Fungi in corals: black bands and density-banding of Porites lutea and P. lobata skeleton

 Dark coloration of coral skeleton forming black bands is commonly observed in fractured, massive-coral colonies (Porites lutea and P. lobata) collected from May- otte Island in the Mozambique Channel and Moorea Island in French Polynesia. Black-banding was similar in corals from the two areas and was associated with an assemblage of microbial endoliths: Ostreobium queketti, a common siphonal chlorophyte, and a type of Aspergillus-like fungus. Fungi of coral skeletons are capable of euendolithic growth entirely within the skeleton, and of cryptoendolithic growth whereby they spread from the skeleton into the skeletal pores. The morphology and size of fungal hyphae differs significantly between euendolithic, cryptoendolithic and reproductive phases. Reproductive phases involve formation of conidiophores. Insoluble residues in black bands involve a dark pigment and a dark membranous veil. When attacked by fungi, the algae are usually destroyed. They darken and are threaded by dense, dark-brown, fibrous excrescences. The fungi excrete a dark pigment that stains the surrounding skeletal carbonate black. The pigment is organic, and its presence correlates with higher concentrations of polysaccharides. Black bands match high-density bands of the coral skeleton. Both black bands and high-density bands form at the end of the rainy season in Mayotte. Thus, black-banding in the corals studied is caused by a series of events, beginning with an increase in the abundance of endolithic algae followed by an increase in skeletal density. The algae are then attacked by fungi, which produce more cryptoendolithic hyphae and conidia that are associated with production of the dark pigment. Received: 29 January 1999 / Accepted: 29 September 1999     

Short-term growth measurements of corals using an accurate buoyant weighing technique

An accurate method for determining the growth rates of the skeleton of isolated branch tips (nubbins) of corals over intervals of less than 24 h is described. The skeletal weight of the coral was estimated from its buoyant weight in seawater whose density had been accurately determined. The coral tissues accounted for between 1 and 5% of the total buoyant weight in Pocillopora verrucosa and Acropora humilis with differing relative tissue biomass. After correcting for tissue buoyant weight, predictions of skeletal weight were accurate to within 1%. The method was used to estimate the growth of sample nubbins of Porites porites of similar diameter, in 2 m of water at Discovery Bay, Jamaica. Since growth of these branch tips is apical, growth rate could be expressed without correction for the size. The mean 24 h skeletal growth rate ranged between 40 and 47 mg. Differences could be measured between day-time and night-time growth, the day: night ratio being 3.7. The method also showed that P. porites virtually ceases calcification during the 4 to 5 d periods that it becomes enclosed in a mucus tunic. Nubbins of P. porites attached to the reef at different locations showed clear differences in growth rate with depth, and between clear and turbid water sites. The growth rate of nubbins was compared with that of branch tips of whole corals by measuring the linear extension after staining with Alizarin Red S. After 3 1/2 mo, the mean linear extension was 4.1 mm in each case, indicating that the growth rate of nubbins is the same as that of branch tips of the whole colony. It is suggested that this buoyant weighing technique will find applications in laboratory experiments with calcification mechanisms and as a bioassay on reefs exposed to environmental stress.Contribution No. 464 of the Discovery Bay Marine Laboratory     

Pink-line syndrome, a physiological crisis in the scleractinian coral Porites lutea

Coral diseases are one of the major factors that alter coral cover and their diversity. We have earlier reported the “Pink-line syndrome” (PLS) in the scleractinian coral Porites lutea wherein a colored band appears between the dead and healthy tissue of a colony. About 20% of the P. lutea colonies were affected in Kavaratti of the Lakshadweep Islands in the Arabian Sea during April 1996 and the incidence increased fourfold within the next 4 years. Fungi were associated in both PLS-affected and healthy specimens, whereas the cyanobacterium Phormidium valderianum occurred exclusively in the PLS-affected specimens. There was an increased expression of a 29 kDa protein without any significant increase in total protein content in the PLS-affected colonies. A reduced number of zooxanthellae and an increase in zooxanthellae size, mitotic index, and chl a concentrations were some of the characteristics of the PLS-affected colonies. PLS induction experiments conducted using selected fungi and the cyanobacterium P. valderianum isolated from the affected colonies and abiotic factors, such as CO₂ enrichment and the effect of cyanobacterial photosynthesis inhibition, indicated that the CO₂ build-up around the host tissue caused the pink coloration. We hypothesize that these physiological changes disturb the mutualism between the zooxanthellae and the host. When the symbiosis is disturbed by the external CO₂, the host loses control over the zooxanthellae, causing their uncontrolled division. This process may lead to a break in photosynthate transfer to the host, thereby resulting in starvation and finally leading to partial mortality. We further hypothesize that these degenerative processes are triggered by the CO₂ produced by P. valderianum through its carbon concentration mechanism. In this context, any opportunistic cyanobacteria or other agents having potential to interfere with the physiology of the host or the symbiont can cause such a physiological disorder. The mechanism of PLS formation is an early warning to protect corals as the increasing atmospheric CO₂ could induce PLS-like physiological disorder in corals.     

Variability of stable isotopes and maximum linear extension in reef-coral skeletons at Kaneohe Bay, Hawaii

Stable-isotope and growth records of coral skeletons are often used to reconstruct tropical paleoclimate, yet few surveys have systematically examined the natural variability in coral skeletal ¹³C, ¹⁸O and maximum linear skeletal extension (MLSE) across depth. Here, interspecific, intraspecific, and geographical variations in coral skeletal ¹³C, ¹⁸O, and MLSE were examined in the corals Porites compressa, P. lobata, and Montipora verrucosa grown at 1.7, 5.0, and 8.3 m depth from August 1996 to March 1997 at The Point Reef and Patch Reef #41 field sites in Kaneohe Bay, Hawaii. Coral skeletal ¹³C values significantly decreased with depth and differed between species, but did not vary between field sites. ¹⁸O values were not significantly different across depth within a species, but did differ among species and field sites. High-resolution analysis of the intra-annual variation in skeletal ¹³C and ¹⁸O in P. compressa at 2.0 m depth confirms that these isotopes reflect changes in solar irradiance and temperature, respectively. Changes in MLSE across depth were consistent within, but highly variable among, species. Peak MLSE occurred at 1.7, 5.0, and 8.3 m for P. lobata, P. compressa, and M. verrucosa, respectively. Such interspecific variation in MLSE patterns may be attributable to one or more of the following: increases in zooplankton in the diet, changes in metabolic processes, or changes in growth form with depth. Overall, these results imply that natural inter- and intraspecific variability in coral skeletal ¹³C, ¹⁸O, and MLSE should be considered when interpreting and comparing coral-based tropical paleoclimate data from various coral species, depths, and field sites. Received: 6 October 1998 / Accepted: 8 July 1999     

Tetracycline reduces sedimentation damage to corals

Sediment deposition on coral reefs occurs naturally and is also caused by man-made disturbances such as dredging; it can result in the death of scleractinian corals by an unknown mechanism. Sedimentation experiments with corals were carried out in El Nido, Northern Palawan, Philippines, in 1986, and in Honolulu, Oahu, Hawaii in 1988. Four species of Indo-Pacific reef corals (Oxypora glabra, Montipora verrucosa, Porites lobata, Pocillopora meandrina) were subjected to sedimentation tests with and without the antibiotic tetracycline to investigate the possible role of microorganisms in the process of sedimentation damage to corals.O. glabra, Porites lobata andPocillopora meandrina were rapidly damaged andO. glabra was always killed by sedimentation.Montipora verrucosa was not injured and may be physiologically resistant to sedimentation damage. Tetracyclinetreated seawater reduced the rate of tissue necrosis and prevented colony mortality, suggesting that tetracycline-sensitive bacteria are involved in the process of tissue necrosis and may be partially responsible for coral mortality following sediment deposition.     

Association of <Emphasis Type="Italic">Waminoa</Emphasis> sp. (Acoela) with corals in the Wakatobi Marine Park,South-East Sulawesi,Indonesia

This is the first quantitative study on the prevalence of epizoic Waminoa sp. acoel worms and their association with corals in the Wakatobi Marine National Park (WMNP), South-East Sulawesi, Indonesia. Three replicate transects were laid on the reef crest, flat and slope at six sites in 2006 and eight sites in 2007. Four of the sites were common in both years. In total 69 transects were surveyed in 2006, and 87 transects in 2007. A total of 4.8% of all observed hard corals were associated with acoel worms in 2006 and 2.6% of hard and soft corals in 2007. Acoels were present on 16 and 21 of the coral taxa studied in 2006 and 2007 respectively. The worms were strongly associated with the azooxanthellate coral Tubastrea spp. and were rare or absent on the most abundant coral genera Montipora and Porites. The mean number of corals having acoels was highest on reef slopes, whereas acoels were virtually absent on reef flats. Corals that had a high and a medium cover of worms were more common in 2007 than in 2006. No significant trend in the adaptation of the zooxanthellae of Waminoa sp. to different depths at different sites was revealed. The impact of the worm on the coral is unknown, but high numbers may have a shading effect and a negative impact on the coral’s photophysiology. This acoel merits more study of its life cycle, its photophysiology, and its impact on its host corals. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Annual density banding in massive coral skeletons: result of growth strategies to inhabit reefs with high microborers’ activity?

Porites and Montastraea are the major reef-building massive coral genera in the Indo-Pacific and Atlantic oceans, respectively. They are also the most commonly used genera in sclerochronological studies. Despite the marked differences in the way these genera use calcareous material to construct their skeletons (growth strategies) and in their skeletal architectural structure, they form annual high and low density bands in their skeletons, that result from the positive relationship of coral calcification rate with sea surface temperature and seasonal changes of the latter. Evidence in the literature suggests that the different growth strategies allow these organisms to construct denser skeletons far from terrigenous inputs, on reefs where microborers’ activity is high. It seems quite probable that this has consequences for the evolution, diversity, distribution and abundance of reef corals.     

Recovery of corals a decade after a bleaching event in Dubai, United Arab Emirates

Elevated sea surface temperatures in the late 1990s were associated with widespread coral mortality in the Arabian Gulf, particularly in Acropora dominated areas. This study investigates the composition, condition, and recruitment patterns of coral communities in Saih Al-Shaib, Dubai, United Arab Emirates, a decade after mass bleaching. Five statistically distinct communities were identified by cluster analysis, with grouping optimized from 17 significant indicator species. Overall, 25 species of scleractinian coral were observed, representing 35 ± 1.6% coral cover. Densities of recruits were low (0.8 ± 0.2 m⁻²), and composition generally reflected that of the surrounding adult community. Ten years after mass mortality, Acropora dominated assemblages were observed in three of the six sites examined and coral cover (41.9 ± 2.5%) was double post-bleaching cover. One shallow near-shore site appears to have had recovery of Acropora reset by a further bleaching event in 2002. However, the prevalence of young Acropora colonies here indicates that recovery may recur in several years. One area formerly dominated by Acropora is now dominated by faviids and poritids, with adult and juvenile composition suggesting this dominance shift is likely to persist. Porites lutea and Porites harrisoni dominated communities were negligibly impacted by the bleaching events, and the limited change in coral cover and composition in intervening years likely results from slow growth and low recruitment. Despite strong recovery of several dominant Acropora species, five formerly common species from this area were not observed suggesting local extinction. Dubai coral communities exhibit both resistance and resilience to elevated sea temperatures. The conservation of these patch reefs is warranted given the predicted increase in bleaching events, and the role that these communities may play in regional recovery.     

Hydrolithon spp. (Rhodophyta, Corallinales) overgrow live corals (Cnidaria, Scleractinia) in Yemen

In Yemen, off the northwestern coast in the Gulf of Aden, the coralline algae Hydrolithon rupestre (Foslie) Penrose 1996 and H. murakoshii Iryu and Matsuda 1996 have been observed to overgrow and kill living Porites lutea Milne-Edwards and Haime, 1860. Similarly, Hydrolithon onkodes (Heydrich) Penrose and Woelkerling 1992 and H. rupestre were observed overgrowing Stylophora pistillata (Esper, 1797). Competitive interactions between P. lutea and H. murakoshii were monitored from 2006 to 2009 at two sites and showed an average linear growth of 8.3 (±1.9 SD) mm?year^?1 over the coral. The small polyps of S. pistillata and P. lutea combined with putative chemical compounds produced by Hydrolithon spp. are likely to allow the coralline overgrowth. Although corallines can locally kill coral tissues, the CCA/coral interactions do not seem to affect the overall live coral cover at the study sites.     

Cyclical mucous sheet formation on poritid corals in the San Blas Islands,Panama

Mucous sheets are common on poritid corals as well as other reef coelenterates, but the frequency, cause and function of these sheets have rarely been investigated.Porites furcata Lamarck andPorites astreoides Lamarck colonies at three sites in the San Blas Islands, Panama, were monitored for the presence or absence of mucous sheets every 2 d between 11 May and 27 August 1983. Concurrent measurements of polyp expansion, particulate matter concentrations, salinity, water temperature and sedimentation rates were also made at each site. Mucous sheet formation was not correlated with any of the environmental parameters measured. Mucous sheet formation by both species had a lunar periodicity.P. furcata formed mucous sheets around the time of the full moon, whileP. astreoides formed mucous sheets during the first quarter (around a week before full moon). Mucous sheet formation was correlated with polyp contraction behavior and may be a secondary effect of a lunar cycle in polyp activity.     

Water flow and prey capture by three scleractinian corals, Madracis mirabilis, Montastrea cavernosa and Porites porites, in a field enclosure

Scleractinian corals experience a wide range of flow regimes which, coupled with colony morphology, can affect the ability of corals to capture zooplankton and other particulate materials. We used a field enclosure oriented parallel to prevailing oscillatory flow on the forereef at Discovery Bay, Jamaica, to investigate rates of zooplankton capture by corals of varying morphology and polyp size under realistic flow speeds. Experiments were carried out from 1989 to 1992. Particles (Artemia salina cysts) and naturally occurring zooplankton attracted into the enclosures were used as prey for the corals Madracis mirabilis (Duchassaing and Michelotti) (narrow branches, small polyps), Montastrea cavernosa (Linnaeus) (mounding, large polyps), and Porites porites (Pallas) (wide branches, small polyps). This design allowed corals to be used without removing them or their prey from the reef environment, and avoided contact of zooplankton with net surfaces. Flow speed had significant effects on capture rate for cysts (M. mirabilis), total zooplankton (M. mirabilis, M. cavernosa), and non-copepod zooplankton (M. mirabilis). Zooplankton prey capture increased with prey concentration for M. mirabilis and M. cavernosa, over a broad range of concentrations, indicating that saturation of the feeding response had not occurred until prey density was over 10⁴ items m⁻³, a concentration at least an order of magnitude greater than the normal range of reef zooplankton concentrations. Location of cyst capture on coral surfaces was not uniform; for M. cavernosa, sides and tops of mounds captured most particles, and for P. porites, capture was greatest near branch tops, but was close to uniform for M. mirabilis branches in all flow conditions. The present study confirms laboratory flume results, and field results for other species, suggesting that many coral species experience particle flux and encounter rate limitations at low flow speeds, decreasing potential zooplankton capture rates. Received: 17 September 1996 / Accepted: 22 November 1997     

Pit structure and trophic relationship of the coral pit crab Cryptochirus coralliodytes

Individuals of the pit crabs Cryptochirus coralliodytes Heller inhabit massive corals of the family Faviidae. Their pit walls were observed to be covered by blue-green algae and fungi. We suggest that the crabs enhance the growth of these algae and fungi with their metabolic excretions, which contain ammonium. The endolithic algae and the fungi may facilitate the abrasion of the coral skeleton by the crabs, by perforating it and thus weakening the skeletal structure. Computerized tomography analysis revealed dense skeletal material around the pits. Transverse sections showed that the calcification around the pit was similar to other parts of the colony, whereas the macro-architecture was different. Such a difference is the result of the crabs' influence on the corals' living tissue, possibly on the calicoblast which deposits the coenosteum. Crabs, which were exposed to carbon-labeled corals for 1, 7 and 18 d, accumulated labeled carbon, indicating transfer of carbon from the coral tissue to the crabs. Histochemical examination of the stomach and gut of crabs revealed the presence of mucopolysaccharids in the gut, supporting the hypothesis that the crabs eat coral products. The findings of this study provide additional evidence that C. coralliodytes are parasites and support the general hypothesis that a nutritional relationship may have served as a basis for selection. Received: 20 October 1998 / Accepted: 29 April 1999     

Growth trajectories of corallites and ages of polyps in massive colonies of reef-building corals of the genus Porites

Massive colonies of the reef-building coral genus Porites were collected at inshore, midshelf and shelf-edge reefs in the central section of the Great Barrier Reef in November 1987. These colonies were comprised of 4 species: P. lobata, P. lutea, P. solida and P. mayeri. X-radiographs made of skeletal slices cut from the skeletons displayed the annual density-banding pattern characteristic of massive corals, and appeared to show corallites within each slice. The average age of the 36 colonies was 41±12 yr (mean±SD). The images of corallites displayed by the X-radiographs were not images of actual corallites, but approximated the position and size of actual corallites. Consequently, X-radiographs provide information about the formation and growth trajectories of corallites, and about the history of the polyps which deposited the corallites. Individual corallites were always normal to the growth surface. The growth surface of the colonies became bumpy when they reached 50 to 80 mm in height and, as a result, corallites took on a fan-shaped arrangement within a bump. New corallites were initiated at the summit of each bump and grew upwards and outwards. Thus, growth of colonies resulted in corallites becoming increasingly displaced from the summit of a bump. The X-radiographs showed that corallite growth becomes occluded at the bottom of valleys between adjacent bumps. Corallite growth then stops and the associated polyps are probably resorbed. Annual density banding showed that the average age of polyps in these colonies was 2 to 3 yr, average life expectancy 5 yr, and that no polyp was likely to be older than 8 yr. Small but significant variations in polyp longevity between corals from different reefs were probably associated with significant differences in bumpiness of growth surfaces. Even in Porites colonies which have been growing for several centuries, polyp longevity is likely to be 5 yr.     

Effects of temperature on photosynthesis and respiration in hermatypic corals

Photosynthesis and respiration rates of the reef corals Pocillopora damicornis (Linn.), Montipora verrucosa (Lamarck), Porites compressa Dana and Fungia scutaria Lamarck were measured under controlled temperatures. Results indicate that coral metabolism is closely adapted to ambient temperature conditions. Tropical corals measured at Enewetak, Marshall Islands, showed greater primary production compared to maintenance requirements at elevated temperatures than did subtropical varieties of the same species in Hawaii. Photosynthesis: respiration (P:R) ratios were significantly and negatively related with temperature between 18° and 31°C for all Hawaiian corals, whereas at Enewetak this ratio generally showed a curvilinear relationship for this temperature range. Extrapolations of P:R regressions on temperatures to a value of 2.0 (estimated as a minimum required for long-term functional autotrophy) coincide for Hawaiian specimens with published upper lethal temperatures. Extrapolation of P:R regressions for Enewetak specimens at temperatures above 25°C suggests lethal temperatures for these corals to be 2 to 5 C° higher than for Hawaiian corals, in good agreement with recent experimental findings. Interspecific differences in P:R temperature regressions for Hawaiian corals correlating with upper lethal temperature tolerances are described.Contribution No. 505 of the Hawaii Institute of Marine Biology.     

δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N values in reef corals <Emphasis Type="Italic">Porites lutea</Emphasis> and <Emphasis Type="Italic">P. cylindrica</Emphasis> and in their epilithic and endolithic algae

In summer 1998, shallow water corals at Sesoko Island, Japan (26°38′N, 127°52′E) were damaged by bleaching. In August 2003, partially damaged colonies of the massive Porites lutea and the branching P. cylindrica were collected at depths of 1.0–2.5 m. The species composition of epilithic algal communities on dead skeletal surfaces of the colonies (‘red turfs’, ‘green turfs’, ‘red crusts’) and the endolithic algae (living in coral skeletons) growing close to and away from living coral polyps was determined. Carbon and nitrogen stable isotope values of organic matter (δ¹³C and δ¹⁵N) from all six of these biological entities were determined. There were no significant differences in the isotope composition of coral tissues of the two corals, with P. lutea having δ¹³C of −15.3 to −9.6‰ and δ¹⁵N of 4.7–6.1‰ and P. cylindrica having similar values. Polyps in both species living close to an interface with epilithic algae had similar isotope values to polyps distant from such an interface. Despite differences in the relative abundance of the algal species in red turfs and crusts, their δ¹³C and δ¹⁵N values were not significantly different from each other (−18.2 to −13.9, −20.6 to −16.2, 1.1–4.3, and 3.3 to 4.9‰, respectively). The green algal turf had significantly higher δ¹³C values (−14.9 to −9.3‰) than that of red turfs and crusts but similar δ¹⁵N (1.2–4.1‰) to the red algae. The data do not suggest that adjoining associations of epilithic algae and coral polyps exchange carbon- and nitrogen-containing metabolites to a significant extent. The endolithic algae in the coral skeletons had δ¹³C values of −14.8 to −12.3‰ and δ¹⁵N of 4.0–5.4‰. Thus they did not differ significantly from the coral polyps in their carbon and nitrogen isotope values. The similarity in carbon isotope values between the coral polyps and endolithic algae may be attributed to a common source of CO₂ for zooxanthellae and endolithic algae, namely, from respiration by the coral host. While it is difficult to fully interpret similarity in the nitrogen isotope composition of coral tissue and of green endolithic algae and the difference in δ¹⁵N between green epilithic and endolithic algae, the data are consistent with nitrogen-containing metabolites from the scleractinian coral serving as a significant source of nitrogen for the endolithic algae.     

Depth limits of Bermudan scleractinian corals: a submersible survey

Depth distribution, zonation pattern and growth morphology of 17 hermatypic and 4 ahermatypic coral species were investigated at eight different locations along the Bermuda platform with the research submersible GEO and by SCUBA diving in August–September 1983. Hermatypic coral growth occurs to a depth of 50 to 70 m, with a single Montastrea cavernosa growing at 78 m. Dominant forms in shallow-water coral communities are Diploria sp. and Porites astreoides, while M. cavernosa, Agaricia fragilis and Scolymia cubensis occur in deep-water associations below 60 m. Vertical visibilities (up to 178 m) and distribution of the photosynthetically active radiation revealed good light penetration values (1% level at about 100 m depth), which should favour hermatypic coral growth to a much greater depth than it actually occurs. Nor should the prevailing temperatures limit the depth of coral growth. Most deep-water hermatypes observed grow on remnants of Pleistocene reefs down to about 60 m. The vast areas of large massed rhodolith nodules below 50 to 60 m are unsuitable bottom for coral colonisation. Macroalgae growth seems to be the strongest factor controlling coral growth in deep water. Bermuda stony corals have a low growth form diversity. Various intraspecific morphs may occur at the same as well as at different depths, with a general trend towards flatter shapes with depth. Comparison with a similar study on Red Sea corals suggests that annual distribution of radiant energy on the most northern Atlantic reefs of Bermuda may be responsible for the occurrence of flat and cuplike growth forms in relatively shallow water, and for the shallower depth limits of hermatypic growth.     

Experimental tests of suspension feeding in Atlantic reef corals

The ability of 15 species of Atlantic reef corals to act as suspension feeders was demonstrated by their removal of suspended particles from sea water in culture vessels. Mean clearance rates varied from 16.6 to 145.5 ml water cleared/h/cm² of live coral tissue. The lowest rates was found in Porites porites which is primarily a tentacle feeder, and the highest in Diploria clivosa which acts as both a tentacle feeder and suspension feeder. Rates of particle clearance in Agaricia agaricites, which is primarily a suspension feeder, were influenced by current velocity and type of food.     

Effect of elevated temperature on aerobic respiration of coral recruits

Metabolic rates provide a valuable means to assess the condition of early life stages of scleractinians, but their small biomass creates a signal-to-noise problem in a confined respirometer. To avoid this problem, measurements of the oxygen diffusion boundary layer (DBL) and Ficks first law were used to calculate the respiration rate of coenosarc tissue on recruits (i.e., colonies 5–14 mm diameter) of Porites lutea (Edwards and Haime, 1860) exposed to two temperatures at a flow speed of 0.6 cm s^–1. All experiments were completed in Moorea, French Polynesia, between November and December 2003. At 26.8°C, the DBL was 565±55 µm thick, the oxygen saturation adjacent to the tissue was 80±3%, and the mean respiration of the coenosarc was 1.2±0.1 µl O₂ cm^–2 h^–1 (all values mean ± SE, n=10). Exposure to 29.7°C for 24–48 h did not affect the DBL thickness but significantly reduced the oxygen saturation adjacent to the tissue (to 74%) and increased the mean respiration rate by 35%. As the small corals differed slightly in size, in a uniform flow speed they experienced dissimilar flow environments as characterized by the Reynolds number (Re), thereby creating the opportunity to test the flow dependency of respiration. At 26.8°C, respiration and Re were unrelated, but at 29.7°C, the relationship was positive and statistically significant. Thus, respiration of small corals may not be mass transfer limited at low temperature, but relatively small increases in temperature may result in an increased metabolic rate leading to mass transfer limitation and flow-dependent rates of respiration.Communicated by J.P. Grassle, New Brunswick     

Light harvesting in the green alga Ostreobium sp., a coral symbiont adapted to extreme shade

Ostreobium sp. (Chlorophyta: Siphonales) can be found as green bands within the skeletal material of a number of stony corals in the Indo-Pacific and Caribbean regions. Many of these corals also contain symbiotic dinoflagellates in the overlaying coral polyps that effectively screen out all the typical photosynthetically active radiation from the algae in the green bands below. Ostreobium sp., nevertheless, grows photosynthetically. Its action spectrum and absorption spectrum have been shown to extend much further into the near infra-red compared to other green algae. In the present study, carried out in 1987, fluorescence excitation and emission spectra were measured in Ostreobium sp. and compared to spectra obtained from the green alga Ulva sp. and the brown alga Endarachne sp. Xanthophylls, probably siphonein and an unidentified xanthophyll probably related to siphonaxanthin, are photosynthetically active in Ostreobium sp., and can sensitize Photosystem II fluorescence at 688 nm and Photosystem I (PS I) fluorescence at 718 nm. The fluorescence emission spectra of Ostreobium sp. measured at 25° C and 77 K were not remarkably different from those of the green alga Ulva sp. Absorbance changes induced by light were measured in Ostreobium sp. from 670 to 750 nm and were like those normally seen in green plants except that, in addition to the minimum expected for the reaction-center chlorophyll of PS I (P700) at 703 nm, another minimum was seen at 730 nm. It is possible that this spectrumreflects the functioning of a reaction center of Photosystem I that has adapted to function in light highly enriched in far-red wavelengths.CIW-DPB Publication No. 1021     

Monthly skeletal extension rates of the hermatypic corals<Emphasis Type="Italic"> Montastraea annularis</Emphasis> and<Emphasis Type="Italic"> Montastraea faveolata</Emphasis>: biological and environmental controls

Monthly skeletal extension rates were measured in colonies of Montastraea annularis and M. faveolata growing at Mahahual and Chinchorro Bank, in the Mexican Caribbean. Temperature, light extinction coefficient (k_d), sedimentation rate, dissolved nutrients and wave energy were used as indicators of environmental conditions for coral growth. Zooxanthella density and mitotic index, nitrogen, phosphorous and protein in coral tissue, and living tissue thickness were measured during periods of high-density-band (HDB) and low-density-band (LDB) formation. To test their value as indirect measures of competition between zooxanthellae and host, as well as coral health and performance in both species, these biological parameters were also measured, during the HDB-formation period, in corals collected at La Blanquilla. This reef is located in the Gulf of Mexico, in an area of suboptimal environmental conditions for coral growth. M. faveolata had a significantly higher skeletal extension rate than M. annularis. Corals growing in Mahahual had significantly higher skeletal extension rate than those living in Chinchorro Bank. This is consistent with inshore–offshore gradients in growth rates observed by other authors in the same and other coral species. This is probably due to less favorable environmental conditions for coral growth in near shore Mahahual, where there is high hydraulic energy and high sedimentation rate. Contrary to observations of other authors, skeletal extension rate did not differ significantly between HDB- and LDB-formation periods for both species of Montastraea. Both species produced their HDB between July and September, when the seawater temperatures are seasonally higher in the Mexican Caribbean. Tissue thickness indicated that environmental conditions are more favorable for coral health and performance during the HDB-formation period. Mitotic index data support the idea that zooxanthellae have competitive advantages for carbon over the host during the LDB-formation period. So, corals, during the LDB-formation period, with less favorable environmental conditions for coral performance and at a disadvantage for carbon with zooxanthellae, add new skeleton with little or no opportunity for thickening the existing one. This results in an equally extended skeleton with lower density, and the stretching response of skeletal growth, proposed for M. annularis growing under harsher environmental conditions, also occurs during the LDB-formation period.Communicated by P.W. Sammarco, Chauvin