Effect of feeding regime and irradiance on the photophysiology of the symbiotic sea anemone Aiptasia pulchella

To determine how the animal and algal components of the symbiotic sea anemone Aiptasia pulchella respond to changes in food availability and culture irradiance, sea anemones from a single clone were maintained at four irradiance levels (320, 185, 115, and 45 E m^-2 s^-1) and either starved or fed for 5 wk. Changes in protein biomass of sea anemones maintained under these conditions were not related to the productivity of zooxanthellae, since the protein biomass of fed A. pulchella decreased with increase in irradiance and there was no difference in protein biomass among starved sea anemones at the four irradiance levels. Except for the starved high-light sea anemones, the density of symbiotic zooxanthellae was independent of culture irradiance within both starved and fed. A. pulchella. Starved sea anemones contained over twice the density of zooxanthellae as fed sea anemones. Within both starved and fed individuals, chlorophyll per zooxanthella increased with decreasing culture irradiance while algal size remained constant (in fed sea anemones) at about 8.80 m diameter. Chlorophyll a: c ₂ ratios of zooxanthellae increased with decreasing culture irradiance in zooxanthellae from starved sea anemones but remained constant in zooxanthellae from fed sea anemones. As estimated from mitotic index data, the in situ growth rates of zooxanthellae averaged 0.007 d^-1 and did not vary with irradiance or feeding regime. Photosynthesis-irradiance (P-I) responses of fed A. pulchella indicated an increase in photosynthetic efficiency with decreasing culture irradiance. But there was no consistent pattern in photosynthetic capacity with culture irradiance. Respiration rates of fed sea anemones also did not vary in relation to culture irradiance. The parameter I _k , defined as the irradiance at which light-saturated rates of photosynthesis are first attained, was the only parameter from the P-I curves which increased linearly with increasing culture irradiance. The daily ratio of net photosynthesis to respiration for A. pulchella ranged from 1.6 to 2.8 for sea anemones maintained at the three higher irradiances, but was negative for those maintained at 45 E m^-2 s^-1. Since the final protein biomass was greatest for sea anemones maintained at the lowest irradiance, these results indicate that sea anemone growth cannot be directly related to productivity of zooxanthellae in this symbiotic association.     

Effects of ambient levels of solar ultraviolet radiation on zooxanthellae and photosynthesis of the reef coral Montipora verrucosa

Paired flat plates of the hermatypic coral Montipora verrucosa from Kaneohe Bay, Oahu, Hawaii, were acclimated to photosynthetically active radiation (PAR) only and to full sunlight (PAR+UV) for several weeks in the summer of 1990. After the acclimation period, photosynthesis, both in PAR-only and PAR+UV as well as dark respiration were measured. Levels of the UV-absorbing compounds, S320, density of zooxanthellae, and chlorophyll a concentration were determined. Corals acclimated in PAR+UV had higher levels of the UV-protective compounds and lower areal zooxanthellae densities than corals acclimated in PAR-only. Chlorophyll a per unit volume of coral host and per algal cell did not differ between corals from the two acclimation treatments. Corals acclimated to PAR+UV displayed higher photosynthesis in full sunlight than corals acclimated to PAR-only, but when photosynthesis was measured in the light regime to which the corals had been acclimated, there were no differences in photosynthesis. Dark respiration was the same for corals from the two acclimation treatments regardless of the light quality immediately preceding the dark period.Contribution No. 902 HIMB     

Adaptation strategies of the corallimorpharian <Emphasis Type="Italic">Rhodactis rhodostoma</Emphasis> to irradiance and temperature

Corallimorpharians may dominate some habitats on coral reefs and compete with stony corals for access to light, yet little is known concerning their photosynthetic traits. At Eilat in the northern Red Sea, we observed that the abundance of individuals of the corallimorpharian Rhodactis rhodostoma decreased significantly with depth on the reef slope. Field and laboratory experiments revealed that they employ several mechanisms of photoadaptation to high irradiance on the shallow reef flat. Their endosymbiotic microalgae (zooxanthellae) varied significantly in both abundance and chlorophyll content with level of irradiance. Use of a diving pulse amplitude modulated fluorometer revealed that the zooxanthellae of R. rhodostoma effectively disperse excess light energy by expressing significantly higher values of non-photochemical quenching and maximum excitation pressure on photosystem II when experimentally exposed to high light (HL) versus low light (LL). Host corallimorpharian tissues mediated this response by shielding the algal symbionts from high irradiance. The endoderm of host tentacles thickened significantly and microalgal cells were located further from the mesoglea in HL than in LL. The clades of zooxanthellae hosted by the corallimorpharians also varied with depth. In shallow water, all sampled individuals hosted clade C zooxanthellae, while in deep water the majority hosted clade D. The photosynthetic output of individuals of R. rhodostoma was less affected by HL than was that of a stony coral examined. When exposed to both high temperature (HT) and HL, individuals of R. rhodostoma reduced their maximum quantum yield, but not when exposed to HL at low temperature (LT). In contrast, colonies of the scleractinian coral Favia favus reduced their photosynthetic output when exposed to HL in both temperature regimes. After 2 weeks of HT stress, R. rhodostoma polyps appeared to bleach completely but re-established their zooxanthella populations upon return to ambient temperature. We conclude that mechanisms of photoadaptation to high irradiance employed by both the endosymbiotic zooxanthellae and host corallimorpharians may explain in part the abundance of R. rhodostoma on some shallow reef flats. The ability to survive for weeks at HT while bleached also may allow corallimorpharians to repopulate shallow reef areas where scleractinians have been killed by thermal stress. B. Kuguru and G. Winters contributed equally to this work.     

Evidence for facultative heterotrophy in cultured zooxanthellae

The locus of symbiotic dinoflagellates within host cells provides a habitat which could potentially be exploited by the alga through heterotrophic uptake of host-derived organic substrates. Using zooxanthellae (Symbiodinium sp.) isolated from the tropical sea anemone Aiptasia pulchella collected from Kaneohe Bay, Hawaii, the effect of various potential organic substrates on growth in vitro was assessed in Erdschreiber seawater medium (ES) supplemented with organic compounds. Zooxanthellae maintained at 5 to 7 E m^-2 s^-1 (below compensation irradiance) grew heterotrophically when supplied with 100 M glycerol, glycolate, acetate, malate, or propionate, and grew in darkness on 100 M propionate. Zooxanthellae exposed to irradiance below compensation were able to utilize carbon sources in the unsupplemented ES medium for slow growth, but generally the growth rate of cultured zooxanthellae was a function of incubation irradiance. Zooxanthellae incubated for 10 wk in unsupplemented ES at 5 to 7 E m^-2 s^-1 were capable of growth at this low irradiance, but were also capable of net photosynthetic oxygen production at higher irradiances. This suggests that zooxanthellae can be photoautotrophic or facultatively heterotrophic. An estimate for the duration of mitosis (t _d ) is made on the basis of growth rate of cultured zooxanthellae in log-phase; this estimate of t _d =4.88 h is less than half the estimated t _d for zooxanthellae in situ.     

Photoadaptation of zooxanthellae in the sponge Cliona vastifica from the Red Sea, as measured in situ

In the Red Sea, the zooxanthellate sponge Cliona vastifica (Hancock) is mainly present at >15 m depth or in shaded areas. To test whether its scarcity in unshaded areas of shallower waters is linked to the functional inefficiency of its photosymbionts at high irradiances, sponges were transferred from 30 m to a six times higher light regime at 12 m depth, and then returned to their original location. During this time, photosynthetic responses to irradiance were measured as rapid light curves (RLCs) in situ by pulse amplitude modulated (PAM) fluorometry using a portable underwater device, and samples were taken for microscopic determinations of zooxanthellar abundance. The zooxanthellae harboured by this sponge adapted to the higher irradiance at 12 m by increasing both their light saturation points and relative photosynthetic electron transport rates (ETRs). The ETRs at light saturation increased almost fourfold within 15–20 days of transfer to the shallower water, and decreased back to almost their original values after the sponges were returned to 30 m depth. This, as well as the fact that the photosynthetic light responses within an individual sponge were in accordance with the irradiance incident to specific surfaces, shows that these photosymbionts are highly adaptable to various irradiances. There was no significant change in the number of zooxanthellae per sponge area throughout these experiments, and the different photosynthetic responses were likely due to adaptations of the photosynthetic apparatus within each zooxanthella. In conclusion, it seems that parameters other than the hypothesised inability of the photosymbionts to adapt adequately to high light conditions are the cause of C. vastifica's rareness in unshaded shallow areas of the Red Sea. Received: 25 April 2000 / Accepted: 13 October 2000     

Depth-dependent responses to solar ultraviolet radiation and oxidative stress in the zooxanthellate coral Acropora microphthalma

Colonies of Acropora microphthalma (Verrill 1869) were transferred from depths of 2 to 3, 10, 20, and 30 m to UV-transparent and UV-opaque respirometry chambers placed at 1 m depth at Bowl Reef, Great Barrier Reef, in March 1989. Peak rates of photosynthesis in colonies originating at 2 and 10 m were unaffected by solar ultraviolet (UV) radiation at 1 m, whereas photosynthesis showed 30 and 38% inhibition in colonies transferred from 20 and 30 m, respectively. This differential sensitivity of corals to UV radiation was consistent with the five- to tenfold higher concentrations of UV-absorbing, mycosporine-like amino acids (MAAs, putative defenses against UV) in 2- and 10-m colonies compared with 20- and 30-m colonies. Photosynthesis in zooxanthellae freshly isolated from 2- and 10-m corals, however, was inhibited by UV, indicating that the host's tissues, which contain 95% of the total MAAs in corals at these depths, are the first line of defense against solar UV and provide protection to their endosymbiotic algae. The general bathymetric decline in the activities of the antioxidant enzyme superoxide dismutase (SOD) in the host, and SOD, catalase, and ascorbate peroxidase in the zooxanthellae, is related to the decrease in potential for photooxidative stress with increasing depth.     

Glucose and glycerol uptake by isolated zooxanthellae fromCassiopea xamachana: Transport mechanisms and regulation by host homogenate fractions

We investigated the mechanisms by which glycerol and glucose enter freshly isolated zooxanthellae (FIZ),Symbiodinium microadriaticum Freudenthal, of the mangrove jellyfish,Cassiopea xamachana Bigelow, and the specific sites of host factor interaction. Glucose entry into FIZ is accomplished by a Na⁺-dependent symport system driven by an electrochemical gradient generated via a Na⁺-K⁺ ATPase. Inhibition of glucose uptake by a low molecular weight fraction of host homogenates [mol. wt<2 kilodaltons (kD)] occurs through the interaction of a putative host factor with the carrier protein and not the ATPase. Glycerol entry is apparently accomplished by simple or facilitated diffusion and is not affected by host homogenate fractions.     

Tolerance of estuarine benthic diatoms to high concentrations of ammonia,nitrite ion,nitrate ion and orthophosphate

A carbon-14 assimilation method was used to determine action spectra and photosynthesis versus irradiance (P versus I) curves of natural populations of phytoplankton and zooxanthellae from a coral reef fringing Lizard Island in the Australian Barrier Reef. The action spectra were related to the phytoplankton species composition. The curves showed shade adaptation in phytoplankton from deeper waters and in the zooxanthellae. Rates of photosynthesis of zooxanthellae were shown to be highly but variably dependent on their host organisms. Photosynthetic production by zooxanthellae was about 0.9 gC m^-2 day^-1, which is about three times higher than phytoplankton production in the waters close to the reef.     

Photosynthesis,photorespiration, and dark respiration in eight species of algae

The rates of photosynthesis and dark respiration for 7 marine algae and 1 fresh-water alga were measured and compared. The dinoflagellates Glenodinium sp. and zooxanthellae have high dark respiration rates relative to photosynthetic rates, which may decrease their net growth rates. Photorespiration in the 8 algal species was studied by examining the effects of the concentration of oxygen on the rates of photosynthesis, on the incorporation of ¹⁴CO₂ into the photorespiratory pathway intermediates glycine and serine, and on the postillumination burst of carbon dioxide production and oxygen consumption. A combination of these results indicates that all the algae tested can photorespire, but that Glenodinium sp., Thalassiosira pseudonana, and zooxanthellae either have a photorespiratory pathway different from that proposed for freshwater algae (Tolbert, 1974), or an additional pathway for glycolate metabolism.     

Adaptation of solitary corals and their zooxanthellae to low light and UV radiation

Adaptation of solitary corals, Fungia repanda and F. echinata, and their zooxanthellae to low light and ultraviolet light B (UV-B) was studied with respect to changes in their protein contents, photosynthetic pigment contents and the photosynthesis-irradiance (P-I) curves. The corals were collected from 1 to 50 m depths in the Republic of Belau (Paulau) in 1990 and 1991. The chlorophyll a content in a unit surface area of the coral did not change significantly with the depth of the habitat, whereas cellular chlorophyll a in the algae increased with the depth. Zooxanthellae density and protein content in a unit surface area of Fungia spp. decreased with the depth. Photosynthetic parameters normalized by a unit surface area of the Fungia spp., maximum gross photosynthetic rate (P _gmax area^-1) and dark respiration rate (R area^-1), were negatively correlated with the depth, while initial slope of the P-I curve () did not show significant correlation with the depth. Compensation light intensity (Ic) decreased with the depth. In isolated zooxanthellae, P _max chl a ^-1, and R chl a ^-1 decreased with the depth, while _{chl a} was constant. P _gmax cell^-1 and R cell^-1 did not change significantly but _cell increased with the depth. Ic decreased with the depth as in the intact corals. Reduction of protein content in a unit area of the coral from deeper habitat implies decrease of host animal tissues. Reduction of Ic can be explained by decrease of R area^-1, which may be due to the diminution of animal tissues. The photoadaptational response to low light intensity of intact Fungia spp. was found to be a combination of the photoadaptation of symbiotic algae and the decrease of host animal tissue. In order to study their adaptation to ultraviolet (UV) radiation, P-I curves of Fungia spp. and isolated zooxanthellae were analyzed before and after UV-B irradiation. 1 h UV-B irradiation showed no effect on the photosynthetic rate of the shallow water (1 m) corals, while it inhibited the photosynthesis of the deep water (30 m) corals and zooxanthellae isolated from both shallow and deep water corals. These results indicate that the host, Fungia spp., in shallow water have protective mechanism for intense UV-B in their habitat. These photoadaptational mechanisms seem to allow the Fungia spp. to have wide vertical distribution where light intensity spans more than two orders of magnitude.     

A “CO2 supply” mechanism in zooxanthellate cnidarians: role of carbonic anhydrase

Carbonic anhydrase (CA, EC 4.2.1.1) activity was detected in 22 species of tropical cnidarians which contain endosymbiotic dinoflagellates (=zooxanthellae). CA activity was 2 to 3 times higher in animal tissue than in algae and ca. 29 times higher in zooxanthellate than azooxanthellate species. It was also higher in the zooxanthellate tentacle tissue than in the azooxanthellate column tissue of the anemone Condylactis gigantea. CA was therefore significantly related to the presence of endosymbiotic algae. Further results indicated that CA functions in the photosynthetic carbon metabolism of zooxanthellate cnidarians as evidenced by (1) low CA activity in shade-adapted and deep water colonies compared to the more productive shallow water, light-adapted colonies of the coral Stylophora pistillata, and (2) the 56 to 85% reduction in photosynthetic carbon assimilation by zooxanthellae in situ in the presence of Diamox, an inhibitor of CA. Although CA has been proposed to function in calcification, its association with zooxanthellae and photosynthetic activity in both calcifying and non-calcifying associations suggests a role in photosynthetic metabolism of algal/cnidarian symbioses. It is proposed that CA acts as a CO₂ supply mechanism by releasing CO₂ from bicarbonate, and enabling zooxanthellae to maintain high rates of photosynthesis in their intracellular environment.     

Light absorption and utilization among hermatypic corals: a study in Jamaica,West Indies

The chlorophyll specific absorption coefficient ( _c) was measured for zooxanthellae from six hermatypic coral species obtained, where possible, from four depths (1, 10, 30, 50 m) on reef sites near Discovery Bay, Jamaica in February and March 1983. Measurements of photosynthetic rates versus irradiance, as well as cellular and areal chlorophyll a, were also performed on these colonies or sister colonies. Together the data were used to compare minimum quantum requirements (1/Φ m) among species and depths and to assess the importance of light utilization to the growth and depth distribution of these corals. Our data suggest that, although _c was found to decrease with depth, interspecific differences in _c do not occur for zooxanthellae from the corals investigated. Minimum quantum requirements (1/Φ m) decreased significantly with depth, thereby reflecting an increase in photosynthetic light utilization efficiency with decreasing irradiance. Interspecific differences in 1/Φ m determinations were suggested but not statistically conclusive. We conclude that interspecific differences in gross photosynthesis, and perhaps growth and depth distribution, are primarily attributable to differences in the light utilization capacity of the whole coral, as reflected by the product of _c ^′ and chlorophyll per unit surface area, and in-situ quantum efficiencies. This research was performed under the auspices of the US Department of Energy under Contract No. DE-AC02-76CH00016     

Two new UV-absorbing mycosporine-like amino acids from the sea anemoneAnthopleura elegantissima and the effects of zooxanthellae and spectral irradiance on chemical composition and content

Many tropical cnidarians living in shallow water contain a class of ultraviolet-A (UV-A, 320 to 400 nm) and ultraviolet-B (UV-B, 280 to 320 nm) absorbing compounds known as mycosporine-like amino acids (MAAs). These compounds may provide protection from the deleterious effects of solar UV radiation. Using a novel application of reverse-phase high performance liquid chromatography, we find that the temperate sea anemoneAnthopleura elegantissima (collected in 1988 from Bodega Bay, California, and in 1991 from Santa Barbara, California) contains four major MAAs: shinorine, porphyra-334, and two new compounds, mycosporine-taurine and mycosporine-2 glycine. Analysis of zooxanthellate (containing zooxanthellae) and naturally apozooxanthellate (lacking zooxanthellae) specimens acclimated in the presence and absence of UV for 28 d in the spring of 1988 suggests that this anemone, unlike some other anthozoans, does not regulate the concentration of its MAAs in response to UV radiation. The presence of similar concentration of MAAs in apozooxanthellate and zooxanthellate specimens indicates that symbiosis with algae is not required for these compounds to be present in the anemone. The total concentration of MAAs in the zooxanthellae is only about 12% of that in their host's tissues.     

Effects of dissolved ammonium addition and host feeding with Artemia salina on photoacclimation of the hermatypic coral Stylophora pistillata

 Effects of nutrient treatments on photoacclimation of the hermatypic coral Stylophora pistillata (Esper) were studied. Studies on photoacclimation of colonies from different light regimes in the field were evaluated and used to design laboratory experiments. Coral colonies were collected in the Gulf of Eilat (Israel) from January to March 1993. Exterior branches of colonies from different depths (1 to 40 m) displayed different trends in production characteristics at reduced and very low levels of illumination. From 24 ± 3% to 12 ± 2% of incident surface photosynthetic active radiation (PAR_o), zooxanthella population density and chlorophyll a+c per 10⁶ zooxanthellae increased, a trend seen in the range of light levels optimal for coral growth (90 to 30% PAR_o). The P _max of CO₂ per 10⁶ zooxanthellae decreased, while P _max of CO₂ per 10³ polyps increased, indicating an increase in zooxanthella population density at low light levels. Proliferous zooxanthella frequency (PZF, a measure of zooxanthella division) declined significantly at light levels <18 ± 3% PAR_o. At the lowest levels of illumination (<5% PAR_o), zooxanthella population density decreased, as did the PZF; chl a+c per 10⁶ zooxanthellae was unchanged. In 28-d experiments, exterior coral branches from the upper surfaces of colonies from 3 m depth (65 ± 4% PAR_o) were incubated in aquaria under bright (80 to 90% PAR_o), reduced (20 to 30% PAR_o), and extremely low (2 to 4% PAR_o) light intensities. At each light intensity, the corals were maintained in three feeding treatments: sea water (SW); ammonium enriched SW (SW + N); SW with Artemia salina nauplii (SW + A). An increase in P _max of CO₂ per 10³ polyps was found in corals acclimated to reduced light (20 to 30% PAR_o) in nutrient-enriched SW, while in SW, where the increase in zooxanthella population density was smaller, it did not occur. Nutrient enrichments (SW + N at 2 to 4% PAR_o and SW + A at 20 to 30% PAR_o) increased zooxanthella population density, but had no effect on chl a+c per 10⁶ zooxanthellae. Acclimation for 14 d to reduced (10 to 20% PAR_o) and extremely low (1 to 3% PAR_o) light intensities shifted ¹⁴C photoassimilation into glycerol and other compounds (probably glycerides), rather than sugars. Both ammonium addition and feeding with Artemia salina nauplii resulted in an increase in photosynthetic assimilation of ¹⁴C into amino acids. We conclude that acclimation to reduced light consists of two processes: an increase in photosynthetic pigments and in zooxanthella population density. Both processes require nitrogen, the increase in zooxanthella population density needing more; this adaptation is therefore limited in nitrogen-poor sea water. Received: 19 June 1998 / Accepted: 13 June 2000     

Interplay of host morphology and symbiont microhabitat in coral aggregations

The Belizean reef coral Agaricia tenuifolia Dana forms aggregations in which rows of thin, upright blades line up behind each other. On average, the spacing between blades increases with depth and hence with decreasing ambient irradiance. We designed and built a small, inexpensive light meter and used it to quantify the effect of branch spacing on light levels within colonies at varying distances from branch tips. Concurrently, we measured photosynthetic pigment concentrations and population densities of symbiotic dinoflagellates (zooxanthellae) extracted from coral branches of colonies with tight (≤3 cm) vs wide (≥6 cm) branch spacing, collected at 15 to 17 m and from colonies with tight branch spacing collected at 1 to 2 m. Light levels decreased significantly with tighter branch spacing and with distance from the branch tips. Total cellular pigment concentrations (chlorophylls a, c ₂ and peridinin) as well as chlorophyll a:c ₂ and chlorophyll a: peridinin ratios all increased significantly with distance from the branch tip, indicating very localized differences in photoacclimation within individual branches. Zooxanthellae from colonies with widely-spaced branches displayed significantly lower chlorophyll a:c ₂ and chlorophyll a:peridinin ratios, and were present at significantly higher population densities than those from colonies with tightly-spaced branches collected at the same depth (15 m). Tightly-spaced colonies collected from shallow environments (1 to 2 m) displayed pigment ratios similar to those from widely-spaced colonies from deeper water (15 m), but maintained zooxanthellae populations at levels similar to those in tightly-branched colonies from deeper water. Thus, variation in colony morphology (branch spacing and distance from branch tip) can affect symbiont physiology in a manner comparable to an increase of over 15 m of water depth. These results show that a host's morphology can strongly determine the microhabitat of its symbionts over very small spatial scales, and that zooxanthellae can in turn display steep gradients in concordance with these altered physical conditions. Received: 12 June 1997 / Accepted: 24 June 1997     

UV-absorbing substances in zooxanthellate and azooxanthellate clams

The effects of UV-A and UV-B radiation on photosynthesis of zooxanthellae within the siphonal mantle of the giant clam, Tridacna crocea, and in isolation were studied. While UV-B irradiation (2.4 W m⁻², 20 min) completely suppressed photosynthesis of the isolated zooxanthellae, it had little effect on their photosynthetic ability if they were irradiated while within the siphonal mantle of the host tissue. Chemical analysis of the siphonal mantle of T. crocea showed the presence of significant amounts of mycosporine-like amino acids (MAAs), which absorb UV-A and -B light. However, no MAA was detected in the isolated zooxanthellae. MAAs were concentrated in the siphonal mantle and kidney tissues in comparison with other tissues. In the siphonal mantle, MAA concentrations were the highest in the outermost surface layer where most of the zooxanthella cells resided. This indicates that the zooxanthellae are protected from UV radiation by a screen of concentrated MAAs in the host clam. Aside from T. crocea, significant amounts of MAAs were found not only in other zooxanthellate clams, such as T. derasa, Hippopus hippopus, Colculum cardissa and Fragum unedo, but also in a closely related azooxanthellate clam, Vasticardium subrugosum. On the other hand, no MAA was detected in any of the zooxanthellae from these zooxanthellate clams. No MAA was detected in the tissues of a deep-sea bivalve, Calyptogena soyoae. Although MAAs seem to block strong UV radiation in the shallow-water clam, they are probably not essential for the clam's life in the dark. MAAs in shallow-water clams may be derived from food and accumulated in their tissues, especially in the siphonal mantle and kidney. Received: 29 November 1996 / Accepted: 13 January 1997     

Viable algae released by the seastar <Emphasis Type="Italic">Dermasterias</Emphasis><Emphasis Type="Italic">imbricata</Emphasis> feeding on the symbiotic sea anemone <Emphasis Type="Italic">Anthopleura elegantissima</Emphasis>

Echinoderms are major predators of anemones in temperate ecosystems. The fate of two algae, zooxanthellae and zoochlorellae, after their host anemone (Anthopleura elegantissima Brandt) was consumed by the leather star Dermasterias imbricata Grube was determined in experiments conducted in July and August 2004. Productivity, photosynthetic pigments, and mitotic index (percent of cells dividing) were used as indicators of algal health; algae released after leather stars consumed their host were compared with algae freshly isolated from anemones. Two types of waste products contained algae: pellets resulting from extraoral digestion, and feces. Zooxanthellae and zoochlorellae isolated from these waste products were photosynthetic, although to different extents. For algae from feces and pellets, light-saturated photosynthetic rates (P _max) were 85 and 13%, respectively, of P _max of freshly isolated zooxanthellae; and were 20 and 46%, respectively, for zoochlorellae. The photosynthetic pigments and mitotic index (percent of dividing cells) were not altered by the feeding activities of the leather star. These results show that algae released by seastar predation on their hosts remain viable, and are hence available for establishing symbioses in A. elegantissima and other potential hosts.     

Experimental ecology of the temperate scleractinian coral Astrangia danae I. Partition of respiration,photosynthesis and calcification between host and symbionts

Calcification, photosynthesis and respiration of the scleractinian coral Astrangia danae were calculated from the changes in total alkalinity, pH, calculated total CO₂, and oxygen concentration produced by colonies incubated in glass jars. A correction for changes in ammonia, nitrate and nitrite was taken into account and the method evaluated. The fluxes of oxygen and CO₂ were highly correlated (r=0.99). The statistical error of alkalinity determinations was less than 10% of the changes observed in the slowest calcifying samples. Metabolism of polyparium alone was estimated by difference after removal of tissue and reincubation of bare corallum. Zooxanthellae concentration in the polyps was obtained from cell counts made on homogenates of polyp tissue. The calculated photosynthetic rate of the zooxanthellae in vivo was 25 mol O₂ (10⁸ cell)^-1 h^-1 at a light intensity of 120 Ein m^-2 s^-1. In corals having 0.5x10⁹ zooxanthellae/dm² of colony area up to 8% of the total photosynthesis was attributed to the corallum microcosm. Polyp respiration, photosynthesis, and CaCO₃ uptake rates were all much higher than rates previously reported from A. danae, apparently because in these experiments the organisms were better fed. This increased photosynthesis in turn enhanced calcification still further. The symbiosis therefore appears to provide a growth advantage even to fed corals, under the conditions of these experiments.     

Photosynthetic and optical properties of the marine chlorophyte Dunaliella tertiolecta grown under fluctuating light caused by surface-wave focusing

Photosynthetic and optical properties of the marine chlorophyte Dunaliella tertiolecta Butcher were studied in response to irradiance fluctuations caused by surface-wave focusing. The experimental conditions simulated the prominent features of the light field (high average irradiance, spectral composition and statistical properties) in the uppermost few meters of the water column under sunny surface conditions. The properties of algae grown under high-frequency fluctuations were compared with control cells grown under constant light at the same average irradiance (800 mol quantam^-2s^-1). No significant differences were found for a number of parameters, including growth rate, cellular chlorophyll a and pigment ratios, photosynthetic unit size and density of Photosystem I reaction centers, the rate of photosynthesis at the growth irradiance, dark respiration, and in vivo fluorescence of chlorophyll a per cell. Photosynthetic parameters were not affected by whether the incident light for oxygen exchange measurements was fluctuating or constant. This was the case whether the cells had been previously acclimated to either fluctuating or constant irradiance. Such a photosynthetic response indicates that cells are accomplishing a time integration of the fluctuating light. In addition, although D. tertiolecta is capable of dramatically changing its optical properties in response to low or high growth irradiance levels, the refractive index of the cells, the efficiency factors for light absorption and scattering by individual cells, and chlorophyll-specific absorption and scattering coefficients of cell suspensions, were all very similar under high irradiance, whether or not wave focusing was present.Contribution to the program of GIROQ (Groupe Interuniversitaire de Recherches Océanographiques du Québec)     

双酚A对紫背浮萍生长和光合色素及抗氧化系统影响

以紫背浮萍为实验对象,探究双酚A(bsiphenol A, BPA)对其生长、光合色素含量、抗氧化系统和渗透压调节物质的影响。结果表明,不同浓度(0、1、5、20和50 mg·L~(-1))BPA连续暴露7 d后,与对照组相比,随暴露浓度升高,紫背浮萍湿重和叶绿素含量呈现先显著增加后降低的趋势;暴露组过氧化氢(H_2O_2)含量和抗超氧阴离子自由基活性显著降低;丙二醛(MDA)含量在20和50 mg·L~(-1)组显著升高;暴露组抗氧化酶活性包括超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)和总抗氧化能力(T-AOC)均低于对照组;谷胱甘肽(GSH)含量在高浓度组显著升高,20 mg·L~(-1)组可溶性糖含量显著升高,可溶性蛋白含量在中高浓度组显著增加。研究表明,中低浓度BPA会提高紫背浮萍光合色素含量,有机物积累增多,促进其生长;但随BPA浓度不断升高,紫背浮萍体内产生氧化损伤,抗氧化酶活性及叶绿素含量降低,生长受到抑制。本研究结果将为BPA污染控制及对水生植物生态毒性效应评价提供理论基础。