A long-term study (1949–2015) of the aftermaths of the deliberate experimental introduction of an invasive freshwater amphipod (Crustacea) to a small Island

Calum Macneil,Marnie Campbell

doi:10.3391/ai.2018.13.4.07

Abstract

The ability to track changing distributions and long-term inter actions between native and introduced species provides insights into forecasting impacts of invaders. We used data from deliberate field introduction experiments of a freshwater Gammarus amphipod (Crustacea) to the rivers of a small British island, The Isle of Man. The deliberate introductions commenced in 1949 and re-sampling occurred in the ‘60s, ‘70s ‘80s, ‘90s, 200 5 and finally in 2015. The findings generally confirmed the failure of introductions of Gammarus pulex into sites previously dominated by the native Gammarus duebeni celticus even with high propagule pressure in terms of numbers of individual invaders released and repeated introductions. Despite this, the island-wide 2015 survey revealed that G. d. celticus occurred in fewer sites and G. pulex in more sites than a decade earlier, indicating at this island-wide scale, the displacement of G. pulex by G. d. celticus seems to be continuing. In addition, one of the introduction sites, Arbory Stream which contained G. d. celticus from 1951–2005 contained only G. pulex in 2015, showing that even after six decades, assumptions cannot be made as to the limits of invader range expansion. Multivariate analysis of physico-chemical data from the 2015 island-wide sur vey revealed water quality as a crucial environmental gradient that influences the distributions of the native and invader species, with the former in higher organic water quality sites than sites with the invader or where invader and native co-occurred. The North American amp hipod Crangonyx pseudogracilis had expanded its range since 2005, including invading low biological water quality sites previously devoid of both Gammarus spp.. Pollution from historic metal mining is implicated as a potential major factor excluding amphipods. This deliberate ecological experiment, through long-term monitoring, continues to provide insights into the factors determining the distributions of natives and invaders.

Highlights

Freshwater amphipod crustaceans feature in many global invasions, via both unintentional and deliberate introductions
Regarding the original six G. pulex introduction sites of Hynes (Table 1), the original three sites that contained G. d. celticus still contained only G. d. celticus throughout all subsequent surveys. This pattern persists despite deliberate introductions and high propagule pressure in terms of numbers of individuals released in repeated bouts in several sites (Lockwood et al 2005)
Sites 8–10 remained similar in amphipod species composition between 1995 and 2015 (Table 1), except for site 9, where C. pseudogracilis was detected for the first time in 2015

Summary

Introduction

Freshwater amphipod crustaceans feature in many global invasions, via both unintentional and deliberate introductions These invasions are often related to industrial and recreational shipping, fish farming, sport fishing and even ecological experiments (MacNeil et al 1999, 2009; Dick et al 2017). Focusing on the underlying reasons for the success and failure of introductions remains a crucial issue for ecological management and protection of native flora and fauna, as it may provide insights for the prediction of future invader impacts (Bollache et al 2008; Dodd et al 2014; Dick et al 2017) In this regard, very long-term studies with well monitored sites, including sites of initial introduction / invasion and detailed data-sets of native-invasive assemblages and abiotic variables are both increasingly rare and invaluable. Periodic reporting on long-term data sets offers opportunities to continuously monitor changes and bring new insights to invasion biology

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Conclusion