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Abstract. This study tested the bleaching response of the Pacific coral Seriatopora caliendrum to short-term exposure to high temperature and elevated partial pressure of carbon dioxide (pC[O.sub.2]). Juvenile colonies collected [...]

Early life stages of the coral Seriatopora caliendrum were used to test the hypothesis that the depression of dark respiration in coral recruits by high pC[O.sub.2] is caused by perturbed protein metabolism. First, the contribution of protein anabolism to respiratory costs under high pC[O.sub.2] was evaluated by measuring the aerobic respiration of S. caliendrum recruits with and without the protein synthesis inhibitor emetine following 1 to 4 days at 45 Pa versus 77 Pa pC[O.sub.2]. Second, protein catabolism under high pC[O.sub.2] was evaluated by measuring the flux of ammonium (N[H.sub.4.sup.+]) from juvenile colonies of S. caliendrum incubated in darkness at 47 Pa and 90 Pa pC[O.sub.2]. Two days after settlement, respiration of recruits was affected by an interaction between emetine and pC[O.sub.2], with emetine reducing respiration 63% at 45 Pa pC[O.sub.2] and 27% at 77 Pa pC[O.sub.2]. The interaction disappeared 5 days after settlement, when respiration was reduced 27% by emetine under both pC[O.sub.2] conditions. These findings suggest that protein anabolism accounted for a large proportion of metabolic costs in coral recruits and was affected by high pC[O.sub.2], with consequences detected in aerobic respiration. Juvenile S. caliendrum showed net uptake of N[H.sub.4.sup.+] at 45 Pa pC[O.sub.2] but net release of N[H.sub.4.sup.+] at 90 Pa pC[O.sub.2], indicating that protein catabolism, N[H.sub.4.sup.+] recycling, or both were affected by high pC[O.sub.2]. Together, these results are consistent with the hypothesis that high pC[O.sub.2] affects protein metabolism in corals., Introduction Ocean acidification (OA) caused by the dissolution of atmos[pH.sub.e]ric pC[O.sub.2] in seawater is a serious threat to marine life (Hoegh-Guldberg et al., 2007). Of the many taxa likely to [...]

. Juvenile colonies of massive Porites spp. were exposed to manipulated pH and bicarbonate ([HC[O.sub.3.sup.-]]) in situ to test the hypothesis that ocean acidification (OA) does not affect respiration and calcification. Incubations lasted 28 h and exposed corals to ambient temperature and light with ecologically relevant water motion. Three treatments were applied: (1) ambient conditions of pH 8.04 and 1751 µmol] [HC[O.sub.3.sup.-]] k[g.sup.-1] (Treatment 1), (2) pC[O.sub.2]-induced ocean acidification of pH 7.73 and 2011 µmol [HC[O.sub.3.sup.-]] k[g.sup.-1] (Treatment 2), and (3) pC[O.sub.2] and HC[O.sub.3.sup.-]-enriched seawater of pH 7.69 and 2730 µmol HC[O.sub.3.sup.-] k[g.sup.-1] (Treatment 3). The third treatment providing elevated [HC[O.sub.3.sup.-]] was used to test for stimulatory effects of dissolved inorganic carbon on calcification under low pH and low saturation of aragonite ([Ω.sub.arag]), but it does not reflect conditions expected to occur under C[O.sub.2]-driven OA. Calcification of juvenile massive Porites spp. was affected by treatments, with an 81% elevation in Treatment 3 versus Treatment 1, but no difference between Treatments 1 and 2; respiration and the metabolic expenditure concurrent with calcification remained unaffected. These findings indicate that juvenile massive Porites spp. are resistant to short exposures to OA in situ, and separately, that they can increase calcification at low pH and low [Ω.sub.arag] if [HC[O.sub.3.sup.-]] is elevated. Juvenile Porites spp. may therefore be limited by dissolved inorganic carbon under ambient pC[O.sub.2] conditions., Introduction Coral reefs are threatened by natural and anthropogenic factors, including global climate change and ocean acidification (OA) (Hoegh-Guldberg et al., 2007; Wilkinson, 2008). OA poses a particularly severe threat, [...]

In comparison to some corals, massive Porites spp. is physiologically resilient to environmental assaults and is becoming more abundant on coral reefs. To evaluate the extent to which thick tissues contribute to this physiological resilience, we tested the hypothesis that the Symbio-dinium in Porites lutea are phenotypically and genetically homogeneous with regard to their distribution vertically within the tissue, and in their response to temperature. Symbiodinium density, genetic identity, and photophysiol-ogy were compared between outer and inner tissues defined as adjacent layers--2 mm thick and beneath the skeleton surface. Symbiodinium densities were 5-fold greater and their cells contained less chlorophyll a in outer versus inner tissue, but ITS2 sequence identities were genetically uniform between layers. Maximum photochemical efficiency ([F.sub.v] /[F.sub.m]) in inner and outer tissue from the top and sides of the corals differed 6%-7%, with F rn greater in inner versus outer tissue on the top of colonies. On the tops of colonies, the initial slopes of the rETR versus irradiance relationship were not different between tissue layers, although they tended to be less steep for inner tissue. When exposed for 12 h to 28 °C, 30 °C, or 32 °C at--700 Amol quanta [m.sup.-2] [s.sup.-1], there was a trend for [F.sub.v]/[F.sub.m], of the Sym-biodinium in both tissue layers to be reduced at 32 °C. Our results do not conform well to shade acclimatization in inner versus outer tissue of P. lutea, and they imply within-tissue heterogeneity that may be an important determinant of physiological performance in perforate corals., Introduction Corals vary in biomass and tissue thickness among seasons, depths, and species (Brown et al., 1999; Fitt et al., 2000), but it is unclear how this variation is achieved [...]

To test for threshold effects in the response of coral physiology to increasing seawater flow, field and laboratory experiments were conducted in Moorea. First, the growth of juvenile massive Porites spp. and branching P. irregularis was compared among habitats differing in water motion. Growth of massive Porites spp. responded to flow in a pattern consistent with a threshold effect, whereas growth of P. irregularis increased linearly with flow. Second, a recirculating flume was used to test the effect of flow on photophysiology ([increment of F]/[F.sub.m] effective photochemical efficiency) for massive Porites spp.; [increment of F]/[F.sub.m]' displayed a threshold response at 23 cm [s.sup.-1] and 28 ° C, but not at 31 ° G. Finally, intra-colony variation in the response of AF/Fm' to flow and temperature was explored to evaluate the functional significance of colony shape in small corals. [increment of F]/[F.sub.m]' on the top and upstream surfaces of massive Porites spp. responded with a threshold effect of flow at 28 ° C (but not 31 ° C), but [increment of F]/[F.sub.m]' on downstream surfaces was unresponsive to flow. [increment of F]/[F.sub.m]' for P. irregularis was less responsive to flow than for massive Porites spp., suggesting that the photophysiological response of corals to varying flow speeds may differ between species and morphologies. Together, these results emphasize that flow can have diverse effects on the physiology of corals, with the outcome depending on flow speed, temperature, location on the colony, and perhaps morphology., Introduction Over the last 25 years, large-scale bleaching of scleractinian corals through the loss of Symhiodinium algae, their chlorophyll, or both has become common (Fitt et ai, 2001), and is [...]

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°C, 25°C (ambient), and 29°C at light intensities of ≅ 150 µmol photons [m.sup.-2] [s.sup.-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 ([F.sub.v]/[F.sub.m]) 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 °C) reduced the percentage of larvae swimming by 81%, and increased the percentage choosing CCA nearly 7-fold, both relative to the outcomes at 23°C. 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, [F.sub.v]/[F.sub.m] 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 [...]

In this study, two factorial experiments were used to investigate the role of tissue age in affecting the phenotypic expression of calcification in scleractinian corals. Both experiments tested whether calcification was altered by tissue age and whether corals of different ages exploit plasticity to differing degrees by altering calcification rates under new environmental conditions. To isolate age and size effects, branches of the Caribbean coral Madracis mirabilis were broken into a distal portion that was functionally young and a proximal portion that was functionally old. Fragments were transplanted from a deep (17 m) to a shallow (9 m) site in a Jamaican lagoon to test whether age affected the plasticity of calcification. Both experiments demonstrated that calcification scaled isometrically in the two age groups, and although scaling exponents were indistinguishable statistically among ages, young fragments calcified faster than old fragments. Thus, the effect of age on calcification rate was absolute and independent of size. However, the interactive effect of age and depth was not significant, demonstrating that ability to alter calcification rate (i.e., the extent of phenotypic plasticity for this trait) was unaffected by age. Together, these patterns are consistent with the hypothesis that the proximal modules (i.e., polyps) of M. mirabilis are subject to physiological senescence, as has been reported for other clonal organisms, including algae, fungi, plants, bryozoans, ascidians, and other cnidarians., Introduction The modular design of many benthic marine invertebrates, including cnidarians, bryozoans, and ascidians, has profound implications for their biology (Jackson et al., 1985). In particular, the ecological success of [...]

The recruitment and survival of juvenile corals is central to the maintenance of coral reef communities and the repopulation of denuded reef substrata. Although it is widely accepted that the mortality of scleractinians is inversely proportional to size, the biotic and abiotic factors that drive this trend remain unclear. Here we measure the mortality of corals on the reefs of St. John (U.S. Virgin Islands) to demonstrate that small corals are more likely to die than their larger counterparts, and we explore whether the photophysiological performance of juveniles in two size classes can provide some insight into why smaller corals are so vulnerable. To evaluate photophysiological performance, we examined chlorophyll fluorescence in two size classes (mean diameters 15 mm and 45 mm) of juvenile colonies of Porites astreoides exposed for short periods to ambient and elevated temperatures. Our results show that the photophysiology of these size classes differs under ambient conditions, with dark-adapted quantum yield ([F.sub.v]/[F.sub.m]) being significantly higher in smaller compared to bigger juveniles. As expected, the photophysiology of both size classes is negatively impacted by thermal stress, and although size-related trends are evident in our data, the interaction between size and temperature is not statistically significant. Thus, while there is size dependency in the photophysiological performance of juvenile colonies of P. astreoides, the link between this aspect of scleractinian biology and the higher mortality of small juvenile corals in the face of high thermal stress remains unclear., As a context for this study, we draw on mortality data for different size classes of corals at five sites on the shallow reefs of St. John. Between 1996 and [...]

STEVEN V. VOLLMER [*] Abstract. Although most physiological traits scale allometrically in unitary organisms, it has been hypothesized that modularity allows for isometric scaling in colonial modular taxa. Isometry would [...]

This study tested the bleaching response of the Pacific coral Seriatopora caliendrum to short-term exposure to high temperature and elevated partial pressure of carbon dioxide ( pCO2). Juvenile colonies collected from Nanwan Bay, Taiwan, were used in a factorial experimental design in which 2 temperatures (~27.6 °C and ~30.4 °C) and 2 pCO2 values (~47.2 Pa and ~90.7 Pa) were crossed to evaluate, over 12 days, the effects on the densities and physiology of the symbiotic dinoflagellates (Symbiodinium) in the corals. Thermal bleaching, as defined by a reduction of Symbiodinium densities at high temperature, was unaffected by high pCO2. The division, or mitotic index (MI), of Symbiodinium remaining in thermally bleached corals was about 35% lower than in control colonies, but they contained about 53% more chlorophyll. Bleaching was highly variable among colonies, but the differences were unrelated to MI or pigment content of Symbiodinium remaining in the coral host. At the end of the study, all of the corals contained clade C Symbiodinium (either C1d or C15), and the genetic variation of symbionts did not account for among-colony bleaching differences. These results showed that high temperature causes coral bleaching independent of pCO2, and underscores the potential role of the coral host in driving intraspecific variation in coral bleaching. [ABSTRACT FROM AUTHOR]

Early life stages of the coral Seriatopora caliendrum were used to test the hypothesis that the depression of dark respiration in coral recruits by high pCO2 is caused by perturbed protein metabolism. First, the contribution of protein anabolism to respiratory costs under high pCO2 was evaluated by measuring the aerobic respiration of S. caliendrum recruits with and without the protein synthesis inhibitor emetine following 1 to 4 days at 45 Pa versus 77 Pa pCO2. Second, protein catabolism under high pCO2 was evaluated by measuring the flux of ammonium (NH4+) from juvenile colonies of S. caliendrum incubated in darkness at 47 Pa and 90 Pa pCO2. Two days after settlement, respiration of recruits was affected by an interaction between emetine and pCO2, with emetine reducing respiration 63% at 45 Pa pCO2 and 27% at 77 Pa pCO2. The interaction disappeared 5 days after settlement, when respiration was reduced 27% by emetine under both pCO2 conditions. These findings suggest that protein anabolism accounted for a large proportion of metabolic costs in coral recruits and was affected by high pCO2, with consequences detected in aerobic respiration. Juvenile S. caliendrum showed net uptake of NH4+ at 45 Pa pCO2 but net release of NH4+ at 90 Pa pCO2, indicating that protein catabolism, NH4+ recycling, or both were affected by high pCO2. Together, these results are consistent with the hypothesis that high pCO2 affects protein metabolism in corals. [ABSTRACT FROM AUTHOR]

Juvenile colonies of massive Porites spp. were exposed to manipulated pH and bicarbonate ([HCO3-]) in situ to test the hypothesis that ocean acidification (OA) does not affect respiration and calcification. Incubations lasted 28 h and exposed corals to ambient temperature and light with ecologically relevant water motion. Three treatments were applied: (1) ambient conditions of pH 8.04 and 1751 µmol HCO3- kg-1 (Treatment 1), (2) pCO2-induced ocean acidification of pH 7.73 and 2011 µmol HCO3- kg-1 (Treatment 2), and (3) pCO2 and HCO3--enriched seawater of pH 7.69 and 2730 µmol HCO3- kg-1 (Treatment 3). The third treatment providing elevated [HCO3-] was used to test for stimulatory effects of dissolved inorganic carbon on calcification under low pH and low saturation of aragonite (Ωarag), but it does not reflect conditions expected to occur under CO2-driven OA. Calcification of juvenile massive Porites spp. was affected by treatments, with an 81% elevation in Treatment 3 versus Treatment 1, but no difference between Treatments 1 and 2; respiration and the metabolic expenditure concurrent with calcification remained unaffected. These findings indicate that juvenile massive Porites spp. are resistant to short exposures to OA in situ, and separately, that they can increase calcification at low pH and low Ωaragif [HCO3-] is elevated. Juvenile Porites spp. may therefore be limited by dissolved inorganic carbon under ambient pCO2 conditions. [ABSTRACT FROM AUTHOR]

This study tested the bleaching response of the Pacific coral Seriatopora caliendrum to short-term exposure to high temperature and elevated partial pressure of carbon dioxide (pCO 2 ). Juvenile colonies collected from Nanwan Bay, Taiwan, were used in a factorial experimental design in which 2 temperatures (∼27.6 °C and ∼30.4 °C) and 2 pCO 2 values (∼47.2 Pa and ∼90.7 Pa) were crossed to evaluate, over 12 days, the effects on the densities and physiology of the symbiotic dinoflagellates (Symbiodinium) in the corals. Thermal bleaching, as defined by a reduction of Symbiodinium densities at high temperature, was unaffected by high pCO 2 . The division, or mitotic index (MI), of Symbiodinium remaining in thermally bleached corals was about 35% lower than in control colonies, but they contained about 53% more chlorophyll. Bleaching was highly variable among colonies, but the differences were unrelated to MI or pigment content of Symbiodinium remaining in the coral host. At the end of the study, all of the corals contained clade C Symbiodinium (either C1d or C15), and the genetic variation of symbionts did not account for among-colony bleaching differences. These results showed that high temperature causes coral bleaching independent of pCO 2 , and underscores the potential role of the coral host in driving intraspecific variation in coral bleaching.