Response of cold-acclimated, farmed South African abalone (Haliotis midae) to short-term and long-term changes in temperature

Characterization and expression patterns of the Fox gene family under heat and cold stress in Manila clam Ruditapes philippinarum based on genome-wide identification

In this study, the Fox gene family of Ruditapes philippinarum was identified by bioinformatics analysis and genome data. The results showed that a total of 21 Fox genes were identified in R. philippinarum, which were divided into 16 subfamilies, including two members of Foxa subfamily (Foxa1, Foxa2), three members of Foxl subfamily (Foxl1b, Foxl1a, FOXL2), three members of Foxn subfamily (FOXN3, FOX4A, Foxn4b) and one member of other families. The chromosome distribution, domains, conserved motifs, introns, exons and protein tertiary structures of these 21 Fox genes were predicted. By analyzing the RNA-seq data of R. philippinarum, it was found that the Fox gene family was differentially expressed in different tissues, different developmental stages and under heat and cold stress. Most of Fox genes were highly expressed in four tissues: labial palp, gonad, gill and foot. Most of the Fox genes were highly expressed in blastula stage. Most of the Fox genes were highly expressed in high temperature group of two populations, and Foxo, FOXG1 were highly expressed in low temperature group. In addition, qPCR showed that the expression levels of Foxo and Foxj1b genes increased significantly under acute cold stress. Therefore, we speculate that Fox genes may play important roles in embryo development and the temperature stress of R. philippinarum, and this study provides a basis for further exploring the molecular mechanism of low temperature tolerance mediated by Fox.

Development of a semi-quantitative scoring protocol for gill lesion assessment in greenlip abalone Haliotis laevigata held at elevated water temperature

Water temperatures that exceed thermal optimal ranges (~19 to 22°C for greenlip abalone Haliotis laevigata, depending on stock genetics) can be associated with abalone mortalities. We assessed histopathological changes in H. laevigata gills held in control (22°C) or elevated (25°C) water temperature conditions for 47 d by developing a new scoring protocol that incorporates histopathological descriptions and relative score summary. Lesions were allocated to 1 of 3 reaction patterns, (1) epithelial, (2) circulatory or (3) inflammatory, and scored based on their prevalence in gill leaflets. Indices for each reaction pattern were calculated and combined to provide an overall gill index. H. laevigata held in 25°C water temperature had significantly more epithelial lifting and hemolymph channel enlargement and significantly higher gill and circulatory reaction pattern indices than H. laevigata held in 22°C water temperature. One H. laevigata had a proliferation of unidentified cells in the v-shaped skeletal rod of a gill leaflet. The unidentified cells contained enlarged nuclei, a greater nucleus:cytoplasm ratio and, in some cases, mitotic figures. This cell population could represent a region of hematopoiesis in response to hemocyte loss or migration to a lesion. Without thorough diagnostic testing, the origin of these larger cells cannot be confirmed. The new scoring protocol developed will allow the standard quantification of gill lesions for H. laevigata, specifically for heat-related conditions, and could further be adapted for other Haliotis spp.

Behaviors and biochemical responses of macroinvertebrate Corbicula fluminea to polystyrene microplastics

Microplastic, a well-documented emerging contaminant, is widespread in aquatic environments resulting from the production and fragmentation of large plastics items. The knowledge about the chronic toxic effects and behavioral toxicity of microplastics, particularly on freshwater benthic macroinvertebrates, is limited. In this study, adult Asian clams (Corbicula fluminea) were exposed to gradient microplastic solutions for 42 days to evaluate behavioral toxicity and chronic biotoxicity. The results showed that microplastics caused behavior toxicity, oxidative stress, and tissue damage in high-concentration treatments. Siphoning, breathing, and excretion was significantly inhibited (p < 0.05) at high-concentration treatments, suggesting that high-concentration microplastics induced behavioral toxicity in C. fluminea. Malondialdehyde content, superoxide dismutase, catalase, and glutathione reductase activities were significantly enhanced (p < 0.05) and the acetylcholinesterase was significantly inhibited (p < 0.05) throughout the exposure period in high-concentration treatments. Enzymes associated with energy supply were significantly higher at high-concentration microplastics treatments on D7 and D21. However, they recovered to a normal level on D42. The instability of the enzymes indicated that high-concentration microplastics induced oxidative stress and disorder in neurotransmission and energy supply. The gills of C. fluminea in treatments underwent cilia degeneration, which indicated that microplastics caused tissue damage in the gills. The analysis of integrated biomarker response values revealed that high-concentration microplastics led to long-term effects on the health of C. fluminea. In conclusion, continuous exposure to microplastics (10 mg L^-1) would damage physical behavior and the antioxidant system of C. fluminea.

Growth Performance and Transcriptomic Response of Warm-Acclimated Hybrid Abalone Haliotis rufescens (♀) × H. corrugata (♂)

Along the Pacific coast of the Baja California Peninsula (Mexico), abalone represents one of the most lucrative fisheries. As wild populations are currently depleted, abalone farm production aims to balance the decreasing populations with the increasing demand. The Mexican abalone aquaculture is almost entirely based on red abalone (Haliotis rufescens). However, the increasing frequency of extreme temperature events is hampering this activity. The use interspecific hybrids can potentially improve abalone culture, as species have differences in their thermal tolerance. Therefore, the hybrid progeny between H. rufescens (♀) and pink abalone H. corrugata (♂), a temperate and a warmer water abalone species, respectively, will naturally support higher temperature. To test this hypothesis, growth rate, mortality and metabolic rate of both pure (RR) and hybrid abalone (RP) were assessed under the H. rufescens' optimum (18 °C) and thermally stressed (22 °C) conditions. To unveil the molecular pathways involved in the heat response, transcriptional profiling of both crosses was also investigated. At high temperature, we observed constrained growth and survival in RR while RP showed a significant increase in both rates, supporting the improved performance of the hybrid compared. These results match with the transcriptional profiling of hybrids showing higher expression of genes involved in growth and calcification, whereas in the pure red progeny, the transcriptional profile was mainly associated with the regulation of necroptosis process. Our results may contribute to propose new management plans to increase farm abalone production in Baja California.

Metabolomics Adaptation of Juvenile Pacific Abalone Haliotis discus hannai to Heat Stress

Temperature fluctuation is a key abiotic factor for the growth and survival of Pacific abalone Haliotis discus hannai, particularly during climate change. However, the physiological mechanism underlying the abalones’ response to heat stress remains unknown. We sought to understand the metabolic adaptation mechanism of Pacific abalone to heat stress for further analyzing its heat tolerance capacity. For two groups experienced different acclimate temperature (10 °C and 30 °C for 62 days), the Pacific abalone juveniles displayed significantly different survival rates under 31 °C acute heat treatment. A total of 1815 and 1314 differential metabolites were identified from the 10 °C and 30 °C acclimate groups respectively, by comparing mass spectrometry data of the samples before and after heat stimulation. Heat stress led to mitochondrial failure, resulting in incomplete oxidative metabolism of amino acids and fatty acids in the mitochondria, and massive accumulation of unstable metabolic intermediates in cells. The 10 °C acclimated group accumulated more harmful substances after heat stimulation, provoking further stress responses and pathophysiological processes. In comparison, the 30 °C acclimated group showed stronger regulation capacity to produce beneficial substances for metabolic homeostasis. The findings provided insight into the heat response of marine animals, especially concerning mitochondrial metabolism.

Transcriptome analysis of the Yesso scallop, Patinopecten yessoensis gills in response to water temperature fluctuations

Water temperature fluctuations are considered to be a major factor affecting the immune functions and metabolic processes of scallops. To better understand the immune defense mechanisms of Yesso scallop, Patinopecten yessoensis following exposure to water temperature fluctuations, transcriptomic profiles in the gills from high-frequency fluctuations (HF_G), low-frequency fluctuations (LF_G), and no fluctuations (NF_G) groups were obtained using HiSeq™ 2500 (Illumina). For HF_G, scallops were transferred directly between 18 and 8 °C every 4 h and for 10 fluctuations, while scallops in LF_G were transferred between 18 and 13 °C every 12 h, for a total of 4 fluctuations. A total of 442,922,590 clean reads were generated in 9 libraries and then assembled into 210,780 unigenes with an average length of 705 bp and an N50 of 1253 bp. Based on sequence similarity, 54,529 unigenes (25.87%) were annotated in at least one database. Comparative analysis revealed that 696 unigenes differentially expressed in temperature stressed groups compared with the control, including 229 unigenes between HF_G and NF_G, and 548 unigenes between LF_G and NF_G, respectively. Additionally, among these differentially expressed genes (DEGs), there were 41 immune-related unigenes and 16 protein metabolism-related unigenes. These results provide fundamental information on the molecular defense mechanisms in the Yesso scallop gills after exposure to water temperature fluctuations.

Local oceanographic variability influences the performance of juvenile abalone under climate change

Climate change is causing warming, deoxygenation, and acidification of the global ocean. However, manifestation of climate change may vary at local scales due to oceanographic conditions. Variation in stressors, such as high temperature and low oxygen, at local scales may lead to variable biological responses and spatial refuges from climate impacts. We conducted outplant experiments at two locations separated by ~2.5 km and two sites at each location separated by ~200 m in the nearshore of Isla Natividad, Mexico to assess how local ocean conditions (warming and hypoxia) may affect juvenile abalone performance. Here, we show that abalone growth and mortality mapped to variability in stress exposure across sites and locations. These insights indicate that management decisions aimed at maintaining and recovering valuable marine species in the face of climate change need to be informed by local variability in environmental conditions.

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

Functional 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.

Summary: We report, for the first time, a metabolic map of abalone metabolism in response to functional hypoxia, compiled from results obtained by metabolomics analysis.

Uncovering the metabolic response of abalone (Haliotis midae) to environmental hypoxia through metabolomics

INTRODUCTION

Oxygen is essential for metabolic processes and in the absence thereof alternative metabolic pathways are required for energy production, as seen in marine invertebrates like abalone. Even though hypoxia has been responsible for significant losses to the aquaculture industry, the overall metabolic adaptations of abalone in response to environmental hypoxia are as yet, not fully elucidated.

OBJECTIVE

To use a multiplatform metabolomics approach to characterize the metabolic changes associated with energy production in abalone (Haliotis midae) when exposed to environmental hypoxia.

METHODS

Metabolomics analysis of abalone adductor and foot muscle, left and right gill, hemolymph, and epipodial tissue samples were conducted using a multiplatform approach, which included untargeted NMR spectroscopy, untargeted and targeted LC-MS spectrometry, and untargeted and semi-targeted GC-MS spectrometric analyses.

RESULTS

Increased levels of anaerobic end-products specific to marine animals were found which include alanopine, strombine, tauropine and octopine. These were accompanied by elevated lactate, succinate and arginine, of which the latter is a product of phosphoarginine breakdown in abalone. Primarily amino acid metabolism was affected, with carbohydrate and lipid metabolism assisting with anaerobic energy production to a lesser extent. Different tissues showed varied metabolic responses to hypoxia, with the largest metabolic changes in the adductor muscle.

CONCLUSIONS

From this investigation, it becomes evident that abalone have well-developed (yet understudied) metabolic mechanisms for surviving hypoxic periods. Furthermore, metabolomics serves as a powerful tool for investigating the altered metabolic processes in abalone.

Epipodial Tentacle Gene Expression and Predetermined Resilience to Summer Mortality in the Commercially Important Greenlip Abalone, Haliotis laevigata

"Summer mortality" is a phenomenon that occurs during warm water temperature spikes that results in the mass mortality of many ecologically and economically important mollusks such as abalone. This study aimed to determine whether the baseline gene expression of abalone before a laboratory-induced summer mortality event was associated with resilience to summer mortality. Tentacle transcriptomes of 35 greenlip abalone (Haliotis laevigata) were sequenced prior to the animals being exposed to an increase in water temperature-simulating conditions which have previously resulted in summer mortality. Abalone derived from three source locations with different environmental conditions were categorized as susceptible or resistant to summer mortality depending on whether they died or survived after the water temperature was increased. We detected two genes showing significantly higher expression in resilient abalone relative to susceptible abalone prior to the laboratory-induced summer mortality event. One of these genes was annotated through the NCBI non-redundant protein database using BLASTX to an anemone (Exaiptasia pallida) Transposon Ty3-G Gag Pol polyprotein. Distinct gene expression signatures were also found between resilient and susceptible abalone depending on the population origin, which may suggest divergence in local adaptation mechanisms for resilience. Many of these genes have been suggested to be involved in antioxidant and immune-related functions. The identification of these genes and their functional roles have enhanced our understanding of processes that may contribute to summer mortality in abalone. Our study supports the hypothesis that prestress gene expression signatures are indicative of the likelihood of summer mortality.

The role of hybridization in improving the immune response and thermal tolerance of abalone

Recently, frequent death of cultured abalone drew our attention to the stress tolerance of abalone. Hybridization is an effective way of genetic improvement in aquaculture, which can introduce improved traits to the hybrids. In this study, we challenged the hybrids between Haliotis discus hannai and Haliotis gigantea, and their parents with bacteria (vibrio harveyi, vibrio alginolyticus and vibrio parahemolyticus), then held them at 20 °C and 28 °C, survival rates of the parental populations and hybrid populations were recorded. Then we tested the immune responses and thermal-induced responses of the four populations at different temperatures. Total hemocyte count (THC), respiratory burst, superoxide dismutase activity (SOD), acid phosphatase activity (ACP), alkaline phosphatase activity (AKP), myeloperoxidase activity (MPO), and HSP70 expression were determined on day 1 and day 7 of the temperature exposure. Results showed higher survival rates of the hybrids than their parents against bacteria challenge. For immune parameters, THCs were evaluated at 28 °C, while increased THC was also observed in H. discus hannai ♀ × H. gigantea ♂ (DG) and H. discus hannai ♀ × H. discus hannai ♂ (DD) at 12 °C (day 7); at 28 °C, respiratory burst was activated (day 1 and 7), while SOD activity first rose then fell over 7-days exposure; AKP activity was elevated at 12 °C and 28 °C (day 1), most notably in DG, and an increased level of ACP was observed in DG at 28 °C (day 7); MPO activity was suppressed at 12 °C and 28 °C on day 1, but recovered on day 7. For HSP70, increased HSP70 levels were observed in all populations at 28 °C (day 1), and DD got the lowest HSP70 level after 7-days exposure at 28 °C. Overall, the results suggest that temperature changes could significantly affect the physiological status of abalone, and hybrids may be more resistant to disease and thermal stresses than their parents.

Acute responses of brown mussel (Perna perna) exposed to sub-lethal copper levels: integration of physiological and cellular responses

This study examined the effect of sub-lethal copper levels on selected physiological and cellular responses of the marine bivalve Perna perna. Animals were exposed to five environmentally relevant concentrations of 12.5, 25.0, 37.5 and 50.0 μg L⁻¹ copper and metal accumulation was found to be significantly increased at the two higher copper concentrations after 24 h of exposure. Physiological responses found to increase during acute copper exposure included mucus secretion rate (at 25 and 50 μg L⁻¹ copper), nitrogen excretion rates and oxygen consumption rates (both at 25 and 50 μg L⁻¹ copper). Perna perna changed its substrate utilisation at 25, 37.5 and 50 μg L⁻¹ copper in favour of protein-based metabolism. A higher degree of ROS induced DNA damage was observed at acute exposure to 37.5 and 50 μg L⁻¹ copper. Filtration rate was unchanged during acute copper exposure. A model is proposed that integrates cellular and physiological responses to copper during short-term acute and long-term chronic exposures.