Effect of Temperature on the Settlement Choice and Photophysiology ...

Reference: Biol. Bull. 215: 135–142. (October 2008) © 2008 Marine Biological Laboratory

Effect of Temperature on the Settlement Choice and Photophysiology of Larvae From the Reef Coral Stylophora pistillata HOLLIE M. PUTNAM1, PETER J. EDMUNDS1, AND TUNG-YUNG FAN2,3,* 1

Department of Biology, California State University, 18111 Nordhoff Street, Northridge, California 91330-8303; 2National Museum of Marine Biology and Aquarium, 2 Houwan Road, Checheng, Pingtung 944, Taiwan, ROC; and 3Institute of Marine Biodiversity and Evolution, National Dong Hwa University, 2 Houwan Road, Checheng, Pingtung 944, Taiwan, ROC

Abstract. To better understand the consequences of climate change for scleractinian corals, Stylophora pistillata was used to test the effects of temperature on the settlement and physiology of coral larvae. Freshly released larvae were exposed to temperatures of 23 oC, 25 oC (ambient), and 29 oC at light intensities of ⬇150 ␮mol photons m⫺2 s⫺1. The effects were assessed after 12 h as settlement to various substrata (including a choice between crustose coralline algae [CCA] and limestone) and as maximum quantum yield of PSII (Fv /Fm) in the larvae versus in their parents. Regardless of temperature, 50%–73% of the larvae metamorphosed onto the plastic of the incubation trays or in a few cases were drifting in the water, and 14% settled on limestone. However, elevated temperature (29 oC) reduced the percentage of larvae swimming by 81%, and increased the percentage choosing CCA nearly 7-fold, both relative to the outcomes at 23 oC. Because temperature did not affect settlement on limestone or plastic, increased settlement on CCA reflected temperature-mediated choices by larvae that otherwise would have remained swimming. Interestingly, Fv /Fm was unaffected by temperature, but it was 4% lower in the larvae than in the parents. These results are important because they show that temperature can affect the settlement of coral larvae and because they reveal photophysiological differences between life stages that might provide insights into the events associated with larval development.

Introduction High diversity and relatively high productivity are classic characteristics of tropical coral reefs (Hatcher, 1997; Paulay, 1997), yet these features are being eroded by declining coral cover and impaired ecosystem functionality (Bellwood et al., 2004). Although coral cover can be replaced through the growth of coral fragments (Highsmith, 1982), the only means of restoring both the cover and the genetic diversity of coral populations is through sexual recruitment (Baums et al., 2006). Because sexual reproduction and recruitment are relatively well described for corals (Richmond, 1997), a concise picture can be constructed of the events associated with population dynamics under conditions that have prevailed during the recent decades of investigation. However, it is difficult to know whether similar events are occurring on contemporary reefs, because environmental conditions are changing rapidly in this ecosystem (Buddemeier et al., 2004), and little is known regarding the effects of these factors on the early life stages of corals. Global climate is changing in various ways (Buddemeier et al., 2004; IPCC, 2007), but for scleractinians the most important trends are rising levels of CO2 and increasing temperature (Buddemeier et al., 2004). There is a long history of studying the effects of temperature on corals (e.g., Mayer, 1917), as there is for many marine ectotherms (Hochachka and Somero, 2002). Most recent studies focus on the effects of high temperature on adult corals, with the goal of understanding the causes of thermal bleaching (Dove and Hoegh-Guldberg, 2006). For the early life stages of marine organisms, the effects of physical environmental

Received 20 June 2007; accepted 2 April 2008. * To whom correspondence should be addressed. E-mail: tyfan@ nmmba.gov.tw 135

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conditions, such as high temperature, can have greater biological significance than for adults (Thorson, 1950; Gosselin and Qian, 1997). For instance, sublethal increases in temperature accelerate the development of pelagic larvae, thereby curtailing their longevity, altering the capacity for dispersal, and reducing the exposure to the risk of mortality (O’Connor et al., 2007). For corals, few studies have addressed the effects of temperature on early life stages, but the available data suggest that planula development, mortality, and substratum selection are sensitive to rising temperature (Jokiel and Guinther, 1978; Coles, 1985; Edmunds et al., 2001, 2005; Nozawa and Harrison, 2002, 2007; Bassim and Sammarco, 2003), as are juvenile colonies (Edmunds, 2002, 2005, 2006). Given the critical roles played by pelagic larvae in dispersal and in population recovery (Underwood and Keough, 2001), as well as the lifelong consequences resulting from acute ability for substratum discrimination (Raimondi and Morse, 2000), thermal effects on this early life stage can have important impacts. The objective of this study was to explore the effects of temperature on brooded coral larvae immediately after their release from the parent. We used Stylophora pistillata (Esper, 1797) from Nanwan Bay (southern Taiwan) to test the effects of temperature on larval substratum selection and the photophysiology of adults versus larvae. Use of this regionally ubiquitous species (Veron, 2000) strengthened our ability to generalize results to other locations. In addition, by working in southern Taiwan, we were able to exploit local knowledge about the reproductive biology of scleractinian corals (Fan et al., 2006), including the predictable timing of larval release for S. pistillata (Fan et al., 2002). Physically, however, the reefs of Nanwan Bay are unusual, because a large annual range in monthly mean seawater temperature (22.5 to 29.0 °C [Dai et al., 1992]) is augmented by daily downward anomalies as high as ⬇9 oC and driven by tidal-induced upwelling (Lee et al., 1999). Thus, corals from Nanwan Bay have potentially been exposed to a history of thermal variation that may increase their tolerance for thermal perturbations (Brown et al., 2000; Castillo and Helmuth, 2005); consequently, the response of their larvae to elevated temperature might provide insight into the potential of scleractinians to tolerate thermal stress. Materials and Methods Larvae of Stylophora pistillata were obtained from eight colonies collected on 27 February 2007 from 5–7 m depth in Nanwan Bay (21°56⬘29⬙N, 120°44⬘70⬙E). The colonies were returned to the National Museum of Marine Biology and Aquarium (NMMBA), and placed in individual tanks (1 colony per tank) supplied with filtered seawater that overflowed into a cup fitted with plankton mesh to retain larvae. Because S. pistillata releases larvae in loose synchrony with

the lunar phase—although release occurs continuously (Fan et al., 2002)—this study was completed close to the full moon on 3 March 2007, with the expectation that the greatest larval release would occur in the days following this date (Fan et al., 2002). Larvae were harvested shortly after overnight release, which peaked near dawn (⬇0630 h; Fan et al. 2006), and immediately counted and allocated to treatments. To test the effects of temperature on settlement, the larvae were pooled among parent colonies; to compare the photophysiology of adults and larvae, they were kept separate by parent colony. Temperature treatments were established in closed-circuit tanks (⬇40 l) located indoors and controlled for temperature and light. The tanks were filled with sand-filtered (50 ␮m) seawater, which was replaced on average at a rate of 30% day⫺1, and their temperature was regulated at mean values of 22.6 oC, 25.4 oC (ambient), or 28.6 oC (all with SEs ⱕ 0.1 o C, n ⫽ 49 –51), with mean light levels of 139 –165 ␮mol photons m⫺2 s⫺1 (all with SEs ⱕ 2.1 ␮mol photons m⫺2 s⫺1, n ⫽ 4 days). The experimental design consisted of three temperatures established in duplicate, with the goal of analyzing the results with a nested ANOVA using temperature as a fixed factor and the duplicate tanks as a nested factor. This nested design ultimately was utilized for the settlement analyses, but limited numbers of larvae precluded its use in the photophysiological experiments. The settlement experiments were completed in the wells (35-mm diameter) of polystyrene tissue culture trays that were floated in the treatment tanks. The wells were filled with 13 ml of sand-filtered seawater, with half of the seawater changed daily at noon, and 2–3 wells in each tray were used, depending on the number of larvae obtained. Preliminary experiments showed that the temperature in the wells (n ⫽ 42 measurements) differed ⱕ0.9 oC from that of the tanks (n ⫽ 149 measurements). In addition to seawater, the wells were stocked with 10 actively swimming larvae, a piece of calcareous rubble covered with crustose coralline algae (CCA), and a piece of weathered coral gravel (free of coral tissue and CCA). The larvae were thus provided with a choice between CCA and limestone. The CCA rubble was chipped from a coral skeleton encrusted with living Neogoniolithon spp., and the pieces were sized uniformly at 9 ⫻ 7 mm (mean length ⫻ mean width, with SEs ⱕ 0.4 mm, n ⫽ 21) with ⬇50% coverage of CCA (as determined by eye). The coral gravel was soaked in seawater prior to use, and the grains were selected to be similar in size to those of the CCA to test the settlement preference of larvae by presenting them with “targets” of similar dimensions. The grains of coral gravel were uniformly sized at 11 ⫻ 5 mm (mean length ⫻ mean width with SEs ⱕ 0.5 mm, n ⫽ 21). No morphological or behavioral abnormalities were observed in the larvae after they were added to the temperature treatments. Settlement studies were completed on 2, 3, and 4 March

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2007, using larvae pooled among parent colonies, and the experiments began between 0800 and 0900 h. The larvae were left for ⬇12 h in each treatment, and then visually inspected, using a dissecting microscope, for condition. Following incubation, larvae were categorized into one of four conditions: (i) swimming, (ii) metamorphosed and attached to CCA, (iii) metamorphosed and attached to limestone, and (iv) metamorphosed and either attached to the plastic of the tray or drifting in the water. Metamorphosed larvae were identified by their orally-aborally compressed, polyp-like appearance that included signs of mesenteries. Larvae were scored as metamorphosed to limestone if they occurred on the coral gravel or the bare limestone surface exposed when the CCA rubble was fractured. The investigation of the comparative effects of temperature on the photophysiology of adults and larvae was completed on 4, 5, and 6 March 2007. Three colonies were used, and for each of the 3 days, larvae and a branch (⬇3 cm long) from each of the parent colonies were incubated for 12 h at 22.6 oC, 25.4 oC (ambient), and 28.6 oC, using the same tanks used for the settlement experiments. Because there were too few larvae to stock duplicate tanks at each temperature (described in the nested design above), an orthogonal design was employed to test the effects of temperature (fixed factor 1), life stage (fixed factor 2), and genotype (i.e., colony, random factor 1), after pooling the results among days. In this design, single branches and groups of 10 larvae were statistical replicates, and two replicates per life stage were used for each temperature. The branches were removed from the colonies and immediately suspended upright with nylon monofilament in the seawater within each tank, and the groups of 10 larvae were incubated in the wells of tissue culture trays containing 13 ml of filtered seawater alone (with half changed at midday), that were floated in the same tanks. Photophysiology was assessed using pulse amplitude modulated (PAM) fluorometry, which measures a change in dark-adapted maximal quantum yield [Fv /Fm ⫽ (Fm-Fo)/ Fm,] of PS II (Genty et al., 1989). This measurement enables the user to detect damage to the photosynthetic apparatus of the Symbiodinium (Fitt et al. 2001; Jones et al. 2003). The photophysiological experiments began between 0800 and 0900 h, and ended 12 h later when the maximum quantum yield was measured using a diving PAM (Walz, GmbH) fitted with an 8-mm diameter fiber-optic cable. Dark adaptation was accomplished by taking the measurements after 2⫹ h of natural darkness (i.e., after 1900 h). For branches, a single measurement of Fv /Fm was made ⬇2 cm from the branch tip, and for larvae, a single measurement was taken from 10 larvae suspended in a small volume of seawater (⬇250 ␮l) placed directly onto the tip of the fiber-optic cable. To reduce the possibility of photochemical quenching caused by the measuring light of the diving PAM, the instrument was operated with a constant intensity

of measuring light (setting “8”) in the “burst mode” for both life stages, although the gain was increased from “4” to “12” for the larvae. Initial measurements of Fo, Fm, and Fv as a function of larval density with between 2 and 20 larvae per measurement were used to test for bias caused by the small size of the larvae and the low quantities of chlorophyll. The results of the settlement experiment were expressed as the percentage of the larvae categorized in each condition, and these values were arcsine-transformed (Sokal and Rohlf, 1995) prior to all analysis. Descriptive statistics were back-transformed and reported in the text as means and 95% confidence intervals (CI). The effects of the treatment on larval condition were tested with nested ANOVA, using tanks as the nested factor and temperature as a fixed factor; post hoc analyses were completed using Fisher’s least significant difference (LSD) test. Data from the photophysiological comparison of the adults and larvae were analyzed with a three-way ANOVA using temperature and life stage as fixed factors, genotype as a random factor, and Fv /Fm as the dependent variable. For both sets of ANOVAs, when the nested factor or interaction terms were nonsignificant at ␣ ⬎ 0.25 they were pooled with the residual error, and the adjusted error term was used for significance testing (Quinn and Keough, 2003). The assumptions of normality and homoscedasticity for the ANOVAs were tested through graphical analyses of the residuals. Results The larvae from Stylophora pistillata were light brown or speckled brown in color, and typically were pear-shaped with a mean length of 1.10 ⫾ 0.07 mm and mean diameter of 0.83 ⫾ 0.05 mm (⫾ SE, n ⫽ 15). Many of the larvae were competent to settle almost immediately following release, and larvae frequently settled on the glass of the beakers while being counted within ⬇2.5 h of release. When placed into the wells of the culture trays, there was a strong tendency for the larvae to settle quickly onto the plastic of the trays, or to be drifting in the water in a metamorphosed condition. Many of the spat on the plastic were readily removed with a weak jet of water, and therefore the drifting spat probably had settled on the plastic but failed to form a strong adhesion. For those larvae that did not settle on the plastic, anecdotal observations throughout the 12-h experiments showed that the larvae swam actively in the chambers and encountered the rubble pieces multiple times before settling. At the conclusion of the 12-h experiments, a mean of between 50% (28%–73%, CI, n ⫽ 12) of the larvae at 23 oC, and 73% (59%– 86%, CI, n ⫽ 12) of the larvae at 29 oC metamorphosed and either attached to the plastic or, in a few cases (ⱕ 5.4%), were drifting in the water (Fig. 1). These percentages were not significantly affected by temperature (F2,33 ⫽ 1.744, P ⫽ 0.190). A small mean percent-

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low temperature was associated with reduced settlement on CCA. Stylophora pistillata larvae were small, but it was relatively easy to measure their chlorophyll fluorescence when the diving PAM was used at a high gain. Fluorescence values (Fo and Fm) were unstable when only 2– 4 larvae were used, but stabilized at ⱖ8 larvae, and maximum quantum yield (Fv /Fm) was unaffected by larval densities of between 8 and 20 per measurement (Fig. 2). Because the experimental determinations were completed with 10 larvae per measurement, the measurements of larval Fv /Fm were not biased by the small quantities of chlorophyll present. The maximum quantum yield for branches of S. pistillata freshly collected from the holding tanks was 0.68 ⫾ 0.04, and for their larvae it was 0.67 ⫾ 0.02 (after dark-adapting for 2 h; mean ⫾ SD, n ⫽ 2). After exposure to the treatments for 12 h, the branches appeared identical to one another and unchanged relative to freshly collected pieces (i.e., there were no signs of bleaching). However, some of the larvae showed signs of metamorphosis (i.e., they were Figure 1. Effect of 12-h exposure to temperature treatments on the percentage of Stylophora pistillata larvae that either remained as pelagic larvae, metamorphosed on crustose coralline algae (CCA), metamorphosed on limestone, and metamorphosed on the plastic of the containers or were drifting as metamorphosed larvae. The metamorphosed larvae in the water were assumed to have detached from plastic, or may have responded to a soluble inducer. Mean ⫾ SE (n ⫽ 12 trials of 10 larvae each) are shown for values derived by back-transformation from arcsine-transformed data (therefore, error bars are asymmetric). Note the break in the ordinate scale, which is used to display the percentage of the larvae metamorphosed on the plastic or metamorphosed and drifting. For each dependent variable, bars marked with dissimilar letters are significantly different from one another (Fisher’s LSD test, P ⬍ 0.05), and unmarked bars do not differ significantly among temperatures (P ⱖ 0.190).

age of the larvae (14% [6%–24%, CI, n ⫽ 3 averaged across treatments]) metamorphosed and attached to limestone; this response also was not significantly affected by temperature (F2,3 ⫽ 1.944, P ⫽ 0.161), although there was a trend for fewer to settle on limestone at warmer temperatures. In contrast, the percentage of the larvae that remained swimming or metamorphosed to CCA was affected by temperature. The number of swimming larvae declined significantly from a mean of 18% (9%–29%, CI, n ⫽ 12) at 23 oC, to 3% (0%–11%, CI, n ⫽ 12) at 29 oC (F2,33 ⫽ 3.468, P ⫽ 0.043); there was a trend for the mean percentage of the larvae metamorphosing to CCA to vary among temperatures (F2,33 ⫽ 2.487, P ⫽ 0.099): significantly fewer larvae settled on CCA at 23 oC (1% [0%–5%, CI, n ⫽ 12]) than at 25 oC (9% [1%–22%, CI, n ⫽ 12]) (Fisher’s LSD, P ⫽ 0.047) (Fig 1). Thus, although most of the larvae settled onto the plastic regardless of temperature and the number settling on limestone was statistically indistinguishable among temperatures, the elevated temperature shortened the duration of the larval phase for the rest of the larvae, and the

Figure 2. Effect of temperature on the photophysiology of branches of Stylophora pistillata and their freshly released larvae. (A) Maximum quantum yield of adults and larvae after 12-h exposure to one of three temperature treatments; Fv /Fm differed significantly between adults and larvae (P ⬍ 0.01), but no other main effects or their interactions were significant. Means ⫾ SE are based on three replicate genotypes (i.e., colonies) per bar, where each replicate was the average of duplicate determinations for each genotype/treatment/life stage, except for the larvae of two genotypes at 29 oC (where only one measurement was made). (B) Inset shows the fluorescence (Fo, Fm and Fv) versus the number of larvae in a drop of water on the fiber-optic sensor of the diving PAM. All larvae were dark-adapted for 2⫹ h prior to measurement, and fresh larvae were used for each trial. Importantly, Fv /Fm was unaffected by larval number when ⱖ8 larvae were used.

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becoming compressed), and in most trials several had formed a loose attachment to the incubation trays. Newly attached larvae were removed carefully from the plastic and placed directly on the PAM sensor together with the freeswimming larvae. After the treatments, the mean Fv /Fm for adults ranged from 0.69 ⫾ 0.01 to 0.71 ⫾ 0.01, and values for the larvae ranged from 0.66 ⫾ 0.01 to 0.67 ⫾ 0.01 (all mean ⫾ SE, n ⫽ 3 genotypes). Mean Fv /Fm values were lower for the larvae compared to the adults in all treatments (Fig. 2), and the effect of life stage was significant (F1,26 ⫽ 11.890, P ⫽ 0.002). Overall (i.e., pooled among temperatures), Fv /Fm was depressed 4% in the larvae compared to the adults. None of the other main effects, or the interactions, were significant (P ⱖ 0.295). The statistical test of life stage was accomplished using an adjusted MS error derived by pooling the MS error with the nonsignificant life stage ⫻ genotype interaction (F2,16 ⫽ 0.719, P ⫽ 0.502). Discussion The objective of this study was to determine the effects of temperature on larvae freshly released from Stylophora pistillata and exposed for 12 h to three temperatures of ecological relevance to the reefs of southern Taiwan (Dai et al., 1992). The results reveal that these larvae favor crustose corralline algae (CCA) for settlement at warmer, but not at a cooler, temperature; and moreover, photophysiologically the larvae differ slightly from their parents. Although the warm temperature had no effect on the Fv /Fm of either life stage, this outcome must be interpreted in the context of the low irradiances supplied, which would have greatly reduced the potentially negative effects of thermal stress acting on the Symbiodinium symbionts (Jones et al., 1998). Regardless of the lessened photophysiological consequences of the temperature treatments, the significant effects on settlement, as well as the difference between life stages, are biologically meaningful for at least two reasons. First, because the early survivorship of corals can be influenced by the type of CCA they settle onto (Harrington et al., 2004), temperature-mediated changes in the preference for CCA could affect post-settlement success. Second, the reduced Fv /Fm in the larvae compared to the adults corresponds to a striking contrast in developmental stages. The role of CCA as inducers for coral settlement has been known for nearly 20 years (Morse et al., 1988), and now it is clear that some CCA, such as Titanoderma and Hydrolithon, are powerful inducers (Raimondi and Morse, 2000; Harrington et al., 2004), while others, like Neogoniolithon used in the present study, have only a weak effect (Morse et al., 1988; Harrington et al., 2004). CCAs that function as inducers contain a chemical morphogen that causes coral larvae to settle and metamorphose when they contact the algae (Morse et al., 1988), which is the outcome of a series of tactical mechanisms that place the larvae close to the

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CCA (Raimondi and Morse, 2000). In several cases, coral larvae can also be induced to settle and metamorphose by microbial biofilms (Webster et al., 2004), and therefore the morphogens causing settlement are not necessarily limited to CCA. However, the chemical stimulus for settlement can function only when the larvae are metamorphically competent (sensu Hadfield et al., 2001), which for brooded coral larvae like those from S. pistillata ranges from immediately post-release (this study), to days, weeks, or months (Harrison and Wallace, 1990). For larvae from broadcast spawners, metamorphic competency is typically attained after 1– 6 days in the water column (Harrison and Wallace, 1990; Miller and Mundy, 2003; Nozawa and Harrison, 2005). These differences between life histories in time to metamorphic competency reflect the consequences of brooded development within the parental polyp, which includes larval maturation and the vertical acquisition of maternally inherited Symbiodinium (Harrison and Wallace, 1990). In the present study, 50%–73% of the larvae metamorphosed rapidly after release, and the majority of these apparently exercised little substratum discrimination before settling on the plastic of the incubation trays. It is not unusual for coral larvae to settle to surfaces that are uncommon in their natural environment (e.g., glass, polystyrene) in the laboratory (Lewis, 1974; Heyward and Negri, 1999; Bassim and Sammarco, 2003), but the brooded larvae of pocilloporid corals are particularly well known for rapid settlement and a catholic choice of settlement surfaces (Richmond, 1985, 1987; Nishikawa et al., 2003; Baird and Morse, 2004). Yet they also have the capacity for lengthy planktonic periods (Richmond, 1987) and retain the ability to discriminate CCA for the purpose of settlement (Baird and Morse, 2004). Together, these features suggest that pocilloporid larvae may not all be created equal within a single species (Isomura and Nishihira, 2001; see also Edmunds et al., 2001), with the result that members of the larval population exhibit phenotypic plasticity for settlement characteristics. At one end of this putative gradient, larvae exhibit substratum opportunism, and at the other, substratum discrimination (Baird and Morse, 2004), which would make pocilloporids in general, and S. pistillata in particular, well suited to function as early successional species (Loya, 1976; Baird and Morse, 2004). Presumably the selective value of nuanced larval settlement choices would be context specific, and for S. pistillata (as for any species) it is unknown what conditions would favor larvae practicing substratum-opportunism versus substratum-discrimination (i.e., favoring CCA). Regardless of these factors, the global distribution and high abundance of S. pistillata (Veron, 2000) demonstrates that together these settlement strategies are associated with considerable ecological success. Temperatures similar to that of ambient seawater in southern Taiwan during March (25 oC), or 4 oC warmer,

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resulted in the swimming larvae (i.e., those defined above as “substratum discriminators”) curtailing their pelagic phase and settling on CCA, while at the lower temperature (close to winter seawater temperature for the region [Dai et al., 1992]) a different trend was observed (Fig. 1). As has been recently noted as a general property of marine pelagic larvae (O’Connor et al., 2007), as well as of coral larvae (Edmunds et al., 2001), elevated temperatures accelerate development, shorten the larval phase, and thereby modify dispersal distances and losses to mortality (O’Connor et al., 2007). These trends probably contribute to the effects of temperature reported here, but for the first time we show that temperature also affects the preference of some coral larvae to settle on CCA. Our results for S. pistillata show that the preference for CCA is increased between 23 oC and 25 oC, with this change possibly being traded against a declining preference for limestone surfaces. This finding, together with the discovery that salinity also can affect the larvae of at least one broadcast-spawning coral, notably to alter the preference for substratum types (Vermeij et al., 2006), provides a strong incentive to investigate further the roles of pre-settlement events in determining the settlement patterns and distribution of reef corals. Because the CCA provided as a choice to the larvae in the present study—Neogoniolithon spp.—is not the taxon most preferred as a settlement cue by coral larvae, at least on the Great Barrier Reef (Harrington et al., 2004) and on the reefs of Moorea, French Polynesia (N. Price, University of California, Santa Barbara, pers. comm.), the temperature-dependent trend for some larvae to settle on CCA has at least two interpretations. These interpretations depend on the extent to which Neogoniolithon is a weak inducer versus a weak repellent for the settlement of S. pistillata larvae. If Neogoniolithon is simply a weak inducer of larval settlement, then elevated temperatures may accentuate the suitability of this CCA to coral larvae, perhaps by increasing the potency of the morphogen or lowering the detection threshold. Interestingly, because low temperatures deter larvae from settling to Neogoniolithon, in habitats with strong upwelling of cool water—like Nanwan Bay (Lee et al., 1999) and the Florida Keys (Leichter and Miller, 1999)— the coincidence of cool water with the release of coral larvae could deter them from settling, and therefore promote dispersal. In contrast, if Neogoniolithon serves as a weak repellent for larval settlement, in part due to epithelial shedding that could decrease spat survival (Harrington et al,. 2004), the settlement to this CCA observed here could reflect a temperature-mediated deterioration of substrate discrimination. In this interpretation, lower temperature would deter larvae from selecting less suitable surfaces (e.g., Neogoniolithon spp.), perhaps in favor of alternative CCAs that are more suitable for the survival of coral recruits. Finally, the analysis of the effects of temperature on

Fv /Fm of adults and their larvae was noteworthy, not because of the insight it provided into the effects of thermal stress based on life stage, but because it revealed an apparently innate difference between life stages for one photophysiological parameter. This effect cannot be attributed simply to the low chlorophyll content of the larvae (a potential effect we tested through the analysis of fluorescence versus number of larvae), although conceivably it could have been caused by an instrumentation bias. While such a bias could arise from photochemical quenching initiated by the measurement intensity used by the diving PAM, we minimized this possibility by employing a low measuring intensity (⬇0.03 ␮mol quanta m⫺2 s⫺1) that was constant for both life stages. Moreover, we believe that the present results are unlikely to be an artifact, because one of us recently recorded a very similar effect for larvae versus adults of Pocillopora damicornis (HM Putnam, unpubl. data) where the maximal quantum yield of the larvae was reduced ⬇50% compared to adults. Such a large reduction in Fv /Fm cannot be explained as an artifact attributed to a small amount of photochemical quenching in the larvae but not the parent colony. Therefore, we conclude tentatively that the ⬇4% reduction in Fv /Fm of the larvae versus the adult S. pistillata reflects the effect of developmental stage. There are multiple reasons why Fv /Fm could differ between these stages, but the possibility that the difference reflects the ontogeny of larval development and the initiation of a mutualistic symbiosis between the cnidarian host and the Symbiodinium dinoflagellates is particularly intriguing. If this possibility is correct, then comparisons of the physiology of adult corals and their larvae may prove a valuable means to understand the origins of the metabolic architecture that links coral hosts and their dinoflagellate symbionts. For instance, the anabolic demands of larval development might lead to a depression of Fv /Fm through nitrogen limitation, as occurs in free-living phytoplankton (Gorbunov et al., 2000), and the changes in protein profiles of coral larvae during the first few days of life (deBoer et al., 2007) might reflect the expression of functional proteins that regulate the physiology of the Symbiodinium. Acknowledgments This research was completed with support from the National Science Council of Taiwan (to PJE), and grants from the United States National Science Foundation (OCE 0417412, OISE 07-14434). PJE and HMP thank Profs. K. T. Shao (Taiwan), R. Schmitt and S. Holbrook (USA) for initiating this collaboration, and the staff and students at the National Museum of Marine Biology and Aquarium (NMMBA) who contributed greatly to all aspects of the success of this work. We are grateful to N. Price for advice that was valuable in designing the experiments, and for identifying the CCA used in our trials. Comments from two

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anonymous reviewers improved an earlier draft of this work. This is a contribution of the Moorea Coral Reef LTER Site, and is contribution number 147 of the Marine Biology Program of California State University, Northridge. Literature Cited Baird, A. H., and A. N. C. Morse. 2004. Induction of metamorphosis in larvae of the brooding corals Acropora palifera and Stylophora pistillata. Mar. Freshw. Res. 55: 469 – 472. Bassim, K. M., and P. W. Sammarco. 2003. Effects of temperature and ammonium on larval development and survivorship in a scleractinian coral (Diploria strigosa). Mar. Biol. 142: 241–252. Baums, I. B., C. B. Paris, and L. M. Che´rubin. 2006. A bio-oceanographic filter to larval dispersal in a reef-building coral. Limnol. Oceanogr. 51: 1969 –1981. Bellwood, D. R., T. P. Hughes, C. Folke, and M. Nystro¨m. 2004. Confronting the coral reef crisis. Nature 429: 827– 833. Brown, B. E., R. P. Dunne, M. S. Goodson, and A. E. Douglas. 2000. Bleaching patterns in reef corals. Nature 404: 142–143. Buddemeier, R. W., J. A. Kleypas, and R. B. Aronson. 2004. Coral Reefs and Global Climate Change: Potential Contributions of Climate Change to Stresses on Coral Reef Ecosystems. Pew Center on Global Climate Change Report. Pew Center, Arlington, VA. Castillo, K. D., and B. S. T. Helmuth. 2005. Influence of thermal history on the response of Montastraea annularis to short-term temperature exposure. Mar. Biol. 148: 261–270. Coles, S. L. 1985. The effects of elevated temperature on reef coral planula settlement as related to power plant entrainment. Antenne Museum–EPHE Moorea, French Polynesia. Proc. 5th Int. Coral Reef Symp. 4: 171–176. Dai, C. F., K. Soong, and T. Y. Fan. 1992. Sexual reproduction of corals in northern and southern Taiwan. University of Guam Press, UOG Station, Guam. Proc 7th Int. Coral Reef Symp. 1: 448 – 455. deBoer, M. L., D. A. Krupp, and V. M. Weis. 2007. Proteomic and transcriptional analyses of coral larvae newly engaged in symbiosis with dinoflagellates. Comp. Biochem. Physiol. D 2: 63–73. Dove, S. G., and O. Hoegh-Guldberg. 2006. The cell physiology of coral bleaching. Pp. 55–71 in Coral Reefs and Climate Change: Science and Management, J. T. Phinney, O. Hoegh-Guldberg, J. Kleypas, W. Skirving, and A. Strong, eds. American Geophysical Union, Washington, DC. Edmunds, P. J. 2002. Long-term dynamics of coral reefs in St. John, US Virgin Islands. Coral Reefs 21: 357–367. Edmunds, P. J. 2005. Effect of elevated temperature on aerobic respiration of coral recruits. Mar. Biol. 146: 655– 663. Edmunds, P. J. 2006. Temperature-mediated transitions between isometry and allometry in a colonial, modular invertebrate. Proc. R. Soc. Lond. B 273: 2275–2281. Edmunds, P. J., R. D. Gates, and D. F. Gleason. 2001. The biology of larvae from the reef coral Porites astreoides and their response to temperature disturbances. Mar. Biol. 139: 981–989. Edmunds, P. J., R. D. Gates, W. Leggat, O. Hoegh-Guldberg, and L. Allen-Requa. 2005. The effect of temperature on the size and population density of dinoflagellates in larvae of the reef coral Porites astreoides. Invertebr. Biol. 124: 185–193. Fan, T. Y., J. J. Li., S. X. Ie, and L. S. Fang. 2002. Lunar periodicity of larval release by pocilloporid corals in southern Taiwan. Zool. Stud. 41: 288 –294. Fan, T. Y., K. H. Lin, F. W. Kuo, K. Soong, L. L. Liu, and L. S. Fang. 2006. Diel patterns of larval release by five brooding scleractinian corals. Mar. Ecol. Prog. Ser. 321: 133–142. Fitt, W. K., B. E. Brown, M. E. Warner, and R. P. Dunne. 2001. Coral

141

bleaching: interpretation of thermal tolerance limits and thresholds in tropical corals. Coral Reefs 20: 51– 65. Genty, B., J. Briantais, and N. Baker. 1989. The relationship between the quantum yield of photosynthetic electron transport and quenching of chlorophyll fluorescence. Biochim. Biophys. Acta 990: 87–92. Gorbunov, M. Y., P. G. Falkowski, and Z. S. Kolber. 2000. Measurement of photosynthetic parameters in benthic organisms in situ using a SCUBA-based fast repetition rate fluorometer. Limnol. Oceanogr. 45: 242–245. Gosselin, L. A., and P. Y. Qian. 1997. Juvenile mortality in benthic marine invertebrates. Mar. Ecol. Prog. Ser. 146: 265–282. Hadfield, M. G., E. J. Carpizo-Ituarte, K. del Carmen, and B. T. Nedved. 2001. Metamorphic competence, a major adaptive convergence in marine invertebrate larvae. Am. Zool. 41: 1123–1131. Harrington, L., K. Fabricius, G. De’ath, and A. Negri. 2004. Recognition and selection of settlement substrata determine post-settlement survival in corals. Ecology 85: 3428 –3437. Harrison, P. L., and C. C. Wallace. 1990. Reproduction, dispersal and recruitment of scleractinian corals. Pp. 133–207 in Ecosystems of the World: Coral Reefs, Vol 25, Z. Dubinsky, ed. Elsevier, Amsterdam. Hatcher, B. G. 1997. Organic production and decomposition. Pp. 140 – 174 in Life and Death of Coral Reefs, C. Birkeland, ed. Chapman and Hall, New York. Heyward, A. J., and A. P. Negri. 1999. Natural inducers for coral larval metamorphosis. Coral Reefs 18: 273–279. Highsmith, R. C. 1982. Reproduction by fragmentation in corals. Mar. Ecol. Prog. Ser. 7: 207–226. Hochachka, P. W., and G. N. Somero. 2002. Biochemical Adaptations. Oxford University Press, Oxford. IPCC (Intergovernmental Panel on Climate Change). 2007. Climate Change 2007: The Physical Science Basis. Fourth Assessment Report of the Intergovernmental Panel on Climate Change, S. Solomon, ed. Cambridge University Press, Cambridge. Isomura, N., and M. Nishihira. 2001. Size variation of planulae and its effect on the lifetime of planulae in three pocilloporid corals. Coral Reefs 20: 309 –315. Jokiel, P. L., and E. B. Guinther. 1978. Effects of temperature on reproduction in the hermatypic coral Pocillopora damicornis. Bull. Mar. Sci. 28: 786 –789. Jones, R. J., O. Hoegh-Guldberg, A. W. D. Larkum, and U. Schreiber. 1998. Temperature-induced bleaching of corals begins with impairment of the CO2 fixation mechanism in zooxanthellae. Plant Cell Environ. 21: 1219 –1230. Jones, R. J., J. Muller, D. Haynes, and U. Schreiber. 2003. Effects of herbicides diuron and atrazine on corals of the Great Barrier Reef, Australia. Mar. Ecol. Prog. Ser. 251: 153–167. Lee, H. J., S. Y. Chao, K. L. Fan, and T. Y. Kuo. 1999. Tide-induced eddies and upwelling in a semi-enclosed basin: Nan Wan. Estuar. Coast. Shelf Sci. 49: 775–787. Leichter, J. J., and S. L. Miller. 1999. Predicting high-frequency upwelling: spatial and temporal patterns of temperature anomalies on a Florida coral reef. Cont. Shelf Res. 19: 911–928. Lewis, J. B. 1974. The settlement behaviour of planulae larvae of the hermatypic coral Favia fragum (Esper). J. Exp. Mar. Biol. Ecol. 15: 165–172. Loya, Y. 1976. The Red Sea coral Stylophora pistillata is an r strategist. Nature 259: 478 – 480. Mayer, A. G. 1917. Is death from high temperature due to the accumulation of acid in the tissues? Proc. Natl. Acad. Sci. USA 3: 626 – 627. Miller, K., and C. Mundy. 2003. Rapid settlement in broadcast spawning corals: implications for larval dispersal. Coral Reefs 22: 99 –106. Morse, D. E., N. Hooker, A. N. C. Morse, and R. A. Jensen. 1988.

142

H. M. PUTNAM ET AL.

Control of larval metamorphosis and recruitment in sympatric agariciid corals. J. Exp. Mar. Biol. Ecol. 116: 193–217. Nishikawa, A., M. Katoh, and K. Sakai. 2003. Larval settlement rates and gene flow of broadcast-spawning (Acropora tenuis) and planulabrooding (Stylophora pistillata) corals. Mar. Ecol. Prog. Ser. 256: 87–97. Nozawa, Y., and P. L. Harrison. 2002. Larval settlement patterns, dispersal potential, and the effect of temperature on settlement of larvae of the reef coral, Platygyra daedalea, from the Great Barrier Reef. Ministry of Environment: Indonesian Institute of Sciences, and International Society for Reef Studies Bali, Indonesia. Proc. 9th Int. Coral Reef Symp. 1: 409 – 416. Nozawa, Y., and P. L. Harrison. 2005. Temporal settlement patterns of larvae of the broadcast spawning reef coral Favites chinensis and the broadcast spawning and brooding reef coral Goniastrea aspera from Okinawa, Japan. Coral Reefs 24: 274 –282. Nozawa, Y., and P. L. Harrison. 2007. Effects of elevated temperature on larval settlement and post-settlement survival in scleractinian corals, Acropora solitaryensis and Favites chinensis. Mar. Biol. 152: 1181– 1185. O’Conner, M. I., J. F. Bruno, S. D. Gaines, B. S. Halpern, S. E. Lester, B. P. Kinlan, and J. M. Weiss. 2007. Temperature control of larval dispersal and the implications for marine ecology, evolution, and conservation. Proc. Natl. Acad. Sci. USA 104: 1266 –1271. Paulay, G. 1997. Diversity and distribution of reef organisms. Pp. 298 – 353 in Life and Death of Coral Reefs, C. Birkeland, ed. Chapman and Hall, New York. Quinn, G. P., and M. J. Keough. 2003. Experimental Design and Data Analysis for Biologists. Cambridge University Press, Cambridge.

Raimondi, P. T., and A. N. C. Morse. 2000. The consequences of complex larval behavior in a coral. Ecology 81: 3193–3211. Richmond, R. H. 1985. Reversible metamorphosis in coral planula larvae. Mar. Ecol. Prog. Ser. 22: 181–185. Richmond, R. H. 1987. Energetics, competency, and long-distance dispersal of planula larvae of the coral Pocillopora damicornis. Mar. Biol. 93: 527–533. Richmond, R. H. 1997. Reproduction and recruitment in corals: critical links in the persistence of reefs. Pp. 175–197 in Life and Death of Coral Reef, C. Birkeland, ed. Chapman and Hall, New York. Sokal, R. R. and F. J. Rohlf. 1995. Biometry. W. H. Freeman, New York. Thorson, G. 1950. Reproductive and larval ecology of marine bottom invertebrates. Biol. Rev. 25: 1– 45. Underwood, A. J., and M. J. Keough. 2001. Supply-side ecology: the nature and consequences of variations in recruitment of intertidal organisms. Pp. 183–200 in Marine Community Ecology, M. D. Bertness, S. D. Gaines, and M. E. Hay, eds. Sinauer Associates, Sunderland, MA. Vermeij, M. J. A., N. D. Fogarty, and M. W. Miller. 2006. Pelagic conditions affect larval behavior, survival, and settlement patterns in the Caribbean coral Montastrea faveolata. Mar. Ecol. Prog. Ser. 310: 119 –128. Veron, J. E. N. 2000. Corals of the World. Australian Institute of Marine Science, Townsville. Webster, N. S., L. D. Smith, A. J. Heyward, J. E. M. Watts, R. I. Webb, L. L. Blackall, and A. P. Negri. 2004. Metamorphosis of a scleractinian coral in response to microbial biofilms. Appl. Environ. Microbiol. 70: 1213–1221.