the humboldt current system of northern and central chile - figema

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MARTIN THIEL ET AL.enhancement (Vásquez & Tala 1995), (3) cultivation (Edding & Tala 2003, Westermeier et al. 2006,Gutierrez et al. 2006), and (4) conservation programmes including Marine Protected Areas (MPAs;CONAMA 2006). Considering the high variability of kelp populations in northern Chile, the limiteddispersal capability of Lessonia species, and in particular the patchy distribution of beds of Macrocystisintegrifolia, sustainable exploitation of natural kelp forests requires integrated managementplans with continuous monitoring of standing stocks.Export and import processes within the HCSKelp forests, as other EEs, strongly influence trophic fluxes in benthic environments (e.g., Grahamet al. 2007). In the HCS, some of the most important trophic connections occur in the verticaldirection, such as dissolved nutrients released from sediments into the water column, upwelling ofnutrient-rich waters from subsurface layers to the sea surface, or POM sinking from the euphoticzone toward deeper water layers and finally to the sea floor. In addition, there exist numerous typesof horizontal transfer of particulate or dissolved components between the marine and the terrestrialrealm, between the benthic and the pelagic environment, or between benthic habitats. In thefollowing section the importance, intensity and frequency of these exchange processes in the HCSof northern-central Chile are considered, with a focus on coastal habitats.Exchange between realmsExchange between the marine and the terrestrial environment occurs in both directions. Flux ofmaterials toward the sea is via rivers, which (due to limited freshwater flow) is usually only ofminor importance between 18°S and 30°S. In some areas in northern-central Chile, dissolved andsolid components from human activities are continuously supplied to the marine environment,impacting local intertidal and subtidal communities (Vásquez et al. 1999, Gutiérrez et al. 2000,Lancellotti & Stotz 2004). During certain time periods (EN events or summer rains in the Andeshighlands), river flow increases dramatically, transporting mainly sediments but also large quantitiesof terrestrial vegetation to nearshore coastal waters (Vásquez et al. 2001a). Shallow subtidal habitatsalong the coast of northern-central Chile are infrequently impacted by these mud flows (Miranda2001, Vásquez et al. 2001a, Lancellotti & Stotz 2004), and it is considered likely that these impactsoccur in parallel over a large geographic range.In the reverse direction, several natural exchange mechanisms are relevant in the HCS, namely,energy transfer by seabirds and marine mammals from offshore waters to coastal habitats, whichoccurs in a highly concentrated manner on breeding or roosting sites. Additionally, some terrestrialvertebrates (rodents, lizards, songbirds) from coastal environments forage along the drift line or inthe intertidal zone (Navarrete & Castilla 1993, Fariña et al. 2003a, Sabat et al. 2003). Most of theseorganisms maintain relatively stable territories along the coastline, and thus material transfer fromthe intertidal to the upper supralittoral zone is dispersed in space, but relatively continuous in time.The same process has been reported from coastal habitats in California, where populations of insects,spiders, lizards, rodents and coyotes are mainly maintained and modulated by the food subsidyfrom the marine environment (Polis & Hurd 1995, 1996, Polis et al. 1997).Under certain conditions, marine resources are also transported toward the shore without theaid of biotic agents (invertebrate or vertebrate consumers defecating on land). Mortality of seabirdsand marine mammals during EN events results in large numbers of animal carcasses accumulatingon local beaches (e.g., Guppy 1906, Arntz & Fahrbach 1991). Similarly, during storm events, algaeor benthic invertebrates are detached and cast onto the shore (González et al. 2001). These foodbounties attract large numbers of terrestrial vertebrate scavengers but since supply is highly infrequent(e.g., Moore 2002), no quantitative estimates of material transfer during these events are available.244
THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILEFisheries also contribute to the transfer of OM from the marine toward the terrestrial realm.This not only includes direct (extraction) but also indirect forms of transfer, such as by scavengingseabirds around fishing vessels at sea (Weichler et al. 2004) or in fishing ports (Ludynia et al. 2005).Populations of kelp gulls (Larus dominicanus) near main population centres in northern-centralChile depend to a large extent on these human-derived food sources, and they then distribute remainsin terrestrial environments (Ludynia et al. 2005).Exchange between environmentsThere is a wide range of exchange processes between the pelagic and the benthic environments.This includes, for example, supply of POM from the water column to soft bottoms where microandmacroorganisms remineralise this POM, returning dissolved materials to the water column(Graf 1989, Marcus & Boero 1998, Dunton et al. 2005). Suspension feeders are important agents,which aid in transfer of suspended material (e.g., phytoplankton and kelp detritus) from the watercolumn to the benthic system (Wolff & Alarcón 1993). In some of the bays of northern-centralChile dense stocks of natural or culture beds may significantly affect these fluxes (Uribe & Blanco2001, Avendaño & Cantillánez 2005). The intensity and direction of transfer can be affected byregional discontinuities in the oceanographic conditions (e.g., distance from upwelling areas), whichinfluence the transport and flux of POM and nutrients (Graco et al. 2006). These processes are alsoexposed to large-scale temporal variations in oceanographic conditions (e.g., ENSO cycles) (Faríaset al. 2004, P. Muñoz et al. 2004b). Fisheries in small fishing ports contribute POM in the form offish remains to soft bottoms (Sahli 2006).On hard bottoms, macroalgae and suspension feeders take up nutrients and suspended POMfrom the water column, returning algal remains, repackaged faeces or dissolved excretions to thewater column. Most large kelps are continuously shedding senescent parts (e.g., Tala & Edding2005). These authors estimated that annual export of shed plant detritus from a kelp forest ofLessonia trabeculata may amount to 18 kg wet wt m −2 . What proportion of this detritus remainssuspended in the water column or sinks immediately to the bottom is not known at present. Kelpproductivity shows some seasonal variation, but kelp detritus is supplied throughout the year, atleast in northern-central Chile (Tala & Edding 2005). This suspended kelp detritus may also sustainthe large proportion of suspension-feeding organisms on intertidal and subtidal hard bottoms (seealso Intertidal and subtidal hard-bottom communities, p. 235ff. and Bustamante & Branch 1996).Little is known about the role of DOC released by kelp forests. It enhances bacterial populations(Delille et al. 1997) and contributes to foam lines at the sea surface, which are thought to play arole in propagule dispersal and survival (Meneses 1993, Shanks et al. 2003a). Foam lines arefrequently observed along the coast of northern-central Chile.Fish consumers also have an important role in energy transfer from benthic toward pelagicenvironments (Angel & Ojeda 2001). This transfer includes all feeding guilds of fishes fromherbivores to omnivores and carnivores (Angel & Ojeda 2001). Studies of trophic coupling betweenhard bottoms and the water column have mainly focused on kelp forests and little is known aboutthese trophic interactions in other hard-bottom communities (see also Intertidal and subtidal hardbottomcommunities, p. 235ff.).Exchange between benthic habitatsExchange between neighbouring communities (NCs) occurs throughout the shallow subtidal zone.The form of materials exchanged between NCs and the direction of transport can be highly variable.Algal detritus exported from kelp forests contributes an important food source for animal communitieson intertidal hard bottoms (Bustamante et al. 1995, Bustamante & Branch 1996, Rodríguez-Graña245
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