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Reef Dynamics

Spur and Groove Dynamics

Spur and groove reefs are a common feature of windward shores of islands, likely due to the continued effects of erosion caused by swell and trade wind waves (Roberts et al. 1992). The topography of these structures consists of parallel linear spur (ridges) of active coral growth separated by grooves (depressions) of accumulated sediment and coral debris. Spur and grooves are highly variable in size, ranging from 8 to 65 m in width and up to 10 m in height that can be found at depths between sea level and 45 m. The physical force of wave and current energy controls the morphology of these formations as erosive processes along the side of the spurs form the grooves. Spurs and grooves act as effective breakwaters and dissipate wave energy and current intensity (Roberts et al. 1992). The dissipative processes produce high surge and over-the-reef flows that force sediment from the reef surface. Reef degradation and subsequently structural losses in coral coverage have shown to be affected by a widening of the grooves and reduction of spurs (Lewis 2002). The following footage shows a spur and groove system with noticeable surge flow along the sedimentation in the grooves.

Credits
Cinematography: Dr. Stuart Sandin
Edited by: Neilan Kuntz
Written by: Neilan Kuntz
Location: Palmyra Island, Line Islands, Central Pacific (2004)

Lewis, J.B. (2002) Evidence from aerial photography of structural loss of coral reefs at Barbados, West Indies. Coral Reefs 21: 49-56

Roberts, H.H., P.A., Wilson, A., Lugo-Fernandez (1992) Biologic and geologic responses to physical processes: examples from modern reef systems of the Caribbean-Atlantic. Continental Shelf Research 12: 809-834



Parrotfish

Parrotfish are important herbivorous reef fish that can reduce significantly the algal abundance and biomass on coral reefs (Carpenter 1986). By biting with tough, specialized fused teeth, parrotfish substantially erode reef substrata while grazing on algae often producing large amounts of sediments (i.e., white, coral sand) on reefs. For example, Frydl & Stearn (1978) found that an individual Caribbean parrotfish (Scarus iserti) produced nearly 0.5 kg CaCO3 m-2 yr-1. Large communities of parrotfish have shown erosion rates as high as 9 kg CaCO3 m-2 yr-1 (Cloud, 1959). The following footage shows a parrotfish grazing on algae and then releasing the excavated coral as fine sediment from its gills.




Credits
Cinematography: Dr. Stuart Sandin
Edited by: Neilan Kuntz
Written by: Neilan Kuntz
Location: Bonaire Island, Dutch Territory (2001)

Carpenter, R.C. (1986) Partitioning herbivory and its effects on coral reef algal communities. Ecological Monograph 56: 345-363.

Cloud, P.E., Jr. (1959) Geology of Saipan, Mariana Islands, Part 4. Submarine topography and shoal-water ecology. US Geological Survey Professional Paper 280-K: 361-445.

Frydl, P., G.W. Stearn (1978) Rate of bioerosion by parrotfish in Barbados reef environments. Journal of Sediment Petrology 48: 1149-1157.



Mucus Production


Hermatypic or reef-building corals acquire a large proportion of their energy from their zooxanthellae, the endosymbiotic microalgae that reside within their endodermal tissue layer. However, up to half of the carbon translocated from the zooxanthellae to the coral host tissues is converted into mucus, which is then is exuded by the coral host (Davies 1984). Corals produce mucus in their ectodermal goblet cells or mucocytes which is then excreted on to the poly surface. A recent study by Wild et al. (2004) showed that coral mucus plays a critical role in the cycling of energy and nutrients within the reefs system. The endosymbiotes harvest solar energy and producing sugars through photosynthesis. This energy is then passed on to the rest of the reef community as the released mucus containing carbohydrate polymers, proteins, and lipids. (Meikle et al. 1988). More than half of the released mucus is soluble and immediately dissolves in the seawater providing an energy source for planktonic bacteria (review by Wilde et al. 2004). The less soluble mucus fraction accumulates in the water column, trapping organic matter transporting the energy and nutrients to the sediments where it is degraded by benthic fauna and bacteria. Increased mucus production and excretion is a recognized first response by the coral animal to mechanical and physical stress. For example, when corals are exposed to the air during extreme low tides increased mucus production and excretion helps to prevent the desiccation of the tissues (Krupp 1984). The following footage shows a Caribbean coral, Montastraea franksii, releasing large quantities of mucus.

Credits
Cinematography: Neilan Kuntz
Edited by: Neilan Kuntz Written by: Dr. Olga Pantos
Location: Bocas del Toro, Panama (2004)

Davies, P. S. (1984)The role of zooxanthellae in the nutritional energy requirements of Pocillopora eydouxi. Coral Reefs 2: 181-186.

Krupp, D. A. (1984) Mucus production by corals exposed during an extreme low tide. Pacific Science 38:1-11.
Meikle P., G. N., Richards, D., Yellowlees (1988) Structural investigations on the mucus from six species of coral. Marine Biology 99, pp 187-193.

Wild, C., M., Huettel, A., Klueter, S. G., Kremb, M. Y., Rasheed, B. B. Jorgenson (2004) Coral mucus functions as an energy carrier and particle trap in the reef ecosystem. Nature 428: 66-70.



Calcareous Algae

Calcareous algae are important producers of calcium carbonate and organic matter in both tropical and subtropical marine environment (Millman 1980). Calcareous green algae, such as members of the genus Halimeda, are one of the key players in the production of reef substrate by laying precipitated calcium carbonate, i.e. limestone. For example, Halimeda spp. were found to be the primary contributor to the carbonate budget in a Tahitian reef system (Payri 1988). Growth rates suggest that Halimeda spp. can renew their biomass approximately once every month during their growing season (Wefer 1980). The calcareous sand is deposited as a result of the natural die-off of the algae leaving the skeletal remains and the consumption by some herbivores such as parrotfish. The high rate of productivity from calcareous algae is critical in the maintenance and balance of a healthy reef from bio-erosion processes.

Credits
Cinematography: Dr. Stuart Sandin
Edited by: Neilan Kuntz
Written by: Dr. Olga Pantos
Location: Palmyra Island, Line Islands, Central Pacific (2004)

Milliman JD. (1974) Marine Carbonates. Springer, Berlin Heidelberg New York, p 375.

Payri, CE (1988) Halimeda contribution to organic and inorganic production in a Tahitian reef system. Coral Reefs 6:251-262.

Wefer G (1980) Carbonate production by algae Halimeda, Penicillus and Padina. Nature 285:323-324.