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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.KEY WORDS: El Niño · Fresh water input · Geographic distribution · Reproductive cycle · Sandy beach ecology · Submarine groundwater discharge · Macroecology Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 385: [151][152][153][154][155][156][157][158][159][160][161][162][163] 2009 25 cm when disturbed (Tarifeño 1980, Jaramillo et al. 1994. In Chile, adult clams are primarily confined to the subtidal, at water depths ranging between 3 and 15 m, while the vast majority of juveniles occur mainly in the intertidal zone, often in the outlets of estuarine areas (Tarifeño 1980, Jaramillo et al. 1994, Riascos et al. 2008a, although an inverse depth pattern between juvenile and adult clams has been described for Peruvian populations (Arntz et al. 1987). The reproductive cycle of M. donacium has been found to be influenced by local variability in water temperature and food availability (Tarifeño 1980, McLachlan et al. 1996. The long meroplanktonic larval stage (30 to 45 d) allows plenty of time for the phytoplanktophagous larvae to find suitable unoccupied sediments in which to settle (Tarifeño 1980). Environmental conditions in the HCS are broadly characterized by nutrient-rich, cool waters, showing limited seasonal temperature variability compared to that in other coastal ecosystems...

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In situ experiments were run with the seastar Asterias rubens to investigate the influence of epibiosis on predation preferences. Mussels (Mytilus edulis) monospecifically fouled by different epibiont species (the barnacle Balanus improvisus, the red filamentous alga Ceramium strictum, the sponge Halichondria panicea and the hydrozoan Laomedea flexuosa) and macroscopically clean mussels were exposed and seastar predation was monitored by SCUBA. Asterias rubens preferred macroscopical unfouled mussels as prey. Fouling generally reduced predation pressure on the mussel hosts (associational resistance). Barnacles protected mussels less efficiently than hydrozoans or algae. We hypothesize that in top‐down controlled communities this influence of epibiosis on predation pressure should affect mussel community patterns. A survey of natural mussel‐epibiont distribution in the presence or absence of A. rubens showed that the prevalence of differently fouled mussels differed between predation‐exposed and predation‐protected habitats. Natural mussel‐epibiont associations reflected the preferential predation of the major local predators. Additionally, higher epibiotic diversity and evenness could be observed at locations accessible to benthic predators as compared with habitats protected from predation. As blue mussels and seastars are important structuring and controlling elements in the shallow water community of Kiel Fjord, major consequences of epibiosis on the entire system are discussed.

Population structure, growth and production of the surf clam Donax serra (Bivalvia, Donacidae), inhabiting highly exposed sandy beaches of Namibia, were investigated between November 1997 and December 1999. From length-frequency distribution and tagging-recapture data, a von Bertalanffy growth function with an asymptotic length (L 1 ) of 82 mm and a growth constant (K) of 0.274 yr ÿ1 was established. Regarding growth performance of Donacidae, D. serra fits in a group of species inhabiting cold temperate and upwelling regions. The intertidal biomass of the studied population ranged between 141 and 546 g ash-free dry mass (AFDM) m ÿ2 yr ÿ1 . Individual production was maximal at 56.5 mm shell length (0.83 g AFDM ind. ÿ1 yr ÿ1 ), and annual production ranged between 167 and 637 g AFDM m ÿ2 yr ÿ1 , resulting in productivity values ðP=B Þ between 1.167 and 1.589 yr ÿ1 . These data underline the importance of D. serra for the beach/surf ecosystem. Further, the findings of this study are crucial to support future aquaculture or exploitation activities and management.