Final Report Summary - LARVDEVOPTI (Larval quality in oyster hatcheries: Effects of ocean acidification, temperature change and food availability on reproductive success and survival of the European flat oyster)
Summary
The project investigated ecophysiological factors affecting O. edulis larval development and grow-out in Swedish waters, with the goal of advancing development of a Scandinavian flat oyster aquaculture industry. Specific research objectives were to:
1. determine causes of instability in broodstock conditioning and larval productivity, including the effects of ocean acidification, temperature and salinity changes on larval development in O. edulis;
2. optimize ecophysiological conditions for O. edulis larval development in a commercial-scale hatchery to allow sufficient spat production;
3. identify coastal grow-out sites that were suitable for aquaculture operations in order to optimize the growth of O. edulis to marketable size.
Results
1) Effects of ocean acidification, water quality and diet on larval growth and survival In order to address the first objective, a number of experiments were conducted to examine the role of water quality on larval development in European flat oysters O. edulis. Research on larval responses to environmental stressors – including changes in pH and aragonite saturation state as a result of ocean acidification, as well as temperature stressors, and salinity changes related to climate change – can provide important information about optimal parameters for growth and survival during vulnerable early stage of the lifecycle. A series of water quality studies were conducted in spring 2012 at the hatchery Ostrea Sverige AB to assess the role of various environmental changes on current larval production. Many of the new Swedish hatchery’s difficulties appear to be related to poor seasonal water quality. Research indicates that the high mortality observed Sweden’s commercial hatchery may be an indirect result of fluctuating pH of intake seawater, as well as toxic metabolites and bacterial pathogens following degradation of plankton blooms related to extreme eutrophication of Baltic waters (water from the Baltic moves upwards along the Swedish west coast fjords during certain weather conditions). Results from these experiments were conclusive in determining that low pH (7.8) during periods of deep water upwelling was not a direct cause of mortalities, but rather exerted an indirect effect due to deterioration of biological water quality. Modifications were nonetheless implemented at the commercial hatchery to treat all intake water for low pH conditions, as should this level drop below 7.8 it is clear that larval survival would be compromised (tested also pH 7.6 at which 80% of larvae did not survive) Bacterial pathogens were causatively linked to some mortalities, but were likely symptomatic of other stressors linked to low pH, low salinity and poor feed quality.
2) Optimize eco-physiological conditions for hatchery production A number of feed-optimization trials were conducted to examine growth and survival of oyster larvae at different development stages. These included lipid-enrichment studies, studies of essential fatty acid profiles of the microalgae used as feed, as well as timing of lipid delivery. A recent paper (Joyce et al. 2013 Journal of Shellfish Research) summarizes some of this work. An internationally respected oyster pathologist (Royal Swedish Academy grant) was invited to work with the applicant on the effects of bacterial and viral pathogens, with an emphasis on minimizing stress factors which lead to mortality events. Pathogenic marine bacteria colonize hatchery environments and cause mass mortality in early-stage oyster larvae. In order to reduce the risk of epidemics in hatcheries, continued research is needed on optimal hygiene protocols and especially to develop antimicrobial approaches (probiotic treatments) to reduce potential for infection. The Applicant conducted a number of studies using histopathology and molecular biology to shed light on ostreid herpes virus (OsHV), as it was suspected that a lethal microvariant of this virus may have been introduced from mainland Europe with the invasive species Crassostrea gigas, which was first reported in Sweden in 2007. Identification, by DNA sequencing, of the OsHV strain in Swedish oysters concluded that the strain found in broodstock from hatchery was not the virulent strain which was so lethal for the French and Spanish oyster industries.
3) Optimize grow out conditions and selective breeding opportunities for commercial production A number of aquaculture siting studies were conducted by students working with the Marie Curie Fellow. These included studies of optimal biophysical parameters for growout (bathymetry, currents, salinity, temperature gradients and phytoplankton productivity) as well as identifying technologies and locations for pilot grow-out trials. Oyster aquaculture is a new industry in Sweden (since 2009), thus limited knowledge was available about grow out conditions and biofouling. Genetic quality of broodstock from natural populations is variable and research specifically targeted to selective breeding of O. edulis was also initiated in order to improve growth and survival rates.
Socio-economic benefits of the project
The nascent flat oyster aquaculture industry in Scandinavia still needs to overcome a number of difficulties in order to provide a reliable product for European markets. There is considerable demand for flat oysters in Europe, but despite considerable investment, a number of research questions still need to be addressed.
One of the key focuses of this project included physiological and morphological changes induced by decreasing seawater pH, which is a significant concern for shellfish aquaculture hatcheries as they rely on pumped seawater to maintain broodstock and support larval development. One of the more interesting applications that has emerged from recent ocean acidification research is the superior survival of larvae under pre-industrial levels of pH, a finding that has had widespread hatchery application. Many hatcheries now routinely adjust seawater pH in larval tanks to pre-industrial levels of 8.2 to increase larval yields. The implications of this observation are rather serious, as it suggests that marine molluscs are already being exposed to sub-optimal conditions in their natural environment. In 2011, after detailed study of pH control systems, the Swedish Hatchery Ostrea Sverige AB installed pH monitoring and feedback controllers on their entire production system. The benefits of this research have thus been translated into tangible results for industry. However, even though this practice works well in hatchery conditions, tolerance to increasing acidification under natural conditions remains worrisome.
In future, it is potentially possible to select for bred lines that are more resistant to low pH. I recently visited the Hatfield Marine Science Center (HMSC) of Oregon State University (August 15-September 15, 2013) to participate in a project on the effects of ocean acidification (OA) within selected oyster families that have been developed as part of the Pacific Molluscan Broodstock Program (MBP). In this research, I had access to unique genetic lines (several generations of bred lines of Crassostrea gigas), where I was able to examine genotype and phenotype alterations in selected broodstock lines that were reported by commercial hatcheries to be more resistant to the effects of low pH. This opportunity allowed me to collaborate with an important researcher in my field, Professor Chris Langdon, who currently holds a US N.S.F supported project on OA effects in bivalve larvae. Last year, I was able to host Chris Langdon for a sabbatical visit at my institute in Sweden, where we conducted various experiments with Swedish oysters. However, as no bred lines of oysters existed in Sweden, it was also important to do a reciprocal exchange to Dr. Langdon’s lab in order to access genetic resources and access to several facilities that were lacking for final biomineralization studies.
Several experiments were established to understand how the feeding behavior of larval oysters changes under ocean acidification conditions, and how physiological plasticity can help mitigate the effects of OA for the shellfish aquaculture industry. Several experiments were conducted to scan the transcriptomes of larval/juvenile oysters for biomineralization and metabolic genes involved in adaptation to ocean acidification, and to identify genotypes that result in oysters that are more tolerant to low calcium carbonate saturation states. These results were designed to elucidate genotype-phenotype interactions in oysters exposed to high CO2 stress by combining behavioral and genetic data.
During my short one-month visit to Dr. Langdon’s lab, I was able to build crucial links with other researchers who are working on ocean acidification (Drs. Hurst, Waldbusser, Hales, Menge) and also discuss applied aspects of my work with commercial oyster hatcheries in America that have been strongly impacted by ocean acidification. Pacific USA coastal hatcheries have had 40-50% declines in larval survival during upwelling periods when CO2 enriched deep seawater rises to the surface. These hatcheries are therefore pioneering a number of novel new projects in order to remain commercially viable.
Results of my Marie Curie have led to a better understanding of the genetic and physiological responses of oyster larvae to a variety of environmental conditions. I have had the opportunity to learn a number of new skills and to build important networks. The project has had several outreach components, including results from experiments that are useful to the aquaculture industry.
The project investigated ecophysiological factors affecting O. edulis larval development and grow-out in Swedish waters, with the goal of advancing development of a Scandinavian flat oyster aquaculture industry. Specific research objectives were to:
1. determine causes of instability in broodstock conditioning and larval productivity, including the effects of ocean acidification, temperature and salinity changes on larval development in O. edulis;
2. optimize ecophysiological conditions for O. edulis larval development in a commercial-scale hatchery to allow sufficient spat production;
3. identify coastal grow-out sites that were suitable for aquaculture operations in order to optimize the growth of O. edulis to marketable size.
Results
1) Effects of ocean acidification, water quality and diet on larval growth and survival In order to address the first objective, a number of experiments were conducted to examine the role of water quality on larval development in European flat oysters O. edulis. Research on larval responses to environmental stressors – including changes in pH and aragonite saturation state as a result of ocean acidification, as well as temperature stressors, and salinity changes related to climate change – can provide important information about optimal parameters for growth and survival during vulnerable early stage of the lifecycle. A series of water quality studies were conducted in spring 2012 at the hatchery Ostrea Sverige AB to assess the role of various environmental changes on current larval production. Many of the new Swedish hatchery’s difficulties appear to be related to poor seasonal water quality. Research indicates that the high mortality observed Sweden’s commercial hatchery may be an indirect result of fluctuating pH of intake seawater, as well as toxic metabolites and bacterial pathogens following degradation of plankton blooms related to extreme eutrophication of Baltic waters (water from the Baltic moves upwards along the Swedish west coast fjords during certain weather conditions). Results from these experiments were conclusive in determining that low pH (7.8) during periods of deep water upwelling was not a direct cause of mortalities, but rather exerted an indirect effect due to deterioration of biological water quality. Modifications were nonetheless implemented at the commercial hatchery to treat all intake water for low pH conditions, as should this level drop below 7.8 it is clear that larval survival would be compromised (tested also pH 7.6 at which 80% of larvae did not survive) Bacterial pathogens were causatively linked to some mortalities, but were likely symptomatic of other stressors linked to low pH, low salinity and poor feed quality.
2) Optimize eco-physiological conditions for hatchery production A number of feed-optimization trials were conducted to examine growth and survival of oyster larvae at different development stages. These included lipid-enrichment studies, studies of essential fatty acid profiles of the microalgae used as feed, as well as timing of lipid delivery. A recent paper (Joyce et al. 2013 Journal of Shellfish Research) summarizes some of this work. An internationally respected oyster pathologist (Royal Swedish Academy grant) was invited to work with the applicant on the effects of bacterial and viral pathogens, with an emphasis on minimizing stress factors which lead to mortality events. Pathogenic marine bacteria colonize hatchery environments and cause mass mortality in early-stage oyster larvae. In order to reduce the risk of epidemics in hatcheries, continued research is needed on optimal hygiene protocols and especially to develop antimicrobial approaches (probiotic treatments) to reduce potential for infection. The Applicant conducted a number of studies using histopathology and molecular biology to shed light on ostreid herpes virus (OsHV), as it was suspected that a lethal microvariant of this virus may have been introduced from mainland Europe with the invasive species Crassostrea gigas, which was first reported in Sweden in 2007. Identification, by DNA sequencing, of the OsHV strain in Swedish oysters concluded that the strain found in broodstock from hatchery was not the virulent strain which was so lethal for the French and Spanish oyster industries.
3) Optimize grow out conditions and selective breeding opportunities for commercial production A number of aquaculture siting studies were conducted by students working with the Marie Curie Fellow. These included studies of optimal biophysical parameters for growout (bathymetry, currents, salinity, temperature gradients and phytoplankton productivity) as well as identifying technologies and locations for pilot grow-out trials. Oyster aquaculture is a new industry in Sweden (since 2009), thus limited knowledge was available about grow out conditions and biofouling. Genetic quality of broodstock from natural populations is variable and research specifically targeted to selective breeding of O. edulis was also initiated in order to improve growth and survival rates.
Socio-economic benefits of the project
The nascent flat oyster aquaculture industry in Scandinavia still needs to overcome a number of difficulties in order to provide a reliable product for European markets. There is considerable demand for flat oysters in Europe, but despite considerable investment, a number of research questions still need to be addressed.
One of the key focuses of this project included physiological and morphological changes induced by decreasing seawater pH, which is a significant concern for shellfish aquaculture hatcheries as they rely on pumped seawater to maintain broodstock and support larval development. One of the more interesting applications that has emerged from recent ocean acidification research is the superior survival of larvae under pre-industrial levels of pH, a finding that has had widespread hatchery application. Many hatcheries now routinely adjust seawater pH in larval tanks to pre-industrial levels of 8.2 to increase larval yields. The implications of this observation are rather serious, as it suggests that marine molluscs are already being exposed to sub-optimal conditions in their natural environment. In 2011, after detailed study of pH control systems, the Swedish Hatchery Ostrea Sverige AB installed pH monitoring and feedback controllers on their entire production system. The benefits of this research have thus been translated into tangible results for industry. However, even though this practice works well in hatchery conditions, tolerance to increasing acidification under natural conditions remains worrisome.
In future, it is potentially possible to select for bred lines that are more resistant to low pH. I recently visited the Hatfield Marine Science Center (HMSC) of Oregon State University (August 15-September 15, 2013) to participate in a project on the effects of ocean acidification (OA) within selected oyster families that have been developed as part of the Pacific Molluscan Broodstock Program (MBP). In this research, I had access to unique genetic lines (several generations of bred lines of Crassostrea gigas), where I was able to examine genotype and phenotype alterations in selected broodstock lines that were reported by commercial hatcheries to be more resistant to the effects of low pH. This opportunity allowed me to collaborate with an important researcher in my field, Professor Chris Langdon, who currently holds a US N.S.F supported project on OA effects in bivalve larvae. Last year, I was able to host Chris Langdon for a sabbatical visit at my institute in Sweden, where we conducted various experiments with Swedish oysters. However, as no bred lines of oysters existed in Sweden, it was also important to do a reciprocal exchange to Dr. Langdon’s lab in order to access genetic resources and access to several facilities that were lacking for final biomineralization studies.
Several experiments were established to understand how the feeding behavior of larval oysters changes under ocean acidification conditions, and how physiological plasticity can help mitigate the effects of OA for the shellfish aquaculture industry. Several experiments were conducted to scan the transcriptomes of larval/juvenile oysters for biomineralization and metabolic genes involved in adaptation to ocean acidification, and to identify genotypes that result in oysters that are more tolerant to low calcium carbonate saturation states. These results were designed to elucidate genotype-phenotype interactions in oysters exposed to high CO2 stress by combining behavioral and genetic data.
During my short one-month visit to Dr. Langdon’s lab, I was able to build crucial links with other researchers who are working on ocean acidification (Drs. Hurst, Waldbusser, Hales, Menge) and also discuss applied aspects of my work with commercial oyster hatcheries in America that have been strongly impacted by ocean acidification. Pacific USA coastal hatcheries have had 40-50% declines in larval survival during upwelling periods when CO2 enriched deep seawater rises to the surface. These hatcheries are therefore pioneering a number of novel new projects in order to remain commercially viable.
Results of my Marie Curie have led to a better understanding of the genetic and physiological responses of oyster larvae to a variety of environmental conditions. I have had the opportunity to learn a number of new skills and to build important networks. The project has had several outreach components, including results from experiments that are useful to the aquaculture industry.