Ocean acidification (OA) can negatively affect early-life stages of marine organisms, with the key processes of larval settlement and metamorphosis potentially vulnerable to reduced seawater pH. Settlement success depends strongly on suitable substrates and environmental cues, with marine biofilms as key settlement inducers for a range of marine invertebrate larvae. This study experimentally investigated (1) how seawater pH determines growth and community composition of marine biofilms, and (2) whether marine biofilms developed under different pH conditions can alter settlement success in the New Zealand serpulid polychaete Galeolaria hystrix. Biofilms were developed under six pH_(T) treatments (spanning from 7.0 to 8.1 [ambient]) in a flow-through system for up to 14 months. Biofilms of different ages (7, 10 and 14 months) were used to assay successful settlement of competent G. hystrix larvae reared under ambient conditions. Biofilm microbiomes were characterized through amplicon sequencing of the small subunit ribosomal rRNA gene (16S and 18S). Biofilm community composition was stable over time within each pH treatment and biofilm age did not affect larval settlement selectivity. Seawater pH treatment strongly influenced biofilm community composition, as well as subsequent settlement success when biofilms were presented to competent Galeolaria larvae. Exposure to biofilms incubated under OA-treatments caused a decrease in larval settlement of up to 40% compared to the ambient treatments. We observed a decrease in settlement on biofilms relative to ambient pH for slides incubated at pH 7.9 and 7.7. This trend was reversed at pH 7.4, resulting in high settlement, comparable to ambient biofilms. Settlement decreased on biofilms from pH 7.2, and no settlement was observed on biofilms from pH 7.0. For the first time, we show that long-term incubation of marine biofilms under a wide range of reduced seawater pH treatments can alter marine biofilms in such a way that settlement success in marine invertebrates can be compromised.

海洋酸化（OA）可能会对海洋生物的早期生长阶段产生负面影响，其中幼虫沉降和变态的关键过程可能容易受到海水pH值降低的影响。沉降成功很大程度上取决于合适的基质和环境提示，海洋生物膜是一系列海洋无脊椎动物幼体的关键沉降诱因。这项研究实验研究（1）海水pH值如何决定海洋生物膜的生长和群落组成，以及（2）在不同pH条件下形成的海洋生物膜是否可以改变新西兰蛇蝎子多毛龟Galeolaria hystrix的定居成功。生物膜在六个pH _（T）下显影在流通系统中进行的治疗（范围从7.0到8.1 [环境]）长达14个月。使用不同年龄（7、10和14个月）的生物膜来分析在环境条件下饲养的感受态G. hystrix幼虫的成功沉降。通过对小亚基核糖体rRNA基因（16S和18S）的扩增子测序来表征生物膜微生物群。在每个pH处理中，生物膜群落组成随时间稳定，并且生物膜年龄不影响幼虫沉降选择性。海水pH值处理强烈影响了生物膜群落组成，以及当将生物膜呈递给合格的Galeolaria时随后的定居成功幼虫。与环境处理相比，暴露于在OA处理下孵育的生物膜可导致幼虫沉降减少多达40％。对于在pH 7.9和7.7下孵育的玻片，我们观察到相对于环境pH的生物膜沉降减少。在pH 7.4时，这种趋势被逆转，导致高沉降，与周围的生物膜相当。pH 7.2以上的生物膜上的沉降减少，pH 7.0以上的生物膜上没有观察到沉降。我们首次表明，在广泛的降低海水pH值处理范围内长期培养海洋生物膜可以改变海洋生物膜，从而破坏海洋无脊椎动物的定居成功。