Inter-polyp genetic and physiological characterisation of <Emphasis Type="Italic">Symbiodinium</Emphasis> in an <Emphasis Type="Italic">Acropora valida</Emphasis> colony

Corals harbouring genetically mixed communities of endosymbiotic algae (Symbiodinium) often show distribution patterns in accordance with differences in light climate across an individual colony. However, the physiology of these genetically characterised communities is not well understood. Single stranded conformation polymorphism (SSCP) and real time quantitative polymerase chain reaction (qPCR) analyses were used to examine the genetic diversity of the Symbiodinium community in hospite across an individual colony of Acropora valida at the spatial scale of single polyps. The physiological characteristics of the polyps were examined prior to sampling with a combined O₂ microelectrode with a fibre-optic microprobe (combined sensor diameter 50–100 μm) enabling simultaneous measurements of O₂ concentration, gross photosynthesis rate and photosystem II (PSII) quantum yield at the coral surface as a function of increasing irradiances. Both sun- and shade-adapted polyps were found to harbour either Symbiodinium clade C types alone or clades A and C simultaneously. Polyps were grouped in two categories according to (1) their orientation towardps light, or (2) their symbiont community composition. Physiological differences were not detected between sun- and shade-adapted polyps, but O₂ concentration at 1,100 μmol photons m⁻² s⁻¹ was higher in polyps that harboured both clades A and C symbionts than in polyps that harboured clade C only. These results suggest that the acclimatisation of zooxanthellae of individual polyps of an A. valida colony to ambient light levels may not be the only determinant of the photosynthetic capacity of zooxanthellae. Here, we found that photosynthetic capacity is also likely to have a strong genetic basis and differs between genetically distinct Symbiodinium types.     

Irradiance and temperature regulation of oxygenic photosynthesis and O2 consumption in a hypersaline cyanobacterial mat (Solar Lake, Egypt)

 Short-term effects of temperature and irradiance on oxygenic photosynthesis and O₂ consumption in a hypersaline cyanobacterial mat were investigated with O₂ microsensors in a laboratory. The effect of temperature on O₂ fluxes across the mat–water interface was studied in the dark and at a saturating high surface irradiance (2162 μmol photons m⁻² s⁻¹) in the temperature range from 15 to 45 °C. Areal rates of dark O₂ consumption increased almost linearly with temperature. The apparent activation energy of 18 kJ mol⁻¹ and the corresponding Q ₁₀ value (25 to 35 °C) of 1.3 indicated a relative low temperature dependence of dark O₂ consumption due to mass transfer limitations imposed by the diffusive boundary layer at all temperatures. Areal rates of net photosynthesis increased with temperature up to 40 °C and exhibited a Q ₁₀ value (20 to 30 °C) of 2.8. Both O₂ dynamics and rates of gross photosynthesis at the mat surface increased with temperature up to 40 °C, with the most pronounced increase of gross photosynthesis at the mat surface between 25 and 35 °C (Q ₁₀ of 3.1). In another mat sample, measurements at increasing surface irradiances (0 to 2319 μmol photons m⁻² s⁻¹) were performed at 25, 33 (the in situ temperature) and 40 °C. At all temperatures, areal rates of gross photosynthesis saturated with no significant reduction due to photoinhibition at high irradiances. The initial slope and the onset of saturation (E _k = 148 to 185 μmol photons m⁻² s⁻¹) estimated from P versus E _d curves showed no clear trend with temperature, while maximal photosynthesis increased with temperature. Gross photosynthesis was stimulated by temperature at each irradiance except at the lowest irradiance of 54 μmol photons m⁻² s⁻¹, where oxygenic gross photosynthesis and also the thickness of the photic zone was significantly reduced at 40 °C. The compensation irradiance increased with temperature, from 32 μmol photons m⁻² s⁻¹ at 25 °C to 77 μmol photons m⁻² s⁻¹ at 40 °C, due to increased rates of O₂ consumption relative to gross photosynthesis. Areal rates of O₂ consumption in the illuminated mat were higher than dark O₂ consumption at corresponding temperatures, due to an increasing O₂ consumption in the photic zone with increasing irradiance. Both light and temperature enhanced the internal O₂ cycling within hypersaline cyanobacterial mats. Received: 30 November 1999 / Accepted: 11 April 2000     

<Emphasis Type="Italic">Symbiodinium</Emphasis> sp. associations in the gorgonian<Emphasis Type="Italic"> Pseudopterogorgia elisabethae</Emphasis> in the Bahamas: high levels of genetic variability and population structure in symbiotic dinoflagellates

Little is known concerning the fine-scale diversity, population structure, and biogeography for Symbiodinium spp. populations inhabiting particular invertebrate species, including the gorgonian corals, which are prevalent members of reef communities in the Gulf of Mexico, the Caribbean, and the western Atlantic. This study examined the Symbiodinium sp. clade B symbionts hosted by the Caribbean gorgonian Pseudopterogorgia elisabethae (Bayer). A total of 575 colonies of P. elisabethae were sampled in 1995 and 1998–2000 from 12 populations lying along an ~450 km transect in the Bahamas and their Symbiodinium sp. clade B symbionts genotyped at two polymorphic dinucleotide microsatellite loci. Twenty-three unique, two-locus genotypes were identified in association with these P. elisabethae colonies. Most colonies hosted only a single Symbiodinium sp. clade B genotype; however, in some instances ( n=25), two genotypes were harbored simultaneously. For 10 of the 12 populations, 66–100% of the P. elisabethae colonies hosted the same symbiont genotype. Added to this, in 9 of the 12 populations, a Symbiodinium sp. clade B genotype was either unique to a population or found infrequently in other populations. This distribution of Symbiodinium sp. clade B genotypes resulted in statistically significant ( P<0.05 or <0.001) differentiation in 62 of 66 pairwise comparisons of P. elisabethae populations. Tests of linkage disequilibrium suggested that a combination of clonal propagation of the haploid phase and recombination is responsible for maintaining these distinct Symbiodinium sp. clade B populations.     

Aerobic metabolic rates of swimming juvenile mako sharks, <Emphasis Type="Italic">Isurus oxyrinchus</Emphasis>

The shortfin mako shark, Isurus oxyrinchus, is a highly streamlined epipelagic predator that has several anatomical and physiological specializations hypothesized to increase aerobic swimming performance. A large swim-tunnel respirometer was used to measure oxygen consumption (MO₂) in juvenile mako sharks (swimming under controlled temperature and flow conditions) to test the hypothesis that the mako shark has an elevated maintenance metabolism when compared to other sharks of similar size swimming at the same water temperature. Specimen collections were conducted off the coast of southern California, USA (32.94°N and 117.37°W) in 2001-2002 at sea-surface temperatures of 16.0–21.0°C. Swimming MO₂ and tail beat frequency (TBF) were measured for nine mako sharks [77–107 cm in total length (TL) and 4.4 to 9.5 kg body mass] at speeds from 28 to 54 cm s⁻¹ (0.27–0.65 TL s⁻¹) and water temperatures of 16.5–19.5°C. Standard metabolic rate (SMR) was estimated from the extrapolation to 0-velocity of the linear regression through the LogMO₂ and swimming speed data. The estimated LogSMR (±SE) for the pooled data was 2.0937 ± 0.058 or 124 mg O₂ kg⁻¹ h⁻¹. The routine metabolic rate (RMR) calculated from seventeen MO₂ measurements from all specimens, at all test speeds was (mean ± SE) 344 ± 22 mg O₂ kg⁻¹h⁻¹ at 0.44 ± 0.03 TL s⁻¹. The maximum metabolic rate (MMR) measured for any one shark in this study was 541 mg O₂ kg⁻¹h⁻¹ at 54 cm s⁻¹ (0.65 TL s⁻¹). The mean (±SE) TBF for 39 observations of steady swimming at all test speeds was 1.00 ± 0.01 Hz, which agrees with field observations of 1.03 ± 0.03 Hz in four undisturbed free-swimming mako sharks observed during the same time period. These findings suggest that the estimate of SMR for juvenile makos is comparable to that recorded for other similar-sized, ram-ventilating shark species (when corrected for differences in experimental temperature). However, the mako RMR and MMR are apparently among the highest measured for any shark species.     

Do corals select zooxanthellae by alternative discharge?

Loss of zooxanthellae (dinoflagellate Symbiodinium) from corals will sometimes lead to mass mortality of corals. To detect and quantify Symbiodinium released from corals, we developed a zooxanthellae “trap” and a quantitative PCR (qPCR) system with Symbiodinium clades A–F-specific primer sets. The trap was attached to a branch or the surface of several wild stony corals, and the water samples within the traps, including released Symbiodinium, were subjected to qPCR. All tested corals released clade C Symbiodinium at estimates of ~5,900 cells h⁻¹ cm⁻² of coral surface. Although all tested Pocillopora eydouxi harboured both clades C and D, some of these colonies released only clade C or released a lesser amount of clade D than that in the tissues. Our Symbiodinium quantification system revealed that wild hermatypic corals constantly release Symbiodinium to the environment. Our result suggests that some corals may discharge certain clades of Symbiodinium alternatively.     

Growth and development of nauplii and copepodites of the estuarine copepod Acartia tonsa from southern Europe (Ria de Aveiro, Portugal) under saturating food conditions

A temperature-dependent growth model is presented for nauplii and copepodites of the estuarine calanoid copepod Acartia tonsa from southern Europe (Portugal). Development was followed from egg to adult in the laboratory at four temperatures (10, 15, 18 and 22°C) and under saturating food conditions (>1,000 μg C l⁻¹). Development times versus incubation temperature were fitted to a Belehradek’s function, showing that development times decreased with increasing incubation temperature: at 10°C, A. tonsa need 40.3 days to reach adult stage, decreasing to 8.9 days when reared at 22°C. ANCOVA (homogeneity of slopes) showed that temperature (P<0.001) and growth phase (P<0.01) had a significant effect on the growth rate. Over the range of temperatures tested in this study, highest weight-specific growth rates were found during naupliar development (NI–NVI) and varied from 0.185 day⁻¹ (10°C) to 0.880 day⁻¹ (22°C) with a Q ₁₀ equal to 3.66. During copepodite growth (CI–CV), the weight-specific growth rates ranged from 0.125 day⁻¹ (10°C) to 0.488 day⁻¹ (22°C) with a Q ₁₀ equal to 3.12. The weight-specific growth rates (g) followed temperature (T) by a linear relationship and described as ln g=−2.962+0.130 T (r ²=0.99, P<0.001) for naupliar stages and ln g=−3.134+0.114T (r ²=0.97, P<0.001) for copepodite stages. By comparing in situ growth rates (juvenile growth and fecundity) for A. tonsa taken from the literature with the temperature-dependent growth model defined here we suggest that the adult females of A. tonsa are more frequently food limited than juveniles.     

The effects of temperature and salinity on reproductive success of <Emphasis Type="Italic">Temora longicornis</Emphasis> in the Baltic Sea: a copepod coping with a tough situation

At specific locations within the Baltic Sea, thermoclines and haloclines can create rapid spatial and temporal changes in temperature (T) and salinity (S) exceeding 10°C and 9 psu with seasonal ranges in temperature exceeding 20°C. These wide ranges in abiotic factors affect the distribution and abundance of Baltic Sea copepods via species-specific, physiological-based impacts on vital rates. In this laboratory study, we characterized the influence of T and S on aspects of reproductive success and naupliar survival of a southwestern Baltic population of Temora longicornis (Copepoda: Calanoida). First, using ad libitum feeding conditions, we measured egg production (EP, no. of eggs female⁻¹ day⁻¹) at 12 different temperatures between 2.5 and 24°C, observing the highest mean EP at 16.9°C (12 eggs female⁻¹ day⁻¹). Next, the effect of S on EP and hatching success (HS, %) was quantified at 12°C for cohorts that had been acclimated to either 8, 14, 20 or 26 psu and tested at each of five salinities (8, 14, 20, 26 and 32 psu). The mean EP was highest for (and maximum EP similar among) 14, 20 and 26 psu cohorts when tested at their acclimation salinity whereas EP was lower at other salinities. For adults reared at 8 psu, a commonly encountered salinity in Baltic surface waters, EP was relatively low at all test salinities—a pattern indicative of osmotic stress. When incubated at 12°C and 15 different salinities between 0 and 34 psu, HS increased asymptotically with increasing S and was maximal (82.6–84.3%) between 24 and 26 psu. However, HS did depend upon the adult acclimation salinity. Finally, the 48-h survival of nauplii hatched and reared at 14 psu at one of six different temperatures (10, 12, 14, 16, 18 and 20°C) was measured after exposure to a novel salinity (either 7 or 20 psu). Upon exposure to 7 psu, 48-h naupliar mortality increased with increasing temperature, ranging from 26.7% at 10°C to 63.2% at 20°C. In contrast, after exposure to 20 psu, mortality was relatively low at all temperatures (1.7% at 10°C and ≤26.7% for all other temperatures). An intra-specific comparison of EP for three different T. longicornis populations revealed markedly different temperature optima and clearly demonstrated the negative impact of brackish (Baltic) salinities. Our results provide estimates of reproductive success and early survival of T. longicornis to the wide ranges of temperatures and salinities that will aid ongoing biophysical modeling examining climate impacts on this species within the Baltic Sea.     

Population structure of <Emphasis Type="Italic">Symbiodinium</Emphasis> sp. associated with the common sea fan, <Emphasis Type="Italic">Gorgonia ventalina</Emphasis>, in the Florida Keys across distance,depth, and time

Numerous marine invertebrates form endosymbiotic relationships with dinoflagellates in the genus Symbiodinium. However, few studies have examined the fine-scale population structure of these symbionts. Here, we describe the genetic structure of Symbiodinium type “B1/B184” inhabiting the gorgonian Gorgonia ventalina along the Florida Keys. Six polymorphic microsatellite loci were utilized to examine 16 populations along the Upper, Middle, and Lower Keys spanning a range of ~200 km. Multiple statistical tests detected significant differentiation in 54–92% of the 120 possible pairwise comparisons between localities, suggesting low levels of gene flow in these dinoflagellates. In general, populations clustered by geographic region and/or reefs in close proximity. Some of the sharpest population differentiation was detected between Symbiodinium from deep and shallow sites on the same reef. In spite of the high degree of population structure, alleles and genotypes were shared among localities, indicating some connectivity between Symbiodinium populations associated with G. ventalina. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effect of temperature fluctuations and food supply on the growth and metabolism of juvenile sea scallops (Placopecten magellanicus)

On the eastern shore of Nova Scotia late summer atmospheric systems cause upwelling of shelf water; the associated temperature variations of 10 °C with a 6 to 8 d period are comparable in magnitude to the seasonal variation. A laboratory study was undertaken to assess the effects of these temperature fluctuations on sea scallop (Placopecten magellanicus) growth and metabolism. In a factorial design, scallops were subjected to constant (10 °C) or a variable (6 to 15 °C) 8 d temperature cycle, and either a low (seston in filtered seawater) or high (seston supplemented with cultured phytoplankton) food diet. During the 48 d experiment scallop mortality was low and growth positive in all treatments. Shell and total tissue growth rate did not differ between temperature treatments, but growth in the high food treatments was 40 to 50% higher than in the low food treatments. However, soft tissue (excluding adductor) growth did show a temperature treatment effect; growth rates were significantly higher in the fluctuating temperature treatment, due in part to greater gonad development. Weight-standardized rates of scallop oxygen consumption (V _sO₂ , μmol O₂ g⁻¹ h⁻¹) were 20 to 25% higher in high food than in low food treatments, consistent with the expected increase in respiration due to the higher growth rates. Scallop metabolism did not acclimate to the fluctuating temperature cycle; V _sO₂ and ammonium excretion (V _sNH⁺ ₄, μmol O₂ g⁻¹ h⁻¹) remained dependent on ambient temperature throughout the experiment. V _sNH⁺ ₄ Q₁₀ (2.77) was higher than V _sO₂ Q₁₀ (2.01) which was reflected in a decrease in the O:N ratio at 15 °C, indicating a shift toward increased protein catabolism and a stressed state. At 10 °C, V _sO₂ and V _sNH⁺ ₄ in the variable temperature treatments were 15 to 18% lower than in the constant temperature treatments, a difference that was not detected in growth measurements. Results demonstrate that the metabolism of Placopecten magellanicus, unlike some bivalve species, is tightly coupled to fluctuations in ambient temperature. Although an absence of compensatory acclimation had a minimal effect on growth in this study, if high temperatures were combined with low food conditions a reduction in scallop production could result. Received: 23 June 1998 / Accepted: 8 February 1999     

The effect of ration size, temperature and body weight on specific dynamic action of the common cuttlefish Sepia officinalis

The effect of meal size (shrimp Crangon crangon) [0.83–18.82% dry body weight (Dw)] on specific dynamic action (SDA) was assessed in cuttlefish Sepia officinalis (1.03–6.25 g Dw) held at 15 and 20°C. Cuttlefish <2 g significantly expended less energy in feeding and digesting their meal than cuttlefish >2 g when given the same quantity of food. Handling, eating and digesting a shrimp meal was temperature dependent with cuttlefish processing and digesting a similar sized shrimp meal faster at 20°C than at 15°C. The proportional increase in oxygen consumption (2.07 ± 0.02) was not correlated with feeding rate (FR) and was independent of temperature and cuttlefish size. The SDA peak was not correlated with FRs, and increased as cuttlefish size and temperature increased. The mean SDA coefficient was 0.87 ± 0.07% of the ingested energy; one of the lowest SDA values recorded amongst vertebrates and invertebrates. Daily energy requirements (KJ day⁻¹) for S. officinalis were calculated from laboratory estimates of energy losses due to standard (MO_{2 Standard}), routine (MO_{2 Routine}) and feeding (MO_{2 SDA}) oxygen consumption. Laboratory estimates of daily metabolic expenditures were combined with results from previous investigations to construct an energy budget for 1 and 5 g cuttlefish consuming a meal of 5 and 15% Dw at 20°C and the amount of energy available for growth was estimated to be between 35 and 80.3% of the ingested energy.     

Reproduction in Balanus amphitrite Darwin (Cirripedia: Thoracica): influence of temperature and food concentration

Balanus amphitrite, an acorn barnacle, is distinctly euryhaline, eurythermal and a dominant fouling organism found in warm and temperate waters throughout the world. In this study, the influence of temperature and food concentration on the reproductive biology of this species collected from a tropical habitat was evaluated. Adult barnacles were maintained at 20, 25 and 30°C temperatures at different concentrations of food (50, 100, 150 and 200 Artemia ind⁻¹ day⁻¹). In this previously believed obligatory cross-fertilizing hermaphrodite, self-fertilization was observed. The rise in temperature from 20 to 30°C resulted in a longer interbreeding interval (6–7 days, 200 Artemia ind⁻¹ day⁻¹; 11–13 days, 50 Artemia ind⁻¹ day⁻¹). Computed carbon gained through feeding during the interbreeding interval indicated an inverse relationship to the temperature. At 20°C, although a greater amount of carbon was gained through feeding, the numbers of larvae produced were fivefold less when compared to those raised at 30°C. At 20°C, 2.3 μg C was required to produce a single larva, whereas at 30°C it was 0.4 μg C. A rise in rearing temperature also influenced the molting rate positively. Observations on temporal variation in the gonad development of this species in a tropical coastal environment influenced by the monsoons indicated gonad development to be positively related to chlorophyll a concentration.     

The effects of temperature on the growth of juvenile scleractinian corals

Tropical reef corals are well known for their sensitivity to rising temperature, yet surprisingly little is known of the mechanisms through which temperature acts on intact coral colonies. One such mechanism recently has been suggested by the association between the growth of juvenile corals and seawater temperature in the Caribbean, which suggests that temperature causes a transition between isometric and allometric growth scaling in warmer versus cooler years, respectively (Edmunds in Proc R Soc B 273:2275–2281, 2006). Here, this correlative association is tested experimentally for a cause-and-effect relationship. During April and May 2006, juvenile colonies (8–35 mm diameter) of massive Porites spp. from Moorea, French Polynesia, were incubated at warm (27.8°C) and cool (25.7°C) temperatures for 15 days, and their response assessed through the scaling of growth (change in weight) with colony size. The results reveal that the scaling of colony-specific growth (mg colony⁻¹ day⁻¹) was unaffected by temperature, although growth absolutely was greater at the cool compared to the warm temperature, regardless of colony size. This outcome was caused by contrasting scaling relationships for area-specific growth (mg cm⁻² day⁻¹) that were negatively allometric under warm conditions, but independent of size under cool conditions. In April 2007, a 22 days field experiment confirmed that the scaling of area-specific growth in juvenile Porites spp. is negatively allometric at a warm temperature of 29.5°C. Based on strong allometry for tissue thickness, biomass, and Symbiodinium density in freshly collected Porites spp., it is hypothesized that the temperature-dependency of growth scaling in these small corals is mediated by the interaction of temperature with biomass.     

Life on the edge: physiological problems in penaeid prawns <Emphasis Type="Italic">Litopenaeus stylirostris</Emphasis>, living on the low side of their thermopreferendum

The underlying physiological mechanisms explaining why the adult penaeid prawn Litopenaeus stylirostris cannot successfully face heavy stressful events on the low edge of its thermopreferendum (20–22°C) were studied during the austral winter. Prawns were studied during recovery from net fishing and rapid transfer from outdoor earthen ponds into indoor facilities. This was assimilated to a predator–prey interaction. O₂-consumption, hemolymph osmotic pressure (OP_h), arterial O₂ partial pressure (PO₂), a–v O₂-capacitance and mortality rates were analysed. Data were compared to similar challenges performed at 28°C during the austral summer. At 20–22°C, mortality of up to 70% was observed after 2 days whereas at 28°C, maximum mortality was 3–5%. Mortality occurred when OP_h shifted towards equilibrium with seawater, the resting O₂-consumption, the a–v O₂-capacitance and the arterial PO₂ went down to minimal values. These events can be counterbalanced by transiently hyper-oxygenating the hemolymph or by blocking the OP_h shift in isosmotic water (Wabete et al. in Aquaculture 260:181–193, 2006): both led to a dramatic decrease in mortality. It is concluded that in penaeid prawns L. stylirostris, a mismatch between O₂-demand and O₂-supply contributes to setting the geographical limits for this animal species through an impairment of their hemolymph O₂-carrying capacity during heavy stressful events like chasing by predators.     

Effect of acclimatization to low temperature and reduced light on the response of reef corals to elevated temperature

This study tested the effects of acclimatization on the response of corals to elevated temperature, using juvenile massive Porites spp. and branching P. irregularis from Moorea (W149°50′, S17°30′). During April and May 2006, corals were acclimatized for 15 days to cool (25.7°C) or ambient (27.7°C) temperature, under shaded (352 μmol photons m⁻² s⁻¹) or ambient (554 μmol photons m⁻² s⁻¹) natural light, and then incubated for 7 days at ambient or high temperature (31.1°C), under ambient light (659 μmol photons m⁻² s⁻¹). The response to acclimatization was assessed as biomass, maximum dark-adapted quantum yield of PSII (F _v/F _m), and growth, and the effect of the subsequent treatment was assessed as F _v/F _m and growth. Relative to the controls (i.e., ambient temperature/ambient light), massive Porites spp. responded to acclimatization through increases in biomass under ambient temperature/shade, and low temperature/ambient light, whereas P. irregularis responded through reduced growth under ambient temperature/shade, and low temperature/ambient light. Acclimatization affected the response to thermal stress for massive Porites spp. (but not P. irregularis), with an interaction between the acclimatization and subsequent treatments for growth. This interaction resulted from a lessening of the negative effects of high temperature after acclimatizing to ambient temperature/shade, but an accentuation of the effect after acclimatizing to low temperature/shade. It is possible that changes in biomass for massive Porites spp. are important in modulating the response to high temperature, with the taxonomic variation in this effect potentially resulting from differences in morphology. These results demonstrate that corals can acclimatize during short exposures to downward excursions in temperature and light, which subsequently affects their response to thermal stress. Moreover, even con-generic taxa differ in this capacity, which could affect coral community structure. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effect of sub-lethal damage to juvenile colonies of massive Porites spp. under contrasting regimes of temperature and water flow

In this study, juvenile colonies of massive Porites spp. (a combination of P. lutea and P. lobata) from the lagoon of Moorea (W 149°50′, S 17°30′) were damaged and exposed to contrasting conditions of temperature and flow to evaluate how damage and abiotic conditions interact to affect growth, physiological performance, and recovery. The experiment was conducted in April and May 2008 and consisted of two treatments in which corals were either undamaged (controls) or damaged through gouging of tissue and skeleton in a discrete spot mimicking the effects of corallivorous fishes that utilize an excavating feeding mode. The two groups of corals were incubated for 10 days in microcosms that crossed levels of temperature (26.7 and 29.6°C) and flow (6 and 21 cm s⁻¹), and the response assessed as overall colony growth (change in weight), dark-adapted quantum yield of PSII (F _v/F _m), and healing of the gouged areas. The influence of damage on growth was affected by temperature, but not by flow. When averaged across flow treatments, damage promoted growth by 25% at 26.7°C, but caused a 25% inhibition at 29.6°C. The damage also affected F _v/F _m in a pattern that differed between flow speeds, with a 10% reduction at 6 cm s⁻¹, but a 4% increase at 21 cm s⁻¹. Regardless of damage, F _v/F _m at 21 cm s⁻¹ was 11% lower at 26.7°C than at 29.6°C, but was unaffected by temperature at 6 cm s⁻¹. The lesions declined in area at similar rates (4–5% day⁻¹) under all conditions, although the tissue within them regained a normal appearance most rapidly at 26.7°C and 6 cm s⁻¹. These findings show that the response of poritid corals to sub-lethal damage is dependent partly on abiotic conditions, and they are consistent with the hypothesis that following damage, calcification and photosynthesis can compete for metabolites necessary for repair, with the outcome affected by flow-mediated mass transfer. These results may shed light upon the ways in which poritid corals respond to biting by certain corallivorous fishes.     

Life history and production of <Emphasis Type="Italic">Corophium urdaibaiense</Emphasis> (Crustacea: Amphipoda) in the Urdaibai estuary (NE Spain)

The population of species Corophium urdaibaiense has been studied for a year in the Urdaibai estuary (NE Spain). The new species is characterised by its preference for muddy sand sediments (15% of mud) and the long body size (with a maximum length of 10.24 mm). The maximum abundance occurs in November (11,600 ind m⁻²); it almost disappears at the end of spring. The juveniles represent 79% of the population and the recruitment is concentrated within the October–December period. The breeding period begins in May, when the temperature is above 15°C, and it ceases in November, when the temperature is below 15°C. Bivoltinism is probable, taking into account the latitude (43°), temperature range (12–25°C) and breeding period (May and August–October), but the data are not sufficiently consistent to confirm the hypothesis. The production ranges from 2.93 to 5.85 g m⁻² year⁻¹, considering one and two generations per year, respectively. Some aspects concerning the food availability, predation and intraspecific competition could have an influence on the dynamics of the population and are discussed.     

Net negative growth detected in a population of <Emphasis Type="Italic">Leptogorgia sarmentosa</Emphasis>: quantifying the biomass loss in a benthic soft bottom-gravel gorgonian

Gorgonian species may contribute to the three-dimensional seascape in soft bottom-gravel areas, but the information on their biology and ecology is very scarce. The biometry and secondary production of the Mediterranean soft bottom-gravel passive suspension feeder Leptogorgia sarmentosa (Cnidaria: Octocorallia) was studied using photographic monitoring of the primary branches from May 1998 to September 2000. The primary branches observed had a high density of polyps (2.2 ± 0.2 SD polyps mm⁻¹) and a high organic matter content (63.2 ± 9.1 SD %). During the two-year sampling period, there was a net negative growth in 90% of the gorgonian population. The mean loss during the 27-month period was −2.9 ± 0.9 SD cm per branch (5.7 mg C branch⁻¹). However, considering only the initial and final diameters and maximum height in the 27 months elapsed time, the gorgonians showed positive growth, which meant that photographic sampling of single branches was a more appropriate method for gorgonian secondary production monitoring. A water mass anomaly detected in 1999 in the north-western Mediterranean Sea may have been the cause of the net negative growth in L. sarmentosa in the studied area. Partial mortality due to different factors, such as strong currents, predation, disease, etc., could be a common strategy in sessile colonial benthic populations that would facilitate their maintenance even during very stressful circumstances.     

Metabolism and elemental composition of four oncaeid copepods in the western subarctic Pacific

Respiration rates and elemental composition (carbon and nitrogen) were determined for four dominant oncaeid copepods (Triconia borealis, Triconia canadensis, Oncaea grossa and Oncaea parila) from 0–1,000 m depth in the western subarctic Pacific. Across the four species of which dry weight (DW) varied from 2.0 to 32 μg, respiration rates measured at in situ temperature (3°C) increased with DW, ranging from 0.84 to 7.4 nl O₂ individual⁻¹ h⁻¹. Carbon (C) and nitrogen (N) composition of the four oncaeid species ranged from 49–57% of DW and 7.0–10.3% of DW, respectively, and the resultant C:N ratios were 4.8–8.3. The high C contents and C:N ratios were reflected by large accumulation of lipids in their body. Specific respiration rates (SR, a fraction of body C respired per day) ranged between 0.5 and 1.3% day⁻¹. Respiration rates adjusted to a body size of 1 mg body N (i.e. adjusted metabolic rates, AMR) of the four oncaeid species [0.6–1.1 μl O₂ (mg body N)^−0.8 h⁻¹ at 3°C] were significantly lower than those (1.7–5.1) reported in the literature for oithonid and calanoid copepods at the same temperature. The present results indicate that lower metabolic expenditure due to less active swimming (pseudopelagic life mode) together with rich energy reserve in the body (as lipids) are the characters of oncaeid copepods inhabiting in the epi- and mesopelagic zones of this region.     

Thermal dependency of burrowing in three species within the bivalve genus <Emphasis Type="Italic">Laternula</Emphasis>: a latitudinal comparison

The upper thermal limits for burrowing and survival were compared with micro-habitat temperature for anomalodesmatan clams: Laternula elliptica (Antarctica, 67°S); Laternula recta, (temperate Australia, 38°S) and Laternula truncata (tropical Singapore, 1°N). Lethal limits (LT₅₀) were higher than burrowing limits (BT₅₀) in L. elliptica (7.5–9.0 and 2.2°C) and L. recta (winter, 32.8–36.8 and 31.1–32.8°C) but the same range for L. truncata (33.0–35.0 and 33.4–34.9°C). L. elliptica and L. truncata had a BT₅₀ 0.4 and 2.4–3.9°C, respectively, above their maximum experienced temperature. L. recta, which experience solar heating during midday low tides, had a BT₅₀ 0.7–2.4°C below and a range for LT₅₀ that spanned their predicted environmental maximum (33.5°C). L. recta showed no seasonal difference in LT₅₀ or BT₅₀. Our single genus comparisons contrast with macrophysiological studies showing that temperate species cope better with elevated temperatures. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Symbiont specificity and bleaching susceptibility among soft corals in the 1998 Great Barrier Reef mass coral bleaching event

Considerable variability in bleaching was observed within and among soft coral taxa in the order Alcyonacea (Octocorallia: Cnidaria) on the central Great Barrier Reef (GBR, latitude 18.2°–19.0°S, longitude 146.4°–147.3°E) during the 1998 mass coral bleaching event. In April 1998, during a period of high sea surface temperatures, tissue samples were taken from bleached and unbleached colonies representative of 17 soft coral genera. The genetic identities of intracellular dinoflagellates (Symbiodinium spp.) in these samples were analyzed using PCR-denaturing gradient gel electrophoresis fingerprinting analysis of the internal transcribed spacer regions 1 and 2. Alcyonaceans from the GBR exhibited a high level of symbiont specificity for Symbiodinium types mostly in clade C. A rare clade D type (D3) was associated only with Clavularia koellikeri, while Nephthea sp. hosted symbionts in clade B (B1n and B36). Homogenous Symbiodinium clade populations were detected in all but one colony. Colonies that appeared bleached possessed symbiont types that were genetically indistinguishable from those in nonbleached conspecifics. These data suggest that parameters other than the resident endosymbionts such as host identity and colony acclimatization are important in determining bleaching susceptibility among soft corals. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.