Gill development, functional and evolutionary implications in the Pacific oyster Crassostrea gigas (Bivalvia: Ostreidae)

Development of the Crassostrea gigas gill was studied in order to better understand the feeding biology of early life stages, identify potentially critical developmental stages which may influence rearing success or recruitment to wild populations, and shed light on the evolution of the basic bivalve gill types. Larvae and juveniles were reared in an experimental hatchery, and larger specimens were obtained from a commercial hatchery. Specimens were relaxed, fixed, dried, and observed using scanning electron microscopy (SEM). The right and left gills developed symmetrically, via a “cavitation–extension” process from the gill buds. The inner demibranchs developed first (V-stage, 0.29–2.70 mm), in a sequential postero-anterior series of homorhabdic filaments. The outer demibranchs developed later (W-stage, from 2.70 mm), also as homorhabdic filaments, synchronously along the gill axis. The principal filaments (PF) developed from the progressive fusion of three ordinary filaments (OF), at a size of 7.50 mm, and the consequent plication was accentuated by the formation of extensive tissue junctions. Effective filament number (number of descending and ascending filaments) showed a marked discontinuity at the transition from the V- to the W- stage of the gill. Filament ciliation showed several important changes: establishment of OF ciliation in the homorhabdic condition (2.70 mm), ciliary de-differentiation of the PF in the heterorhabdic condition (7.50 mm), and establishment of a latero-frontal cirri length gradient from the plical crest to the PF base. Reversal of direction of ciliary beat is also necessary prior to adult functioning of the PF. Three major transitions were identified in C. gigas gill development, each potentially important in rearing success or wild population recruitment: (1) transition from velum to gill at settlement, (2) transition from a V- to a W-shaped gill (2.70 mm), and (3) transition from the homorhabdic to the heterorhabdic condition (7.50 mm). Complete gill development was much more prolonged than in species previously studied. The major ontogenetic differences between the C. gigas heterorhabdic pseudolamellibranch gill and the pectinid heterorhabdic filibranch gill suggest that the heterorhabdic condition evolved independently in these two bivalve families.     

Development of the skull in Dentex dentex (Osteichthyes: Sparidae)

The development of the skull skeleton in common dentex, Dentex dentex (Linnaeus, 1758), was studied under extensive rearing conditions. Skull ontogeny started after hatching and went through three stages: (a) the yolk-sac (during the phase of no growth) and the early larval stage (up to 6.9 mm in vivo total length, TL) in which the majority of the skull elements formed; (b) the late larval stage (up to 11.3 mm TL) in which the basisphenoid, infraorbital 1, parethmoids, nasals, ethmoids, pleurosphenoids, opisthotics and orbitosphenoids developed; and (c) the metamorphosis stage (up to 24.0 mm TL) during which the remaining infraorbitals formed, the cartilaginous areas of the neu- roskull regressed and the sclerotics started to ossify. Teeth first appeared at 5.2 mm TL, and gill filaments formed between 5.7 and 6.9 mm TL. The results are discussed in view of the ontogeny of functions and in comparison with the skull ontogeny of other teleosts. Received: 1 July 1998 / Accepted: 1 September 1999     

Role of protein in larval swimming and metamorphosis of Bugula neritina (Bryozoa: Cheilostomatida)

Larvae of the marine cheilostomatid bryozoan Bugula neritina (L.) were prevented from settling for 1, 4 and 8 h by mechanical agitation, following which settlement and metamorphosis success were examined. Settlement rates were significantly affected by swimming time, which decreased from 100% after 2 h to 93.7 ± 4.3% after 8 h. Similarly, metamorphosis to the feeding ancestrula was significantly impaired following a swimming time of 8 h, declining from 93.7 ± 4.3% after 1 h to 65.9 ± 7.0% after 8 h. The resultant colonies grew well for the first 3 wk, following which time, growth patterns became erratic. Growth rate was in all cases highly variable, and did not correlate with enforced swimming times. Larval protein composition was examined after 1, 4 and 8 h swimming time, and post-larval composition 1, 2, 5, 24 and 48 h after settlement using sodium-dodecyl-sulphate polyacrylamide-gel electrophoresis (SDS-PAGE). Individual protein content was measured using a densitometer. Larvae did not consume protein during swimming, however a protein measuring 170 kdaltons was consumed during metamorphosis. These results are discussed in the context of larval settlement and energetics. Received: 19 July 1998 / Accepted: 3 December 1998     

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     

Mortality of newly metamorphosed eastern oysters (Crassostrea virginica) in mesohaline Chesapeake Bay

 Stocks of eastern oysters, Crassostrea virginica (Gmelin), in mesohaline Chesapeake Bay, USA, exhibit a high degree of inter-annual and spatial variability in recruitment. We found that cumulative oyster spatfall on off-bottom collector plates, measured throughout the summer in 14 years over a span of three decades, was highly positively correlated (r ² = 0.8) with juvenile oyster recruitment on adjacent oyster bars. Total abundances of juvenile oysters on these bars were, however, generally 99.7% lower than predicted from cumulative seasonal larval settlement on collector plates. We propose that although the number of larvae metamorphosing was the key factor in determining the gross annual pattern of recruitment to these mesohaline oyster bars, the actual magnitude of recruitment was governed by post-settlement processes, such as competition for limited resources and predation. We tested the hypothesis that predation may be partly responsible for high post-settlement juvenile oyster mortality. We performed a series of 3-d field investigations over two summers (1989, 1990) at a mesohaline site, employing cages of various mesh sizes (400, 800, 1500 μm) to protect hatchery-reared spat of 0.5 to 4.0 mm shell height. Mortality rates for spat held for 3 d in the estuary (17.8%) were significantly higher (P = 0.0001) for the smallest spat (0.5 to 2.0 mm) compared with those of 2.01 to 4.0 mm (4.2%). In 1990, but not in 1989, enclosure within 400 and 800 μm mesh cages significantly (P = 0.004) increased survival during 3-d deployments (9.4 and 10.1%, respectively) compared with spat unprotected by mesh cages (21.9%). In a series of laboratory predation studies that used the entire community of invertebrates that could penetrate the cages, microscopic juvenile polyclad flatworms, Stylochus ellipticus, were the only organisms that we observed crawling into living oysters and feeding on oyster tissue. Large flatworms (50 to 200 mm²) are known to be important predators on oysters, but this ability of flatworms that were so small (<ca. 5 mm²) and translucent as to be almost invisible without magnification to feed on immediate post-metamorphic oysters has not been documented previously. Our results suggest that the rate of mortality due to predation in mesohaline Chesapeake Bay is much reduced once spat survive for 2 to 3 weeks post-metamorphosis. Thus, it is likely that predation in the 1 to 2 week period immediately after settlement may be a crucial factor in the structuring of eastern oyster populations. Received: 21 December 1998 / Accepted: 2 December 1999     

Ontogenic change of gill chloride cells in leptocephalus and glass eel stages of the Japanese eel, <Emphasis Type="Italic">Anguilla japonica</Emphasis>

The development of gill chloride cells was examined in premetamorphic larvae (leptocephali) and juveniles (glass eels) of the Japanese eel, Anguilla japonica. Branchial chloride cells were detected by immunocytochemistry using an antiserum specific for Na⁺,K⁺-ATPase. The specificity and availability of the antiserum for the detection of Japanese eel chloride cells were confirmed by Western blot analysis. The chloride cells first appeared on the developing gill filaments in a mid larval stage of leptocephalus (32.2 mm). Both immunoreactivity and the number of chloride cells gradually increased as the fish grew to a late stage of leptocephalus over 54 mm. In glass eels just after metamorphosis, gill lamellae developed from the gill filaments, and a rich population of chloride cells was observed in the gill filaments. In glass eels collected at a coastal area, chloride cells were extensively distributed in the gill filaments. The chloride cell size decreased progressively in glass eels transferred from seawater (SW) to freshwater (FW), whereas there was no difference in cell number. In contrast, some Na⁺,K⁺-ATPase immunoreaction distinct from typical chloride cells was observed in the gill lamellae throughout FW-transferred fish, but disappeared in control fish maintained in SW for 14 days. These findings indicate that the gill and gill chloride cells developed slowly during the extremely long larval stage, followed by rapid differentiation during a short period of metamorphosis. The excellent euryhalinity of glass eels may be due to the presence of the filament chloride cells and lamellar Na⁺,K⁺-ATPase-immunoreaction, presumably being responsible for SW and FW adaptation, respectively.     

Ontogenetic changes in gill morphology and potential significance for food acquisition in the scallop <Emphasis Type="Italic">Placopecten</Emphasis><Emphasis Type="Italic">magellanicus</Emphasis>

Sources of mortality in both wild and cultured populations of marine bivalves during postlarval stages remain largely unknown, but may be partly associated with the inability to meet energetic demands during intense morphogenesis. The development of the gills in postsettlement scallops (Placopecten magellanicus) from 0.35 to 14 mm in shell height (SH) was investigated using scanning electron microscopy to determine the degree of size-specific differentiation of the gills and evaluate potential ontogenetic constraints in food acquisition. Key transitional stages in morphogenesis, likely to exert pronounced effects on feeding function, were identified and correlated with scallop size. The gill was initially homorhabdic, with unreflected inner demibranchs forming a basket-like structure maintained by ciliary junctions. Gill reflection, immediately followed by accelerated proliferation of gill filaments and formation of outer demibranchs, occurred at ~1 mm SH. Outer demibranchs were fully formed at ~2 mm SH. Suspension-feeding is probably rather inefficient prior to attaining 1-2 mm sizes. The onset of the heterorhabdic, adult form of the gill, which allows bidirectional particle transport and the potential for selection and for volume regulation of ingested material on the gill, occurred fairly late in development, at ~3.3-5.0 mm SH. Full development of gill plication was delayed until scallops attained ~7 mm. Gill differentiation in this species is thus relatively protracted and punctuated by critical transitional stages, which may be important in determining feeding and growth capacity of postlarval wild and cultured populations.     

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     

Growth and differentiation during delayed metamorphosis of feeding gastropod larvae: signatures of ancestry and innovation

Extent of larval growth among marine invertebrates has potentially profound implications for performance by benthic recruits because body size influences many biological processes. Among gastropods, feeding larvae often attain larger size at metamorphic competence than non-feeding larvae of basal gastropod clades. Delay of metamorphosis can further influence size at recruitment if larvae continue to grow during the delay. Some caenogastopod larvae grow during delayed metamorphosis, but opisthobranch larvae do not. Data on larval growth of neritimorph gastropods are needed to help determine which of these growth patterns for planktotrophic gastropod larvae is more derived. We cultured planktotrophic larvae from all three major gastropod clades with feeding larvae through delays of metamorphosis of 3–10 weeks. Larvae of the caenogastropod Euspira lewisii and the euthyneurans Haminoea vesicula (Opisthobranchia) and Siphonaria denticulata (Pulmonata) conformed to previously described growth patterns for their respective major clades. Furthermore, the caenogastropod continued to lengthen the prototroch (ciliary band for swimming and feeding) and to differentiate prospective post-metamorphic structures (gill filaments and radular teeth) during delayed metamorphosis. Larvae of the neritimorph Nerita atramentosa arrested shell growth during delayed metamorphosis but the radula continued to elongate, a pattern most similar to that of non-feeding larvae of Haliotis, a vetigastropod genus. Character mapping on a phylogenetic hypothesis suggests that large larval size and capacity for continued growth during delayed metamorphosis, as exhibited by some caenogastropods, is a derived innovation among feeding gastropod larvae. This novelty may have facilitated post-metamorphic evolution of predatory feeding using a long proboscis.     

Osteological development of Dentex dentex (Osteichthyes: Sparidae): dorsal, anal, paired fins and squamation

The osteological development of dorsal, anal and paired fins and the squamation in common dentex, Dentexdentex (Linnaeus, 1758), was studied under extensive larval rearing conditions. The ontogeny of the fins was determined in three stages: (1) the yolk-sac and the early larval stage (up to 6.7 mm in vivo total length, TL), in which the majority of the elements of the pectoral fins and the predorsals, dorsal and anal proximal pterygiophores formed; (2) the late larval stage (up to 11.6 mm TL), in which the majority of the pectoral lepidotrichia, the lower extrascapulae, all the elements of the pelvic fins, as well as the lepidotrichia, spines and the distal radials of the rest fins developed; and (3) the metamorphosis stage (up to 24.0 mm TL), when the upper extrascapulae formed and the pectoral lepidotrichia attained their full count. The ontogeny of squamation was carried out during the metamorphosis stage; it started at 13.4 mm TL with laterally symmetric points on the middle of each side of the body, followed by one ventral centre (15.6 mm TL) which was located anterior to the pelvic fins, and two bilateral pairs of centres which appeared on the head (17.8 and 21.2 mm TL). The results are discussed from a functional viewpoint and in comparison with the fin and scale ontogeny of other teleosts. Received: 1 March 2000 / Accepted: 20 September 2000     

The relationship between allele frequency and tidal height in a mussel hybrid zone: a test of the differential settlement hypothesis

The blue mussels Mytilus edulis L. and M. galloprovincialis Lmk. hybridize in western Europe. Within hybrid populations nuclear alleles specific to M. galloprovincialis increase in frequency with age and size. This relationship changes with tidal height; alleles from M. galloprovincialis occur more frequently high in the intertidal zone, while M. edulis alleles predominate in the low intertidal zone. We tested the hypotheses that larvae with M. galloprovincialis alleles tend to settle higher in the intertidal zone, or that mussels redistribute themselves with respect to tidal height after initial larval settlement. We sampled recently metamorphosed mussels every 2 weeks in a hybrid mussel population at Whitsand Bay in southwest England throughout the summer of 1996. We observed four cohorts of newly settled mussels. There was no evidence of differential settlement of mussels with different genotypes in connection with tidal height, or into shaded versus unshaded microsites. Therefore, we rejected the preferential settlement hypothesis. There was substantial movement of juvenile mussels in the first 4 weeks following initial settlement, but this “secondary settlement” did not result in genetic differentiation with respect to tidal height. Further, significant differences in allele frequencies were found between primary and secondary spat. This allele frequency change was in the opposite direction of that seen in the adult population, suggesting newly settled larvae may be experiencing different selective pressures than adults. We propose that the genetic structure of hybrid mussel populations with respect to tidal height is the consequence of differences in selection intensity. Received: 30 April 1999 / Accepted: 5 May 2000     

Ontogeny and allometric plasticity of Dentex dentex (Osteichthyes: Sparidae) in rearing conditions

The ontogeny of Dentex dentex (Linnaeus, 1758) was studied comparatively under extensive and semi-extensive rearing conditions. The exotrophic phase was divided into three distinct developmental stages (a) larval, from feeding onset up to 10 mm total length (TL); (b) metamorphosis, from 10 mm TL up to 24 mm TL; and (c) further juveniles. The majority of all ontogenic changes was expressed during the larval stage and integrated during the metamorphosis stage. The juvenile stage was characterized by developmental stability. The normal development of D. dentex was seriously affected by the rearing conditions applied during the early exotrophic phase. The two differently reared populations followed similar developmental patterns of general morphology, pigmentation and behaviour, but they presented high developmental plasticity where allometric growth was concerned. Rearing conditions influenced both the boundaries of the sequential stages (in 50% of the morphometric ratios) and the allometry coefficient of each morphometric character in the various developmental stages (in 80% of the characters). The results are discussed with respect to the ontogeny of the functional morphology under both ecological and aquaculture considerations. Received: 1 August 1998 / Accepted: 1 September 1999     

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     

Experimental investigation into the effects of suspended sediment on fertilisation, larval survival and settlement in a scleractinian coral

Laboratory and field experiments were used to determine whether high (≃100 mg l⁻¹), low (≃50 mg l⁻¹) and control (≃0 mg l⁻¹) levels of suspended sediment affected fertilisation, larval survival, and larval settlement in the scleractinian coral Acropora digitifera (Dana, 1846). Both high- and low-sediment treatments significantly decreased fertilisation, but post-fertilisation embryonic development was not inhibited by suspended sediments. Larval survival and larval settlement were significantly reduced in high- and low-sediment treatments. No difference was found between high- and low-sediment treatments in any of the three post-spawning processes investigated, suggesting that they are susceptible to sediment concentrations which are not exceptionally high even under natural conditions (>50 mg l⁻¹). The introduction of an additional stress in the form of high levels of suspended sediments coupled with naturally high variability in recruitment may have a considerable effect on the successful supply and settlement of coral larvae to a reef. Given that many coral communities are open reproductive systems, the consequences of disturbance events are not likely to be restricted to the impact area. Recruitment to a population may be reduced significantly in the presence of high levels of suspended sediments because of effects on larval survival and settlement. Recruitment of larvae to adjacent populations may also be affected due to a decreased fertilisation success and potential increases in mortality of larvae passing through the affected site. Received: 13 August 1998 / Accepted: 22 July 1999     

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     

Role of bacteria in larval settlement and metamorphosis of the polychaete Hydroides elegans

The serpulid polychaete Hydroides elegans Haswell, 1883 is an early colonist of new substrata in Pearl Harbor, Oahu, Hawaii. When metamorphically competent, larvae of H. elegans will settle rapidly upon an acceptably biofilmed surface, but not on a clean surface. In this study we found the ability of larvae to respond selectively to inductive surfaces to be retained for at least 3 wk. Of a series of bacterial strains isolated from Hawaiian marine biofilms, 13 induced larval settlement, 11 gave moderate or mixed results, and 10 others did not stimulate the settlement of H. elegans. The amount of settlement induced by monospecific strains was rarely as great as with natural, multispecies films. Most of the isolated bacteria were motile Gram-negative rods, but Gram-positive strains were also present, and diverse metabolic types were represented in the study. Biofilms killed by treatment with heat, ultraviolet radiation or chemical fixatives were no longer inductive. Soluble, dialyzable, heat-stable bacterial products induced settlement and metamorphosis more slowly. The range of bacteria producing an inductive signal suggests either that there are multiple cues, or that the cue is common to many bacteria. Chemical signals characteristic of early microbial biofilms may indicate freshly available substrata with optimal potential for the growth and survival of H. elegans. Received: 30 January 1998 / Accepted: 12 September 1998     

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     

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     

Reproduction and recruitment of scleractinian corals in a high-latitude coral community, Amakusa, southwestern Japan

Reproduction and recruitment in high-latitude coral populations in Japan have been little studied. A comprehensive study of the reproduction and early life history was conducted on nine common scleractinian coral species in Amakusa, southwestern Japan (32°N) from 2001 to 2003 including; (1) fecundity (the proportion of colonies with mature eggs), (2) timing and synchrony of spawning, (3) initial larval settlement pattern, (4) recruitment, (5) post-settlement mortality. The fecundity was high (76.7–100%) in six of seven species examined in 2002 and 2003. Annual spawning of the seven species occurred from mid July to August in 2001–2003, when seawater temperature was at the annual maximum. Spawning was highly synchronised among conspecific colonies and species in 2002 and 2003, with five species spawning five to nine nights after the full moon and another two spawning around the new moon. Temporal patterns of larval settlement of three spawning species during the first 10 days after spawning were similar to those of other spawning species from low latitudes. The number of scleractinian recruits on settlement plates, deployed from July to October (the major recruitment period at the study site), was low (2 recruits/m²) for the three consecutive years. Post-settlement mortality of 1–1.5 month old spat of five species ranged between 88 and 100% over 3–10 months in the field, similar to the values reported for both high and low latitude species (>94–99%). Among the key stages examined, the low recruitment rate may be the most important step in limiting successful reproduction and recruitment of these high-latitude scleractinian populations. The low recruitment rate may be attributable to (1) the reduced influx of larval supply from other coral populations, which are smaller and more isolated at high-latitudes and (2) the longer precompetent larval phase of broadcast-spawning corals which results in an increased chance of larvae being dispersed away from parent populations.     

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