derived from theoretical 

 winds blow from the E to NE 



where d is the depth in meters. The equations predict the midday irradiance at 

 various depths on clear, sunny days as a percentage of the surface irradiance. 

 These expressions for I were modified to take into account the slope, s, of the 

 substrate on which the coral was growing, using a relationship also developed from 

 regression analysis: 



F = exp[(4.61 - 0.02 s)/100] 

 The light score, L, for each coral was further modified by the exposure, E, of the 

 coral (a measure of the amount of shading by overarching branches of neighboring 

 corals and other reef features described above): 



L ■ I F [1 - (E/6)]. 

 Estimates of water movement 



A relative water movement score for each coral was 

 calculations. In the belt of the NE trade winds, the 

 88% of the time with a maximum velocity of 35 km/hr (U.S. Weather Bureau, 1962). 

 According to the wave forecasting curves of Bretschneider (1966), winds of this 

 direction and magnitude for 8 hours would generate waves with a period, T, of 5.9 

 sec, and a significant wave height, H, of 159 cm on the north coast of Jamaica. 

 Empirical observations of wave height (Reiswig, 1 971 :114; U.S. Weather Bureau, 1959) 

 fall in the same range as the Dredictions. Under the maximum trade wind conditions 

 specified, the fore reef (sites 4-7) would be under the influence of the surface 

 conditions given above. On the leeward side of the reef crest (sites 1-3), the 

 maximum fetch is 1 km, limiting wave conditions to H = 61 cm, T = 2.5 sec 

 according to the wave prediction curves. 



The effect of surface waves diminishes with increasing depth, d, below the 

 surface, in such a manner that the major axis, A, of the ellipse traced out by a 

 particle as the wave passes over is approximated by the following equation, 

 modified from Eagleson and Dean (1966): 



A = H exp[(-47T2d)/(gT 2 )], 

 where g is the universal gravitational constant. Simplifying all the constants, 

 this reduces to: 



A = H exp[(-4.062 d)/T2]. 

 The wave movement score for each colony was then defined as: 



W = A/T, 

 to give an arbitrary, but reproducible 

 measure of the average expected wave- 

 induced water movement. 

 Measurement of colony shape 



Although an elaborate multivariate 

 analysis of various aspects of colony 

 morphology can be done (see Brakel , 1976), 

 for the purposes of this discussion a 

 simple measure of the degree of flattening 

 of the colony will suffice. I used the 

 relative colony height, defined as the 

 average diameter of the colony in the 

 plane of the substrate divided by its 

 height measured perpendicular to the 

 substrate. For a perfectly hemispherical 

 colony the relative colony height would 

 be 0.5; for a very flat colony it could 

 1 10 20 30 be as little as 0.05. To avoid the 



DEPTH (m) allometric complications inherent in such 



a ratio of morphological measurements, it 

 was found necessary to exclude all very 

 small colonies (less than 9 cm in diameter) 



i 

 eg 



LU 



I 



> 

 Z 



o 



_i 

 o 

 o 



0.8 



0.6 



0.4 



0.2 



0.0 



Fig. 2. 

 height as 



Graph of relative colony 

 a function of depth. 



23 



