Behaviour traits like sociality have been identified as factors promoting invasiveness. Studying the manner in which animals are distributed in their natural environment relative to conspecifics and other species provides basic information about behavioural aspects, including social tendencies, aggressiveness, nesting and mating system, among others. The invasive shrimp Palaemon macrodactylus has shown aggressive behaviour in laboratory conditions, whereas in natural conditions it seems to live aggregated, sharing patchy habitats with other species such as the small goby fish Gobiosoma parri. In this study we investigated the abundance, density, group structure (i.e. size, sex, reproductive condition), and the possible coexistence of P. macrodactylus with G. parri in the fouling community of Mar del Plata harbour (Argentina), where this shrimp has invaded and established a stable population since 2000. Samples taken included all individuals present in each fouling patch. The results show that P. macrodactylus, inhabiting in the fouling community, are in groups of up to 20 individuals, without sex or size structure and that a positive correlation exists with the goby fish. This suggests a gregarious behaviour, and tolerance to other species using the same area, at least in an environment with high availability of refuges, traits that may be crucial for a successful invader. The persistence of such behaviour in different contexts and the effect of refuge should be investigated in order to fully understand and make predictions of new invasions.

社交等行为特征已被确认为促进侵袭性的因素。研究动物在自然环境中相对于特定物种和其他物种的分布方式，可提供有关行为方面的基本信息，包括社会趋势，侵略性，筑巢和交配系统等。入侵虾Palaemon macrodactylus在实验室条件下表现出侵略性，而在自然条件下，它似乎生活在聚集状态，与其他物种（如小虾虎鱼Gobiosoma parri）共享斑驳的栖息地。在这项研究中，我们调查的丰富度，密度，集团结构（即大小，性别，生殖状况），以及可能的共存P.趾鼠耳蝠与G. parri位于马德普拉塔港口（阿根廷）的结垢群落中，自2000年以来，该虾已在那里入侵并建立了稳定的种群。所采集的样本包括每个结垢斑块中的所有个体。结果表明，生活在结垢群落中的大型假单胞菌（P. macrodactylus）最多由20个个体组成，没有性别或大小结构，并且与虾虎鱼呈正相关。这表明，至少在避难所的可用性高的环境中，该群居的行为和对使用同一区域的其他物种的耐受性对成功入侵者可能至关重要。为了充分理解和预测新的入侵，应研究这种行为在不同情况下的持久性以及避难所的影响。