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Mass balanced and dynamic simulations of trophic models of kelp ecosystems near the Mejillones Peninsula of northern Chile (SE Pacific): Comparative network structure and assessment of harvest strategies

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  • Ortiz, Marco

Abstract

Mass balanced trophic models for kelp ecosystems which include subsystems dominated by Macrocystis integrifolia, Lessonia trabeculata and areas of barren ground (BG) were constructed for subtidal areas near the Mejillones Peninsula (SE Pacific), Chile. Information on biomass, P/B ratios, catches, food spectrum, consumption and dynamics of commercial and non-commercial populations was obtained and examined using Ecopath with Ecosim software analyses. The biomass of blades of L. trabeculata and M. integrifolia represented the compartments most relevant to the subsystems studied. Within the herbivores, the sea urchin Tetrapigus niger was dominant, followed by the snails Turritella sp. and Tegula sp. The fishes Pinguipes chilensis and Cheilodactylus variegatus were the dominant predators, followed by the asteroids Heliaster helianthus and Meyenaster gelatinosus. The highest system throughput (72,512gwetweightm−2year−1) was calculated for the subsystem dominated by M. integrifolia. The mean trophic level of the catch ranged from 1.1 (subsystem dominated by L. trabeculata) to 1.3 (subsystem dominated by M. integrifolia) to 3.2 (barren ground subsystem), showing that harvesting in each system was concentrated either on primary producers (blades of kelp species) or top predator fishes. Although the values for the Relative Ascendency (A/C) fluctuated from 36.5 to 45%, suggesting that all the systems were immature, the subsystem dominated by M. integrifolia emerged as the least resistant to external disturbances (e.g. fisheries). This result agreed with the high value of the system recovery time (SRT) for the M. integrifolia subsystem as a response to combined fisheries scenarios. The results obtained using mixed trophic impact (MTI) and Ecosim [increasing the fishing mortality Fi by 4×] showed that in most of the cases the predictions had the same qualitative tendencies. One of the most important results obtained in this study was that exploitation of kelp blades as an alternative strategy to harvesting the whole plants appeared to be ecologically sustainable, since harvesting the blades propagated only small effects on the entire subsystem. The fish P. chilensis may be considered as a top predator species with a strong top-down control since an increase in its fishing mortality in the subsystem dominated by M. integrifolia produced a high SRT value, and the FMSY was less than the originally entered Fi in Ecopath. Based on the results obtained, it was concluded that the trophic mass balanced models and simulated management scenarios offered good possibilities for the planning of interventions and manipulations or the planning of more sustainable management strategies in highly disturbed natural systems.

Suggested Citation

  • Ortiz, Marco, 2008. "Mass balanced and dynamic simulations of trophic models of kelp ecosystems near the Mejillones Peninsula of northern Chile (SE Pacific): Comparative network structure and assessment of harvest strateg," Ecological Modelling, Elsevier, vol. 216(1), pages 31-46.
  • Handle: RePEc:eee:ecomod:v:216:y:2008:i:1:p:31-46
    DOI: 10.1016/j.ecolmodel.2008.04.006
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    Cited by:

    1. Ortiz, Marco & Avendaño, Miguel & Campos, Leonardo & Berrios, Fernando, 2009. "Spatial and mass balanced trophic models of La Rinconada Marine Reserve (SE Pacific coast), a protected benthic ecosystem: Management strategy assessment," Ecological Modelling, Elsevier, vol. 220(23), pages 3413-3423.
    2. Ortiz, Marco & Berrios, Fernando & Campos, Leonardo & Uribe, Roberto & Ramirez, Alejandro & Hermosillo-Núñez, Brenda & González, Jorge & Rodriguez-Zaragoza, Fabián, 2015. "Mass balanced trophic models and short-term dynamical simulations for benthic ecological systems of Mejillones and Antofagasta bays (SE Pacific): Comparative network structure and assessment of human ," Ecological Modelling, Elsevier, vol. 309, pages 153-162.
    3. Ortiz, Marco & Campos, Leonardo & Berrios, Fernando & Rodriguez, Fabián & Hermosillo, Brenda & González, Jorge, 2013. "Network properties and keystoneness assessment in different intertidal communities dominated by two ecosystem engineer species (SE Pacific coast): A comparative analysis," Ecological Modelling, Elsevier, vol. 250(C), pages 307-318.
    4. Ramírez, Alejandro & Ortiz, Marco & Steenbeek, Jeroen & Christensen, Villy, 2015. "Evaluation of the effects on rockfish and kelp artisanal fisheries of the proposed Mejillones Peninsula marine protected area (northern Chile, SE Pacific coast)," Ecological Modelling, Elsevier, vol. 297(C), pages 141-153.

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