Lipid reserves used by pueruli of the spiny lobster Jasus edwardsii in crossing the continental shelf of New Zealand.

Lipid is known to fuel the movement of the nektonic puerulus stage of the spiny lobster Jasus edwardsii across the continental shelf of New Zealand. Lipid class analysis of pueruli caught from two locations across the continental shelf showed that phospholipid predominated (86-96% of total lipid), with only smaller proportions of sterol (0.9-8.7%) and diacylglycerol (1.2-7.6%). Only traces of triacylglycerol, hydrocarbon and wax ester were present (<0.1% of total lipid). Comparison of the lipid class content of pueruli caught onshore and offshore showed that phospholipid reserves are primarily utilised during this important phase in the lifecycle and that diacylglycerol plays a less significant secondary role. Histology identified concentrations of phospholipid in fat bodies located in the haemocoel. The use of phospholipid as the dominant storage medium in the puerulus stage is unlike many other marine taxa, including crustacea, which tend to use triacylglycerol and wax ester. The use of phospholipid as a storage medium may well be related to its characteristic transparency, an important feature of this nektonic stage of lobster development that is highly vulnerable to pelagic visual predators.     

Marked depletion of polar lipid and non-essential fatty acids following settlement by post-larvae of the spiny lobster Jasus verreauxi

The development from the non-feeding post-larva (puerulus) to the first instar juvenile of spiny lobsters is highly energetically demanding. These demands may greatly compromise the energy reserves of the lobsters following settlement, leading to reduced growth and survival in the wild, and also in aquaculture. Therefore, the lipid class and fatty acid composition of wild caught pueruli and first instar juveniles of the spiny lobster Jasus verreauxi (H. Milne Edwards, 1851) were analysed by thin layer chromatography-flame ionisation detection and capillary gas chromatography. Pueruli contained substantially more lipid than first instar juveniles (mean difference =3.5 mg, or 41.9%) and most of this difference was due to the presence of greater amounts of polar lipid (mean difference =3.9 mg or 49.2%) in pueruli. First instar juveniles contained significantly more triacylglycerol (mean =0.2 mg), consistent with the polar lipid being converted to a more readily metabolised lipid class in the hepatopancreas. These results indicate that polar lipid is the major energy store during the non-feeding puerulus stage of spiny lobsters from the genus Jasus. Overall, the essential, polyunsaturated linoleic, docosahexaenoic and eicosapentaenoic acids did not show a significant decrease between the two developmental stages, despite the absence of feeding. However, significant reductions in the abundance of both saturated and monounsaturated fatty acids between the two stages were identified (decrease of 811 and 783 microg per individual, respectively). This suggested that selective depletion of non-essential fatty acids may be occurring, with resultant sparing of the essential fatty acids. Supplying diets rich in these depleted fatty acids, and in particular the essential fatty acids, preferably in polar lipid, is likely to result in increased survival and growth of J. verreauxi and other spiny lobsters from first instar juveniles in aquaculture.     

Spiny lobster development: where does successful metamorphosis to the puerulus occur?: a review

This review re-addresses the question: Where does metamorphosis to the puerulus mainly take place among the shallow-water palinurids? A decade ago we reviewed this ecological question in a paper that focused on phyllosomal development of the western rock lobster, Panulirus cygnus. The main region of occurrence of its metamorphosis was found to be in the slope region beyond the shelf break. Because the puerulus of P. cygnus is a non-feeding stage, it was hypothesised that metamorphosis will not occur until the final phyllosoma has reached some critical, and specific, level of stored energy reserves. For late larval development and successful metamorphosis of P. cygnus, the richest food resources seem to be located in the slope waters adjoining the shelf break off Western Australia. This, like most shelf break areas, is a region of higher zooplankton and micronekton biomass than is usually found further offshore, and is dominated (in winter-spring months) by the warm south-flowing Leeuwin Current. In this new review, distribution and abundance data of final phyllosomas and pueruli are examined from, Panulirus argus, Panulirus cygnus, Panulirus japonicus, Panulirus ornatus and Jasus edwardsii, and where possible, related to features of the satellite imagery of the areas in which they occur. We hypothesise that metamorphosis will occur where the final stages have partaken of sufficient, appropriate nutrition to provide them with a reserve of bioenergetic resources, and this can occur where oceanographic fronts effect greater planktonic productivity and concentrations of food organisms. This may be near the shelf-break, or out to large distances offshore, because of large-scale oceanographic events such as the prevailing current system, its off-shoots, mesoscale eddy fronts, counter-currents, etc. However, we contend that, in terms of population recruitment, metamorphosis in most shallow-water palinurid species occurs mainly in the slope waters adjoining the shelf break of the region to which the species is endemic. Although some final phyllosomas may metamorphose much further offshore, it is unlikely that these pueruli will reach the shore, let alone settle and successfully moult to the juvenile stage. All of the data indicate that successful metamorphosis from the final-stage phyllosoma to the puerulus stage in all species occurs offshore but close to the continental shelf.     

Ontogenetic changes in enzyme activities associated with energy production in the spiny lobster, Jasus edwardsii

The larval life of the spiny lobster Jasus edwardsii is one of the longest and most complex of any marine organism and is poorly understood due to the difficulty of studying cryptic, pelagic organisms. Hence, the capacity for active swimming in the phyllosoma, puerulus and juvenile stages and the use of possible metabolic fuel reserves was inferred from a number of enzyme activities, including citrate synthase, lactate dehydrogenase, and HOAD. High activities of CS and LDH in abdominal tissues of Stage 11 phyllosoma and pueruli are consistent with a capacity to commence active on-shore movement. The activities of LDH and HOAD showed positive allometry while CS was independent of body mass. The body mass dependence of LDH activity may reflect the developing ability of the lobster to initiate brief escape manoeuvres, and the scaling of HOAD reflects an increased use of lipid fuel reserves. Aerobic enzyme activities were higher in abdominal tissues than in cephalic tissues of pelagic pueruli, but high activities appear in the cephalic tissues of juveniles. These changes mirror a developmental shift in activity from pelagic oceanic swimming to a benthic existence on the seabed of the near shore. The low LDH activity in pueruli confirmed previous findings that they have limited feeding capacity, with carbohydrate contributing little towards the major energy reserves. The highest LDH activities occur in the abdominal muscles of juveniles and correlate with rapid tail-flicking escape behaviour. The activities of HOAD increased throughout development, and in the abdominal tissues of juveniles, may reflect lipid transformation and accumulation as an energy reserve. Enzyme activities, therefore, provide useful information concerning migratory behaviour that is presently unavailable from ecological studies.     

Lipid,fatty acid and protein content of late larval to early juvenile stages of the western rock lobster,Panulirus cygnus

Lipid, fatty acid and protein content were determined individually on 7 phyllosomata, 69 clear pueruli, 286 pre-moult pueruli, and 86 juvenile western rock lobster (WRL) collected from four locations between the settlement seasons 2000 to 2006 to evaluate compositional changes during the non-feeding puerulus stage. Only the lipid content, particularly the phospholipids, decreased significantly with development. Protein declined sharply following moult to the juvenile. PL comprised between 86–94% of total lipid in all animals, and declined most between phyllosomata and clear pueruli (238.5 to 121.4 mg g^? 1 DW) (p < 0.001). Triacylglycerols were the only lipid to increase in absolute amounts with development, but declined 53% on average following moult to juvenile. This increase in TAG is likely due to the conversion of phospholipids to triacylglycerols. Monounsaturated fatty acids were the main energy form utilised during benthic development while polyunsaturated fatty acids showed a high degree of sparing. The n-3:n-6 fatty acid ratio of juveniles indicates that they may be approaching critically low levels of stored lipid energy reserves. Both protein, and lipid, declined sharply from the final puerulus phase to the juvenile confirming that a high energetic demand is required to fuel the moulting process.     

The Western Rock lobster Panulirus cygnus (George, 1962) (Decapoda: Palinuridae): the effect of temperature and developmental stage on energy requirements of pueruli

Pueruli of the Western Rock Lobster Panulirus cygnus (George, 1962) are thought to be nonfeeding. Consequently, the metabolic rate is expected to be low during this stage in order to conserve energy reserves. Furthermore, since water temperature potentially has a substantial impact on energetic needs, the puerulus possibly exhibits mechanisms to reduce the effect of temperature on energy consumption. To test these propositions the metabolic rate was measured in post-settlement pueruli and in juveniles at two water temperatures. A respirometer of variable volume (10–50 ml) was designed for this purpose, incorporating a dark-type oxygen sensor. Results were compared with data available from the literature.

Oxygen consumption in pre-molt pueruli and in intermolt juveniles (1.48 to 5.65 μmol O₂· individual⁻¹·h⁻¹ on average) was substantially higher than in post-settlement pueruli (1.06–1.41μmol O₂·ind.⁻¹h⁻¹). These significant changes could only partly be explained through changes in biomass. Furthermore, no significant effect of an increased water temperature (from 18 to 23 ° C) could be detected on the metabolic rate in post-settlement pueruli, and the effect is moderate in pre-molt pueruli (Q₁₀ = 1.95). The water temperature has, however, a substantially greater impact on first and second molt juveniles (Q₁₀ = 2.46 to 4.80).

The energetic demand was calculated from oxygen consumption and indicate that energetic needs of post-settlement pueruli is low compared with both pre-molt pueruli and juveniles. A low energetic demand and a reduced effect of temperature on energy consumption is of considerable benefit to a non-feeding larva, and may provide the puerulus with a means of extending the duration of the non-feeding stage and increasing the chance for survival beyond metamorphosis to the first feeding stage. Results indicate that the energetic demand during metamorphosis may be considerable. It is postulated that energetic requirements of the planktonic (actively swimming) puerulus larvae are considerably higher and are likely to be more temperature dependent.     

Recent settlement trends in Panulirus argius (Decapoda: Palinuridae) pueruli around St. Thomas, U.S. Virgin Islands

Puerulus settlement of the western Atlantic spiny lobster, Panulirus argus, was monitored using modified Witham collectors from December 1996 to March 1998 at seven sites around St. Thomas, U.S. Virgin Islands. A total of 605 pueruli were collected from 553 samples for a catch per unit effort (CPUE) for all sites of 1.09 pueruli. The greatest settlement occurred on sites within a recently declared marine reserve, which had an overall CPUE of 1.77 pueruli. Settlement in non-reserve sites was much lower with an overall CPUE of 0.31 pueruli. Pueruli recruitment declined 67% at inshore sites and 53% at offshore sites between July 1992 - April 1994 and February 1997 - March 1998. Also, only 10% of months sampled in 1997-98 had a CPUE > 0.5 compared to 55% in a previous study in 1992 - 1993. Despite the decline in pueruli CPUE in 1997-98 compared to 1992-94, the commercial lobster catch in the 2000-01 fishing season, and by inference the adult lobster population (legal lobster size in the US Virgin Islands is > or = 3.5 cm carapace length), remained stable.     

Changes in lipid and fatty acid composition of late larval and puerulus stages of the spiny lobster (Panulirus cygnus) across the continental shelf of Western Australia

The feeding of the late larval stages of the spiny lobster, Panulirus cygnus, and the energy reserves used by the non-feeding post-larvae for crossing the continental shelf of Western Australia were examined through their lipid composition. Lipid was a significant component of the biomass of all larval and post-larval samples (range 63-213 mg g(-1) of dry biomass). The fatty acid profiles of late stage larvae (8-9) suggest that they were feeding on salps and small crustaceans, such as euphausids, from oligotrophic pelagic communities where herbivorous and microbial grazing is an important basis to the food web. There was a marked decrease in lipid content of post-larvae progressively across the continental shelf, and this corresponded closely with decreasing dry mass, suggesting that post-larvae were using lipid as an energy source during cross-shelf movement at a rate of 1.6 J km(-1). This is considerably lower than for other spiny lobster species, suggesting that the post-larvae of the western rock lobster may use physical processes as well as active swimming for onshore transport. This may help to explain the large inter-annual variability in the post-larval settlement of this species, which is closely related to differences in weather patterns capable of greatly varying onshore advection processes.     

Temporal genetic patterns of diversity and structure evidence chaotic genetic patchiness in a spiny lobster

Population structure of many marine organisms is spatially patchy and varies within and between years, a phenomenon defined as chaotic genetic patchiness. This results from the combination of planktonic larval dispersal and environmental stochasticity. Additionally, in species with bi‐partite life, postsettlement selection can magnify these genetic differences. The high fecundity (up to 500,000 eggs annually) and protracted larval duration (12–24 months) and dispersal of the southern rock lobster, Jasus edwardsii, make it a good test species for chaotic genetic patchiness and selection during early benthic life. Here, we used double digest restriction site‐associated DNA sequencing (ddRADseq) to investigate chaotic genetic patchiness and postsettlement selection in this species. We assessed differences in genetic structure and diversity of recently settled pueruli across four settlement years and between two sites in southeast Australia separated by approximately 1,000 km. Postsettlement selection was investigated by identifying loci under putative positive selection between recently settled pueruli and postpueruli and quantifying differences in the magnitude and strength of the selection at each year and site. Genetic differences within and among sites through time in neutral SNP markers indicated chaotic genetic patchiness. Recently settled puerulus at the southernmost site exhibited lower genetic diversity during years of low puerulus catches, further supporting this hypothesis. Finally, analyses of outlier SNPs detected fluctuations in the magnitude and strength of the markers putatively under positive selection over space and time. One locus under putative positive selection was consistent at both locations during the same years, suggesting the existence of weak postsettlement selection.     

Microbial communities across nearshore to offshore coastal transects are primarily shaped by distance and temperature

Recent studies have focused on linking marine microbial communities with environmental factors, yet, relatively little is known about the drivers of microbial community patterns across the complex gradients from the nearshore to open ocean. Here, we examine microbial dynamics in 15 five-station transects beginning at the estuarine Piver's Island Coastal Observatory (PICO) time-series site and continuing 87 km across the continental shelf to the oligotrophic waters of the Sargasso Sea. 16S rRNA gene libraries reveal strong clustering by sampling site with distinct nearshore, continental shelf and offshore oceanic communities. Water temperature and distance from shore (which serves as a proxy for gradients in factors such as productivity, terrestrial input and nutrients) both most influence community composition. However, at the phylotype level, modelling shows the distribution of some taxa is linked to temperature, others to distance from shore and some by both factors, highlighting that taxa with distinct environmental preferences underlie apparent clustering by station. Thus, continental margins contain microbial communities that are distinct from those of either the nearshore or the offshore environments and contain mixtures of phylotypes with nearshore or offshore preferences rather than those unique to the shelf environment.     

In Memoriam: Professor Walter James Harman, PhD (1928–2002)

The Mediterranean spiny lobsters, the common spiny lobster Palinurus elephas (Fabricius, 1758) and the pink spiny lobster P. mauritanicus Gruvel, 1911, are important target species for commercial fisheries. In this study, we focus our attention on the DNA sequence variation of the mitochondrial cytochrome oxydase I gene (COI) in the two species of Palinurus. Spiny lobster DNA samples from four Mediterranean localities were analysed to examine the genetic variability at both the intra- and interspecific level. Furthermore, the phylogenetic relationships within the family Palinuridae (among the two species of Palinurus, most of the species of Panulirus and all the species of Jasus) are examined.     

Population structure of an introduced species (Dreissena polymorpha) along a wave-swept disturbance gradient

The zebra mussel Dreissena polymorpha was introduced to North America during the mid-1980s, and is now a dominant member of many benthic communities in the lower Great Lakes. In this study, I explored the abundance, biomass, size structure and settlement of Dreissena inhabiting rocks along a wave-swept disturbance gradient near Middle Sister Island in western Lake Erie. Ten rocks were collected from quadrats at six sites along each of three transect lines oriented perpendicular to shore. Occurrence, abundance and biomass of Dreissena on smaller, movable rocks were positively associated with rock distance from shore (lake depth) and with rock area; rocks at nearshore sites supported little, if any, Dreissena, whereas those at offshore sites were heavily colonized. Mussel size distributions also differed in relation to shore distance. Large mussels (19 mm) were underrepresented or absent on rocks collected at nearshore sites, but were overrepresented at offshore locations (37 m). Settlement of larval mussels on settling pads was positively correlated with distance offshore and with time of exposure, though settlement was substantial even at a nearshore (10 m) location. Area-adjusted mussel dry mass increased more rapidly with distance offshore on large than on small rocks. Large rocks also required more force to displace and were significantly less likely to be disturbed when transplanted at the study site. Results from this study indicate that occurrence, abundance and size structure of Dreissena in nearshore waters of Lake Erie correspond with the frequency of habitat disturbance, though other factors including food limitation and larval supply may also contribute to these patterns. These patterns complement studies that established the significance of physical disturbance in other aquatic systems.     

An evaluation of lipid‐ and morphometric‐based indices of nutritional condition for early benthic stage spiny lobsters,Panulirus argus

Assessing the nutritional condition of field‐caught animals has obvious ecological utility, but few indices of condition have been developed for spiny lobsters. We evaluated two potential indices of nutritional condition for the Caribbean spiny lobster, Panulirus argus, using early benthic stage lobsters maintained in the laboratory on two food treatments (100% and 25% of maximum daily consumption) for four months. Every two weeks, we sampled lobsters to ascertain their condition using both a weight/carapace length ratio and triacylglycerol/bodyweight ratio. Triacylglycerol (TAG) content in the hepatopancreas, abdominal, and periopod tissue was determined using thin‐layer chromatography‐flame ionization detection. There was a significant difference in both carapace length and weight of lobsters in the two experimental treatments through time, confirming that our feeding treatments created a detectable difference in growth. We also found a corresponding significant difference between treatments for the weight/carapace length ratio, but the TAG/bodyweight ratio did not differ between treatments, and the variance among individuals was high.     

The biology of pygmy whitefish, Prosopium coulterii, in a closed sub-boreal lake: spatial distribution and diel movements

Using gillnets and trap nets, we examined the spatial distribution, diel movements, and environmental tolerances of pygmy whitefish, Prosopium coulterii, in a small boreal lake in north-central British Columbia. Most gillnets were set below the thermocline but we also fished a shore net in the littoral zone. During the ice-free season (May to November) there was a strong diel onshore–offshore movement: during the day pygmy whitefish were offshore and below the thermocline (water temperatures of 4–6°C) but at night they were inshore and above the thermocline (water temperatures of 12–18°C). This onshore–offshore movement occurred close to the bottom and, regardless of where they were caught, most fish were <4 m off the bottom. Oxygen concentrations in most of the hypolimnion dropped to <5.0 mg l⁻¹ in June and by late August to <1.0 mg l⁻¹; indicating pygmy whitefish can tolerate low oxygen conditions. The catch of pygmy whitefish in gillnets set below the thermocline was highly skewed: 53% of the nets were empty, 37% caught 18 or less fish, and 10% caught 70% of the total catch (742 fish). Trap nets produced similarly skewed results: most trap net sets caught no pygmy whitefish but one set caught over 2,000 individuals. Our catch data suggest that in Dina Lake #1 some pygmy whitefish aggregate.     

Morphological changes in external and internal feeding structures during the transition phyllosoma-puerulus-juvenile in the Western Rock Lobster (Panulirus cygnus,Decapoda: Palinuridae)

External and internal feeding structures of the pelagic final phyllosoma, the transitional puerulus, and the benthic juvenile Western Rock Lobster, Panulirus cygnus, were studied by means of scanning electron microscopy. The study revealed that the external feeding structures of phyllosomata are well equipped for capture and mastication of food. The foregut, however, is not clearly divided into pyloric and cardiac regions and a gastric mill is absent, although a comb row and gland filter are present. Juveniles, on the other hand, have a well-developed gastric mill and gastric teeth, and a cardiopyloric valve separates the foregut into cardiac and pyloric regions. External mouthparts of juveniles are suitable for mastication of solid food particles and bear numerous setae. In contrast, external mouthparts of pueruli are largely non-setose. Furthermore, although the foregut is differentiated into pyloric and gastric regions and a gland filter and comb row are present, a functional gastric mill is absent during the puerulus stage. Absence of such structures indicates that the puerulus may be a non-feeding stage. It is postulated that absence of (or reduced) feeding may be a response to an increased risk of predation rather than a result of the considerable morphological changes taking place during the transition from a planktonic to a benthic lifestyle, as has been previously proposed. © 1994 Wiley-Liss, Inc.     

Diversity of developmental patterns in achelate lobsters—today and in the Mesozoic

Modern achelate lobsters, slipper and spiny lobsters, have a specific post-embryonic developmental pattern with the following phases: phyllosoma, nisto (slipper lobsters) or puerulus (spiny lobsters), juvenile and adult. The phyllosoma is a peculiar larva, which transforms through a metamorphic moult into another larval form, the nisto or puerulus which largely resembles the juvenile. Unlike the nisto and puerulus, the phyllosoma is characterised by numerous morphological differences to the adult, e.g. a thin head shield, elongate appendages, exopods on these appendages and a special claw. Our reinvestigation of the 85 million years old fossil “Eryoneicus sahelalmae” demonstrates that it represents an unusual type of achelatan lobster larva, characterised by a mixture of phyllosoma and post-phyllosoma characters. We ascribe it to its own genus: Polzicaris nov. gen. We study its significance by comparisons with other cases of Mesozoic fossil larvae also characterised by a mixture of characters. Accordingly, all these larvae are interpreted as ontogenetic intermediates between phyllosoma and post-phyllosoma morphology. Remarkably, most of the larvae show a unique mixture of retained larval and already developed post-larval features. Considering the different—and incompatible—mixture of characters of each of these larvae and their wide geographical and temporal distribution, we interpret all these larvae as belonging to distinct species. The particular character combinations in the different larvae make it currently difficult to reconstruct an evolutionary scenario with a stepwise character acquisition. Yet, it can be concluded that a larger diversity of larval forms and developmental patterns occurred in Mesozoic than in modern faunas.     

Polymorphic tetranucleotide microsatellite markers in the Caribbean spiny lobster,Panulirus argus

Ten tetranucleotide microsatellite loci are described for the Caribbean spiny lobster Panulirus argus. Loci were polymorphic (4–15 alleles per locus) and exhibited high levels of expected (0.553–0.921) and observed heterozygosity (0.469–0.906) from samples caught off Belize and Puerto Rico coasts. No significant departure from Hardy–Weinberg equilibrium conditions were observed for any locus. All microsatellite loci should be useful for assessing population discrimination for this valuable marine animal currently subjected to excessive fishing efforts.     

Rotifer distributions in the coastal waters of the northeast Pacific Ocean

Absolute abundance of rotifers was assessed from 5 to 80 km across the continental shelf off of the southern Oregon coast (U.S.A.) in the northeast Pacific Ocean. A total of 97 vertically stratified water samples were collected at 49 stations from two depths, 3 and 30 m. Coastal upwelling conditions were indicated, with decreased temperature, increased salinity and higher chlorophyll-a concentrations closer to shore. Two rotifer genera, Synchaeta and Trichocercaoccurred within 16 km of shore with densities increasing closer to shore. Synchaeta reached densities of 64 inds l^–1 while Trichocerca was sparse (<1 inds. l^–1). Rotifers were most abundant at 3 m and the densest aggregations appear to be associated with estuary outlets, suggesting that estuaries may be important in exporting rotifers to nearshore coastal waters.     

Diapause in the life cycle of Calanoides carinatus (Kroyer), (Copepoda, Calanoida)

The distribution and stage composition of Calanoidescarinatus (Kroyer) are described together with changes in protein and lipid content, respiration rate and gonad development in copepodite stages IV and V (CV) and adults in the Northern Benguela current (17°S, 23°S and 25°S).During active upwelling the population consisted of two parts: the surface part over the shelf was represented by all development stages, while the deep part offshore was dominated (90–95%) by diapausal CVs. In the surface CVs the surplus assimilated energy was allocated to structural growth and maturation or to synthesis of reserve lipids. CVs with large oil sacs and high lipid content descended into deeper layers and formed diapausal stock; they were characterized by a dramatic decrease of respiration rate. Increase of gonad size in association with decrease of oil sac volume in diapausal CV suggests that reserve lipids were expended not only for respiration but also for gonad development. The moulting of dispausal CVs into adults took place in deep water.These results are discussed in relation to the life cycle of the C. carinatus population and the factors causing the formation and termination of the diapausal phase.     

Early life‐history of the spiny siganid Siganus spinus (Linnaeus 1758) inferred from otolith microstructure

Juveniles of the spiny siganid Siganus spinus were sampled from three sources in April, May and June 2008 for a study of its early life‐history through otolith microstructure analysis. Specimens were obtained from bagnet catches in off‐reef sites and seine nets in seagrass beds operating in Lagonoy Gulf, Philippines, and from the guts of skipjack tuna Katsuwonus pelamis caught by hand‐line in an offshore area about 72 km east of the mouth of the gulf. The core, hatch ring, first feeding rings, and settlement increment of spiny siganid were identified and their widths measured. Mean daily otolith ages were 20.6, 22.1 and 21.7 of specimens from the gut, off‐reef site and seagrass bed, respectively. Sagittae of the youngest (17‐, 18‐ and 19‐day‐old) specimens from the tuna gut do not have settlement marks. Planktonic larval duration is 17 days. Most settlement (59%) occurred at the 20th increment on the evidence of its highest reduction in width and lessening of opacity. During the settlement process the juveniles swim from the fringing coral reefs to the seaweed beds then finally to the seagrass beds, wherein settlement volume is highest on or about the new moon date. The short, pelagic larval duration and restricted settlement timed on or 1–2 days near the new moon are integral elements in the settlement strategy of the fish.