Entrainment of the larval release rhythm of the crab Rhithropanopeus harrisii (Brachyura: Xanthidae) by cycles in hydrostatic pressure

This study investigated the entrainment of a larval release rhythm by determining whether a tidal cycle in hydrostatic pressure could entrain the circatidal rhythm in larval release by the crab Rhithropanopeus harrisii (Gould). Ovigerous females were collected from a non-tidal estuary. The time of larval release by individual crabs was monitored under constant conditions with a time-lapse video system. Crabs with mature embryos at the time of collection had a pronounced circadian rhythm in larval release with a free running period of 25.1 h. Crabs with immature embryos that were maintained under constant conditions from the time of collection until larval release retained a weak circadian rhythm. Other crabs with immature embryos were exposed to a tidal cycle in step changes in hydrostatic pressure equivalent to 1 m of water. This cycle entrained a circatidal rhythm in larval release. The free-running period was 12.1 h and larvae were released at the time of the transition from low to high pressure. Although past studies demonstrated that a tidal cycle in hydrostatic pressure could entrain activity rhythms in crustaceans, this is the first study to show that pressure can entrain a larval release rhythm.     

Present and past depth distribution of bladderwrack (Fucus vesiculosus) in the Baltic Sea

This study aimed to (1) assess the present depth distribution of Fucus vesiculosus in the Baltic Sea and evaluate differences between districts and (2) assess long-term and recent changes in depth distribution and evaluate reasons for such changes. This was done through compilation and analysis of existing data (3356 obs.). Depth limits were shallowest in the Kattegat, the Danish Belts and the Øresund (∼1.5 m on average), located at the entrance of the Baltic Sea and markedly deeper in the central and inner parts of the Baltic (up to ∼4.5 m on average). This increase in depth limits to some extent matched the decline in salinity and may in part be explained by reduced competition when species diversity decreases successively along the Baltic salinity gradient. In the central and inner Baltic Sea, Secchi depths explained part of the variation (16%) in depth limits and the majority (85%) of the variation in maximum attainable depth limits whereas at the entrance of the Baltic Secchi depths explained a negligible part of the variation (∼1%). In most districts, depth limits moved upwards during the 20th century. In many cases this happened during or shortly after the 1960s/1970s, and was most likely due to eutrophication.     

Survival,osmoregulation and ammonia-N excretion of blue swimmer crab, Portunus pelagicus, juveniles exposed to different ammonia-N and salinity combinations

Ammonia-N toxicity to early Portunus pelagicus juveniles at different salinities was investigated along with changes to haemolymph osmolality, Na⁺, K⁺, Ca²⁺ and ammonia-N levels, ammonia-N excretion and gill Na⁺/K⁺-ATPase activity. Experimental crabs were acclimated to salinities 15, 30 and 45‰ for one week and 25 replicate crabs were subsequently exposed to 0, 20, 40, 60, 80, 100 and 120 mg L^− 1 ammonia-N for 96-h, respectively. High ammonia-N concentrations were used to determine LC₅₀ values while physiological measurements were conducted at lower concentrations. When crabs were exposed to ammonia-N, anterior gill Na⁺/K⁺-ATPase activity significantly increased (p < 0.05) at all salinities, while this only occurred on the posterior gills at 30‰. For crabs exposed to 20 and 40 mg L^− 1 ammonia-N, both posterior gill Na⁺/K⁺-ATPase activity and ammonia-N excretion were significantly higher at 15‰ than those at 45‰. Despite this trend, the 96-h LC₅₀ value at 15‰ (43.4 mg L^− 1) was significantly lower (p < 0.05) than at both 30‰ and 45‰ (65.8 and 75.2 mg L^− 1, respectively). This may be due to significantly higher (p < 0.05) haemolymph ammonia-N levels of crabs at low salinities and may similarly explain the general ammonia-N toxicity pattern to other crustacean species.     

Seasonal variability in feeding behaviour, metabolic rates and carbon and nitrogen balances in the Sydney oyster, Saccostrea glomerata (Gould)

To establish if nutrients limit the growth of bivalves requires information not only on the quality of food available, but also the animals' feeding behaviour and endogenous metabolic demands. We hypothesized that growth of the Sydney rock oyster (Saccostrea glomerata) would vary in response to seasonal changes in food quality rather than quantity. We also predicted that the oysters would show feeding preferences for nitrogen over carbon, and this behaviour would result in carbon/nitrogen (C/N) ratios for ingested and absorbed matter that would be lower than the C/N of both the seston and the oysters' estimated metabolic maintenance requirements. The experiments were done in two phases under natural conditions. In phase 1, feeding behaviour was assessed on a single occasion and the results used to pose hypotheses for testing in phase 2, which included measurements made on three occasions encompassing autumn, winter and spring conditions. Growth rates varied with changes in ambient food quality and not with the concentration of total suspended matter. Feeding behaviour responded to food quality and, in most cases, resulted in nitrogen enrichment. For example, when nitrogen was potentially limiting to growth and/or maintenance, due to high food C/N (July) or high nitrogen demand (March), pre-ingestive selection ensured nitrogen enrichment of ingested matter and C/N ratios of ingested matter which were below the maintenance requirement. However, in November, when endogenous demands indicated an increased requirement for carbon, feeding behaviour resulted in carbon enrichment, an increase in carbon conversion efficiency, and ingested C/N ratios greater than the maintenance requirement. The results support the assertion of variable feeding physiology in oysters, responsive to both exogenous (seasonal differences in carbon and nitrogen availability) and endogenous (cycles of reproduction and growth) factors.     

Osmoregulatory disturbances induced by the parasitic barnacle Loxothylacus texanus (Rhizocephala) in the crab Callinectes rathbunae (Portunidae)

The osmoregulatory response of the blue crab Callinectes rathbunae parasitized with the rhizocephalan barnacle Loxothylacus texanus, and subjected to sudden salinity changes, was experimentally measured in the laboratory. Parasitized and control crabs were exposed to salinity changes every 3 h and their hemolymph osmolality measured. Two experiments, one with increasing salinity conditions (5‰, 12‰, 19‰, 25‰) and a second one with decreasing salinities (35‰, 25‰, 15‰, 5‰) were conducted. The results show that L. texanus significantly alters the hemolymph osmolality of C. rathbunae maintaining it at lower than normal levels. In the increasing salinity trial, the hypoosmotic hemolymph condition of parasitized crabs was present at all salinities tested, whereas in the decreasing salinity trial a significant effect was found only at salinities of 5‰ and 15‰. Since C. rathbunae is constantly subjected to abrupt salinity changes in the tropical estuaries where it occurs, moving into high salinity areas may be the only way to cope with the impact of L. texanus.     

The environmental effects of salinity and temperature on the oxygen consumption and total body osmolality of the marine flatworm Procerodes littoralis

The present study examined the effect of salinity and temperature on the rate of oxygen consumption and total body osmolality of the triclad turbellarian Procerodes littoralis, a common marine flatworm normally found in areas where freshwater streams run out over intertidal areas. Extremes in environmental factors encountered by P. littoralis were recorded at the study site. These were salinity (0-44 psu), temperature (2.7-24.9 °C) and oxygen concentration (2.8-16.1 mg l⁻¹). Respirometry experiments showed minimal oxygen consumption rates at the salinity extremes encountered by the study species (0 and 40 psu). Further experiments showed relatively constant oxygen consumption rates over the temperature range 5-20 °C and elevated consumption rates at temperatures above 25 °C. Total body osmolality of P. littoralis increased with increasing salinity. The study illustrates how a marine flatworm uses integrated physiological and behavioural mechanisms to successfully inhabit an environment that is predominantly freshwater for up to 75% of the tidal cycle.     

Density of Monoporeia affinis and biogeochemistry in Baltic Sea sediments

This study focused on effects from Monoporeia affinis reworking and ventilation activities on benthic fluxes and mineralization processes during a simulated bloom event. The importance of M. affinis density for benthic solute (O₂, ΣNO₂⁻ + NO₃⁻, NH₄⁺ and HPO₄²⁻) fluxes and sediment reactivity (mobilization of NH₄⁺ and HPO₄²⁻) following additions of organic material to the sediment surface was experimentally investigated using sediment-water and closed sediment (jar) incubations. Three different densities of M. affinis were used to resemble a low, medium and high density situation (1300, 2500 and 6400 ind. m^− 2, respectively) of a natural amphipod community. The degradation of phytodetritus (Tetraselmis sp., 5 g C m^− 2) added to the sediment surface was followed over a period of 20 days. Benthic solute fluxes of O₂, ΣNO₂⁻ + NO₃⁻ and NH₄⁺ were generally progressively stimulated with increasing number of M. affinis, while no such correlation was found for HPO₄²⁻. Solute fluxes were initially enhanced 1 to 2 days after the addition of phytodetritius, caused by mineralization of the most labile organic material and a food-stimulated irrigation by the amphipods. There was no effect from the activity of M. affinis on total denitrification (Dtot = Dn + Dw) or denitrification utilizing nitrate from coupled nitrification/denitrification (Dn) for any of the densities examined. Denitrification utilizing overlying water nitrate (Dw) was only about 10% of Dtot. Dw was significantly enhanced for the highest M. affinis density investigated. The reactivity of the sediment decreased progressively with increasing density of M. affinis and with time of the experiment. However, enhanced ammonium production at least 6 days after the organic addition indicated excretion of N-containing organic compounds by M. affinis. In conclusion, large spatial and temporal variations in density of M. affinis may be of significant importance for benthic solute fluxes and overall mineralization of organic material in Baltic Sea sediments.     

3-Decanol in the haemolymph of the hermit crab Clibanarius vittatus signals shell availability to conspecifics

Hermit crabs with poor fitting shells are chemically attracted to dying gastropods and conspecifics where a shell may become available. For land hermit crabs, the shell cue is a volatile compound found in the haemolymph. Based on this knowledge, we tested the hypothesis that shell investigation behavior in aquatic hermit crabs, the ancestral predecessors of terrestrial hermit crabs, is also triggered by volatile cues. Volatile compounds from haemolymph of Clibanarius vittatus and Pagurus pollicaris and brachyuran decapod crustaceans were purged from a water-haemolymph solution, trapped in seawater and tested for induction of shell investigation behavior with juvenile C. vittatus. Only volatiles from C. vittatus haemolymph stimulated shell investigation. Volatile compounds were isolated from haemolymph by headspace solid-phase microextraction (SPME) and analyzed by coupled gas chromatography-mass spectrometry (GC-MS). Two prominent compounds were identified, 3-decanol, which was unique to C. vittatus haemolymph, and 2-ethyl-1-hexanol, which was present in the haemolymph of all 4 crustacean species. In shell investigation bioassays, 3-decanol from C. vittatus haemolymph stimulated shell investigation behavior, while 2-ethyl-1-hexanol did not. In bioassays with synthetic 1-, 2-, 4-, and 5-decanol, shell investigation behavior was evoked by 1-decanol, 5-decanol and 3-undecanol. There was no response to 2- and 4-decanol. The response of C. vittatus to volatile shell cues supports the hypothesis that volatile cue detection evolved prior to the occupation of terrestrial niches by crustaceans.     

Effect of water temperature,salinity, and their interaction on growth,plasma osmolality,and gill Na,K-ATPase activity in juvenile GIFT tilapia Oreochromis niloticus (L.)

We used a central composite rotatable experimental design and response surface methodology to evaluate the effects of temperature (18–37 °C), salinity (0–20‰), and their interaction on specific growth rate (SGR), feed efficiency (FE), plasma osmolality, and gill Na⁺, K⁺-ATPase activity in GIFT tilapia juveniles. The linear and quadratic effects of temperature and salinity on SGR, plasma osmolality, and gill Na⁺, K⁺-ATPase activity were statistically significant (P<0.05). The interactive effects of temperature and salinity on plasma osmolality were significant (P<0.05). In contrast, the interaction term was not significant for SGR, FE, and gill Na⁺, K⁺-ATPase activity ⁽P>0.05). The regression equations for SGR, FE, plasma osmolality, and gill Na⁺, K⁺-ATPase activity against the two factors of interest had coefficients of determination of 0.944, 0.984, 0.966, and 0.960, respectively (P<0.01). The optimal temperature/salinity combination was 28.9 °C/7.8‰ at which SGR (2.26% d¹) and FE (0.82) were highest. These values correspond to the optimal temperature/salinity combination (29.1 °C/7.5‰) and the lowest plasma osmolality (348.38 mOsmol kg⁻¹) and gill Na⁺, K⁺-ATPase activity (1.31 µmol Pi. h⁻¹ g⁻¹ protein), and resulted in an energy-saving effect on osmoregulation, which promoted growth.     

Sexual and seasonal variations in osmoregulation and ionoregulation in the estuarine crab Chasmagnathus granulatus (Crustacea, Decapoda)

The estuarine crab Chasmagnathus granulatus (Crustacea, Decapoda, Brachyura) inhabits salt marshes along the South Atlantic coast from Rio de Janeiro (Brazil) to Patagonia (Argentina). In the present study, salinity tolerance (0-45‰; 16-1325 mOsm/kg H₂O) and hemolymph osmotic and ionic (Na⁺, Cl⁻, and K⁺) regulation in both female and male C. granulatus were analyzed in summer and winter. Results showed that both female and male C. granulatus are euryhaline. Mortality was only observed in extremely low salinity (0‰; 16 mOsm/kg H₂O) for both sexes. For females, the LT₅₀ at 0‰ salinity was similar in summer (20.1 h) and winter (17.4 h). Males were more tolerant to salinity than females in both seasons, and mortality was observed only in summer (LT₅₀ = 50.9 h). Results from freshly collected crabs or long-term (16-day) osmotic and ionic regulation experiments in the laboratory showed that male C. granulatus is a better hyper-osmoregulator than female in summer and winter. However, a hypo-osmoregulatory ability was only observed in females experimentally subjected to salinity 40‰ (1176 ± 11 mOsm/kg H₂O) in both seasons. In both sexes, hyper-osmotic regulation was achieved by hyper-regulating hemolymph Na⁺, Cl⁻, and K⁺ concentration. In females, hypo-osmotic regulation was achieved by hypo-regulating hemolymph Na⁺ and Cl⁻ concentration. Long-term (16-day) osmotic and ionic regulations in different salinities were similar in males or females collected and tested in summer and winter. Despite this lack of a seasonal effect on hemolymph osmoregulatory and ionoregulatory patterns in males or females, a marked seasonal difference in the dynamics of these processes was observed for both sexes. In the first 2 days after hypo-osmotic shock (20‰→5‰; 636→185 mOsm/kg H₂O), variations in female osmolality and ion (Na⁺ and Cl⁻) concentration were larger and faster in winter than in summer, while in males the opposite was observed. Furthermore, a seasonal effect on the crab response to hyper-osmotic shock (20‰→40‰; 636→1176 mOsm/kg H₂O) was only observed in males. A new osmolality and ion (Na⁺ and Cl⁻) concentration steady state was faster achieved in winter than in summer. Regarding sexual differences, females showed a better capacity to hypo-regulate the hemolymph osmolality and Na⁺ concentration than males, even after a sudden increase in salinity (hyper-osmotic shock) in both seasons. On the other hand, males showed a better capacity to hyper-regulate the hemolymph osmolality and Na⁺ concentration than females, even after a sudden decrease in salinity (hypo-osmotic shock), especially in winter. Taken together, results reported in the present study suggest the need to consider both sex and collection season as important factors in future osmotic and ionic regulation studies in estuarine crabs.     

Effects of food concentration on clearance rate and energy budget of the Arctic bivalve Hiatella arctica (L) at subzero temperature

The influence of food concentration on clearance rate, respiration, assimilation, and excretion at −1.3 °C was studied on individuals of the bivalve Hiatella arctica (L.) from Young Sound, NE Greenland. Clearance rate, assimilation efficiency, respiration, and excretion rates were determined over a range of food concentrations using the microalga Rhodomonas baltica as food source. Physiological rates were generally low but responded significantly to increased food levels. Clearance rates and assimilation efficiency were reduced at increased food levels, whereas respiration and excretion increased. Assimilation efficiency was generally high, which may be an adaptation to the low food concentration during most of the year in NE Greenland. Low filtration rates limited ingestion rates and resulted in a low maximum assimilation of 3 J h⁻¹. Despite the low food intake, very low food concentrations were required for individual specimens to obtain a positive energy budget. Predicted growth based on rates of assimilation and respiration were compared to published estimates of annual growth in Young Sound. We estimate that 3 weeks of growth in the laboratory under optimal food conditions could match annual growth in situ. We interpret this as evidence that food limitation is the primary impediment to growth in this Arctic population.     

Salinity effects on osmoregulation and growth of the euryhaline flounder Paralichthys orbignyanus

The flounder, Paralichthys orbignyanus, is found in coastal and estuarine waters of the Western South Atlantic Ocean. It is being considered for aquaculture due to its high market price and wide tolerance to environmental factors such as salinity, pH, and nitrogenous compounds. The objective of this study was to characterize the ionic and osmotic regulation of P. orbignyanus over the range of its tolerated ambient salinities (0-40‰) and to evaluate the survival and growth in freshwater (0‰) and seawater (30‰) over 90 days. After 15 days of exposure to different salinities (0‰, 10‰, 20‰, 30‰ and 40‰), plasma osmolality and ionic (Na⁺, Cl⁻, K⁺ and Ca²⁺) concentrations slightly increased with salinity. The isosmotic point was estimated as 328.6 mOsm kg⁻¹ H₂O and corresponded to 10.9‰ salinity. After 90 days, survival was similar in freshwater and seawater, but osmo- and ionoregulation was significantly affected in freshwater and flounders reared in this medium showed a lower growth rate than those reared in seawater. Based on the results from this study, P. orbignyanus can be characterized as a marine/estuarine euryhaline teleost capable of hyper/hypo iono- and osmoregulation over the fluctuating salinity regime faced by this species in the environment. Furthermore, results suggest that the lower growth rate exhibited by P. orbignyanus in freshwater could be due, at least partially, to a higher energy expenditure associated to a higher branchial Na⁺, K⁺-ATPase activity in this environment.     

Predatory behavior and preference of a successful invader, the mud crab Dyspanopeus sayi (Panopeidae), on its bivalve prey

Predator-prey relationships between the panopeid crab, Dyspanopeus sayi, and the mytilid, Musculista senhousia, were investigated. Through laboratory experiments, prey-handling behavior, prey size selection, predator foraging behavior and preferences for two types of prey (M. senhousia and the Manila clam Ruditapes philippinarum) were assessed. Handling time differed significantly with respect to the three prey sizes offered (small: 15.0-20.0 mm shell length, SL; medium: 20.1-25.0 mm SL; and large: 25.1-30.0 mm SL); mud crabs were more efficient in predating medium-small than large prey. Although differences in prey profitability were not evident, D. sayi exhibited a marked reluctance to feed on larger-sized prey whilst smaller, more easily predated mussels were available. Size selection may be the result of a mechanical process in which encountered prey are attacked but rejected if they remain unbroken after a certain number of opening attempts. D. sayi exhibited inverse density-dependent foraging. A significant higher mortality of prey was evident at low prey density. Thus, at low predator density, the D. sayi-M. senhousia interaction was a destabilizing type II functional response. Interference responses affected the magnitude of predation intensity by D. sayi on M. senhousia, since as the density of foraging crabs increased, their foraging success fell. At high density (4 crabs tank⁻¹), crabs engaged in a high amount of agonistic activity when encountering a conspecific specimen, greatly diminished prey mortality. Finally, presenting two types of prey, Manila clam juveniles were poorly predated by mud crabs, which focused their predation mostly on M. senhousia. It is hypothesized that, when more accessible prey is available, mud crabs will have a minimal predatory impact on commercial R. philippinarum juvenile stocks.     

The effect of salinity change on the heart rate of Mytilus edulis specimens from different ecological zones

The heart rate of specimens of Mytilus edulis (L.) both from the sublittoral and littoral zones exposed to normal and altered salinity was investigated in a long-term experiment. The heart rate was monitored by a non-invasive method for nine days. The heart rate of sublittoral mussels was higher than that of littoral ones. This suggests a higher level of metabolic activity in sublittoral mussels. When exposed to moderate hyposalinity (15 g l⁻¹) M. edulis from both zones showed a significant decrease in the heart rate with respect to the control salinity (25 g l⁻¹), but sublittoral mussels had a more prominent bradycardia. The heart beat quickly accelerated in all organisms when they were returned to the control salinity medium. Throughout the experiment, heart contractions halted with distinct periodicity in all mussels.     

Lack of correlation between body mass and metabolic rate in Drosophila melanogaster

We examined the association between body mass and metabolic rate in Drosophila melanogaster under a variety of conditions. These included comparisons of body mass and metabolic rate in flies from different laboratory lines measured at different ages, over different metabolic sampling periods, and comparisons using wet versus dry mass data. In addition, the relationship between body mass and metabolic rate was determined for flies recently collected from wild populations. In no case was there a significant correlation between body mass and metabolic rate. These results indicate that care must be taken when attempting to account for the effects of body mass on metabolic rate. Expressing such data in mass-specific units may be an inappropriate method of attempting to control for the effects of differences in body mass.     

盐度、温度对卵形鲳鲹选育群体肝抗氧化酶活力的影响

通过盐度渐变和温度骤变的方法,分别研究了不同盐度(10、20、30、40)处理和不同温度(18.0℃、21.0℃、24.6℃、29.0℃、32.0℃)处理对卵形鲳鲹(Trachinotus ovatus)选育群体肝超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和谷胱甘肽过氧化物酶(GPX)活力的影响.在实验结束时,盐度10组酶活力与对照组无显著差异(P＞0.05),盐度20组SOD活力极显著低于对照组(P＜0.01);盐度40组120 h时,SOD和GPX活力极显著低于对照组(P＜0.01),CAT活力与对照组差异不显著(P＞0.05).18.0℃和21.0℃ SOD活力在1、3、6、12、24 h这5个取样时间点均高于对照组,CAT活力在实验结束时(24 h)极显著高于对照组(P ＜0.01);29.0℃SOD和CAT活力在实验结束时(24 h)显著高于对照组(P＜0.05);32.0℃ SOD和CAT活力在5个取样时间点均显著低于对照组(P＜0.05).结果表明,适当的盐度或温度变化可以改变卵形鲳鲹肝抗氧化酶活力,达到机体耐受极限时酶活力下降.     

Ion composition and osmolarity of Caspian Sea ctenophore, Mnemiopsis leidyi, in different salinities

The aim was to study osmotic and ionic regulation in alien ctenophore, Mnemiopsis leidyi (total length of 1.5-3 cm), acclimated gradually to artificial sea water of different salinities (8, 13, 18 and 23 ppt) in laboratory conditions (24 ± 2 °C) with the salt composition and proportion of the Caspian Sea. Results showed that this species is hyper-osmoconformer (maintaining internal osmolarity 2-22 mOsmol l^{− 1} above external) in non-lethal salinities ranging from 8 to 23 ppt. The results of ionic regulatory investigations revealed that this species can regulate Ca²⁺ and SO₄²⁻ so that the concentration of Ca²⁺ in the internal fluid and SO₄²⁻ in the external fluid were significantly more in 8 and 13 ppt, respectively. No regulation was observed about other ions such as Cl⁻, Mg²⁺ and K⁺ in the mentioned salinities.     

Limb autotomy patterns in Paralithodes camtschaticus (Tilesius, 1815), an invasive crab, in the coastal Barents Sea

We examined levels of limb injury in the red king crab Paralithodes camtschaticus at 3 sites in the coastal waters of the Barents Sea. High incidences of autotomy were registered at all sites examined averaging 46.6% in Dolgaya Bay (DLB), 42.6% in Yarnyshnaya Bay (YRB) and 45.6% in Dalnezelenetskaya Bay (DZB). These levels were greater than in deep waters of the Barents Sea. Significant inter-annual increases in limb loss rates were observed in DZB. The positive correlation of autotomy frequency with the body size was observed for the females in YRB and DZB. The frequency of autotomy was independent of sex for all sites and size groups except for the crabs with CL > 135 mm in DZB where the females had autotomized limbs more often than the males. The chance of injury was higher for posterior legs. Right-side limbs (especially, claws) were lost more often than left-side limbs. The observed frequency of crabs within limb loss patterns did not differ significantly from the expected levels in P. camtschaticus collected in DLB and in YRB but was significantly different than a frequency expected if limb losses were independent in DZB. Our results suggest that crabs in DZB are more affected by limb-inducing factors than individuals from DLB or YRB. The main factors affecting limb injuries in P. camtschaticus in the coastal Barents Sea are predator pressure (mainly for immature crabs), and illegal fishing and recreational diving (for mature crabs).     

Effects of seston variability on the clearance rate and absorption efficiency of the mussels Aulacomya maoriana, Mytilus galloprovincialis and Perna canaliculus from New Zealand

The clearance rates (CR in l g⁻¹ h⁻¹) and net absorption efficiencies (AE) of three co-occurring mytilid species were estimated to determine the effects of variation in ambient seston quantity (total particulate matter, TPM, mg l⁻¹) and quality (particulate organic matter, POM, mg l⁻¹; percent organic matter, PCOM=POM/TPM) on these physiological functions. CR_S estimates were significantly different among the species (Mytilus galloprovincialis>Perna canaliculus=Aulacomya maoriana), but were not correlated with differences in species-dependent mean body size (P. canaliculus>M. galloprovincialis>A. maoriana). AE estimates were independent of mean body weight, and did not differ among the species. For all three species, CR responded in a simple linear manner to seston organic content, either in terms of POM (for A. maoriana and M. galloprovincialis), or PCOM (for P. canaliculus). The AE response, although also of a simple linear type, was species-dependent and involved interactions of two or three seston components: TPM, POM and PCOM for A. maoriana; POM and PCOM for M. galloprovincialis; and TPM and PCOM for P. canaliculus. For all three species, seston variation explained 15-20% of the variation in CR and 52-59% of the variation in AE. Comparisons among the species indicated that two very different responses to variation in seston quantity and quality exist. First, significant differences in CR result from species-dependent differences in the magnitude of the response to seston variation. Second, species-dependent responses to variation in seston variation resulted in the similarity of the AE responses. Thus, the three species appear to have evolved different strategies for dealing with seston variation, but with the end result that their AE responses do not differ. Finally, no evidence was found of a negative association between CR and AE for any of the three species, suggesting that under the seston conditions experienced in this work, these species do not have the physiological compensatory capacity to reduce CR in order to increase AE. The importance of a comparative (i.e., multi-species) approach utilising ambient seston is emphasised by the findings of this research if we are to understand better the feeding and digestive physiologies of suspension-feeding organisms such as mussels.     

The complete mitochondrial genome sequence and gene organization of the mud crab (Scylla paramamosain) with phylogenetic consideration

The complete mitochondrial genome is of great importance for better understanding the genome-level characteristics and phylogenetic relationships among related species. In the present study, we determined the complete mitochondrial genome DNA sequence of the mud crab (Scylla paramamosain) by 454 deep sequencing and Sanger sequencing approaches. The complete genome DNA was 15,824 bp in length and contained a typical set of 13 protein-coding genes, 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes and a putative control region (CR). Of 37 genes, twenty-three were encoded by the heavy strand (H-strand), while the other ones were encoded by light strand (L-strand). The gene order in the mitochondrial genome was largely identical to those obtained in most arthropods, although the relative position of gene tRNA^His differed from other arthropods. Among 13 protein-coding genes, three (ATPase subunit 6 (ATP6), NADH dehydrogenase subunits 1 (ND1) and ND3) started with a rare start codon ATT, whereas, one gene cytochrome c oxidase subunit I (COI) ended with the incomplete stop codon TA. All 22 tRNAs could fold into a typical clover-leaf secondary structure, with the gene sizes ranging from 63 to 73 bp. The phylogenetic analysis based on 12 concatenated protein-coding genes showed that the molecular genetic relationship of 19 species of 11 genera was identical to the traditional taxonomy.