Rocky Intertidal Zonation Pattern in Antofagasta, Chile: Invasive Species and Shellfish Gathering

Abstract

BackgroundBiological invasions affecting rocky intertidal zonation patterns, yield information on species interactions. In the Bay of Antofagasta, northern Chile, the non-indigenous tunicate Pyura praeputialis, originally from Australia, has invaded (in the past century or so) and monopolized a major portion of the mid-intertidal rocky shore, displacing upshore the native mussel Perumytilus purpuratus. In Antofagasta the tunicate is subjected to intensive exploitation. Monitoring protocols show that in the past 10 years Antofagasta's tunicate population has experienced a drastic decline, affecting the intertidal zonation pattern.Methodology/Principal FindingsA 12.5 km of coastline, on the southern eastern shore of the Bay of Antofagasta, was studied. Eight sites were systematically (1993–1994) or sporadically (2003–2014) monitored for the seaward-shoreward expansion or reduction of the tunicate Pyura praeputialis, and native mussel and barnacle bands. A notable reduction in the mid-intertidal band of P. praeputialis and a seaward expansion of the mussel, Perumytilus purpuratus, and barnacle bands was observed. We suggest that the major cause for the decline in the tunicate is due to its intensive exploitation by rocky shore Pyura-gathers. The rate of extraction of tunicates by professional Pyura-gathers ranged between 256–740 tunicates hour−1. Between 2009–2014 the density of professional Pyura-gather ranged between 0.5–4.5 km−1 per low tide. Hence, 10 professional Pyura-gathers working 1 h for 10 low tides per month, during 6 months, will remove between 307–888 m2 of tunicates. A drastic decline in tunicate recruitment was observed and several P. praeputialis ecosystems services have been lost.Conclusion and SignificanceIn Antofagasta, the continuous and intensive intertidal gathering of the invasive tunicate Pyura praeputialis, has caused a drastic reduction of its population modifying the zonation pattern. Thereby, native mussel Perumytilus purpuratus has regained its ecological center in the intertidal zone. We recorded a Pyura recruitment failure and loss of ecosystem services.

Empirical evidence for large‐scale human impact on intertidal aggregations, larval supply and recruitment of Pyura praeputialis around the Bay of Antofagasta, Chile

“…Sampling sites along the SE shore of the bay were: El Lenguado (23°46′ S; 70°28′ W), south of Coloso Point; MEL, on the shore within the Minera Escondida Limitada facility (23°45′ S; 70°28′ W), at Coloso Point; El Way (23°44′ S; 70°26′ W) and AAA (23°4 2′ S; 70°25′ W), north of Coloso Point. All these sites are open to shellfish gathering and show complete or significant reductions in size of the tunicate aggregations (Castilla et al 2014). On the EC shore of the bay, Trocadero (23°35′ S; 70°23′ W), is a rocky shore next to a remodelled artificial beach that opened to the public in 2012.…”

“…At Antofagasta, the species has monopolized a major portion of the mid-intertidal rocky shore, displacing upshore the native dominant mussel P. purpuratus (Castilla et al 2004a). Within this extremely restricted range P. praeputialis plays an important role as a bioengineer species, providing habitat for invertebrates and algae (Cerda & Castilla 2001;Castilla et al 2004b) and as an invertebrate resource, because it is extracted by local rocky shore food-gatherers (Castilla et al 2014). A recent study (Castilla et al 2014) has suggested that along the south-eastern shore of the Bay of Antofagasta (approximately 12 km of coastline) the intertidal aggregations of P. praeputialis have declined notably as a consequence of their intensive and long-term exploitation by rocky shore Pyura gatherers.…”

“…However, the population structure of intertidal invertebrates might also depend on the impact of human access and the distance to major urban centres or human recreational activities (Keough et al 1993). According to Castilla et al (2014) the effect of Pyura gatherers on the intertidal abundances of P. praeputialis depends on the number of gatherers and their efficiency. Therefore, it is expected that the effects of Pyura gathering on the intertidal abundances of P. praeputialis will also depend on the level of accessibility of gatherers to the intertidal zone.…”

“…Moreover, following the opening in 2012 of a remodelled artificial beach on the central eastern shore of the bay at Trocadero (Fig. 1), the shore accessibility increased and enhanced the extractive activities of Pyura gatherers (Castilla et al 2014) on adjacent rocky shores. Thus, we hypothesized that at Trocadero this recent enhancement of human access (i.e.…”

“…We hypothesized that this reserve may also have preserved the intertidal abundances of tunicates, and that this in turn maintained or enhanced the abundance of larvae and recruits at the site; compared with other open access sites around the bay. Although human accessibility appears to be a major force driving abundances of P. praeputialis in the Bay of Antofagasta (Castilla et al 2014), negative consequences derived from other coastal human activities may also be part of it. For instance, metal pollution associated with the shipping of copper concentrate from Coloso Point Pier and from the Port of Antofagasta, as well as the potential impact of marine organic pollution associated with a population of about 622 thousand inhabitants in the city of Antofagasta.…”