62 SEPTEMBER 2016 • WORLD AQUACULTURE • WWW.WAS.ORG help recycle nutrients in oligotrophic tropical waters where reefs typically are found. Zooxanthellae need light for photosynthesis and survival. Water clarity, which affects light penetration and intensity, is critical for corals as well as coralline algae. Therefore, a minimum water clarity (light intensity) is needed. The amount of surface light reaching a given depth can be determined from the equation IZ = I0e-kz, where I 0 is surface light intensity; IZ is the light intensity at depth z (in m); e is the natural logarithm; and k is the extinction coefficient. The extinction coefficient is related to light wavelength and the level of suspended particulate matter. In clear coastal waters, k is about 0.15, while in turbid coastal waters it is around 0.46. In highly turbid waters of many harbors and estuaries, values of k may be as high as 1.5 (Clark and Denton 1962). An extinction coefficient (or attenuation coefficient), Kd, can be estimated from Secchi disk depth measurements using the equation Kd = 1.7/ Secchi disk depth (in meters). A live rock culture study was conducted by Hillsboro Community College at five locations in Florida coastal waters (Falls et al. 2003b). Using the light transmittance data reported for the five culture sites, calculated Kd values ranged from 0.096 to 1.05. The overall average Kd value was 0.36. Looe Key Reef is located in the Looe Key National Marine Sanctuary (LKNMS) just off the coast of the Florida Keys. The reef and sanctuary are close to the latitude of the marine quarry under consideration. Most of LKNMS lies in shallow water 0-7 m deep (Lidz et al. 1985). Removing outliers from Kd data collected at Looe Key Reef from 1995-2014 (Briceno 2015), the average (n=56) Kd was 0.116 ± 0.053 (± SD). Approximately 1.21 ha of quarry bottom lies within the 0-7 m depth range of Looe Key Reef. The reef Kd value of 0.116 represents an approximate Secchi disk depth of 14.7 m. Local SCUBA divers report good visibility to an estimated depth of 1012 m in the quarry. Quarry water appears to be sufficiently clear to allow adequate light penetration for live rock/coral survival and growth. While light is critical for living reefs, water movement is equally important. Beyond wave action and strong currents created by storms, there is a continuous movement of water over coral reefs. Many of the organisms that colonize reefs are sessile. A constant flow of water is needed to distribute food and nutrients, enable oxygen and carbon dioxide exchange for respiration and photosynthesis, and facilitate reproduction and dispersal of larvae. Ocean surface current speeds can be estimated as a percentage of the wind speed 10 m above the water. For wind speeds from 5 to 30 m/sec, total surface current speed would be 3.1 percent to 3.4 percent of wind speed (Weber 1983). Based on 36 years of data, the annual average prevailing wind speeds for Miami and Key West, Florida are 4.0 and 4.9 m/sec (NCDC 1998), respectively. Looe Key Reef is only a few miles from shore. It is reasonable to assume that the average prevailing wind speed at Looe Key Reef is within this range. Estimated total ocean surface current velocity for those wind speeds would be between 12.4 to 16.6 cm/sec. Water current velocities were recorded at a Looe Key Reef moored monitoring station from 2005-2010 (Gramer 2015). The current had an average velocity of 20.5 ± 14.4 (± SD) cm/sec in water with an average depth of 23.1 ± 0.9 (± SD) m. It is reasonable to assume that a live-rock reef in a quarry must have continuous water flow over its surface. A current of 12.4 to 20.5 cm/sec would be a reasonable target velocity for live rock and coral culture in a large closed system. Research in this area could be instructive. Solar-powered airlift technology using regenerative blowers represents a viable method for water circulation Construction As with environmental requirements, there is limited information about commercial live rock culture sites regarding substrate size, type, shape, quantity, structure and its placement. The Hillsboro Community College live-rock research project placed substrate pieces of unspecified size in circular piles on the sea bottom in Florida coastal waters (Falls et al. 2003a, 2003b). These piles were 1.5-15.2 m in diameter and 0.9-1.5 m high. Substrate piles were placed at depths of 2-15 m. Various types of limestone and artificial substrate were used. Commercial live rock culture businesses have used 45.5 to 272.7 t of limestone/substrate to create individual reef sites in Florida’s public offshore waters (Falls et al. 2003a). Circular piles would not be an efficient use of horizontal space. Long rectangular ridges, triangular in cross section, would provide more surface area for live rock growth. The size, spacing, lengthwise orientation (north-south vs. east-west), and triangular cross-section shape (Fig. 2) of ridges will affect the amount of substrate surface receiving light and the duration of light exposure. Basically the quarry is a large closed system. A 4.86-ha surface area with an average depth 9.1 m would hold 444,200 m3 of water. The estimated bottom area suitable for live rock/reef culture in the quarry is 1.2 ha. Assuming limestone density is 2,300 kg/m3 and the open spaces within the ridges of limestone riprap account for 25 percent of ridge volume, it should be FIGURE 2. Conceptual diagrams of triangular cross-section shapes for substrate ridges placed in north-south (A, isosceles triangle) and east-West (B, right triangle) directional orientations.
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