Müller, Jens (2012) The Two Mytilids Aulacomya atra and Mytilus chilensis from the Chilean Fjord Region: Aspects of Population Dynamics, Production and Metabolism. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 48 pp.

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Abstract

The commercially targeted and habitat forming Mytilidae Aulacomya atra and Mytilus chilensis from the rocky slopes of Chilean Patagonia were investigated. Field experiments were performed by scientific divers in the fjord Comau between February 2011 and March 2012. Population structure analysis by quantitative sampling revealed highest abundance of M. chilensis in the intertidal zone (Mean: 2015 Ind m-2) and A. atra in the shallow subtidal zone (Mean: 400 Ind m-2). Allometric relationships relating length to biomass are described. The biomass of the standing stock was calculated for M. chilensis and A. atra (both 630g AFDM m-2). In vitro respiration experiments revealed the mass specific respiration rates to decrease with increasing size of the mussels. From long-term mark-recapture data a von Bertalanffy growth function with an asymptotic length (L∞) of 110 mm and a growth constant (K) of 0.42 yr-1 was established for A. atra. The overall growth performance of A. atra was found to be 5.7 and is thus between values reported for Mytilus spp. and Perna spp. The individual somatic production of A. atra was highest for the size class 70-75 mm (0.73g AFDM lnd-1 yr-1). It is thus recommended to exclude smaller specimens from harvesting. The annual population production of A. atra (157 g AFDM m-2 yr-1) is linked to a production-to-biomass ratio of 0.24. The results of a short-term growth experiment performed in February 2012 supports the hypothesis that the downward extension of M. chilensis is limited by interspecific competition with A. atra, which itself was incapable of survival in the intertidal zone. A Low Salinity Layer covering the fjords water body excludes fully marine predators from the shallow subtidal zone and thus creates a spatial refuge for A. atra.

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