The Effect of Zooxanthellae Availability on the Rates of Skeletal Growth in the Red Sea Coral Acropora Hemprichii 179
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Egyptian Journal of Aquatic Research (2013) 39, 177–183 National Institute of Oceanography and Fisheries Egyptian Journal of Aquatic Research http://ees.elsevier.com/ejar www.sciencedirect.com FULL LENGTH ARTICLE The effect of zooxanthellae availability on the rates of skeletal growth in the Red Sea coral Acropora hemprichii Montaser Aly Mahmoud Al-Hammady * National Institute of Oceanography and Fisheries, Red Sea Brach, Hurghada, Egypt Received 2 September 2013; accepted 24 October 2013 Available online 5 December 2013 KEYWORDS Abstract Zooxanthellae density affects growth rate of Acropora hemprichii at reef flat and 10 m Zooxanthellae; depth, where the correlations were significantly moderate at reef flat (r = 0.461 & P < 0.01) and Growth rates; significantly high at 10 m depth (r = 0.636 & P = 0.424). While non interactive effects were Depths; obtained at 20 and 25 m depth, where the correlations were non significant (r = 0.346 & Acropora hemprichii; P < 0.19 and r = 0.103 & P < 0.706, respectively). Either zooxanthellae density, hosted by Red Sea A. hemprichii, or growth rate was decreased with depth increase. Zooxanthellae density at reef flat (1.55 ± 0.303 · 106 cells/cm2) was twice higher than at 25 m depth (0.706 ± 0.253 · 106 cells/cm2). However, growth rate at reef flat was approximately three times higher than 25 m depth (0.013 ± 0.0024 mm/day). The maximum growth rate (0.0335 mm/day) and zooxanthellae density (1.32 · 106 cells/cm2) were recorded during summer season, and the minimum growth rate (0.01769 mm/day) and zooxanthellae density (0.931106 cells/cm2) were recorded during autumn. ª 2013 Production and hosting by Elsevier B.V. on behalf of National Institute of Oceanography and Fisheries. Introduction between corals and their zooxanthellae (Muscatine and Porter, 1977; Barnes and Crossland, 1980; Furla et al., 2000; Al-Horani The success of coral reefs, considered to be one of the most et al., 2005; Winters et al., 2009; Fitt et al., 2009; Ammar et al., biodiverse ecosystems in the world, is due in large part to 2012). Corals receive photosynthetic products (sugar and ami- obligate mutualistic symbioses involving invertebrates and no acids) in return for supplying zooxanthellae with crucial photosynthetic dinoflagellate symbionts (Dustan, 1999: Stone plant nutrients (ammonia and phosphate) from their waste et al., 1999; Obura, 2009 and Al-Hammady, 2011). Scientists metabolism (Trench, 1979; Furla et al., 2000). Muscatine have been interested in the nutritional interrelationship (1990) found that, zooxanthellae provide energy and nutrients for coral host by translocating up to 95% of their photosyn- thetic production to it. Swanson and Hoegh-Guldberg (1998) * Tel.: +20 1005308218. E-mail address: [email protected] mentioned that, zooxanthellae selectively leak amino acid, Peer review under responsibility of National Institute of Oceanography sugar, complex carbohydrates and small peptides across the and Fisheries. host–symbiont barrier. Moreover, Papina et al. (2003) postu- lated that zooxanthellae provide the coral host not only with saturated fatty acid, but also with diverse polyunsaturated fatty acid. For the scleractinian corals, whose skeletons comprise the Production and hosting by Elsevier physical structure of reefs, calcification rate is also influenced 1687-4285 ª 2013 Production and hosting by Elsevier B.V. on behalf of National Institute of Oceanography and Fisheries. http://dx.doi.org/10.1016/j.ejar.2013.10.005 178 M.A.M. Al-Hammady by the presence of Symbiodinium (Pearse and Muscatine 1971; 11 km south of Al-Qusier City (Fig. 1). Four colonies of the Barnes & Chalker 1990). One of the biggest threats to the health studied species were chosen and marked at four different of coral reefs today is the increasing frequency of bleaching of depths (Reef Flat, 10, 20, and 25 m depth). Branches from hermatypic corals (whitening of corals due to loss of either sym- each colony were tagged by a plastic string about 1.5–2.0 cm biotic algae or their pigments, or both). In severe cases corals from the tip of the branch. The linear extension was measured do not recover and subsequently die (Brown 1997; Hoegh- seasonally using vernier caliper to measure the length of the Guldberg 1999). The severity of the bleaching response differs Fig. 1. Location map of the study site tagged branch from greatly between species of corals (Marshall and Baird 2000; the plastic string to the tip of the branch. Loya et al., 2001) and even across individual colonies (Ralph et al. 2002). It also varies spatially on local and regional scales Biomass measurements (Glynn 2001). Zooxanthellae inhabiting the tissue of corals nor- mally show low rates of migration or expulsion to water col- Skirt fragments (<5 cm fragment) from three separate colo- umn (Hoegh-Guldberg and Smith, 1989a; Winters et al., nies of A. hemprichii were seasonally collected at the same 2009). Despite these low rates, population densities have been depths of the measured growth rates (reef flat, 10, 20 and reported to undergo a seasonal change (Fagoonee et al., 25 m depth). Only one terminal portion of the branch was 1999). Population densities of zooxanthellae in reef building sampled per coral colony, using a long nosed bone cutter. 6 6 À2 corals range between 0.5 · 10 and 5 · 10 cells/cm Samples were kept in the dark by wrapping them in aluminium (Drew,1972; Porter et al., 1984; Hoegh-Guldberg and Smith, foil and placed in whirl-package under water. On the deck, 1989b). The aim of this work is to study the effect of the density water was removed from the bags and immediately transferred of zooxanthellae on the growth rate of the scleractinian coral to a foam box filled with ice waiting for transportation to Acropora hemprichii from the Red Sea, at different sea depths NIOF laboratories for analysis of zooxanthellae densities. In and seasons of the year. the laboratory, a tip of approximately equal size (1–2 cm) from each replicate was taken to measure the population densities of Material and methods zooxanthellae. Tissues were striped from the skeletons with a jet of recirculated 0.45 lm membrane filtered sea water using The growth rate measurements a water pikTM (Johannes and Wiebe, 1970). The slurry pro- duced from the tissue-stripping process was homogenated in Growth rates as linear extension of A. hemprichii were mea- a blender for 30 S and the volume of homogenate was re- sured at the fringing reef of Al-Fanader site, that is located corded. The number of zooxanthellae in 10 ml aliquotes of homogenate was measured in triplicate by light microscope (X 400) using Count Rafter Cell. The total number of zooxan- thellae per coral was measured after correcting the volume of homogenate. Zooxanthellae density was calculated as a num- ber per unit surface area. Zooxanthellae number=cm2 ¼ counted cells=cell surface area  cell depth  dilution Surface area of the bare skeletons remaining after removal of tissue was measured independently using the paraffin wax technique (Stambler et al., 1991), by immersing the skeleton bar in hot wax, the mass of wax added to the skeleton bare was determined by weighing the skeleton bare before and after immersion. A relationship between change in mass and surface area was obtained by immersing known surface area cubes in the wax. Results Growth rates and zooxanthellae densities of Acropora hemprechii differed according to different depths and seasons (Table 1). For growth rate the differences between depths and seasons were highly significant (ANOVA, p < 0.01) (Table 2). Turkey’s Studentized Rang Statistical Analysis (HSD) (Table 3) indicated that, growth rate at reef flat was highly significantly different from those at 10, 10 and 25 m depth. Recorded data indicated that the mean growth rate decreased with increased depth, Acropora hemprechii grows faster at reef flat (0.0412 ± 0.034 mm/day) than at 10 m depth (0.0172 ± 0.003 mm/day). Moreover, 10 m depth Figure 1 Location map of the study site. grows still faster than at 20 m depth (0.0159 ± 0.0023 mm/ The effect of zooxanthellae availability on the rates of skeletal growth in the Red Sea coral Acropora hemprichii 179 Table 1 Seasonal mean of growth rate (mm/ day) and zooxanthellae densities (106 cells/cm2)ofAcropora hemprichii at four different Depths. Reef Flat 10 m depth 20 m depth 25 m depth Autumn G.r. X0 ± S.D. 0.023 ± 0.0013 0.0167 ± 0.00017 0.0164 ± 0.00037 0.0147 ± 0.0012 Zoox. X0 ± S.D. 1.45 ± 0.389 1.235 ± 0.793 0.525 ± 0.005 0.51 ± 0.028 Winter G.r. X0 ± S.D. 0.0203 ± 0.0004 0.0188 ± 0.00032 0.018 ± 0.0008 0.0162 ± 0.00079 Zoox. X0 ± S.D. 1.42 ± 0.309 1.31 ± 0.295 0.98 ± 0.539 0.707 ± 0.44 Spring G.r. X0 ± S.D. 0.0223 ± 0.00034 0.0202 ± 0.00021 0.0172 ± 0.00058 0.0135 ± 0.001 Zoox. X0 ± S.D. 1.56 ± 0.279 1.46 ± 0.211 0.827 ± 0.116 0.507 ± 0.061 Summer G.r. X0 ± S.D. 0.0988 ± 0.0027 0.0129 ± 0.0046 0.0123 ± 0.0012 0.0102 ± 0.00013 Zoox. X0 ± S.D. 1.79 ± 0.15 1.23 ± 0.264 1.2 ± 0.216 1.09 ± 0.095 Annual mean G.r. X0 ± S.D. 0.0412 ± 0.034 0.0172 ± 0.003 0.0159 ± 0.0023 0.013 ± 0.0024 Annual mean Zoox. X0 ± S.D. 1.55 ± 0.303 1.311 ± 0.22 0.88 ± 0.036 0.706 ± 0.253 G. r: growth rate (mm/ day), Zoox.