Habitat-Forming Bryozoans in New Zealand: Their Known and Predicted Distribution in Relation to Broad-Scale Environmental Variables and Fishing Effort

Frame-building bryozoans occasionally occur in sufficient densities in New Zealand waters to generate habitat for other macrofauna. The environmental conditions necessary for bryozoans to generate such habitat, and the distributions of these species, are poorly known. Bryozoan-generated habitats are vulnerable to bottom fishing, so knowledge of species’ distributions is essential for management purposes. To better understand these distributions, presence records were collated and mapped, and habitat suitability models were generated (Maxent, 1 km2 grid) for the 11 most common habitat-forming bryozoan species: Arachnopusiaunicornis, Cellariaimmersa, Cellariatenuirostris, Celleporariaagglutinans, Celleporinagrandis, Cinctiporaelegans, Diaperoeciapurpurascens, Galeopsisporcellanicus, Hippomenellavellicata, Hornerafoliacea, and Smittoideamaunganuiensis. The models confirmed known areas of habitat, and indicated other areas as potentially suitable. Water depth, vertical water mixing, tidal currents, and water temperature were useful for describing the distribution of the bryozoan species at broad scales. Areas predicted as suitable for multiple species were identified, and these ‘hotspots’ were compared to fishing effort data. This showed a potential conflict between fishing and the conservation of bryozoan-generated habitat. Fishing impacts are known from some sites, but damage to large areas of habitat-forming bryozoans is likely to have occurred throughout the study area. In the present study, spatial error associated with the use of historic records and the coarse native resolution of the environmental variables limited both the resolution at which the models could be interpreted and our understanding of the ecological requirements of the study species. However, these models show species distribution modelling has potential to further our understanding of habitat-forming bryozoan ecology and distribution. Importantly, comparisons between hotspots of suitable habitat and the distribution of bottom fishing in the study area highlight the need for management measures designed to mitigate the impact of seafloor disturbance on bryozoan-generated habitat in New Zealand waters.

造架苔藓虫（frame-building bryozoans）有时会在新西兰海域以足够高的种群密度出现，为其他大型底栖动物提供栖息生境。目前学界对这类苔藓虫形成栖息生境所需的环境条件，以及该类物种的分布范围仍知之甚少。苔藓虫营造的栖息生境极易受到海底拖网捕捞的破坏，因此掌握该类物种的分布信息对于渔业管理至关重要。为更好地厘清上述分布规律，研究人员整理了该类物种的出现记录并进行空间制图，同时针对11种最常见的造架苔藓虫物种构建了生境适宜性模型（最大熵物种分布模型（Maxent），1 km²网格），分别为：Arachnopusia unicornis、Cellaria immersa、Cellaria tenuirostris、Celleporaria agglutinans、Cellepora grandis、Cinctipora elegans、Diaperoecia purpurascens、Galeopsis porcellanicus、Hippomenella vellicata、Hornea foliacea以及Smittoidea maunganuiensis。该模型不仅验证了已知的生境分布区域，还预测出其他潜在适宜生境区域。在大空间尺度下，水深、水体垂直混合作用、潮流以及水温均能有效解释该类苔藓虫的分布格局。研究人员识别出同时适宜多种苔藓虫生存的区域（即"生境热点"），并将其与捕捞努力量数据进行对比，结果显示海底拖网捕捞与苔藓虫生境保护之间存在潜在冲突。现有研究已证实部分区域受到了捕捞活动的破坏，但整个研究区域内的大片造架苔藓虫生境大概率也已遭受不同程度的损伤。本研究中，因使用历史记录带来的空间误差，以及环境变量的原生粗分辨率，既限制了模型解读的精细尺度，也阻碍了我们对研究物种生态需求的深入理解。尽管如此，本研究构建的模型仍证实，物种分布建模技术可有效提升我们对造架苔藓虫生态特征与分布规律的认知水平。尤为重要的是，通过对比适宜生境热点区域与研究区域内海底拖网捕捞的分布情况，本研究明确了亟需制定相关管理措施，以缓解海底扰动对新西兰海域内苔藓虫营造生境的破坏影响。