Northern Coastal Basin Intertidal Oyster Reefs 2015

The eastern oyster, Crassostrea virginica, has been classified as an ecosystem engineer as well as a keystone species because of the important benefits that oysters and oyster reefs provide. Due to their three-dimensional structure, oyster reefs are able to maintain high levels of biodiversity. Many economically and ecologically important species can be found using the oyster reefs, including shrimp, stone crabs, blue crabs, and spotted sea trout. Certain fish species also use oyster reefs as nesting areas. Oyster coverage has decreased for several reasons: habitat destruction, disease, overharvesting and reduced water quality. The severe loss of the eastern oyster, Crassostrea virginica, has encouraged different types of conservation, mapping, monitoring and restoration efforts throughout its native range, including within the Northern Coastal Basins (NCB) region. The purpose of this project is assess the current area of natural and dead oyster reefs within the NCB area using a suite of aerial photographs and supplemental imagery information provided by Saint Johns River Water Management District using ArcGIS software. UCF developed a photointerpretation key that contains examples of all oyster habitat classification types delineated for the study and includes both textural descriptions of the classification types along with aerial photo clips that are clearly delineated to show users the different oyster signatures. All oyster habitats were mapped to the level of detection (no minimum mapping unit). Oyster reefs were identified based on the following criteria (i.e. "signature"): globular or irregular in shape, dark margins with a slightly lighter middle area, and with a smooth texture. Most reefs were located near mangrove islands at a shallow bathymetry, due to the fact that oysters are intertidal throughout the NCB area. Narrow, fringing oyster reefs that were obscured by vegetation may not have been detected in our study. Scattered live clusters were included if they were detectable on the aerial imagery, and were assigned the subclass of 'aggregate' within the 'live' class. Only dense clusters of live oysters were included in the 'live' class and the 'continuous' subclass. Dead reefs were identified based on the following criteria: bright white reflection due to bleached disarticulated shells that are continuously exposed, even at high tide. Dead reefs are found either adjacent to existing oyster reefs or standing alone, typically located on main boating channels. The results of this project create a baseline for oyster habitat within the region, which can serve to study potential negative impacts to reef area coverage over time. An accuracy assessment was performed and found the oyster reef habitat classification to be 96% accurate. The original mapping effort by UCF will continue to be edited and refined as more resources become available. Updates will be described in the maintenance section of the metadata.美洲东部牡蛎（Crassostrea virginica）被归类为生态系统工程师（ecosystem engineer）与关键物种（keystone species），缘由为牡蛎及其牡蛎礁可提供诸多关键生态服务。得益于三维立体结构，牡蛎礁能够维持极高的生物多样性水平。诸多兼具经济与生态价值的物种均依托牡蛎礁栖息，涵盖虾类、石蟹、蓝蟹以及斑点海鳟；部分鱼类亦将牡蛎礁作为产卵栖息地。 牡蛎种群覆盖范围已因多重因素出现缩减，包括栖息地破坏、病害、过度捕捞与水质下降。美洲东部牡蛎的大规模衰退，促使其原生分布范围内（含北海岸盆地（Northern Coastal Basins，NCB）区域）开展了各类保护、测绘、监测与修复工作。 本项目旨在借助ArcGIS软件，结合圣约翰河水资源管理区（Saint Johns River Water Management District）提供的系列航空影像与补充图像数据，评估NCB区域内天然牡蛎礁与死亡牡蛎礁的当前分布面积。佛罗里达中央大学（UCF）构建了影像解译密钥（photointerpretation key），其中涵盖本研究划定的全部牡蛎栖息地分类类型示例，既包含各类分类类型的纹理特征描述，也附带清晰标注的航空影像片段，便于向使用者展示不同的牡蛎特征标识（oyster signatures）。所有牡蛎栖息地均按可识别精度进行测绘（无最小制图单元限制）。 牡蛎礁的识别依据以下标准（即“特征标识”）：呈球状或不规则形状，边缘色调较深而中部区域色调略浅，且表面纹理平滑。由于NCB区域内的牡蛎均为潮间带（intertidal）物种，多数牡蛎礁分布于浅水区的红树林岛屿附近。本研究或未识别到被植被遮蔽的狭长沿岸牡蛎礁。若在航空影像上可识别到零散活牡蛎集群，则将其纳入“活牡蛎”类下的“聚集”子类；仅将密集分布的活牡蛎集群纳入“活牡蛎”类下的“连续分布”子类。 死亡牡蛎礁的识别依据以下标准：因潮汐持续暴露的漂白脱壳壳体而呈现亮白色反射特征。死亡牡蛎礁要么毗邻现存牡蛎礁，要么孤立存在，通常分布于主要通航航道区域。 本项目成果为该区域牡蛎栖息地建立了基准数据库，可用于后续研究牡蛎礁覆盖面积随时间推移可能遭受的负面影响。本次研究开展了精度验证，结果显示牡蛎礁栖息地分类的准确率达96%。后续随着可获取资源的增加，UCF将持续对初始测绘成果进行编辑与优化，相关更新内容将在元数据的维护章节中予以说明。