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

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

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

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

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

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

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

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)

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, reef structure complexity

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.)

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

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

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

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

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

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

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

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

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 m 2 Blasting of channels and passes during WWII with no increase in population Triton – possible removal?

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

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

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 -2 yr -1 upstream/downstream-- 2 changes 3500g  all values exceed open ocean productivity 2900g

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

Black-Band Disease: cyanobacterium Phormidium corallyticum separates coral tissue from underlying CaCO 3 skeleton coral species differ in susceptibility bleaching and Black-Band Disease more common in Atlantic corals Florida Keys - both conditions prevail (Lapointe)

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

Biology of Scleractinian Corals: secrete skeleton of CaCO 3 (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

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

Growth: Acropora - as much as 10cm yr -1 ; massive hemispherical colonies Montastrea annularis cm yr -1 Montastrea has different forms - in shallow H 2 O (10m), the spp. grow massive - hemispherical colonies with the growth vector upward platelike growth is favored in deeper H 2 O (30m) favors light capture and avoids rolling when base is bioeroded

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)

Nutrition - Massive Debate: Zooxanthellae - taken from one host may not be beneficial to others Symbiosis - food source source of O 2 aid in lipogenesis facilitate excretory process through absorption of CO 2, aid in calcification

Food Source: primarily microcarnivores (Young, ) - 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

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)

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

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

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