the humboldt current system of northern and central chile - figema

THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILEFrequency and intensity of exchange processesExchange of nutrients or particulate matter among marine communities in northern-central Chilevaries in frequency and intensity (Table 4). Some of the most important and frequent exchangeprocesses in northern Chile occur in the vertical direction (sedimentation of POM, release ofnutrients into the water column, upwelling of nutrient-rich waters). Horizontal transfer processesappear to be most intense and frequent in coastal habitats, such as, for example, supply of kelpdetritus to NCs. In contrast to this relatively continuous exchange of material, depositions ofterrestrial sediments to coastal waters or of dead plants and animals to local beaches appear to besome of the least frequent and unpredictable transfer events. When these events occur, their intensityis often so high (e.g., Arntz 1986) that they exceed the escape or ingestion capacity of the organismsin the receiving habitats. This can result in the destruction of local communities and the incorporationof materials to deeper sediment layers. Transfer of marine-derived materials in colonies ofseabirds and sea lions is also very intense (and frequent), but in northern-central Chile cannot beutilised by terrestrial organisms due to lack of water. A similar effect is observed in the watercolumn and sediments of the OMZ where recycling processes are suppressed due to the lack ofoxygen (Graco et al. 2006). Thus the intensity of the fluxes, which overcome the recycling capacityof receiving communities, may favour the long-term storage of POM not only in shelf sediments(H.E. González et al. 2004a), but also in terrestrial, intertidal and subtidal habitats of the HCS(islands with seabird and sea lion colonies, sandy beaches, subtidal kelp accumulations). It appearsto be important to estimate carbon and nutrient export (and storage) not only to shelf sedimentsbut also to terrestrial soils and intertidal and subtidal bottoms along the HCS.Propagule supply, dispersal and recruitment variabilityExchange of biological information (i.e., gene flow) depends on the dispersal ability of the organismsin question. Dispersal of individuals determines the scale at which species interact with thephysical environment, the nature and consequences of the interaction with other species, the wayin which they respond to perturbations and ultimately the selective forces and rates to evolve,speciate or go extinct. Because in most benthic habitats there is a predominance of species withcomplex life cycles, which include a free-swimming larval stage (Thorson 1950, Strathmann 1990),high dispersal capabilities are intuitively associated with most marine organisms. However, this isnot a rule since coexisting with species with planktonic larvae there always exists a myriad ofspecies with very limited dispersal potential, such as most macroalgae and direct developers orbrooding species (Reed et al. 1992, Kinlan & Gaines 2003, Shanks et al. 2003b). Moreover and tofurther complicate things, many species use rafting as an alternative method of long-distancedispersal (Santelices 1990a, Thiel & Gutow 2005). Despite the early realisation of the high diversityof life cycles found in every marine habitat, the ecological consequences of such diversity onspecies interactions and on the structure and dynamics of benthic communities are only beginningto be unveiled (Kinlan & Gaines 2003, Leibold et al. 2004, Velázquez et al. 2005).Methodological approaches to the study of dispersalThe study of dispersal in the ocean is fraught with methodological problems imposed by thedifficulty of following the usually microscopic propagules over extended time. Indirect methods toestimate aspects of dispersal have been developed. For instance, the use of highly variable neutralDNA markers offers an unprecedented opportunity to estimate realised dispersal distances (Palumbi247