Gulf Watch Alaska Nearshore Component: Intertidal Mussel Site Data from Prince William Sound, Katmai National Park and Preserve, and Kenai Fjords National Park, 2016

This data is part of the Gulf Watch Alaska (GWA) long term monitoring program, nearshore monitoring component. Specifically, these data describe mussel sampling and observations conducted in the northern Gulf of Alaska within the GWA program. The dataset consists of five comma separated files exported from a Microsoft excel workbook. The data consists of 1. Mussel sampling site layout information, 2. Mussel count and 3. Size measurements for mussels greater than 20 millimeters, 4. Mussel count and 5. Size measurements for all mussels collected from core samples. Samplers used transect tapes, quadrat frames, rulers, and core tools to sample mussels from mussel sites. Mussels greater than 20 millimeters were collected from a quadrat and measured with dial calipers to the nearest millimeter. Associated with the quadrat, but not within it, a small core sample was collected and all mussels greater than 1mm were counted and measured (measurements began in 2014). Sampling year, region, block, site, quadrat number, quadrat size (overall area sampled), and number of mussels in the core were recorded. Sites are in Alaska and include locations in Katmai National Park and Preserve, Kenai Fjords National Park and Prince William Sound. There are five mussel sites in each of those three regions. The time interval includes 2016. Pacific blue mussels (Mytilus trossulus) are a conspicuous and abundant filter feeding marine invertebrate in the intertidal zone. Mussels are widely distributed, but also form relatively monotypic stands of larger individuals that are termed mussel beds. Although a number of factors such as environment, disturbance, predation and competition influence the abundance and distribution of mussels, they can be a competitively dominant intertidal species. Within the nearshore foodweb, mussels area a source of energy to a wide array of invertebrate, avian, and mammalian predators and are critically important prey for sea otters, black oystercatchers, harlequin ducks, Barrows goldeneye, and several species of sea stars. The purpose of this task is to assess change in the density and size distribution of mussels (Mytilus trossulus) in mussel beds. These data are primarily to be used as an indicator of mussel prey for various predators, including sea otters, black oystercatchers, sea ducks and sea stars. Specifically, the objectives of this task are to assess changes in: 1) The size (area) of selected mussel beds, 2) The density of mussels within these beds, and 3) The size distribution of mussels within the beds. Sampling will be conducted in sheltered rocky habitats within each of the regions (Kenai Peninsula (KEP), Alaska Peninsula (AKP), and Prince William Sound (PWS).

本数据集隶属于阿拉斯加海湾观测（Gulf Watch Alaska, GWA）长期监测项目的近岸监测子项。具体而言，其记录了GWA项目框架下，于阿拉斯加海湾北部开展的贻贝采样与观测工作。
本数据集包含5个由Microsoft Excel工作簿导出的逗号分隔值（Comma-Separated Values, CSV）文件，涵盖5类数据：1. 贻贝采样点位布局信息；2. 体长大于20毫米的贻贝计数数据；3. 该类贻贝的尺寸测量数据；4. 岩芯样本采集的全部贻贝计数数据；5. 岩芯样本采集的全部贻贝的尺寸测量数据。
采样人员使用样带卷尺、样方框、直尺与岩芯采样工具采集点位处的贻贝样本：体长大于20毫米的贻贝取自样方，采用游标卡尺测量至最邻近毫米精度；在每个样方的周边而非样方内部，采集小型岩芯样本；自2014年起，研究人员对其中所有体长大于1毫米的贻贝开展计数与尺寸测量工作。
研究人员记录的采样元数据包括：采样年份、区域、区块、点位编号、样方编号、样方面积（即采样总区域）以及岩芯样本中的贻贝数量。
所有采样点位均位于阿拉斯加境内，涵盖卡特迈国家公园与保护区、基奈峡湾国家公园以及威廉王子湾，上述三个区域各设有5个贻贝采样点位，采样时间范围覆盖2016年。
太平洋蓝贻贝（Mytilus trossulus）是潮间带中辨识度高、数量丰富的滤食性海洋无脊椎动物。该物种分布范围极广，常形成以大型个体为主的单优群落，即贻贝床。尽管环境、扰动、捕食与种间竞争等诸多因素会影响贻贝的丰度与分布，但它们仍是潮间带中具有竞争优势的物种。在近岸食物网中，贻贝为众多无脊椎动物、鸟类与哺乳类捕食者提供能量来源，是海獭、黑蛎鹬、丑鸭、巴罗氏金眼鸭以及多种海星的关键猎物。
本数据集的核心目标为评估太平洋蓝贻贝（Mytilus trossulus）贻贝床的种群密度与尺寸分布变化，其主要用途是作为各类捕食者（包括海獭、黑蛎鹬、海鸭与海星）的贻贝猎物丰度指标。
本任务的具体目标为评估以下三项变化：1）选定贻贝床的面积；2）这些贻贝床内的贻贝种群密度；3）贻贝床内贻贝的尺寸分布。
采样工作将在上述三个区域——基奈半岛（Kenai Peninsula, KEP）、阿拉斯加半岛（Alaska Peninsula, AKP）以及威廉王子湾（Prince William Sound, PWS）——内的遮蔽岩礁生境中开展。