Invading oysters and native mussels: from hostile takeover to compatible bedfellows

Karsten Reise,Heike Büttger,K Mathias Wegner,Christian Buschbaum

doi:10.1002/ecs2.1949

Abstract

AbstractUnintended species introductions may offer valuable insights into the functioning of species assemblages. A spectacular invasion of introduced Pacific oysters Magallana (formerly Crassostrea) gigas in the northern Wadden Sea (eastern North Sea, NE Atlantic) has relegated resident mussels Mytilus edulis on their beds to subtenant status. At the beginning of feral oyster establishment, mussel beds offered suitable sites with ample substrate to settle upon. After larval attachment to mussels, the fast‐growing M. gigas overtopped and smothered their basibionts. With increasing Pacific oyster abundance and size, oyster larvae preferentially settled upon oysters, and the ecological impact of the invaders on the residents changed from competitive displacement to accommodation of mussels underneath a canopy of oysters. Oysters took the best feeding positions while mussels received shelter from predation and detrimental epibionts. The resident's mono‐dominance has turned into co‐dominance with an alien, persisting in novel, multi‐layered mixed reefs of oysters with mussels, which we term “oyssel reefs.” The first 26 yr of the Pacific oyster's conquest of mussel beds in the northern Wadden Sea may question the overcome notions of natural balance, superiority of pristine over novel species combinations, and of introduced alien species threatening biodiversity and ecosystem stability in general.

Highlights

In spite of the ecological insights that have been inferred from species invasions (Sax et al 2005, 2007), invasions and impacts of nonnative species are usually considered a great threat to biodiversity and ecosystem functioning (Simberloff et al 2013, Murcia et al 2014, Wilson 2016)
We investigated the effects of Pacific oysters Magallana gigas (Thunberg 1793; Salvi et al [2014] divided the former genus Crassostrea into Pacific Magallana and Atlantic Crassostrea species based on large genetic divergence) settling on Atlantic mussels Mytilus edulis L. in the sedimentary Wadden Sea
In 2006, the successful establishment of Magallana gigas had changed mussel beds, with large oysters projecting beyond the layer of mussels, attracting most of the competent oyster larvae which found ample attachment on oyster shells >100 mm on most beds (Fig. 3, Table 3)

Summary

Introduction

In spite of the ecological insights that have been inferred from species invasions (Sax et al 2005, 2007), invasions and impacts of nonnative species are usually considered a great threat to biodiversity and ecosystem functioning (Simberloff et al 2013, Murcia et al 2014, Wilson 2016). In 2006, the successful establishment of Magallana gigas had changed mussel beds, with large oysters projecting beyond the layer of mussels, attracting most of the competent oyster larvae which found ample attachment on oyster shells >100 mm on most beds (Fig. 3, Table 3).

Results

Conclusion