Effects of heavy metals on the development and survival of abalone Haliotis midae larvae

Despite a growing abalone Haliotis midae industry in South Africa, few studies have measured the effects of heavy metals on larval survival and growth in the face of recent increases in marine pollution. The aim of this study was to quantify the effect of copper on survival and zinc on development of H. midae larvae. Larvae 24 hours old were exposed to either copper (0–30 μg l^–1) or zinc (0–200 μg l^–1) for 48 h before mortality or larval development respectively were quantified. Copper significantly reduced survival, with an LC₅₀ of 5.58 μg l^–1 (5.07–6.15, 95% CI). Although the concentrations of zinc used in the study did not have a significant effect on mortality, there was a significant effect on the incidence of abnormal larvae with an EC₅₀ of 102.25 μg l^–1 (96.68–105.94, 95% CI). At concentrations above the EC₅₀, more than 50% of the larvae showed severe developmental abnormalities. Results suggest that copper poses the greatest risk to abalone larvae as the LC₅₀ was similar to the target concentration for this metal for South African coastal waters. By contrast, zinc is potentially less problematic, with the EC₅₀ for larval development being four times the target concentration for this metal.     

Integrated culture of silver kob Argyrosomus inodorus and bloodworm Arenicola loveni loveni in abalone farm effluent

South African abalone Haliotis midae farms utilise large volumes of seawater (c. 500–1 500 l s^–1) and produce relatively dilute effluents that are potentially suitable for the integrated culture of other species. To test this hypothesis, a marine finfish, silver kob Argyrosomus inodorus, and a detritivorous polychaete, bloodworm Arenicola loveni loveni, were cultured in abalone farm effluent and the results compared to controls reared in unused seawater. The silver kob were fed a nutritionally complete pelleted diet whereas the bloodworm were placed in shallow tanks with a low water velocity that allowed suspended organic solids to settle for the detritivorous worms to feed on. Silver kob growth rate (0.48% body weight d^–1; SE = 0.01%), mortality (1.8 ± 0.5%), feed conversion ratio (3.0 ± 0.2) and protein efficiency ratio (1.0 ± 0.1) did not differ significantly between the effluent and control treatments. Bloodworm reared in abalone effluent grew well on the particulate organic waste matter in the effluent (0.39% body weight gain d^–1; SE = 0.07%), whereas those in the seawater control lost weight at 0.19 ± 0.04% body weight d^–1 over the experimental period. Bloodworm mortality did not differ significantly between effluent (6 ± 3%) and unused seawater (11 ± 8%) treatments. The faster growth of bloodworm in the abalone farm effluent was ascribed to the higher deposition rate of enriched organic solids (182 ± 56 g m^–2 d^–1) compared with those grown in the seawater control (46 ± 13 g m^–2 d^–1). It was concluded that abalone farm effluent is potentially suitable for the culture of both bloodworm and silver kob.     

Effects of kelp Ecklonia maxima inclusion in formulated feed on the growth,feed utilisation and gut microbiota of South African abalone Haliotis midae

The effect of kelp Ecklonia maxima inclusion in formulated feeds on abalone growth and gut bacterial communities has not been previously investigated in South Africa. An eight-month on-farm growth trial was conducted with sub-adult Haliotis midae (～43 mm shell length) fed graded levels of kelp in formulated feeds. Kelp inclusion (0.44–3.54% of pellet dry mass) promoted faster growth (65.7–74.5% total mass gain), with better feed and protein conversions (apparent feed conversion ratio [FCR] 1.4–1.8, apparent protein efficiency ratio [PER] 2.3–2.7), as compared with the non-supplemented feed (52.3% total mass gain, FCR 2.1, PER 1.9; p < 0.001). Abalone-gut bacterial DNA was sequenced using 16S rRNA gene pyrosequencing and the sequences were clustered into operational taxonomic units (OTUs) at a 97% similarity level. A supplementary 16S rRNA gene denaturing gradient gel electrophoresis (DGGE) analysis was employed. The dominant OTUs differed in terms of their relative abundances, with an autochthonous Mycoplasma strain being significantly more abundant (p = 0.03) in the gut of abalone fed a kelp-supplemented feed. The DGGE band patterns displayed higher within-group variability for abalone fed the control diet, suggesting that dietary kelp inclusion promotes gut-bacteria homeostasis. This may contribute to better feed utilisation and growth in abalone fed kelp-supplemented feeds.     

The effect of low-level kelp supplementation on digestive enzyme activity levels in cultured abalone Haliotis midae fed formulated feeds

Previous studies have found that macroalgal inclusion in formulated diets for cultured abalone improves feed utilisation, and it was suggested that seaweed-associated bacteria supply enzymes that aid in the animal's digestion. In the present study, we hypothesised that kelp supplementation in formulated feed affects the profile of digestive enzymes in farmed Haliotis midae. Commercially reared sub-adult abalone fed a kelp-supplemented (Ecklonia maxima; 0.88% dry weight) or kelp-free control feed were collected for analysis of the amylase, alginate lyase, laminarinase, fucoidanase and protease activities in the gut. Levels of polysaccharidase and protease activity did not significantly differ between the diet treatments. However, enzyme-activity levels were more variable in abalone fed the kelp-free diet as compared with those fed the kelp-supplemented diet (coefficients of variation: 73%, 48.3–60.2% and 31.9% [control diet] versus 42.7%, 13.6–33.8% and 14.6% [KS diet] for amylase, macroalgal polysaccharidases and acid protease activity, respectively). We suggest that the presence of dietary kelp modulates the abalone's gut bacteria and their nutrient exchange. Proteomic identification of proteins in abalone gut sections showed that exogenous enzymes associated with the gut microbiome aid in bacterial utilisation of digested molecules, whereas abalone endogenous enzymes degrade the macronutrients in formulated feeds.     

Evidence for a positive relationship between juvenile abalone Haliotis midae and the Sea urchin Parechinus angulosus in the South-Western Cape,South Africa

Previous field observations have suggested an association between the urchin Parechinus angulosus and juveniles of the abalone Haliotis midae. To test the generality and nature of this association, surveys were carried out at five sites between Cape Point and Danger Point in the kelp beds of the South-Western Cape, South Africa. These showed that both species occupy primarily hard substrata, showing preferences for encrusting coralline algae. They also confirmed a strong, positive relationship between urchins and juvenile abalone. Of the juvenile abalone sampled, more than 98% were found beneath sea urchins. All small (3–10 mm) and medium-sized(11–20 mm) juvenile abalone were under urchins, whether on flat or vertical reef, or in crevices. A small proportion (～10%) of larger juveniles(21–35 mm) was not found under urchins, and in these instances they occupied crevices instead. These findings are of particular importance in terms of their implications for the lucrative commercial abalone fishery in South Africa, indicating that urchins are of critical importance to the continued survival of viable abalone populations. There has been a dramatic decrease in natural populations of sea urchins over the past five years in the heart of the abalone fishing grounds, and the present findings suggest that this will lead to recruitment failure of abalone, because juvenile abalone seem dependent on the urchins. The long-term consequences for the industry may be crucial.     

Neurophysiological control of swimming behaviour,attachment and metamorphosis in black-footed abalone (Haliotis iris) larvae

Experiments were conducted to test the effect of a range of chemicals on larval responses in swimming behaviour, attachment and metamorphosis of the black-footed abalone (Haliotis iris). The effect of antibiotics on larval survival was first tested within negative (filtered seawater) and positive (GABA at 10^?5, 10^?4 and 10^?3 mol L^?1) control assays over 3 days. This experiment corroborated the effectiveness of using antibiotics to improve survival of larvae without obvious synergistic interactions with the GABA inducer or confounding effects of potential bacterial interactions. Chemical treatments (acetylcholine, potassium chloride, dopamine and glutamine) were then tested at various concentrations for their ability to modulate swimming behaviour and induce larval attachment and metamorphosis over 14 days. Generally, larval state shifted from swimming to attached, and from attached to metamorphosed, in the control and treatments over time. However, the peak percentage of attached and metamorphosed larvae varied in time among chemicals and concentrations. While overall percent metamorphosis was minimally enhanced after 14 days of exposure to some chemical treatments at certain concentrations, all treatments displayed significant capacities to down-regulate larval swimming and induce early attachment and metamorphosis. Mortality was recorded throughout the duration of the experiment, and was generally low (<20%) across controls and most treatments for exposures of less than 12 days. Interpretations of specific results from this study are used to elucidate neurophysiological control of larval activities for this abalone species. Comparisons with other marine invertebrates highlight the specificities of chemical cues and endogenous regulatory mechanisms across relatively closely related taxa.     

Boulders or urchins? Selecting seeding sites for juvenile Haliotis midae along the Namaqualand coast of South Africa

The extent to which the relationship between juvenile abalone Haliotis midae and sea urchins Parechinus angulosus is induced by their physical habitat along the Namaqualand coast of South Africa was investigated. Correlation analyses between the proportion of abalone utilising sea urchins for refuge and the proportion of habitat defined as exposed were computed from 28 experimental seeding sites in Port Nolloth on the north-west coast of South Africa. A highly significant positive correlation was found (r = 0.72, p < 0.05). It was concluded that, along the Namaqualand coast, under-boulder habitat was the most important factor determining the survival of juvenile abalone (size 12–26mm). Site selection should therefore be based on the suitability of the physical substratum to provide shelter for juvenile abalone along that coast.     

Metabolic activity throughout early development of dusky kob Argyrosomus japonicus (Sciaenidae)

The physiology of fishes in the early stages of development remains poorly assessed despite the importance of identifying energy bottlenecks in organisms faced with changing environmental conditions. This study describes the metabolic activity of dusky kob Argyrosomus japonicus throughout its early development, from hatchling to settlement stage. Standard, routine and active metabolic rates (SMR, RMR and AMR, respectively) were assessed to determine the species’ metabolic scope and identify how metabolism changes with growth and development. Distinct metabolic changes occurred in association with developmental changes during the early life stages, with flexion-stage larvae showing significantly reduced metabolic scope (approx. 0.30 µmol O₂ ind.^–1 h^–1), representing an energy bottleneck. Based on these findings, it is likely that larvae of A. japonicus are most susceptible to environmental perturbations during flexion. The variability of metabolic rates during the diel cycle was also assessed and revealed that the early-stage larvae showed no preference for daylight, although settlement-stage juveniles were more active during daylight hours (RMR = 12.78 µmol O₂ ind.^–1 h^–1) than at night (RMR = 5.87 µmol O₂ ind.^–1 h^–1). These results suggest that metabolic measurements of the SMR of A. japonicus larvae can be taken at any time of the diel cycle until the settlement phase, when readings should take place at night.     

Relationships between recruits of abalone Haliotis midae,encrusting corallines and the sea urchin Parechinus angulosus

In kelp beds of the South-Western Cape, South Africa, a strong positive relationship exists between the sea urchin Parechinus angulosus and juveniles of the abalone Haliotis midae. Field surveys reported here revealed a positive, but weak, association between this urchin and H. midae recruits (i.e. individuals <3 mm shell length). Selectivity indices showed that recruits occurred exclusively on encrusting coralline algae and showed preferences for strongly textured corallines, rather than those with smooth texture. On smooth corallines, around 80% of recruits were under urchins, compared with about 25% on textured corallines, suggesting that any need for shelter beneath urchins is greatest on smooth surfaces.     

Effects of waterlogging,salinity and light on the productivity of Bruguiera gymnorrhiza and Heritiera littoralis seedlings

This study aimed to establish the effects of waterlogging, salinity and light on the early development of mangroves. Seedlings of Bruguiera gymnorrhiza (L.) Lamk. and Heritiera littoralis Dryand were exposed to 12 weeks of waterlogging, during which time growth and photosynthesis were measured every two weeks. The salinity of the water inundation ranged from fresh water to full-strength sea water (salinity 35). Seedlings were exposed to either full sunlight of 1 500 µmol photon m^–2 s^–1 (SD 397) at midday or shade conditions of 325 µmol photon m^–2 s^–1 (SD 40) of light at midday, to explore whether the plants would be differently affected by prolonged waterlogging in increased salinities and under different light conditions. Heritiera littoralis was more sensitive to waterlogging, salinity and light, displaying a least relative growth rate of 0.127 g g^–1 week^–1 (SE 0.032) under shade, and 0.025 g g^–1 week^–1 (SE 0.021) in full light; while under shade, photosynthesis continued only in fresh water, but photosynthetic yield decreased from 0.7 to 0.4 with increasing duration of waterlogging. By 12 weeks, all H. littoralis seedlings treated with any saltwater mixture had died. Bruguiera gymnorrhiza seedlings maintained a moderate rate of photosynthesis throughout inundation in both shade and full light, with yields of 0.7 and 0.3, respectively. Furthermore, B. gymnorrhiza survived waterlogging in up to 66% seawater, and maintained comparable relative growth rates of 0.164 g g^–1 week^–1 (SE 0.066) with 0.083 g g^–1 week^–1 (SE 0.065) and 0.074 g g^–1 week^–1 (SE 0.036) with 0.052 g g^–1 week^–1 (SE 0.037) under shade and in full light between fresh water and the highest salinity conditions, respectively. These results suggest that B. gymnorrhiza is broadly tolerant, making it a potential candidate species for restoring vulnerable mangrove forests.     

Coulometric total carbon dioxide analysis for marine studies: Automation and calibration

An automated instrument for the coulometric detection of total carbon dioxide (TCO₂) was developed from the manual prototype of Johnson et al. Pure CO₂ was used to calibrate the detector, the whole analytical procedure was controlled by a microcomputer, and the unit was compact enough for field and shipboard use. Some 67 samples from the Askö field station on the Baltic Sea (salinity = 6; TCO₂ ranging from 1224.3 to 1276.1 μmol l⁻¹ with a mean of 1245.6 μmol l⁻¹) and 31 samples from Swedish lakes (TCO₂ ranging from 19.5 to 252.3 μmol l⁻¹ with a mean of 72.9 μmol l⁻¹) were analyzed. The pooled standard deviation of these analyses was ± 1.0 μmol l⁻¹ (% CV of 0.08 and 1.3%, respectively). Precisions of < 0.1% were routine for waters exceeding 1000 μmol l⁻¹ TCO₂. At Askö on the Baltic Sea, the mean absolute difference between coulometric and pH-alkalinity determinations of TCO₂ on 22 parallel samples was 6.7 μmol kg⁻¹ or 0.5% of the mean. Community metabolism studies gave maximum rates of net production (TCO₂ uptake) and respiration (TCO₂ production) of 0.9-1.2 and 0.3-0.5 μmol l⁻¹ b⁻¹, respectively. The results of this study provide solutions to the problems observed with the earlier manual prototype.     

Non-destructive sampling of juvenile abalone using epipodial tentacles and mucus: method and application

Good-quality biological material is needed to obtain intact deoxyribonucleic acid (DNA) for use in molecular techniques such as the polymerase chain reaction (PCR). Non-destructive sampling protocols of juvenile abalone Haliotis midae (7–15 months old) were tested in order to collect material for DNA extraction. DNA was successfully extracted from epipodial tentacles and mucus samples. PCR results confirmed the good quality of the DNA and the reliability of the method.     

Influence of water column dynamics on sulfide oxidation and other major biogeochemical processes in the chemocline of Mariager Fjord (Denmark)

Major electron donors (H₂S, NH₄⁺, Mn²⁺, Fe²⁺) and acceptors (O₂, NO₃⁻, Mn(IV), Fe(III)), process rates (³⁵SO₄²⁻ reduction, dark ¹⁴CO₂ fixation) and vertical fluxes were investigated to quantify the dominant biogeochemical processes at the chemocline of a shallow brackish fjord. Under steady-state conditions, the upward fluxes of reductants and downward fluxes of oxidants in the water column were balanced. However, changes in the hydrographical conditions caused a transient nonsteady-state at the chemocline and had a great impact on process rates and the distribution of chemical species. Maxima of S⁰ (17.8 μmol l⁻¹), thiosulfate (5.2 μmol l⁻¹) and sulfite (1.1 μmol l⁻¹) occurred at the chemocline, but were hardly detectable in the sulfidic deep water. The distribution of S⁰ suggested that the high concentration of S⁰ was (a) more likely due to a low turnover than a high formation rate and (b) was only transient, caused by chemocline perturbations. Kinetic calculations of chemical sulfide oxidation based on actual conditions in the chemocline revealed that under steady-state conditions with a narrow chemocline and low reactant concentrations, biological sulfide oxidation may account for more than 88% of the total sulfide oxidation. Under nonsteady-state conditions, where oxic and sulfidic water masses were recently mixed, resulting in an expanded chemocline, the proportion of chemical sulfide oxidation increased. The sulfide oxidation rate determined by incubation experiments was 0.216 μmol l⁻¹ min⁻¹, one of the highest reported for stratified basins and about 15 times faster than the initial rate for chemical oxidation. The conclusion of primarily biological sulfide oxidation was consistent with the observation of high rates of dark ¹⁴CO₂ fixation (10.4 mmol m⁻² day⁻¹) in the lower part of the chemocline. However, rates of dark ¹⁴CO₂ fixation were too high to be explained only by lithoautotrophic processes. CO₂ fixation by growing populations of heterotrophic microorganisms may have additionally contributed to the observed rates.     

The effect of age on the reproductive output of the abalone pest Terebrasabella heterouncinata (Polychaeta: Sabellidae: Sabellinae)

High levels of infestation by the polychaete Terebrasabella heterouncinata on cultured abalone may be attributed to elevated levels of fecundity in comparison with conspecifics in their natural habitat. It is not, however, known if a high reproductive output is sustained throughout the animal's life. The present study therefore measured the effect of age on various reproductive parameters of T. heterouncinata from cultured abalone Haliotis midae. Age did not have a significant effect on body size, fecundity or rate at which eggs were laid. However, age had an affect on the proportion of the population that was brooding offspring, because a significantly lower percentage of the youngest age-group was brooding eggs or young, in comparison with the older groups. T. heterouncinata are long-lived, surviving for over four years on abalone farms and can therefore spread their reproductive effort over an extended period, instead of restricting it to a limited period during its early life. The ability to maintain a high fecundity irrespective of age may contribute to the success of this pest on abalone farms.     

L-DOPA对西施舌眼点幼虫附着变态诱导的研究

采用试验水体中添加化学诱导物的方法研究L-DOPA(L-多巴)对西施舌(Coelomctraantiquata)眼点幼虫附着变态的诱导作用。结果表明,L-DOPA能诱导西施舌眼点幼虫变态,但对其附着的诱导效果不明显。用直径小于1 mm的细沙为附着基质,1×10-6mol/L的L-DOPA处理西施舌眼点幼虫12 h,变态率为73.3%,对照组为62.6%。浓度为1×10-7mol/L的L-DOPA处理西施舌幼虫12 h,生长速率为25.6%,对照组为14.7%,表明适当浓度的L-DOPA能促进西施舌幼虫的生长。在无沙附着的条件下,西施舌幼虫可正常附着变态,但生长速率较低且变态后死亡率高。     

A spatial- and age-structured assessment model to estimate the impact of illegal fishing and ecosystem change on the South African abalone Haliotis midae resource

The management of abalone stocks worldwide is complicated by factors such as illegal fishing combined with the difficulties of assessing a sedentary (but not immobile) resource that is often patchily distributed. The South African abalone Haliotis midae fishery is faced with an additional problem in the form of a relatively recent movement of rock lobsters Jasus lalandii into much of the range of the abalone. The lobsters have heavily reduced sea urchin Parechinus angulosus populations, thereby indirectly negatively impacting juvenile abalone which rely on the urchins for shelter. A model is developed for abalone that is an extension of more standard age-structured assessment models because it explicitly takes spatial effects into account, incorporates the ecosystem change effect described above and estimates the magnitude of substantial illegal (‘poached’) catches. The model is simultaneously fitted to catch per unit effort and Fishery-Independent Abalone Survey abundance data, as well as to several years of catch-at-age (cohort-sliced from catch-at-size) data for the various components of the fishery and different spatial strata. It constitutes the first quantitative approach applied to the management of this commercially valuable resource in South Africa and has provided a basis for management advice over recent years by projecting abundance trends under alternative future catch levels.     

Temporal changes in kelp forest benthic communities following an invasion by the rock lobster Jasus lalandii

The rock lobster Jasus lalandii expanded its centre of distribution south-eastwards into an area known as ‘East of Cape Hangklip’ on the south-west coast of South Africa in the early 1990s. Using historical and present data, we analysed differences in the abundance of key species and functional groups between the pre- and post-rock lobster invasion periods at two sites along that coast: Cape Hangklip and Betty's Bay. Pre-1989, lobsters were absent, but after 1995 they reached densities approximating 0.4–0.8 m^?2. Benthic community composition also changed significantly with herbivores being abundant whereas macroalgae and sessile invertebrates were scarce pre-invasion. We attribute the decline of herbivores to the direct effects of lobster predation, in turn indirectly promoting macroalgae. Post-invasion sessile invertebrates and macroalgae increased by 2 600% and 453% respectively, whereas herbivores declined by 99.3%. The virtual elimination of the sea urchin Parechinus angulo-sus by rock lobsters has substantial implications for the commercial harvesting of the abalone Haliotis midae, because its juveniles are intimately associated with this urchin. The lobster invasion has thus not only led to a regime shift of the ecosystem but has also substantial economic consequences, which calls for an ecosystem approach to the management of the pool of commercially exploited resources in this region.     

Polydorid polychaetes (Spionidae) on farmed and wild abalone (Haliotis midae) in South Africa: an epidemiological survey

Although there has been an increase in our understanding of the shell-boring polydorids that infest abalone Haliotis midae in South Africa, abalone from a limited number of farms, and wild populations from east of Cape Agulhas only, have been examined. To gain further knowledge and a more complete understanding of the local distribution of polydorids, we examined up to 30 abalone from each of 14 farms in the Northern, Western and Eastern Cape provinces, and five wild sites in the Western Cape, west of Cape Agulhas. Farm and wild communities were significantly different from each other (ANOSIM, r = 0.632, p < 0.002) and Bray–Curtis cluster analysis showed that most farms clustered separately from wild sites. Boccardia proboscidea was present on all but one of the infested farms, whereas some were also infested by Dipolydora capensis. By contrast, D. capensis was present at all wild sites sampled, whereas B. proboscidea was absent from these sites. Polydora hoplura, a common shell-boring pest, was present at only two farms and two wild sites. There appeared to be some exchange of polydorids among farms and between farms and wild abalone. The farm on the East Coast did not cluster with any other sites, indicating a unique composition of polydorids on that coast. No new, potentially problematic, species was encountered, although four species showed an increase in their known distribution.     

Acclimations of macroalgae as reflected in photosynthetic parameters derived from PAM fluorometry, and possible implications for abundance patterns

The presences of the common macroalgae Ulva sp. and Jania rubens vary between seasons along the Israeli Mediterranean intertidal zone. To reveal some of the potential acclimation mechanisms of these algae, we examined their photosynthetic traits during the year using rapid light curves (RLC) derived from pulse amplitude modulated (PAM) fluorometry. In addition, the relationships between those photosynthetic traits and the relative abundances of the two algae were investigated. Ulva sp. showed high maximal electron transport rates (ETR_max) (49.7–68.8 μmol electrons m⁻² s⁻¹) and onsets of light saturation values (E_k) (75.8–85.6 μmol photons m⁻² s⁻¹) in the winter months of December–February, while low values were found in the summer months of June–July (5.2–20.6 μmol electrons m⁻² s⁻¹ and 6.0–23.7 μmol photons m⁻² s⁻¹, respectively). At noon time (during the highest irradiance of the day), the maximal effective quantum yield (Y₀) did not vary significantly during the year. These results indicate that seasonal irradiance influences the number of reaction centres per thallus area. Both algae showed depressions in Y₀ at noon (23.8% for Ulva sp. and 20.3% for Jania rubens), indicating an efficient non‐photochemical quenching mechanism. A positive correlation between the relative abundance and the photosynthetic parameter Y₀ was found for Jania rubens when Y₀ was sampled in the morning or noon, indicating that growth rate and primary production for this alga can be estimated from RLCs. No such correlation was found for Ulva sp., indicating that, in addition to photosynthetic traits, the relative seasonal abundance of this alga is influenced by other factors such as grazing and/or catastrophic events.     

A microsatellite panel for triploid verification in the abalone Haliotis midae

A method for ploidy verification of triploid and diploid Haliotis midae was developed using molecular microsatellite markers. In all, 30 microsatellite loci were tested in control populations. A final micro satellite multiplex consisting of seven markers were optimised and a complete protocol is reported. This protocol was successfully applied in identifying the ploidy levels of 42 ploidy-unknown abalone, showing the utility of microsatellite markers as tools for verifying the ploidy of individual abalone. The protocol can be applied in larger animals for which the isolation of nuclei and metaphase chromosomes from tissues is difficult.