Non-Indigenous Species Dynamics in Time and Space within the Coastal Waters of The Netherlands

Abstract

Information on temporal and spatial trends with regard to the introduction of non-indigenous species (NIS) is often sparsely available. These trends may potentially help improve the design and focus of monitoring programs, give insights into new pathways and hotspots, and facilitate horizon scanning. We provide an overview of 215 marine and brackish water NIS recorded in The Netherlands. Temporal trends over the most recent three decades for taxonomic groups, species origin, introduction vectors, and water systems were analysed. We attempt to explain the observed patterns and discuss factors that hamper their explanation. A shift in the region of origin from Pacific to W Atlantic can potentially be linked to legislation prohibiting Pacific oyster imports, whereas a subsequent shift backwards cannot. Case studies illustrate that NIS may not be first detected in the water systems where they were originally introduced. Additionally, it is shown that changes in allegedly native species’ distribution or seasonal pattern should be linked to an introduced cryptic NIS instead. We also discuss the shortcomings of monitoring programs that were originally not focused on NIS, the importance of naturalists’ observations, and the added value of a more recent network that is focused on NIS detection in the coastal waters of The Netherlands.

DNA metabarcoding-based detection of non-indigenous invertebrates in recreational marinas: influence of sample type and seasonal variation

“…All these factors contribute to fluctuations in species composition and abundance. These differences due to seasonality further justify the need to sample broader time spans to better understand species, NIS communities and their dynamics and to further correlate NIS introductions with biotic and abiotic factors (Gittenberger et al 2023).…”

“…Many efforts have been made recently to publish updated lists of NIS in European waters and to further monitor its distribution as well as to study its introduction history (Gittenberger et al 2023; Jensen et al 2023; Png-Gonzalez et al 2023). In a recent NIS inventory in Spanish marine waters, approximately 65% of NIS were invertebrates (Png-Gonzalez et al 2023).…”

“…In a study of NIS in the coastal waters of the Netherlands, the majority of invertebrate NIS belonged to Crustacea, Mollusca, and Annelida. With a mention that bryozoans have become a very relevant group of NIS, which may be connected to hull fouling as one of the most important vector in NIS introduction in recent years (Gittenberger et al 2023). The same study also concluded that the number of introductions by biofouling appears to have increased in the last decade, while introductions by aquaculture and fisheries seem to have decreased (Gittenberger et al 2023).…”

“…With a mention that bryozoans have become a very relevant group of NIS, which may be connected to hull fouling as one of the most important vector in NIS introduction in recent years (Gittenberger et al 2023). The same study also concluded that the number of introductions by biofouling appears to have increased in the last decade, while introductions by aquaculture and fisheries seem to have decreased (Gittenberger et al 2023). In addition, it is very common to observe detached gear and other floating litter, namely plastic, in ports and recreational marinas.…”

“…The employment of these techniques constitutes an important complement or early warning system that will enable to manage in a timelier manner the detection of an invasive species at an early stage of introduction. For example, in the Port of Vlissingen, the genetic material of a NIS was detected three years before the specimens were physically found (Gittenberger et al 2023). Early detection of NIS is also important to determine pathways and vectors of introductions, as well as to resolve cryptic species (Gittenberger et al 2023).…”