Changes in the structure of a shallow sandy-beach community in Peru during an El Niño event

Abstract

Many infaunal sandy-bottom communities in shallow waters of the Peruvian upwelling system are inhabited by large coexisting populations of the surf clams Mesodesma donacium and Donax peruvianus as well as by the anomuran mole crab Emerila ana/oga. Under normal conditions, equilibrium states are possible with any one of these species dominating. A Mesodesma community south of Lima in Peru was investigated over 2,5 years, covering periods prior to, during and after the EI Nino (EN) of 1982-83. It was revisited several times later. Growth, recruitment and mortality and, therefore. production of Mesodesma and Donaxvaried to some extent before EN. However, during the event Mesodesma became locally extinct and had not recoloniz.ed the area by July 1986, three years after the return of normal temperatures. Donax, which took over immediately after EN, never reached the densities of the former dominant Mesodesma. Emerila remained a rare species as well, whereas spionid polychaetes increased in importance. The medium-term effect of the exceptionally strong EN of 1982-83 appears to have been very marked on Peruvian sandy beaches. A comparison is made with other shallow-water communities of the upwelling system, and the importance of EN in terms of oscillations of clam stocks off Peru and Chile is discussed.

Recurrent, thermally-induced shifts in species distribution range in the Humboldt current upwelling system

“…In the period before and during EN 1982e1983 Arntz et al (1987) followed recently-recruited cohorts of D. obesulus off southern Lima (w12 S). This species showed significantly reduced growth when SST peaked in February and March 1983, but was able to survive this strong warming event (Arntz and Fahrbach, 1991).…”

“…Whereas D. obesulus is restricted to the intertidal zone, M. donacium inhabits both, the intertidal (juveniles) and the shallow subtidal (adults) . Both species show high abundance along their distribution range in the HCS (Carstensen, 2010;Arntz et al, 1987). These species occupy the same niche and have similar ecological roles (Tarazona et al, 1986;Beu, 2006).…”

“…Within their distributional range both species are affected differently by extreme phases of ENSO (Soto, 1985;Arntz et al, 1987, 1988, Arntz and Fahrbach, 1991Díaz and Ortlieb, 1993;Thiel et al, 2007). Historically, D. obesulus (synonyms: D. marincovichi and D. peruvianus; Carstensen et al, 2009) was distributed from the Ecuadorian coast (0 26 0 S) to the North of Chile (23 05 0 S) (Coan, 1983; Fig.…”

“…1). During EN, the species suffers mass mortalities in the northern part of its geographical range (Tomicic, 1985;Arntz et al, 1987;Guzmán et al, 1998b).…”

“…Apart from purely descriptive accounts, some evidences suggest that distribution shifts may not be entirely explained by corresponding shifts in temperature. First, it is not clear whether sympatric D. obesulus and M. donacium develop competitive interactions (Arntz et al, 1987). Second, M. donacium reveals a remarkably poor ability to recover its former distribution following EN events in spite of several cycles of warm and cold (Arntz et al, 2006).…”