Densities Of Zooxanthellae Research Articles

Phototrophic potential and form II ribulose-1,5-bisphosphate carboxylase/oxygenase expression in five organs of the fluted giant clam, Tridacna squamosa

Despite living in oligotrophic tropical waters, giant clams can grow to large sizes because they live in symbiosis with extracellular phototrophic dinoflagellates (zooxanthellae) and receive photosynthates from them. The physical presence of zooxanthellae in five organs (colorful outer mantle, whitish inner mantle, ctenidium, hepatopancreas and foot muscle) of Tridacna squamosa had been confirmed by microscopy, and high densities of zooxanthellae were detected in specific regions of the inner mantle and foot muscle. Symbiotic dinoflagellates use form II ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) to fix inorganic carbon during C3 photosynthesis. Using qPCR primers that were designed comprehensively against all known zooxanthellal form II RuBisCO gene sequences (rbcII) in existing databases, we demonstrated that the outer mantle of T. squamosa (TS) had the greatest phototrophic potential as reflected by its high zooxanthellal rbcII (TSZrbcII) transcript level, which varied among different regions of the outer mantle. The other four organs also expressed moderate levels of TSZrbcII, despite the lack of iridophores and direct light exposure. Importantly, light exposure led to significant increases in the protein abundance of TSZRBCII in the outer mantle but not the other four organs. Taken together, these results indicate that organs inside the mantle cavity had low phototrophic potentials, but zooxanthellae residing inside these organs might serve some unidentified functions to benefit the host.

A study on bacteria associated with three hard coral species from Ninh Thuan waters by epifluorescence and most diluted culture method

Coral associated bacteria and their host are currently one of the interested issues for research and scientists worldwide. The densities of zooxanthellae and bacteria associated with three most prevalent species Acropora hyacinthus, Acropora muricata and Acropora robusta in Hang Rai, Ninh Thuan was evaluated over time by staining with SYBR Gold and direct counting with epifluorescence method. The most dominant bacteria were isolated by culture dependent method. The densities of zooxanthellae and bacteria ranged from 0.39–1.83×107 cell/g, and 0.83–2.52×108 cell/g, respectively. Bacterial density in the 3 months was significantly different compared to the density of the bacteria in ambient water. Total heterotrophic bacteria, comma shaped bacteria and bacillus form showed negatively correlated with pH, PO4, while zooxanthellae showed no correlation with all factors.

Loss of zooxanthellae in a coral under high seawater temperature and nutrient enrichment

To investigate the effect of nutrient concentrations on coral–algal symbiosis under thermal stress, the abundance and release of zooxanthellae in the coral Acropora tenuis were quantified under laboratory conditions. The coral fragments were first cultured in either low-nutrient (LN) or high-nutrient (HN) seawater condition at 27°C for 25days and the seawater temperature was then elevated and kept at 31°C for 1week for both nutrient conditions. Nutrient enrichment at 27°C increased the densities of symbiotic algae and chlorophyll a and the algal release rates (AR) from the host coral to the ambient seawater. The percentage of algal release rate to the standing stock (AR%) was approximately 0.015%h−1 for both nutrient conditions at 27°C. After the seawater temperature was elevated to 31°C, the densities of zooxanthellae in the corals decreased by 21–61%, and AR and AR% increased. The corals in HN lost more zooxanthellae per unit surface area than those in LN, but the lost percentages were not significantly different between LN and HN. AR% was also not significantly different between LN and HN at 31°C. These results indicated that the percentage rate of symbiotic algal loss was not affected by the nutrient condition, implying that nutrient incorporation itself would not accelerate coral bleaching susceptibility.

A comparison of two methods of obtaining densities of zooxanthellae in Acropora millepora

Galaxea, Journal of Coral Reef Studies 13: 29-34(2011) Abstract Quantifi cation of zooxanthellae densities in tissues of reef-building corals aids in the assessment of the extent and severity of coral bleaching. Various meth- ods are available to quantify zooxanthellae densities; how ever, a direct comparison of these techniques has yet to been done. Here, we compare estimates of zooxanthellae densities obtained using conventional airbrushing coupled with post-tissue-blasting surface area determination, ver- sus a technique whereby zooxanthellae densities are quantifi ed from a known area (0.25 cm 2 ) of tissue after corals have been fi xed and decalcifi ed. Estimates of zoo- xanthellae densities obtained were correlated across re- plicate colonies (R 2 =0.40, n=81), and both techniques revealed similar patterns of variation among locations. The main benefi t of the decalcifi cation technique was reduced processing time, because the technique eliminates the time-consuming process of tissue blasting and re- trospective estimates of surface area. We estimate that decalcifi cation halves the processing time per sample, and produces a more accurate estimate of zooxanthellae density.

A comparison of the thermal bleaching responses of the zoanthid Palythoa caribaeorum from three geographically different regions in south Florida

Coral bleaching involves the loss of symbiotic algae (zooxanthellae) from reef corals and other cnidarians during periods of environmental stress, particularly elevated temperature. In this study we compared the thermal bleaching responses of the zoanthid Palythoa caribaeorum from three populations along the southeast coast of Florida. Winter (2002–2003) and summer (2003) samples from three geographically separate sites were experimentally exposed to increased temperatures and the loss of zooxanthellae was measured. Population densities of zooxanthellae were analyzed and their genetic identity determined using PCR-DGGE analysis of the internal transcribed spacer region 2. The results showed that samples of P. caribaeorum from reefs that experienced the smallest range in annual seawater temperature released the most zooxanthellae. Seasonal comparisons revealed that winter samples lost more zooxanthellae than summer samples. P. caribaeorum harbored two genetic types of zooxanthellae, C1 and D1a. Individual colonies contained populations of only C1 or D1a, or combinations of C1 and D1a. However, these genotypic patterns did not relate latitudinal distribution nor to differences in experimental thermal tolerance.

Interspecific comparison of the symbiotic relationship in corals with high and low rates of bleaching-induced mortality

Some coral species are more resistant than others to environmental factors that cause bleaching and bleaching-related mortality. This study compared aspects of the coral/zooxanthellae symbiosis in species and genera that suffered either high or low mortality during a bleaching event. These characteristics were assessed in Okinawa between March and June 1999, 5–10 months after the bleaching event there in August–September 1998. Species with low mortality rates generally had higher densities of zooxanthellae per square centimeter and a very low rate of release of degraded zooxanthellae. Low-mortality species also had more total coral tissue per square centimeter of coral surface area. The size of zooxanthellae varied little among species. The differences in these characteristics among coral species suggest that the symbiotic relationship operates very differently among coral species.

Host-symbiont specificity during onset of symbiosis between the dinoflagellates Symbiodinium spp. and planula larvae of the scleractinian coral Fungia scutaria

Many corals which engage in symbioses with dinoflagellates from the genus Symbiodinium (zooxanthellae) produce offspring which initially lack zooxanthellae. These species must choose their symbionts from numerous genetically distinct strains of zooxanthellae co-occurring in the environment. In most cases, symbiosis onset results in an association between a specific host coral and a specific strain of algal symbiont. This is the first study to examine host-symbiont specificity during symbiosis onset in a larval cnidarian, and the first to examine such events in a scleractinian of any life stage. We infected planula larvae of the solitary Hawaiian scleractinian Fungia scutaria with both homologous zooxanthellae, freshly isolated from F. scutaria adults, and heterologous zooxanthellae, isolated from Montipora verrucosa, Porites compressa, and Pocillopora damicornis, three species of scleractinians which co-occur with F. scutaria. We found that homologous zooxanthellae were better able to establish symbioses with larval hosts than were heterologous isolates, by two separate measures: percent of a larval population infected, and densities of zooxanthellae per larva. We also measured algal densities in larvae over a 4-day period until the onset of settlement and metamorphosis. We found no changes in zooxanthella population densities, regardless of zooxanthella type or the light environment in which they were incubated. Strong infection of host larvae with homologous algae compared to heterologous algae suggests that there is a specificity process which occurs sometime during the early stages of infection between the partners, and which results in the establishment of a specific symbiosis.

Dimethylsulfoniopropionate in giant clams (Tridacnidae).

The tridacnid clams maintain symbiotic associations with certain dinoflagellates (termed zooxanthellae). Tridacnids are thus candidates to have high tissue concentrations of dimethylsulfoniopropionate (DMSP), a tertiary sulfonium compound that is not synthesized by animals but is commonly produced by dinoflagellates. This study establishes that DMSP is about an order of magnitude more concentrated in the light-exposed and shaded mantle and gills of Tridacna maxima and T. squamosa than in any other known animal tissues. The DMSP concentration in the light-exposed, siphonal mantle--the location of most zooxanthellae--is an inverse function of body size, paralleling an inverse relation between apparent density of zooxanthellae (measured as pheophytin concentration) and body size. The shaded mantle and gills are high in DMSP despite having low densities of zooxanthellae, indicating that high DMSP concentrations occur in molluscan tissue, not just in algal cells. DMSP is almost an order of magnitude less concentrated in the adductor muscle than in other tissues. The high DMSP concentrations found in tridacnids, by providing abundant substrate for formation of volatile dimethylsulfide, probably explain the peculiar tendency of tridacnids to rapidly develop offensive odors and tastes after death: a serious problem for their exploitation as food. Tridacnids are the one group of animals in which DMSP concentrations are high enough in some tissues to be in the range capable of perturbing enzyme function at high physiological temperatures. Thus, tridacnids may require enzyme forms adapted to DMSP.

Cellular growth of host and symbiont in a cnidarian-zooxanthellar symbiosis.

The hydroid Myrionema ambionense, a fast-growing cnidarian (doubling time = 8 days) found in shallow water on tropical back-reefs, lives in symbiosis with symbiotic dinoflagellates of the genus Symbiodinium (hereafter also referred to as zooxanthellae). The symbionts live in vacuoles near the base of host digestive cells, whereas unhealthy looking zooxanthellae are generally located closer to the apical end of the host cell. Cytokinesis of zooxanthellae occurred at night, with a peak in number of symbionts with division furrows (mitotic index, MI = 12%-20%) observed at dawn. The MI of zooxanthellae decreased to near zero by the middle of the afternoon and remained there until the middle of the next night. Densities of live zooxanthellae living inside of host digestive cells peaked following cytokinesis, whereas densities of unhealthy looking symbionts were highest just before the division peak. Mitosis of host digestive cells was highest in the evening, also preceding the peak in zooxanthellar MI. This is the first study relating phased host cell division to diel zooxanthellar division in marine cnidarians. Food vacuoles were prevalent inside of digestive cells of field-collected hydroids within a few hours after sunset and throughout the night, coinciding with digestion of captured demersal plankton. Laboratory experiments showed that food vacuoles appeared in digestive cell cytoplasm within 2 h of feeding with nauplii of Artemia. The number and size of food vacuoles per digestive cell and the percentage of digestive cells with food vacuoles all decreased 5-7 h following feeding in laboratory experiments, and by mid-day in field-collected hydroids. Light and external food supply were important in maintaining phased division of the symbionts, with a lag in response time to both parameters of 11-36 h. Altering light and feeding during the night did not influence the level of the peak MI the next morning, though in one experiment the absence of light slowed final separation of daughter cells at the end of cytokinesis. In another experiment, hydroids starved for 3-7 d and "pulse-fed" Artemia nauplii for 1 h at the beginning of the dark period showed continued low symbiont division (< 5%) after 11 h, whether maintained in constant light or darkness, implying that most algal division is set more than 24 h prior to actual cytokinesis. Transferred to a 14:10 h light:dark cycle for another 24 h (36 h after feeding), the same hydroids exhibited a "normal" peak MI (ca. 15%) at dawn, but zooxanthellae from hydroids kept in constant darkness still showed a low MI. These results show that mitosis of symbiotic dinoflagellates requires three factors: external food; a minimum period of time following feeding (11-36 h), presumably for digestion; and a period of light following feeding, presumably to provide carbon skeletons necessary for completing cytokinesis.

Ultraviolet‐B radiation stimulates shikimate pathway‐dependent accumulation of mycosporine‐like amino acids in the coral Stylophora pistillata despite decreases in its population of symbiotic dinoflagellates

Colonies of Stylophora pistillata maintained for four years in indoor aquaria in the near absence of ultraviolet radiation (UVR) contained only small amounts (&lt;5 nmol mg−1 protein) of 10 identified mycosporine‐like amino acids (MAAs, which act as UV sunscreens), the largest number reported in any organism. The concentrations of most MAAs increased linearly or exponentially when colonies were exposed to ultraviolet‐A (UVA) and ultraviolet‐B (UVB) for 8 h d−1 in the presence of photosynthetically active radiation (PAR). Total MAA concentration reached 174 nmol mg−1 protein after 30 d, with palythine and mycosporine−2 glycine constituting more than half of the final total. UVB specifically stimulated MAA accumulation: after 15 d, MAA levels in colonies exposed to PAR alone and to PAR and UVA did not differ (7 and 5 nmol MAA mg−1 protein, respectively), while those in colonies exposed to PAR and UVA + UVB were significantly higher (28 nmol mg−1 protein). Glyphosate, an inhibitor of the shikimate pathway, eliminated or reduced the UV‐induced accumulation of most MAAs during 7 d of exposure, providing the first experimental evidence of their synthesis via this pathway in a coral symbiosis. Densities of zooxanthellae in colonies of S. pistillata, Acropora sp., and Seriatopora hystrix exposed to UVR for 15 d were only one‐third of those in control colonies unexposed to UVR. This net decrease in the number of zooxanthellae in the corals (bleaching) occurred despite UV stimulated increases in algal cytokinesis and in the host cell‐specific density of zooxanthellae in hospite, increases that apparently destabilized the symbiosis and caused expulsion of the zooxanthellae.

Translocation of Photosynthetic Carbon From Two Algal Symbionts to the Sea Anemone Anthopleura elegantissima.

The intertidal sea anemone Anthopleura elegantissima contains two symbiotic algae, zoochlorellae and zooxanthellae, in the Northern Puget Sound region. Possible nutritional advantages to hosting one algal symbiont over the other were explored by comparing the photosynthetic and carbon translocation rates of both symbionts under different environmental conditions. Each alga translocated 30% of photosynthetically fixed carbon in freshly collected anemones, although zoochlorellae fixed and translocated less carbon than zooxanthellae. The total amount of carbon translocated to the host was equivalent because densities of zoochlorellae were two to three times greater than were densities of zooxanthellae. In A. elegantissima maintained under high and low irradiance (100 and 10 {mu}mol photons/m2/s) at 20{deg}C and 13{deg}C for 21 days, both algae fixed and translocated carbon at greater rates at 20{deg}C (translocation rates: 0.38 pg C /zoochlorella/h; 1.12 pg C /zooxanthella/h) than at 13{deg}C (translocation rates: 0.06 pg C /zoochlorella/h; 0.37 pg C /zooxanthella/h). However, zoochlorellate anemones received 3.5 times less carbon at 20{deg}C than at 13{deg}C because the higher temperature caused a significant reduction in the density of zoochlorellae. Environmental variables, like temperature, that influence the densities of the two symbionts will affect their relative nutritional contribution to the host. Whether these differences in carbon translocation rates of the two algal symbionts affect the ecology of their anemone host awaits further investigation.

Uptake and Persistence of Homologous and Heterologous Zooxanthellae in the Temperate Sea Anemone Cereus pedunculatus (Pennant).

The uptake and persistence of symbiotic dinoflagellates (zooxanthellae) were measured in the temperate sea anemone Cereus pedunculatus (Pennant). Aposymbiotic specimens of C. pedunculatus were inoculated with zooxanthellae freshly isolated from a range of temperate and subtropical Anthozoa. Each inoculate consisted of zooxanthellae from a single host species and was either homologous (zooxanthellae from a host of the same species as the one being inoculated) or heterologous (from a host of a different species than the one being inoculated). The densities of zooxanthellae in host tissues were determined at regular intervals. C. pedunculatus took up homologous and heterologous zooxanthellae to similar degrees, except for zooxanthellae from the temperate Anthopleura ballii, which were taken up to a lesser extent. The densities of all zooxanthellae declined between 4 hours and 4 days after uptake, indicating that zooxanthellae were expelled, digested, or both during this period. The densities of all zooxanthellae increased between 2 and 8 weeks after inoculation, indicating zooxanthella growth. Over the entire 8-week period after uptake, densities of homologous zooxanthellae were always greater than those of heterologous zooxanthellae. Between 8 and 36 weeks after infection, densities of homologous zooxanthellae declined markedly and densities of some heterologous zooxanthellae increased further, resulting in homologous and heterologous zooxanthella densities being the same at 36 weeks. These densities were the same as those in naturally infected C. pedunculatus of similar size. The results suggest that zooxanthellae from a range of host species and environments can establish symbioses with C. pedunculatus and that, over long periods under laboratory conditions, heterologous zooxanthellae may populate C. pedunculatus to the same extent as homologous zooxanthellae.

Zooxanthellae loss as a bioassay for assessing stress in corals

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 149:163-171 (1997) - doi:10.3354/meps149163 Zooxanthellae loss as a bioassay for assessing stress in corals Jones RJ Branch tips from colonies of a staghorn coral Acropora formosa were exposed to elevated concentrations of copper in order to examine the potential of the 'bleaching' response as a means of assessing stress in corals. Two identical toxicity tests were conducted over 48 h using 2 colonies with naturally different algal (zooxanthellae) densities. The tips from both colonies bleached in proportion to the copper concentrations, through loss of zooxanthellae to the surrounding water. A higher incidence of mortality was observed in tips from the colony with fewer zooxanthellae. During the tests, control corals lost zooxanthellae at a rate of <1% of the algal standing stock d-1, zooxanthellae release from both control and experimental corals occurred 2x faster during the daytime than night time, and the number of zooxanthellae appearing as doublets (the mitotic index) was 5 to 8x higher in zooxanthellae released from the corals' tips than inside the tips (in hospite)at the end of the experiment. The implications of these findings for future toxicity tests using the bleaching response, and for using changes in the number of zooxanthellae appearing as doublets to assess stress are discussed. Results suggest (1) that loss of zooxanthellae can be used within the framework of a standardised laboratory-based bioassay with universal integrity for assessing stress in zooxanthellate corals, and (2) that inherent differences in the densities of zooxanthellae between coral colonies are likely to affect the outcome of experiments using the bleaching response and of other biochemical or physiological stress responses. Bleaching · Copper · Stress assessment · Zooxanthellae · Acropora formosa Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 149. Publication date: April 10, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Periodic mass-bleaching and elevated sea temperatures:bleaching of outer reef slope communities in Moorea, French Polynesia

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 121:181-190 (1995) - doi:10.3354/meps121181 Periodic mass-bleaching and elevated sea temperatures: bleaching of outer reef slope communities in Moorea, French Polynesia Hoegh-Guldberg O, Salvat B Mass-bleaching events (in which corals and other symbiotic invertebrates lose their zooxanthellae) have been occurring every 3 to 4 yr since 1979. The last report of widespread mass-bleaching in the Pacific (which included bleaching around French Polynesia) was in February-April 1991. This paper reports on mass-bleaching along the outer reef slope of Moorea, French Polynesia, in April 1994. Mass-bleaching was extensive at all sites visited, with corals being bleached down to 25 m. Colour loss by corals was due to low areal densities of zooxanthellae and the percentage of live coral affected ranged between 39.6 (+/- 7.12, SEM) (NW sites) and 72.4 (+/- 7.11, SEM) (NE sites). Bleaching also varied as a function of depth and included a wide range of species. Acropora spp. showed the most severe bleaching (89.0 to 100% of all colonies completely bleached) and Porites spp. showed the least amount of bleaching (12.9 to 42.5% of all colonies partly bleached). Pocillopora spp. showed intermediate bleaching (73.9 to 92.1% of all colonies either partly or completely bleached). The results of this report indicate that current bleaching is on a scale equal to that of the 1991 bleaching event. Temperatures recorded hourly at 14 m off the outer reef slope from July 1991 to August 1994 (and those from satellite sea surface temperature readings) indicate unusually warm sea temperatures in March 1994, which were approximately 1.0*C higher than the highest temperatures recorded in 1992 and 1993, years in which bleaching on a massive scale did not occur. The appearance of warmer temperatures preceded the onset of bleaching by 2 to 3 wk, which strongly confirms the hypothesis that positive thermal anomalies are responsible for recent bleaching events in the Central and Western Pacific. Coral . Mass-bleaching . Zooxanthellae . Temperature . Stress . Moorea . Tahiti . French Polynesia Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 121. Publication date: May 25, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Recovery of the coral Montastrea annularis in the Florida Keys after the 1987 Caribbean ?bleaching event?

Many reef-building corals and other cnidarians lost photosynthetic pigments and symbiotic algae (zooxanthellae) during the coral bleaching event in the Caribbean in 1987. The Florida Reef Tract included some of the first documented cases, with widespread bleaching of the massive coral Montastrea annularis beginning in late August. Phototransects at Carysfort Reef showed discoloration of >90% of colonies of this species in March 1988 compared to 0% in July 1986; however no mortality was observed between 1986 and 1988. Samples of corals collected in February and June 1988 had zooxanthellae densities ranging from 0.1 in the most lightly colored corals, to 1.6x106 cells/cm2 in the darker corals. Minimum densities increased to 0.5x106 cells/cm2 by August 1989. Chlorophyll-a content of zooxanthellae and zooxanthellar mitotic indices were significantly higher in corals with lower densities of zooxanthellae, suggesting that zooxanthellar at low densities may be more nutrientsufficient than those in unbleached corals. Ash-free dry weight of coral tissue was positively correlated with zooxanthellae density at all sample times and was significantly lower in June 1988 compared to August 1989. Proteins and lipids per cm2 were significantly higher in August 1989 than in February or June, 1988. Although recovery of zooxanthellae density and coral pigmentation to normal levels may occur in less than one year, regrowth of tissue biomass and energy stores lost during the period of low symbiont densities may take significantly longer.

Photosynthesis and Retention of Zooxanthellae and Zoochlorellae Within the Aeolid Nudibranch Aeolidia papillosa.

Both zooxanthellae and zoochlorellae are found in the cerata of Aeolidia papillosa after it has ingested symbiotic Anthopleura elegantissima containing these algae. High rates of photosynthesis were found in algae present in the cerata and in algae isolated from nudibranch feces. For algal cells present in the cerata of nudibranchs collected in June 1991, carbon fixation by zooxanthellae (1.18 +/- 0.36 pg C/cell/h) was significantly greater than carbon fixation by zoochlorellae (0.55 +/- 0.32 pg C/cell/h). Algal densities within the cerata of laboratory fed nudibranchs were significantly greater for zoochlorellae (175 +/- 82 cells/μg protein, light treatment; 131 +/- 106 cells/μg protein, dark treatment) than for zooxanthellae (38 +/- 18 cells/μg protein, light; 53 +/- 30 cells/ μg protein, dark). Ceratal densities of zooxanthellae (16 +/- 8 cells/μg protein) in the field during January 1992 were low in comparison to ceratal densities in the laboratory--several of the nudibranchs in the field lacked any symbiotic algae, and zoochlorellae were always absent. Nudibranch algal densities were not stable and dropped rapidly if the nudibranchs were starved. Both zoochlorella and zooxanthella densities dropped to 0 cells/μg protein within 11 days of starvation. While these results show that the relationship between A. papillosa and the two algae is not a stable symbiosis, the photosynthetic activity of the algae in the cerata suggests that the nudibranch and/or the algae may benefit from the association while it lasts.

The effects of prolonged ?bleaching? on the tissue biomass and reproduction of the reef coral Montastrea annularis

Colonies of Montastrea annularis from Carysfort Reef, Florida, that remained bleached seven months after the 1987 Caribbean bleaching event were studied to determine the long term effects of bleaching on coral physiology. Two types of bleached colonies were found: colonies with low numbers of zooxanthellae with normal pigment content, and a colony with high densities of lowpigment zooxanthellae. In both types, the zooxanthellae had an abnormal distribution within polyp tissues: highest densities were observed in basal endoderm and in mesenteries where zooxanthellae are not normally found. Bleached corals had 30% less tissue carbon and 44% less tissue nitrogen biomass per skeletal surface area, but the same tissue C:N ratio as other colonies that either did not bleach (normal) or that bleached and regained their zooxanthellae (recovered). Bleached corals were not able to complete gametogenesis during the reproductive season following the bleaching, while recovered corals were able to follow a normal gametogenic cycle. It appears that bleached corals were able to survive the prolonged period without nutritional contribution from their zooxanthellae by consuming their own structural materials for maintenance, but then, did not have the resources necessary for reproduction. The recovered corals, on the other hand, must have regained their zooxanthellae soon after the bleaching event since neither their tissue biomass nor their ability to reproduce were impaired.

The effect of sudden changes in temperature, light and salinity on the population density and export of zooxanthellae from the reef corals Stylophora pistillata Esper and Seriatopora hystrix Dana

Bleaching (loss of pigmentation by corals) is a widespread phenomenon in coral-reef ecosystems. Despite this, the underlying causes of some forms of bleaching are poorly understood. This study explores the conditions that induce bleaching in two species of reef coral-zooxanthellae associations from Lizard Island, Great Barrier Reef, Australia. Naturally bleached Stylophora pistillata Esper and Seriatopora hystrix Dana, collected from the edge of Lizard Island lagoon, had the same amount of Chl a · zooxanthellae −1, yet had reduced population densities of zooxanthellae when compared to normal-looking colonies. In this case, the lack of pigment in the bleached corals was explained by low numbers of zooxanthellae and not by pale zooxanthellae. This is contrary to results obtained by some other workers and suggests that closer inspection of the underlying reasons for the pale color of bleached corals is warranted. In laboratory experiments, sudden exposures to full sunlight induced the bleaching of S. pistillata previously grown at 25% sunlight. The pale color of colonies exposed to full sunlight was explained by the low pigment content of the zooxanthellae rather than by low population densities of zooxanthellae. In addition, the specific expulsion rate of zooxanthellae from S. Pistillata and S. hystrix was not influenced by sudden increases in solar irradiance. Sudden exposures to reduced salinities (30%.) did not affect S. Pistillata or S. hystrix in this study. Both species bleached rapidly, however, when exposed to water temperatures of > 30 °C. Bleached corals in this case had reduced population densities of zooxanthellae despite normal zooxanthella pigment contents. The specific expulsion rate of zooxanthellae from both species of coral was very sensitive to temperature. 7-h exposures to 30 and 32 °C resulted in specific expulsion rates of > 1000 times that of controls. Specific expulsion rates remained high, even when corals were returned to control temperatures (27 °C). After high temperature stress, S. Pistillata and S. hystrix had high and sustained colony respiratory rates ( r c ), reduced colony photosynthetic rates ( p c net max ) and reduced P c g max : r c ratios. The O 2 metabolism of the S. pistillata and S. hystrix symbioses remained abnormal for up to 4 days after a 7-h exposure to 32 °C. Evidence suggestive of recovery was apparent 19 days later. By this time, the mean population density of zooxanthellae and p c g max : r c ratios of exposed fragments had returned to normal.

Seasonal variation in light-shade adaptation of natural populations of the symbiotic sea anemone Aiptasiapulchella (Carlgren, 1943) in Hawaii

The productivity and biomass parameters of the symbiotic anemone Aiptasia pulchella (Carlgren, 1943) from a shaded mangrove lagoon (maximum summer irradiance of 100 μE m −2 · s −1) and a sunlit reef flat (maximum summer irradiance of 1400 μE · m −2 · s −1) were examined in Hawaii. Light-shade adaptation was evident in the summer populations (1981) but not observed during the fall (1982). In the summer, zooxanthellae from the lagoon A. pulchella (shade anemones) contained 2.97 pg Chl a cell −1 and those from the reef flat (sun anemones) contained 1.70 pg Chl a · cell −1; but Chl a : c 2 ratios were 2.5 in zooxanthellae from both shade and sun anemones. During the fall, there were no significant differences in Chl a and c 2 of zooxanthellae (2.25 pg Chl a · cell −1) in shade and sun anemones, but Chl a : c 2 ratios averaged 3.9. During both seasons, shade anemones were larger and contained higher densities of zooxanthellae than sun anemones. In addition to differences between shade and sun habitats, there was localized photoadaptation of zooxanthellae within individual anemones due to microhabitat variations in ambient irradiance. Growth rates of zooxanthellae in A. pulchella differed in shade and sun anemones. Specific growth rates for zooxanthellae in situ were the same for shade populations in both summer and fall (0.016 day −1). However, zooxanthellae in sun anemones grew four times faster in the fall (0.033 day −1) than during the summer (0.008 day −1). These results suggest that growth of zooxanthellae in these anemones was independent of ambient irradiance. Photosynthesis-irradiance ( P- I) responses of shade and sun anemones during the summer showed that shade anemones had greater photosynthetic efficiencies (α) but lower photosynthetic capacities ( P max) than sun anemones. Dark-respiration rates of sun anemones were twice those obtained with shade anemones. In the fall, these populations of anemones did not exhibit P- I responses characteristic of light-shade adaptation. Both α and P max of shade and sun anemones were higher in the fall, indicating that zooxanthellae in A. pulchella adapted to seasonal reduction in irradiance.

Errata

Proc. R. Soc. Loud . B 228, 493-509 (1986) Studies on a nudibranch that contains zooxanthellae. I. Photosynthesis, respira­tion and the translocation of newly fixed carbon by zooxanthellae in Pteraeolidia ianthina By O. Hoegh-Guldberg and Rosalind Hinde Page 502, ordinate of figure 5: for R /(pg per cell h -1 ) read R /(gC mg -1 protein h -1 ). Proc. R. Soc. Lond . B 228, 511-521 (1986) Studies on a nudibranch that contains zooxanthellae. II. Contribution of zooxan­thellae to animal respiration (CZAR) in Pteraeolidia ianthina with high and low densities of zooxanthellae By O. Hoegh-Guldberg, Rosalind Hinde and L. Muscatine Page 514, legend to figure 1: for Diameters read Volumes. Page 518, table 3, fourth row of third column: for 0.80 read 12.28.