Data from: Unusual but consistent latitudinal patterns in macroalgal habitats and their invertebrate communities across two countries

Aim: The physical characteristics of biogenic habitats and environmental conditions are important determinants of biodiversity, yet their relative importance can change across spatial scales. We aimed to understand how relationships between the physical characteristics of macroalgal habitats and their invertebrate communities varied across spatial scales and whether general ecological patterns occurred across two countries.

Location: 18 sites across the temperate east coasts of Australia (over 1,300 km) and New Zealand (over 1,000 km), with the latitudinal gradient in the two countries overlapping by 6.73 decimal degrees.

Time period: January to early April 2012.

Major taxa studied: Three intertidal macroalgal habitats in each country and the invertebrate communities within them.

Methods: We measured variation in patch- and individual-level characteristics of macroalgal habitats and their invertebrate communities. Patterns in macroalgal characteristics and communities were compared across latitude, and at smaller spatial scales, and correlated with 26 abiotic environmental variables using multiple multivariate analyses.

Results: Separately, macroalgal habitat characteristics and communities showed unusual but consistent non-linear latitudinal patterns, with greater similarity among sites at the edges of the sampled distribution (i.e. north and south) than at centrally-located sites. Macroalgal characteristics did not correlate with a particular set of environmental variables, however, communities were structured by sea surface temperature at the country scale, and by macroalgal habitat type and biomass within countries. Anthropogenic variables were also important and may have contributed to the unusual non-linear patterns observed between macroalgal characteristics and communities across latitude.

Main conclusions: Our results support other studies showing that large-scale patterns can emerge from systems where there is high local-scale variability. The results show that communities within macroalgal habitats respond to both the physical characteristics of the habitat and external environmental conditions (e.g. temperature). Suggesting that local-scale environmental factors, including anthropogenic stressors may modulate environmental gradients over larger scales.

Methods

Study sites

We sampled a single rock platform (25 – 75 m long) at each of 18 sites across the temperate east coasts of Australia and New Zealand (Fig. 1). In Australia, we surveyed 10 sites from Bonny Hills in Northern NSW to Eaglehawk Neck in Tasmania, ranging across more than 1,300 km (linear distance) (Fig. 1). In New Zealand, we surveyed eight sites from Leigh (northern New Zealand) to Shag Point, Otago (southern New Zealand) ranging across more than 1,000 km (Fig. 1). We selected Bonny Hills as the upper latitudinal limit of the study, as this coincides with the transition from temperate to sub-tropical climate, based on Köppen climate classes (Bureau of Meteorology, 2014). Within countries, sites were at least 10 km apart; however, sites were generally over 100 km linear distance from each other (Fig. 1). The latitudinal gradients sampled in both countries overlapped by 6.73 decimal degrees (Fig. 1). The east coasts of both countries were suitable for comparison as they have similar macroalgae and physiographic conditions – including large, flat rock platforms and moderate wave climates (National Institute of Water and Atmospheric Research, 2016; Shand & Carley, 2011).

Study organisms

We sampled three macroalgal species/complexes with distinctive physical characteristics in each country; two of which were shared between countries: Hormosira banksii (Turner) and red turfing algae (hereafter Coralline) (see Appendix Fig. S1 in Supporting Information). Hormosira banksii is a prostrate brown alga with beaded vesicles that are connected in chains 10 – 30 cm long. It is distributed in Tasmania and NSW in Australia and is widely distributed on both islands in New Zealand (Edgar, 2008). Coralline included several morphologically similar species from the family Corallinaceae (e.g. Corallina officinalis, Amphiroa spp., Jania spp.). Species from the family Corallinaceae are widely distributed in temperate Australia and New Zealand (Atlas of living Australia website, 2018 at http://www.ala.org.au. Accessed 01 July 2018) and different species occurred interchangeably throughout the study area. Grouping of Coralline species at the family level as a morphologically similar complex has also been done in other similar studies on habitat-community associations (Kelaher, 2002, 2003a). The third macroalgal habitat sampled was Sargassum spp. (hereafter Sargassum) in Australia and Cystophora spp. (hereafter Cystophora) in New Zealand, which are closely related brown algae that occur in the lower intertidal zone (Edgar, 2008). These two habitats are both brown frondose, branching seaweeds, with receptacles either on branches in Sargassum or on vegetative fronds in Cystophora (Edgar, 2008). Cystophora was sampled at the genus level as multiple species occurred throughout the study area (e.g. Cystophora retroflexa, Cystophora scalaris, and Cystophora torulosa) that would provide a broadly similar physical habitat structure compared to the other habitats, as fucoids with branching fronds. For Sargassum, numerous, morphologically similar, species co-occur in Australia and accurate identification is difficult, being based on the seasonal size and shape of receptacles (reproductive structures at the end of the algal branches) (Edgar, 2008); therefore, this habitat was categorised to genus. Sargassum are broadly distributed in Australia (though absent at some specific study sites, see below) and Cystophora are widely distributed in New Zealand (Atlas of living Australia website, 2018 at http://www.ala.org.au. Accessed 01 July 2018; Edgar, 2008). At each site, we sampled three macroalgal habitats except in: 1) Leigh and Picton in New Zealand where H. banksii was absent, 2) Cook’s Beach in New Zealand where Cystophora was absent, 3) Coles Bay in Australia where Coralline was absent, and 4) Eden and the two Tasmanian sites in Australia where Sargassum was absent (Fig. 1).

Spatial patterns in macroalgal habitat characteristics

All macroalgal taxa were surveyed from January 2012 to early April 2012. Australian sites were sampled in a random order between January and April and New Zealand sites were sampled over a three-week period in February. As ocean temperatures lag seasonally, the sampling period represented summer water temperatures. At each site we sampled six replicate patches of each macroalgal habitat during low tide across the length of the rock platform (Fig. 2). The habitat patches selected occurred as discrete mono-specific patches with less than 10% of other habitat-forming organisms present.

Two patch-level characteristics were measured (patch area and percentage cover), plus two individual-level characteristics (frond length and biomass) of the macroalgae. Patch area was estimated by multiplying the longest and widest dimensions of each patch. Frond length was determined from the average of 10 randomly selected fronds measured at the patch centre. Percentage cover of algae was approximated using a grid of regularly spaced points in a 25 x 25 cm quadrat. Macroalgal biomass was determined from two replicate core samples per patch. PVC cores (10 cm diameter) were collected near the centre of each patch, with algae scraped off at the rock surface with a paint scraper and placed into labelled plastic bags (Kelaher, Castilla, & Seed, 2004; Thrush et al., 2011). Biomass samples were rinsed over a 1 mm sieve to remove trapped sediment. After excess water was drained, the algae were weighed in the field on digital scales (nearest 1 g). The two samples were then pooled to determine patch biomass. To ensure wet weight was an appropriate measure of biomass, samples of each macroalgal taxa were taken back to the lab and oven dried at 60°C for 48 hours to determine dry weight (n=12 cores/habitat). For each macroalga, wet and dry weights all were significantly correlated (Pearson’s Correlation coefficient; r >0.90).

Spatial patterns in communities

Invertebrate communities in macroalgal patches were sampled using one of the PVC cores and collecting the invertebrates retained on the 1 mm sieve. To capture large or benthic invertebrates that may not be collected in the cores, a 25 x 25 cm quadrat with a 5 x 5 cm grid was used to survey larger, benthic invertebrates in each patch. The survey was conducted by searching the fronds and substrate in each of the quadrat grid cells for macroinvertebrates (>2cm). All invertebrates from each patch (core + quadrat) were combined in a labelled plastic bag to capture one composite replicate patch (Fig. 2). The sample was later fixed in 7% formalin for a minimum of one week before being washed and transferred to 80% ethanol for preservation.

In the laboratory, all animals were identified and counted under a dissecting microscope. Molluscs were identified to family level and below (down to species), polychaetes to family level, crustaceans to order or suborder, echinoderms to class, Anthozoa to order, and foraminifera to phylum. The level of taxonomic identification related to the taxonomic group’s dominance among samples and the condition of the samples required for fine scale identification (e.g. although amphipods were a dominant group due to the high volume of collections and the time required to process the samples, some diagnostic features degraded after collection). It was also deemed more useful to include a large range of taxonomic groups identified to a coarse taxonomic level rather than a smaller range of taxa identified to species level in order to maximise chances of detecting habitat-community associa....see Dryad link for full text

目标：生物源栖息地的物理特征与环境条件是生物多样性的重要决定因素，但其相对重要性会随空间尺度变化。本研究旨在阐明大型藻类栖息地（macroalgal habitats）物理特征与其无脊椎动物群落的关系如何跨空间尺度变化，以及两国间是否存在普遍的生态模式。

地点：澳大利亚温带东海岸（超过1300公里）与新西兰温带东海岸（超过1000公里）的18个站点，两国纬度梯度重叠6.73十进制度。

时间范围：2012年1月至4月初。

主要研究类群：两国各三种潮间带大型藻类栖息地及其内的无脊椎动物群落。

方法：我们测量了大型藻类栖息地的斑块水平特征（patch-level characteristics）与个体水平特征（individual-level characteristics）及其无脊椎动物群落的变异。通过多变量分析，比较了纬度间及更小空间尺度下大型藻类特征与群落的模式，并将其与26个非生物环境变量关联。

结果：大型藻类栖息地特征与群落各自呈现出不同寻常但一致的非线性纬度模式——采样分布边缘（即北部和南部）站点间的相似性高于中部站点。大型藻类特征与特定环境变量集无显著关联，但群落结构在国家尺度上受海表温度调控，在国家内部则受大型藻类栖息地类型及生物量影响。人为变量同样重要，可能是导致纬度梯度上大型藻类特征与群落间观察到的异常非线性模式的原因之一。

主要结论：本研究结果支持其他研究的观点——高局部尺度变异性的系统中可涌现大尺度模式。结果表明，大型藻类栖息地内的群落同时响应栖息地物理特征与外部环境条件（如温度），提示包括人为压力在内的局部环境因素或可调节更大尺度的环境梯度。

方法

研究站点

我们在澳大利亚与新西兰温带东海岸的18个站点各选取一个岩石平台（25-75米长）进行采样（图1）。澳大利亚境内，从新南威尔士州北部的Bonny Hills到塔斯马尼亚州的Eaglehawk Neck共调查10个站点，跨度超过1300公里（直线距离）（图1）；新西兰境内，从北部的Leigh到南部奥塔哥的Shag Point共调查8个站点，跨度超过1000公里（图1）。选择Bonny Hills作为研究的最高纬度界限，因其符合柯本气候分类（Köppen climate classes）中温带向亚热带气候的过渡带（澳大利亚气象局，2014）。同一国家内的站点间距至少10公里，且通常超过100公里直线距离（图1）。两国采样的纬度梯度重叠6.73十进制度（图1）。两国东海岸具有相似的大型藻类与地貌条件（包括大型平坦岩石平台与中等波浪气候），适合对比研究（新西兰水与大气研究所，2016；Shand & Carley，2011）。

研究生物

我们在两国各采样三种具有独特物理特征的大型藻类物种/复合体，其中两种为两国共有：Hormosira banksii（Turner）与珊瑚藻（Coralline）（见支持信息附录图S1）。Hormosira banksii是一种匍匐状褐藻，具有串状连接的珠状囊泡，长度10-30厘米，分布于澳大利亚的塔斯马尼亚与新南威尔士州，以及新西兰的两大岛屿（Edgar，2008）。珊瑚藻包括珊瑚藻科（Corallinaceae）中几种形态相似的物种（如Corallina officinalis、Amphiroa spp.、Jania spp.），广泛分布于温带澳大利亚与新西兰（澳大利亚生物地图集网站，2018，http://www.ala.org.au，2018年7月1日访问），且不同物种在研究区域内交替出现。将珊瑚藻科物种作为形态相似复合体进行分组的方法，也应用于其他栖息地-群落关联研究（Kelaher，2002，2003a）。第三类大型藻类栖息地：澳大利亚为马尾藻属（Sargassum spp.），新西兰为囊藻属（Cystophora spp.），二者均为亲缘关系较近的褐藻，分布于低潮间带（Edgar，2008）。这两类栖息地均为褐藻门叶状分枝海藻，马尾藻的生殖托位于分枝上，囊藻则位于营养叶上（Edgar，2008）。囊藻属以属级采样，因其研究区域内存在多种物种（如Cystophora retroflexa、Cystophora scalaris、Cystophora torulosa），作为具有分枝叶的墨角藻目，其提供的物理栖息地结构与其他栖息地大致相似。澳大利亚的马尾藻属因多种形态相似物种共存，且准确鉴定需基于生殖托（藻枝末端的生殖结构）的季节性大小与形状（Edgar，2008），难度较大，故也以属级分类。马尾藻属广泛分布于澳大利亚（部分研究站点缺失，见下文），囊藻属广泛分布于新西兰（澳大利亚生物地图集网站，2018，http://www.ala.org.au，2018年7月1日访问；Edgar，2008）。每个站点采样三种大型藻类栖息地，以下情况除外：1）新西兰Leigh与Picton站点缺失H. banksii；2）新西兰Cook’s Beach站点缺失囊藻属；3）澳大利亚Coles Bay站点缺失珊瑚藻；4）澳大利亚Eden及两个塔斯马尼亚站点缺失马尾藻属（图1）。

大型藻类栖息地特征的空间模式

所有大型藻类类群的采样时间为2012年1月至4月初。澳大利亚站点在1月至4月间随机采样，新西兰站点在2月的三周内完成采样。因海洋温度存在季节滞后，采样期代表夏季水温。每个站点低潮时，沿岩石平台长度方向对每种大型藻类栖息地采样6个重复斑块（图2）。所选栖息地斑块为离散的单物种斑块，其他造境生物占比低于10%。

测量指标包括两种斑块水平特征（斑块面积与覆盖度）及两种大型藻类个体水平特征（叶长与生物量）。斑块面积通过斑块最长与最宽维度相乘估算；叶长为斑块中心随机选取10片叶的平均值；藻类覆盖度通过25×25厘米样方内规则分布的点网格近似估算；大型藻类生物量通过每个斑块的两个重复核心样本测定。在每个斑块中心附近采集PVC cores（直径10厘米），用刮刀从岩石表面刮下藻类，放入标记塑料袋（Kelaher，Castilla，& Seed，2004；Thrush等，2011）。生物量样本经1毫米筛网冲洗以去除截留沉积物，沥干多余水分后，在野外使用电子秤称重（精确至1克），两个样本合并得到斑块生物量。为验证湿重作为生物量指标的适用性，将每种大型藻类的样本带回实验室，60℃烘干48小时测定干重（n=12核心/栖息地）。所有大型藻类的湿重与干重均显著相关（皮尔逊相关系数r>0.90）。

群落的空间模式

大型藻类斑块中的无脊椎动物群落通过其中一个PVC core采样，收集1毫米筛网截留的无脊椎动物。为捕获核心采样可能遗漏的大型或底栖无脊椎动物，每个斑块使用25×25厘米、含5×5厘米网格的样方调查大型底栖无脊椎动物（>2厘米）：搜索样方网格单元内的藻叶与基质。每个斑块的无脊椎动物（核心+样方）合并至标记塑料袋，形成一个复合重复斑块（图2）。样本经7%福尔马林固定至少一周后，清洗并转移至80%乙醇中保存。

实验室中，在解剖镜下鉴定并计数所有动物：软体动物鉴定至科及以下（物种级），多毛类至科级，甲壳类至目或亚目，棘皮动物至纲级，珊瑚虫至目级，有孔虫至门级。分类鉴定水平取决于类群在样本中的优势度及精细鉴定所需的样本状态（例如，端足类虽为优势类群，但因样本量大且处理耗时，部分诊断特征在采集后降解）。研究认为，纳入大量粗分类水平的类群比少量物种级类群更有助于检测栖息地-群落关联……详见Dryad链接获取全文