Thèse (Ph. D.) -- Université Laval, 2003. / Bibliogr.: f. 8-14. Publié aussi en version électronique.

Titre de l'écran-titre (visionné le 12 février 2024) / L'homéostasie du calcium (Ca) et du phosphore (P) est affectée par l'équilibre acido-basique systémique, par des mécanismes de régulation qui affectent les os et le système respiratoire. Le bilan électrolytique (BÉ) alimentaire, combiné à l'acidification de l'eau expose les oiseaux à l'acidose. Cette recherche visait à étudier l'impact de l'acidification et du type d'acidifiant : 1) aucun, 2) inorganique (INORGACID; acide phosphorique) et 3) organiques (ORGACID; mix) avec des niveaux de P et Ca normaux (NCaP) ou limitant (FaibleCaP; -15 % Ca et P) dans un dispositif en factoriel 3 x 2. Le niveau du BÉ était de 220 mÉq/kg MS. Un septième traitement alimentaire avait un niveau de BÉ faible 120 mÉq/kg MS avec l'INORGACID et des apports FaibleCaP. Les traitements expérimentaux ont été évalués sur les performances, le statut phosphocalcique et acido-basique et la minéralisation osseuse des poulets. Au total de 3710 poulets mâles âgés d'un jour (Ross 308) ont été distribuée au hasard dans les 7 traitements, avec 10 répétitions de 53 poussins par répétition pendant 3 phases de croissance (0-10, 11-21 et 22-28 jours). Les performances de croissance ont été déterminées par phase. La consommation d'eau a été mesurée quotidiennement par parquet. À la fin de chaque étape, un échantillon de sang de poulet à chair par cage (n = 60) a été prélevé avant l'abattage pour mesurer les paramètres systémiques à l'aide d'un analyseur de gaz dans le sang (i-STAT Alinity v, Abott) et d'un analyseur d'électrolyte, d'immunodosage et de gaz dans le sang (VETSCAN VS2, Abaxis) et DXA pour obtenir le contenu minéral osseux (CMO) et la masse grasse et maigre. Les résultats ont montré que pendant la phase de début et de croissance, les performances étaient réduites chez les poulets FaibleCaP-ORGACID, avec un gain quotidien moyen (GMQ; -5 %) et le poids corporel diminué (PV final -7%). Le Ca plasmatique (Acidifiant x CaP; P=0,016, 0,031, 0,07 respectivement au début). Ainsi que le PV final et l'indice de conversion (IC) au croissance (Acidifiant x CaP; P = 0,06, 0,07 respectivement). Le CMO diminuait dans le régime FaibleCaP pendant le début seulement lorsque les poulets avaient reçu l'INORGACID (Acidifiant x CaP; P=0,047). Une diminution du gain quotidien moyen (GMQ; -5 %), poids corporel (PV -7 %) et une tendance pour une diminution du Ca plasmatique a également été observée dans le régime FaibleCaP pendant le début, mais au contraire seulement quand les poulets ont reçu l'ORGACID (Acidifiant x CaP; P=0,016, 0,031, 0,07 respectivement). Pendant la phase de croissance, la CMO a également diminué ainsi que le P plasmatique dans le régime FaibleCaP (-15 % et -16 %; CaP, P<0,001). Pour la finition la réduction du CaP a eu un impact plus faible (-10 %) sur la CMO/PV avec INORGACID que l'ORGACID (-18 %) et aucune acidification (-28 %; Acidifiant x CaP; P=0,05). L'évolution de la CMO au fil du temps a montré que les oiseaux recevants de l'INORGACID n'avaient pas un CMO réduit lorsqu'ils recevaient un régime FaibleCaP (temps x CaP x acidifiant; P<0,001). Cela indique que l'apport en P sous forme d'acide inorganique est suffisant pour faire face à l'effet de réduction de Ca et P sur la minéralisation osseuse. Néanmoins, les acidifiants d'eau testés n'ont pas amélioré les performances de croissance. D'autres études sont nécessaires pour comprendre leurs effets et optimiser les pratiques d'acidification de l'eau. / Calcium (Ca) and phosphorus (P) homeostasis is affected by systemic acid-base balance, by regulatory mechanisms that affect the bones and respiratory system. Dietary electrolyte balance (DEB) combined with water acidification creates a bacteriostatic effect that exposes birds to acidosis. This research aimed to study the impact of acidification and the type of acidifier: 1) none, 2) inorganic (INORGACID; phosphoric acid) and 3) organic (ORGACID; mix) with normal P and Ca levels (NCaP) or limiting Ca and P (LowCaP; -15% Ca and P) in a 3 x 2 factorial device. The DEB level was 220 mEq/kg DM. A seventh treatment had a low level of DEB (120 mEq/kg DM) with INORGACID and LowCaP intakes on performance, phosphocalcic and acid-basic status and mineralization in broilers. A total of 3710 male day-old broilers (Ross 308) were randomly distributed to the 7 treatments, with 10 repetitions of 53 chicks per repetition during 3 growth phases (0-10, 11-21 and 22-28 days). Growth performance was determined at each phase. Water consumption was measured daily by cage. At the end of each step, one broiler blood sample per cage (n = 60) was taken before slaughter to measure systemic parameters with a blood gas analyzer (i-STAT Alinity v, Abott) and an electrolyte, immunoassay, and blood gas analyzer (VETSCAN VS2, Abaxis) and DXA scanning to obtain bone mineral content (BMC) and fat and lean mass. The results showed that during the start and growth phase, broilers are more sensitive to LowCaP level and ORGACID, mainly in average daily gain (ADG; -5%), body weight (BW -7%) and plasma Ca (Acidifier x CaP; P=0.016, 0.031, 0.07 respectively at start). As well as the BW and conversion index (CI) to growth (Acidifier x CaP; P = 0.06, 0.07 respectively). BMC decreased in the LowCaP diet during the start phase only when broilers received INORGACID (Acidifier x CaP; P=0.047). A decrease in average daily gain (ADG; -5%), body weight (BW -7%) and a trend for decreased plasma Ca was also observed in the LowCaP diet during the start phase, but only when broilers received ORGACID (Acidifier x CaP; P=0.016, 0.031, 0.07 respectively). During the growth phase, BMC also decreased as well as plasma P in the LowCaP regime (-15% and -16%; CaP, P<0.001). For finishing CaP reduction had a lower impact (- 10%) on BMC/BW with INORGACID than ORGACID (-18%) and no acidification (-28%; Acidifier x CaP; P=0.05). The evolution of BMC over time showed that birds receiving INORGACID did not have a reduced BMC when given a LowCaP regime (time x CaP x acidifying; P<0.001). This indicates that the intake of P as inorganic acid is sufficient to support the reducing effect of Ca and P on bone mineralization. However, the water acidifiers tested did not improve growth performance. Further studies are needed to understand their effects and optimize water acidification practices.

Anthropogenic carbon dioxide (CO2) emissions are increasing the atmospheric CO2 concentration and the oceans are absorbing around 1/3 them. The CO2 hydrolysis increases the H+ concentration, decreasing the pH, while the proportions of the HCO3- and CO32- ions are also affected. This process already led to a decrease of 0.1 pH units in surface seawater. According to "business-as-usual" models, provided by the Intergovernmental Panel on Climate Change (IPCC), the pH is expected to decrease 0.3-0.5 units by 2100 and 0.7-0.8 by 2300. As a result the surface ocean carbonates chemistry will also change: with increasing pCO2, dissolved inorganic carbon will increase and the equilibrium of the carbonate system will shift to higher CO2 and HCO3– levels, while CO32– concentration will decrease. Surface seawaters will progressively become less saturated towards calcite and aragonite saturation state and some particular polar and cold water regions could even become completely undersaturated within the next 50 years. <p>Responses of marine organisms to environmental hypercapnia, i.e. to an excess of CO2 in the aquatic environment, can be extremely variable and the degree of sensitivity varies between species and life stages. Sea urchins are key stone species in many marine ecosystems. They are considered to be particularly vulnerable to ocean acidification effects not only due to the nature of their skeleton (magnesium calcite) whose solubility is similar or higher than that of aragonite, but also because they lack an efficient ion regulatory machinery, being therefore considered poor acid-base regulators. Populations from polar regions are expected to be at an even higher risk since the carbonate chemical changes in surface ocean waters are happening there at a faster rate. <p>The goal of this work was to study the effects of low seawater pH exposure of different life stages of sea urchins, in order to better understand how species from different environments and/or geographic origins would respond and if there would be scope for possible adaptation and/or acclimatization.<p>In a first stage we investigated the effects of ocean acidification on the early stages of an intertidal species from temperate regions, the Atlantic Paracentrotus lividus sea urchin, and of a sub-Antarctic species, Arbacia dufresnei. The fertilization, larval development and larval growth were studied on specimens submitted through different pH experimental treatments. The fertilization rate of P. lividus gametes whose progenitors came from a tide pool with high pH decrease was significantly higher, indicating a possible acclimatization or adaptation of gametes to pH stress. Larval size in both species decreased significantly in low pH treatments. However, smaller A. dufresnei echinoplutei were isometric to those of control treatments, showing that size reduction was most likely due to a slower growth rate. In the pH 7.4 (predicted for 2300) treatment, P. lividus presented significantly more abnormal forms than control ones, but A. dufresnei did not. The latter does not seem to be more vulnerable than temperate species, most likely due to acclimatization/adaptation to lower pH seasonal fluctuations experienced by individuals of this population during spring time.<p>In a second stage, adult physiological responses of P. lividus and A. dufresnei to low pH seawaters were studied. Intertidal field P. lividus specimens can experience pH fluctuations of 0.4 units during low tidal cycles, but their coelomic fluid pH will not change. During experimental exposure to low pH, the coelomic fluid (extracellular) pH of both species decreased after weeks of exposure to low seawater pH. However, it owned a certain buffer capacity (higher than that of seawater) which did not seem to be related to passive skeleton dissolution. In laboratory studies, the feeding rate of P. lividus, the RNA/DNA ratio (proxy for protein synthesis and thus metabolism) of both the gonads and the body wall of the studied species and the carbonic anhydrase activity in the body wall (an enzyme involved in calcification and respiratory processes) of A. dufresnei did not differ according to seawater pH. The same was true for spine regeneration (a proxy for calcification) of both species. This shows that both P. lividus and A. dufresnei are able to cope when exposed to mild hypercapnia (lowest investigated pH 7.4) for a mid-term period of time (weeks). In a different set of experiments, pH effects were tested on P. lividus individuals together with two temperatures (10ºC and 16ºC). The pH decrease of the coelomic fluid did not vary between temperatures, neither did its buffer response. The oxygen uptake rates of P. lividus (as a proxy for global metabolic state of the whole organism) increased in lower pH treatments (7.7 and 7.4) in organisms exposed to lower temperatures (10ºC), showing that this was upregulated and that organisms experienced a higher energetic demand to maintain normal physiological functions. For instance, gonad production (given by the RNA/DNA ratio) was not affected neither by temperature, nor pH.<p>Finally, possible morphological and chemical adaptations of cidaroid (“naked”) spines, which are not covered by epidermis, to low magnesium calcite saturation states were investigated. Deep sea field specimens from the Weddell Sea (Antarctica), Ctenocidaris speciosa were studied. Cidaroid spines have an exterior skeleton layer with a polycrystalline constitution that apparently protects the interior part of the monocrystaline skeleton, the stereom (tridimensional magnesium calcite lattice). The cortex of C. speciosa was by its turn divided into two layers. From these, it presented a thicker inner cortex layer and a lower Mg content in specimens collected below the aragonite saturation horizon. The naked cortex seems able to resist to low calcium carbonate saturation state. We suggest that this could be linked to the important organic matrix that surrounds the crystallites of the cortex.<p>Some echinoid species present adaptive features that enable them to deal with low pH stresses. This seems to be related to the environmental conditions to which populations are submitted to. Therefore, organisms already submitted to pH daily or seasonal fluctuations or living in environments undersaturated in calcium carbonate seem to be able to cope with environmental conditions expected in an acidified ocean. Under the realistic scenario of a decrease of ca. 0.4 units of pH by 2100, sea urchins, and echinoderms in general, appear to be robust for most studied processes. Even thought, this general response can depend on different parameters such as exposure time, pH level tested, the process and the life stage considered, our results show that there is scope for echinoids to cope with ocean acidification.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Les changements globaux ont le potentiel d'altérer les cycles biogéochimiques entraînant des répercussions pour tout le réseau alimentaire. Puisque l'azote est généralement l'élément limitant en milieu estuarien, une altération de son cycle pourrait influencer l'ampleur et le type de production primaire ainsi que la composition de la communauté phytoplanctonique qui l'effectue. Il en va de même pour la composition de la matière organique qui peut affecter la valeur nutritive des algues pour les consommateurs de même que l'efficacité de la pompe biologique. Actuellement, aucune étude portant sur les impacts combinés de l'acidification et du réchauffement des eaux de l'estuaire maritime du Saint-Laurent n'a été réalisée. L'objectif de ce projet de maîtrise fut d'évaluer expérimentalement, à l'aide de mésocosme, les impacts cumulés que ces changements pourraient avoir sur la dynamique des nutriments et de l'azote en particulier ainsi que sur la composition élémentaire de la matière organique. Une combinaison factorielle de six pH (7,2; 7,4; 7,6; 7,8; 8,0 et un pH sans contrôle) et de deux températures (10 et 15°C) fut employée. Les résultats de l'expérience suggèrent que les organismes responsables des processus à l'étude sont tolérants à une diminution considérable du pH. Ceux-ci furent toutefois affectés par la hausse de température, qui entraîna une diminution du ratio N:P de consommation des nutriments, accéléra le développement de la floraison phytoplanctonique et l'épuisement des nutriments, puis mena à un changement taxonomique en fin d'expérience. Ce changement est possiblement responsable des différences observées dans la composition de la matière organique particulaire (POM) lors du déclin de la floraison planctonique (diminution des ratios POC:PON, POC:POP, POC:BSi et hausse du ratio BSi:PON). Ces résultats suggèrent que pour l'estuaire maritime du Saint-Laurent, le réchauffement pourrait entraîner des changements stœchiométriques au sein de la POM avec des conséquences probables pour les niveaux trophiques supérieurs et la pompe biologique.