The importance of nonnative Pacific oyster reefs as supplementary feeding areas for coastal birds on estuary mudflats

Abstract

A combined empirical and modelling approach was used to investigate the value of a Pacific oyster reef to feeding shorebirds and to observe and predict the impact of reef clearance on bird populations in the Colne Estuary, a protected area in south‐east England. Macro‐invertebrate biomass and numbers of feeding birds were measured on a Pacific oyster reef, an adjacent uncolonized mudflat, and an area of mudflat that had been cleared of oysters 6 months previously. These data were used to parameterize an individual‐based model (MORPH) to predict the impact of clearance of the reef on winter bird survival. Feeding success and intake rates of Eurasian oystercatcher, Eurasian curlew, and Eurasian common redshank were also recorded during the course of a winter. The macro‐invertebrate diversity and biomass within both the oyster reef and the cleared area were significantly greater than the adjacent uncolonized mudflat. The density and biomass of large invertebrate prey in the mudflat were low, yet the Pacific oyster reef had much higher densities and biomass of large prey, especially annelids and shore crabs. The winter assemblage of feeding birds differed significantly between each of the areas. The mean total number of feeding birds was significantly greater on the uncolonized mudflat; however, mean peak counts, feeding success rate and prey intake rate of Eurasian oystercatcher were greater on the reef. Significantly greater intake rates and feeding success rates were also observed on the reef for Eurasian curlew, a species of conservation concern. Field data and model predictions show that Pacific oyster reefs can provide valuable supplementary feeding areas for some shorebirds, yet other species avoided the reef. However, as estuaries vary in available feeding resources, it is important that the value of reefs and their management is determined regionally.

The global fall and rise of oyster reefs

“…However, the Pacific oyster also provides functional services that may benefit human society or increase the resilience of coastal communities to change (Troost 2010; Herbert et al . 2018). We consider new ways of thinking about the pros and cons of the expanding global range of Pacific oysters, which appear to be on the verge of re‐establishing oyster habitat in many coastal areas where native oyster reefs have been lost, and as such, are increasingly a topic of intense debate in coastal societies.…”

“…2015; Herbert et al . 2018) and exploit the new economic opportunities they offer (eg gastronomic tourism; Figure 4; Mortensen et al . 2019).…”

Evidence for self-sustaining populations of Arcuatula senhousia in the UK and a review of this species’ potential impacts within Europe

“… Cultural ecosystem services + /− A. senhousia impacts and observations + /− Supporting information + /− Priority questions Recreation – Provides habitat and food for a toxic sea slug ( Pleurobranchaea maculata ) in New Zealand which is harmful to dogs 110 + /− Introduced molluscs such as M. gigas can provide feeding grounds for some shorebird spp. but destroy it for others 111 + /− Impacts bird watching? + Reduces Escherichia coli in bathing waters?…”

Evidence‐based conservation in a changing world: lessons from waterbird individual‐based models

“…Management of the biotic (e.g., Baie de Somme—A and C shellfishing; Goss‐Custard et al 2004, dit Durell et al 2008; Dee Estuary shellfishing, West and McGrorty 2003, Stillman and Wood 2013 b ; Solway Firth shellfishing, Stillman 2008 a , Stillman and Wood 2013 a ; Exe Estuary—E and G shellfishing, Stillman et al 2014, Goss‐Custard et al 2019) and physical environment (e.g., Baie de Cadiz sea‐level rise, Stillman et al 2005 a ). Interaction with living organisms, including humans (e.g., Southampton Water—B recreation, Stillman et al 2012; Baie de Somme—B human activities, Goss‐Custard et al 2006 b ) and other biota (e.g., Poole Harbour—B Manila Clam Venerupis philippinarum, Caldow et al 2007; Colne Estuary Pacific Oyster Crassostrea gigas, Herbert et al 2018). External physical changes (e.g., extreme weather in Izembek Lagoon, Stillman et al 2021; and Exe Estuary—D, Stillman et al 2005 a , c , dit Durell 2007; or sea‐level rise in Humber Estuary—A and B, Stillman et al 2005 b , Bowgen 2016).…”