Acute waterborne cadmium toxicity in the estuarine pulmonate mud snail, Amphibola crenata.

Freshwater pulmonate snails are sensitive to trace metals, but to date, the sensitivity of estuarine pulmonate snails to these important environmental toxicants is undescribed. Using the estuarine mud snail Amphibola crenata, effects of a 48-h exposure to waterborne cadmium (Cd) were investigated. The 48-h median lethal concentration (LC50) was 50.4 mg L-1, a value higher than that previously reported for any gastropod mollusc. Cadmium levels in the tissues of mud snails were highest in the viscera (digestive gland and gonad), with the foot muscle and remaining tissue compartment (kidney, mantle, remaining digestive tissues and heart) displaying significantly lower concentrations. Over a Cd exposure concentration range of 0-32 mg L-1, Amphibola exhibited reduced oxygen consumption and elevated ammonia excretion in response to increasing Cd, the latter effect likely reflecting a switch to protein metabolism. This finding was supported by a declining oxygen: nitrogen ratio (O:N) as exposure Cd concentration increased. Other energy imbalances were noted, with a decrease in tissue glycogen (an effect strongly correlated with Cd burden in the viscera and foot muscle) and an elevated haemolymph glucose observed. An increase in catalase activity in the visceral tissues was recorded, suggestive of an effect of Cd on oxidative stress. The magnitude of this effect was correlated with tissue Cd burden. The induction of antioxidant defence mechanisms likely prevented an increase in levels of lipid peroxidation, which were unchanged relative to Cd exposure concentration in all measured tissues.

Behavioural, physiological and biochemical responses to aquatic hypoxia in the freshwater crayfish, Paranephrops zealandicus.

Hypoxia resulting from aquatic eutrophication threatens the population health of the New Zealand freshwater crayfish (koura), Paranephrops zealandicus. An integrated study, combining behavioural, physiological and biochemical approaches, was therefore conducted to characterise the tolerance of this species to hypoxia. When provided with a choice between water flows of high or low dissolved oxygen in short-term laboratory assays, crayfish did not preferentially inhabit waters of higher PO2. However, when an aerial refuge was provided and dissolved oxygen was progressively decreased, crayfish emersed at a PO2 of 0.56±0.03kPa, suggesting a relatively high tolerance to hypoxia. Closed-box respirometry delineated a Pcrit, the point at which crayfish transition from oxyregulating to oxyconforming, of 6.0kPa. Simultaneous measurement of heart rate showed no changes across the PO2 range. In response to 6-h exposures to fixed dissolved oxygen levels (normoxia, 19.3kPa; moderate hypoxia, 3.5kPa; and severe hypoxia, 1.7kPa), P. zealandicus showed a haemolymph PO2 that declined with the magnitude of hypoxia, and while plasma pH declined in severe hypoxia, there were no changes in plasma PCO2. Plasma glucose concentrations fell, and plasma lactate increased in both hypoxic groups. There were no changes in tissue glucose or lactate concentrations. These data indicate that P. zealandicus is relatively tolerant of hypoxia, and possesses biochemical and physiological mechanisms that facilitate survival during short-term exposures to acute hypoxia. If hypoxia is severe and/or prolonged, then this species is capable of escaping to aerial refugia.

Acute and sub-chronic effects of sub-lethal cadmium exposure on energy metabolism in the freshwater shrimp, Paratya curvirostris.

Cadmium (Cd) is a toxic trace element enriched in waters through activities such as mining and agriculture. The freshwater shrimp Paratya curvirostris inhabits near-coastal, lowland streams potentially impacted by Cd, but nothing is known regarding its sensitivity to this metal. An acute (96h) median lethal concentration (LC50) of 405µgL-1 was derived for P. curvirostris, placing it among the most tolerant of freshwater shrimp species. Acute (4 d; 0, 50 and 100µgL-1) and sub-chronic (10 d; 0, 25 and 50µgL-1) exposures then investigated effects of Cd on energy metabolism (respiration rate, excretion rate, O:N ratio). In contrast to effects in previously studied species, Cd induced an increased respiration rate, which when coupled with an unchanged excretion rate, resulted in an increased O:N ratio. These data were explained by an increased reliance on carbohydrate and/or lipid as a metabolic substrate stimulated by increased metabolic costs of toxicant exposure. Similar effects were seen across all time-points, although the lowest effective Cd concentration decreased with increased exposure time. Overall, results suggest that Cd is unlikely to be a significant environmental stressor to P. curvirostris, except in highly contaminated freshwaters, and/or where Cd co-occurs with hypoxia.

Field-to-laboratory transport protocol impacts subsequent physiological biomarker response in the marine mussel, Perna canaliculus.

The transfer of mussels from field to laboratory, or transplantation between clean and contaminated field settings, is a common protocol in ecotoxicology. However, collection and transport of mussels could lead to stress that may impact biomarker responses, and thus confound interpretation of results. Physiological responses (clearance rate, absorption efficiency, excretion rate, respiration rate and scope-for-growth) of green-lipped mussels (Perna canaliculus) exposed to four different transportation protocols were investigated. These protocols included immersion in site seawater (SSW), immersion in artificial seawater (ASW), and emersion (aerial transport; EMS) at two temperatures (15°C and 5°C). Physiological measurements were conducted after a simulated 24h "transport" phase and a 48h "recovery" phase. Clearance rates were significantly inhibited by the EMS 5°C and ASW protocols relative to SSW treatment, although the clearance rate of the latter recovered after 48h. A similar pattern was observed for excretion and respiration rates for ASW. Decreased excretion rates for EMS 15°C and respiration rates for EMS 5°C were also recorded relative to values for SSW following "recovery". Negative scope-for-growth was observed for all treatments except EMS 15°C. These data suggest transport emersed at ambient air temperatures is the best method to maintain physiological health of green-lipped mussels.

Physiological and biochemical responses of the estuarine pulmonate mud snail, Amphibola crenata, sub-chronically exposed to waterborne cadmium.

Physiological and biochemical responses of the pulmonate mud snail, Amphibola crenata, to waterborne cadmium (Cd) were investigated to determine the mechanisms of toxicity and impacts of a 21-d Cd exposure. Mud snails were exposed to nominal Cd concentrations of 0, 0.2, 4 and 8 mg L - 1 and bioaccumulation, whole animal physiological (oxygen consumption, ammonia excretion and oxygen:nitrogen), and tissue level biochemical (catalase activity, lipid peroxidation, glycogen, glucose and protein) endpoints were measured every 7 days. At the two highest Cd exposure concentrations complete mortality was observed over 21-d. In surviving animals, oxygen consumption declined and ammonia excretion rate increased with Cd exposure concentration and duration. The increased ammonia excretion likely reflected enhanced protein metabolism as suggested by a reduced oxygen:nitrogen (O:N). Increasing waterborne Cd concentration and exposure time led to increasing metal accumulation in all tissues. The snail viscera showed the highest Cd accumulation. Both catalase activity and lipid peroxidation in the viscera significantly increased with Cd exposure concentration and time, whereas, the foot muscle and remaining tissues (kidney, mantle, remaining digestive tissues and heart) showed increased catalase activity and lipid peroxidation at higher Cd concentrations (4 and 8 mg L - 1), suggestive of an effect of Cd on oxidative stress. Over the course of 21 days, Cd exposure resulted in significantly lower levels of glycogen in viscera relative to Cd-free controls, reflecting an increased energy demand. Haemolymph glucose rose initially and then fell with increased exposure duration, while haemolymph protein generally exhibited an increased concentration in Cd-exposure groups, reflecting the changes in energy substrates noted for somatic tissues. These results suggest that the physiological and biochemical responses of A. crenata to Cd are conserved relative to other aquatic animals, and were tissue-specific, dose- and time-dependant.

Diversity and distribution of benthic dinoflagellates in Tonga include the potentially harmful genera Gambierdiscus and Fukuyoa.

Benthic dinoflagellates that can cause illness, such as ciguatera poisoning (CP), are prevalent around the Pacific but are poorly described in many locations. This study represents the first ecological assessment of benthic harmful algae species in the Kingdom of Tonga, a country where CP occurs regularly. Surveys were conducted in June 2016 in the Tongatapu island group, and in June 2017 across three island groups: Ha'apai, Vava'u, and Tongatapu. Shallow subtidal coastal habitats were investigated by measuring water quality parameters and conducting quadrat surveys. Microalgae samples were collected using either macrophyte collection or the artificial substrate method. Benthic dinoflagellates (Gambierdiscus and/or Fukuyoa, Ostreopsis, and Prorocentrum) were counted using light microscopy, followed by molecular analyses (real-time PCR in 2016 and high throughput sequencing (metabarcoding) in 2017) to identify Gambierdiscus and Fukuyoa to species level. Six species were detected from the Tongatapu island group in 2016 (G. australes, G. carpenteri, G. honu, G. pacificus, F. paulensis, and F. ruetzleri) using real-time PCR. Using the metabarcoding approach in 2017, a total of eight species (G. australes, G. carpenteri, G. honu, G. pacificus, G. cheloniae, G. lewisii, G. polynesiensis, and F. yasumotoi) were detected. Species were detected in mixed assemblages of up to six species, with G. pacificus and G. carpenteri being the most frequently observed. Ha'apai had the highest diversity with eight species detected, which identifies this area as a Gambierdiscus diversity 'hotspot'. Vava'u and Tongatapu had three and six species found respectively. Gambierdiscus polynesiensis, a described ciguatoxin producer and proposed causative agent of CP was found only in Ha'apai and Vava'u in 2017, but not in Tongatapu in either year. Ostreopsis spp. and Prorocentrum spp. were also frequently observed, with Prorocentrum most abundant at the majority of sites. In 2016, the highest number of Gambierdiscus and/or Fukuyoa cells were observed on seagrass (Halodule uninervis) from Sopu, Tongatapu. In 2017, the highest numbers of Gambierdiscus and/or Fukuyoa from artificial substrate samples were recorded in the Halimeda dominant habitat at Neiafu Tahi, Vava'u, a low energy site. This raised the question of the effect of wave motion or currents on abundance measurements from artificial substrates. Differences in detection were noticed between macrophytes and artificial substrates, with higher numbers of species found on artificial substrates. This study provides a baseline of benthic dinoflagellate distributions and diversity for Tonga that may be used for future studies and the development of monitoring programmes.

The relationship between population attributes of the mud snail Amphibola crenata and sediment contamination: A multi-estuary assessment.

This study assessed the potential of the New Zealand mud snail Amphibola crenata to act as a bioindicator of contaminated estuarine sediment. Seventeen sites with varying contaminant burdens were identified within six New Zealand regions. Attributes (population density, individual length distribution and individual dry weight condition index) were measured for field-collected A. crenata, and related to measurements of sediment trace metals and nutrients. Population density of the mud snail was relatively high in sites with elevated nutrients and organic matter. The length distribution of A. crenata showed significant regional and site-specific variations. Minimum, mean, and median shell length of A. crenata were positively correlated with sediment cadmium and zinc concentration. Overall, the sites were able to be distinguished by A. crenata population attributes and the sediment metal and nutrient content. These results suggest that A. crenata population information has potential value for assessing estuarine sediment metal and nutrient contamination.

Does physiological tolerance to acute hypoxia and salinity change explain ecological niche in two intertidal crab species?

Intertidal biota is subjected to significant fluctuations in environmental parameters such as salinity and dissolved oxygen (DO). In the current study, the effects of salinity and DO on metabolic rate, critical oxygen partial pressure (P crit), heart rate and osmoregulation in two intertidal crab species commonly found on New Zealand coastlines, Hemigrapsus crenulatus and Hemigrapsus sexdentatus, were measured. Based on its habitation of burrows in the lower intertidal zone, H. crenulatus was predicted to be more resilient to these environmental stressors than H. sexdentatus, which is distributed in the mid to high tidal zone. However, relative to the full-strength seawater control, there were no consistent salinity-dependent changes in respiratory or cardiovascular endpoints in either species following acute 6-h exposures mimicking a tidal cycle. Analysis of haemolymph osmolality and ions determined that both crab species were strong osmotic and ionic regulators over the 6-h exposure period. However, the threshold salinities at which significant changes in osmotic and ionic regulation occurred did differ and generally indicated that H. crenulatus was the better regulator. Respiratory and cardiovascular responses to DO were prominent, with a strong bradycardia observed in both species. Changes in osmolality and sodium ion regulation were also seen as DO declined. The effect on sodium ion levels had its onset at a higher oxygen partial pressure in H. sexdentatus than in H. crenulatus, indicative of a relatively poorer hypoxia tolerance in the former species. The relative resilience of respiratory, cardiovascular and osmoregulatory processes to salinity and DO variations likely contribute to distinct habitat distributions of the two crab species on New Zealand shorelines, although behaviour and inter-specific interactions may also play important roles. Environmental change, in the form of coastal erosion and anthropogenic contamination of estuaries, has the potential to disturb the delicate niche separation that exists between these species.

Assessment of a mussel as a metal bioindicator of coastal contamination: relationships between metal bioaccumulation and multiple biomarker responses.

This is the first study to use a multiple biomarker approach on the green-lipped mussel, Perna canaliculus to test its feasibility as a bioindicator of coastal metal contamination in New Zealand (NZ). Mussels were collected from six low intertidal sites varying in terms of anthropogenic impacts, within two regions (West Coast and Nelson) of the South Island of NZ. Trace elements, including arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn), were measured in the gills, digestive gland, foot and mantle, and in the surface sediments from where mussels were collected. Metal levels in the sediment were relatively low and there was only one site (Mapua, Nelson) where a metal (Ni) exceeded the Australian and New Zealand Interim Sediment Quality Guideline values. Metal levels in the digestive gland were generally higher than those from the other tissues. A variety of biomarkers were assessed to ascertain mussel health. Clearance rate, a physiological endpoint, correlated with metal level in the tissues, and along with scope for growth, was reduced in the most contaminated site. Metallothionein-like protein content and catalase activity in the digestive gland, and catalase activity and lipid peroxidation in the gill, were also correlated to metal accumulation. Although there were few regional differences, the sampling sites were clearly distinguishable based on the metal contamination profiles and biomarker responses. P. canaliculus appears to be a useful bioindicator species for coastal habitats subject to metal contamination. In this study tissue and whole organism responses provided insight into the biological stress responses of mussels to metal contaminants, indicating that such measurements could be a useful addition to biomonitoring programmes in NZ.

Effects of environmental and physiological variables on the accumulated concentrations of trace metals in the New Zealand cockle Austrovenus stutchburyi.

We examined potential causes of variation in trace element accumulation in an estuarine bivalve Austrovenus stutchburyi from two estuarine systems in South Island, New Zealand which differed in their metal contamination and salinity regimes. Concentrations of Ag, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V and Zn were measured (ICP-OES) in whole body tissues of bivalves collected from 10 sites, seston collected at high tide (a potential food resource) and in the sediment at the sites. All 13 elements showed a relationship between log bioaccumulated trace element concentration (mgkg(-1) dry weight tissue) and log shell length (mm), either in the whole data set or at least one site (ANCOVA). Growth rates of cockles varied significantly amongst sites. Accumulated soft tissue concentrations of Ag, As, Co and Cr increased with age of cockle, those of Pb and Zn decreased, with no clear age-related trend for the remaining metals (ANCOVA). Shell length was generally a good proxy for age when allowing for any size effect in metal accumulation by the cockle. There was no consistent pattern between the estuarine systems, probably reflecting unidentified contaminant inputs. Following depuration, tissue concentrations decreased significantly for some elements (Fe, Mn, Ti and V), indicating high concentrations of these metals in the gut contents. Trace element concentrations in the seston generally did not correlate with the bivalve tissue concentrations. There were few (Spearman's Rank) correlations between environmental variables at the time of sampling and cockle tissue trace element concentrations. The main sources of variation in bioaccumulated trace metal concentrations in the whole tissues of the cockle are location, shell length and age.

Waterborne cadmium impacts immunocytotoxic and cytogenotoxic endpoints in green-lipped mussel, Perna canaliculus.

Mussels are sentinel species that can be used to monitor coastal metal pollution through the application of biomarkers. Among the several important metal toxicants in coastal settings, cadmium (Cd) is of particular concern, being a non-essential metal that is known to cause harmful impacts in aquatic organisms at low concentrations. The aim of the present study was to examine the immunocytotoxic and cytogenotoxic effects of Cd on the green-lipped mussel, Perna canaliculus, under laboratory conditions. The acute (96 h; 0, 2000 and 4000 µg Cd L(-1)) and subchronic (28 d; 0, 200 and 2000 µg Cd L(-1)) toxic effects of waterborne Cd were measured in haemocytes and gill cells using differential haemocyte cell count, the micronucleus test and the comet assay. During subchronic exposure to Cd the relative counts of eosinophils and hyalinocytes increased significantly in Cd-exposed mussels while the proportion of basophils decreased. All of these effects were time- and concentration-dependent. Conversely, the relative numbers of basophils and eosinophils increased significantly during acute Cd exposure. Nuclear aberrations such as the formation of micronuclei, nuclear buds, fragmented-apoptotic cells and binuclei were observed in gill cells of Cd-exposed mussels. All of these parameters increased significantly at 2000 µg Cd L(-1) during subchronic exposure to Cd, and all showed a strong and significant correlation to gill Cd accumulation. Comet assay results demonstrated a significant increase in DNA damage in the haemocytes of mussels exposed to subchronic Cd concentrations. The results indicate that Cd has the capacity to induce immune system and genotoxic damage in green-lipped mussels, an impact that may have implications such as reduced disease resistance and compromised survival. These data also suggest that immunocytotoxic and cytogenotoxic biomarkers would be a valuable addition to environmental monitoring programmes using green-lipped mussels.

Biochemical biomarker responses of green-lipped mussel, Perna canaliculus, to acute and subchronic waterborne cadmium toxicity.

The biochemical responses of the green-lipped mussel, Perna canaliculus, to waterborne cadmium (Cd) were investigated in order to delineate toxic mechanisms, and the impacts of exposure dose and duration, of this important toxicant in a potential sentinel species. Mussels were exposed for either 96 h (acute: 0, 2000, 4000 µgL(-1) Cd) or for 28 d (subchronic: 0, 200, 2000 µgL(-1) Cd), and the digestive gland, gill and haemolymph were examined for impacts. Biochemical responses measured included those associated with metal detoxification (metallothionein-like protein; MTLP), oxidative stress (catalase, lipid peroxidation), cellular homeostasis (alkaline phosphatase, Na(+), K(+)-ATPase; NKA), and energy utilisation (glycogen, haemolymph protein). Following acute exposure, digestive gland glycogen and gill NKA activity were significantly altered by Cd exposure relative to levels in mussels exposed to Cd-free seawater. Subchronic Cd exposure resulted in a significant increase in MTLP levels in both the gill and the digestive gland. This increase was correlated strongly with the levels of Cd accumulation measured in these tissues (R=0.957 for gill, 0.964 for digestive gland). Catalase activity followed a similar pattern, although the correlation with tissue Cd accumulation was not as strong (R=0.907 for gill, 0.708 for digestive gland) as that for MTLP. Lipid peroxidation increased in the digestive gland at Days 7 and 14 at both subchronic Cd levels tested, but this effect had largely dissipated by Days 21 and 28 (with the exception of the 2,000 µgL(-1) group at Day 28). Alkaline phosphatase activity decreased significantly with Cd exposure in both tissues. This effect was observed at both tested concentrations in the gill, but only at the highest concentration for digestive gland. A decrease in digestive gland glycogen levels was observed in Cd-exposed mussels (Days 14 and 21 at 2,000 µgL(-1)), while haemolymph protein levels increased as a result of subchronic Cd exposure. These findings indicated that biochemical responses in Cd-exposed mussels were tissue-specific, dose- and time-dependent, with duration of exposure being the predominant effect. This study shows that biochemical changes in Cd-exposed green-lipped mussels can be linked to tissue metal accumulation and are consistent with previously reported physiological effects. It also suggests that green-lipped mussels are amenable to a multiple biomarker approach and may be of use as a bioindicator species for monitoring coastal metal pollution.

Impairment of green-lipped mussel (Perna canaliculus) physiology by waterborne cadmium: relationship to tissue bioaccumulation and effect of exposure duration.

Laboratory studies were performed to assess the impact of acute and subchronic cadmium (Cd) exposure on the green-lipped mussel, Perna canaliculus. A 96 h median lethal concentration (LC(50)) value of 8160 µg L(-1) was determined, characterising this species as relatively tolerant to Cd exposure. Acute (96 h; at 2000 and 4000 µg Cd L(-1)) and subchronic (28 d; at 200 and 2000 µg Cd L(-1)) waterborne exposures were then conducted to investigate the impact of Cd exposure on physiological responses (e.g. clearance (feeding) rate, absorption efficiency, oxygen uptake, ammonia production, oxygen to nitrogen ratio, scope for growth) and tissue Cd accumulation. Cd accumulation in digestive gland showed saturation with respect to increasing exposure concentration, while the gill tissue Cd accumulation followed a positive linear relationship with Cd exposure level. Clearance rates declined during both acute and subchronic exposures at levels of 2000 µg Cd L(-1) or higher. Impairments of clearance rates were strongly correlated with tissue Cd accumulation. Coupled with their importance as a food source, and their wide coastal distribution, these data suggests that P. canaliculus may be a species useful as an indicator species for trace metal pollution in coastal environments.

The influence of salinity on copper accumulation and its toxic effects in estuarine animals with differing osmoregulatory strategies.

Copper is an important ionoregulatory toxicant in freshwater, but its effects in marine and brackish water systems are less well characterised. The effect of salinity on short-term copper accumulation and sublethal toxicity in two estuarine animals was investigated. The osmoregulating crab Hemigrapsus crenulatus accumulated copper in a concentration-dependent, but salinity-independent manner. Branchial copper accumulation correlated positively with branchial sodium accumulation. Sublethal effects of copper were most prevalent in 125% seawater, with a significant increase in haemolymph chloride noted after 96h at exposure levels of 510 microg Cu(II) L(-1). The osmoconforming gastropod, Scutus breviculus, was highly sensitive to copper exposure, a characteristic recognised previously in related species. Toxicity, as determined by a behavioural index, was present at all salinities and was positively correlated with branchial copper accumulation. At 100% seawater, increased branchial sodium accumulation, decreased haemolymph chloride and decreased haemolymph osmolarity were observed after 48h exposure to 221 microg Cu(II) L(-1), suggesting a mechanism of toxicity related to ionoregulation. However, these effects were likely secondary to a general effect on gill barrier function, and possibly mediated by mucus secretion. Significant impacts of copper on haemocyanin were also noted in both animals, highlighting a potentially novel mechanism of copper toxicity to animals utilising this respiratory pigment. Overall these findings indicate that physiology, as opposed to water chemistry, exerts the greatest influence over copper toxicity. An understanding of the physiological limits of marine and estuarine organisms may be critical for calibration of predictive models of metal toxicity in waters of high and fluctuating salinities.

Spatial and temporal variations in trace metal concentrations in the cockle, Austrovenus stutchburyi from Otago, New Zealand.

This is the first comprehensive study of sources of variation in metal concentrations within the whole tissues of a shallow burrowing, filter-feeding intertidal clam, Austrovenus stutchburyi. Samples were collected from 12 sites in April, August, November and February in 1993-1994 in the vicinity of Otago Harbour and Peninsula, New Zealand. Total tissue trace metal concentrations (microg g(-1) dry weight) were measured in individual animals for the essential metals : Mn, Cu, Zn, Ni and the non-essential Cr using trace-metal clean acid-digestion and ICP-OAES techniques. Average metal concentrations were 3-60 microg g(-1) for Cu, 40-118 microg g(-1) for Zn, 2-12 microg g(-1) for Mn, 5-35 microg g(-1) for Ni and 1-44 microg g(-1) for Cr. These levels decreased with body weight and differed amongst sites except for Cr in February (mid-summer). Highest concentrations occurred at sites close to a city (Dunedin) and within the central harbour region although the Cu, Zn, Ni and Cr concentrations did not correlate with the environmental gradient or season. At one coastal site, samples of both the blue mussel Mytilus galloprovincialis and cockles gave similar trends in trace metal levels. These results suggest that the cockle could be a useful trace metal biomonitor within NZ estuaries.

Temporal variation in the specific dynamic action of juvenile New Zealand rock lobsters, Jasus edwardsii.

To enhance the on-growing of Jasus edwardsii in culture, it is important to understand the feeding physiology of juveniles. In crustaceans, there is a loss of energy and an increase in oxygen consumption (specific dynamic action or SDA) associated with feeding. The present research measured the SDA of juvenile J. edwardsii fed either in the morning or at night held at 15 degrees C. Closed box respirometry was used to measure oxygen consumption (MO(2)) and ammonia excretion in juvenile lobsters. Juveniles exhibited a nocturnal rhythm in both MO(2) and ammonia excretion. The factorial rise in MO(2) (1.58+/-0.03 times) for lobsters fed in the morning was significantly less than lobsters fed at night (1.80+/-0.01 times). Lobsters fed in the morning had a significantly shorter SDA (30+/-1.2 h) response compared to lobsters fed at night (36+/-1 h). Energy loss as a result of digestion was less for lobsters fed in the morning. Therefore, if juvenile J. edwardsii are fed in the morning, they could optimise the energy content of the meal and this could result in increased growth.