Northern Coastal Basin (NCB) Intercoastal Oysters (SJRWMD)

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 Basin (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）凭借自身及牡蛎礁所提供的关键生态服务，被归类为生态系统工程师（ecosystem engineer）与关键物种（keystone species）。依托自身三维立体结构，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以牡蛎礁为栖息生境，包括虾类、石蟹、蓝蟹与斑海鳟；部分鱼类还会将牡蛎礁作为产卵繁育的场所。
美洲东部牡蛎的分布覆盖范围持续缩减，其成因包括栖息地破坏、病害爆发、过度捕捞以及水质恶化。该物种的严重衰退，促使其原生分布区域（含北海岸盆地（NCB））内启动了各类保护、制图、监测与修复工作。
本项目的目标为：依托圣约翰河水资源管理区提供的全套航空影像及补充影像资料，结合ArcGIS软件，评估NCB区域内天然牡蛎礁与死亡牡蛎礁的现存面积。
佛罗里达中央大学（UCF）开发了一套影像解译标志集（photointerpretation key），其中涵盖本研究划定的全部牡蛎生境分类类型示例，既包含各类分类类型的纹理特征描述，也配有清晰标注的航空影像片段，以便向使用者直观展示不同的牡蛎影像识别特征。所有牡蛎生境均按照检出精度完成制图，未设置最小制图单元（minimum mapping unit）。
牡蛎礁的识别依据以下“影像特征”准则：呈球状或不规则形态，边缘色调较深且中部色调略浅，纹理平滑。由于NCB区域内的牡蛎均为潮间带（intertidal）物种，多数礁体分布于浅水区且邻近红树林岛。被植被遮蔽的狭长边缘式牡蛎礁可能未被本研究检出。
在航空影像上可识别的零散活牡蛎群被纳入统计，并划分为“活牡蛎类”下的“聚合”亚类；仅密集连片的活牡蛎群被纳入“活牡蛎类”下的“连续”亚类。
死亡牡蛎礁的识别依据为：因持续裸露（即使在高潮位时）的经漂白脱壳牡蛎壳而呈现亮白色反射特征。死亡礁体要么毗邻现存牡蛎礁，要么单独存在，通常分布于主要通航航道内。
本项目的研究结果构建了该区域牡蛎生境的基准本底，可用于后续追踪评估牡蛎礁覆盖面积随时间推移所受到的潜在负面影响。本研究开展了精度评估，结果显示牡蛎礁生境分类的准确率达96%。UCF最初的制图工作将随着后续资源的到位持续进行编辑与优化，相关更新信息将在元数据（metadata）的维护章节中予以说明。