Range-extending tropical herbivores increase diversity, intensity and extent of herbivory functions in temperate marine ecosystems

Surveys of herbivorous fish were conducted over inshore habitats along the coastline of south-western Australia during summer (April-May) of 2018 and 2019, from the Perth metropolitan area to Cape Naturaliste in the south of the state. The abundances of temperate (Girella zebra, Olisthops cyanomelas, Pelates octolineatus, Kyphosus cornelii and Kyphosus sydneyanus) and tropical herbivorous fish (Scarus spp. and Siganus fuscescens) were measured via a GPS-tracked roving underwater visual census with 15 minutes per sampling location. One surveyor swam at a constant pace, registering all individuals of the species of interest in an approximate area of 2000 m2 per transect. A second surveyor followed the same path recording the seascape with an underwater camera for subsequent assessment of habitat features. Videos were analyzed with the program TransectMeasure (SeaGIS), each video transect was paused at one minute intervals (n=15 per transect) to extract information on topographic complexity (Wilson, Graham & Polunin 2007), substrate type, species composition, species diversity, and abundance of morpho-functional groups of sessile biota based on the CATAMI classification scheme (Althaus et al. 2015). Fish abundance was standardized to density (individuals 125 m-2); however, we also considered a new metric: MaxS (maximum number of fish per school in each survey), a similar approach to abundance assessments of pelagic schooling fish (i.e. school size; Beare 2002) and abundance estimates from static video methods (i.e. MaxN; Cappo et al. 2003).2018年和2019年夏季（4-5月），研究人员在澳大利亚西南部沿岸的近岸生境开展植食性鱼类调查，调查范围从珀斯都会区延伸至该州南部的纳多鲁列斯角（Cape Naturaliste）。本次调查采用每个采样点耗时15分钟的GPS追踪式漫游水下视觉普查（GPS-tracked roving underwater visual census），测定了温带植食性鱼类（Girella zebra、Olisthops cyanomelas、Pelates octolineatus、Kyphosus cornelii及Kyphosus sydneyanus）与热带植食性鱼类（Scarus属物种及褐篮子鱼Siganus fuscescens）的丰度。一名调查员以恒定游速行进，记录每条样带内约2000平方米范围内所有目标物种的个体数；第二名调查员沿同一路径行进，使用水下相机记录海域景观，用于后续生境特征分析。所获视频通过TransectMeasure（SeaGIS开发）软件进行分析，每个视频样带以每分钟为间隔暂停（每条样带共设15个暂停节点），以提取地形复杂度（Wilson, Graham & Polunin, 2007）、底质类型、物种组成、物种多样性，以及基于CATAMI分类方案（CATAMI classification scheme）的固着生物形态功能群丰度信息。鱼类丰度被标准化为密度单位（单位：个体·125 m⁻²）；此外，本研究还引入了一项新指标：MaxS（每次调查中单个鱼群的最大个体数），该指标与中上层集群鱼类丰度评估（即鱼群规模；Beare, 2002）及静态视频法丰度估算（即MaxN；Cappo et al., 2003）采用的思路一致。