Invasive ecosystem engineers threaten benthic nitrogen cycling by altering native infaunal and biofouling communities

O Floerl,L W Tait,G J Inglis,J Atalah,M Townsend,A M Lohrer

doi:10.1038/s41598-020-58557-8

Abstract

Predicting the effects of invasive ecosystem engineering species in new bioregions has proved elusive. In part this is because separating biological effects from purely physical mechanisms has been little studied and yet could help predict potentially damaging bioinvasions. Here we tested the effects of a large bio-engineering fanworm Sabella spallanzanii (Sabella) versus worm-like structures (mimics) on gas and nutrient fluxes in a marine soft bottom sediment. Experimental plots of sediment in Hauraki Gulf (New Zealand) were used to test the hypothesis that ecosystem engineers negatively influence benthic ecosystem function through autogenic mechanisms, facilitating activity by biofouling organisms and competitive exclusion of native infauna. Enhanced physical structure associated with Sabella and mimics increased nitrogen fluxes, community metabolism and reduced denitrification from 23 μmol m−2 h−1 to zero at densities greater than 25 m2. Sabella plots on average had greater respiration (29%), NH4 release (33%), and greater NO3 release (52%) compared to mimics, suggesting allogenic (biological) mechanisms occur, but play a secondary role to autogenic (physical) mechanisms. The dominance of autogenic mechanisms indicates that bio-engineers are likely to cause significant impacts when established, regardless of fundamental differences in recipient regions or identity of the introduced bio-engineer. In the case of Sabella spallanzanii, compromised denitrification has the potential to tip the balance of net solute and gas exchanges and cause further ecological degradation in an already eutrophic system.

Highlights

Predicting the effects of invasive ecosystem engineering species in new bioregions has proved elusive
Community respiration (O2, Fig. 2a; Table 1) and NO3 flux rates were greater in Sabella plots (Fig. 2e; Table 1), while dissolved reactive phosphorus (DRP) flux rates were greater in plots with mimics (Fig. 2c)
Ammonium (NH4, Fig. 2d, Table 1) and total dissolved inorganic N (DIN) flux (Fig. 2f, Table 1) increased with density of both Sabella and mimics (Fig. 2b, Table 1), but the significant density × treatment interaction suggested that the increase in fluxes of Sabella plots was greater than mimics

Summary

Introduction

Predicting the effects of invasive ecosystem engineering species in new bioregions has proved elusive. The impacts of introduced species on the ecology of recipient communities are most commonly reported as changes in native species populations, e.g., declines or extirpations of native species following outbreaks of non-native predators or competitors[3,9,14] This approach is problematic when attempting to translate introduced species impacts on a global scale, as each recipient ecosystem has highly variable species assemblages and ecosystem structures. Introduced species that disrupt native ecosystem engineers will, have greater consequences on the functioning of native ecosystems[18] In this sense, identifying the alteration of ecosystem functions performed by native functional groups (e.g., bioturbators, habitat-formers) may enable generalisation of introduced species impacts over broad scales, allow more accurate predictions of potential impact, and improve prioritisation of limited resources for management of marine bioinvasions. Allogenic engineering includes chemical modification effects such as increased production of organic rich biodeposits or enhanced excretion of ammonium[28]; interception and consumption of organic material[27]; and alteration of pore water solute concentrations and gradients (via oxygen respiration, ammonium excretion)

Methods

Results

Conclusion