pH Control in Recirculating Aquaculture Systems for Pāua (Haliotis iris)

<p>In high intensity recirculated aquaculture systems (RAS), metabolic carbon dioxide can accumulate quickly and have a significant impact on the pH of the culture water. A reduction in growth rate and increased shell deformation have been observed in farmed abalone that has been attributed to reduced pH levels that occur in RAS due to accumulation of CO2 in the culture water. The overall aim of this research programme was to assess two methods of pH control (physical vs. chemical) used in land-based aquaculture systems for the culture of the New Zealand abalone, pāua. In the first study the efficiency of physical carbon dioxide removal from seawater using a cascade column degassing unit was considered. Hydraulic loading, counter current air flow, packing media height, and water temperature were manipulated with the goal of identifying the most effective column configuration for degassing. Three influent water treatments were tested between a range of pH 7.4 to 7.8 (~3.2 to 1.2 mg L-1 CO2 respectively). For all influent CO2 concentrations the resulting pH change between influent and effluent water (immediately post column) were very low, the most effective configuration removed enough CO2 to produce a net gain of only 0.2 of a pH unit. Manipulating water flow, counter current air flow and packing media height in the cascade column had only minor effects on removal efficiency when working in the range of pH 7.4 – 7.8. A secondary study was undertaken to examine the effects on pāua growth of adding chemicals to increase alkalinity. Industrial grade calcium hydroxide (Ca(OH)2) is currently used to raise pH in commercial pāua RAS, however it is unknown if the addition of buffering chemicals affects pāua growth. Replicate pāua tanks were fed with seawater buffered with either sodium hydroxide, food grade Ca(OH)2 or industrial grade Ca(OH)2, with the aim of identifying the effects of buffered seawater on the growth of juvenile pāua (~30 mm shell length). Growth rate ([micrometre]/day) was not significantly affected by the addition of buffering chemicals into the culture water, and the continued use of industrial grade Ca(OH)2 is recommended for the commercial production of pāua in RAS. Shell dissolution is observed in cultured pāua reared in low pH conditions, however there is limited information surrounding the direct effect of lowered pH on the rate of biomineralisation and shell dissolution in abalone. A preliminary investigation was undertaken to examine shell mineralogy, the rate of biomineralisation and shell dissolution of pāua grown at pH 7.6 and 7.9 to determine their sensitivity to lowered pH. It was found that the upper prismatic layer of juvenile pāua shell (~40 mm) was composed almost exclusively of the relatively stable polymorph calcite, that suggests pāua are relatively tolerant to a low pH environment, compared to other abalone species that have proportionately more soluble aragonite in their prismatic layer. Regardless of shell composition, significant shell dissolution was observed in pāua reared in water of pH 7.6. Over the duration of the trial, the rate of mineralisation ([micrometre]/day) was significantly different between pāua reared in pH 7.6 and in pH 7.9 water. However, after a period of acclimation, low pH did not appear to effect rate of mineralisation in pāua.</p>

The Geochemistry of Pāua as a Potential Proxy for Past and Present Environmental Change

<p>Nearshore New Zealand mollusca (shellfish) have the potential to be important archives of environmental conditions and change. Ambient ocean chemistry can be incorporated into the calcium carbonate (CaCO3) shell during the life span of the mollusc providing a high resolution temporal record of the chemical and physical changes of the environments the mollusc lived in. Previous studies on foraminifera and coral have shown that the substitution of magnesium or strontium for calcium (Mg, Sr/Ca) during the formation of the CaCO3 shell is directly correlated with ocean temperatures. Other divalent cations (e.g., Sr2+, Ba2+, Pb2+) can also provide information on ambient salinity, primary productivity or nutrient levels, and local anthropogenic pollution. This study uses new geochemical techniques that have been developed to measure the trace element chemistry of CaCO3 mollusc shells at high temporal resolution, using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in order to calibrate shell chemistry with environmental conditions. This study is the first to explore the use of the geochemistry of Haliotis iris as a potential proxy for (paleo-) environmental conditions. Pāua (Haliotis iris) were collected from six different localities around New Zealand and the Chatham Islands as well as a cultured environment (OceaNZ Blue Ltd). The shells were sectioned following the axis of maximum growth exposing both CaCO3 layers; the prismatic (predominantly calcite) and nacreous (aragonite) layers. The shells were analysed by LA-ICP-MS at 25 μm spot sizes through a high temporal transect of both layers. Observed differences in the element/Ca ratios between the prismatic and nacreous layer reflect the differing crystallinity of each layer. High temporal resolution Mg/Ca ratio data of the prismatic layer of the samples which grew in a cultured environment were compared with temperature and growth data supplied by OceaNZ Blue Ltd. The results showed that temperature was not the primary control on the uptake of Mg within the shells and that influences from biological factors including increased growth rate were also evident. Sr/Ca ratios show a weak inverse relationship with increased growth rate assumed. These results, however, are not reproducible within samples collected from the wild, showing that external factors (high wave energy, diet, predation, lack of food) place metabolic stress on the pāua. The monitoring of other element/Ca including Ba/Ca, Al/Ca, Pb/Ca and Zn/Ca ratios have the potential to provide information into the past frequency of storm events that deliver sediment into the oceans and remobilise other sediments and changing levels of environmental pollution. This is reflected through increased Al/Ca, Pb/Ca and Zn/Ca ratios during the winter season in a number of samples (n = 3) gained from the high resolution analysis of the prismatic layers. Overall, element/Ca ratios are difficult to correlate environmental conditions in samples from the wild as there are many different parameters influencing the uptake of element/Ca ratios with the shells of pāua. Uncertainties lie with a lack of understanding of the biological controls influencing pāua during biomineralisation including the transportation of the elements within organism to the extrapallial fluid to be biomineralised, ontogeny, and the rate and regularity of biomineralisation of shell material.</p>

The Geochemistry of Pāua as a Potential Proxy for Past and Present Environmental Change

<p>Nearshore New Zealand mollusca (shellfish) have the potential to be important archives of environmental conditions and change. Ambient ocean chemistry can be incorporated into the calcium carbonate (CaCO3) shell during the life span of the mollusc providing a high resolution temporal record of the chemical and physical changes of the environments the mollusc lived in. Previous studies on foraminifera and coral have shown that the substitution of magnesium or strontium for calcium (Mg, Sr/Ca) during the formation of the CaCO3 shell is directly correlated with ocean temperatures. Other divalent cations (e.g., Sr2+, Ba2+, Pb2+) can also provide information on ambient salinity, primary productivity or nutrient levels, and local anthropogenic pollution. This study uses new geochemical techniques that have been developed to measure the trace element chemistry of CaCO3 mollusc shells at high temporal resolution, using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in order to calibrate shell chemistry with environmental conditions. This study is the first to explore the use of the geochemistry of Haliotis iris as a potential proxy for (paleo-) environmental conditions. Pāua (Haliotis iris) were collected from six different localities around New Zealand and the Chatham Islands as well as a cultured environment (OceaNZ Blue Ltd). The shells were sectioned following the axis of maximum growth exposing both CaCO3 layers; the prismatic (predominantly calcite) and nacreous (aragonite) layers. The shells were analysed by LA-ICP-MS at 25 μm spot sizes through a high temporal transect of both layers. Observed differences in the element/Ca ratios between the prismatic and nacreous layer reflect the differing crystallinity of each layer. High temporal resolution Mg/Ca ratio data of the prismatic layer of the samples which grew in a cultured environment were compared with temperature and growth data supplied by OceaNZ Blue Ltd. The results showed that temperature was not the primary control on the uptake of Mg within the shells and that influences from biological factors including increased growth rate were also evident. Sr/Ca ratios show a weak inverse relationship with increased growth rate assumed. These results, however, are not reproducible within samples collected from the wild, showing that external factors (high wave energy, diet, predation, lack of food) place metabolic stress on the pāua. The monitoring of other element/Ca including Ba/Ca, Al/Ca, Pb/Ca and Zn/Ca ratios have the potential to provide information into the past frequency of storm events that deliver sediment into the oceans and remobilise other sediments and changing levels of environmental pollution. This is reflected through increased Al/Ca, Pb/Ca and Zn/Ca ratios during the winter season in a number of samples (n = 3) gained from the high resolution analysis of the prismatic layers. Overall, element/Ca ratios are difficult to correlate environmental conditions in samples from the wild as there are many different parameters influencing the uptake of element/Ca ratios with the shells of pāua. Uncertainties lie with a lack of understanding of the biological controls influencing pāua during biomineralisation including the transportation of the elements within organism to the extrapallial fluid to be biomineralised, ontogeny, and the rate and regularity of biomineralisation of shell material.</p>

pH Control in Recirculating Aquaculture Systems for Pāua (Haliotis iris)

<p>In high intensity recirculated aquaculture systems (RAS), metabolic carbon dioxide can accumulate quickly and have a significant impact on the pH of the culture water. A reduction in growth rate and increased shell deformation have been observed in farmed abalone that has been attributed to reduced pH levels that occur in RAS due to accumulation of CO2 in the culture water. The overall aim of this research programme was to assess two methods of pH control (physical vs. chemical) used in land-based aquaculture systems for the culture of the New Zealand abalone, pāua. In the first study the efficiency of physical carbon dioxide removal from seawater using a cascade column degassing unit was considered. Hydraulic loading, counter current air flow, packing media height, and water temperature were manipulated with the goal of identifying the most effective column configuration for degassing. Three influent water treatments were tested between a range of pH 7.4 to 7.8 (~3.2 to 1.2 mg L-1 CO2 respectively). For all influent CO2 concentrations the resulting pH change between influent and effluent water (immediately post column) were very low, the most effective configuration removed enough CO2 to produce a net gain of only 0.2 of a pH unit. Manipulating water flow, counter current air flow and packing media height in the cascade column had only minor effects on removal efficiency when working in the range of pH 7.4 – 7.8. A secondary study was undertaken to examine the effects on pāua growth of adding chemicals to increase alkalinity. Industrial grade calcium hydroxide (Ca(OH)2) is currently used to raise pH in commercial pāua RAS, however it is unknown if the addition of buffering chemicals affects pāua growth. Replicate pāua tanks were fed with seawater buffered with either sodium hydroxide, food grade Ca(OH)2 or industrial grade Ca(OH)2, with the aim of identifying the effects of buffered seawater on the growth of juvenile pāua (~30 mm shell length). Growth rate ([micrometre]/day) was not significantly affected by the addition of buffering chemicals into the culture water, and the continued use of industrial grade Ca(OH)2 is recommended for the commercial production of pāua in RAS. Shell dissolution is observed in cultured pāua reared in low pH conditions, however there is limited information surrounding the direct effect of lowered pH on the rate of biomineralisation and shell dissolution in abalone. A preliminary investigation was undertaken to examine shell mineralogy, the rate of biomineralisation and shell dissolution of pāua grown at pH 7.6 and 7.9 to determine their sensitivity to lowered pH. It was found that the upper prismatic layer of juvenile pāua shell (~40 mm) was composed almost exclusively of the relatively stable polymorph calcite, that suggests pāua are relatively tolerant to a low pH environment, compared to other abalone species that have proportionately more soluble aragonite in their prismatic layer. Regardless of shell composition, significant shell dissolution was observed in pāua reared in water of pH 7.6. Over the duration of the trial, the rate of mineralisation ([micrometre]/day) was significantly different between pāua reared in pH 7.6 and in pH 7.9 water. However, after a period of acclimation, low pH did not appear to effect rate of mineralisation in pāua.</p>

Biomineralization in Polychaete Annelids: A Review

Polychaete annelids are a very important group of calcifiers in the modern oceans. They can produce calcite, aragonite, and amorphous phosphates. Serpulids possess very diverse tube ultra-structures, several unique to them. Serpulid tubes are composed of aragonite or calcite or a mixture of both polymorphs. The serpulid tubes with complex oriented microstructures, such as lamello fibrillar, are exclusively calcitic, whereas tubes with prismatic structures can be composed either of calcite or aragonite. In serpulids, the calcareous opercula also have complex microstructures. Evolutionarily, calcitic serpulid taxa belong to one clade and the aragonitic taxa belong to another clade. Modern ocean acidification affects serpulid biomineralization. Serpulids are capable of biomineralization in extreme environments, such as the deepest part (hadal zone) of the ocean. The tubes of calcareous sabellids are aragonitic and have two layers, the inner irregular spherulitic prismatic layer and the outer spherulitic layer. The tube wall of cirratulids is composed of aragonitic lamellae with a spherulitic prismatic structure. In some other polychaetes, biominerals are formed in different parts of the animal body, such as chaetae or body shields, or occur within the body as granule-shaped or rod-shaped inclusions.

Long-term experimental diagenesis of aragonitic biocarbonates: from organic matter loss to abiogenic calcite formation

Carbonate biological hard tissues are valuable archives of environmental information. However, this information can be blurred or even completely lost as hard tissues undergo diagenetic alteration. This is more likely to occur in aragonitic skeletons because bioaragonite commonly transforms into calcite during diagenesis. For reliably using aragonitic skeletons as geochemical proxies, it is necessary to understand in depth the diagenetic alteration processes that they undergo. Several works have recently investigated the hydrothermal alteration of aragonitic hard tissues during short term experiments at high temperatures (T > 160 °C). In this study, we conduct long term (4 and 6 months) hydrothermal alteration experiments at 80 °C using burial-like fluids. We document and evaluate the changes undergone by the outer and inner layers of Arctica islandica shell, the prismatic and nacreous layers of Haliotis ovina shell, and the skeleton of Porites sp. combining a variety of analytical tools (X-ray diffraction, thermogravimetry analysis, laser confocal microscopy, scanning electron microscopy, electron backscatter diffraction and atomic force microscopy). We demonstrate that this approach is the most adequate to trace subtle, diagenetic alteration-related changes in aragonitic biocarbonates. Furthermore, we unveil that the diagenetic alteration of aragonitic hard tissues is a complex multi-step process where major changes occur even at the low temperature used in this study and well before any aragonite into calcite transformation takes place. Alteration starts with biopolymer decomposition and concomitant generation of secondary porosity. These processes are followed by abiogenic aragonite precipitation that partially or totally obliterates the secondary porosity. Only afterwards any transformation of aragonite into calcite takes place. The kinetics of the alteration is highly dependent on primary microstructural features of the aragonitic biomineral. While the skeleton of Porites sp. remains virtually unaltered within the time spam of the experiments, Haliotis ovina nacre undergoes extensive abiogenic aragonite precipitation, the outer and inner layers of Arctica islandica shell are significantly affected by aragonite transformation into calcite and this transformations extensive in the case of the prismatic layer of Haliotis ovina shell. Our results suggest that most aragonitic fossil archives may be overprinted, even those free of clear diagenetic alteration signs. This finding may have major implications for the use of these archives as geochemical proxies.

PU14, a Novel Matrix Protein, Participates in Pearl Oyster, Pinctada Fucata, Shell Formation

Biomineralization is a widespread biological process, involved in the formation of shells, teeth, and bones. Shell matrix proteins have been widely studied for their importance during shell formation. In 2015, our group identified 72 unique shell matrix proteins in Pinctada fucata, among which PU14 is a matrix protein detected in the soluble fraction that solely exists in the prismatic layer. However, the function of PU14 is still unclear. In this study, the full-length cDNA sequence of PU14 was obtained and functional analyses of PU14 protein during shell formation were performed. The deduced protein has a molecular mass of 77.8 kDa and an isoelectric point of 11.34. The primary protein structure contains Gln-rich and random repeat units, which are typical characteristics of matrix protein and indicate its potential function during shell formation. In vivo and in vitro experiments indicated PU14 has prismatic layer functions during shell formation. The tissue expression patterns showed that PU14 was mainly expressed in the mantle tissue, which is consistent with prismatic layer formation. Notching experiments suggested that PU14 responded to repair and regenerate the injured shell. After inhibiting gene expression by injecting PU14-specific double-stranded RNA, the inner surface of the prismatic layer changed significantly and became rougher. Further, in vitro experiments showed that recombinant protein rPU14 impacted calcite crystal morphology. Taken together, characterization and functional analyses of a novel matrix protein, PU14, provide new insights about basic matrix proteins and their functions during shell formation.