Reduced performance of native infauna following recruitment to a habitat-forming invasive marine alga

Abstract

Despite well-documented negative impacts of invasive species on native biota, evidence for the facilitation of native organisms, particularly by habitat-forming invasive species, is increasing. However, most of these studies are conducted at the population or community level, and we know little about the individual fitness consequences of recruitment to habitat-forming invasive species and, consequently, whether recruitment to these habitats is adaptive. We determined the consequences of recruitment to the invasive green alga Caulerpa taxifolia on the native soft-sediment bivalve Anadara trapezia and nearby unvegetated sediment. Initially, we documented the growth and survivorship of A. trapezia following a natural recruitment event, to which recruitment to C. taxifolia was very high. After 12 months, few clams remained in either habitat, and those that remained showed little growth. Experimental manipulations of recruits demonstrated that all performance measures (survivorship, growth and condition) were significantly reduced in C. taxifolia sediments compared to unvegetated sediments. Exploration of potential mechanisms responsible for the reduced performance in C. taxifolia sediments showed that water flow and water column dissolved oxygen (DO) were significantly reduced under the canopy of C. taxifolia and that sediment anoxia was significantly higher and sediment sulphides greater in C. taxifolia sediments. However, phytoplankton abundance (an indicator of food supply) was significantly higher in C. taxifolia sediments than in unvegetated ones. Our results demonstrate that recruitment of native species to habitat-forming invasive species can reduce growth, condition and survivorship and that studies conducted at the community level may lead to erroneous conclusions about the impacts of invaders and should include studies on life-history traits, particularly juveniles.

Larval settlement preference of a native bivalve: the influence of an invasive alga versus native substrata

“…Acceptance or rejection of a surface has also been correlated to the surface profile (roughness), including microtexture (Berntsson et al 2000, Scardino & de Nys 2004, Schumacher et al 2007 or the number of adhesion points an organism can make on a surface (Callow et al 2002, Scardino et al 2008. Although habitat selection by larvae should be adaptive, studies demonstrate that larvae can make poor or maladaptive settlement choices that reduce individual fitness or key performance traits (Connell 1961, Williamson et al 2004, Gribben et al 2009a.…”

“…The invasive green alga Caulerpa taxifolia has invaded several temperate regions worldwide where it covers large areas of soft-sediment habitat and forms high density beds (Meinesz et al 2001, Anderson 2005, Wright 2005, modifying chemical and physical sediment properties (Chisholm & Moulin 2003, Gribben et al 2009a). For example, sediments invaded by C. taxifolia are higher in sulphides, are more anoxic and have lower redox potential than those in nearby unvegetated sediments (Gribben et al 2009a, McKinnon et al 2009).…”

“…For example, sediments invaded by C. taxifolia are higher in sulphides, are more anoxic and have lower redox potential than those in nearby unvegetated sediments (Gribben et al 2009a, McKinnon et al 2009). In southeastern Australia, C. taxifolia has invaded 14 estuaries since it was first reported in 2004 and many of these areas contain populations of the soft-sediment bivalve Anadara trapezia, commonly known as the Sydney cockle (Wright et al 2007, McKinnon et al 2009.…”

“…Alternatively, sediment properties influence the settlement of soft-sediment invertebrates including bivalves (Butman 1987, Woodin 1991, Snelgrove et al 1998). Because C. taxifolia has negative effects on sediment quality and on the life-history traits of juvenile and adult A. trapezia (Wright & Gribben 2008, Gribben et al 2009a, McKinnon et al 2009), larvae may avoid invaded sediments and recruit to C. taxifolia itself.…”

Science, biodiversity and Australian management of marine ecosystems

“…Benthic communities contain organisms with a diversity of life strategies and spans and so they may be far more responsive to environmental changes than others. Some advancement has been made in understanding the impact of introduced species in nearshore shallow water environments (Galluci et al, in press;Gribben and Wright, 2006;Gribben et al, 2009) but we know far less about the impacts of introduced species in deeper water. Deeper water benthic communities are almost completely unstudied and even benthic communities closer inshore are poorly studied especially with regard to natural pertubations over time (Stephenson et al, 1970;Hutchings and Jacoby, 1994).…”