Survival and growth of transplants of laboratory raised axenic seedlings of Enhalus acoroides (L.f.) Royle and field-collected plants of Syringodium isoetifolium (Aschers.) Dandy, Thalassia hemprichii (Ehrenb.) Aschers. and Halodule pinifolia (Miki) den Hartog

Experimental transplantation investigations, using laboratory raised axenic seedlings of Enhalus acoroides and natural populations of Syringodium isoetifolium, Thalassia hemprichii and Halodule pinifolia in the Gulf of Mannar Marine Biosphere Reserve, found that the denuded seagrass ecosystem of this Gulf can effectively be restored with plug and turfs methods of seagrass transplantation. Axenically developed E. acoroides, transplanted by the staples method, established by adapting to the prevailing environmental conditions. 0% seedlings “washed ashore” when the staples method was adopted using ‘L’ shaped bamboo sticks for transplanting E. acoroides and S. isoetifolium seedlings. This suggests that the seagrass transplantation using “L” shaped bamboo sticks, as staples will be technically feasible and eco-friendly for future seagrass transplantation programmes. Substratum type, duration of low tide exposure and environmental parameters like surface water temperature and turbidity are key parameters determining the success of the transplantation attempts.     

Measurement of chlorophyll fluorescence reveals mechanisms for habitat niche separation of the intertidal seagrasses <Emphasis Type="Italic">Thalassia hemprichii</Emphasis> and <Emphasis Type="Italic">Halodule uninervis</Emphasis>

In Taiwan, Thalassia hemprichii dominates the upper intertidal zone, whereas Halodule uninervis occupies the lower intertidal zone. We tested the hypothesis that T. hemprichii is better adapted to high irradiance and more resistant to air exposure than H. uninervis. The photosynthetic efficiency, damage, and extent of recovery were determined by measuring chlorophyll fluorescence using pulse amplitude modulated fluorometry. Both species growing in tidal pools, in response to high irradiance alone, revealed a small depression in maximal quantum yield of photosystem II (Fv/Fm) at noon. The second experiment compared the effect of air exposure alone and the combined effect of air exposure with high irradiance by interposing a shading screen on both species, growing in the intertidal zone over a diurnal cycle. Values of Fv/Fm of both the shaded and irradiated T. hemprichii remained high at low tide. However, H. uninervis exhibited a marked depression following air exposure and a synergistic depression under the combined effect. The experimental manipulations of exposure time demonstrated that the tolerance of T. hemprichii to the combined effect was longer and the recovery from air exposure following re-submersion was better than those of H. uninervis. Both species were more susceptible to the combined effect in the dry season than in the wet season. Our results suggest that air exposure is more important than high irradiance in constraining the distribution of H. uninervis in the upper intertidal zone. This was confirmed by transplantation experiments in which a rapid decline of H. uninervis was observed after transplantation into the upper intertidal zone. In the lower intertidal zone, measurements of the response of the photosynthetic electron transport rate to irradiance demonstrated that the transplanted T. hemprichii exhibited a sun-type response and H. uninervis a shade-type response.     

Juvenile life stages of the brown alga Fucus serratus L. are more sensitive to combined stress from high copper concentration and temperature than adults

The combined effects of exposure to copper and temperature were investigated in adult specimens and germlings of the canopy-forming brown alga Fucus serratus. A matrix of four temperatures, 6, 12, 17 and 22 °C, and three concentrations of copper, 0, 100 and 1,000 nM total copper were used. Measured endpoints were growth rate, chlorophyll fluorescence parameters and for germlings also survival. The growth rate of adult specimens of F. serratus changed with increasing temperature. Growth tended to be negatively affected by high concentrations of copper when exposed to heat (22 °C) though not significantly so. The photosynthetic performance (i.e., chlorophyll fluorescence parameters: F _v/F _m, maximum electron transport rate (ETR_max) and maximum non-photosynthetic quenching (NPQ_max) of adults was largely unaffected by both copper and temperature. Germling survival, growth rate and chlorophyll fluorescence parameters were affected by the combination of copper concentration and temperature. Increasing temperature led to reduced survival, increased rhizoid growth and higher F _v/F _m and ETR_max, whereas high copper concentration had a negative effect on the latter three endpoints. The negative effect of high copper concentration was amplified by high temperature. We conclude that juveniles of F. serratus are more susceptible to environmental stressors than adult specimens and recommend therefore including early life stages when assessing the risk of exposure to toxic compounds. Considering the response of adult specimens only may lead to false conclusions regarding the ecological impact of environmental stress.     

Mechanisms for the uptake of inorganic carbon by two species of symbiont-bearing foraminifera

The mechanisms for uptake of inorganic carbon (Ci) for photosynthesis and calcification of a perforate foraminifer, Amphistegina lobifera Larsen, and an imperforate species, Amphisorus hemprichii Ehrenberg, from the Gulf of Eilat, Red Sea were studied in 1986–1987 using ¹⁴C tracer techniques. Total Ci uptake of A. lobifera and photosynthetic carbon uptake of A. hemprichii fit the Hill-Whittingham equation that describes the overall rate of enzymatic reactions that are provided with their substrate through a diffusion barrier. This suggests that diffusion is the rate limiting step for total Ci uptake in A. lobifera. Photosynthesis by the isolated symbionts and uptake of CO₃ ^2- for calcification obey Michaelis-Menten kinetics indicating that enzymatic reactions determine the rate of the separate processes. Both photosynthesis and calcification can be inhibited without affecting each other. Calcification rates in A. lobifera were optimal at Ca levels around normal seawater concentration and were sensitive to inhibitors of respiratory adenosine triphosphate (ATP) generation and Ca-ATP-ase. This indicates that Ca uptake is also active. Calcification rates of A. hemprichii increased linearly as a function of external Ci concentration over the entire experimental range (0 to 4 mM Ci). In contrast, photosynthetic rates showed Hill-Whittingham type kinetics. The dependence of calcification on the CO₃ ^2- concentration was also linear, suggesting that its diffusion is the rate limiting step for calcification in A. hemprichii. Increasing Ca concentrations yielded higher calcification rates over the entire range measured (0 to 40 mM Ca). Calcification in A. hemprichii was less sensitive to inhibitors of ATP generation than in A. lobifera, suggesting that in A. hemprichii energy supply is less important for this process.     

Utilisation of mangroves and seagrasses by fishes in the Negombo Estuary,Sri Lanka

In two years of sampling, 10 287 fishes belonging to 62 species (39 families) were collected from mangroves and seagrasses of the Negombo Estuary. Of the species collected, 70% were marine, 27% estuarine and 3% freshwater. Aplocheilus melastigma, Ambassis dayi, Etroplus suratensis, E. maculatus, Bathygobius fuscus and Arothron immaculatus constituted 90% of the catch. Sixteen species were caught only from mangroves, 6 only from seagrasses, and 40 from both. The number of species, individuals, biomass and diversity were higher in seagrasses than in mangroves. Gobies and some siganids moved to the mangrove habitat as they grew, but cichlids, triacanthids, some eleotrids and tetraodontids preferred seagrasses. The number of species and individuals caught increased at the beginning of the north-east monsoon when the rainfall was low. The number of species and individual numbers were positively correlated with salinity and dissolved oxygen and negatively correlated with water temperature. Of the 33 species examined, seagrasses formed >25% of the gut content in juvenile Lates calcarifer, Apogon thermalis, E. suratensis, E. maculatus, Siganus javus, Butis butis and Bathygobius fuscus. Mangrove litter was the main gut content of the family Syngnathidae. E. suratensis, E. maculatus and S. javus from seagrasses contained more filamentous algae than seagrasses in their stomachs. S. javus collected from mangroves also contained more seagrasses in their stomachs than mangrove litter, indicating that the association of juvenile fishes with mangroves or seagrasses may not be obligate in estuaries subject to low tidal fluctuations.     

Photosynthetic utilisation of inorganic carbon by seagrasses from Zanzibar, East Africa

Photosynthetic rates of eight seagrass species from Zanzibar were limited by the inorganic carbon composition of natural seawater (2.1 mM, mostly in the form of HCO₃ ⁻), and they exhibited more than three time higher rates at inorganic carbon saturation (>6 mM). The intertidal species that grew most shallowly, Halophila ovalis, Halodule wrightii and Cymodocea rotundata, showed the highest affinity for inorganic carbon (K _1/2 = ca. 2.5 mM), followed by the subtidal species (K _1/2 > 5 mM). Photosynthesis of H. wrightii, C. rotundata, Cymodocea serrulata and Enhalus acoroides was >50% inhibited by acetazolamide, a membrane-impermeable inhibitor of carbonic anhydrase, indicating that extracellular HCO₃ ⁻ dehydration is an important part of their inorganic carbon uptake. Photosynthetic rates of H. wrightii, Thalassia hemprichii, Thalassodendron ciliatum, C. serrulata and E. acoroides were strongly reduced by changing the seawater pH from 8.2 to 8.6 in a closed system. In H. ovalis, C. rotundata and Syringodiumisoetifolium, photosynthesis at pH 8.6 was maintained at a higher level than could be caused by the ca. 30% CO₂ concentration which remained in the closed experimental systems at that pH, pointing toward HCO₃ ⁻ uptake in those species. It is suggested that the ability of H. ovalis and C. rotundata to grow in the high, frequently air-exposed, intertidal zone may be related to a capability to take up HCO₃ ⁻ directly, since this is a more efficient way of HCO₃ ⁻ utilisation than extracellular HCO₃ ⁻ dehydration under such conditions. The inability of all species to attain maximal photosynthetic rates under natural conditions of inorganic carbon supports the notion that seagrasses may respond favourably to any future increases in marine CO₂ levels. Received: 19 March 1997 / Accepted: 31 March 1997     

Intraspecific physiological variability of the gastropod Littorina saxatilis related to the vertical shore gradient in the White and North Seas

 Physiological responses to desiccation and temperature stress as well as behavioural responses to fast and abrupt environmental changes were investigated in high- and low-shore Littorina saxatilis (Olivi) from several populations from the White and North Seas. Variations in evaporation rates, resistance to air exposure and to acute and chronic temperature stress between animals from different shore levels were similar in White and North Sea periwinkles, consistent with the adaptive nature of these variations. High-shore snails were found to be able to conserve body water reserves better, to resist higher temperatures and to survive longer under conditions of combined temperature and desiccation stress than their low-shore counterparts. In a temperature range of 25 to 35 °C, the rate of evaporative water loss was positively correlated with temperature in low-shore snails while being largely temperature-independent in high-shore snails. Median lethal time during air exposure in L. saxatilis was negatively but not linearly related to the temperature of exposure. In a temperature range of 30 to 38 °C, the resistance to heat exposure in air was only slightly dependent on the temperature, with Q ₁₀ = 1.4 for the median lethal time; the heat resistance dropped drastically at temperatures above 38 °C, with Q ₁₀ = 593.8. This suggests different mechanisms of temperature resistance in different parts of the studied temperature range. In contrast, behavioural response to extreme salinity fluctuations was not uniform in the high- and low-shore periwinkles from the White and North Seas, which may reflect specific environmental conditions at different shore levels in the two areas studied. Observed physiological and behavioural variations are discussed from the viewpoint of different adaptive strategies employed by eulittoral and eulittoral-fringe animals within populations of a single species. Received: 13 December 1999 / Accepted: 11 April 2000     

Desiccation stress in two intertidal beachrock biofilms

Chlorophyll a fluorescence was used to look at the effect of desiccation on the photophysiology in two beachrock microbial biofilms from the intertidal rock platform of Heron Island, Australia. The photophysiological response to desiccation differed between the beachrock microbial communities. The black biofilm from the upper shoreline, dominated by Calothrix sp., showed a response typical of desiccation-tolerant cyanobacteria, where photosynthesis closed down during air exposure with a rapid and complete recovery upon rehydration. In contrast, the pink biofilm from the mid-intertidal zone, dominated by Blennothrix sp., showed no distinct response to desiccation stress and instead maintained reduced photosynthesis throughout drying and re-wetting cycles. Spatial differences in photosynthetic activity within the black biofilm were evident with a faster recovery rate of photosynthesis in the surface cyanobacteria than in the deeper layers of the biofilm. There was no variation with depth in the pink biofilm. The photophysiological differences in desiccation responses between the beachrock biofilms exemplify the ecological niche specialisation of these complex microbial communities, where the functional differences help to explain their vertical distribution on the intertidal shoreline.     

Buffer sensitivity of photosynthetic carbon utilisation in eight tropical seagrasses

Some of the mechanisms involved in inorganic carbon (Ci) acquisition by tropical seagrasses from the western Indian Ocean were described by Björk et al. (Mar Biol 129:363–366, 1997). However, since then, it has been found that an additional, buffer-sensitive, system of Ci utilisation may operate in some temperate seagrasses (Hellblom et al. in Aquat Bot 69:55–62, 2001, Hellblom and Axelsson in Photos Res 77:173–191, 2003); this buffer sensitivity indicates a mechanism in which electrogenic H⁺ extrusion may form acidic diffusion boundary layers, in which either HCO ₃ ^? –H⁺ is co-transported into the cells, or where HCO ₃ ^? is converted to CO₂ (as catalysed by carbonic anhydrase) prior to uptake of the latter Ci form. Because a buffer was used in the 1997 study, we found it important to reinvestigate those same eight species, taking into account the direct effect of buffers on this potential mode of Ci acquisition in these plants. In doing so, it was found that all seagrass species investigated except Cymodocea serrulata were sensitive to 50 mM TRIS buffer of the same pH as the natural seawater in which they grew (pH 8.0). Especially sensitive were Halophila ovalis, Halodule wrightii and Cymodocea rotundata, which grow high up in the intertidal zone (only ca. 50–65% of the net photosynthetic activity remained after the buffer additions), followed by the submerged Enhalus acoroides and Syringodium isoetifolium (ca. 75% activity remaining), while Thalassia hemprichii and Thalassodendron ciliatum, which grow in-between the two zones, were less sensitive to buffer additions (ca. 80–85% activity remaining). In addition to buffer sensitivity, all species were also sensitive to acetazolamide (AZ, an inhibitor of extracellular carbonic anhydrase activity) such that ca. 45–80% (but 90% for H. ovalis) of the net photosynthetic activity remained after adding this inhibitor. Raising the pH to 8.8 (in the presence of AZ) drastically reduced net photosynthetic rates (0–14% remaining in all species); it is assumed that this reduction in rates was due to the decreased CO₂ concentration at the higher pH. These results indicate that part of the 1997 results for the same species were due to a buffer effect on net photosynthesis. Based on the present results, it is concluded that (1) photosynthetic Ci acquisition in six of the eight investigated species is based on carbonic anhydrase catalysed HCO ₃ ^? to CO₂ conversions within an acidified diffusion boundary layer, (2) C. serrulata appears to support its photosynthesis by extracellular carbonic anhydrase catalysed CO₂ formation from HCO ₃ ^? without the need for acidic zones, (3) H. ovalis features a system in which H⁺ extrusion may be followed by HCO ₃ ^? –H⁺ co-transport into the cells, and (4) direct, non-H⁺-mediated, uptake of HCO ₃ ^? is improbable for any of the species.     

Uptake of inorganic carbon and internal carbon cycling in symbiont-bearing benthonic foraminifera

Incorporation rates of inorganic carbon and its distribution between the organic matter and the skeleton have been measured using ¹⁴C tracer techniques on two species of symbiont-bearing benthonic foraminifera in the Gulf of Elat: Amphistegina lobifera (a perforate species) and Amphisorus hemprichii (an imperforate species). Under constant experimental conditions, incorporation rates of the radiotracer become linear with time after several hours in A. hemprichii and after one day in A. lobifera. A. lobifera showed a lag time of 24 h for skeletal incorporation, whereas in A. hemprichii uptake into the skeleton started within 2 h. Pulse-chase incubations in radioactive seawater, followed by unlabelled incubations, demonstrate transfer of photosynthetically acquired ¹⁴C into the skeleton of A. lobifera. No such transfer was found in A. hemprichii. The total ¹⁴C uptake by A. lobifera increased during the first 24 h of cold chase incubation. This increase suggests the existence of an internal inorganic carbon pool that was lost (probably evaporated) during the analysis of pulse incubations. However, during the following chase incubations, the ¹⁴C in this pool was incorporated mainly into the skeleton and retained during analysis, causing the increase in the total uptake. No such increase was found in A. hemprichii. Additional ¹⁴C uptake experiments on other species of the genera Operculina, Heterostegina and Borelis suggest that the differences in pathways for incorporation of carbon between A. lobifera and A. hemprichii can be generalized to the perforate and imperforate foraminiferal groups. In perforate species, respired carbon originally taken up through photosynthesis is partly recycled into the skeleton. In imperforate species such a transfer has not been demonstrated. Perforate species seem to have a large internal inorganic carbon pool which serves mainly for calcification and possibly also for photosynthesis, while imperforate species may take up carbon for calcification directly from seawater or have a very small inorganic carbon pool.     

Photosynthetic response to temperature and desiccation of the intertidal alga Mastocarpus papillatus

When exposed to air during low tide, intertidal macroalgae experience a terrestrial environment and often encounter extreme levels of heating and desiccation. Two aspects of photosynthesis may be influenced by this increase in temperature and decrease in water content during exposure to air: (1) the rate of aerial photosynthesis itself, and (2) the rate at which aquatic photosynthesis recovers upon immersion in water at high tide. This laboratory study examines the effect of air temperature and desiccation on photosynthesis of the intertidal macroalga Mastocarpus papillatus Kützing. Plants were collected at Hopkins Marine Station, California, USA (36°37N; 121°54W) between July and December 1990. When apical tips were exposed to 15 to 25°C air for 2 h, photosynthesis was rapidly recovered upon reimmersion in seawater. Recovery was delayed, but complete, when tissue was exposed to 30°C air, but did not occur after exposure to 35°C air. Desiccation did not influence either the rate or the ultimate level of recovery upon reimmersion. Photosynthesis in air generally decreased with increasing desication, with no net photosynthesis occurring below 25% relative water content. Net photosynthesis of hydrated thalli increased with air temperature from 15 to 30°C, then decreased at 35°C. Dark respiration of hydrated thalli increased over the entire temperature range. This study indicates that thallus heating and desiccation during periods of exposure to air can potentially influence the total carbon budget of M. papillatus.     

Effects of in situ CO2 enrichment on the structural and chemical characteristics of the seagrass Thalassia testudinum

Seagrasses commonly display carbon-limited photosynthetic rates. Thus, increases in atmospheric pCO₂, and consequentially oceanic CO_2(aq) concentrations, may prove beneficial. While addressed in mesocosms, these hypotheses have not been tested in the field with manipulative experimentation. This study examines the effects of in situ CO_2(aq) enrichment on the structural and chemical characteristics of the tropical seagrass, Thalassia testudinum. CO_2(aq) availability was manipulated for 6 months in clear, open-top chambers within a shallow seagrass meadow in the Florida Keys (USA), reproducing forecasts for the year 2100. Structural characteristics (leaf area, leaf growth, shoot mass, and shoot density) were unresponsive to CO_2(aq) enrichment. However, leaf nitrogen and phosphorus content declined on average by 11 and 21 %, respectively. Belowground, non-structural carbohydrates increased by 29 %. These results indicate that increased CO_2(aq) availability may primarily alter the chemical composition of seagrasses, influencing both the nutrient status and resilience of these systems.     

An assessment of the potential health benefits of realizing the goals for PM<Subscript>10</Subscript> in the updated Chinese Ambient Air Quality Standard

As a response to the severe air quality problems in China, the Chinese Ministry of Environmental Protection in 2012 issued an updated Ambient Air Quality Standard (GB3095-2012), which set a stricter grade II PM₁₀ standard. A successful implementation of this standard will have an impact on human health through reduction of exposure to air pollution in the population. Using the methods of adjusted human capital and value of statistical life, the authors in this article estimate the economic impact of a successful implementation of the updated Ambient Air Quality Standard on human health in China. The key results are: 1) The human health benefits from reaching the updated standard for PM₁₀ would equal CNY 51.1 billion using adjusted human capital, accounting for 18.5% of total human health costs in China, and CNY 83.5 billion using the value of a statistical life; 2) the benefit of reaching the updated standard for PM₁₀ is highest in the east coastal areas and gradually declines for more Western provinces; and 3) the marginal benefit of public health increases as the environmental quality standard PM₁₀ improves. If the annual concentration of PM₁₀ were to be reduced from the target number in the original grade II standard to that in the updated standard, the mortality rate of long-term exposure would be reduced by 6.5% due to reduced chronic exposure. In addition, if the annual concentration were to be reduced further from updated grade II to grade I standard, the mortality rate for long-term exposure would be lowered by 32.8%.     

Analysis and prediction of the influence of energy utilization on air quality in Beijing

This work evaluates the influence of energy consumption on the future air quality in Beijing, using 2000 as the base year and 2008 as the target year. It establishes the emission inventory of primary PM₁₀, SO₂ and NO_x related to energy utilization in eight areas of Beijing. The air quality model was adopted to simulate the temporal and spatial distribution of each pollutant concentration in the eight urban areas. Their emission, concentration distribution, and sectoral share responsibility rate were analyzed, and air quality in 2008 was predicted. The industrial sector contributed above 40% of primary PM₁₀ and SO₂ resulting from energy consumption, while vehicles accounted for about 65% of NO_x. According to the current policy and development trend, air quality in the eight urban areas could become better in 2008 when the average concentrations of primary PM₁₀, SO₂ and NO₂ related to energy utilization at each monitored site are predicted to be about 25, 50 and 51 μg/m³, respectively.     

Brooded coral larvae differ in their response to high temperature and elevated pCO2 depending on the day of release

To evaluate the effects of temperature and pCO₂ on coral larvae, brooded larvae of Pocillopora damicornis from Nanwan Bay, Taiwan (21°56.179′N, 120°44.85′E), were exposed to ambient (419–470 μatm) and high (604–742 μatm) pCO₂ at ~25 and ~29 °C in two experiments conducted in March 2010 and March 2012. Larvae were sampled from four consecutive lunar days (LD) synchronized with spawning following the new moon, incubated in treatments for 24 h, and measured for respiration, maximum photochemical efficiency of PSII (F _v/F _m), and mortality. The most striking outcome was a strong effect of time (i.e., LD) on larvae performance: respiration was affected by an LD × temperature interaction in 2010 and 2012, as well as an LD × pCO₂ × temperature interaction in 2012; F _v/F _m was affected by LD in 2010 (but not 2012); and mortality was affected by an LD × pCO₂ interaction in 2010, and an LD × temperature interaction in 2012. There were no main effects of pCO₂ in 2010, but in 2012, high pCO₂ depressed metabolic rate and reduced mortality. Therefore, differences in larval performance depended on day of release and resulted in varying susceptibility to future predicted environmental conditions. These results underscore the importance of considering larval brood variation across days when designing experiments. Subtle differences in experimental outcomes between years suggest that transgenerational plasticity in combination with unique histories of exposure to physical conditions can modulate the response of brooded coral larvae to climate change and ocean acidification.     

Photosynthesis in Codium fragile (Chlorophyta) from a Nova Scotia estuary: responses to desiccation and hyposalinity

Codium fragile ssp. tomentosoides from Caribou Harbour, an estuarine site in the southern Gulf of St. Lawrence, was extremely tolerant to stresses from desiccation and reduced salinity. Photosynthetic responses of both rhizomatous and erect growth forms were measured using pulse amplitude modulation (PAM) fluorometry of chlorophyll a fluorescence to determine effective quantum yield (Φ_PSII) and relative electron transport rate (rETR). After 5 h of desiccation, thalli lost 20% of their mass, but still showed high levels of Φ_PSII. Thalli survived for at least 6 h in freshwater, and showed virtually complete recovery of photosynthetic capacity within a few hours of return to full seawater. Immersion in 8 psu showed virtually complete recovery until the 24 h treatment period. Combining desiccation and salinity stresses produced a synergistic effect, but plants still showed strong recovery even after 86% dehydration and reimmersion in 16 psu. These results suggest that the photosynthetic physiology of Codium fragile is highly adapted to growth in estuarine conditions.     

Tolerance of Hyas araneus zoea I larvae to elevated seawater PCO2 despite elevated metabolic costs

Early life stages of marine crustaceans respond sensitively to elevated seawater PCO₂. However, the underlying physiological mechanisms have not been studied well. We therefore investigated the effects of elevated seawater PCO₂ on oxygen consumption, dry weight, elemental composition, median developmental time (MDT) and mortality in zoea I larvae of the spider crab Hyas araneus (Svalbard 79°N/11°E; collection, May 2009; hatch, December 2009). At the time of moulting, oxygen consumption rate had reached a steady state level under control conditions. In contrast, elevated seawater PCO₂ caused the metabolic rate to rise continuously leading to a maximum 1.5-fold increase beyond control level a few days before moulting into the second stage (zoea II), followed by a pronounced decrease. Dry weight of larvae reared under high CO₂ conditions was lower than in control larvae at the beginning of the moult cycle, yet this difference had disappeared at the time of moulting. MDT of zoea I varied between 45 ± 1 days under control conditions and 42 ± 2 days under the highest seawater CO₂ concentration. The present study indicates that larval development under elevated seawater PCO₂ levels results in higher metabolic costs during premoulting events in zoea I. However, H. araneus zoea I larvae seem to be able to compensate for higher metabolic costs as larval MDT and survival was not affected by elevated PCO₂ levels.     

An improved method for the measurement of CO2 in marine animals,applied to three species of decapods

Previous methods for measuring CO₂ respired in sea water were inaccurate bacause of the high concentration of bound CO₂ (carbonates). The method developed here “refluxes” a fixed volume of air through a fixed volume of sea water while simultaneously trapping the respired CO₂. Tests were run long enough for the volume of respired CO₂ to approximately equal the CO₂ bound in the water, thus decreasing the former cause of inaccuracies. The method was tested with 3 species of crabs: Maia aquinado, Carcinus meanas, and Cancer pagurus. Tests lasted overnight (20 h). Six respirometers were used, 5 containing crabs and 1 control for the measurement of bound CO₂. The volume of respired CO₂ was given by the weight of trapped CO₂ (as BaCO₃) from the test units (the total of respired CO₂ and that in the test water) minus the weight of the control CO₂. In both fed and starved crabs, of all 3 species, CO₂ output followed the average trend of oxygen consumption, especially after feeding when both CO₂ and O₂ rose sharply. RQ's (respiratory quotients) could not be determined because O₂ was measured intermittently, but the relative ratio of CO₂ and O₂ was essentially unchanged throughout the experiments. In general, CO₂ was less variable than O₂ and may be a better indicator of average metabolic rate.     

Drought stress,rain and recovery of the intertidal seaweed <Emphasis Type="Italic">Fucus spiralis</Emphasis>

Non-motile organisms of intertidal shores such as seaweeds have to cope with a great variability of environmental factors. In this survey, we studied whether different morphotypes of the intertidal seaweed Fucus spiralis L. are also reflected in a characteristic performance. Desiccation and recovery of this Phaeophyceae were investigated in field experiments near Aljezur, Portugal. Fucus spiralis is exposed to serious desiccation during periods of falling tide, resulting in a tissue water loss of about 90%. Due to large semidiurnal tidal ranges in this area, two morphotypes can be distinguished: F. spiralis growing in the lower intertidal (LZ) is thicker and fleshier compared with plants in the upper intertidal (HZ), and this is reflected in a significant difference in fresh and dry mass. During sunny days and at low tide, effective quantum yields (Φ_PSII) decreased significantly after 2 h desiccation. This continued until re-submersion. The photosynthetic performances of HZ and LZ plants also differed significantly after LZ plants were already submerged and photosynthetisizing, but the HZ specimens still exposed to air. Recovery experiments after desiccation treatments showed fast recovery within 6 min after re-submersion in both morphotypes. HZ specimens showed a slower recovery, which indicates a protection measure to the adverse conditions in the upper intertidal. In 24 h desiccation treatments, however, HZ specimens expressed a significantly higher maximum fluorescence yield F _v /F _m recovery. Simulated rainfalls during low tides caused photosynthetic activity to drop to 50% of initial F _v /F _m , independent of the length of the rain period. Treated plants also fully recovered after 6 min re-submersion in seawater. A comparison of single fronds and tufts clearly indicated advantages of the tuft growth strategy: tufts showed higher Φ_PSII at prolonged emersion times. Our study indicated a clear relationship between size and drought resistance, which was primarily due to the smaller and hardy HZ plants that withstand longer desiccation times without damage.     

Salinity stress and hydrogen peroxide regulation of antioxidant defense system in Ulva fasciata

The regulation of antioxidant defense system in macroalgae exposed to salinity stress was examined in Ulva fasciata Delile. As compared to the 30‰ control, a long-term (4 days) exposure to hyposaline (5, 15‰) and hypersaline (60, 90, 120, 150‰) conditions inhibited growth rate and TTC reduction ability. A decrease in maximum quantum efficiency (F _v/F _m ratio) and the maintenance of superoxide dismutase activity under salinity stress indicate the potential generation of reactive oxygen species in chloroplasts. An exposure to 15, 60, and 90‰ decreased seawater H₂O₂ contents but increased thallus H₂O₂ contents that are positively correlated with TBARS and peroxide contents. Alleviation of oxidative damage and H₂O₂ accumulation at 15 and 90‰ by a H₂O₂ scavenger, dimethylthiourea, suggests that oxidative damage occurring under moderate hyposaline and hypersaline conditions is ascribed to accumulated H₂O₂. Increased glutathione reductase activity and glutathione content and decreased ascorbate content are responsible for accumulated H₂O₂ at 15, 60, and 90‰, while ascorbate peroxidase activity increased only at salinity ≥ 90‰. Catalase and peroxidase activities also increased at 60 and 90‰ for H₂O₂ removal, but only catalase showed activity increase at 15‰. For the regeneration of ascorbate, the activities of both dehydroascorbate reductase and monodehydroascorbate reductase were increased at 5 and 15‰ while only monodehydroascorbate reductase activity increased at 60 and 90‰. It is hypothesized that the availability of antioxidants and the activities of antioxidant enzymes are increased in U. fasciata to cope with the oxidative stress occurring in hyposaline and hypersaline conditions.