Competition between a native mussel and a non-indigenous invader for primary space on ­intertidal rocky shores in Chile

Abstract

Non-indigenous marine species have significant effects on rocky intertidal native biota and ecological processes. The tunicate Pyura praeputialis, a recent invader in the Bay of Antofagasta, Chile, has monopolized the low and mid-low rocky intertidal fringe and apparently constrained the native mussel Perumytilus purpuratus to the mid-upper fringe. We performed field experiments to determine interspecific competitive strengths and quantify survival and growth rates between these species at 2 intertidal heights: mid-low and mid-upper intertidal fringes. Our results showed that at the mid-low fringe P. praeputialis had greater competitive strength than P. purpuratus. In fact, the survival and growth rates of P. praeputialis were not significantly affected by the presence of P. pur-puratus. Further, while the survival of P. purpuratus was not significantly affected by the presence of P. praeputialis, its growth rate was affected by the degree of encroachment by the tunicate. Mussels encroached by P. praeputialis grew significantly less than non-encroached ones. At the mid-upper intertidal fringe, the survival of P. praeputialis was significantly decreased by the presence of P. pur-puratus: the tunicate is unable to grow at this intertidal fringe. At the low-intertidal fringe mussel growth rates were significantly greater than at the mid-upper fringe, while survival rates were similar. Our results support the hypothesis that in the Bay of Antofagasta the invading tunicate P. praeputialis is responsible for a major rocky intertidal ecological impact, outcompeting the native mussel from the mid-low fringe and thereby substantially modifying the zonation pattern. KEY WORDS: Invasion · Pyura praeputialis · Perumytilus purpuratus · Tunicate · Rocky intertidal · Antofagasta Bay Resale or republication not permitted without written consent of the publisher Editorial responsibility: Roger Hughes,

Biotic consequences of a shift in invertebrate ecosystem engineers: Invasion of New Zealand rocky shores by a zone‐forming ascidian

“…While in Chile, virtually all of the polychaete species recorded were restricted to the ascidian clumps. Further comparison with our findings is difficult to draw from the work in Chile as these studies contrasted fauna in the ascidian clumps with that on bare substrata (rock), although in Chile, P. praeputialis has displaced native mussels (Caro, Guinez, Ortiz, & Castilla, 2011).…”

Heterogeneity of ecological patterns, processes, and funding of marine manipulative field experiments conducted in Southeastern Pacific coastal ecosystems

“…Results of these studies showed how the specific environmental context could influence/modulate the intensity of species interaction, which is a matter of broad interest in different ecological systems (Chamberlain, Bronstein, & Rudgers, ). Studies which evaluated concurrently the effect of competition and predation on intertidal communities of habitat‐forming species (e.g., ascidians; Caro, Guiñez, Ortiz, & Castilla, ; Castilla, Lagos, & Cerda, ) showed the importance of considering concurrently these ecological processes and their joint role in shaping intertidal structure (see Chesson & Kuang, ). Only a few experimental attempts have been made considering the role of positive interactions (i.e., facilitation and mutualism) (Irving & Witman, ), or the effects of invasive species on native species and biotic resistance (Caro et al., ; Dumont, Gaymer, & Thiel, ) along the SE Pacific coast.…”

“…Results of these studies showed how the specific environmental context could influence/modulate the intensity of species interaction, which is a matter of broad interest in different ecological systems (Chamberlain, Bronstein, & Rudgers, 2014 showed the importance of considering concurrently these ecological processes and their joint role in shaping intertidal structure (see Chesson & Kuang, 2008). Only a few experimental attempts have been made considering the role of positive interactions (i.e., facilitation and mutualism) (Irving & Witman, 2009), or the effects of invasive species on native species and biotic resistance (Caro et al, 2011;Dumont, Gaymer, & Thiel, 2011) along the SE Pacific coast. It is not clear, however, whether lack of studies on this topic in the SE Pacific coast is related to the low frequency of these interactions or if there is still a prevailing view among ecologists that negative interactions (predation and competition) are the main processes determining species distributions and abundance (see Bruno, Stachowicz, & Bertness, 2003;Bulleri, 2009 for discussion).…”

Ecological Dominance Along Rocky Shores, with a Focus on Intertidal Ascidians

“…Members of the P.s.s.c. are fierce competitors for space, outcompeting individuals at intra-specific (Dalby 1995 and inter-specific (Castilla et al 2004a, Caro et al 2011, Manríquez et al 2016 levels. Experimental studies of intertidal aggregations of Pyura praeputialis in Antofagasta Bay, Chile (where this species is invasive), showed that as aggregates reach high population densities, a negative relationship exists between the number of individuals per unit area and mean individual mass .…”