Invest in arms: behavioural and energetic implications of multiple autotomy in starfish (Asterias rubens)

The autotomy of body parts as a means of escaping predation or renewing damaged tissues has evolved in a number of animal groups. Starfishes are unique in that they can autotomise >75% of their body mass and continue to survive. Presumably, multiple autotomy of tissue has energetic costs in terms of potential fitness and may affect the allocation of energy reserves accordingly. We investigated arm autotomy, predatory capabilities and subsequent regeneration in common starfish, Asterias rubens, that were induced to lose one, two or three arms. Initially, both regeneration of autotomised arms and the rate of growth of intact arms was slowest in animals that had lost the most arms (i.e. three arms missing vs two arms missing vs one arm missing). However, 8 months later, the growth of intact arms since the start of the experiment was not significantly different between groups of starfish that had autotomised different numbers of arms. However, the average dry weight per regnerating arm was significantly higher in starfish that had autotomised the most arms. Arm loss decreased the ability of starfish to open mussels and those that had autotomised two arms were significantly less likely to feed successfully on a mussel in a 24-h period than intact starfish. Our data suggest that proportionally more energy is allocated to arm regeneration in starfish that have suffered multiple arm loss and this may compensate a potential decrease in fitness that results from decreased feeding capability.     

Damage, autotomy and arm regeneration in starfish caught by towed demersal fishing gears

Arm damage and loss were examined in the starfish Asterias rubens that had been caught in a variety of towed commercial fishing gears deployed on different sea bed types. Between 7% and 38% of the starfish in each catch lost one or more arms, and arm loss was positively correlated with the volume of the catch for two of the fishing gears examined. Subsequent monitoring of damaged animals showed that arms were autotomised for at least 3 weeks following capture. Mortality was highest in starfish with damaged or missing arms, compared with those that appeared intact after fishing. Arm regeneration was delayed in a small proportion of the animals caught by commercial gears. In a parallel study, 17% of starfish caught by a 4 m beam trawl had a damaged ambulacral ossicle at the point of autotomy (cf. none from a control group that were induced to autotomise under controlled conditions). There was no difference in regeneration rates between the animals caught by commercial gears and a control set (caught by a small trawl and forced to autotomise an arm in the laboratory) once the animals that delayed regeneration were excluded from the dataset. After 1 year under laboratory conditions the starfish had, on average, regenerated the missing arm to 75% of the length of the other four arms. During this time period the lengths of the undamaged arms increased by ca. 50%. The implications of this study for using arm loss in starfish as an indicator of fishing disturbance are discussed. Received: 16 August 2000 / Accepted: 20 October 2000     

Responses of Asterias rubens to bivalve prey in a Y-maze

Experiments carried out in a Y-maze apparatus using a constant number of mussels, Mytilus edulis L., as prey showed the presence of a food-seeking period in the predatory starfish Asterias rubens L. collected in the Menai Strait, Anglesey, North Wales. The starfish orientated towards the mussels in the experiment conducted from Novemeber-December to May. The food-seeking activity was not significantly different from random expectation between June and October. It is suggested that this seasonal change in the behaviour of A. rubens can be due either to a lowering of chemo-sensitivity and failure to respond by A. rubens, or to a seasonal change in production of attractant(s) by the prey, or to a combination of the above. A. rubens does not move towards a bait of oyster spat (Ostrea edulis L.) in the Y-maze unless it has been previously conditioned to eat the oysters for about a month. In the Menai Strait, oysters would rarely be encountered by A. rubens and, therefore, the experiments confirmed the concept of ingestive conditioning (Wood, 1968).     

Changes in the biochemical composition of the pyloric caeca of female seastars,Asterias rubens,during their annual reproductive cycle

The biochemical composition of the pyloric caeca of female seastars (Asterias rubens) was studied throughout the annual reproductive cycle. The pyloric caeca index is high during the pseudo-rest stage of the ovaries and decreases gradually during ovarian growth. The pyloric caeca dry weight varies between 20 and 38% of the fresh weight. Lipids, and less prominently carbohydrates (both glycogen and other reducing sugars), seem to constitute the primary nutrient reserves for gonad growth. Proteins are also available to meet ovarian requirements during vitellogenesis. Glycogen levels are high in late autumn and winter and low at spawning time and in summer, whereas levels of the other reducing sugars are high in post-spawning months and subsequently gradually decrease during gonad development. The total lipid level is extremely variable (averaging 75 mg g^-1 organ fresh weight), peak levels of over 200 mg g^-1 being found in some individuals in summer and at spawning time. The free amino acid level is constant at about 20 mg g^-1. The protein level is rather high throughout the annual cycle, and displays only minor changes. The observed patterns of decrease in major constituents suggest a rapid release of nutrient reserves from the pyloric caeca (deposited during the summer) at the onset of vitellogenesis. Moreover, the needs of the ovaries during further development seem to be so tremendous that during the winter months the digested food may be transported to the ovaries without prior deposition in the pyloric caeca. The changes observed in the pyloric caeca are discussed and compared with those occurring simultaneously in the ovaries.     

Avoidance behaviour of Asterias rubens to extracts of Mytilus edulis,solutions of bacteriological peptone,and selected amino acids

The effect of some homogenates, peptones and amino acids upon the positive rheotactic behaviour of Asterias rubens L. is studied. It was found that homogenates of Mytilus edulis, solutions of bacteriological peptone L 37, L-glutamic acid and a mixture of 10 common amino acids acted as repellents and altered the positive rheotactic behaviour of A. rubens. The experimental evidence suggests that the active compound(s) of the homogenates of M. edulis and of the solution of L 37 is a heat stable substance whose molecular weight is lower than ca. 30,000. It was found that A. rubens sensed L-glutamic acid in concentrations of the part per million range. Sinergistic interaction was found between L-glutamic acid and a mixture of one or more other 9 common amino acids. It is shown that the sensitivity of A. rubens to one of the repellents, bacteriological peptone L 37, changes during the year. Among other factors, seasonal changes in sea-water temperature could account for this.     

Changes in the biochemical composition of the ovaries of the seastar Asterias rubens during its annual reproductive cycle

The biochemical composition of the ovaries of the asteroid echinoderm Asterias rubens was studied, with emphasis on the changes which are manifest during the annual reproductive cycle. Ovarian dry weight displays only minor changes during ovarian development, constituting about 20% of the organ fresh weight. Levels of all constituents show some variation, but in general increase with ovarian growth. Only the free amino acid level is rather constant. Except for glycogen, the contents of other constituents (total lipids, other reducing sugars, free amino acids and proteins) show a rectilinear increase with ovarian growth. Glycogen content increases rectilinearly with time during early vitellogenesis, but remains constant during further development until ovarian maturity. By plotting constituent levels and contents against a non-linear gonad index axis rather than against sampling date, results can be correlated more easily with ovarian growth stages. The possibility of endocytosis of a vitellogenin-like yolk precursor by the ovary is discussed.     

Response of Asterias vulgaris to bivalves and bivalve tissue extracts

The sea star Asterias vulgaris was observed in aquaria and in a flow tank in the presence of oysters, oyster tissue, and extracts of four shellfish species. Oysters were approached after varying delays, opened, and consumed; oyster tissue was rapidly approached and eaten. Dilute (ppb) shellfish extracts were approached in a flow tank. High concentrations of extracts elicited posturing and stomach eversion responses. Some suspended materials in flowing seawater inhibited the approach of A. vulgaris to oyster extract. The behavior of A. vulgaris and A. forbesi to food stimuli are compared. Asteroids appear to distinguish between intact and injured tissue, and exhibit variable responses. These tendencies provide a possible mechanism for forming feeding aggregates.Contribution No. 2703 of the Woods Hole Oceanographic Institution, USA     

Morphological basis and mechanics of arm movement in the stalked crinoid Metacrinus rotundus (Echinodermata,Crinoida)

We obtained live specimens of the stalked crinoid Metacrinus rotundus from Suruga Bay, Japan, in 1992 and managed to keep them for several months in aquaria. Video observations of crawling individuals showed that both the aboral bending of the arm and the oral bending can be power strokes. When climbing up a lattice, the crinoids bend their arms aborally to pull the body upward. The oral side of the arm contains muscles, but the aboral side has ligaments without muscles. We found that ligaments on the aboral side are divided into two parts, the aboral ligament and the newly found fossa ligament. Ultrastructurally, the aboral ligament resembles typical echinoderm catch connective tissue. Its microfibrils exhibit a variable banding pattern after special staining and might be an elastic material. The fossa ligament contains only collagen fibrils which are often closely connected. Biomechanically the frozen and rethawed aboral ligament behaves like a spring. It shows between 2.4 and 29.1% stress relaxation, and it is so stiff that the oral muscles would not be able to stretch it. We suggest that the connective tissue of the ligament is a catch connective tissue and softens when the arm moves. During long-term filtration posture the ligament would stiffen so as to maintain its posture for a long time without muscle contraction and thus without using much energy.     

Interactive accumulation of mercury and selenium in the sea starAsterias rubens

Interactions between mercury and selenium accumulation and subcellular binding inAsterias rubens (L.), collected in 1987 from Lille Bælt at Middelfart, Funen, Denmark, were investigated in laboratory experiments. Sea stars exposed to 10µg Hg l^–1 for 30 d accumulated mercury in body wall, tube feet and stomach linearly with time at 1.2, 1.2 and 0.5µg Hg g^–1 dry wt d^–1, respectively. Mercury was accumulated in pyloric caeca and coelomic fluid initially at 1.4µg Hg g^–1 dry wt d^–1 and 9.4 ng Hg ml^–1 d^–1, respectively; after 10 d uptake rates decreased. Sea stars exposed to 75µg Se-SeO ₃ ^{- -} l^–1 accumulated selenium linearly with time over 30 d in the stomach, pyloric caeca, tube feet and body wall at 2.0, 1.2, 1.2 and 0.6µg Se g^–1 dry wt d^–1. Sea stars exposed to 75µg Se-SeO ₄ ^{- -} l^–1 maintained selenium levels in the coelomic fluid at 75µg Se l^–1 over 30 d. Exposure to selenate did not alter the selenium concentrations in the tissues. Sea stars exposed concurrently to 75µg Se-SeO ₃ ^{- -} and 10µg Hg l^–1 accumulated more mercury and selenium in tube feet and body wall than did sea stars exposed to the two elements alone. In pyloric caeca and stomach concurrent exposure reduced accumulation of both elements. Mercury was bound predominantly in the insoluble fraction of the tissues, and soluble mercury was bound in proteins of high (> 70 kilodaltons) or very low (< 6000 daltons) molecular weight. Ca. half of the selenium recovered was bound in the insoluble fraction, and soluble selenium was bound in proteins of high (> 70 kilodaltons) or very low (< 6000 daltons) molecular weight. Interaction between the two elements was exerted predominantly in the insoluble fraction of the tissues.     

Distribution of tetrodotoxin in various organs of the starfish Astropecten polyacanthus

Tissues of various organs of the starfish Astropecten polyacanthus collected in the Hiroshima Prefecture from April 1985 to June 1986 were analyzed for lethal potency by the assay method for tetrodotoxin. The ovary showed the highest potency (47 to 1 450 MU g^-1), followed by the digestive organs (<10 to 960 MU g^-1) and the exoskeleton including spines and tube-feet (<10 to 170 MU g^-1). The pyloric caecum and testis were less toxic. Overall toxicity was remarkably higher in females (2 060±382 MU, mean±SE) than in males (1 106±214 MU).     

Reproduction of asteroids from Balsfjorden,Northern Norway: Analyses of lipids in the gonads of Ctenodiscus crispatus,Asterias lincki and Pteraster militaris

Seasonal lipid analyses were performed on the gonads and residual bodies of Ctenodiscus crispatus (Retzius) and Asterias lincki (Müller & Troschel), collected from Balsfjorden, northern Norway during March 1978–February 1980. The ovaries of both species had high percentages of total lipid (in the region of 60% of the dry weight) that were relatively constant throughout the season. Testes from both species had in the region of 20% of their dry weight as lipid, again with little seasonal variation. The majority of the total lipid in the ovaries of C. crispatus was accounted for by alkyldiacylglycerols and there was little seasonal variation in lipid class composition. Phospholipid accounted for the bulk of the lipid in the testes of C. crispatus, where alkyldiacylglycerols were present but in minor amounts. A slight degree of seasonal variation occurred in the composition of testis lipid in that maximal percentages of triacylglycerols and alkyldiacylglycerols occurred in January–April. The ovaries of A. lincki contained both triacylglycerols and alkyldiacylglycerols as major neutral lipids. Significant seasonal variation occurred in lipid class composition in the ovaries in that neutral lipids showed transient minima in February–April. The testes of A. lincki had substantial amounts of both triacylglycerols and alkyldiacylglycerols: maximal percentages of these lipids occurred in January–March. Analyses of gonads of near-mature Pteraster militaris (O. F. Müller) revealed that the ovaries were rich in lipid that was predominantly alkyldiacylglycerols, whereas the testes had much lower levels of lipid accounted for mainly by phospholipids. The residual bodies of all three asteroids had significant but small amounts of alkyldiacylglycerols in their lipids. A. lincki had triacylglycerols as a major lipid class in its body lipids, whereas in C. crispatus the major body lipid was phospholipid. Little seasonal variation was seen in the composition of the residual body lipid of either C. crispatus or A. lincki. The results are consistent with an aseasonal reproductive pattern in C. crispatus, although a main breeding activity occurred in mid-winter. A. lincki is a more seasonal breeder, but also had maximal activity in winter. Irrespective of their breeding habits, all three asteroids produced eggs rich in alkyldiacylglycerols. A major role for this lipid in the development of the large lecithotrophic eggs of asteroids is indicated.     

Temperature effects on accumulation and retention of radionuclides in the sea star,Asterias forbesi: implications for contaminated northern waters

Radioactive waste disposal and nuclear testing concentrated in high latitudes in the northern hemisphere have resulted in the accumulation of radionuclides in Arctic marine ecosystems, but little is known of the consequences for marine biota in these waters. Under controlled laboratory conditions in May through September 1994, we examined the bioaccumulation in sea stars, Asterias forbesi (Desor), or the radionuclides ²⁴¹Am, ⁵⁷Co and ¹³⁷Cs, all of which are important components of disposed radioactive wastes. Experiments at 2 and 12°C determined the relative importance of food (the bivalve, Macoma balthica) and water as sources of radionuclides and assessed the influence of temperature on radionuclide influx and efflux rates. The lower temperature greatly increased the retention of radionuclides ingested with food; for instance, the biological half-life (tb _1/2) of ²⁴¹Am in the sea stars was 31 d at 12°C, but was virtually infinite at 2°C. Retention of ingested ⁵⁷Co was also increased at 2°C (tb _1/2=41 d). ¹³⁷Cs was not accumulated from food. Low temperature significantly reduced net influx rates of ¹³⁷Cs from water, but did not affect net uptake of ²⁴¹Am or ⁵⁷Co. Temperature had little effect on the retention of all three isotopes obtained from the dissolved phase. These experiments suggest that extrapolation of results of previous radioecological studies, conducted at warmer temperatures, to polar or temperate winter environments may be problematic, and that nuclear waste isotopes obtained through trophic transfer may be retained far more efficiently in high latitude marine biota than by fauna from warmer ecosystems.     

Sex, intimidation and severed limbs: the effect of simulated predator attack and limb autotomy on calling and emergence behaviour in the field cricket Gryllus bimaculatus

Crickets can autotomize a limb in order to evade predation; however, this autotomy compromises their escape speed and, therefore, their ability to avoid subsequent predation events. We recorded two measures of predator-avoidance behaviour in field crickets (Gryllus bimaculatus) exposed to varying levels of predation threat, with the most extreme level leading to autotomy of a limb. Our first measure of caution was time to emergence from cover, which was affected by perceived predation treatment, with both autotomized males and females being significantly more cautious than intact individuals. For males (but not females), the presence of a calling conspecific encouraged earlier emergence. Our second measure of caution was alteration of male calling behaviour. Autotomized males remained silent for significantly longer time after disturbance than intact males, but there was no difference in call rate once they had resumed calling, suggesting that behavioural changes were not merely a result of injury response but a controlled modification of behaviour as a result of autotomy. These data suggest that autotomy in field crickets results in altered calling behaviour, which was not significantly altered with different acoustic environments.     

Fatty acid compositions of neutral glycerides from the ovaries of the asteroids Ctenodiscus crispatus,Asterias lincki and Pteraster militaris from Balsfjorden,northern Norway

Fatty acid analyses of lipids in the asteroids Ctenodiscus crispatus (Retzius), Asterias lincki (Müller and Troschel) and Pteraster militaris (O. F. Müller) collected in Balsfjorden, near Tromsø, northern Norway in 1978–1980, were performed to further our understanding of the asteroids' reproductive biology. Fatty acid compositions were determined in phospholipids, triacylglycerols and alkyldiacylglycerols isolated from ovaries of frozen C. crispatus. The major polyunsaturates in phospholipids were 20:4(n-6) followed by 20:5(n-3). Both the triacylglycerols and alkyldiacylglycerols were relatively deficient in polyunsaturates but had 20:1(n-13) and 18:1(n-7) as major components. Both these liqid classes had additionally 15% of their fatty acids as a variety of odd-numbered and branched-chain fatty acids. The fatty acid composition of neutral glycerides, largely alkyldiacylglycerols, from heat-dried ovaries of C. crispatus was not materially different from that of alkyldiacylglycerols isolated from the ovaries of frozen individuals. The fatty acid composition of neutral glycerides, largely alkyldiacylglycerols, from heat-dried ovaries of P. militaris was similar to that for C. crispatus in that 20:1(n-13) and 18:1(n-7) were major components, and odd-numbered together with branched-chain fatty acids accounted for about 15% of the total fatty acids. The fatty acid composition of neutral glycerides, consisting of equal amounts of triacylglycerols and alkyldiacylglycerols, from heat-dried ovaries of A. lincki differed from those of the previous two species in that 20:1(n-9) and 18:1(n-9) were major components and odd-numbered together with branched-chain fatty acids accounted for less than 5% of the total fatty acids. The results are discussed mainly in terms of lipid biosynthetic mechanisms within the asteroids and the interplay between internal biosynthetic activities and dietary fatty acids, particularly those from bacterial sources, is considered.     

Effects of autotomy on long-term survival and growth of painted spiny lobster (Panulirus versicolor) on the Great Barrier Reef, Australia

The effects of autotomy (shedding of appendages) on survival and growth rates of painted spiny lobster were investigated at Northwest Island (23^° 18?? S, 152^° 43?? E) during the period 2003?C2006. Adult lobsters were captured, tagged, and classified as either uninjured (n?=?68), minimally injured (n?=?39) or moderately injured (n?=?19) depending on the number and type of appendages that were autotomized during capture and handling. Six to thirty-six months after release, 86 lobsters were recaptured (mean time at large?=?305?days). Recapture rates of uninjured (64.7%), minimally injured (71.8%), and moderately injured lobsters (73.7%) were not significantly different. Similarly, mean annualized growth rates of uninjured, minimally injured, and moderately injured lobsters were not significantly different. This suggests that the energetic cost of a single episode of autotomy is either negligible or exists as a trade-off with some other life history trait, such as reduced reproductive performance. These results support the use of certain management tools (e.g., size limits) that prescribe release of non-legal lobsters, regardless of their injury status.     

Seasonal changes in pyloric caecum and gonad indices during the annual reproductive cycle in the seastar Asterias forbesi

Seasonal changes in pyloric caecum and gonad indices were studied in a population of the seastar Asterias forbesi (Desor) from East Rockaway Inlet (Long Island, New York) during two annual cycles (1980/81, 1982/83). Pyloric caeca indices increased during fall, reached a maximum about April, and declined sharply to a minimum in mid-summer. Gonad indices increased during fall and winter and reached a maximum about May. Judging from gonad size analysis, spawning occurred in late June to early July, at bottom temperatures of 16° to 18°C. There was no long-term inverse relationship between pyloric caecum and gonad indices. Since nutrients and energy ingested during the important fall feeding period are utilized simultaneously for body growth and gonad development, it is unnecessary for the pyloric caeca to store nutrients over long periods as occurs in A. rubens and many other species. The specific caeca-gonad relationship is probably an adaptation to the extreme seasonal thermal fluctuations of the NW Atlantic, which constrain the feeding activity of A. forbesi and limit the possibility of long-term storage. In this population, most individuals grow rapidly in their first year (including first two summers) and spawn in their third summer. Few seastars survive to spawn again in their fourth summer. However, gametogenesis may take place in some individuals in their second summer. Year-to-year variability in mean size at spawning may reflect temporal variation in environmental conditions (weather, food availability) at this site.     

Introduction of the northern Pacific asteroid Asterias amurensis to Tasmania: reproduction and current distribution

The northern Pacific asteroid Asterias amurensis (Lütken) has been recently introduced to Tasmania and is now well-established in east and southeast Tasmania. This sea star is conspicuous throughout the Derwent River estuary and is particularly abundant in the Hobart port area. Reproduction of two populations of A. amurensis at Sullivans Cove and at Sandy Bay was investigated from August 1993 to October 1994 by gonadal histology and measurement of the gonad index (GI). An intense period of vitellogenic and spermatogenic growth started in April, with the breeding condition reached by June. In 1994, peak GI was recorded at Sullivans Cove in July and at Sandy Bay in August. Although these data indicated that the Sullivans Cove population spawned before the Sandy Bay population, histological examination revealed that major spawning activity occurred in both populations from July onwards. In the early part of the breeding season, gametogenesis proceeded in parallel with spawning, with released gametes being replaced by continual gametogenesis. Maintenance of a higher GI during the early part of the breeding season at Sandy Bay was due to prolonged gametogenic replacement at this site. Spawning continued to October 1994, resulting in a sharp decline in the GI. The cyclic expansion and regression of the genital haemal sinus coincident with germinal proliferation and growth, respectively, support the contention that haemal fluid provides nutrients for gametogenesis. In Tasmania, A. amurensis experiences temperature and photoperiod regimes similar to those experienced by endemic populations of this species in the north Pacific. Comparison of reproduction of A. amurensis in Japan and Tasmania at similar latitudes shows that gametogenesis of the northern and southern populations is 6 mo out of phase. This phase shift provides evidence for photoperiodic regulation of gametogenesis in A. amurensis. The similar trend in sea-temperature regimes associated with the stages of gametogenesis in northern and southern populations suggests that temperature also plays a modulatory role. Based on the periodicity of reproduction and the ontogeny of A. amurensis, the planktotrophic larvae of this species would be expected to be in the plankton for several months from the end of winter through summer. Considering the highly fecund, dispersive life-history of A. amurensis, the southeast Tasmanian populations have considerable potential to serve as a seed source for establishment of new populations of this asteroid elsewhere in Tasmania and in mainland Australia. Received: 18 October 1996 / Accepted: 22 October 1996     

Storage and depletion of lipid components in the pyloric caeca and ovaries of the seastarAsterias rubens during its annual reproductive cycle

Detailed information is presented on the changes in lipid-class profiles (polar lipids, total neutral lipids, free sterols, steryl esters, triacylglycerols, neutral ether lipids and free fatty acids), which are manifest during the annual reproductive cycle of the seastarAsterias rubens for both the storage organs (pyloric caeca) and utilizing organs (ovaries). The ovaries appear to accumulate all individual lipid components proportional to progression of vitellogenesis. Pyloric caeca, in contrast, show variable lipid-class levels, probably due to more complex processes in these organs, operating simultaneously: digestion of food, accumulation of storage lipids, mobilization of stored lipids and their release. The results are discussed in terms of current knowledge on the role of lipids in echinoderm reproduction.     

Temperature effects on the metabolism of larvae of the Antarctic starfish Odontaster validus, using a novel micro-respirometry method

Oxygen consumption of individual larvae of the Antarctic sea-star Odontaster validus was measured during the 50-day period following fertilisation. Values ranged from 0.76 pmol O₂ h^-1 for one specimen at the coeloblastula stage to 77.6 pmol O₂ h^-1 for one bipinnaria larva. At 0°C the mean oxygen consumption rate of an individual larva increased from 10.9 pmol O₂ h^-1 (standard error of the mean, SEM, 0.13) for a gastrula larva, 13 days post-fertilisation, to 25.4 pmol O₂ h^-1 (SEM 3.5) at the bipinnaria stage (50 days post-fertilisation). Gastrulae reared at -0.5°C did not have significantly different oxygen consumption rates between days 13 and 45 post-fertilisation (mean=11.4 pmol O₂ h^-1). Individual metabolic rates were highly variable, covering more than a 40-fold range. At 2°C gastrula oxygen consumption was on average 45% higher (17.35 pmol O₂ h^-1), giving a Q₁₀ temperature effect of 4.4. For bipinnaria, mean oxygen consumption in 2°C larvae (31.4 pmol O₂ h^-1) was not significantly different from that in larvae at -0.5°C, suggesting bipinnaria metabolism may be less sensitive to temperature change than earlier stages. At 2°C the bipinnaria stage was reached at 30-35 days compared with 45-50 days at 0°C, giving a Q₁₀ of 4.5 for temperature effects on development. The method here used a new, highly sensitive micro-respirometry method that is inexpensive and straightforward in design. Individual larvae of O. validus were held in 35- to 50-µl respirometers. These larvae have very low metabolic rates, and published work on such organisms have utilised at least 25 individuals per chamber. The oxygen content of the respirometers was measured using a 25-µl sample injected into a couloximeter. Oxygen consumption rates down to -1 pmol h^-1 can be detected. Under optimum conditions oxygen consumption of a single larva of -4 pmol O₂ h^-1 was measured with an accuracy of ᆨ%. Values of ~15 pmol h^-1 could routinely be measured with this accuracy. This method would allow oxygen consumption to be evaluated in individual field-caught larvae of most marine ectotherms.