eilat, Israel - Stoddant, 1969 - reef structure complexity

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ATOLLS: mainly Pacific, a few in Indian Ocean Darwin - Subsidence Theory - confirmed by reef capping – 1400 m at Enewetak Atoll dates back to Eocene (40-60 mya) windward side of reef - Acropora, Pocillopora, Millepora, Heliopora (see fig.)

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COASTAL REEFS: Parallel shorelines - see fig. 1) back-reef 4) staghorn 2) reef crest 5) break in slope (55-65 m) 3)buttress zone Indo-Pacific - share similar feature with that of the Caribbean - Acropora - wave swept areas

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Order of decreasing exposure: 1) Algal ridge 2) Pocillopora 3) Acropora 4) Faviid - Musiid 5) Porites

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Reef Topography - Accretion and Erosion At low sea level - erosional terrain may have controlled reef growth Although during massive erosion, reef accretion has also occurred during post-glacial rises in sea level. Curves of reef growth developed from C-14 dating of coral skeletons in both Atlantic and Pacific show strong concordance with sea level rises

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CORAL REEFS Mutualisms - mutualistic interactions among spp. are a major determining force in reef community structure Pocillopora harbors - an assemblage of symbionts - crabs, shrimp, fishes protect coral; also protect against “crown of thorns” sea star - Acanthaster plani other species - cleaning stations

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Interspecific competition: Lang 1971 - How can solitary corals maintain some space on reefs in the presence of the rapidly growing Acroporids: Acropora spp. Scolymia spp. - New Caledonia - within 12 hrs. mesenterial filaments had completely digested competitior

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The most aggressive corals tend to be solitary small corals and occupy minor parts of the reefs (Lang 1972) Exception: weakly aggressive and slow growing corals such as Porites and Siderastera tend to be abundant; may be due to high larval recruitment

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3 General Mechanisms of Competition: 1) Interspecific digestion 2) Direct overgrowth 3) Shading effects East Pacific Panama reefs (low diversity) dominated by Pocilliopora spp.

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Large number of coral predators: fishes - Arothron snails - Jenneria Pagurid crabs Acanthaster - Triton - Charonia tritonis is predator of Acanthaster

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Acanthaster Problem: 1960’s in Pacific - Australia, Guam Devastation of corals soon followed by recolonization of algae Origin of outbursts? Higeh densities occur at 1 per 50 m2 Blasting of channels and passes during WWII with no increase in population Triton – possible removal?

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In some cases, you can find higher #’s of coral species with more Acanthaster (Panama, Porter, 1972) However, Glynn also observed that Acanthaster selectively grazed on non-branchy species over the dominant Pocillopora Anti-predatory devices - very elaborate on reefs (Bakus, 1981) - 73% of sponges, coelenterates, echinoderms and ascidians were toxic

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Transition Element Vanadium – 1000 ppm in the tunicate Phallosia similar concentration of Arsenic found in Tridacna Also, Saponins - Triterpene glycosides Gorgonian (Plexaura) have prostaglandin, fish cannot eat it – only fireworms (Hermodice) and some gastropods “The Flamingo tongue” (Cyphoma) have resistance to prostaglandin

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Productivity: Coral reefs are islands of high production in an open sea of very low primary productivity (Odum & Odum, 1955) Very few phytoplanktivores are present on reefs Coral reef primary productivity: 1500g C m-2yr-1 upstream/downstream--2changes 3500g  all values exceed open ocean productivity 2900g

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Pacific - El Nino events - can have drastic effects warm, nutrient-poor waters to shallow coastal waters in east Pacific El Nino causes “bleaching” (also when water column is clean and stable --UV from ozone holes) (Gleason) reefs replaced by filamentous algae corals affected by diseases

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Black-Band Disease: cyanobacterium Phormidium corallyticum separates coral tissue from underlying CaCO3 skeleton coral species differ in susceptibility bleaching and Black-Band Disease more common in Atlantic corals Florida Keys - both conditions prevail (Lapointe)

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Bioerosion: Numerous species of animals and plants destroy the skeletal output of reef accretion Urchins and grazing fishes bite epibionts and remove coral pieces Also, endolithic - boring into substratum (bivalves, sipunculids, polychaetes Sponges - Clionidae - found at point of breakage

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Biology of Scleractinian Corals: secrete skeleton of CaCO3 (aragonite) some corals are solitary up to 25-30cm in diameter polyp - tentacles, gastrovascular cavities, nematocysts many spp. are sequential hermaphrodites - internal fertilization planula larvae (which develop in the gastrovascular cavity) are ejected through the mouth

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Asexual budding also allows colony to grow planula may be in water column as long as 2 days Hermatypic - high rates of calcification and #’s of zooxanthellae in gastroderm Ahermatypic - Other organisms with high calcification rates - giant clams Hippopus and Tridacna

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Growth: Acropora - as much as 10cm yr-1; massive hemispherical colonies Montastrea annularis - 0.25-0.70 cm yr -1 Montastrea has different forms - in shallow H2O (10m), the spp. grow massive - hemispherical colonies with the growth vector upward platelike growth is favored in deeper H2O (30m) favors light capture and avoids rolling when base is bioeroded

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Corals have fewer zooxanthellae in deeper water The most simple technique is to measure increments of growth relative to spike on coral head; also, growth bands - cut cross- sections Measurement of radioisotope Ca-45 and C-14 permits short-term studies of calcification (<1hr.) Ca-45 - estimates 20 mm yr-1 for Porites in Pacific (Goreau, 1959)

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Nutrition - Massive Debate: Zooxanthellae - taken from one host may not be beneficial to others Symbiosis - food source source of O2 aid in lipogenesis facilitate excretory process through absorption of CO2, aid in calcification

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Food Source: primarily microcarnivores (Young, 1930-31) - C-14 fixed by zooxanthellae found widely throughout tissues (Trench, 1974); photosynthate polyp diameter and position correlate with tentacle length S = surface area of live tissue V = value of shell + tissue S/V = good indicator of light-capturing ability

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S/V and polyp diam. inversely correlated - thus, corals with shape well-adapted to zooxanthellae capture have large polyps As S/V increases in branching, more light is intercepted - results in a multilayered morphology, as in Acropora palmata allows S to be 3x surface area of bottom substrate S/V and polyp diameter are hyperbolically inversely correlated; thus, corals with a shape well-adapted for zooxanthellae capture have large polyps (Montastrea)

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DOM also an important source of food C-14 glucose taken up by Fungia perhaps through mesentarial filaments

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Lipogenesis: Pocillopora elevates lipid synthesis 300% in the light relative to dark zooxanthellae very important! Zooxanthellae convert acetate to lipids polyunsaturated fatty acids less common in corals may indicate lipogenesis by animal instead of zooxanthellae

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Excretion: P and N reduced with zooxanthellae present Calcification: zooxanthellae play major role; cloudy day = calcification reduced inhibition of enzyme carbonic anhydrase decreases calcification