In situ swimming and settlement behaviour of larvae of an Indo-Pacific coral-reef fish, the coral trout Plectropomus leopardus (Pisces: Serranidae)

Late larvae of the serranid coral trout Plectropomus leopardus (Lacepède), captured in light traps, were released during the day both in open water and adjacent to two reefs, and their behaviour was observed by divers at Lizard Island, northern Great Barrier Reef. Coral trout larvae (n = 110) were present in light-trap catches from 18 November to 3 December 1997, including new moon (30 November). The swimming speed of larvae in open water or when swimming away from reefs was significantly greater (mean 17.9 cm s⁻¹) than the speed of larvae swimming towards or over reefs (mean 7.2 cm s⁻¹). Near reefs, larvae swam at average depths of 2.7 to 4.2 m, avoiding 0 to 2 m. In open water, swimming depth varied with location: larvae >1 km east of Lizard Island swam steeply downward to >20 m in 2 to 4 min; larvae >1 km west oscillated between 2.6 and 13 m; larvae 100 to 200 m east of Lizard Island oscillated between 0.8 and 15 m. Nearly all larvae swam directionally in open water and near reefs. In open water, the average swimming direction of all larvae was towards the island, and 80% (4 of 5) swam directionally (p < 0.05, Rayleigh's test). Larvae swam directionally over the reef while looking for settlement sites. The frequency of behaviours by larvae differed between two reefs of different exposure and morphology. Depending on site, 26 to 32% of larvae released adjacent to reefs swam to open water: of these, some initially swam towards or over the reef before swimming offshore. In some cases, offshore-swimming seemed to be due to the presence of predators, but usually no obvious cause was observed. Depending on the reef, 49 to 64% of the larvae settled. Non-predatory reef residents aggressively approached 19% of settlers. Between 5 and 17% of the larvae were eaten while approaching the reef or attempting to settle, primarily by lizardfishes but also by wrasses, groupers and snappers. A higher percentage of larvae settled in the second week of our study than in the first. Average time to settlement was short (138 s ± 33 SE), but some larvae took up to 15 min to settle. Average settlement depth was 7.5 to 9.9 m, and differed between locations. No settlement took place on reef flats or at depths <4.2 m. Larvae did not appear to be selective about settlement substrate, but settled most frequently on live and dead hard coral. Late-stage larvae of coral trout are capable swimmers with considerable control over speed, depth and direction. Habitat selection, avoidance of predators and settlement seem to rely on vision. Received: 7 July 1998 / Accepted: 26 January 1999     

Behaviour that influences dispersal and connectivity in the small,young larvae of a reef fish

Determining the scale of larval dispersal and population connectivity in demersal fishes is a major challenge in marine ecology. Historically, considerations of larval dispersal have ignored the possible contributions of larval behaviour, but we show here that even young, small larvae have swimming, orientation and vertical positioning capabilities that can strongly influence dispersal outcomes. Using young (11–15 days), relatively poorly developed (8–10 mm), larvae of the pomacentrid damselfish, Amblyglyphidodon curacao (identified using mitochondrial DNA), we studied behaviour relevant to dispersal in the laboratory and sea on windward and leeward sides of Lizard Island, Great Barrier Reef. Behaviour varied little with size over the narrow size range examined. Critical speed was 27.5 ± 1.0 cm s⁻¹ (30.9 BL s⁻¹), and in situ speed was 13.6 ± 0.6 cm s⁻¹. Fastest individuals were 44.6 and 25.0 cm s⁻¹, for critical and in situ speeds, respectively. In situ speed was about 50% of critical speed and equalled mean current speed. Unfed larvae swam 172 ± 29 h at 8–10 cm s⁻¹ (52.0 ± 8.6 km), and lost 25% wet weight over that time. Vertical distribution differed between locations: modal depth was 2.5–5.0 and 10.0–12.5 m at leeward and windward sites, respectively. Over 80% of 71 larvae observed in situ had directional swimming trajectories. Larvae avoided NW bearings, with an overall mean SE swimming direction, regardless of the direction to nearest settlement habitat. Larvae made smaller changes between sequential bearings of swimming direction when swimming SE than in other directions, making it more likely they would continue to swim SE. When swimming NW, 62% of turns were left (more than in other directions), which would quickly result in swimming direction changing away from NW. This demonstrates the larvae knew the direction in which they were swimming and provides insight into how they achieved SE swimming direction. Although the cues used for orientation are unclear, some possibilities seemingly can be eliminated. Thus, A. curacao larvae near Lizard Island, on average swam into the average current at a speed equivalent to it, could do this for many hours, and chose different depths in different locations. These behaviours will strongly influence dispersal, and are similar to behaviour of other settlement-stage pomacentrid larvae that are older and larger.     

Role of biochemical energy reserves in the metamorphosis and early juvenile development of the oyster Ostrea chilensis

Metamorphosis in the Chilean oyster Ostrea chilensis was complete 36 h after release of the larvae, when 100% of the individuals showed edge growth of the dissoconch. The size of the larval shell did not change during metamorphosis, although the total dry weight of the larva decreased considerably. During this period, when the gill ciliature was undeveloped and the oyster therefore unable to feed, energy demands were met by biochemical reserves retained from the larval phase. Proteins contributed the largest quantity of energy to the metamorphosing oyster, 69.3% of the total expended, whereas lipids supplied 24.3% and carbohydrates only 6.4%. The process of metamorphosis consumed 64.5% of the energy reserves held by the pediveliger at the time of release. When metamorphosis was complete, growth began and tissue reserves were replenished, protein and carbohydrate accumulating rapidly early in the juvenile stage. Received: 26 December 1997 / Accepted: 8 July 1998     

Early life history and recruitment of the tropical eel Anguilla bicolor pacifica, as revealed by otolith microstructure and microchemistry

Otolith microstructure and microchemistry of the tropical eel Anguilla bicolor pacifica Schmidt were examined in glass eels collected at the mouth of the Dumoga River, North Sulawesi Island, Indonesia. Ages of the glass eels examined (age at recruitment) ranged from 124 to 202 d (167 ± 19.3 d; mean ± SD), hatching being estimated as having occurred between November 1995 and March 1996. Otolith increment widths markedly increased from age 101 to 172 d (135 ± 18.2 d; mean ± SD), coincident with a drastic decrease in otolith Sr:Ca ratios, suggesting that metamorphosis began during that period. The duration of metamorphosis was estimated as 20 to 40 d, on the basis of otolith microstructural characteristics. The fluctuation patterns in otolith increment widths and Sr:Ca ratios were similar to those of the temperate Japanese eel A. japonica. Received: 20 May 1998 / Accepted: 7 October 1998     

Growth, carbon, nitrogen and caloric content of Solea senegalensis (Pisces: Soleidae) from egg fertilization to metamorphosis

Eggs and larvae of the Senegal sole, Solea senegalensis Kaup, were reared from fertilization until the end of metamorphosis, which occurs by Day 17 after hatching at 19.5 °C. Changes in energy content and biomass quality were studied in terms of dry weight and of carbon, nitrogen and energy content. S. senegalensis spawned eggs of about 1 mm diameter which hatched 38 h after fertilization. Average dry weight of individual eggs was 46 μg, the chorion accounting for about 18% of total dry weight. Gross energy of recently fertilized sole eggs was approximately 1 J egg⁻¹. From fertilization to hatching, eggs lost 8% of their total energy (chorion not included). After hatching, larvae lost 14% of their initial energy until the start of feeding which occurred about 48 h afterwards. The principal components catabolized during embryogenesis were carbon-rich compounds that decreased by 26%, while nitrogen-rich compounds decreased by only 10% and were practically unaltered from hatching to the start of feeding. Feeding larvae displayed constant growth during the period studied (specific growth rate on a dry weight basis was 0.26 d⁻¹). The relative proportion of carbon and nitrogen content revealed an accumulation of high energy compounds in the days before metamorphosis. By Day 14, the energy content reached values similar to those of recently hatched embryos, but decreased again during metamorphosis. Received: 10 June 1998 / Accepted: 28 January 1999     

Timing of metamorphosis and larval segregation of the Atlantic eels Anguilla rostrata and A. anguilla, as revealed by otolith microstructure and microchemistry

Otolith microstructure and microchemistry were examined in juveniles of American (Anguilla rostrata) and European (A. anguilla) eels. Otolith increment width markedly increased from age 132 to 191 d (156 ± 18.9 d; mean ± SD) in A. rostrata and 163 to 235 d (198 ± 27.4 d; mean ± SD) in A. anguilla, both of which were coincident with drastic decreases in otolith Sr:Ca ratios, suggesting that metamorphosis from leptocephalus to glass eel began at those ages in each species. The duration of metamorphosis was estimated to be 18 to 52 d from otolith microstructure, for both species studied. Ages at recruitment were 171 to 252 d (206 ± 22.3 d; mean ± SD) in A. rostrata and 220 to 281 d (249 ± 22.6 d; mean ± SD) in A. anguilla. In these two species, positive linear relationships were found in ages between the beginning of metamorphosis and recruitment, suggesting that early metamorphosing larvae recruited at younger ages. Duration of the leptocephalus stage to recruitment in A. anguilla was about 40 d longer than that in A. rostrata. The geographical segregation between the two species in the Atlantic Ocean seems to be involved in the differences in the duration of the leptocephalus stage (age at metamorphosis). Received: 8 November 1999 / Accepted: 8 May 2000     

Cyclic AMP-dependent protein kinase: role in anoxia and freezing tolerance of the marine periwinkle Littorina littorea

A key regulatory mechanism underlying the switch between aerobic and anaerobic metabolism amongst anoxia-tolerant marine molluscs is reversible protein phosphorylation. To assess the role of cAMP-dependent protein kinase (PKA) in aerobic–anaerobic transitions, the effects of anoxia on the activity and subcellular distribution of PKA were assessed in foot and hepatopancreas of the marine periwinkle, Littorina littorea. Exposure to N₂ gas at 5 °C caused a rapid decline in the percentage of total enzyme present as the free catalytic subunit (PKAc) in both tissues; the percentage of PKAc fell from ∼30% in controls to 3% after 1 h anoxia and remained low over 72 h. Total PKA also fell by 30% after 72 h anoxia in hepatopancreas but rebounded during aerobic recovery. Freezing at −8 °C elicited parallel results for both percentage of PKAc and total PKA, suggesting that PKA responses to freezing were stimulated by the ischemia that develops when hemolymph freezes. Anoxia also led to a shift in PKA subcellular distribution in hepatopancreas (but not in foot), the percentage of total PKA activity associated with the nuclear fraction dropping from 25% in controls to 8% in 12 h anoxic snails with opposite changes in the cytosolic fraction. The catalytic subunit (PKAc) of foot PKA was purified to a final specific activity of 63.5 nmol phosphate transferred per minute per milligram protein. Enzyme properties included a molecular weight of 33 to 35 kDa, an activation energy from Arrhenius plots of 65.1 ± 4.8 kJ mol⁻¹, and substrate affinity constants of 151 ± 6 μM for the phosphate acceptor, Kemptide, and 72 ± 9 μM for Mg.ATP. Activity was strongly reduced by mammalian PKA inhibitors (H-89, PKA-I), by neutral chloride salts (I₅₀ values 165 to 210 mM) and by NaF (I₅₀ 62 mM). Reduced PKA activity under anoxic or freezing conditions would facilitate the observed suppression of the activities of numerous enzymes that are typically PKA-activated and thereby contribute to the overall anoxia-induced metabolic rate depression. Received: 19 November 1997 / Accepted: 30 September 1998     

Availability of dissolved organic matter offsets metabolic costs of a protracted larval period for <Emphasis Type="Italic">Bugula neritina</Emphasis> (Bryozoa)

For nearly a century researchers have investigated the uptake and utilization of dissolved organic matter (DOM) by marine invertebrates, but its contribution to their growth, reproduction, and survival remains unclear. Here, the benefit of DOM uptake was assessed for the marine bryozoan Bugula neritina (Linnaeus 1758) through performance comparisons of individuals in the presence and absence of DOM. The experiments were performed using B. neritina collected from floating docks in Beaufort, NC, USA from July to September 2004. Seawater was subjected to ultraviolet irradiation to reduce naturally occurring DOM, and then enriched with either 1 μM of palmitic acid or a mixture containing 1 μM each of glucose, alanine, aspartic acid and glycine. Larvae in DOM-enriched and DOM-reduced treatments were sampled and induced to metamorphose following 1, 6, 12, and 24 h of continuous swimming at 25°C. Sampled larvae were assessed for initiation of metamorphosis, completion of metamorphosis, and ancestrular lophophore size to determine the extent to which energy acquired from DOM uptake could offset the metabolic costs of prolonged larval swimming. DOM treatment had no significant effect on initiation of metamorphosis, but did have a significant effect on completion of metamorphosis and lophophore size. Larvae swimming in DOM-enriched treatments for 24 h experienced a 20% increase in metamorphic completion rate, compared to larvae swimming for 24 h in the DOM-reduced treatment. In addition, larvae in the amino acid and sugar mixture for 24 h had a significantly larger lophophore surface area and volume (23 and 31%, respectively), compared to larvae in DOM-depleted seawater. To ensure that the increases in performance found in larvae with access to DOM were not due to a decrease in metabolic activity, the respiration rates for these larvae were compared to those of larvae in DOM-depleted seawater. There were no significant differences between these treatments, indicating that the increases in performance were due to the energy acquired from DOM. These results clearly show that for B. neritina, DOM uptake results in increased metamorphic success and in the size of the feeding apparatus following an extended larval swimming duration.     

Gill morphogenesis in the oyster Ostrea chilensis

Despite the importance of the gills in the acquisition of food by suspension-feeding bivalve mollusks, there is almost no information on gill organogenesis. By means of a series of stereoscan electron micrographs, this paper describes gill development in the Chilean oyster, Ostrea chilensis, from the brooded larval stages to 1-month-old spat. A single gill rudiment was observed on each side of the mantle at a shell length of 320 μm, and the rudiments increased in number and size until the end of the brooding period. During metamorphosis the gill filaments increased in number from 5 or 6 to between 7 and 9. The loss of the velum and the absence of functional gill filaments during metamorphosis are consistent with previous observations of weight loss during this critical period of the life history, because the newly settled juvenile lacks the ability to remove particles from suspension. The end of metamorphosis (100% of spat with dissoconch edge) was reached 36 h after larval settlement, when the gill filaments began to grow cilia, which increased in density and differentiated as the spat developed and acquired the capability of suspension-feeding, accounting for the increase in body weight previously recorded during this stage. The larval rudiments gave rise to the inner demibranchs. The outer demibranchs were observed 10 days after settlement, located between the inner demibranch and the mantle. In 1-month-old spat, the gill did not show differentiation between primary and secondary filaments, indicating that the heterorhabdic condition characteristic of adult oysters had yet to be attained. Received: 11 December 1998 / Accepted: 21 August 2000     

Biofilm cue for larval settlement in Hydroides elegans (Polychaeta): is contact necessary?

Larvae of many sessile marine invertebrates settle in response to surface microbial communities (biofilms), but the effects of soluble compounds from biofilms in affecting larval behavior prior to settlement, attachment, and metamorphosis have been little studied. This question was addressed by videotaping the behavior of competent larvae of the serpulid, Hydroides elegans, above settlement-inducing biofilms. Adult worms were collected in Pearl Harbor, Hawaii, USA in November 2012 and spawned almost immediately. Six-day old larvae were placed in five replicated treatments in small cups: (1) with a natural biofilm; (2) with a natural biofilm on an 8-µm screen, 1 mm above the bottom of a clean cup; (3) with a natural biofilm beneath a clean screen; (4) in a clean cup; and (5) in a clean cup with a clean screen. Using the videotapes, larval swimming speeds and trajectories were quantified within 5 min of the larvae being placed in a treatment. Only larvae that touched a biofilm, i.e., in treatments (1) and (2), slowed their swimming speed and increased the amount of time spent crawling rather than swimming. This shows that under these conditions, any soluble cues emanating from a biofilm do not affect settlement behavior. Furthermore, after 24 h close to 100 % of larva in the two accessible biofilm treatments had metamorphosed and <15 % in treatments that included a biofilm under a clean screen and no biofilm at all, strongly suggesting that soluble cues for settlement were not produced by the biofilms over the longer time period.     

Differences in the early life history of the Australasian shortfinned eel Anguilla australis from Australia and New Zealand, as revealed by otolith microstructure and microchemistry

Otolith microstructure and microchemistry were examined in juveniles of Australasian shortfinned eel, Anguilla australis, from Australia and New Zealand. Patterns in otolith increment widths were similar in these two stocks. A marked increase in otolith increment width was found from age 138 to 198 d (mean ± SD: 164 ± 18.6 d) from Australia, 161 to 208 d (185 ± 17.3 d) from the western coast of New Zealand and 161 to 211 d (187 ± 18.9 d) from the eastern coast. These changes coincided with a drastic decrease in otolith Sr:Ca ratios, suggesting that metamorphosis began at these ages in each species. The duration of metamorphosis estimated from otolith microstructure was the same in the different stocks, 17 to 41 d (mean ± SD: 27 ± 5.4 d). Ages at recruitment were 186 to 239 d (mean ± SD: 208 ± 17.4 d) from Australia, 214 to 263 d (232 ± 19.8 d) from the western coast of New Zealand and 208 to 266 d (237 ± 20.0 d) from the eastern coast. There was a significant difference in the age between the Australian stock and the two stocks from New Zealand. No significant difference was found in the age between the latter two stocks. The difference in the period for the recruitment between Australian and New Zealand stocks seems to reflect their geographical separation. Received: 1 March 1999 / Accepted: 19 July 1999     

Tracking adult North Atlantic bluefin tuna (Thunnus thynnus) in the northwestern Atlantic using ultrasonic telemetry

Ultrasonic, depth-sensitive transmitters were used to track the horizontal and vertical movements, for up to 48 h, of 11 adult (136 to 340 kg estimated body mass) North Atlantic bluefin tuna (Thunnus thynnus Linnaeus). Fish were tracked in October 1995, September and October 1996, and August and September 1997 in the Gulf of Maine, northwestern Atlantic. The objective was to document the behavior of these fish and their schools in order to provide the spatial, temporal, and environmental information required for direct (i.e. fishery-independent) assessment of adult bluefin tuna abundance using aerial surveys. Transmitters were attached to free-swimming fish using a harpoon attachment technique, and all fish remained within the Gulf of Maine while being followed. Most of the bluefin tuna tagged on Stellwagen Bank or in Cape Cod Bay (and followed for at least 30 h) held a predominately easterly course with net horizontal displacements of up to 76 km d⁻¹. Mean (±SD) swimming depth for all fish was 14 ± 4.7 m and maximum depth for individuals ranged from 22 to 215 m. All but one fish made their deepest excursions, often single descents, at dawn and dusk. In general, adult bluefin tuna spent <8% of their time at the surface (0 to 1 m), <19% in the top 4 m, but >90% in the uppermost 30 m. Mean (±SD) speed over ground was 5.9 km h⁻¹, but for brief periods surpassed 20 to 31 km h⁻¹. Sea surface temperatures during tracking were 11.5 to 22.0 °C, and minimum temperatures encountered by the fish ranged from 6.0 to 9.0 °C. Tagged bluefin tuna and their schools frequented ocean fronts marked by mixed vertebrate feeding assemblages, which included sea birds, baleen whales, basking sharks, and other bluefin schools. Received: 19 July 1999 / Accepted: 25 March 2000     

Energy expenditure of swimming bottlenose dolphins (Tursiops truncatus)

The aim of our investigations was to determine, via oxygen and carbon-dioxide respirometry, how much energy dolphins (Tursiops truncatus) require when swimming at different speeds. Experiments were conducted on two female bottlenose dolphins (mean mass 162 kg) in the dolphinarium in Nuremberg Zoo, Germany, between March and August 1997. Animals were stationed in a respiration chamber for a minimum of 90 s after performing a variety of activities. We measured respiration frequency and oxygen requirements during (1) resting, (2) swimming at various velocities and (3) leaping to various heights. Resting metabolic rate of our bottlenose dolphins (2.15 W kg⁻¹) was comparable to previously published data. Metabolic rate in swimming dolphins increased to 2.47 W kg⁻¹ at 2 m s⁻¹, while leaps to 2.2 and 3 m height required a power input of 3.5 and 4 W kg⁻¹, respectively. Transport costs of swimming dolphins were lowest (1.16 J kg⁻¹ m⁻¹, corresponding to 0.12 J N⁻¹ m⁻¹) at a speed of 2.5 m s⁻¹, yielding an optimal range speed of between 1.9 and 3.2 m s⁻¹ (corresponding to minimum cost of transport ±10%). Breathing rates during all experiments correlated very well with oxygen consumption (r ² > 0.89) and could be used to derive metabolic rates in unencumbered dolphins at sea. Received: 18 December 1998 / Accepted: 27 April 1999     

Endogenous control of timing of metamorphosis in megalopae of the shore crab Carcinus maenas

Batches of hundreds of freshly collected megalopae of the shore crab Carcinus maenas (L.) showed persistent circatidal rhythms of moulting to the juvenile crab stage when maintained in constant laboratory conditions. Peaks of moulting occurred around expected times of high tides, with few megalopae moulting at other times. In larvae collected offshore, the highest tidally-timed peak of metamorphosis occurred during the second to fifth expected times of high tide, and metamorphosis of 50% of each batch took about 22 h or longer. In contrast, in larvae collected at the water's edge, 70% metamorphosed during the first expected episode of high tide, within 6 to 8 h after collection. However, although inshore megalopae moulted before offshore ones, the tidal timing of moulting remained unaltered whether megalopae were collected at neaps or springs, from the water's edge or farther offshore, in the presence or absence of natural substratum, and under various light–dark and salinity regimes. Metamorphosis of C. maenas megalopae around the times of high tides may enhance settlement into the upper intertidal zone. Early juveniles of the crab apparently prefer that zone as they are most abundant there and, unlike adults, do not undertake up-and-down-shore migration with tides. The present finding demonstrates, for the first time, endogenous physiological timing of circatidal periodicity in the metamorphic moult of crab megalopae, suggesting that endogenous factors, as well as exogenous ones should be taken into account in considering the process of settlement by crab megalopae. Received: 21 February 1996 / Accepted: 27 November 1996     

Facultative lecithotrophy during larval development of the burrowing shrimp Callianassa tyrrhena (Decapoda: Callianassidae)

Survival, developmental and consumption rate (Artemia nauplii ingested per day) as well as predation efficiency (ingested per available Artemia nauplii) were studied during the larval development of the shallow-water burrowing thalassinid Callianassa tyrrhena (Petagna, 1792), which exhibits an abbreviated type of development with only two zoeal stages and a megalopa. The larvae, hatched from berried females from S. Euboikos Bay (Aegean Sea, Greece), were reared at 10 temperature–food density combinations (19 and 24 °C; 0, 2, 4, 8 and 16 Artemia nauplii d⁻¹). Enhanced starvation resistance was evident: 92 and 58% of starved zoeas I molted to zoea II, while metamorphosis to megalopa was achieved by 76 and 42% of the hatched zoeas at 19 and 24 °C, respectively. The duration of both zoeal stages was affected by temperature, food density and their interaction. Nevertheless, starvation showed different effects at the two temperatures: compared to the fed shrimp, the starved zoeae exhibited accelerated development at 19 °C (8.4 d) but delayed metamorphosis at 24 °C (5.9 d). On the other hand, both zoeal stages were able to consume food at an increased rate as food density and temperature increased. Predation efficiency also increased with temperature, but never exceeded 0.6. Facultative lecithotrophy, more pronounced during the first zoeal stage of C.tyrrhena, can be regarded as an adaptation of a species whose larvae can respond physiologically to the different temperature–food density combinations encountered in the wide geographical range of their natural habitat. Received: 28 February 1998 / Accepted: 21 October 1998     

Physiological effects of the detergent linear alkylbenzene sulphonate on blue mussel larvae (Mytilus edulis) in laboratory and mesocosm experiments

A series of laboratory (short-term exposure in small beakers) studies and a 19 d mesocosm (6 m³ polyethylene bags filled with fjord water) study were conducted on blue mussel, Mytilus edulis, larvae and plantigrades exposed to a concentration gradient of the detergent linear alkylbenzene sulphonate (LAS, 0 to 39 mg l⁻¹). LAS is increasingly found in nearshore environments receiving wastewater from urban treatment plants. The aims were to observe physiological effects on swimming, grazing and growth in the laboratory and effects on settling and population development at in situ conditions (in field mesocosms) in order to evaluate the damages on ciliated meroplankton caused by LAS. In the laboratory the larvae showed a 50% mortality at 3.8 mg LAS l⁻¹ after 96 h exposure whether or not food was provided. Additionally the swimming behaviour was affected at 0.8 mg LAS l⁻¹ (i.e. a more compact swimming track, a smaller diameter of the swimming tracks, and reduced swimming speed). The larval particle grazing was reduced 50% at 1.4 mg LAS l⁻¹. The specific growth rate of the larvae was reduced to half at 0.82 mg LAS l⁻¹ over 9 d. During the mesocosm experiment, the larval population showed a dramatic decrease in abundance within 2 d at concentrations as low as 0.08 mg LAS l⁻¹, both due to a significantly increased mortality, but also due to settling. The settling success was reduced at the same LAS concentration as that at which mortality was observed to increase significantly. In addition to reduced settling rate, the larvae showed delayed metamorphosis and reduced shell growth as a response to LAS. Our hypothesis that the larval ciliary apparatus, crucial for normal swimming, orientation, and settling behaviours and for particle uptake, was damaged due to LAS exposure is supported by our results. This is confirmed by the physiological data (grazing, growth) and in the direct video-based observations of larval performance (swimming) and provides a reasonable explanation for what was observed in the bags (abundance, settling, mortality). These physiological effects on blue mussel larvae/plantigrades occurred at LAS concentrations reported to occur in estuarine waters. Received: 15 January 1997 / Accepted: 12 February 1997     

Microstructure of settlement-marks in the otoliths of tropical reef fishes

The morphology and ultrastructure of the otolith settlement-mark was examined in 44 tropical reef-fish species spanning nine families. A classification scheme based on similar otolith characteristics is presented. Three major categories are identified based on changes in increment width and optical qualities of the settlement-mark. Of the 44 species examined, 39 possessed “abrupt” settlement-marks (Type I) characterised by a rapid decrease in increment width (up to 50% reduction) over settlement. Type I settlement-marks were found in all nine families examined. The 39 species spanned the whole range of possible larval durations (Pomacentrus moluccensis, 15 d ± 0 SE; Naso hexacanthus, 91.2 d ± 2.97 SE). Four of the 44 species possessed “zonal” settlement-marks (Type II), featuring a band of increments that are wider than pre-settlement increments. Species in this category are the labrids Corisaygula, Thalassoma bifasciatum, T. lunare and an unidentified acanthurid (Acanthurus sp. 2). One species of acanthurid (N. brevirostris) possessed a “gradual” settlement-mark (Type III), manifest as a gradual decrease in increment width during the settlement period. A possible fourth type was identified from the literature. Gnatholepis thompsoni and Coryphopterus glaucofraenum possessed a settlement-mark with increment widths that increased post-settlement. Available data suggest a poor relationship between the structure of the settlement-mark and the magnitude of metamorphosis (previously reported as internal and external morphological change). Evidence suggests that the increment profile over early development and the increment transitions associated with the settlement event are taxon-specific and may enable late-larval stage fishes to be identified to species level. Received: 21 May 1997 / Accepted: 3 February 1999     

Ontogenetic variation in metabolism, biochemical composition and energy content during the early life stages of Farfantepenaeus paulensis (Crustacea: Decapoda: Penaeidae)

Dry weight (DW), oxygen consumption, ammonia-N excretion, proximate biochemical composition (total protein, carbohydrate, lipid, water and ash), and energy content (estimated from biochemical composition and by wet combustion) were determined in early developmental stages of cultured Farfantepenaeus paulensis. Pooled samples from embryonic, larval and postlarval stages (at 26 ± 1 °C and 34 ± 1‰) were used for measurements. The study focused on physiological and biochemical processes during transitional periods of ontogeny, such as hatching, lecithotrophic and planktotrophic stages, metamorphosis, and the attainment of a benthic existence in postlarva. DW showed higher increment between protozoea I (PZ I) and mysis I (M I) than in the next mysid and postlarval stages. Individual rates of oxygen consumption and ammonia-N excretion increased, while weight-specific rates presented significant reduction throughout development. Higher weight-specific oxygen consumption was registered in nauplius III (N III) and PZ I, following a decrease in subsequent stages. Postlarval stages PL V–VI and PL X–XII exhibited the lowest values among the stages studied. Weight-specific excretion was high in N III and protozoeal stages, with maximum values in PZ II, while the following stages were marked by lower rates. O:N ratios indicated higher protein catabolism in the stages between egg and M I and a shift to more lipid utilization close to metamorphosis. Water content was higher in the protozoeal stages and decreased afterwards. Higher percentages of protein, lipid and carbohydrate (%DW) were observed in egg and nauplius stages. Protein and lipid decreased from the egg through the naupliar and protozoeal stages, rising again in mysis stages. Lipid content (%DW) decreased in PL V–VI and PL X–XII. Lipid:protein ratios showed an increase of the importance of lipid between PZ III and M II. Carbohydrates represented a minor fraction of body composition, and ash percentages increased from egg to a maximum in PZ II, decreasing in subsequent stages. Energy content determined by wet combustion or calculated by energy equivalents presented the same trend throughout development, varying similarly to protein. Protein was the main energy contributor to body energy in all stages, while the importance of lipid was higher in egg and early naupliar stages. Trends observed in metabolic rates and body composition may be associated to morphological and behavioral changes during the early stages of penaeid development, such as the transition from herbivory to omnivory, and the adoption of a benthic existence. Different ontogenetic energy strategies contribute to succeed through such diverse type of development. Received: 4 July 2000 / Accepted: 6 December 2000     

Effect of development rate on the swimming, escape responses, and morphology of yolk-sac stage larval American plaice, Hippoglossoides platessoides

To examine the impact of development rate on swimming performance, escape response, and morphology, yolk-sac larvae of American plaice (Hippoglossoides platessoides, Fabricius) were reared at two temperatures (5 and 10 °C). Videomicroscopy and silhouette collimation videography were used to examine swimming, escape behaviour, and morphology (standard length, finfold area, and yolk-sac area) of individual larvae. Larvae were examined from 0 d post hatch (dph) to 14 dph for the 5 °C treatment group and from 0 to 6 dph for the 10 °C treatment group (3 August to 17 August 1996). Since larvae were not fed, yolk-sac reserves were essentially exhausted by 14 and 6 dph for the 5 and 10 °C treatment groups, respectively. To control for the effect of testing temperature on behaviour, larvae from each temperature treatment were tested at both 5 and 10 °C. Testing temperature had an effect on some swimming parameters but not on escape response. Swimming performance, escape response, and morphology varied with age, while only morphology and escape response varied with development rate. Morphology and swimming performance, and morphology and escape response were found to be correlated as determined by canonical correlation. This study suggests that both types of swimming behaviours should be examined when developing models of the impacts of predation on the early life history of larval fish. Received: 13 September 1999 / Accepted: 21 June 2000     

Cell cycle and toxin production in the benthic dinoflagellate Prorocentrum lima

Profiles of diarrhetic shellfish poisoning (DSP) toxins produced throughout the growth cycle and the cell cycle of the toxigenic marine dinoflagellate Prorocentrum lima were studied in triplicate unialgal batch cultures. Cells were pre-conditioned at 18 ± 1 °C, under a photon flux density (PFD) of 90 ± 5 μmol m⁻² s⁻¹ on a 14 h light:10 h dark photoperiod. In exponential growth phase, cultures were synchronized in darkness for 17 d. After dark synchronization, cultures were transferred back to the original photoperiod regime. Cells were harvested for DSP toxin analysis by LC-MS (liquid chromatography with mass spectrometry), and double-stranded (nuclear) DNA was quantified by flow cytometry. The cell populations became asynchronous within approximately 3 d after transition from darkness to the 14 h light:10 h dark photoperiod. This may be due to the prolonged division cycle (5 to 7 d) that is not tightly phased by the photoperiod. Unlike other planktonic Prorocentrum spp., cytokinesis in P. lima occurred early in the dark and ceased by “midnight”. Cellular levels of the four principal DSP toxins, okadaic acid (OA), OA C8-diol-ester (OA-D8), dinophysistoxin-1 (DTX1) and dinophysistoxin-4 (DTX4), ranged from 0.37 to 6.6, 0.02 to 1.5, 0.04 to 2.6, and 1.8 to 7.8 fmol cell⁻¹, respectively. No toxin production was evident during the extended period of dark synchronization nor during the initial period when NH₄ was consumed as the major nitrogen source. Soon after the cells were returned to the 14 h light:10 h dark cycle and they began to take up NO₃, cellular levels of all four toxins gradually increased. This increase in DSP toxins usually occurred in the light, marked by a rise in DTX4 levels that preceded an increase in the cellular concentration of OA and DTX1 (delayed by 3 to 6 h). Thus, DTX4 synthesis is initiated in the G1 phase of the cell cycle and persists into S phase (“morning” of the photoperiod), whereas OA and DTX1 production occurs later during S and G2 phases (“afternoon”). No toxin production was measured during cytokinesis, which happened early in the dark. The evidence indicates that toxin synthesis is restricted to the light period and is coupled to cell cycle events. Received: 3 September 1998 / Accepted: 30 March 1999