VELYGER Database: The Oyster Larvae Monitoring French Project

worldwide, shellfish aquaculture and fisheries in coastal ecosystems represent crucial activities for human feeding. but these biological productions are under the pressure of climate variability and global change. anticipating the biological processes affected by climate hazards remains a vital objective for species conservation strategies and human activities that rely on. within marine species, filter feeders like oysters are real key species in coastal ecosystems due to their economic and societal value (fishing and aquaculture) but also due to their ecological importance. indeed oysters populations in good health play the role of ecosystem engineers that can give many ecosystem services at several scales: building reef habitats that contribute to biodiversity, benthic-pelagic coupling and phytoplankton bloom control through water filtration, living shorelines against coastal erosion… the pacific oyster, crassostrea gigas (thunberg, 1793), which is currently widespread worldwide, was introduced into the atlantic european coasts at the end of the 19th century for shellfish culture purposes and becomes the main marine species farmed in france (around 100 000 tons) despite severe mortalities crisis. but in the same time and because of warming, natural oysters beds has spread significantly along the french coast and are supposed to have reach approximately 500 000 tons. in that context, pacific oyster populations (natural and cultivated) in france are the subjects of many scientific projects. among them, a specific long-term biological monitoring focuses on the reproduction of these populations at a national scale: the velyger national program. with more than 8 years of weekly data at many stations in france, this field-monitoring program offers a valuable dataset for studying processes underpinning reproduction cycle of this key-species in relation to environmental parameters, water quality and climate change. database content: larval concentration (number of individuals per 1.5 m3) monitored, since 2008, at several stations in six bays of the french coast (from south to north): thau lagoon and bays of arcachon, marennes oléron, bourgneuf, vilaine and brest (see map below). methods used to monitor larval concentration: an important volume of seawater (1.5 m3) is pumped twice a week throughout the spawning season (june-september), at one meter below the surface at high tide (+/- 2h) in several sites within each velyger ecosystem. water is filtered trough plankton net fitted with 40 µm mesh. after a proper rinsing of the net, the retained material is transferred into a polyethylene bottle (1 liter) and fixed with alcohol. at laboratory, sample is then gently filtered and rinse again and transferred into eprouvette. two sub-samples of 1 ml are then taken using a pipette and examined on a graticule slide for microscope. the microscopic examination is made with a conventional binocular optical microscope with micrometer stage at a magnification of 10 x (or above). during the counting, a special care is necessary as larvae of other bivalves are also collected and confusion is possible. larvae of c. gigas are also classified into four stage of development: stage i = d-shaped straight hinge larvae (shell length <105 µm) stage ii = early umbo evolved larvae (shell length between 105 and 150 µm) stage iii = medium umbo larvae (shell length between 150 and 235 µm) stage iv*= large umbo eyed pediveliger larvae (shell length > 235 µm)* larvae that are very closed to settle are sometimes identified into a separated 5th stage, but generally this stage is included in stage iv. illustrations:location of the different velyger sites along the french coast. from south to north: thau lagoon and bays of arcachon, marennes oléron, bourgneuf, vilaine and brest. legend: pacific oyster larvae (left side) and natural oyster bed (right side). photos : © s. pouvreau/ifremer

在全球范围内，沿海生态系统中的贝类养殖和渔业活动对于人类饮食至关重要。然而，这些生物产量正受到气候变率和全球变化的压力。预测受气候灾害影响的生物过程，对于物种保护策略及依赖于此的人类活动而言，实为至关重要的目标。在海洋物种中，如牡蛎之类的滤食性生物是沿海生态系统中的关键物种，这不仅因其经济和社会价值（渔业和养殖）而备受关注，亦因其生态重要性。确实，健康良好的牡蛎种群扮演着生态系统工程师的角色，能够在多个尺度上提供多种生态系统服务：构建礁石栖息地，促进生物多样性、底栖-浮游耦合及通过水质过滤控制浮游植物水华，抵御海岸侵蚀……太平洋牡蛎，即大蚝（Crassostrea gigas Thunberg, 1793），目前在全球范围内广泛分布，于19世纪末被引入大西洋欧洲海岸进行贝类养殖，成为法国（约10万吨）养殖的主要海洋物种，尽管经历了严重的死亡率危机。然而，在同一时期，由于气候变暖，天然牡蛎床在法国海岸显著扩张，预计已达到约50万吨。在此背景下，法国的太平洋牡蛎种群（自然和养殖）成为众多科学项目的研究对象。其中，一项针对这些种群繁殖的长期生物监测项目，旨在国家尺度上研究这些关键物种的繁殖周期与环境参数、水质及气候变化之间的关系：Velyger国家项目。该项目在法国多个站点（从南至北）连续8年每周收集数据，为研究这一关键物种的繁殖周期及其与生态环境参数、水质和气候变化之间的相互关系提供了宝贵的数据集。数据库内容：自2008年起，在法国海岸六个海湾的多个站点（从南至北）监测的幼虫浓度（每1.5立方米个体数量）：图卢兹泻湖和阿尔卡松湾、马雷内奥尔松、布尔热努夫、维莱讷和布雷斯特（见下地图）。监测幼虫浓度的方法：在产卵季节（6月至9月），每周两次从高潮时一米以下的位置抽取大量海水（1.5立方米），在Velyger生态系统的多个地点进行。水通过40微米网孔的浮游生物网过滤。在彻底清洗网孔后，保留的物质被转移到聚乙烯瓶（1升）中，并用酒精固定。在实验室中，样品随后被轻轻过滤并再次冲洗，转移到试管中。然后使用移液管取两个1毫升的子样本，并在显微镜载玻片上检查。使用带有微米尺的双目光学显微镜以10倍（或以上）放大倍数进行显微镜检查。在计数过程中，需要特别注意，因为也会收集其他双壳类的幼虫，存在混淆的可能。C. gigas的幼虫还被分为四个发育阶段：阶段I = D形直铰链幼虫（壳长<105微米）；阶段II =早期铰合部发育的幼虫（壳长介于105至150微米）；阶段III =中等铰合部幼虫（壳长介于150至235微米）；阶段IV =大铰合部有眼足幼虫（壳长>235微米）*。即将定居的幼虫有时被识别为独立的第5阶段，但通常这一阶段包含在阶段IV中。插图：不同Velyger站点沿法国海岸的分布。从南至北：图卢兹泻湖和阿尔卡松湾、马雷内奥尔松、布尔热努夫、维莱讷和布雷斯特。图例：太平洋牡蛎幼虫（左侧）和天然牡蛎床（右侧）。照片：© S. Pouvreau/IFREMER