Satellite remote sensing reveals a positive impact of living oyster reefs on microalgal biofilm development

Satellite remote sensing (RS) is routinely used for the large-scale monitoring of microphytobenthos (MPB) biomass in intertidal mudflats and has greatly improved our knowledge of MPB spatio-temporal variability and its potential drivers. Processes operating on smaller scales however, such as the impact of benthic macrofauna on MPB development, to date remain underinvestigated. In this study, we analysed the influence of wild Crassostrea gigas oyster reefs on MPB biofilm development using multispectral RS. A 30-year time series (1985-2015) combining high-resolution (30 m) Landsat and SPOT data was built in order to explore the relationship between C. gigas reefs and MPB spatial distribution and seasonal dynamics, using the normalized difference vegetation index (NDVI). Emphasis was placed on the analysis of a before-after control-impact (BACI) experiment designed to assess the effect of oyster killing on the surrounding MPB biofilms. Our RS data reveal that the presence of oyster reefs positively affects MPB biofilm development. Analysis of the historical time series first showed the presence of persistent, highly concentrated MPB patches around oyster reefs. This observation was supported by the BACI experiment which showed that killing the oysters (while leaving the physical reef structure, i.e. oyster shells, intact) negatively affected both MPB biofilm biomass and spatial stability around the reef. As such, our results are consistent with the hypothesis of nutrient input as an explanation for the MPB growth-promoting effect of oysters, whereby organic and inorganic matter released through oyster excretion and biodeposition stimulates MPB biomass accumulation. MPB also showed marked seasonal variations in biomass and patch shape, size and degree of aggregation around the oyster reefs. Seasonal variations in biomass, with higher NDVI during spring and autumn, were consistent with those observed on broader scales in other European mudflats. Our study provides the first multi-sensor RS satellite evidence of the promoting and structuring effect of oyster reefs on MPB biofilms

Satellite remote sensing reveals a positive impact of living oyster reefs on microalgal biofilm development

Satellite remote sensing (RS) is routinely used for the large-scale monitoring of microphytobenthos (MPB) biomass in intertidal mudflats and has greatly improved our knowledge of MPB spatio-temporal variability and its potential drivers. Processes operating on smaller scales however, such as the impact of benthic macrofauna on MPB development, to date remain underinvestigated. In this study, we analysed the influence of wild Crassostrea gigas oyster reefs on MPB biofilm development using multispectral RS. A 30-year time series (1985–2015) combining high-resolution (30 m) Landsat and SPOT data was built in order to explore the relationship between C. gigas reefs and MPB spatial distribution and seasonal dynamics, using the normalized difference vegetation index (NDVI). Emphasis was placed on the analysis of a before–after control-impact (BACI) experiment designed to assess the effect of oyster killing on the surrounding MPB biofilms. Our RS data reveal that the presence of oyster reefs positively affects MPB biofilm development. Analysis of the historical time series first showed the presence of persistent, highly concentrated MPB patches around oyster reefs. This observation was supported by the BACI experiment which showed that killing the oysters (while leaving the physical reef structure, i.e. oyster shells, intact) negatively affected both MPB biofilm biomass and spatial stability around the reef. As such, our results are consistent with the hypothesis of nutrient input as an explanation for the MPB growth-promoting effect of oysters, whereby organic and inorganic matter released through oyster excretion and biodeposition stimulates MPB biomass accumulation. MPB also showed marked seasonal variations in biomass and patch shape, size and degree of aggregation around the oyster reefs. Seasonal variations in biomass, with higher NDVI during spring and autumn, were consistent with those observed on broader scales in other European mudflats. Our study provides the first multi-sensor RS satellite evidence of the promoting and structuring effect of oyster reefs on MPB biofilms

Ecological impacts of non-native Pacific oysters (Crassostrea gigas) and management measures for protected areas in Europe

Pacific oysters are now one of the most ‘globalised’ marine invertebrates. They dominate bivalve aquaculture production in many regions and wild populations are increasingly becoming established, with potential to displace native species and modify habitats and ecosystems. While some fishing communities may benefit from wild populations, there is now a tension between the continued production of Pacific oysters and risk to biodiversity, which is of particular concern within protected sites. The issue of the Pacific oyster therefore locates at the intersection between two policy areas: one concerning the conservation of protected habitats, the other relating to livelihoods and the socio-economics of coastal aquaculture and fishing communities. To help provide an informed basis for management decisions, we first summarise evidence for ecological impacts of wild Pacific oysters in representative coastal habitats. At local scales, it is clear that establishment of Pacific oysters can significantly alter diversity, community structure and ecosystem processes, with effects varying among habitats and locations and with the density of oysters. Less evidence is available to evaluate regional-scale impacts. A range of management measures have been applied to mitigate negative impacts of wild Pacific oysters and we develop recommendations which are consistent with the scientific evidence and believe compatible with multiple interests. We conclude that all stakeholders must engage in regional decision making to help minimise negative environmental impacts, and promote sustainable industry development

Does bivalve mucus favour the growth of their main food source, microalgae?

Bivalves, by releasing inorganic nutrients, can stimulate the growth of the primary producers on which they feed. Dissolved excretion and mineralization of biodeposits (pseudofaeces and faeces), two indirect processes related to their feeding activity, have already been identified. This study investigated whether microalgal growth is also dependent on the mucus secreted by bivalves and rejected with their biodeposits. An experimental study based on algal growth tests was conducted to determine whether the mucus coating the pseudofaeces and faeces of the oyster Crassostrea gigas (Thunberg) could stimulate the growth of nine marine microalgae: a Prasinophyceae [Tetraselmis suecica (Butcher)] and eight Diatomophyceae [Amphora sp. (Ehrenberg), Chaetoceros sp. (Ehrenberg), Entomoneis alata (Ehrenberg), Haslea ostrearia (Simonsen), Nitzschia acicularis (Wm Smith), N. closterium (Wm Smith), N. gandersheimiensis (Krasske) and Skeletonema costatum (Cleve)]. Oysters were fed only inorganic particles at a concentration well above the threshold of pseudofaeces production. A fraction of pseudofaeces and faeces was then inoculated into glass tubes containing a single algal species. Algal growth tests showed that mucus stimulated the growth of four of the nine species studied: Chaetoceros sp., H. ostrearia, N. gandersheimiensis and T. suecica. The strongest responses were observed with H. ostrearia and Chaetoceros sp., for which mean algal biomass was significantly higher with mucus originating from pseudofaeces than faeces. Monitoring of the release of dissolved components from mucus showed significant enrichment in inorganic phosporus. The use of an antibiotic treatment suggested that this dissolved component is released by simple solubilization rather than by bacterial breakdown.Les bivalves, en relarguant des sels nutritifs, peuvent stimuler la croissance des microalgues dont ils se nourrissent. L'excrétion dissoute et la minéralisation de leurs biodépôts (pseudofèces et fèces), deux processus liés à leur alimentation, ont déjà été identifiés. Dans ce travail, il est envisagé que la croissance des microalgues puisse être aussi stimulée par le mucus sécrété par les bivalves et rejeté dans leurs biodépôts. Une étude expérimentale fondée sur des tests de croissance algale a été réalisée afin de déterminer si le mucus enrobant les pseudofèces et les fèces de l'huître Crassostrea gigas (Thunberg) pouvait stimuler la croissance de neuf microalgues marines : une Prasinophycée [Tetraselmis suecica (Butcher)] et huit Diatomophycées [Amphora sp. (Ehrenberg), Chaetoceros sp. (Ehrenberg), Entomoneis alata (Ehrenberg), Haslea ostrearia (Simonsen), Nitzschia acicularis (Wm Smith), N. closterium (Wm Smith), N. gandersheimiensis (Krasske) et Skeletonema costatum (Cleve)]. Les huîtres sont alimentées uniquement par des particules inorganiques à une concentration très supérieure au seuil de production des pseudofèces. Une fraction des pseudofèces et fèces est alors inoculée dans des tubes en verre contenant une espèce de microalgue. Les tests de croissance algale montrent que le mucus stimule la croissance de quatre des neuf espèces étudiées : Chaetoceros sp., H. ostrearia, N. gandersheimiensis et T. suecica. Les réponses les plus fortes sont obtenues avec Chaetoceros sp. et H. ostrearia, pour lesquelles la biomasse algale moyenne est significativement plus importante avec le mucus provenant des pseudofèces qu'avec celui provenant des fèces. Un suivi du relargage de composés dissous par le mucus montre un enrichissement significatif en phosphore inorganique. Un traitement antibiotique suggère que ce composé dissous est libéré par simple solubilisation du mucus plutôt que par dégradation bactérienne

Reduction of the developmental competence of sheep oocytes by inhibition of LH pulses during the follicular phase with a GnRH antagonist

International audienc

Growth and biochemical composition of a microphytobenthic diatom (Entomoneis paludosa) exposed to shorebird (Calidris alpina) droppings

International audienc

Possibilités de l'immunisation contre les stéroïdes pour améliorer les performances ovulatoires et la taille de la portée des ovins et caprins

L’immunisation active (par vaccination) ou passive (par injection de sérum) contre un stéroïde ovarien, l’androsiènedione, permet d’améliorer les performances de reproduction et de production dans la plupart des races ovines et certaines races caprines. Le taux d’ovulation est augmenté sans variabilité excessive (il dépasse rarement deux). Ceci s’accompagne d’une augmentation de la taille de la portée, par augmentation du pourcentage de jumeaux, d’autant plus importante que la race traitée est naturellement peu prolifique. La fertilité n’est pas affectée si on respecte strictement les conditions d’emploi (délai minimum de 3 semaines entre la deuxième vaccination et la mise à la lutte). Les poids à la naissance ne diffèrent pas, à taille de portée identique, entre agneaux et chevreaux nés de mères immunisées ou non. Les croissances et l’apparition de la puberté des jeunes issus de mères immunisées sont presque identiques à celles des témoins.Ovulation rate is increased, although seldom over two. It results in an increase in litter size through an increased proportion of twin born. This increase is usually higher when the treated ewes are of poor natural prolificacy. Fertility is not affected by immunization provided the booster to mating time interval is at least three weeks. When analyzed for a given litter size, birth weight is unaffected by immunization. The growth rates of young born from immunized or control ewes are usually close. The onset of puberty is also unaffected by immunization. Hence immunization may be a valuable technique for sheep breeders