Reproductive cycle and gametogenesis in the black abalone Haliotis cracheroidii (Gastropoda: Prosobranchiata)

Seasonal changes in gonald size and stages of gametogenesis in the black abalone Haliotis cracheroidii were related to changes in environmental parameters. H. cracheroidii showed an annual reproductive cycle terminating in a synchronized spawning in late summer. Gametogenesis was initiated immediately after spawning. Gametes were present in the gonad through the winter months. Gametogenesis was initiated a second time in the spring months. Maximal gonad growth (to a gonad index of 20%) occurred during summer months prior to spawning. Changes in gonad size andperiods of initiation of gametogenesis revealed no apparent correlation with changes in seasonal water temperature. Changes in gonad size showed no apparent relation to change in day length. Total polysaccharide levels in foot tissue changed seasonally, indicating that food availability is probably not a factor in directly regulating gonad growth. Gonad index data for the chiton Katharina tunicata (collected over a 10 year period) showed no apparent correlation to seasonal change in water temperature.     

An experimental test of the effect of the abalone Haliotis midae on benthic community composition

The South African abalone Haliotis midae is a commercially valuable species, but its numbers are seriously depleted due to illegal fishing. Overfishing not only affects the targeted species, but also potentially influences the integrity and functioning of the ecosystem through associated changes in community composition. We assessed the herbivorous effects of H. midae on the benthos through a 6-month field experiment involving exclusion/inclusion plots. This showed that benthic community composition remained largely unchanged whether H. midae was present or absent and specifically revealed no evidence that H. midae diminishes algal biomass, probably because in the region where we worked, it feeds mainly by trapping drift kelp rather than grazing on attached algae. The absence of responses to the removal of abalone was additionally evident in comparison with indices of abundance and diversity, functional groups and individual species. In the absence of abalone, there were subtle increases in the green alga Codium stephensiae and the crustose brown alga Zeacarpa leiomorpha and decreases in the four species of foliose macroalgae, but none of these effects were significant. The presence of H. midae thus had no negative grazing effects on any elements of the epilithic community composition. It does, however, have other influences, including occupation of space and provision of habitat in the form of its shell, which supports a community significantly different from the surrounding rocks.     

Repeatability of physiological traits in juvenile Pacific abalone, Haliotis discus hannai

Several studies on individual physiological traits assume that past records may predict future performance. Marine mollusks, as other animals, show a wide range of between- and within-individual variation of physiological traits. However, in this group, almost nothing is known about the relative influence of genetic factors on that variation. Repeatability (R) is a measure of the consistency of the variation of a trait, which includes its genetic variance and represents the maximum potential value of its heritability (h ²). Traits that show high inter-individual variation and high repeatability levels could potentially evolve through selection (natural or artificial). We estimated the repeatability [using intra-class (τ) and Pearson-moment (r) correlation coefficients] of several physiological traits related to energy acquisition and allocation in juvenile Pacific abalone Haliotis discus hannai, maintained under controlled environment growing systems. In order to estimate the range of the R values and the effect of the time elapsed between measurements on these estimates, we measured these traits monthly during 6 months for each individual. Among the physiological traits, those related to energy allocation like oxygen consumption (standard metabolic rate, SMR) and ammonium excretion rates, and oxygen/nitrogen ratio (O/N), showed intermediate levels of repeatability (0.48, 0.55 and 0.39, respectively), when this was estimated by τ coefficient. However, the r estimation showed that SMR and O/N repeatability were significant and high (0.6–0.7 and 0.5–0.7, respectively) during the first 5 consecutive measurements, decreasing strongly (0.3 and 0.2, respectively) during the last measurement. For ammonia excretion, although repeatability (r) decreased from 0.8 to 0.5 during the 6 consecutive measurements, they remain significant during the experimental period. Therefore, our results indicate that for H. discus hannai juveniles, physiological traits like SMR, ammonia excretion and O/N are significantly repeatable (i.e. good predictors of future measurements) during a period of 4–5 months. These significant repeatability values suggest an important genetic control upon the phenotypic variation of these physiological traits, and could potentially respond to natural or artificial selection, and be used in genetic improvement programs. By contrast, those traits related to energy acquisition (i.e. ingestion, absorption and assimilation) and physiological efficiencies (i.e. net growth and scope for growth) showed very low levels of repeatability (0–0.07). This indicates that the phenotypic variation of these traits would be more influenced by environment rather than by genetic factors.     

Tissue and sub-cellular distribution of Fe,Cu, Zn and 210Po in the abalone Haliotis rubra

The tissue and sub-cellular distribution of Fe, Cu, Zn and the naturally occurring radionuclide polonium-210 was determined in the gastropod mollusc Haliotis rubra collected from Western Port Bay, Australia, between March and July 1988. The highest concentrations of the metals, with the exception of Cu, were found in the digestive gland. Copper was more uniformly distributed, with tissues that are more vasculated having higher concentrations. Ultrastructural examination of the digestive gland, gill and kidney showed dense membrane-bound granules within the cytoplasm. Elemental analysis of the granules by electron probe x-ray microanalysis indicated that the granules in the digestive gland and gill contained high concentrations of iron, with small amounts of copper and zinc. In contrast, the metal-containing granules in the kidney were predominantly composed of iron, copper and phosphorus, with variable contributions of sodium potassium, and calcium. Homogenisation and fractionation of the digestive gland by differential centrifugation confirmed that approximately 80, 10, 90 and 50% of the total homogenate Fe, Cu, Zn and ²¹⁰Po, respectively, sedimented at 1200xg. In the haemolymph, all the elements studied were associated with the soluble high molecular weight component of the serum, not with the amoebocytes. ²¹⁰Po was present in the mucus-secreting hypobranchial glands at about half the concentration found in gill tissue.     

Settlement of larval blacklip abalone, Haliotis rubra, in response to green and red macroalgae

Surfaces from the habitat of adult Haliotis rubra were tested as inducers of larval settlement to determine the cues that larvae may respond to in the field. Settlement was high on the green algal species Ulva australis and Ulva compressa (Chlorophyta), the articulated coralline algae Amphiroa anceps and Corallina officinalis, and encrusting coralline algae (Rhodophyta). Biofilmed abiotic surfaces such as rocks, sand and shells did not induce settlement. Ulvella lens was also included as a control. Treatment of U. australis, A. anceps and C. officinalis with antibiotics to reduce bacterial films on the surface did not reduce the settlement response of H. rubra larvae. Similarly, treatment of these species and encrusting coralline algae with germanium dioxide to reduce diatom growth did not significantly reduce larval settlement. These results suggest that macroalgae, particularly green algal species, may play an important role in the recruitment of H. rubra larvae in the field and can be used to induce larval settlement in hatchery culture.     

Biomineralization markers during early shell formation in the European abalone <Emphasis Type=Italic>Haliotis tuberculata</Emphasis>, Linnaeus

Larval shell formation was investigated in the European abalone Haliotis tuberculata. Stages of mineralization as well as enzymatic and endocrine biomarkers were monitored throughout larval development, from hatching to post-larval stages. Polarized light microscopy and infrared spectroscopy analyses revealed the presence of crystallized calcium carbonate arranged in aragonite polymorphs from the late trochophore stage. A correlation between the main steps of shell formation and enzymatic activities of alkaline phosphatase and carbonic anhydrase was seen. The variations of these biologic activities were related to the onset of mineralization, the rapid shell growth, and the switch from larval to juvenile shell following metamorphosis. Furthermore, a strong increase in the level of calcitonin gene-related molecules was measured in post-larvae, suggesting that endocrine control takes place after metamorphosis. The changes measured for the three biomineralization markers together with mineralogical analysis allowed us to correlate physiologic mechanisms with early steps of abalone shell formation.     

Sublethal effects of zinc and municipal effluents on larvae of the red abalone Haliotis rufescens

Experiments were conducted to develop a sensitive sublethal toxicity test protocol to determine the toxicity of municipal wastewater effluents to larvae of the red abalone Haliotis rufescens. In multiple tests, fertilized abalone embryos were exposed for 48 h to dilutions of a reference toxicant, zinc sulfate, and to dilutions of primary-and secondary-treated effluents. The resulting veliger larvae were examined microscopically for larval shell abnormalities. In a longer flowthrough experiment, abalone were exposed for the entire larval phase, from the two-cell stage through metamorphosis, to compare zinc effects on metamorphosis with zinc effects on short-term larval shell development. Dissolved oxygen, pH, salinity and temperature were measured daily in test solutions, and zinc concentrations were verified by chemical analysis. No observed effect concentrations (NOECs) for zinc were 39±2.1 g l^-1 in three 48 h exposures, and 19 g l^-1 for the 9 d exposure through metamorphosis. Median effect concentrations (EC₅₀s) were 68±6.9 g l^-1 in 48 h tests and 50 g l^-1 in the 9 d test. Abalone larvae were affected at lower concentrations of primary than of secondary effluent.     

Cytological study and immunohistochemical location of PSP toxins in foot skin of the ormer, Haliotis tuberculata, from the Galician coast (NW Spain)

The ormer, Haliotis tuberculata Linnaeus, 1758, is able to accumulate paralytic shellfish toxins (PST) in the foot side skin. Epidermal and secretory cells are described separately for the pedal side and sole epithelia, as notable differences have been observed. Melanin and photosynthetic pigment granules in the epidermal cells of the foot side epithelium give this skin its appearance and characteristic color. This epidermis also has abundant secretory cells containing at least three kinds of secretory granules. Conversely, the epidermal cells of foot sole epithelium do not have pigment granules, and the secretory cells are mostly subepithelial. Immunohistochemical reaction against PST (saxitoxin and its derivatives) showed that the toxins are located in specific cells of the foot side epithelium, which are distinct from the epidermal cells. Immunofluorescence also reveals toxins throughout many areas of the mucilage covering the epithelium, suggesting the secretory nature of the cells containing the toxins. These results do not show any apparent relationship between melanin or photosynthetic pigment granules and PST content. PST were not detected in the foot sole epithelium either immunohistochemically or by HPLC. Considering the toxic characteristics of ormers described in previous studies and the results presented here, the authors discuss the role of toxins retained or produced by the foot side epithelium Received: 25 July 2000 / Accepted: 7 November 2000     

Analysis of genetic structure of blacklip abalone (Haliotis rubra) populations using RAPD, minisatellite and microsatellite markers

 We investigated the utility of three polymerase chain-reaction (PCR)-based DNA molecular markers in analysing genetic structure of the populations of the blacklip abalone Haliotis rubra (Leach) of Victoria, Australia. The DNA markers included 84 randomly amplified polymorphic DNA (RAPD) bands amplified using six random primers, two minisatellites, GHR (putative growth-hormone-gene-repeat) and MIPR (putative mollusca-insulin-like peptide-gene-repeat), and three microsatellites, RUBGT1 [containing (GT)_n repeats], RUBCA1 [containing (CA)_n repeats] and RUBGACA1 [containing (GACA)_n repeats]. All three types of DNA markers revealed significant subdivision in the H. rubra populations along the coastline. This is postulated as being related to the abalone's relatively short pelagic period and limited dispersion. Further analysis revealed that a Point Cook population sampled from within the semi-enclosed Port Phillip Bay was distinct from two other central zone populations (Apollo Bay and Cape Schanck). The genotypes of microsatellites indicated excessive homozygotes across all the populations at all three microsatellite loci, and possible causes such as larval recruitment pattern and asynchronous spawning are discussed. The excessive homozygotes recorded for the three microsatellite loci contrast with those observed in the minisatellite loci GHR and MIPR, the heterozygosities of which were at Hardy–Weinberg equilibrium. Received: 17 March 1999 / Accepted: 24 November 1999     

Comparing community structure on shells of the abalone Haliotis midae and adjacent rock: implications for biodiversity

This paper concerns the effects on biodiversity of depletion of the South African abalone Haliotis midae, which is a long-lived species with a large corrugated shell that provides a habitat for diverse benthic organisms. We compared community structure on H. midae shells with that on adjacent rock at three sites (Cape Point and Danger Point sites A and B) and at two different times of the year at one of these sites. Shells of H. midae consistently supported communities that were distinctly different from those on rock. In particular, three species of non-geniculate (encrusting) corallines, Titanoderma polycephalum, Mesophyllum engelhartii and Spongites discoideus, were all found either exclusively or predominantly on shells, whereas another non-geniculate coralline, Heydrichia woelkerlingii, occurred almost exclusively on adjacent rock. The primary rocky substratum, however, supported a higher number of species than abalone shells. Possible reasons for the differences between the two substrata include the relative age, microtopography and hardness of the substrata; the abundance of grazers on them; and the relative age of different zones of the abalone shell, which support communities at different stages of succession. Diversity on shells was lowest in zones that were either very young or very old, in keeping with the intermediate disturbance hypothesis. The distinctiveness of shell epibiota will increase β diversity despite having a lower α diversity than that of adjacent rock. Decimation of H. midae by overfishing therefore has implications for biodiversity conservation.     

Using growth band autofluorescence to investigate large-scale variation in growth of the abalone <Emphasis Type="Italic">Haliotis midae</Emphasis>

Growth of the abalone, Haliotis midae, was investigated at Port Alfred, on the south coast of South Africa, using both new and established techniques. A new method for aging animals is described, which makes use of shell autofluorescence under UV light to visualise internal growth bands. The deposition of growth bands was validated using measurements from shells of known age and, at one site, comparing growth estimates to those from cohort analysis undertaken at the same site. The new technique is far less time consuming and labour intensive than previously described methods; it is also non-destructive and proved to have potential for the reliable and rapid assessment of growth in large-scale studies. Growth of H. midae was also investigated at nine other sites, incorporating the full distribution range of the species. Systematic geographic variation in growth was observed along the South African coastline. Statistically significant differences existed among sites in growth rates for animals <4 years and between 4 and 6 years and in the mean maximum sizes attained. Generally, H. midae from the south/southeast coast were found to have faster growth rates, smaller mean maximum sizes and were assumed to attain sexual maturity (determined in previous studies) earlier than those along the southwest/west coast. The geographic differences in estimates of growth observed have significant implications for future modelling approaches and indicate that present national management strategies are not appropriate as they fail to take regional variability into account.     

Green abalone, <Emphasis Type="Italic">Haliotis fulgens</Emphasis> infected with the agent of withering syndrome do not express disease signs under a temperature regime permissive for red abalone, <Emphasis Type="Italic">Haliotis rufescens</Emphasis>

All California abalone species have been shown to be susceptible to infection with the bacterial agent of abalone withering syndrome (WS), although expression of signs of the disease may vary between species and with environmental conditions. We examined thermal modulation of WS expression in green abalone Haliotis fulgens at temperatures mimicking El Niño (18.0°C) and La Niña (14.2°C) events in southern California. In contrast to results obtained from previous experiments with red abalone, H. rufescens, the higher temperature did not result in higher infection intensities of the causative agent of the disease nor increase in clinical signs of disease. These results demonstrate clear differences in thermal regulation of disease expression between abalone species, and provide further data suggesting that green abalone should be a target species of recovery efforts in southern California, where WS is endemic.     

Reproductive cycle,larval development,juvenile growth and population dynamics of Patiriella pseudoexigua (Echinodermata: Asteroidea) in Taiwan

A field study was conducted at Wanlitung, southern Taiwan, in 1986–1089, to determine the reproductive cycle, development mode, growth rate and population dynamics of the small seastar Patiriella pseudoexigua (Dartnall), which occurs in highly stressful and disturbed intertidal pools in this area. An inverse relationship between gonad index and pyloric-caccum index was only recorded immediately prior to spawning. A short, well-synchronized seasonal spawning occurs in October. When reared at 25 °C, lecithotrophic larvae develop directly, lack a bipinnaria stage, and metamorphose completely on the seventh day after fertilization. The growth curves of field juveniles are linear, those of laboratory-reared juveniles are sigmoid. Juveniles appear in tide pools in spring-early summer of each year. Adults spawn mainly in late fall, enabling spawning to occur in time for the larvae to benefit from the environmentally favorable winter season. Populations in high-tidal pools decrease in later summer, but remain more stable in lowtidal pools and lagoons.     

A morphological and structural study of the larval shell from the abalone <Emphasis Type="Italic">Haliotis tuberculata</Emphasis>

The larval shell of the marine gastropod Haliotis tuberculata was investigated by polarised light microscopy, scanning electron microscopy, Raman microspectroscopy and infra-red spectroscopy. Trochophore and veliger larval sections were used for histological examination of the growing shell and each larval stage was related to the shell development and the appearance of calcified formations. We determined the stage of initial calcification by specific staining combined with polarised light examination. The shell of 30-h-old pre-veliger larvae was found to be mineralized, confirming that calcification occurred before larval torsion. Using both infra-red and Raman spectroscopy, we showed that CaCO₃ deposition occurred at the pre-veliger stage and that the mineral phase initially deposited was essentially composed of aragonite.     

Studies on the growth,reproduction, and life cycle of the supralittoral isopod Ligia pallasii

A two-year study on a field population of Ligia pallasii Brandt has shown that the isopods live for 1.5 to 2 years. Breeding occurs in the spring and early summer, with some females carrying winter broods of eggs. The mean length of breeding females is 22.5±2.2 mm (standard deviation) and the mean brood size is 48±11 eggs. Mature males are larger than mature females (900 and 300 mg live weight, respectively), and are disproportionately broader (31×17 mm and 22.5×9 mm, respectively). The larger size and breadth of the males is an adaptation for copulation, and may be atributed in some measure to slower growth of the female due to the extra energy demands of reproduction. The overall 1:1 ratio of males to females in the population represents the balance between an equal sex ratio in the immature stages, more females in the 18 to 24 mm length category, and more males in the larger length categories. This condition is attributed mainly to the faster growth of the males.     

New genetic markers to identify European resistant abalone to vibriosis revealed by high-resolution melting analysis,a sensitive and fast approach

Increasing temperature of seawater is often associated with increased exposure incidence of disease in field and in aquaculture populations. Numerous episodic mass mortalities of the abalone Haliotis tuberculata have been observed along the northern Brittany coast of France caused by a complex interaction between the host, pathogen and environmental factors. Here, we evaluated the potential of high-resolution melting (HRM) analysis for mutation genotyping and development of genetic markers for resistance to vibriosis in the gastropod species H. tuberculata. Small amplicon assays were developed and revealed genetic polymorphism between surviving and susceptible abalone obtained after two successive infections of aquaculture families in controlled conditions. Together with specific COI haplotypes, we identified particular genotypes in nascent polypeptide-associated complex subunit alpha and ferritin genes linked to the susceptibility or resistance of abalone to vibriosis. Selection of genitors based on these genes may increase the proportion in offspring of resistant individuals of more than 76 %. Finally, HRM assays constitute a very efficient genotyping tool to validate the genetic markers on a representative number of individuals of wild populations and thus identify future resistant genitors for aquaculture or conservation purposes.     

Species composition, biomass and vertical distribution of micronekton over the mid-slope region off southern Tasmania, Australia

Seasonal sampling was carried out based on day/night, vertically stratified tows (100 or 125 m strata) in the upper 900 m of the water column over the mid-slope commercial fishing grounds south of Tasmania. A large midwater trawl (105 m² mouth area) was used with an opening/closing cod-end. Subtropical convergence and subtropical species dominated the fauna, but many less abundant, more widely-distributed species were also present. Fishes, which contributed 89% of micronekton biomass and 135 of 178 species, were dominated by the Myctophidae (48% biomass and 48 species). Twenty micronekton species made up 80% of the total biomass. Overall, the micronekton fish biomass in this region was 2.2 g m⁻² wet weight. A pronounced day/night shift in the distribution of biomass was attributable to diel migratory species. During the day, <0.2% of the total micronekton biomass was found in 0 to 300 m; most biomass was below 400 m, with peaks at 400 to 525 m and 775 to 900 m. At night, 53% of the biomass was found in 0 to 300 m, with progressively less in each deeper stratum. The vertical ranges of individual species typically exceeded 400 to 500 m during the day and night and were non-coincident, although nyctoepipelagic migrators were concentrated in the surface 200 m at night. Distinct epipelagic, lower and upper mesopelagic assemblages were identified, and patterns of epipelagic migration, limited migration and non-migration were categorised for species from each of the lower and upper mesopelagic assemblages. The vertical distribution of these assemblages was coincident with the primary water masses: subantarctic mode water (∼250 to 600 m) and antarctic intermediate water (below ∼700 m). The flux of migrating micronekton, estimated at 0.94 to 3.36 g C m⁻² yr⁻¹ to the lower mesopelagic and 1.14 to 4.06 g C m⁻² yr⁻¹ to the upper mesopelagic, appeared to be considerably outweighed by the consumption needs of aggregated mid-slope benthopelagic predators. We suggest that advection of mesopelagic prey in antarctic intermediate water may sustain aggregated populations of orange roughy (Hoplostethus atlanticus) and other predators on the micronekton in mid-slope depths at this site. Received: 2 April 1997 / Accepted: 21 August 1997     

Elemental composition of otolith growth marks in three geographically separated populations of European hake (Merluccius merluccius)

The composition of the opaque and translucent bands in the otoliths of European hake (Merluccius merluccius) from three different populations (Celtic Sea, Galicia shelf and Cretan Sea) was analysed with wavelength dispersive spectrometry (WDS) and differences in Ca, Sr and Na were compared. The translucent bands (annual marks and checks altogether) were significantly richer in Sr and Ca and significantly poorer in Na than opaque bands. Results support the idea of a more compact arrangement of crystals in translucent bands compared to opaque. Analyses did not help to discriminate between putative annual marks and checks. Clear differences in the range of Sr/Ca variation across the otolith as well as in the composition of the otolith core were observed among the three populations. As a result it was possible to discriminate the natal origin of each fish using the composition of the otolith core in Ca, Sr and Na. Nevertheless, the overall pattern across the otolith was similar among the three populations suggesting the existence of ontogenetic trends. Variation of Na/Ca ratios was largely uninformative. Based on these results, a conceptual model for hake is proposed which integrates the different sources of otolith Sr/Ca variation: ambient Sr/Ca, endogenous cues (ontogeny) and exogenous cues (environment).     

Larval growth and settlement of the European oyster (Ostrea edulis) as a function of food quality measured as fatty acid composition

Larval growth rate and settlement of the European flat oyster Ostrea edulis were experimentally studied as a function of the composition of dietary fatty acids. Diets differing in fatty acid composition were composed by mixtures of the microalgae Isochrysis galbana, Pavlova lutheri and Chaetoceros calcitrans. Fatty acid content in the tissue of the feeding larvae, analyzed by gas chromatography and mass spectrometry, reflected the composition in the diet. Larval growth rate was significantly correlated to the three omega-3 polyunsaturated fatty acids (PUFA) C18:3, C18:4 and C22:6, with minor differences for neutral and polar lipids. No relation between growth rate and the omega-3 PUFA C20:5 was detected, a PUFA often implied as essential for bivalves. It is suggested that naturally occurring variability in fatty acid composition may constrain larval growth. In settlement experiments in both still water and flume flow little substrate selectivity was found for some contrasting substrates. It is concluded that differences in dietary fatty acids may explain as much of settlement success as the variability of substrates. Received: 12 October 1998 / Accepted: 6 April 1999     

Shell growth and mortality rates in the coral reef gastropod Cerithium nodulosum in Pago Bay,Guam, Mariana Islands

Growth and mortality rates of the gastropod Cerithium nodulosum Bruguière were investigated by repetitive mark-and-recapture censuses for the inner and middle reef flat subpopulations of Pago Bay, Guam, from February to October 1975. Overall population density was about 2 individuals per 100 m² in October. Juveniles (28 to 75 mm shell length) grew at mean rates of from 2.3 to 4.6 mm per month, with great (average coefficient of variation, CV: 32% of the mean) individual variations within the cohorts. The adult stage, which ceases growing in length after forming characteristic shell apertures, was reached within 3 years. Individual adult sizes varied markedly within each subpopulation; the mean shell length was 76.3 mm (standard deviation, SD=6.2, N=129) for the inner and middle reef flat subpopulation and 84.3 mm (SD=6.6; N=127) for the outer reef flat subpopulation. The difference in mean adult shell length between the two subpopulations was highly significant (0.01 level). Mortality rates were estimated from the slopes of regression lines fitted to the catch curves. Assuming tag loss of 10%, crude mortality rates were 15 to 20% per month for the population of C. nodulosum.Contribution No. 103, University of Guam Marine Laboratory.