Spatial patterns of richness and abundance of benthic decapod crustaceans and fishes in the North-west Atlantic as measured by cobble-filled bio-collectors

Examination of spatial patterns of organisms in the rocky subtidal zone is logistically challenging, particularly over large geographic distances. In the present study, we describe patterns of richness and abundance of decapod crustaceans and small demersal fishes colonizing cobble-filled bio-collectors in 2008 and 2009 at nearshore sites across an important oceanographic and biogeographic gradient in the North-west Atlantic from Rhode Island, USA to Newfoundland, Canada. At least 17 decapod and 24 fish genera were caught, including cryptic fish taxa not readily sampled with other gear. Species richness and abundance of decapods and fishes in collectors at shallow sites (5–10 m) was similar among nearby sites and was greatest in the southernmost region, but did not follow a simple latitudinal cline. The lack of clear latitudinal patterns is likely to be a result of the complex geography of summer temperatures along this coast, with the lowest temperatures at the mouth of the Bay of Fundy, the centre of the study domain. In 2008, the abundance of crabs was positively related to temperature while that of shrimp was negatively related. There was also a significant interaction between depth and study area, with greater similarity among areas at greater depths (up to 76 m), and greater similarity among depths in areas with little temperature stratification. Our results indicate that bio-collectors are a powerful tool for sampling decapod crustaceans and small demersal fishes in nearshore rocky habitats. Given the anthropogenic impacts in coastal habitats, this information is likely to prove useful for detecting changes in rocky subtidal habitats.

对岩质潮下带生物空间分布格局开展调查，在实地操作层面颇具难度，尤其当研究覆盖大范围地理区域时。本研究针对2008至2009年，在美国罗德岛州至加拿大纽芬兰岛横跨西北大西洋一处重要海洋学与生物地理学梯度的近岸站点中，附着于砾石填充式生物收集器（cobble-filled bio-collectors）的十足目甲壳动物（decapod crustaceans）与小型底栖鱼类（demersal fishes）的物种丰富度和丰度格局进行了描述。本次调查共捕获至少17个十足目甲壳动物属与24个鱼类属，其中包含了难以通过其他采样设备获取的隐秘性鱼类类群。浅海站点（5-10米）内收集器中十足目动物与鱼类的物种丰富度和丰度，在邻近站点间较为相似，且在最南部区域达到峰值，但并未呈现出简单的纬度梯度（latitudinal cline）分布规律。未出现清晰纬度格局的原因，大概率与该沿岸海域夏季水温的复杂空间分布有关——研究区域的核心位置芬迪湾湾口水温最低。2008年，蟹类的丰度与水温呈正相关关系，而虾类丰度则与水温呈负相关关系。此外，水深与研究区域间还存在显著的交互效应：在水深较大（最深达76米）的区域内，不同站点间的群落相似性更高；而在温度层结（temperature stratification）较弱的区域内，不同水深间的群落相似性更强。本研究结果表明，生物收集器是近岸岩质生境中采样十足目甲壳动物与小型底栖鱼类的高效工具。鉴于近岸生境正遭受各类人为活动干扰，本研究所得数据可为岩质潮下带生境的变化监测提供有效支撑。