Peyssonnelid algal crusts (PAC) have rapidly spread on coral reefs throughout the Caribbean since 2010 and have become dominant space holders in multiple locations. In 2019, PAC covered 31–86% of the shallow reefs (< 6-m depth) at two sites in St. John, US Virgin Islands, but within halos around aggregates of the echinoid, Diadema antillarum, PAC was absent and small corals were common. To test the hypothesis that the density of small corals is greater in Diadema halos versus on adjacent substrata, and that this effect is accentuated by high coverage of PAC, the shallow reefs of St. John were surveyed in July/August 2019 and January 2020. Densities of small corals (pooled among taxa) in Diadema halos were equal to, or greater than, densities on adjacent substrata, and were highest in Diadema halos adjacent to areas with high coverage of PAC. Where the cover of PAC was ≥ ~ 10%, the mean (± SE) density of small corals was 23.3 ± 2.1 colonies m⁻² in Diadema halos, but was 67% lower at 7.5 ± 1.2 colonies m⁻² on adjacent substrata; where the cover of PAC was < ~10%, densities of small corals were nearly identical in Diadema halos (9.1 ± 0.9 colonies m⁻²) and on adjacent substrata (9.0 ± 1.1 colonies m⁻²). Similar results were obtained when the analyses were repeated for the common corals, Porites spp., Siderastrea radians, and S. siderea. As Diadema halos remained in the same location for at least 6 months, they may function as refuges for coral recruitment in locations where PAC is becoming spatially dominant.

自2010年以来，佩索内利德藻壳（PAC）在整个加勒比海的珊瑚礁上迅速蔓延，并已成为多个地区的主要空间持有者。2019年，PAC覆盖了美属维尔京群岛圣约翰两个地点的浅礁石（<6米深）的31–86％，但在类棘突类动物Diadema antillarum聚集体周围的光环内，缺少PAC和小珊瑚很常见。为了检验以下假设：迪亚德玛光环中的小珊瑚密度高于相邻地层，并且PAC覆盖率高，加剧了这种影响，在2019年7月/ 8月和2020年1月对圣约翰浅礁进行了调查。迪亚德玛（Diadema）小珊瑚的密度（聚集在分类群中）光晕等于或大于相邻基底的密度，并且在与PAC覆盖率高的区域相邻的Diadema光晕中最高。其中PAC的盖是≥〜10％，小珊瑚的平均（±SE）密度为23.3±2.1菌落中号^-2在迪亚德马光晕，但为67％在7.5±1.2的菌落低位m ^-2上相邻的基质; 当PAC的覆盖率<〜10％时，小珊瑚的密度在Diadema halos（9.1±0.9菌落m ^-2）和相邻基底层（9.0±1.1菌落m ^-2）几乎相同。重复分析常见的珊瑚，Porites spp。，可获得相似的结果。Siderastrea radians和S. siderea。由于Diadema光环在同一位置停留了至少6个月，它们可能在PAC在空间上占主导地位的位置充当珊瑚招募的避难所。