Abstract
The introduction of aquatic non-indigenous species (ANS) has become a major driver for global changes in species biogeography. We examined spatial patterns and temporal trends of ANS detections since 1965 to inform conservation policy and management. Global. We assembled an extensive dataset of first records of detection of ANS (1965-2015) across 49 aquatic ecosystems, including the (a) year of first collection, (b) population status and (c) potential pathway(s) of introduction. Data were analysed at global and regional levels to assess patterns of detection rate, richness and transport pathways. An annual mean of 43 (±16 SD) primary detections of ANS occurred-one new detection every 8.4 days for 50 years. The global rate of detections was relatively stable during 1965-1995, but increased rapidly after this time, peaking at roughly 66 primary detections per year during 2005-2010 and then declining marginally. Detection rates were variable within and across regions through time. Arthropods, molluscs and fishes were the most frequently reported ANS. Most ANS were likely introduced as stowaways in ships' ballast water or biofouling, although direct evidence is typically absent. This synthesis highlights the magnitude of recent ANS detections, yet almost certainly represents an underestimate as many ANS go unreported due to limited search effort and diminishing taxonomic expertise. Temporal rates of detection are also confounded by reporting lags, likely contributing to the lower detection rate observed in recent years. There is a critical need to implement standardized, repeated methods across regions and taxa to improve the quality of global-scale comparisons and sustain core measures over longer time-scales. It will be fundamental to fill in knowledge gaps given that invasion data representing broad regions of the world's oceans are not yet readily available and to maintain knowledge pipelines for adaptive management.
Highlights
Analyses of long-term datasets on species introductions can provide insights into past and future trends to inform conservation management (Seebens et al, 2017; van Kleunen et al, 2015), yet such studies are relatively rare, for aquatic ecosystems where species introductions are often more difficult to detect and study (Ojaveer et al, 2015)
Our analyses identified 2209 primary detection events of 1442 unique aquatic non-indigenous species (ANS) over the past 50 years which, confounded by time-lags between actual introduction and detection, likely is an underestimate of the actual number of introductions during this time period
It is widely recognized that ANS are frequently underreported due to limited search effort, uncertainty about historical biogeography and an insufficiency of taxonomic expertise (Carlton & Fowler, 2018; Ojaveer et al, 2017), especially for smaller-bodied organisms (Carlton, 2009; Lohan et al, 2020)
Summary
Analyses of long-term datasets on species introductions can provide insights into past and future trends to inform conservation management (Seebens et al, 2017; van Kleunen et al, 2015), yet such studies are relatively rare, for aquatic ecosystems where species introductions are often more difficult to detect and study (Ojaveer et al, 2015). Despite the expected surge in species delivery to novel aquatic ecosystems, prior studies examining detection rates and/ or pathways of aquatic non-indigenous species (ANS) have been conducted at local or regional scales As introductions of many different ANS have occurred and continue to occur worldwide, studies are needed at a global scale to provide a robust understanding of invasion dynamics, identify needed management strategies and evaluate policy effectiveness in aquatic ecosystems. In recognition of the urgent need to address the impacts of non-indigenous species, the CBD states that each contracting party shall, as far as possible and as appropriate, “prevent the introduction of, control or eradicate those alien species which threaten ecosystems, habitats or species” (UNEP, 1994). New goals for 2021–2030 are currently being drafted, with prevention and pathway management likely to remain important components of the strategy
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