Thriving and declining: climate variability shaping life-history and population persistence of Mesodesma donacium in the Humboldt Upwelling System

Riascos, José M., Carstensen, Daniel, Laudien, Jürgen, Arntz, Wolf E., Oliva, Marcelo E., Güntner, Andreas and Heilmayer, Olaf (2009) Thriving and declining: climate variability shaping life-history and population persistence of Mesodesma donacium in the Humboldt Upwelling System. Marine Ecology Progress Series, 383, 151-163. (doi:10.3354/meps08042).

Abstract

Large-scale environmental patterns in the Humboldt Current System (HCS) show major
changes during strong El Niño episodes, leading to the mass mortality of dominant species in coastal
ecosystems. Here we explore how these changes affect the life-history traits of the surf clam Mesodesma
donacium. Growth and mortality rates under normal temperature and salinity were compared
to those under anomalous (El Niño) higher temperature and reduced salinity. Moreover, the reproductive
spatial–temporal patterns along the distribution range were studied, and their relationship to
large-scale environmental variability was assessed. M. donacium is highly sensitive to temperature
changes, supporting the hypothesis of temperature as the key factor leading to mass mortality events
of this clam in northern populations. In contrast, this species, particularly juveniles, was remarkably
tolerant to low salinity, which may be related to submarine groundwater discharge in Hornitos,
northern Chile. The enhanced osmotic tolerance by juveniles may represent an adaptation of early
life stages allowing settlement in vacant areas at outlets of estuarine areas. The strong seasonality in
freshwater input and in upwelling strength seems to be linked to the spatial and temporal patterns in
the reproductive cycle. Owing to its origin and thermal sensitivity, the expansion and dominance of
M. donacium from the Pliocene/Pleistocene transition until the present seem closely linked to the
establishment and development of the cold HCS. Therefore, the recurrence of warming events (particularly
El Niño since at least the Holocene) has submitted this cold-water species to a continuous
local extinction–recolonization process.

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