South African Abalone Haliotis Midae Research Articles

A proteomic analysis of the effect of ocean acidification on the haemocyte proteome of the South African abalone Haliotis midae

As a result of increasing CO2 emissions and the prevalence of global climate change, ocean acidification (OA) is becoming more pervasive, affecting many trophic levels, particularly those that rely on succinctly balanced ocean chemistry. This ultimately threatens community structures, as well as the future sustainability of the fishing/aquaculture industry. Understanding the molecular stress response of key organisms will aid in predicting their future survivability under changing environmental conditions. This study sought to elucidate the molecular stress response of the South African abalone, Haliotis midae, an understudied organism with high economic value, utilising a high throughput iTRAQ-based proteomics methodology. Adult abalone were exposed to control (pH 7.9) and experimental (pH 7.5) conditions for 12, 72 and 168 h, following which protein was isolated from sampled haemocytes and subsequently processed. iTRAQ-labelled peptides were analysed using mass spectrometry, while an array of bioinformatics tools was utilised for analysing the proteomic data. COG analysis identified “Cytoskeleton”, “Translation, ribosomal structure and biogenesis”, “Post-translational modification, protein turnover, chaperones”, and “Intracellular trafficking, secretion and vesicular transport” to be the most enriched functional classes, while statistical analysis identified a total of 33 up-regulated and 23 down-regulated effectors of OA stress in abalone. Several of the up-regulated proteins that were identified function in central metabolism (ENO1, PGK, DUOX1, GPD2), the stress/immune response (CAMKI, HSPA5/GRP78, MAPKI), and cytoskeleton, protein sorting and signal transduction (IQGAP1, MYO9B, TLN1, RDX, TCP-1/CCT, SNX6, CHMP1a, VPS13a). Protein-protein interactions were predicted using STRING DB, Cytoscape and Ingenuity Pathway Analysis, providing a model of the effects of OA on the H. midae haemocyte proteome. The data indicated that H. midae underwent a metabolic shift under OA conditions to utilize more energy-efficient mechanisms of ATP generation, while attempts at restoring haemocyte stabilisation and homeostasis were reflected by up-regulation of oxidative stress and cytoskeletal proteins. Our results support other molluscan studies that report a complex array of overlapping functions of both the stress and immune response systems. This interplay of the mounted stress and immune response is maintained and observed through the up-regulation of proteins involved in protein synthesis and turnover, as well as intracellular signalling and transport. The data presented in this study highlight the value of employing sensitive and robust -omics technologies for assessing the effects of changing environmental conditions on marine organisms.

ITRAQ-based quantitative proteomic profiling of the immune response of the South African abalone, Haliotis midae

The South African abalone Haliotis midae is a commercially important species farmed at high densities in land-based aquaculture systems. Disease outbreaks have had a severe financial impact on the abalone industry yet the molecular mechanisms underlying the immune response of H. midae remain obscure. In this study, a comparative shotgun proteomics approach using iTRAQ coupled with LC-MS/MS was employed to investigate H. midae proteome changes in response to Vibrio anguillarum challenge. A total of 118 non-redundant, unique haemocyte proteins were identified and quantified, with 16 proteins significantly regulated. Hierarchical clustering and pathway analysis uncovered a coordinated response dominated by calcium and cAMP signalling via activation of MAPK cascades. Early up-regulated biological processes involve phagocytosis, nitric oxide production and ATP-synthesis, whilst down-regulated responses were predominantly involved in the regulation of apoptosis. The late up-regulated response involved protein kinase activity and detoxification processes. Expression of selected proteins was validated by Western blot. A putative allograft inflammatory factor-1 protein was further selected to establish its functional molecular role in haemocytes. Confocal imaging revealed that allograft inflammatory factor-1 regulates phagocytosis via a functional interaction with filamentous actin. This is the first time a high-throughput proteomics approach has been used to investigate the immune response of H. midae.

An approach to determine the extinction risk of exploited populations

We propose a method for assessing the persistence of species where the resource is harvested. Four sustainability measures are employed, namely a population measure, a harvest measure, a profitability measure and a catchability measure. These are used to assess the sustainability of two natural resources representing terrestrial and aquatic species, namely White Rhino (Ceratotherium simum) and South African abalone (Haliotis Midae) species, respectively. The framework is used to evaluate these two resources against relevant local and international protected species listings. The results show that the proposed framework produces a more conservative approach to listing threatened species, consistent with the precautionary principle. The framework provides a way of conducting a precautionary assessment of extinction risk under conditions of exploitation, across a range of aquatic and terrestrial species. Once developed, we also apply this framework to seven additional species using a scenario analysis. The results highlight the importance of taking into consideration institutional factors under conditions of overexploitation.

The cross-tissue metabolic response of abalone (Haliotis midae) to functional hypoxia.

ABSTRACTFunctional hypoxia is a stress condition caused by the abalone itself as a result of increased muscle activity, which generally necessitates the employment of anaerobic metabolism if the activity is sustained for prolonged periods. With that being said, abalone are highly reliant on anaerobic metabolism to provide partial compensation for energy production during oxygen-deprived episodes. However, current knowledge on the holistic metabolic response for energy metabolism during functional hypoxia, and the contribution of different metabolic pathways and various abalone tissues towards the overall accumulation of anaerobic end-products in abalone are scarce. Metabolomics analysis of adductor muscle, foot muscle, left gill, right gill, haemolymph and epipodial tissue samples indicated that South African abalone (Haliotis midae) subjected to functional hypoxia utilises predominantly anaerobic metabolism, and depends on all of the main metabolite classes (proteins, carbohydrates and lipids) for energy supply. Functional hypoxia caused increased levels of anaerobic end-products: lactate, alanopine, tauropine, succinate and alanine. Also, elevation in arginine levels was detected, confirming that abalone use phosphoarginine to generate energy during functional hypoxia. Different tissues showed varied metabolic responses to hypoxia, with functional hypoxia showing excessive changes in the adductor muscle and gills. From this metabolomics investigation, it becomes evident that abalone are metabolically able to produce sufficient amounts of energy when functional hypoxia is experienced. Also, tissue interplay enables the adjustment of H. midae energy requirements as their metabolism shifts from aerobic to anaerobic respiration during functional hypoxia.This article has an associated First Person interview with the first author of the paper.

Effects of formic acid in abalone diets that contain ingredients derived from fish processing by-products

The study aimed to investigate the effects of formic acid inclusion in abalone diets, which contained ingredients produced from fish processing by-products, and to quantify effects on production performance. Four diets (a commercial reference and iso-nutrient diets containing fish silage oil, unprocessed rainbow trout viscera or shrimp protein hydrolysate) were evaluated both with and without addition of 2 g kg−1 dietary formic acid, thus yielding a total of eight treatments, in feeding trials with cultured South African abalone Haliotis midae. Results indicated that inclusion of unprocessed rainbow trout viscera without formic acid decreased production performance of experimental animals, as evidenced by significantly decreased final animal weight and daily weight gain, and significantly increased feed conversion ratio compared to the iso-nutrient control. The decreased production performance was attributed to decreased feed water stability of the diet incorporating untreated trout viscera. Dietary formic acid supplementation partially mitigated the negative impacts of viscera inclusion on production performance of the experimental animals, as seen in significantly higher final animal weight and daily weight gain, and lower feed conversion ratio when compared to non-formic acid-supplemented, viscera-containing diet. However, no beneficial effects on production performance or water stability were found upon formic acid inclusion in diets not containing trout viscera. In conclusion, dietary formic acid can partially mitigate negative impacts on production performance when unprocessed trout viscera are included in formulated abalone diets by improving feed water stability, but the exact mechanism by which this is achieved was not established.

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.

Short Postspawning Recovery Time Affects Dna Integrity and Fertilization Success of South African Abalone (Haliotis midae) Oocytes

ABSTRACT Hydrogen peroxide (H2O2) is used routinely by the abalone farming industry to induce spawning of adult abalone. The aim of the current study was to quantify DNA integrity of adult hemolymph cells as well as germ cells (oocytes and sperm) with different recovery times between spawning events. In addition, fertilization success of exposed germ cells was quantified. The results indicate that spawning events separated by short recovery (2–6 wk) will not provide sufficient recovery from H2O2-induced DNA fragmentation in adult hemocytes. It is recommended that the industry should ideally allow 6–8 wk between spawning events to prevent accumulation of DNA strand breaks in adults over time and to ensure adequate fertilization success to maximize farm production.

Heritability of growth traits in South African Abalone (Haliotis midae L.) using the ‘internal reference’ method

The South African Abalone Haliotis midae is a vital aquaculture species, accounting for the highest percentage of total aquaculture production revenue. Improving the growth rate and thus, reducing operational costs with associated benefits in production efficiency and profitability is a priority of producers. The industry has been reluctant to implement anything but the most rudimentary breeding practices, due to unreliable tagging methods and the cost of using DNA markers. As such, the current study aimed to estimate genetic parameters for growth traits in the absence of individual tagging or DNA markers using the ‘internal reference’ method. The requirements of the internal reference method are evaluated and the merits and demerits considered. Heritability estimates were low to moderate in magnitude for wet weight (0.06–0.21) and shell length (0.11–0.16). It is concluded that substantial genetic gains can be achieved through selection and further work into developing strategies employing individual identification and DNA markers are warranted. Statement of relevanceWe adapted an existing statistical control method in an innovative way to estimate genetic parameters for growth traits in abalone, without individual tagging or DNA markers. This method facilitates the transition from simple family selection programs to combined selection programs by providing the necessary inputs for bio-economic modelling to inform the design of more advanced breeding programs.

An assessment of spatio-temporal genetic variation in the South African abalone (Haliotis midae), using SNPs: implications for conservation management

The South African abalone (Haliotis midae) is a gastropod mollusc of economic importance. In recent years natural populations have come under considerable pressure due to overharvesting and ecological shifts. The spatial genetic structure of H. midae has been determined; however there has not been a temporal assessment of abalone population dynamics around the South African coast. Using a population genomics approach this study aimed to assess fluctuations in genetic diversity among wild and cultured South African abalone populations through time and space. Various estimates of genetic diversity and population differentiation were calculated using EST-derived SNP markers. All populations had comparable levels of genetic diversity and the long-term effective population size appears to be sufficiently large for the wild populations, despite evidence of recent bottlenecks. Population differentiation was for the most part geographically correlated, with spatial genetic structure maintained across temporal samples. Significant genetic differentiation was, however, detected among temporal samples taken from the same locality. There was evidence for comparatively small short-term effective population sizes that could explain large changes in allele frequencies due to stochastic effects. Temporal heterogeneity could also be explained by changes in selection pressures over time. H. midae populations could, therefore, be more dynamic than previously estimated and this could have implications for effective conservation and fisheries management.

Behavioural responses of farmed South African abalone Haliotis midae L. to disturbances caused by husbandry procedures

The South African abalone, Haliotis midae L., is an important mariculture species. In the natural environment, abalone move and migrate to new sites to escape from disturbances. This is the first study that tested the effect of disturbances on movement and feeding activity of farmed abalone for 6 days post-disturbance. Disturbances were (a) turning over the feeder plate, (b) moving and shaking the feeder plate and (c) briefly lifting the basket containing the abalone out of the water. Abalone in the control treatment were not subjected to disturbance. Activity levels of abalone were elevated in the first 1–2 nights post-disturbance with 2–3 times more abalone appearing on the walls of the baskets and larger numbers on the feeder plate than in the control treatment. Feed uptake was not influenced by treatment. Thus, even minor disturbances resulted in increased activity. As it takes at least 1 year to conduct growth experiments in this slow-growing mollusc, the results provide a motivation for studies of growth and metabolic rate in this species under a range of husbandry conditions, such as regular handling, sorting and moving of abalone.

Characterization of an intracellular bacterium infecting the digestive gland of the South African abalone Haliotis midae

A Rickettsiales-like prokaryote was observed in digestive gland epithelium of farmed South African abalone Haliotis midae sampled for routine surveillance. Histological examination showed basophilic inclusions typical of rickettsial infections in shellfish (Mouton, 2000). This study aimed to identify the Rickettsiales-like prokaryote (RLP) colonising H. midae. Total genomic DNA was extracted from infected digestive gland sampled from cultured H. midae. PCR performed with “Candidatus Xenohaliotis californiensis” specific primers RA 5-1 and RA 3-6 did not yield positive results, indicating that the H. midae RLP is not the withering syndrome agent. The 16S rRNA gene sequence of the intracellular bacterium was determined following nested PCR using universal eubacterial primers fD1/Rp2 and the broad spectrum primers EHR16SD/EHR16SR which are specific for members of the Anaplasmataceae family within the Rickettsiales order. Phylogenetic and evolutionary distance analysis showed that the H. midae RLP is a unique member of the α-proteobacteria. The identity and location of the histologically observed intracellular bacterium was confirmed by in situ hybridization performed on sequential sections of infected H. midae digestive gland using a combination of three digoxigenin-labelled probes specific to various regions of the 16S rRNA gene of the RLP.Statement of relevanceThe manuscript shows that farmed abalone, showing no disease symptoms, can remain healthy despite the presence of intracellular bacteria colonising their digestive glands. The study shows that Rickettsiales-like prokaryotes detected in farmed abalone are not necessarily “Candidatus Xenohaliotis californiensis”, the causative agent of withering syndrome.

A chain of fools: or, why it is so hard to stop overfishing

We fish too much, and by doing so, we threaten marine ecosystems and people’s livelihoods. But the curious thing is: we have known this for a long time. Nonetheless, we continue to overfish. How is that possible? Why can we not stop? This paper recounts our search for an answer. We start by giving an overview of how scientists explain overfishing, and suggest that the riddle of its obduracy has not been addressed systematically. We conceptualize overfishing as an unplanned and unintended outcome of a chain of interrelated social and ecological events. We then analyze the chain of events leading to overfishing for two typical cases – the groundfish fishery in the Gulf of Maine and the South African abalone (Haliotis midae, Haliotidae) fishery – and two atypical cases where overfishing has stopped or been substantially reduced – the Patagonian and Antarctic toothfish (Dissostichus eleginoides, Nototheniidae and Dissostichus mawsoni, Nototheniidae) fishery in the Southern Ocean, and the Atlantic cod (Gadus morhua, Gadidae) fishery in the Barents Sea. Studying and comparing these cases reveals no sufficient set of factors to explain the persistence of overfishing. Rather, distinct pathways emerge from a concatenation of proximate and remote factors, leading to and sustaining overfishing. Understanding these pathways and their mechanisms can assist in locating leverage points for intervention aimed to stop overfishing.

Rainbow trout silage oil as immunity enhancing feed ingredient in formulated diets for South African abalone Haliotis midae

Abstract This study was conducted to evaluate the effects of rainbow trout silage oil on the immune function, growth performance and foot muscle fatty acid profile and proximate composition of South African abalone Haliotis midae . Rainbow trout silage oil was prepared from farmed rainbow trout processing waste, included at 25 g kg − 1 in a formulated diet and compared to a control diet in a 153 day growth trial. It was found that rainbow trout silage oil addition significantly improved abalone cellular immune function by increasing hemocyte phagocytic activity from 48.8% in the control diet to 65.2% in the silage oil diet. However, production performance was negatively impacted: specific growth rate (SGR) and final animal weight were decreased 17% and 5.6% respectively, and feed conversion ratio (FCR) increased by 25.1%. Foot muscle fatty acid profile and proximate composition were unaffected. It is concluded that dietary fish silage oil inclusion can improve cellular immune function in H. midae , but that the optimal inclusion level should be determined in order to negate the negative effects on production efficiency.

The effects of protein hydrolysates on the immunity and growth of the abalone Haliotis midae

Abstract Dietary hydrolysed proteins have been shown to stimulate the non-specific immunity of various finfish species, whilst the potential for immune stimulation of these feed ingredients in abalone has not been investigated. The immune-stimulating potential of two hydrolysed protein sources (self-prepared fish silage and a commercial fish protein hydrolysate) at two dietary inclusion levels in abalone diets was therefore measured in the South African abalone Haliotis midae , using animals of initial mean weight of 123 g–128 g. Diets containing the high inclusion levels were also fed in two feeding regimes: continuous feeding, or phase feeding, where the hydrolysed protein diets were alternated monthly with the control diet. In low inclusion diets, hydrolysate inclusion contributed 6 g·kg − 1 protein in the final diet, whilst in high inclusion diets this was increased to 18 g·kg − 1 . It was found that the low inclusion level of the commercial hydrolysate significantly increased the cellular immunity through increasing the phagocytic activity of haemocytes by 18% compared to the control diet, whilst none of the other diets showed any significant differences compared to the control. Both inclusion levels of the commercial hydrolysed protein significantly improved daily weight increase of animals. Phase feeding had no positive impacts on immunity or production performance. The inclusion of both types of hydrolysed protein sources significantly decreased the water stability of feeds compared to the control, except at the lowest inclusion level of the commercial hydrolysate. It is concluded that the use of dietary hydrolysed proteins can lead to improved cellular immunity and growth in abalone, however it is important to determine appropriate inclusion levels to prevent negative impacts on feed water stability and production performance.

Detection and Localisation of the Abalone Probiotic Vibrio midae SY9 and Its Extracellular Protease, VmproA, within the Digestive Tract of the South African Abalone, Haliotis midae

Probiotics have been widely reported to increase the growth rate of commercially important fish and shellfish by enhancing the digestion of ingested feed through the production of extracellular enzymes such as proteases and alginases. In order to investigate this further, the objective of this study was to localise the bacterial probiont Vibrio midae SY9 and one of the extracellular proteases it produces in the digestive tract of the South African abalone Haliotis midae. This was accomplished by inserting a promotorless gfp gene into the chromosome of the bacterium which was incorporated in an artificial, fishmeal-based abalone feed. In situ histological comparison of abalone fed either a basal diet or the basal diet supplemented with V. midae SY9::Tn10.52 using a cocktail of DNA probes to the gfp gene localised the probiont to the crop/stomach and intestinal regions of the H. midae digestive tract. Generally, the ingested probiotic bacterium occurred in association with feed and particulate matter within the crop/stomach and intestinal regions, as well as adhered to the wall of the crop/stomach. Histological immunohistochemical examination using polyclonal anti-VmproA antibodies localised an extracellular protease produced by V. midae SY9 to the H. midae crop/stomach and intestine where it appeared to be associated with feed and/or other particulate matter in the abalone gut. Thus the data suggests that V. midae SY9 colonises and/or adheres to the mucous lining of the abalone gut. Furthermore, the close association observed between the bacterium, its extracellular protease and ingested feed particles supports the theory that V. midae SY9 elevates in situ digestive enzyme levels and thus enhances feed digestion in farmed abalone.

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.

Metabolic readjustment in juvenile South African abalone (Haliotis midae) acclimated to combinations of temperature and dissolved oxygen levels

When ectotherms are exposed to high temperatures, cellular oxygen demand increases. When oxygen demand exceeds oxygen availability, animals may experience functional hypoxia regardless of environmental oxygen levels.In the current study, we aimed to assess if oxidative or thermal restrictions exist when winter-acclimated Haliotis midae juveniles are re-acclimated to temperatures within their thermal tolerance range, but with one temperature outside the average daily temperatures they would experience in winter. At each acclimation temperature (14, 16 and 19°C), we also manipulated dissolved oxygen levels to obtain oxygen saturation levels of 82%, 98% and 126%.Our results indicate growth restrictions and hypometabolism at all oxygen treatments at 19°C. Efficiency of mitochondrial respiration, as indicated by an increase in cytochrome c oxidase subunits 1 and 2 (cox1 and cox2) transcript level, was improved at 19°C, 98% oxygen. A change in substrate utilisation, from a glycogen/lipid-driven metabolism to almost exclusively protein-driven metabolism provided the fuel for more effective cellular respiration. A further decrease in metabolic rate at 19°C, 126% oxygen, this time without an increase in cox1 and cox2 transcripts, may indicate some improvement in gas exchange, but without improvement in growth.We propose that 19°C is nearing a long-term limiting temperature for winter-acclimated SA abalone, and that animals survive this condition by re-allocating available energy to survival mechanisms instead of growth. This species, already threatened by over-harvesting, may be further threatened by increases in surface seawater temperatures.

Detection of molecular signatures of selection at microsatellite loci in the South African abalone (Haliotis midae) using a population genomic approach

Identifying genomic regions that may be under selection is important for elucidating the genetic architecture of complex phenotypes underlying adaptation to heterogeneous environments. A population genomic approach, using a classical neutrality test and various Fst-outlier detection methods was employed to evaluate genome-wide polymorphism data in order to identify loci that may be candidates for selection amongst six populations (three cultured and three wild) of the South African abalone, Haliotis midae. Approximately 9% of the genome-wide microsatellite markers were putatively subject to directional selection, whilst 6–18% of the genome is thought to be influenced by balancing selection. Genetic diversity estimates for candidate loci under directional selection was significantly reduced in comparison to candidate neutral loci, whilst candidate balancing selection loci demonstrated significantly higher levels of genetic diversity (Kruskal–Wallis test, P<0.05). Pairwise Fst estimates based on candidate directional selection loci also demonstrated increased levels of differentiation between study populations. Various candidate loci under selection showed significant inter-chromosomal linkage disequilibrium, suggesting possible gene-networks underling adaptive phenotypes. Furthermore, several loci had significant hits to known genes when performing BLAST searches to NCBI's non-redundant databases, whilst others are known to be derived from expressed sequences even though homology to a known gene could not be established. A number of loci also demonstrated relatively high similarity to transposable elements. The association of these loci to functional and genomically active sequences could in part explain the observed signatures of selection.

Integrated Linkage Map ofHaliotis midaeLinnaeus Based on Microsatellite and SNP Markers

The South African abalone Haliotis midae Linnaeus is the most important aquaculture species in South Africa. Marker-assisted selection is envisioned to play an integral part of the genetic improvement program of abalone, and therefore the generation of linkage maps for quantitative trait loci analyses are necessary. This study reports on a first-generation linkage map for H. midae based on microsatellite and single nucleotide polymorphism (SNP) markers. Ten full-sib families were screened with a total of 508 molecular markers derived from genomic and expressed sequence tag sequences. Linkage maps were constructed for each of the families and combined to create an integrated linkage map. The integrated linkage map consists of 186 markers that included 116 microsatellites and 70 SNPs. These markers mapped to 18 linkage groups, which corresponds to the haploid chromosome number of H. midae. The average genome length was estimated at 1,312 cM, displaying an average marker interval of 6.88 cM with 80% genome coverage. The female map is 1.16-fold longer than the male map, indicating differences in recombination rate between the sexes. The association of markers with known genes as well as with transposon elements was also investigated. This study resulted in the first linkage map constructed for any haliotid in which both microsatellite and SNP markers were used, and the results provide a framework for future applications in quantitative trait loci identification.

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.