Marine coastal habitats are often characterized by strong gradients of anthropogenic disturbance such as pollution, typically most severe at urban waterfronts. These variations create stress for local organisms leading to their distribution along the disturbance as a function of their tolerance. non-indigenous species (NIS) are considered more tolerant to anthropogenic disturbances than their native counterparts, thriving in urban areas, where native species are sparser. It is however not yet entirely clear if these distribution patterns are due to larval behavior and preferential settlement or post-settlement processes. In the present study, we investigated the abundance of adults and settlers of two native (Ostrea edulis, Mytilus galloprovincialis) and two non-indigenous (Magallana gigas, Xenostrobus securis) bivalves along a strong marine urban environmental gradient. Oysters had sparse abundances of both adults and settlers at all sites, with no obvious distributional gradients. The two mussel species showed different settler-adult distributions along the gradient. Both settlers and adults of the native mussel M. galloprovincialis strongly decreased moving from the outermost periurban site to the innermost urban site, consistent with preferential settlement of larvae according to environmental conditions. The non-indigenous adult mussel X. securis showed a distribution pattern opposite to that of M. galloprovincialis, markedly increasing in abundance from the outermost to the innermost site. This was not paralleled by the distribution of X. securis settlers, which established over a larger area, including sites where adults were essentially absent. The mismatch between settler and adult distributions for X. securis suggests that post-settlement factors dictate spatial adult distribution.

中文翻译：

---

本地和非本地双壳类动物及其定居者沿城市梯度的分布


海洋沿海栖息地的特点往往是污染等人为干扰的强烈梯度，通常在城市滨水区最为严重。这些变化给当地生物体带来了压力，导致它们沿着干扰分布，作为其耐受性的函数。非本土物种（NIS）被认为比本土物种更能耐受人为干扰，在本地物种稀少的城市地区繁衍生息。然而，尚不完全清楚这些分布模式是否是由于幼虫行为和优先定居或定居后过程造成的。在本研究中，我们调查了两种本地人的成年人和定居者的丰度（牡蛎、地中海贻贝）和两个非土著（ Magallana gigas、Xenostrobus securis ）沿着强烈的海洋城市环境梯度的双壳类。所有地点的牡蛎成体和定居者数量均稀疏，没有明显的分布梯度。这两种贻贝物种沿梯度显示出不同的定居者-成体分布。本地贻贝的定居者和成体省马氏菌从最外围的城郊地点到最内部的城市地点的移动强烈减少，这与幼虫根据环境条件优先定居的情况一致。非本地成年贻贝X. 证券表现出与省马氏菌，从最外层到最内层的丰度显着增加。这与分布不平行X. 证券定居者在更大的区域建立定居点，包括成年人基本上不存在的地方。 定居者和成人分布之间的不匹配X. 证券表明定居后因素决定了成人的空间分布。