No document available.
Abstract :
[en] Invasive species are a major threat to biodiversity. They are defined as species that occur outside their native range, complete their life cycle in the non-native ecosystem, and become locally dominant there. Among the 1,400 extant species of sea spiders (i.e., pycnogonids), ubiquitous yet understudied marine chelicerates, none of them fell under the definition of invasive species. That was until a population of Ammothea hilgendorfi (Böhm, 1879) was discovered in 2022 in Belgium. Native from the North Pacific Ocean (i.e., Japan, USA), A. hilgendorfi was introduced in the late 1970s in Italy and the UK, then extended its range to several other European countries. While every record only consisted of punctual observations of a few specimens, the present study demonstrates that, in Belgium, this species meets all the criteria to be defined as invasive.
More than 1,000 individuals were collected in a monthly monitoring over a 24-month period. By discriminating juveniles, females, males, and males bearing eggs, the phenology of A. hilgendorfi was elucidated, and a periodicity in their life cycle was highlighted. In addition, each larval instar was observed in microscopy and morphologically described, a first for this species.
The present study also raises concern on their invasiveness and potential impact. Since no similar case exists elsewhere in the world, there is nothing this population can be compared with, and everything must be studied from scratch. Yet, this population represents a unique opportunity to deepen the general knowledge on sea spiders, understanding how A. hilgendorfi has become so successful, and assessing its impact on invaded ecosystems.
