The Indo-Pacific sea urchin Diadema setosum has invaded the Mediterranean Sea and has spread along many locations in the southeastern part of the basin, where established populations exist on the shallow subtidal rocky shore. Diadema setosum is a ubiquitous species, of particular ecological importance due to the high levels of grazing pressure it imposes on benthic communities. Its biology, however, is not adequately studied, especially along its introduced range of distribution. The present study examines the population status of D. setosum outside its native range, in the Dodecanese island complex, south Aegean Sea. Thirty-four stations located across 16 islands were surveyed by scientific SCUBA-diving (up to a depth of 10 m) in December 2019 and June-July 2020. Samplings included: (i) visual census along transects to estimate relative abundance and population density, and (ii) random collection of specimens from densely populated stations to assess biometry and reproductive condition (histological examination of gonads) of D. setosum. Diadema setosum was found in 21 out of the 34 surveyed stations. The species had sparse populations of well-hidden individuals in rocky crevices, but with dense localized patches in Agathonisi, Leros, Kalymnos, Pserimos, Symi, Alimia and Chalki islands. In those seven islands, mean population density was 2.5 ± 1.48 individuals m−2. Diadema setosum had denser populations in shallower depths but larger dimensions in deeper; these results suggest segregated density and size patterns along a depth gradient. The size structure, according to the size frequency distribution of the test diameter, was unimodal with a fitted mode at 4.0–4.5 and 6.5–7.0 cm in shallow and deep populations, respectively. The examined morphometric relationships followed negative allometry, as previously suggested for the species within its native range of distribution, and test diameter appeared to be a good predictor of biomass. Diadema setosum specimens had immature gonads in winter and mature in summer, suggesting a synchronous reproductive pattern. These results conform to previous data from temperate populations of the species. Differences in local environmental conditions, e.g. hydrodynamics and habitat type, together with biotic interactions, e.g. recruitment and competition, probably shape D. setosum population in the south Aegean distributional range. The establishment of D. setosum has severe implications on benthic communities and local sea urchin populations demanding management measures to prevent the forecasted further expansion of this invasive species.

中文翻译：

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爱琴海南部（地中海东部）侵入性海胆Diadema setosum（Leske，1778）的丰度和种群特征

印度洋-太平洋海胆Diadema setosum入侵了地中海，并在该盆地东南部的许多地方蔓延，浅滩下的多岩石海岸上已有定居的种群。实蝇（Diadema setosum）是一种普遍存在的物种，由于它对底栖生物群落施加了很高的放牧压力，因此具有特别的生态重要性。然而，对其生物学的研究还不够充分，尤其是在其引入的分布范围内。本研究调查了爱琴海南部多德卡尼斯群岛情结中的定居点石outside的种群状况。在2019年12月和2020年6月至2020年6月之间，通过科学的SCUBA潜水（最大深度为10 m）对位于16个岛屿的34个站点进行了调查。抽样包括：（i）沿剖面进行视觉普查，以估计相对丰度和种群密度，以及（ii）从人口稠密的站点中随机采集标本，以评估Setosum的生物特征和生殖状况（生殖腺的组织学检查）。在34个被调查站中的21个中发现了Setdum。该物种在岩石缝隙中藏匿着稀疏的个体，但在Agathonisi，Leros，Kalymnos，Pserimos，Symi，Alimia和Chalki岛上有密集的局部斑块。在这七个岛屿中，平均人口密度为2.5±1.48个个体m-2。硬脂泻在较浅的深度具有较密集的种群，而在较深的则具有较大的种群。这些结果表明，沿深度梯度分离出密度和尺寸模式。尺码结构，根据尺码频率分布的测试直径，是单峰的，在浅层和深层种群中的拟合模式分别为4.0–4.5和6.5–7.0 cm。如先前在其天然分布范围内对物种进行的建议，所检查的形态计量关系遵循负异构法，并且测试直径似乎是生物量的良好预测指标。硬皮水母标本在冬季有不成熟的性腺，而在夏季则成熟，表明其繁殖方式是同步的。这些结果与该物种的温带种群的先前数据相符。当地环境条件的差异（例如水动力和生境类型）以及生物相互作用（例如募集和竞争），可能会影响爱琴海南部分布地区的实蝇（D. setosum）种群。D的建立