Calcium exchange and the measurement of calcification rates in the calcareous coralline red alga Amphiroa foliacea

⁴⁵Ca washout data of living thalli of Amphiroa foliacea Lamouroux in the light and dark show that there are three kinetically distinct Ca²⁺-exchanging compartments with approximate half-times (t 1/2) of 300, 20 and 3 min. The two slower compartments appear to be exchange from organic Ca²⁺-binding components of the cell wall, while the fast compartment probably represents exchange on the CaCO₃ crystal surface. Killed and decalcified thalli have a fourth compartment, with a t 1/2 of 20 to 35 min (other compartment half-times are 300, 40, 3 min), which has been identified as the greatly increased intercellular space produced during drying and decalcification. The ⁴⁵Ca and ¹⁴C uptake data show that a large proportion of the label initially taken up is into compartments other than the CaCO₃. As a result of this uptake, binding, and exchange of radioisotope, significant errors occur during the measurement of calcification rates, unless a kinetic analysis is carried out. Using such a technique, CaCO₃ calcification rates of A. folicea were measured with ⁴⁵Ca or ¹⁴C as tracers. Light stimulates calcification by up to 2.6 times, depending upon the age of the plant. Young segments have a markedly higher rate of calcification and photosythesis than do the older segments.     

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.     

RQ of benthic marine invertebrates

This study investigated an incubation method which employed simultaneous measurement of CO₂ production and O₂ consumption rates to calculate the RQ (respiratory quotient; CO₂ production rate: O₂ consumption rate) of individual benthic marine invertebrates. Carbon dioxide production rates were calculated from changes in CO₂ concentration determined using seawater pH. O₂ consumption rates were calculated from changes in O₂ concentration with a correction applied for O₂ flux across the air/water interface due to gaseous exchange. Species examined were Triphyllozoon sp. cf. moniliferum (MacGillivray 1860), a bryozoan; Herdmania momus (Savigny), a solitary ascidian; Poneroplax albida (Blainville 1825), a chiton; and Haliotis roei (Gray 1826), an abalone. Six individuals of each were collected on 14 November 1985 from the limestone walls of a cave in a nearshore reef off Marmion, Western Australia. After acclimation for 6 h in experimental conditions, rates of CO₂ production and O₂ consumption were measured. A minimum period of 4 h was required to obtain consistent RQ values for each species. The standard error (SE) of the (calculated) RQ ratio was 14 to 33% of the mean in incubations of 4 h, and less than 14% in incubations of 4 to 12 h. The RQ is commonly used as an indicator of unknown catabolic substrates by comparing it with biochemically determined limits for known substrates. This study provides a strong argument against using the RQ of individual animals to draw any conclusions about catabolic substrates. Unexplained variation in the components of the RQ of an individual, measured over short time periods, and the potential involvement of stored reserves in catabolism, over longer time periods, obscure the relationship between the RQ of individual animals and the ratio's biochemically determined limits.     

The use of metabolic ratios for determining the catabolic substrates of a solitary ascidian

In a previous study, Hatcher (1989: Mar. Biol. 102: 445–452) found that variations in CO₂ and O₂ respiration rates in individual marine invertebrates led to RQ (respiratory quotient) values which were variable and often outside theoretical limits. The present study was designed to examine the variability in several excretionbased metabolic ratios which are often used as alternatives for the RQ in qualitative predictions of catabolic substrates. The experimental organism was a solitary ascidian,Herdmania momus (Savigny), collected near Perth, Western Australia, between January and July 1984. Respiration and excretion rates ofH. momus were examined as a function of a progressive nutritional stress, and covariation was examined. Nutritional stress accounted for more of the variation over time in respiration rates (40 to 50%) than in NH ₄ ⁺ excretion rates (20%). Significant net exchanges of dissolved organic compounds were measured. Qualitative predictions of catabolic substrates were based on a comparison of metabolic ratios with theoretical limits. The O:PO ₄ ^3- ratios were lower than the theoretical limits. The values of the O:NH ₄ ⁺ and NH ₄ ⁺ :PO ₄ ^3- ratios were not influenced by nutritional conditions but changed as a function of reproductive condition of the ascidians. Based on the results of this study, it was concluded that metabolic ratios measured on individual ascidians cannot be reliable predictors of catabolic substrates.     

Calcification in the maerl coralline alga Phymatolithon calcareum: Effects of salinity and temperature

The coralline alga Phymatolithon calcareum was dredged from 13 m in the Kattegatt, Baltic Sea, in December, 1980, and its rate of calcification was measured by ⁴⁵Ca⁺⁺-uptake methods. Light-saturated calcification rates at 5°C ranged from 15.8 g CaCO₃ g^-1 dry wt h^-1 for the basal parts of the plants to 38.7 g CaCO₃ g^-1 dry wt h^-1 for the tips. These age gradients were not apparent when calcification rates were expressed on the basis of surface area. Experiments with salinity (10, 20, 30) and temperature (0°, 5°, 10°, 20°C) indicated that optimum conditions for calcification were at 30 S and at temperatures above 10°C. Salinity had a greater influence on calcification rate than did temperature, and there was a positive relationship between salinity and calcification rate at all temperatures. In 6 mo old cultures, salinity was again the important factor, with all plants remaining healthy at 30 except those at the highest temperature (20°C). These trends, and the low calcification rates at 10S (4.6 g CaCO₃ g^-1 dry wt h^-1 at 5°C to 8.6 g CaCO₃g^-1 dry wt h^-1 at 20°C) suggest that low salinity may be the explanation for the general absence of P. calcareum from the brackish waters of the Baltic Sea. Short-term experiments in which salinity was kept constant while Ca⁺⁺ concentration was altered, and experiments in which salinity was varied and Ca⁺⁺ concentration kept constant, suggest that it is the calcium ion concentration and not salinity per se which affects calcification rates.     

Cuttlebone calcification increases during exposure to elevated seawater pCO2 in the cephalopod Sepia officinalis

Changes in seawater carbonate chemistry that accompany ongoing ocean acidification have been found to affect calcification processes in many marine invertebrates. In contrast to the response of most invertebrates, calcification rates increase in the cephalopod Sepia officinalis during long-term exposure to elevated seawater pCO₂. The present trial investigated structural changes in the cuttlebones of S. officinalis calcified during 6 weeks of exposure to 615 Pa CO₂. Cuttlebone mass increased sevenfold over the course of the growth trail, reaching a mean value of 0.71 ± 0.15 g. Depending on cuttlefish size (mantle lengths 44–56 mm), cuttlebones of CO₂-incubated individuals accreted 22–55% more CaCO₃ compared to controls at 64 Pa CO₂. However, the height of the CO₂-exposed cuttlebones was reduced. A decrease in spacing of the cuttlebone lamellae, from 384 ± 26 to 195 ± 38 μm, accounted for the height reduction The greater CaCO₃ content of the CO₂-incubated cuttlebones can be attributed to an increase in thickness of the lamellar and pillar walls. Particularly, pillar thickness increased from 2.6 ± 0.6 to 4.9 ± 2.2 μm. Interestingly, the incorporation of non-acid-soluble organic matrix (chitin) in the cuttlebones of CO₂-exposed individuals was reduced by 30% on average. The apparent robustness of calcification processes in S. officinalis, and other powerful ion regulators such as decapod cructaceans, during exposure to elevated pCO₂ is predicated to be closely connected to the increased extracellular [HCO₃ ⁻] maintained by these organisms to compensate extracellular pH. The potential negative impact of increased calcification in the cuttlebone of S. officinalis is discussed with regard to its function as a lightweight and highly porous buoyancy regulation device. Further studies working with lower seawater pCO₂ values are necessary to evaluate if the observed phenomenon is of ecological relevance.     

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.     

Physiological energetics of the intertidal sea anemone Anthopleura elegantissima

Energy budgets were calculated for individuals of the sea anemone Anthopleura elegantissima (Brandt), collected in 1981 and 1982 from Bodega Harbor, California, USA. Rates of ammonium excretion were measured in high-and low-intertidal, symbiotic and aposymbiotic sea anemones within 24 h of collection. Among symbiotic and aposymbiotic individuals, no differences in excretion rate were found on the basis of intertidal height. However, rates of ammonium excretion in aposymbiotic anemones (2.14 mol NH ₊ ⁴ g^-1 h^-1) were significantly higher than in symbiotic ones (0.288 mol NH ₊ ⁴ g^-1 h^-1). Rates of excretion were used with estimated rates of oxygen uptake to calculate nitrogen quotients (NQ). NQ and RQ values from the literature were used to calculate an oxyenthalpic equivalent [501 kJ (mol O₂)^-1 for R+U], and mass proportions of protein (54%), carbohydrate (44%) and lipid (2%) catabolized during routine metabolism in this species 24 h after feeding. Integrated energy budgets of these experimental anemones were calculated from data on ingestion, absorption and growth, and estimates of translocated energy from the symbiotic algae. Contribution of zooxanthellae to animal respiration based on translocation=90% and RQ=0.97 are 41 and 79% in high-and low-intertidal anemones, respectively. Calculated scope for growth is greater than directly measured growth in both high-and low-intertidal individuals. The deficit, estimated as 30% of assimilated energy in high-intertidal anemones, is attributed to unmeasured costs (specific dynamic effect) or production (mucus). Low-intertidal anemones lost mass during the experiment, implying that the magnitude of the deficit was greater in these anemones than in upper intertidal individuals. Anemones from both shore levels lost zooxanthellae during the experiment, which contributed to energy loss since the contribution of the zooxanthellae is greater in low-intertidal anemones. Scope for growth is preserved in high-intertidal anemones (29% of assimilated energy) because metabolic demands are lower due to aerial exposure, and prey capture rate is higher compared to lowshore anemones. Although possibly underestimated, lower scope for growth in low-shore anemones may result from continuous feeding and digestion processes that are less efficient than those of periodically feeding high-intertidal anemones.     

Gene flow among population of a teleost (painted greenling,Oxylebius pictus) from Puget Sound to southern California

Net photosynthetic oxygen evolution in Amphiroa anceps (Lamarck) Decaisne is inhibited at high oxygen concentrations. Photosynthesis is highest between pH 6.5 and 7.5. At pH 9 to 10 there is still a significant photosynthetic rate, suggesting that this alga can use HCO _- ³ as a substrate for photosynthesis. At pH 7.0 to 8.5, the photosynthetic rate saturates at a total inorganic carbon concentration (C_i) greater than 3 mM. At pH 8.5 and 8.8, calcification rate continues to increase with increasing concentration of C_i. Between pH 7 and 9, the calcification rate in the light in A. foliacea Lamouroux is proportional to the photosynthetic rate, whereas at higher pH where the photosynthetic rate is very low, the calcification rate is stimulated by the higher concentration of CO _2- ³ ion. At all pH values examined, the calcification rate of living plants in the dark and of dead plants is directly proportional to the CO _2- ³ ion concentration, suggesting little metabolic involvement in calcification processes in the dark, whereas calcification in live A. foliacea in the light is influenced both by the photosynthetic rate and the CO _2- ³ ion concentration in the medium.     

Nitrate uptake and assimilation in Thalassiosira weissflogii and Phaeodactylum tricornutum: interactions with photosynthesis and with the uptake of other ions

Interactions of the nitrate, phosphate, and ammonium uptake systems and the interactions of these systems with photosynthesis were investigated for Thalassiosira weissflogii and Phaeodactylum tricornutum preconditioned in continuous culture. The cultures were supplied with NO _- ³ and PO ₌ ⁴ in an N:P atomic ratio of 15:1, and residual concentrations of both nutrients in the growth chamber were very low. The rate of NO _- ³ uptake was reduced by the addition of NH ₊ ⁴ or PO ₌ ⁴ . The rate of PO ₌ ⁴ uptake by T. weissflogii was reduced by the addition of NH ₊ ⁴ . The rate of carbon fixation was reduced by NO _- ³ additions and slightly reduced by the addition of PO ₌ ⁴ . There were two components of NO _- ³ uptake, one light-dependent and one light-independent. Uptake inhibition by added PO ₌ ⁴ acted on the light-independent component. The change in the C fixation rate due to added NO _- ³ was equal to the rate of NO _- ³ uptake by the light-dependent component on a molar basis. Nitrate assimilation (reduction) rates were calculated from the time course of extracellular and intracellular NO _- ³ concentrations. The light-dark change in the assimilation rate was similar to the light-dark change in the uptake rate, suggesting close coupling between the light-dependent components of uptake and assimilation. The assimilation rate dropped upon exhaustion of extracellular NO _- ³ , implying that an uptake-coupled component of assimilation is unavailable for the assimilation of intracellular NO _- ³ . The reduction in the C fixation rate due to NO _- ³ was temporally associated with uptake rather than assimilation, but may reflect interaction with either the light-dependent uptake step or the closely coupled assimilation. Phosphate additions reduced the rate of NO _- ³ uptake, while the rate of assimilation was unaffected.     

Influence of some coral reef communities on the calcium carbonate budget of Tiahura reef (Moorea,French Polynesia)

The calcium carbonate budget of coral reefs is the result of the interaction of the processes of calcification and biological degradation, and is reflected in the chemical properties of the seawater overlying the reefs. A series of experiments at Moorea Island (French Polynesia) in 1988 monitored the diurnal and nocturnal variations in the chemical properties of seawater under field and laboratory conditions. Our results revealed that in the study area (Tiahura barrier reef flat), the calcium carbonate budget varied over space and time as a function of location in the water current. Two in-situ sites were investigated; one was situated 100 m from the algal crest of the barrier reef, the other 300 m further downstream. As a result of cumulative upstream events, the daily net calcification was ten times higher at the downstream (5.22 gm^-2 d^-1) than at the upstream (0.45 gm^-2 d^-1) site. The carbonate uptake by in situ Porites lobata in enclosures (8 kgm^-2 yr^-1) was ten times higher than the uptake by the whole community in the surrounding water (0.8 kgm^-2 yr^-1) and five times higher than that recorded for P. lobata in laboratory experiments (1.4 kgm^-2 yr^-1), where illumination levels were 10% of in situ levels. In laboratory experiments, the planktonic fraction of the seawater had no perceptible influence on the calcium carbonate budget. In the absence of bioeroders, living coral totally depleted the carbonate content of the seawater (3.7 gm^-2d^-1). Bioerosive organisms played an important role in restoring this calcium carbonate; e.g. sea urchins grazing on algal turf covering dead coral ingested CaCO₃ and released this as a carbonate powder (1.26 gm^-2d^-1); a form of carbonate which is extremely accessible to chemical dissolution.     

Experimental ecology of the temperate scleractinian coral Astrangia danae

The combined effects of temperature, light and symbiont density on the metabolic rate and calcification of the temperate coral Astrangia danae were studied experimentally using colonies containing different concentrations of zooxanthellae. After acclimation to five temperatures between 6.5° and 27°C, and incubation at three light levels and in darkness, respiration and photosynthesis were measured and corrected for rates due to commensals alone. Calcification rates were regressed on zooxanthellae concentration and production in order to define “symbiotic” and “non-symbiotic” averages, and the enhancement of calcification by symbiotic interactions in the polyps. Respiration by the polyparium varied less with temperature between 11.5° and 23°C than that of the commensals, suggesting physiological acclimation by the coral tissue. In-vivo zooxanthellae photosynthesis increased linearly with temperature and was near its maximum at 400 μEin m^?2 s^?1, but the photosynthesis of the endolithic algae of the corallum varied little between 11.5° and 27°C. Calcification at any given temperature was near its maximum at 40 μEin m^?2 s^?1 in both symbiotic and non-symbiotic corals. CaCO₃ deposition increased linearly with temperature in non-symbiotic colonies and in symbiotic colonies incubated in the dark. In symbiotic colonies, calcification in the light increased above these basic rates as temperature rose above 15°C. Below 15°C, symbiotic interactions failed to stimulate calcification, apparently due both to a lowering of zooxanthellae photosynthesis and to a decrease in the enhancing effect of any given level of primary production.     

Characterization and role of carbonic anhydrase in the calcification process of the azooxanthellate coral <Emphasis Type="Italic">Tubastrea aurea</Emphasis>

In zooxanthellate corals, the photosynthetic fixation of carbon dioxide and the precipitation of CaCO₃ are intimately linked both spatially and temporally making it difficult to study carbon transport mechanisms involved in each pathway. When studying Tubastrea aurea, a coral devoid of zooxanthellae, we can focus on carbon transport mechanisms involved only in the calcification process. We performed this study to characterize T. aurea carbonic anhydrase and to determine its role in the calcification process. We have shown that inhibition of tissular carbonic anhydrase activity affects the calcification rate. We have measured the activity of this enzyme both in the tissues and in the organix matrix extracted from the skeleton. Our results indicate that organic matrix proteins, which are synthesized by the calcifying tissues, are not only structural proteins, but they also play a crucial catalytic role by eliminating the kinetic barrier to interconversion of inorganic carbon at the calcification site. By immunochemistry we have demonstrated the presence of a protein both in the tissues and in the organic matrix, which shares common features with prokaryotic carbonic anhydrases.     

Inorganic nitrogen metabolism inUlva rigida illuminated with blue light

Inorganic nitrogen metabolism in blue light was studied for the green algaUlva rigida C. Agardh collected in the south of Spain (Punta Carnero, Algeciras) in the winter of 1987. NH₄ ⁺ has been reported to inhibit NO₃ ^- uptake; however,U. rigida showed a net NO₃ ^- uptake even when the NH₄ ⁺ concentration of the external medium was three or four times greater than the concentration of NO₃ ^-. NO₃ ^- uptake rates were similar in both darkness and in blue light of various photon fluence rates (PFR) ranging from 17 to 160 mol m^-2 s^-1. Since NO₃ ^- uptake is an active mechanism involving the consumption of ATP, respiratory metabolism can provide enough ATP to maintain the energetic requirement of NO₃ ^- transport even in darkness. In contrast, NO₃ ^- reduction inU. rigida was highly dependent on the net photosynthetic rate. After 7 h in blue light, intracellular NO₃ ^- concentrations ([NO₃ ^-] _i ) were higher in specimens exposed to intensities below the light compensation point (LCP) than in those incubated at a PFR above the LCP. When PFR is below the light compensation point, NO₃ ^- reduction is low, probably because all the NADH produced by the cells is oxidized in the respiratory chain in order to produce ATP to maintain a steady NO₃ ^- transport rate. The total nitrogen (TN) and carbon (TC) contents decreased from darkness to 33 mol m^-2 s^-1 in blue light. In this range, catabolic processes prevailed over anabolic ones. In contrast, increases in TN and TC contents were observed above the light compensation point. The C : N ratio increased with light intensity, reaching a stable value of 17 at 78 mol m^-2 s^-1 in blue light. Intracellular NO₃ ^- concentration and NO₃ ^- reduction appear to be directly controlled by light intensity. This external control of [NO₃ ^-]_i and the small capacity ofU. rigida to retain incorporated NO₃ ^-, NO₂ ^- and NH₄ ⁺ ions may explain its nitrophilic character.     

Substrate catabolism related to reproduction in the bay scallop Argopecten irradians concentricus,as determined by O/N and RQ physiological indexes

Weight specific rates of oxygen consumption carbon dioxide production, and ammonia-N excretion, measured for a Florida population of the bay scallop Argopecten irradians concentricus between May and September, 1982 and October and November, 1983 were significantly correlated (P<0.0005) to environmental factors that co-varied seasonally with metabolic shifts related to reproduction. Mean O/N and CO₂/O₂ (RQ) molar ratios indicates that scallop energy metabolism varied over the course of the reproductive cycle. Resting stage individuals (May-early June) had RQ values close to 0.7, indicative of a predominantly lipid-based metabolism. During the initial stages of gametogenesis (late June-early July) scallops catabolized primarily carbohydrate, as evidenced by maximum O/N (>22) values and RQ values close to 1.0 RQ values >1.0 indicated a possible carbohydrate to lipid conversion during the period of cytoplasmic growth (late July-early September). As gametes matured and spawning commenced (late September-November), metabolism became primarily protein based, as indicated by O/N and RQ values around 9.0 and 0.8, respectively. This pattern of substrate catabolism supports existing data on the storage and utilization of specific energy reserves with respect to reproduction in this species.     

The influence of macrofauna on estuarine benthic community metabolism: a microcosm study

Effects of benthic macrofauna (Corophium volutator, Hydrobia sp., Nereis virens) on benthic community metabolism were studied over a 65-d period in microcosms kept in either light/dark cycle (L/D-system) or in continuous darkness (D-system). Sediment and animals were collected in January 1986 in the shallow mesohaline estuary, Norsminde Fjord, Denmark. The primary production in the L/D-system after 10 d acted as a stabilizing agent on the O₂ and CO₂ flux rates, whereas the D-system showed decreasing O₂ and CO₂ flux throughout the period. Mean O₂ uptake over the experimental period ranged from 0.38 to 1.24 mmol m^–2 h^–1 and CO₂ release varied from 0.80 to 1.63 mmol m^–2 h^–1 in both systems. The presence of macrofauna stimulated community respiration rates measured in darknes, 1.4 to 3.0 and 0.9 to 2.0 times for O₂ and CO₂, respectively. In contrast, macrofauna lowered primary production. Gross primary production varied from 1.06 to 2.26 mmol O₂ m^–2 h^–1 and from 1.26 to 2.62 mmol CO₂ m^–2 h^–1. The community respiratory quotient (CRQ, CO₂/O₂) was generally higher in the begining of the experiment (0–20 d, mean 1.89) than in the period from Days 20 to 65 (mean 1.38). The L/D-system exhibited lower CRQ (ca. 1) than the D-system. The community photosynthetic quotient varied for both net and gross primary production from 0.64 to 1.03, mean 0.81. The heterotrophic D-system revealed a sharp decrease in the sediment content of chlorophyll a as compared to the initial content. In the autotrophic L/D-system, a significant increase in chlorophyll a concentration was observed in cores lacking animals and cores with C. volutator (The latter species died during the experiment). Due to grazing and other macrofauna activities other cores of the L/D-system exhibited no significant change in chlorophyll a concentration. Community primary production was linearly correlated to the chlorophyll a content in the 0 to 0.5 cm layer. Fluxes of DIN (NH₄ ⁺+NO₂ ^–+NO₃ ^–) did not reveal significant temporal changes during the experiment. Highest rates were found for the cores containing animals, mainly because of an increased NH₄ ⁺ flux. The release of DIN decreased significantly due to uptake by benthic microalgae in the L/D-system. No effects of the added macrofauna were found on particulate organic carbon (POC), particulate organic nitrogen (PON), total carbon dioxide (TCO₂) and NH₄ ⁺ in the sediment. The ratio between POC and PON was nearly constant (9.69) in all sediment dephts. The relationship between TCO₂ and NH₄ ⁺ was more complex, with ratios below 2 cm depth similar to those for POC/PON, but with low ratios (3.46) at the sediment surface.     

A morphological and structural study of the larval shell from the abalone <Emphasis Type="Italic">Haliotis tuberculata</Emphasis>

The larval shell of the marine gastropod Haliotis tuberculata was investigated by polarised light microscopy, scanning electron microscopy, Raman microspectroscopy and infra-red spectroscopy. Trochophore and veliger larval sections were used for histological examination of the growing shell and each larval stage was related to the shell development and the appearance of calcified formations. We determined the stage of initial calcification by specific staining combined with polarised light examination. The shell of 30-h-old pre-veliger larvae was found to be mineralized, confirming that calcification occurred before larval torsion. Using both infra-red and Raman spectroscopy, we showed that CaCO₃ deposition occurred at the pre-veliger stage and that the mineral phase initially deposited was essentially composed of aragonite.     

Different patterns of growth and nitrogen uptake in two clones of marineSynechococcus spp.

We grew marineSynechococcus Clones WH7803 and WH8018 at 150µE m^–2 s^–1 in dilute batch cultures with NH ₄ ⁺ as the limiting nutrient. The maximal uptake capacities for NH ₄ ⁺ and NO ₃ ^- were measured in frequent experiments during log and stationary phases of growth. Clone WH7803, originally isolated from oceanic waters, had a specific uptake rate of NH ₄ ⁺ that approximated the maximum (log phase) specific growth rate (ca ~ 0.025 h^–1). NO ₃ ^- uptake was observed only after nitrogen in the media was depleted; the NO ₃ ^– uptake capacity was ca 12% the capacity for NH ₄ ⁺ uptake throughout the nitrogen depleted period. Growth was arrested upon nitrogen depletion, but resumed soon after reinoculation into fresh media, even after 5 d of starvation. Clone WH8018, originally isolated from coastal waters, revealed a five-fold enhancement in the NH ₄ ⁺ uptake rate relative to growth rate at the time of nitrogen depletion. As nitrogen starvation proceeded, this enhancement was reduced. This clone, too, was able to take up NO ₃ ^- once nitrogen in the media was depleted, but only after ca 20 h. Growth continued for a limited period during nitrogen depletion, but nitrogen-starved cells were slow to recover upon reinoculation into fresh media. We speculate that clonal differences may reflect differences in the molecular regulation of nitrogen assimilation.     

The role of metabolic nitrogen in coral calcification

When pieces of the staghorn coral Acropora acuminata are incubated with ¹⁴C-urea, the label is incorporated into skeletal carbonate. Incorporation of this label differs from that of H¹⁴CO ₃ ^- , suggesting urea is not immediately hydrolysed to provide a further source of HCO ₃ ^- . The effects of certain organic substrates upon calcification suggest the ornithine cycle is involved. Citrulline, an ornithine cycle intermediate, is found in high concentrations in the tissues of hermatypic corals. Urea, allantoins, NH₃ and arginine are also present. These compounds are barely detectable in zooxanthellae or an ahermatypic coral. The allantoins may be present as calcium salts. It is suggested that allantoins are the medium by which Ca²⁺ and CO₂ are transported to sites of calcification. Hydrolysis of urea, formed by breakdown of allantoins, yields CO₂ and NH₃. The NH₃ may neutralise protons formed during precipitation of CaCO₃ and bring about their removal from sites of calcification. As well as providing urea, the ornithine cycle may also be involved in the removal of NH₃ from sites of calcification.     

Uptake and elimination kinetics of triphenyltin hydroxide by two fish species

The uptake from water and the elimination of carbon‐14 radiolabelled triphenyltin hydroxide ([¹⁴C]TPTH) was studied in two fish species: guppy (Poecilia reticulata) and rainbow trout larvae (Salmo gairdneri). During all the experiments no steady state in fish was found. TPTH was rapidly taken up, while elimination was very slow. Uptake and elimination rate constants (k ₁ and k ₂, respectively), and a bioconcentration factor were estimated, assuming first order kinetics.

During eight days of exposure of guppy to TPTH an uptake rate constant k ₁ of 70±7L/kg.d and an elimination rate constant k ₂ of 0.005 ±0.029d ^‐1 was found. This resulted in a biconcentration factor of at least 2.1 × 10³L/kg (wet weight). Comparable results were obtained during a 30 days exposure experiment with guppy: k ₁ was 41±2L/kg.d, k ₂ 0.014 + 0.002d^‐1, and the bioconcentration factor was estimated to be 2.9 × 10³ L/kg (wet weight).

Four days exposure of rainbow trout larvae resulted in a it, of 22+ 2 L/kg.d, and a k ₂ of 0.031 ±0.007d^‐1. Using these k, and k ₂ values it was estimated that the biconcentration factor exceeds 650 L/kg (wet weight).