Time-series patterns and dynamics of species richness, diversity, and community composition of fishes at Stellwagen Bank National Marine Sanctuary (1970-2017)

Here we present analyses conducted in support of the most recent Stellwagen Bank National Marine Sanctuary (SBNMS) Condition Report for 2008-2017. Our focus was on patterns and trends in species richness, diversity, and community composition of fishes in SBNMS and surrounding waters over a nearly 50-year period. These analyses of the larger Gulf of Maine, in which SBNMS is nested, are used to compare regional and local scale patterns and trends. The NOAA Northeast Fisheries Science Center bottom trawl survey data, based on a stratified random sampling design, was used to represent the fish fauna of SBNMS (sampling stratum 26) along with 19 additional strata (i.e., 21-40) for the larger Gulf of Maine. Our results demonstrate that fish communities in SBNMS have changed substantially during the past decade. Following a long period of slowly rising species richness through 2006, richness rose rapidly over the last decade. This change coincided with changes in composition and patterns of numerical dominance for both local (i.e., SBNMS) and large-scale (i.e., Gulf of Maine) fish communities as well. Depth was the most significant correlate of fish community structure, but the threshold between shallow and deep communities has moved from 52.5 to 75.5 m over time. Further, composition and distribution of communities were influenced by temperature. For example, Acadian redfish were more common when bottom temperature was <5.7°C while American plaice, longhorn sculpin, yellowtail and witch flounder, and silver and white hake were associated with warmer bottom conditions. Over the past decade, shallow communities south of 42°N were characterized by higher abundances of warmtolerant species, like Atlantic mackerel and little skate, while the cold-associated species like haddock are much more abundant north of this latitude. Based on related studies, these community scale changes are attributed to changes in fisheries management, changes in species interactions mediated by changes in species and trophic guild abundance, and shifts in the distributions and abundances of fish species due to climate change as a direct or indirect driver. While maintaining and enhancing diversity is a central mission of the sanctuary, the structural changes to its communities is concerning and deserves additional investigation. Identifying the drivers of these changes is important and may provide some insight on what policies might mitigate adverse changes while not sacrificing the benefits of diversity.

本研究开展相关分析，旨在支撑2008-2017年最新版的斯泰尔旺班克国家海洋保护区（Stellwagen Bank National Marine Sanctuary, SBNMS）状况报告。本研究聚焦近50年间，SBNMS及其周边海域鱼类的物种丰富度、多样性及群落组成的格局与动态趋势。针对SBNMS所在的更大尺度缅因湾海域开展的上述分析，用于对比区域与局地尺度的格局及动态趋势。本研究采用美国国家海洋和大气管理局（National Oceanic and Atmospheric Administration, NOAA）东北渔业科学中心的底拖网调查数据，该数据基于分层随机抽样设计，用于表征SBNMS（采样层26）及缅因湾其余19个采样层（即21-40号层）的鱼类区系组成。研究结果显示，近10年来SBNMS的鱼类群落已发生显著变化。在2006年前物种丰富度长期缓慢上升的趋势之后，近10年该指标出现快速增长。这一变化同时伴随局地（即SBNMS）及大尺度（即缅因湾）鱼类群落的组成与数量优势格局的改变。水深是影响鱼类群落结构最显著的环境因子，但浅海与深海群落的分界阈值已随时间从52.5米推移至75.5米。此外，群落组成与分布还受水温影响。例如，当底层水温低于5.7℃时，阿卡迪亚红鱼更为常见；而美洲黄盖鲽、长角杜父鱼、黄尾鲽与庸鲽，以及银无须鳕和白无须鳕则与较高的底层水温相关联。近10年来，北纬42°以南的浅海群落以暖适应性物种（如大西洋鲭与小鳐）的丰度更高为特征；而与此相反，北纬42°以北海域的冷水性物种（如黑线鳕）丰度则显著提升。结合已有相关研究，上述群落尺度的变化可归因于三方面因素：渔业管理政策的调整、由物种类群与营养类群丰度变化介导的物种相互作用改变，以及以气候变化为直接或间接驱动因子的鱼类物种分布与丰度格局偏移。尽管维持并提升生物多样性是该海洋保护区的核心使命之一，但鱼类群落的结构变化仍令人担忧，亟需开展进一步研究。明确上述变化的驱动因子具有重要意义，或可为在不牺牲生物多样性收益的前提下，制定缓解不利变化的相关政策提供参考依据。