Effect of an organophosphorus insecticide, fenitrothion, on survival and osmoregulation of various developmental stages of the shrimp Penaeus japonicus (Crustacea: Decapoda)

The toxicity of fenitrothion was determined in larvae (nauplii, Zoeae 1 to 3, Mysis 1 to 3), postlarvae (PL stages) and juvenile shrimp (Penaeus japonicus Bate), in two media, seawater (SW) and diluted seawater (DSW) (1100 and 550 mosM kg⁻¹, ≃ 37 and 19‰ S). The effects of fenitrothion on the osmoregulatory capacities (OC) of juveniles were recorded. A gill and epipodite histopathological study was also conducted. For larvae in seawater, 24 and 48 h LC₅₀s ranged from 32.9 μg l⁻¹ (Zoeae 2) to 10.7 μg l⁻¹ (Mysis 3), and from 3.9 μg l⁻¹ (Zoeae 3) to 2.0 μg l⁻¹ (Mysis 3), respectively; 48 and 96 h  LC₅₀s in postlarvae (PL) at the same salinity ranged from 1.8 μg l⁻¹ (PL1) to 0.6 μg l⁻¹ (PL5), and from 0.3 μg l⁻¹ (PL7) to 0.4 μg l⁻¹ (PL15). In juveniles, 96 h LC₅₀s were 0.8 μg l⁻¹ in seawater and 1.5 μg l⁻¹ in diluted seawater. From hatching to juvenile stages, the overall trend was a rapid decrease (from nauplii to PL5–PL7) followed by a slight increase (from PL7 to PL15 and juveniles) in the shrimp's ability to tolerate the insecticide. In juveniles kept in seawater and in diluted seawater, fenitrothion decreased the osmoregulatory capacity (OC = difference between the hemolymph osmotic pressure and the osmotic pressure of the medium) at both lethal and sublethal concentrations. This effect was time- and dose-dependent. In SW, the decrease in hypo-OC was ˜ 25% at sublethal concentrations and ˜ 35% at the 96 h LC₅₀. In DSW, the decrease in hyper-OC was ˜ 10 to 15% at sublethal concentrations. In SW, shrimp were able to recover their OC in less than 48 h when transferred to water free of pesticide. In DSW, recovery at 48 h was only possible after exposure to the lowest tested sublethal concentration. Haemocytic congestions (thrombosis) of the gills, lamellae necrosis and other alterations of gills and epipodites (breakage of the cuticle, reduction of the hemolymph lacunae) were noted in juveniles exposed to lethal and sublethal concentrations of fenitrothion. Received: 7 October 1996 / Accepted: 13 November 1996     

Poecilogony in an estuarine opisthobranch: planktotrophy, lecithotrophy, and mixed clutches in a population of the ascoglossan Alderia modesta

A San Diego population of the opisthobranch mollusc Alderia modesta (Lovén, 1844) exhibits poecilogony, the presence of two development modes within a single species. In spring, half of the adults spawned masses containing ∼300 eggs with a mean diameter of 68 μm. After 3 d, these egg masses hatched planktotrophic veligers with a maximum shell dimension of 116 μm. The remaining adults spawned masses containing ∼30 eggs with a mean diameter of 105 μm. These egg masses hatched after 5 to 6 d, releasing lecithotrophic larvae with a maximum shell dimension of 186 μm. About 1% of field-collected adults produced mixed clutches containing a continuum of larval sizes, spanning the size extremes of planktotrophy and lecithotrophy and hatching larvae with a mean maximum shell dimension of 152 μm. Adults producing planktotrophic and lecithotrophic larvae were interfertile, and no hybrid breakdown was observed through the F3 generation. When starved, adults which previously produced only lecithotrophic larvae switched to producing planktotrophic larvae or mixed clutches with both planktotrophic and lecithotrophic larvae. Sequence-polymorphisms from a portion of the mitochondrial cytochrome c oxidase I gene support the conclusion that the two reproductive morphs represent a single species. Most of the lecithotrophic larvae and a small percentage of the larvae from mixed clutches were metamorphically competent within 3 d of hatching. A. modesta is the only molluscan species as yet known to have both planktotrophic and pelagic lecithotrophic development within a single natural population. Received: 14 August 1997 / Accepted: 11 April 1998     

Settlement-competency periods of larvae of three species of scleractinian corals

The pattern of settlement over time of three broadcast spawning coral species (Cyphastrea serailia, Acanthastrea lordhowensis, and Goniastrea australensis) from the Solitary Islands (30°00′S; 153°20′E) was studied in 1995 and 1996 in order to determine the maximum length of time these larvae could remain in the water column and still retain the ability to settle and metamorphose. Larvae were maintained in aquaria and the number which had settled on biologically-conditioned tile pairs was monitored every 5 to 10 d. While the majority of larvae settled quickly after becoming competent, some larvae survived and settled for extended periods after spawning. Competency periods ranged from 26 d for C. serailia to 56 d for G. australensis and 78 d for A. lordhowensis. These data greatly extend the known competency periods for larvae of broadcast-spawning corals and indicate the potential for transport of broadcast-spawned coral larvae over large distances. Medium to long-distance larval dispersal of the species studied provides a mechanism for their widespread distribution in subtropical regions, on reefs which are often widely spaced and relatively isolated. Received: 27 May 1997 / Accepted: 27 November 1997     

Asymptotic growth trajectories of larval sardine (Sardinops melanostictus ) in the coastal waters off western Japan

Growth trajectories of individual larvae of Japanese sardine, Sardinops melanostictus, caught in the coastal waters off western Japan were back-calculated from the first feeding stage up to date of capture (approximate size of 20 to 35 mm total length; TL) based on individually determined allometric relationships between otolith daily ring radii and fish total lengths. The larvae in January-, February-, and March-hatched cohorts in the coastal waters grew faster and more uniformly than those in the oceanic waters offshore of the Kuroshio current. Growth trajectories of the three hatch-month cohorts were similar and could be expressed by the Gompertz model. The inflection points of the growth curves were reached at 9 to 11 d after hatching, when larvae were 10.8 to 11.8 mm TL. Maximum growth rates at these points were 0.80 to 0.85 mm d⁻¹. Growth rates gradually declined after the inflection points, and larval TLs converged into the infinite length of 29 to 32 mm, the sizes at which metamorphosis from larvae to juveniles is initiated. This asymptotic growth pattern in the larval stage resulted in the narrow ranges in TLs in spite of the wide range of ages of the larvae caught by boat seiners in the coastal waters. Slow growth and therefore long duration of the metamorphosing stage could be influential in determining the cumulative total mortality in the early life stages of the Japanese sardine. Received: 14 July 1996 / Accepted: 20 August 1996     

Reproduction, larval development and functional relationships of the burrowing, spionid polychaete Dipolydora armata with the calcareous hydrozoan Millepora complanata

Dipolydora armata (Langerhans, 1880) is a small (4 to 5 mm) spionid polychaete found burrowing in the calcareous hydrozoan Millepora complanata Lamarck, 1816, on coral reefs at Barbados, West Indies. It excavates complex networks of interconnecting burrows and forms aggregations of worms in cavities within branches of the coral. Adult worms have a mixed feeding mode (suspension feeding and deposit feeding). Size–frequency distributions of worms in branch samples suggest that they mature in a single year and that reproduction occurs throughout the year. Burrow openings on the surface of the coral develop distinctive, erect spines caused by combined growth of worm tubes and host tissue. Millepore zooids were absent in the vicinity of tube openings and on spines, and thus the potential feeding surface of the coral will be reduced in heavily colonized branches. Burrows and openings were densest at the bases of millepore branches where weakening of the skeleton would be expected to occur. The absence of openings near the branch tips suggests difficulty in larval settlement there, amongst stinging zooids. Reproduction␣and larval development of the worms were examined, and a sequence of larval stages from one to 20 segments and a juvenile stage of 22 segments are described. Eggs are deposited in brood sacs attached to the burrow wall, and the larvae feed upon nurse eggs (adelphophagy). The presence of larvae and juveniles occurring free in the burrows suggests that larval development may be completed within the host coral as an alternative or in addition to a planktonic larval phase. Lack of provisional larval setae, early development of adult capillary setae, production of special spermatophores and a protracted breeding cycle in D. armata are all traits which would favour complete development within the host skeleton. Received: 6 March 1997 / Accepted: 25 October 1997     

Otolith record of age, growth, and ontogeny in larval and pelagic juvenile Stephanolepishispidus (Pisces: Monacanthidae)

Juveniles of the planehead filefish Stephano-lepishispidus (Pisces: Monacanthidae) (Linnaeus, 1766) are a major component of the Sargassum spp. community, yet little is known of their ecology. In this study, the otolith record of age, growth, and ontogeny in S. hispidus was examined. Juveniles caught off Beaufort Inlet, North Carolina (USA) on 30 June 1996 were marked with alizarin complexone and reared in a flow-through, outdoor tank for up to 19 days. Examination of marked otoliths at several time intervals showed that increment formation was not significantly different than one increment per day, and thus, increment number was used to estimate age. Depth-distribution, morphology, and meristics of larvae and juveniles collected (1990–1992) between Cape Romain, South Carolina, and Cape Hatteras, North Carolina, were examined to identify the timing of the larval to juvenile transition. All indicators suggested the transition occurred between 17 and 20 days. Mean otolith increment widths exhibited a marked change at about 20 days, coinciding with the timing of the larval to juvenile transition and a change in the depth distribution from bottom to surface waters. Increment width of individual juveniles, however, did not exhibit the same pattern; only 40% conformed to the pattern identified for all fish. Thus, the record of the larval to juvenile transition is clear at the population level, but unresolved at the individual level. Received: 1 November 1999 / Accepted: 18 December 2000     

Cementation vs mobility: development of a cemented byssus and flexible mobility in Anomia chinensis

The mobility of Anomia chinensis Philippi was studied in relation to its byssal development stage. This species shows high mobility even after it begins cementation in its post-larval stage. Juveniles develop a calcified byssus in the post-larval stage and cement to substrata. However, juveniles up to about 10 mm in shell length can relocate by repeating a sequence of formation of the calcified byssus, abandonment of it, locomotion by crawling, reattachment, and recementation. Juvenile anomiids up to 25 mm in shell length also can move, without breaking their byssal attachments, by shifting the center of byssal calcification dorsally. Even an adult can change its orientation by forming a twisted byssus. These possible methods of movement are closely related to five stages of byssal development. Anomiids can use this mobility to seek a preferable position for attachment after initial cementation, or to adjust their orientation, and thus promote higher survivorship. Received: 18 August 1997 / Accepted: 19 July 1998     

Carbon content and nutritional condition of sardine larvae (Sardina pilchardus) off the Atlantic coast of Spain

As part of a “European Sardine/Anchovy Recruitment Program” (SARP), sardine larvae (Sardina pilchardus) were sampled off the Atlantic coast of Spain through the spawning season from March to June. The larvae were analysed for carbon and nitrogen content as a measure of nutritional condition and survival potential. There was no significant diel variation in larval carbon content, but there was a small significant diel variation in nitrogen; the absence of a strong diel signal in elemental composition was ascribed to the overnight retention of the gut contents. There was an increase in carbon content with increase in body length which reached an asymptote at ∼40% carbon content at a larval length of 20 mm. It is argued that larvae with a carbon content of <25% of body weight were nutritionally stressed, with the smaller larvae (<10 mm in length) appearing to be more vulnerable to food limitation. Although larvae with the lowest age-specific carbon content (poorest condition) occurred on the cruise with the lowest food availability, there was no consistent relationship between carbon content and food availability. While the successive monthly estimates of carbon content revealed differences in potential recruitment between months, these were not related to the birth-date distribution of the surviving juveniles. Received: 23 November 1998 / Accepted: 3 March 1999     

Effect of diet on growth rate and reproductive fitness of Turbo sarmaticus (Mollusca: Vetigastropoda: Turbinidae)

Experiments were conducted to determine the effect of four algal diets (Corallina spp., Gelidium pristoides, Ulva rigida and an equal volume mixture of these seaweeds) on growth and reproduction of the South African gastropod Turbo sarmaticus Linnaeus, 1758. The best growth rate of juveniles (up to 13.8 mm shell length and 34.26 g wet body weight increase in 12 months), reproductive fitness of mature specimens (gonad index up to 33%) and energy reserves (up to 4.76 mg glycogen/100 mg foot tissue) were achieved when T. sarmaticus was fed U. rigida or a mixed diet. In addition, the gonad index of individuals fed these diets was almost twice that of similar-sized field specimens. Juveniles fed Corallina spp. only, grew very little (only 2.4 mm shell length and 4.23 g wet body weight increase in 12 months). The reproductive fitness of adults fed on such a diet was also poor (gonad index <4.5%) and energy reserves were low (<3.5 mg glycogen/100 mg foot tissue). Along the southeastern coast of South Africa, T. sarmaticus has a distinct reproductive cycle with gametogenesis occurring from March/April until August/September, whilst maturity (gonad index = 15%) was maintained until December, after which spawning occurred until March. Received: 6 July 1998 / Accepted: 8 March 1999     

Transfer of symbiotic luminous bacteria from parental Leiognathus nuchalis to their offspring

Juveniles of Leiognathus nuchalis were raised from fertilized eggs for up to 60 d and examined for luminescence activity. Almost all juveniles raised separately from adults failed to produce detectable light. In contrast, a significant percentage (33 to 100%) of the juveniles became luminescent in less than 48 h when they were either kept with adults or inoculated with a homogenate of the adult light organs. The luminescence tended to increase with time after the treatments. These findings suggest that: (1) most of L. nuchalis offspring typically hatch and develop apo-symbiotically and (2) at least 45 d after hatching, juveniles can be infected with symbiotic luminous bacteria from the light organ of adult fish, and thereby gain the ability to produce light. Received: 16 February 1999 / Accepted: 21 September 1999     

Reproductive biology and ecology of a deep-demersal fish, alfonsino Beryx splendens, over the seamounts off New Caledonia

The reproductive biology of the alfonsino Beryx splendens was studied by histological examinations, gonadosomatic index and macroscopic scales of maturation of a large sample of gonads. Alfonsino is a gonochoric species. The size-frequency distribution of the sex ratio was bimodal and considered to be due to size dimorphism. In New Caledonia, the breeding period of this species occurs during the southern summer, with a peak in December to January. The spawning stage is attained at a minimum fork length of 28 cm for females and 33 cm for males. The size at which 50% of the population attain sexual maturity (FL₅₀) is 33.2 cm for females and 34.5 cm for males. Maximum potential fecundity is estimated to lie between 270 000 to 675 000 eggs for fish between 34 and 40 cm in fork length. It was possible to differentiate vegetative zones, in which juvenile alfonsino grow until they reach maturity, from reproductive zones (fishing grounds) which are inhabited by mature individuals. The larvae and juveniles could be carried from the reproductive zone to the vegetative zone by currents in an oceanic eddy system. Received: 26 April 1996 / Accepted: 20 September 1996     

Exfoliation of epithelial cells by the scallop Placopecten magellanicus : seasonal variation and the effects of elevated water temperatures

Previous studies have shown that large numbers of ciliated and nonciliated epithelial cells (diam.: 6 to 15 μm) are released by adult sea scallops, Placopecten magellanicus (Gmelin), during summer months in Newfoundland when water temperatures are at a maximum and gonads are well developed. Such exfoliation of cells could be a response to stresses associated with elevated water temperatures and/or spawning activity. In the present study an electronic particle counter/sizer was used to further investigate the factors that influence exfoliation of epithelial cells by juvenile and adult scallops throughout the year. We observed release of epithelial cells from juveniles, and from adults collected in months when gametogenic activity was minimal, indicating that exfoliation does not occur as a result of reproductive activity alone. SEM analysis revealed little difference in surface characteristics of the gills, mantle and gonad between scallops that had released cells and those that had not, suggesting that exfoliation of small numbers of cells may be a consequence of cellular turnover and normal physiological function. Adult scallops were monitored in a second experiment to determine the effects of raising water temperatures from 8.5 to 14.7 and to 21.0 °C on the frequency (proportion) and rate of cellular exfoliation. Only at the highest experimental temperature (21.0 °C) were exfoliation rates significantly higher than rates recorded at 8.5 or 14.7 °C. SEM analyses revealed some damage to gill, mantle and gonad tissues when scallops were exposed to 14.7 and then to 21.0 °C for a total of 8 d. Received: 21 August 1996 / Accepted: 13 September 1996     

Feeding ecology of herring (Clupea harengus) larvae in the turbid Blackwater Estuary

Most studies on feeding by herring larvae (Clupea harengus) have taken place in clear, open waters, but several herring stocks around the world spawn in inshore and estuarine regions. An example is the spring-spawning Blackwater Estuary (Essex, England) stock. Samples were collected in this estuary to examine prey selectivity and feeding levels in relation to biological and environmental conditions. Herring larvae negatively selected copepod nauplii, but positively selected the copepodite and adult stages of Acartia spp. Gastropod larvae were also positively selected. Particles >150 μm width were preferred, whilst particles smaller than this value were preferentially rejected. Concentrations of potential prey items in the water were in the range of 6.0 to 49.7 organisms l⁻¹ with a median concentration of 15.0 organisms l⁻¹ (n = 26). These values are towards the low end of prey concentrations quoted in the literature as being required to sustain herring larval growth and survival. However, theoretical considerations suggest that, in this environment, levels of tidally-induced turbulence enhance encounter rates between larval herring and their prey. On the other hand, turbidity is also related to tidal current speed and might reduce feeding success by decreasing underwater light levels. Measurements at two sites in the estuary confirmed that tidally-induced turbidity reduced the effective water depth in which herring larvae could visually feed by up to 50% at times of peak current speed. However, with the gut-content data available in the present study, it was not possible to discern any clear relationships between feeding success and the state of the tide. Feeding success appeared to be more strongly influenced by surface light-levels. Received: 24 June 1998 / Accepted: 17 February 1999     

Ontogeny of diet shifts by a microcarnivorous fish, Cheilodactylus spectabilis : relationship between feeding mechanics, microhabitat selection and growth

The mechanisms leading to ontogenetic shifts in prey selectivity are examined for the temperate microcarnivore Cheilodactylus spectabilis (Cheilodactylidae) in north-eastern New Zealand. These fish prey on invertebrates associated with benthic turf and foliose algae, using a suctorial feeding mode combined with oral sorting. All sizes of fish feed in the same shallow-water habitat using the same feeding mode. Dietary analysis revealed that while all sizes of fish consumed similar taxa, the relative proportion of taxa consumed reflected fish size. Juveniles consumed mainly gammarid amphipods while large adults targeted ophiuroids, with an abrupt shift from feeding predominantly on amphipods at 250 mm standard length. This dietary shift loosely coincided with the onset of sexual maturity and a change in growth trajectory, although dietary trends did not differ between sexes. Both juveniles and adults were found to select particular taxa from the available turf micro-fauna, with juveniles consuming smaller sizes of amphipods than adults. Microhabitat use was also found to change ontogenetically. Detailed observations on feeding mechanics suggested that size-related changes in suctorial force allowed the exploitation of a broader range of microhabitats with increasing fish size. Received: 20 June 1997 / Accepted: 1 April 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     

Reproductive biology of a deposit-feeding amphipod, Casco bigelowi, with extended parental care

The reproductive traits of a deposit-feeding amphipod that engages in extended parental care were examined. At the study site in Lowes Cove, Maine, USA, Casco bigelowi (Blake, 1929) occurred in highest densities in soft sediments just below mean low water (MLW). During most months, the sex ratio was ≃1. Many females hosted males in their burrows throughout the summer, but after fertilization of females in September, all adult males disappeared from the study area. In October almost 80% of the females were ovigerous, and in November about the same percentage was parental, i.e. caring for juveniles in their burrows. The females produced only one brood each in late fall which they accommodated in their burrows for 2 mo or longer. The average number of juveniles per female was ∼20 in November, and continuously decreased until January. Juveniles reached sizes >10 mm length in the maternal burrows. In early December the first juveniles were found in their own burrows, but major recruitment took place in late December and January. It is concluded that for C. bigelowi, the delay of recruitment into the winter months with low predation pressure and the large offspring size at this time are major advantages gained by extended parental care. C. bigelowi is host to the peritrich ciliate Cothurnia sp. on its gills, and during the summer months >70% of all amphipods had ciliates on their gills. Juveniles still living in their mother's burrows showed infestation rates similar to that of the parent; those of highly infested mothers were more heavily infested than those of “clean” mothers. Facilitated epibiont transmission during intimate and long-lasting (2␣mo) parent–offspring associations may be a consequence of extended parental care. Received: 25 November 1997 / Accepted: 14 April 1998     

Effect of temperature on viability and axial muscle development in embryos and yolk sac larvae of the Northeast Arctic cod (Gadus morhua)

Cod (Gadus morhua L.) eggs may develop and hatch within temperatures of −1.5 to 12 °C, but little is known about the effects of very low temperatures on larval characteristics. Eggs of the Northeast Arctic cod (Gadus morhua) were incubated at 1, 5 or 8 °C from Day 1 after fertilisation until hatching, and transferred to 5 °C after hatching. Histological samples of the axial musculature were taken at hatching and 5 d after hatching, and the data on muscle cellularity from these samples were related to survival and hatching, size, developmental data and viability of the yolk sac larvae. All larvae hatched at the same developmental stage. Incubation of eggs at 1 °C produced shorter larvae with a larger yolk sac and more, small deep fibres at hatching than larvae from eggs incubated at 5 or 8 °C. The larval size difference was still present 5 d after hatching, a time at which the larvae from 1 °C-incubated eggs were less developed and less resistant to an acute viability stress test (65 ppt salinity). Although there were no differences between temperature groups in number and size of muscle fibres 5 d after hatching, the deep fibres of the 1 °C-group contained less myofibrils than the two other groups. The phenotype of the larvae at hatching was thus affected within these incubation temperatures. Although all groups were transferred to the same temperature after hatching, the lowest egg incubation temperature (1 °C) still had a negative effect 5 d after hatching, as these larvae were both smaller, less resistant to stress and had less functional muscles at the time of first feeding. Our conclusion is therefore that 1 °C is close to, or below, the lower thermal tolerance limit for normal functional development of Northeast Arctic cod. The results are discussed in relation to larval viability and recruitment of this species in the wild. Received: 4 February 1998 / Accepted: 10 July 1998     

Variability in larval development of the tropical reef fish Pomacentrus amboinensis (Pomacentridae): the parental legacy

The effects of food availability, female size, and social interactions on the quality of Pomacentrus amboinensis larvae at hatching were examined using two field-based experiments. In Experiment 1, food availability and female size significantly influenced size, eye diameter and levels of yolk reserves of larvae at hatching. Small females (47 to 52 mm standard length, SL) whose diets were not supplemented, produced the longest larvae (3.0 ± 0.01 mm total length, TL) with the least yolk reserves (50.1 ± 1.04 μm²). Irrespective of female size, those that received additional food produced larvae with the largest yolk-sacs (large females: 87.60 ± 1.53 μm²; small females: 80.14 ± 1.24 μm²). In Experiment 2, interactions with conspecifics had a greater affect on the somatic development of larvae at hatching than food availability. Increased social interactions resulted in larvae that were ⋍3% longer, with 2% greater head depth, than larvae from females that spawned in isolation on the experimental reefs. Fed females produced larvae with ⋍20% more yolk than larvae from females whose diets were not supplemented. All three factors (food availability, female size, and intensity of social interactions) tested within these experiments vary spatially and temporally among reefs. There is the potential, therefore, for larvae at the onset of the planktonic stage to vary in quality, level of development, and probability of survival. Received: 12 August 1996 / Accepted: 26 August 1996     

Identification of settling and early postlarval stages of mussels (Mytilus spp.) from the Pacific coast of North America, using prodissoconch morphology and genomic DNA

 Detailed inventories of the benthos and field studies of the settlement and recruitment processes of marine benthic invertebrates require accurate identification of newly settled larvae and early juvenile stages. We provide morphological criteria, visible under a good quality dissecting stereomicroscope, by which to discriminate between species of the settling larval and early postlarval stages (∼250 to 700 μm shell length) of mussels of the genus Mytilus on the west coast of Vancouver Island and Southern California. Compared to the bay mussel (M. trossulus), the sea mussel (M. californianus) has: (i) a shallower and flatter umbo, the latter corresponding to a significantly less pronounced prodissoconch I (PI) curvature and (ii) a greater PI length; as well as (iii) a wider separation between the provincular lateral teeth (PLT). The PLT distance is a new term denoting the separation between the midpoint of two reddish pigment spots of the provinculum (larval hinge apparatus) region of settling larvae and early postlarvae of Mytilus spp. from the East Pacific Coast. These spots mark the larger provincular lateral teeth, situated at either end of the provinculum. We confirmed the validity of morphological criteria by comparing PCR products of genomic DNA of provisionally identified postlarvae. Furthermore, measurements of PI lengths and PLT distance from well-preserved postlarvae of sea mussels (M. californianus) and of bay mussels (M. galloprovincialis) from Southern California indicate that the PI morphology and morphometry, and PLT distance criterion apply for that region as well. The criteria presented here can also apply to the advanced (competent) veliger stages, as the latter may settle (i.e. become the “settling” stage) upon encountering a suitable substrate. Our present and previously published work provide economical and effective identification methods that can be used to discriminate among early life history stages (∼250 μm to 5.0 mm shell length) of Mytilus spp. along the west coast of North America. Received: 10 November 1999 / Accepted: 6 September 2000     

Fecundity of the chokka squid Loligo vulgaris reynaudii on the southeastern coast of South Africa

Potential fecundity in Loligo vulgaris reynaudii was estimated to be about 17 000 eggs, calculated as the total number of discernible oocytes in the ovary and oviduct. Squid were observed to spawn up to 8140 eggs over a 36 h period in captivity. First estimations of actual fecundity are therefore between 8000 and 17 000 eggs. Factors complicating a more accurate estimation of actual fecundity in this species include difficulties with aquarium maintenance, their behaviour of spawning over a protracted period and in multiple sites, and atretic oocytes observed in both developing and mature ovaries. Detailed morphological and histological analysis of gonads collected at regular intervals over a complete spawning season will allow a more precise calculation of actual fecundity. Received: 9 October 1998 / Accepted: 22 April 1999