Pavona Clavus Research Articles

Effects of upwelling, depth, morphology and polyp size on feeding in three species of Panamanian corals

We examined the effects of upwelling, depth, morphology and polyp size on coral feeding in 3 coral species in the eastern Pacific. Feeding rates and the species composition of zoo- plankton captured by these species were observed in situ on a shallow patch reef at Isla Contadora, Gulf of Panama, in February (seawater temperature 20.7°C) and May (seawater temperature 28.5°C) 2003 at 1 and 6 m depths. Fragments of the corals Pocillopora damicornis (branching morphology, 1.0 mm diameter polyps), Pavona clavus (mounding morphology, 1.3 mm diameter polyps) and Pavona gigantea (mounding morphology, 3.0 mm diameter polyps) were collected at 3 m, trans- planted to 1 and 6 m depth on the reef, placed inside feeding chambers, and exposed to high concen- trations of natural zooplankton. After feeding, coral fragments were collected, the number and type of zooplankton within 100 polyps of each counted, and feeding rates calculated cm -2 . Feeding rates increased with increasing depth, were lower during periods of upwelling, and were higher in corals with mounding morphology than in those with branching morphology. Feeding rates cm -2 did not vary with polyp size. Assemblages of captured zooplankton did not change with upwelling, depth, morphology or polyp size. The proportionate contributions of poor-swimming and mid-sized (200 to 400 μm) zooplankton taxa eaten were over-represented relative to their abundance. When combined with prior studies, these results suggest that coral feeding rates are facultative and that feeding rates vary due to increased feeding effort and not necessarily due to increased colony morphology or polyp size.

Distribution of magnesium in coral skeleton

Ion micro‐probe imaging of the aragonite skeleton of Pavona clavus, a massive reef‐building coral, shows that magnesium and strontium are distributed very differently. In contrast to strontium, the distribution of magnesium is strongly correlated with the fine‐scale structure of the skeleton and corresponds to the layered organization of aragonite fibers surrounding the centers of calcification, which have up to ten times higher magnesium concentration. This indicates a strong biological control over the magnesium composition of all structural components within the skeleton. Magnesium may be used by the coral to actively control the growth of the different skeletal crystal components.

Strontium in coral aragonite: 2. Sr coordination and the long-term stability of coral environmental records

We have used X-ray Diffraction (XRD) and Sr K-edge Extended X-ray Absorption Fine Structure (EXAFS) to determine the structural state of Sr in a suite of coral aragonite samples. Our samples encompassed a selection of coral species ( Porites lobata, Porites lutea, Pocillopora eydouxi, Montastrea annularis, Pavona gigantea and Pavona clavus) including some commonly used for palaeoenvironmental reconstruction. Aragonite was the only carbonate observed by XRD. We refined the isolated EXAFS against structural models for Sr in aragonite and two-phase strontianite/aragonite mixes. Our data are indistinguishable from Sr ideally substituted in aragonite and strontianite was present below detection levels (estimated at <5% of Sr present). Comparisons of recent and ancient coral aragonite show no sign of exsolution, either by spinodal decomposition or by the direct nucleation of strontianite domains. Published diffusion rates of Sr in ionic solids support the view that exsolution would occur prohibitively slowly. Coral aragonites are metastable materials with slow diffusion kinetics that have the potential to encode environments over timescales of millions of years.

Strontium in coral aragonite: 1. Characterization of Sr coordination by extended absorption X-ray fine structure

Aragonite was analyzed from Porites lobata, Pavona gigantea, Pavona clavus, and Montastrea annularis corals by Sr K-edge extended absorption X-ray fine structure (EXAFS) and compared with aragonite, strontianite, and mechanically mixed standards. Bulk analyses were performed and data compared with equivalent micro-EXAFS analyses on small (∼400 μm 3) analytical volumes with a microfocused X-ray beam. As a result of the architecture of the coral skeleton, the crystals within the microanalytical volume are not randomly oriented, and the microanalytical X-ray absorption spectra show orientational dependence. However, refinement of bulk and microanalytical data provided indistinguishable interatomic distances and thermal vibration parameters in the third shell (indicative of Sr speciation). The Sr K-edge EXAFS of all the coral samples refine, within error, to an ideally substituted Sr in aragonite, in contrast to previous studies, in which significant strontianite was reported. Some samples from that study were also analyzed here. Strontianite may be less widely distributed in corals than previously thought.

Skeletal tumor formations in the massive coral Pavona clavus

Skeletal tumor formations in the massive coral Pavona clavus were investigated for 3 yr on the northern Pacific coast of Costa Rica in a reef composed almost exclusively of this species. A field survey of tumor incidence showed that more than half of the population presented this phe- nomenon and that frequencies increased with depth. Up to 37 tumors per colony were recorded, and the largest tumor size was 37.5 m 2 , covering the whole colony surface area. Tumors and healthy skeletons and tissues were studied by scanning and transmission electron microscopy, histology, in situ alizarin marking for growth rates, and x-ray radiographs of skeletal slabs. Macroscopic and microscopic analyses of skeletons revealed the presence of 3 types of tumors (Types I to III). No cyto- logical changes or intracellular infection by parasitic agents were recorded. The only cellular change observed was the reduced numbers of zooxanthellae in tumorigenic tissues. Tumors begin their growth as a single polyp and develop for scores of years without any sign of cellular necroses. Tumors grew faster than healthy parts; however, their skeletal density was lower, with a higher Mg content making it less resistant to bioerosion. Two yr of in situ isogeneic and allogeneic contacts between healthy and tumor fragments revealed no infection or transfer of the tumor to the healthy tissue, even following isogeneic fusion combinations of healthy versus tumor fragments. We suggest that the ter- minology often used to characterize tumors in hard corals ('tumor', 'neoplasm', 'hyperplasia') does not reflect the pathogenesis and etiology of this phenomenon. The terms 'skeletal tumor' or 'calicoblastic epithelioma' seem more fitting for this de novo genesis.

X-Ray absorption spectroscopy of uranium at low ppm levels in coral skeletal aragonite

We performed X-ray absorption spectroscopy of uranium in three coral specimens and present results of analysis of U L-II edge XANES (X-ray absorption near edge structure) spectra. The XANES of two specimens, Pavona gigantea (collected live at Champion Island, Galapagos) and Pavona clavus (collected live from Bartolme, Galapagos) were most similar to XANES of model compounds of U 6+. In contrast, the XANES of a specimen of Montastrea annularis (Pleistocene age from an exposed reef terrace on Marie Galante, Guadeloupe) showed some features typical of spectra of model compounds of U 4+. These data and interpretations suggest that uranium is incorporated into coral skeletons chiefly in its oxidized U 6+ form. The uranium may be subject to postmortem subaerial reduction to U 4+, or may be replaced or enhanced by addition of U 4+ compounds.

Effect of light and zooplankton on skeletal δ 13 C values in the eastern Pacific corals Pavona clavus and Pavona gigantea

Skeletal δ13C levels in symbiotic reef corals are believed to be predominantly influenced by metabolic fractionation. Therefore, environmental variables influencing coral metabolism should also affect skeletal δ13C levels. To test this hypothesis, we measured the effects of light (which drives photosynthesis) and relative zooplankton levels (heterotrophy) on skeletal δ13C values in the corals Pavona clavus and P. gigantea at two depths (1 m and 7 m). For both species, decreases in light or increases in zooplankton resulted in significant decreases in skeletal δ13C levels. A significant decrease in δ13C values with depth was observed in Pavona gigantea only. Thus, light and zooplankton directly affect coral skeletal δ13C values, supporting the hypothesis that metabolic fractionation significantly contributes to skeletal δ13C levels. Simultaneous decreases in both light and zooplankton resulted in decreases in skeletal δ13C values, reflecting decreases in light. In Pavona clavus, intra-annual variation in skeletal δ13C values over one year correlated with seasonal changes in irradiance. Further study is needed to resolve how skeletal δ13C values vary at intermediate levels of irradiance and zooplankton, and in other coral species.

Calibration of stable oxygen isotope signatures in Galápagos corals

A 2‐year (1993‐1994) study was conducted in the Galápagos Islands (Ecuador) to determine the relationship between δ18O in skeletal carbonate and sea surface temperature (SST) in three species of reef‐building corals: Pavona clavus, Pavona gigantea, and Porites lobata. Coral samples were grown at 3, 10, and 3 m depth at Bartolomé Island, Champion iIsland, and Urvina Bay (Isabela Island), respectively. Hourly measurements of SST and sea surface salinity (SSS) were taken at each site immediately adjacent to colonies which were stained biannually to establish the chronology of growth. In addition, surface waters were sampled periodically (bimonthly to monthly) at each site to determine variation in δ18O seawater. Results indicate the mean annual SSTs were similar between sites, varying from 22.9°C at Champion to 23.8°C at Urvina Bay. Comparisons of monthly SST averages between instrumental and remote sensing (satellite, 1° × 1° grid) data show a high correspondence (r2 ranging from 0.84 to 0.94), indicating that remote sensing data are useful for interpreting the δ18O record in corals when instrumental data are lacking. Here δ18Ocoral analyses of eight specimens show that coralline aragonite is a reliable indicator of SST in Galápagos. In general, higher‐resolution coral sampling/year resolved more of the monthly variation in SST, up to 97% at a sampling resolution of 1.4 samples per millimeter of linear skeletal growth. Comparisions of the δ18Ocoral signal among and between species at the same site showed consistent seasonal patterns of variation closely tracking SST. In addition, comparisons between sites were highly concordant, with some differences reflecting local variation in SST. Seasonal patterns, however, were essentially the same over the entire region. Thus we conclude that the δ18Ocoral signal from coral skeletons in Galápagos can be used to interpret regional changes in SST variation.

Eastern Pacific sea surface temperature since 1600 A.D.: The δ18O record of climate variability in Galápagos Corals

We measured stable oxygen isotope ratios and skeletal growth rates in the massive corals Pavona clavus and P. gigantea from the west coast of Isabela Island, Galápagos, to assess interannual to decadal climate variability in the eastern Pacific. Comparisons of instrumental data sets show that sea surface temperatures (SST) in the Galápagos region are representative of a broad portion of the eastern equatorial Pacific. The site is especially well‐suited for long‐term studies of the El Niño/Southern Oscillation (ENSO) phenomenon, as it lies within the eastern Pacific “center of action” for thermal anomalies associated with ENSO. The P. gigantea isotope record is nearly monthly in resolution, spans the period 1961–1982, and shows strong correlation with a Galápagos instrumental SST record (r = −0.90 for annual averages). Cross‐spectral analysis shows that SST can explain greater than 80% of the variance in δ18O at both the annual cycle and within the high‐frequency portion of the ENSO band (3‐5 years). The P. clavus record is annual in resolution, extends from 1587 to 1953 A.D., and was obtained from a 10‐m diameter colony preserved within the Urvina Bay uplift. Because seawater δ18O variations in the region are very small, we interpret the Urvina Bay coral δ18O record in terms of annual average SST. The isotopic record appears to be a very good, but not perfect, indicator of ENSO events and shows good correspondence with the historical ENSO reconstruction of Quinn et al. (1987). A number of low δ18O excursions that we observe during the 17th and 18th centuries very likely represent ENSO events that are missing from the historical tabulations. Most interannual δ18O variations between 1607 and 1953 A.D. represent annual average temperature excursions of 1° to 2.5°C. During the Little Ice Age, the annual δ18O series correlates well with many North American tree ring records and shows low temperatures during the early 1600s and early 1800s, and relatively warmer conditions during the 1700s. Unlike most northern hemisphere tree ring and instrumental records, we see no evidence at this site for warming between 1880 and 1940 but rather observe a slight cooling (&lt;1°C). Oscillatory modes within the ENSO frequency band dominate the 347‐year δ18O time series, accounting for &gt;28% of the total variance. The main ENSO mode is centered at 4.6 years and accounts for 12% of the total variance. Additional significant oscillations occur at periods of 3.3, 6, 8, 11, 17, 22, and 34 years. Both annual growth rate and δ18O show variance at periods equivalent to the solar and solar magnetic periods (e.g., 11 and 22 years, respectively). In addition, the amplitude of the 11‐year δ18O cycle generally varies with the amplitude of the solar cycle, supporting previous suggestions that the solar cycle may modulate interannual to decadal climate variability in the tropics. The dominant oscillatory modes, both within the ENSO and interdecadal frequency bands, shift to shorter periods from the early to middle 1700s and again from the middle to late 1800s. This may reflect major reorganizations within the tropical ocean‐atmosphere system and suggests that tropical Pacific climate variability is linked across timescales ranging from years to decades.

The [formula omitted]-temperature relationship in coralline aragonite: Influence of variability in [formula omitted] and skeletal growth parameters

This paper provides an evaluation of two of the most likely pitfalls of Sr Ca thermometry, i.e., the effect of biogenic cycling of Sr vs. Ca in the surface ocean and the effect of variable extension rate on Sr incorporation in coralline aragonite. We also report calibration of the Sr Ca -temperature relationship for three coral species, Porites lobata, Pocillopora eydouxi and Pavona clavus, collected from the Hawaiian and Galapagos islands. Analyses of seawater samples show significant spatial and depth variability in the Sr:Ca ratio. The uncertainty introduced by this effect is estimated to be <0.2°C for corals located in tropical oligotrophic waters, and potentially larger for corals located in upwelling areas. Sr Ca analyses along two different growth axes of a Galapagos Pavona clavus, with annual extension rates of ~6 and 12 mm/y, respectively, indicate an offset of 1–2°C, with higher Sr Ca values associated with slower extension rates. The offset observed between the two growth axes may be the result of variations in extension and/or calcification rate.

Seasonal cycles of manganese and cadmium in coral from the Galapagos Islands

Manganese-to-calcium ratios in corals from the eastern and western Galapagos demonstrate regional differences in seasonal trace metal cycling. The variability of trace metal-to-calcium ratios within the Galapagos Islands points to their unique geographic setting as a major factor. This region is influenced by several major oceanic currents (e.g., the South Equatorial Current, the Equatorial Undercurrent, and the Panama, or El Nino, Current) and by extremely intense upwelling. Manganese-to-calcium ratios in a banded coral Pavona clavus from Isabela Island, the westernmost island in the Galapagos, have distinct seasonal cycles for the non-El Nino Southern Oscillation (ENSO) years 1946–1950, with lower ratios following intensified seasonal upwelling. Cadmium/calcium ratios show less distinct seasonal cycles. The near-moderate ENSO event in 1951 is marked by the disruption of seasonal cycles in MnCa and CdCa ratios. In contrast, corals from islands further east in the Galapagos (Hood Island, 1964–1973, Linn et al., 1990; San Cristobal, 1965–1979, Shen and Sanford, 1990), have stronger seasonal CdCa signals, with higher ratios following seasonal upwelling, and less distinct seasonal cycles in MnCa ratios one-half year out of phase with CdCa variations. Average MnCa ratios are lower for these corals from locations further east, indicating that Urvina Bay appears to have an additional localized source of Mn (Shen and Sanford, 1990). In general, these regional variations in seasonal trace metal cycling are consistent with coral stable isotope signals and with their geographic locations. These variations are important to consider in using coral records to reconstruct and interpret oceanographic events occurring prior to historical records.

Surface ocean variability at Galapagos from 1936–1982: Calibration of geochemical tracers in corals

A variety of geochemical tracers has been developed in reef corals as a means of reconstructing the natural variability of the tropical surface ocean over wide ranging time frames. The purpose of this paper is to calibrate the performance of five of these tracers in a modern coral colony, over an extended period. A 47‐year growth interval (1936–1982) in a colony of Pavona clavus taken from San Cristobal Island, Galapagos Islands, was sectioned into 187 quarterly intervals and analyzed for δ18O, δ13O, Ba/Ca, Cd/Ca, and Mn/Ca. The resulting time series are compared with eastern Pacific sea surface temperatures—one of few instrumental data bases available for calibration over this time period. Linear least squares regressions of four of the tracers (δ18O, δ13O, Ba/Ca, Cd/Ca) against Peruvian SST show highly significant correlations (p&lt;0.0001). Over the annual, biennial, and ENSO (3.8 years) frequency bands, cross‐spectral comparisons show even stronger coherency, with SST frequently accounting for 70–80% of the variance in these tracers. These results as well as the phase relationships determined from the spectral analyses suggest that the coupling between SST and δ18O and the nutrientlike tracers Ba and Cd is controlled principally by seasonal upwelling cycles and interannual interruptions of these cycles brought about by El Niño and anti‐El Niño phenomena. An inverse relationship between SST and δ13C has its primary origins in the co‐occurrence of the warm SST phase with high light levels during the first half of the calendar year. The association with sunlight derives from the photosynthetic response of algal symbionts which results in fractionation of light and heavy carbon isotopes between soft tissues and CaCO3 skeleton. The fifth tracer, the transition metal Mn, exhibits poorer correlations against both SST and the other tracers. Slight shifts in phasing of the historical Mn/Ca annual cycle suggest that the general water column distribution of this tracer, which is the reverse of a nutrient, may not be stable. The erratic behavior of Mn illustrates how complex hydrography near Galapagos may influence tracers with diverse source signatures.

Trace metals in contemporary and seventeenth-century Galapagos coral: Records of seasonal and annual variations

We report trace element/calcium ratios for modern ( Cu Ca , Mn Ca , Cd Ca , and Pb Ca ) and seventeenth-century ( Cu Ca , Mn Ca , and Pb Ca ) specimens of Pavona clavus collected in the Galapagos Islands. These data include the first reliable measurements of Cu Ca ratios in coralline aragonite. We estimate that the ratio of Cu Ca in the lattice to that in seawater (i.e., the effective distribution coefficient) is ~0.3, lower than the value of 1 observed for several other divalent elements; we estimate the effective distribution coefficient for Mn is ~ 1. Distribution coefficients in coral aragonite for 8 divalent metals are near unity despite different ionic radii and chemical speciation in seawater. Investigation of where these substituents are incorporated in the aragonite lattice is clearly warranted. In a modern Hood Island coral, quarter-annually sampled from 1964–73, Cu Ca ratios decrease twofold from the late 1960s to early 1970s. Mn Ca and Cd Ca ratios vary seasonally with upwelling and the generic El Niño. The El Nino Southern Oscillation (ENSO) events of 1965, 1969, and 1972 are marked by suppression of Cd Ca ratios by about 2.5 nmol/mol, while the Mn Ca ratio is highest during the strong 1972 ENSO. Pb Ca ratios were relatively constant throughout this period. From the Cu Ca record of a seventeenth-century Urvina Bay coral annually sampled from 1600–1725 and the estimated Cu distribution coefficient, surface seawater Cu concentrations at Galapagos during the seventeenth century were similar to present day at 0.7–1.4 nmol/kg. Estimated Pb concentrations were lower at 5–20 pmol/kg, and Mn concentrations were slightly higher at 1.6–2.8 nmol/kg.

Radiochemical analyses of 210Pb in a massive coral (Pavona clavus) from the Galapagos

Radiochemical, mineralogie, and minor element analyses of three Pavona clavus samples spanning 350 years from Urvina Bay, Isabela Island, Galapagos, are presented here. The 210Pb results, the first reported from corals treated with all the precautions developed for obtaining reliable stable lead measurements, indicate the importance of these procedures for measuring coral 210Pb activities which can be directly related to surface water activities. Sr/Ca and Mg/Ca ratios, mineralogy, uranium concentration and isotopic ratio data, and activities < 0.2 dpm/100 g for 230Th (in the two youngest samples) and 232Th indicate no significant post-depositional alteration or contamination. Calculated initial 210Pb activities in the two youngest samples are ~6 to 9 dpm/100 g, lower than observed for other Galapagos corals and consistent with surface water conditions inferred from other trace element data on these corals. Initial 226Ra activities are typically ~4.4 dpm/100 g. Further investigation is required to document fully the effects of cleaning procedures on coral radionuclide measurements and the relationship of variability in coral radionuclides with water column events.

Coral Reef Community Structure at Caño Island, Pacific Costa Rica

Abstract. Around the Biological Reserve of Caño Island, Pacific Costa Rica, there are five large coral reef flats (with size ranges of 0.8–4.2 ha) built mainly of dead Pocillopora spp. At present, they are covered mainly by crustose coralline algae and microatolls of Porites lobata. From the upper reef slope to the reef base several corals grow in small patches (e. g., Pavona clavus, Pavona varians, Pavona gigantea, Gardineroseris planulata, Psammocora superficialis, Pocillopora elegans, Pocillopora damicornis); the massive coral Porites Iobata is predominant. Pocilloporid species are predominant on most other eastern Pacific reefs.The Caño Island reef is typical of a community whose structure has been controlled by both physical (in shallow water) and biological (in deeper water) factors. Shallow reef areas are influenced by strong wave action and extreme low tides. The distribution, abundance, and feeding preferences of corallivorous organisms (e. g., Acanthaster planci, Arothron meleagris, Pseudobalistes naufragium, Quoyula monodonta) on the deeper reef suggest that most pocilloporids are affected and limited by them. Although there is no evidence of any predator on Porites lobata at Caño Island, the triggerfish Pseudobalistes naufragium breaks off fragments of the coral while searching for food. These fragments often survive to form new colonies. Together, this dispersal mechanism, rapid injury recovery, and high resistance to environmental stress seem to enhance the distribution and dominance of the massive coral Porites lobata at Caño Island.

Evidence of enhanced microbial activity in the interstitial space of branched corals: possible implications for coral metabolism

Water samples from the interstitial space of 4 Indo-Pacific coral species (Acropora sp., Echinopora horrida, Psammocora digita and Pavona clavus) and a Mediterranean coral (Cladocora cespitosa) were analysed for NO 3 - +NO 2 - , NH 4 + , molybdate reactive phosphorus, bacterial and flagellate biomass and dissolved organic matter (DOM) and compared with ambient water concentrations. Higher values of NO 3 - +NO 2 - , bacterial and flagellate biomass were observed within the interstitial space of the corals. The lower DOM pool in the interstitium in combination with the high bacterial biomass suggests high bacterial activity and efficient substrate utilization, necessary to compensate for nanoflagellate predation. Since corals may be able to feed on bacteria, the high microbial biomass (bacterial and flagellate) may be utilized either directly as an additional heterotrophic food source, or indirectly in that microbes may act as attractants for microbe-feeding zooplankters, which in turn serve as food for the corals. The combined effect of reduced flow velocities between the coral branches and its associated fauna are probably the main factors in creating a specific environment more or less independent of the nutritive stage of the surrounding water.

Sedimentologic Succession of Uplifted Coral Community, Urvina Bay, Isabela Island, Galapagos Archipelago, Ecuador: ABSTRACT

In March 1954, along the west-central coast of Isabela Island, an upward movement of magma suddenly raised Urvina Bay over 6 m and exposed several square kilometers of carbonate deposits covering a young aa lava flow (around 1000 years old). Results from 6 transect lines across the uplift, 30 cores, and 10 trenches describe the sedimentologic and ecologic transition from barren basalt to diverse carbonate sediments with small coral reefs. Along horizontal transects spanning from 0 to 7 m paleowater depth, there is a seaward progression from beaches, mangroves, and basalt to thick deposits (> 1.6 m) of carbonate sands and small coral reefs. Variation in water depth, degree of wave exposure, and irregularity of the aa lava topography provided many microhabitats where coral, calcareous algae, and mollusks settled and grew. Eight hermatypic coral species are found throughout the shelf, and three species (i.e., Pavona clavus, Pocillopora damicornis, and Porites lobata) produced five small, isolated, monospecific, coral-reef frameworks. The vertical section seen in cores and trenches shows that calcium carbonate increased upward, whereas volcanic sediments decreased; however, episodic layers occur with high concentrations of basaltic sands. In vertical samples from the central portion of the shelf, the coral population changedmore » from small, isolated colonies of Psammocora (Plesioseris) superficalis near the basalt basement to large reef-forming colonies of Pocillopora damicornis farther upsection. Reefs of the Galapagos Islands are small and less diverse than most Pacific reefs. Nonetheless, understanding their temporal successional development should throw light on the origin and history of larger oceanic reefs in the Pacific.« less

Environmental influences on skeletal banding in eastern Pacific (Panama) corals

The timing of skeletal band formation and concomitant changes in calcification rates and linear skeletal extension were investigated in Pavona corals growing under two distinct thermal regimes along the Pacific coast of Panama: fluctuating, marked by seasonal upwelling (Gulf of Panama) and stable, nonupwelling (Gulf of Chiriqui). The purpose of this study was to test the hypothesis that banding in corals is largely mediated by seasonal variations in temperature (Highsmith 1979). Our results indicate that the timing of band formation is synchronous at these two environmentally distinct locations. The low density (LD) portion of the annual band is accreted over a five month period (January–June) and represents an increase in linear skeletal extension (mm/mo.) as well as a marked increase in calcification rate (g CaCO3 · cm-2 · mo-1) relative to the high density portion which forms over the remaining seven month period (July through December). In contrast to the predictions of the Highsmith model these findings indicate that variations in light levels rather than fluctuation in temperature is a better correlate to changes in skeletal density. Qualitatively, banding patterns were similar at the two sites; however, higher growth rates (particularly with respect to the LD band) for Pavona clavus in the Gulf of Panama indicate that lower water temperatures and higher productivity, or both, may be responsible for quantitative differences in banding between sites. We found that formation of the HD band corresponds to lower light levels and the production of gametes. We propose that banding in corals is a complex phenomenon governed by endogenous processes (e.g. reallocation of energy from growth to reproduction) which may be mediated by exogenous factors (e.g light and productivity).

An experimental analysis of the effects of light and zooplankton on coral zonation.

In Panamá, vertical zonation of coral species is well marked; branching corals (Pocillopora spp.) predominate in shallow (1-6 m) water while massive forms (Pavona spp.) occupy the deeper (6-10 m) areas of the reef. To test the hypothesis that this zonation represents differential resource utilization (i.e., niche partitioning of food resources), one year manipulative field experiments were conducted at two depths (1 m and 7 m below Mean Lower Sea Level) assessing the relative contribution of light and zooplankton to the nutrition of three Pacific corals: Pocillopora damicornis, Pavona clavus and Pavona gigantea. Also tested were the related hypotheses that (i) energy for the maintenance and growth of corals comes mainly from light, independent of zooplankton supply and (ii) Porter's model, in which coral morphology is a predictor of the phototrophic-heterotrophic capabilities of a particular species. That is, corals with a branching morphology and a small polyp diameter (and short tentacle length) should be primarily phototrophic while those species with larger polyps and/or a massive form should show a greater degree of heterotrophy.The comparison of caged versus control corals indicated that the branching coral, Pocillopora damicornis (polyp diameter - 1 mm) grew independent of zooplankton supply (>95μ) but was markedly affected by shading. Pavona clavus (massive form with intermediate size polyps - 2 mm) was also negatively affected by shading but this effect was minimized when zooplankton was present. Surprisingly, under ambient light conditions, the growth of this specics was independent of zooplankton (>95μ); perhaps indicating a facultative reliance on zooplankton especially in shallow water. The third species, Pavona gigan-tea (massive form with largest polyps - 3 mm) was highly dependent on both light and zooplankton and was unable to compensate for the effects of shading by zooplankton feeding. This high dependence on light was unexpected since large polyps, according to Porter's model, would predict a more heterotrophic existence.Under all treatments, in both shallow and deep water, Pocillopora was found to grow more rapidly than either massive species. Thus, this study indicates that zonation on eastern Pacific reefs cannot be explained by depth-related differences in nutritional requirements among the species present. These results do provide the first long-term, experimental field evidence that corals are largely phototrophic organisms. The validity of Porter's model attempting to correlate phototrophic-heterotrophic abilities to morphological characteristics is, at least, partially verified: species with larger tentacles do appear to utilize zooplankton to a greater extent than those species with smaller tentacles. However, the significance of corallum morphology in predicting the mode of nutrient acquisition is unclear. Rather, behavioral patterns (tentacle expansion-contraction cycles) and location on the reef may be more important factors to consider.