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1.
Photoinhibition of photosynthesis on a coral reef 总被引：2，自引：0，他引：2
L. A. FRANKLIN G. G. R. SEATON C. E. LOVELOCK A. W. D. LARKUM 《Plant, cell & environment》1996,19(7):825-836
Photoinhibition of macroalgae in the epilithic algal community (KAC) of coral reefs was studied using chlorophyll fluorescence techniques at One Tree Island, Great Barrier Reef, Australia. Fv/Fm (variable to maximum fluorescence, darkened samples) of shallow macroalgae declined by 50% on fine summer and winter days, recovering in late afternoon. Within a species, thalli from low-light habitats were more photoinhibited (2h at 1400μimol m?2 s?1) than those from high-light habitats. The sensitivity of Lobophora variegata (Phacophyta) and Chlorodesmis fastigiata (Chlorophyta) increased with depth (1 versus 20 m). However, shallow Halimeda tuna (Chlorophyta) plants growing between corals were more photoinhibited than those from deep, open areas. Photoinhibition and recovery were depth- and species-specific. Shallow Lobophora and Chlorodesmis maintained a greater degree of Q A oxidation during photoinhibition. In deep thalli, reduced effective quantum yield of open photosystem II centres reflected lower proportions and excitation capture efficiencies of open centres. In Lobophora, zeaxanthin formation accompanied non-photochemical fluorescence quenching (NPQ), but in Chlorodesmis NPQ was limited and no zeaxanthin or antherxanthin formed. Higher photosynthetic efficiency in the lower storey of the EAC may compensate for photoinhibition in the upper storey, thereby reconciling photoinhibition of individual thalli with previous observations of no net inhibition of community productivity. 相似文献
2.
3.
- While the effects of irradiance on coral productivity are well known, corals along a shallow to mesophotic depth gradient (10–100 m) experience incident irradiances determined by the optical properties of the water column, coral morphology, and reef topography.
- Modeling of productivity (i.e., carbon fixation) using empirical data shows that hemispherical colonies photosynthetically fix significantly greater amounts of carbon across all depths, and throughout the day, compared with plating and branching morphologies. In addition, topography (i.e., substrate angle) further influences the rate of productivity of corals but does not change the hierarchy of coral morphologies relative to productivity.
- The differences in primary productivity for different coral morphologies are not, however, entirely consistent with the known ecological distributions of these coral morphotypes in the mesophotic zone as plating corals often become the dominant morphotype with increasing depth.
- Other colony‐specific features such as skeletal scattering of light, Symbiodiniaceae species, package effect, or tissue thickness contribute to the variability in the ecological distributions of morphotypes over the depth gradient and are captured in the metric known as the minimum quantum requirements.
- Coral morphology is a strong proximate cause for the observed differences in productivity, with secondary effects of reef topography on incident irradiances, and subsequently the community structure of mesophotic corals.
4.
Olivia J. Kalokora Martin Gullstrm Amelia S. Buriyo Matern S. P. Mtolera Mats Bjrk 《Ecology and evolution》2022,12(2)
Seagrass meadows capture and store large amounts of carbon in the sediment beneath, thereby serving as efficient sinks of atmospheric CO2. Carbon sequestration levels may however differ greatly among meadows depending on, among other factors, the plant community composition. Tropical seagrass meadows are often intermixed with macroalgae, many of which are calcareous, which may compete with seagrass for nutrients, light, and space. While the photosynthetic CO2 uptake by both seagrasses and calcareous algae may increase the overall calcification in the system (by increasing the calcium carbonate saturation state, Ω), the calcification process of calcareous algae may lead to a release of CO2, thereby affecting both productivity and calcification, and eventually also the meadows’ carbon storage. This study estimated how plant productivity, CaCO3 production, and sediment carbon levels were affected by plant community composition (seagrass and calcareous algae) in a tropical seagrass‐dominated embayment (Zanzibar, Tanzania). Overall, the patterns of variability in productivity differed between the plant types, with net areal biomass productivity being highest in meadows containing both seagrass and calcareous algae. Low and moderate densities of calcareous algae enhanced seagrass biomass growth, while the presence of seagrass reduced the productivity of calcareous algae but increased their CaCO3 content. Sedimentary carbon levels were highest when seagrasses were mixed with low or moderate cover of calcareous algae. The findings show that plant community composition can be an important driver for ecosystem productivity and blue carbon sequestration. 相似文献
5.
Photosynthesis/photon flux density (PFD) relationships were compared among some of the major components of sparse algal turfs (green endoliths, red crusts, red filaments, Crouania, Sphacelaria)/ from Tague Bay forereef St. Croix, U.S. Virgin Islands. Algal turfs grazed by the sea urchin Diadema antillarum were 2–10 times more productive per unit chl a than when not grazed by sea urchins. The maximum rate of net photosynthesis (Pnetmax) and saturation PFDs, but not the slope of the light-limited portion of the curve (α), differed significantly among the algal turf components examined. The hypothesis that increased biomass-specific primary productivity results from shifts in algal community structure was not supported because the maximum difference in photosynthesis between algal components was only a factor of two, and the less productive components were relatively more abundant under grazing. In the understory, green endoliths exhibited higher α and lower Pnetmax, suggesting shade adaptation. Photon flux density measurements taken with a fiber optic microprobe within the algal turfs indicated that photosynthesis of basal portions of algal filaments and red crusts are light-limited in ungrazed algal turfs. As self-shading changes with grazer-mediated canopy removal, algal sublayers will contribute differentially to whole turf primary productivity. 相似文献
6.
Jeremy Carlot Hloïse Rouz Diego R. Barneche Alexandre Mercire Benoit Espiau Ulisse Cardini Simon J. Brandl Jordan M. Casey Gonzalo Prez&#x;Rosales Mehdi Adjeroud Laetitia Hdouin Valeriano Parravicini 《Ecology and evolution》2022,12(3)
Coral reefs provide a range of important services to humanity, which are underpinned by community‐level ecological processes such as coral calcification. Estimating these processes relies on our knowledge of individual physiological rates and species‐specific abundances in the field. For colonial animals such as reef‐building corals, abundance is frequently expressed as the relative surface cover of coral colonies, a metric that does not account for demographic parameters such as coral size. This may be problematic because many physiological rates are directly related to organism size, and failure to account for linear scaling patterns may skew estimates of ecosystem functioning. In the present study, we characterize the scaling of three physiological rates — calcification, respiration, and photosynthesis — considering the colony size for six prominent, reef‐building coral taxa in Mo''orea, French Polynesia. After a seven‐day acclimation period in the laboratory, we quantified coral physiological rates for three hours during daylight (i.e., calcification and gross photosynthesis) and one hour during night light conditions (i.e., dark respiration). Our results indicate that area‐specific calcification rates are higher for smaller colonies across all taxa. However, photosynthesis and respiration rates remain constant over the colony‐size gradient. Furthermore, we revealed a correlation between the demographic dynamics of coral genera and the ratio between net primary production and calcification rates. Therefore, intraspecific scaling of reef‐building coral physiology not only improves our understanding of community‐level coral reef functioning but it may also explain species‐specific responses to disturbances. 相似文献
7.
Coral reef degradation is often associated with regime shifts from coral‐ to macroalgal‐dominated reefs. These shifts demonstrate that under certain conditions (e.g. coral mortality, decrease in herbivory, increased nutrients supply) some macroalgae may overgrow corals. The outcome of the competition is dependent on algal aggressiveness and the coral susceptibility. In undisturbed reefs, herbivore grazing is regulating macroalgal cover, thus preventing the latter from overgrowing corals. However, some macroalgae have evolved strategies not only to outcompete corals but also to escape herbivory to some extent, allowing overgrowth of some coral species in undisturbed reefs. Epizoism represents one of those successful strategies, and has been previously documented with red algae, cyanobacteria and Lobophora variegata (Dictyotales, Phaeophyceae). Here we report a new case of epizoism leading to coral mortality, involving a recently described species of Lobophora, L. hederacea, overgrowing the coral Seriatopora caliendrum (Pocilloporidae) in undisturbed reefs in New Caledonia. 相似文献
8.
Two new isolates of halotolerant chlorophyte algae from the Salt Plains National Wildlife Refuge in Oklahoma, USA, tentatively identified as Dunaliella sp. Teodoresco and Nannochloris sp. Naumann, were characterized with respect to interaction between growth salinity and short‐term heat tolerance. Cells were cultured at 23–25° C over a wide range of salinity. In both species, salinity alone had little effect on maximum photochemical yield (measured by pulse modulated fluorescence) and integrity of the light harvesting system (77 K fluorescence emission spectra). In contrast, Nannochloris exhibited decreasing growth rate (μ), light‐saturated photosynthetic capacity (Pcellmax), respiration (Rd), light‐harvesting efficiency (αcell), and chl content with increasing salinity. Cultures were heated for 2 h near their upper temperature limits (41.5° C for Dunaliella and 45° C for Nannochloris grown at 50 psu). Dunaliella was progressively more heat‐tolerant with increasing salinity. Photochemical yield of cells at 100 and 50 psu was inhibited by about 15% and 40%, respectively, and largely recovered within 30 min after return to 23° C. Thermal inhibition of photochemical yield in Nannochloris was about 45% at both 50 and 100 psu, but recovery was slower at 100 psu. At 20 psu, both species were almost 90% inhibited by high temperature and required more than a day to recover. In both species, 2 h of heating increased the PSI:PSII fluorescence emission ratio (714:690 nm) at all salinities. This ratio largely recovered within 24 h in Dunaliella at 50 and 100 psu and partially recovered in Nannochloris at 100 psu, but cells of both species heated at 20 psu were chlorotic the next day. 相似文献
9.
Irradiance power and spectral composition as well as nutrient availability strongly influence differentiation of filamentous cyanobacteria. When monitoring the life cycle of Calothrix elenkinii Kossinsk., we found that low nitrogen concentration and growth under green light led to a transient appearance of high‐fluorescence cells that rapidly bleach and disintegrate, thus breaking the parental filament into shorter parts. The dynamics of the process were monitored in a microscope growth chamber by measuring transmission and chl fluorescence of individual cells by a high‐sensitivity camera. Typically, the high‐fluorescence cells appeared near the center of the parental trichome signaled by a rapid 2‐ to 3‐fold rise in their fluorescence emission. By measuring the fluorescence excitation spectra with resolution of individual cells, we showed that the elevated fluorescence emission was largely due to a high absorption by phycoerythrin and energy transfer to chl. Typically, after no more than 20 min, the fluorescence abruptly disappeared with transmission images, indicating loss of pigmentation. The bleaching was a natural process that was not caused by the measuring light. Depending on the mechanical strain, the cell bleaching was followed by breaking of the parental filament. We propose that the high‐fluorescence cells appear as a phase of programmed cell death, allowing the fragmented filaments to escape from unfavorable environmental conditions. 相似文献
10.
Abstract The gametangia of the green seaweed Halimeda tuna are spherical bodies of diameter up to 250–300 μm. They are clustered in groups of 8–10 on hundreds of threads sprouting from all pale white segments of the fertile individuals. In addition to gametes, starch-containing chloroplasts, naked starch grains and two types of spherical bodies different in size and ultrastructure are the main corpuscular components. A layer of amorphous material of irregular thickness underlies the walls which are finely and evenly rough, structureless, electron translucent and 1–1.5 μm thick. Gametangia with superficial wall warts were found also. 相似文献
11.
Both global and local environmental changes threaten coral reef ecosystems. To evaluate the effects of high seawater temperature and phosphate enrichment on reef‐building crustose coralline algae, fragments of Porolithon onkodes were cultured for 1 month under laboratory conditions. The calcification rate of the coralline algae was not affected at 30°C, but it decreased to the negatives at 32°C in comparison to the control treatment of 27°C, indicating that the temperature threshold for maintaining positive production of calcium carbonate lies between 30 and 32°C. Phosphate enrichment of 1–2 μmol L ?1 did not affect the calcification rate. The net oxygen production rate was enhanced by phosphate enrichment, suggesting that the photosynthetic rate was limited by the availability of phosphate. It was concluded that moderate phosphate enrichment does not directly deteriorate algal calcification but instead ameliorates the negative effects of high seawater temperature on algal photosynthesis. 相似文献
12.
P. Gori 《Molecular reproduction and development》1979,2(4):345-355
The mature Halimeda tuna spermatozoid was studied under the electron microscope. It is pear-shaped and biflagellate. The nucleus is an uncondensed structure except for a few opaque (chromatin) aggregations and shows a rounded profile. The endoplasmic reticulum is a rather well-developed system of rough cisternae engaged in synthesis and storage of proteins. Free ribosomes are numerous. A large mitochondrial apparatus shaped like a horseshoe lies in the anterior gamete region. Only one single plastid is found, and it exhibits a deeply indented outline, a partially structured matrix, osmiophilic globules, and three to four starch grains. The axoneme pattern is 9 + 2. B tubules show septate lumina. A peculiar structure provided with a three-layered shell covering materials of varying electrondensity lies on the upper surface of both basal bodies. The flagellar root system exhibits a cruciate pattern and sets having an inconstant number of microtubules – ie, three, four, or five. 相似文献
13.
The composition and trophic structure of reef fish communities in two natural and two artificial reefs along the coast of Paraíba State in north‐eastern Brazil were investigated. A total of 114 species of fish belonging to 47 families were recorded during 120 stationary visual surveys, slightly less than half (46·55%) of which were recorded at all four surveyed localities. Most species are widely distributed on the western Atlantic coast, but several are endemic to Brazil. The greatest diversity and equitability indexes were recorded at the reefs of Sapatas and Cabeço dos Cangulos, whereas the greatest richness and abundance were found at the Queimado shipwreck. The Alvarenga shipwreck reef had the least richness, diversity and equitability. The four localities studied had very similar ichthyofaunas, especially in relation to species composition. The reefs along the Paraíba coast are considered priority conservation areas by the Brazilian Ministry of the Environment, and the information generated by this study will be useful for comparison with other reefs in the region and can be directly applied to programmes seeking to protect and manage these environments. 相似文献
14.
Christiaan van den Hoek 《Journal of phycology》1983,19(1):116-118
The small and ill-known tropical chlorophyte, Brybesia johannae Weber-van Bosse, is redescribed on the basis of living material from the coral reef of Curacao, Netherlands Antilles. Additional records are given from the Canary Islands. One species, B. johannae, is recognized (including, B. cylindrocarpa Howe 1920), and this probably has a wide Atlantic and Indo-Pacific tropical distribution. Bryobesia is not related to Bryopsis and Derbesia (Caulerpales), but belongs to the Cladophorales. It appears to be a rudimentary Cladophora. 相似文献
15.
Aline P. M. Medeiros Beatrice P. Ferreira Fredy Alvarado Ricardo Betancur&#x;R Marcelo O. Soares Brulio A. Santos 《Ecology and evolution》2021,11(9):4413
- The deep reef refugia hypothesis (DRRH) predicts that deep reef ecosystems may act as refugium for the biota of disturbed shallow waters. Because deep reefs are among the most understudied habitats on Earth, formal tests of the DRRH remain scarce. If the DRRH is valid at the community level, the diversity of species, functions, and lineages of fish communities of shallow reefs should be encapsulated in deep reefs.
- We tested the DRRH by assessing the taxonomic, functional, and phylogenetic diversity of 22 Brazilian fish communities between 2 and 62 m depth. We partitioned the gamma diversity of shallow (<30 m) and deep reefs (>30 m) into independent alpha and beta components, accounted for species’ abundance, and assessed whether beta patterns were mostly driven by spatial turnover or nestedness.
- We recorded 3,821 fishes belonging to 85 species and 36 families. Contrary to DRRH expectations, only 48% of the species occurred in both shallow and deep reefs. Alpha diversity of rare species was higher in deep reefs as expected, but alpha diversity of typical and dominant species did not vary with depth. Alpha functional diversity was higher in deep reefs only for rare and typical species, but not for dominant species. Alpha phylogenetic diversity was consistently higher in deep reefs, supporting DRRH expectations.
- Profiles of taxonomic, functional, and phylogenetic beta diversity indicated that deep reefs were not more heterogeneous than shallow reefs, contradicting expectations of biotic homogenization near sea surface. Furthermore, pairwise beta‐diversity analyses revealed that the patterns were mostly driven by spatial turnover rather than nestedness at any depth.
- Conclusions. Although some results support the DRRH, most indicate that the shallow‐water reef fish diversity is not fully encapsulated in deep reefs. Every reef contributes significantly to the regional diversity and must be managed and protected accordingly.
16.
N.I.colas Leclercq J.E.A.N.‐Pierre Gattuso J.E.A.N. Jaubert 《Global Change Biology》2000,6(3):329-334
Previous studies have demonstrated that coral and algal calcification is tightly regulated by the calcium carbonate saturation state of seawater. This parameter is likely to decrease in response to the increase of dissolved CO2 resulting from the global increase of the partial pressure of atmospheric CO2. We have investigated the response of a coral reef community dominated by scleractinian corals, but also including other calcifying organisms such as calcareous algae, crustaceans, gastropods and echinoderms, and kept in an open‐top mesocosm. Seawater pCO2 was modified by manipulating the pCO2 of air used to bubble the mesocosm. The aragonite saturation state (Ωarag) of the seawater in the mesocosm varied between 1.3 and 5.4. Community calcification decreased as a function of increasing pCO2 and decreasing Ωarag. This result is in agreement with previous data collected on scleractinian corals, coralline algae and in a reef mesocosm, even though some of these studies did not manipulate CO2 directly. Our data suggest that the rate of calcification during the last glacial maximum might have been 114% of the preindustrial rate. Moreover, using the average emission scenario (IS92a) of the Intergovernmental Panel on Climate Change, we predict that the calcification rate of scleractinian‐dominated communities may decrease by 21% between the pre‐industrial period (year 1880) and the time at which pCO2 will double (year 2065). 相似文献
17.
Sanja Milovi&#x; Ivan Stankovi&#x; Dejan Nikoli&#x; Jelena Radovi&#x; Marina Kolundi&#x; Vesna Nikoli&#x; Tatjana Stanojkovi&#x; Slavica Petovi&#x; Tatjana Kundakovi&#x;‐Vasovi&#x; 《化学与生物多样性》2019,16(10)
Three seaweeds (Halimeda tuna, Codium bursa and Cystoseira barbata) and one seagrass (Cymodocea nodosa) were collected from the Coast of Montenegro, Gulf of Boka Kotorska and their chemical analysis was performed. In seagrass C. nodosa, three phenolic compounds were identified (diosmetin 7‐sulfate, caftaric and coutaric acid). The content of β‐glucan, fatty acids, sterols and micro‐ and macro‐elements were investigated among all samples. The highest content of β‐glucan was detected in C. nodosa seagrass (13.04±0.42 g/100 g). The highest polyunsaturated fatty acids (PUFAs) level was reported in C. barbata, the brown alga (7.157 mg/g), which also had the significant sterol content (fucosterol, 21.76±0.1 μg/g). Green algae, C. bursa and H. tuna, showed the highest level of sterols (β‐sitosterol, 95.21±0.16 μg/g and 73.90±0.08 μg/g, respectively). H. tuna had the highest content of calcium (Ca) in amount of 55125 μg/g. In C. bursa, C. barbata and C. nodosa, the Na/K ratio was low (0.43, 0.46 and 0.69, respectively). 相似文献
18.
Joo Serdio 《Journal of phycology》2003,39(1):33-46
An index based on chl a fluorescence quenching analysis was tested as a predictor of photosynthetic rates of undisturbed intertidal microphytobenthic assemblages. The fluorescence index, Pfluo, was derived from the combination of different chl a fluorescence parameters chosen to represent the two main sources of short‐term variability in the community‐level microphytobenthic photosynthesis: 1) the quantum yield of photosynthesis of the microalgae present in the photic zone of the sediment, φP, and 2) the community‐level efficiency of photosynthetic light absorption, ?, determined by the microalgal concentration in the photic zone. Variations in φP were traced by the fluorescence index ΔF/Fm′ (the effective quantum yield of charge separation at PSII), whereas changes in ? were followed by the fluorescence parameter Fo (dark or minimum fluorescence level). Gross photosynthetic rate, P, and fluorescence parameters were measured nondestructively and simultaneously under in situ conditions, on the same samples, using oxygen microelectrodes and pulse amplitude modulation fluorometry, respectively. Despite the large and uncorrelated hourly variability in irradiance, photosynthetic rate, and fluorescence parameters included in Pfluo, highly significant correlations between Pfluo and P were found for all the sampling periods, encompassing hourly, biweekly, and seasonal time scales. The variability in P explained by Pfluo ranged from 84.3% to 91.4% when sampling periods were considered separately and reached 81.1% when all data were pooled. The results of the study show that despite its simplicity, the index Pfluo can be used to trace short‐term variations in the photosynthetic rate of undisturbed microphytobenthic assemblages undergoing rhythmic vertical migration. 相似文献
19.
Kate Osborne Angus A. Thompson Alistair J. Cheal Michael J. Emslie Kerryn A. Johns Michelle J. Jonker Murray Logan Ian R. Miller Hugh P. A. Sweatman 《Global Change Biology》2017,23(9):3869-3881
Climate change threatens coral reefs across the world. Intense bleaching has caused dramatic coral mortality in many tropical regions in recent decades, but less obvious chronic effects of temperature and other stressors can be equally threatening to the long‐term persistence of diverse coral‐dominated reef systems. Coral reefs persist if coral recovery rates equal or exceed average rates of mortality. While mortality from acute destructive events is often obvious and easy to measure, estimating recovery rates and investigating the factors that influence them requires long‐term commitment. Coastal development is increasing in many regions, and sea surface temperatures are also rising. The resulting chronic stresses have predictable, adverse effects on coral recovery, but the lack of consistent long‐term data sets has prevented measurement of how much coral recovery rates are actually changing. Using long‐term monitoring data from 47 reefs spread over 10 degrees of latitude on Australia's Great Barrier Reef (GBR), we used a modified Gompertz equation to estimate coral recovery rates following disturbance. We compared coral recovery rates in two periods: 7 years before and 7 years after an acute and widespread heat stress event on the GBR in 2002. From 2003 to 2009, there were few acute disturbances in the region, allowing us to attribute the observed shortfall in coral recovery rates to residual effects of acute heat stress plus other chronic stressors. Compared with the period before 2002, the recovery of fast‐growing Acroporidae and of “Other” slower growing hard corals slowed after 2002, doubling the time taken for modest levels of recovery. If this persists, recovery times will be increasing at a time when acute disturbances are predicted to become more frequent and intense. Our study supports the need for management actions to protect reefs from locally generated stresses, as well as urgent global action to mitigate climate change. 相似文献
20.
Natalia Herrn Gita R. Narayan Steve S. Doo Andr Klicpera Andr Freiwald Hildegard Westphal 《Ecology and evolution》2022,12(3)
Marine symbioses are integral to the persistence of ecosystem functioning in coral reefs. Solitary corals of the species Heteropsammia cochlea and Heterocyathus aequicostatus have been observed to live in symbiosis with the sipunculan worm Aspidosiphon muelleri muelleri, which inhabits a cavity within the coral, in Zanzibar (Tanzania). The symbiosis of these photosymbiotic corals enables the coral holobiont to move, in fine to coarse unconsolidated substrata, a process termed as “walking.” This allows the coral to escape sediment cover in turbid conditions which is crucial for these light‐dependent species. An additional commensalistic symbiosis of this coral‐worm holobiont is found between the Aspidosiphon worm and the cryptoendolithic bivalve Jousseaumiella sp., which resides within the cavity of the coral skeleton. To understand the morphological alterations caused by these symbioses, interspecific relationships, with respect to the carbonate structures between these three organisms, are documented using high‐resolution imaging techniques (scanning electron microscopy and µCT scanning). Documenting multi‐layered symbioses can shed light on how morphological plasticity interacts with environmental conditions to contribute to species persistence. 相似文献