Ecological Modeling to Understand the Energy Flows and Interactions along the Kona Coastline

The near shore marine resources of the Kona region have long provided sustenance and a venue for cultural practices by Hawaiian and non-Native local people. In more recent decades these resources have become central to an expanding tourism industry and provide opportunities for recreational and commercial, as well as traditional subsistence fisheries (Friedlander et al. 2008). Past work in the region has shown that the benthic habitats are still relatively healthy (Jokiel et al. 2004), with diverse fish populations and few signs of diseased corals (Beets et al. 2006). However, increases in activities such as fishing and coastal development may be severely disrupting processes supporting the ecosystems along the Kona region (Marrack et al. 2009; Weijerman et al. 2009). A thorough understanding of the ecosystem and the processes that drive it are an important component of an Integrated Ecosystem Assessment (IEA), and ecological models can help in identifying important pathways and drivers of the ecosystem. More specifically, ecosystem models allow the integration of a wide range of social, economic and ecological data to assess the ecosystem condition relative to specific goals, and represent an important element of IEAs (e.g., Puget Sound (Ruckelshaus et al. 2008) and California Current (C. Ainsworth, pers. comm.)).

Specific Project Objectives

This project's overarching goal is to develop a "reef" and a "coastal" ecosystem model for Kona and West Hawai'i. These will be used to provide scientific information to assist in the sustainable management of western Hawai'i 's natural marine resources by conserving the natural environment while ensuring economic opportunities. By integrating social, ecological and economic data these models will lead to a better understanding of the ecological interactions between species and the effects of fishing and nutrient input on the ecology and economy of the greater Kona region.

Specifically, the project proposal aims to:

  1. Develop an ecosystem model for the reef system along the Kona coast:
    1. Define the food web structure of the Kona region's reef system through trophic modeling;
    2. Assemble time series data of nutrient input to the coastal zone;
    3. Assemble catch (and effort) time series data for target species in the region;
    4. Assess the potential impacts to this environment of increased nutrient input deliveries as a result of expanding development under two scenarios: (1) concomitant increased removal of target species; and (2) no changes in fishing pressure.

    This model will significantly benefit from, and expand upon, a base model that was developed for the National Historical Park of Kaloko Honokōhau (Wabnitz et al. in press) (Figure 1).

    Figure 1 – Map of Kaloko-Honokōhau (Kaloko) National Historical Park (modified from www.nps.gov).
    Figure 1 – Map of Kaloko-Honokōhau (Kaloko) National Historical Park (modified from www.nps.gov).

    The Kaloko ecosystem model synthesized available data for the year 2005 and included 26 groups, spanning the trophic web of the ecosystem (including detritus) (Figure 2). Model results showed that the combined grazing pressure of the different herbivore groups at Kaloko (i.e., reef fish, sea urchins and green turtles) matched total algal production. Sea urchins exerted the strongest control over algal resources, partly because of their large biomass in park waters. Results further demonstrated that the Kaloko green turtle aggregation has reached carrying capacity. Green turtles help maintain low algal cover, and thus resilience of reefs in the face of disturbance and should be explicitly included in studies of ecosystem dynamics on reefs.

    Figure 2 - Graphical representation of the trophic linkages (i.e., who-eats-who) within the Kaloko reef ecosystem. Each 
                         animal group within the system is identified here by an illustration (© M. Bailey); where relevant, an image of a species 
                         representative of its group is depicted. Images are not drawn to scale or proportional to the group's biomass. The light 
                         grey horizontal lines and associated numbers represent trophic levels (position in the food web); lines connecting 
                         individual groups represent trophic links. Zoo = Zooplanktivorous fish; MIF = Mobile Invertebrate Feeding fish; SIF = 
                         Sessile Invertebrate Feeding fish; TurfLB = turf growing on the lava bench area; CCA = Crustose Coralline Algae; Benthic 
                         Invts = Benthic invertebrates.
    Figure 2 - Graphical representation of the trophic linkages (i.e., who-eats-who) within the Kaloko reef ecosystem. Each animal group within the system is identified here by an illustration (© M. Bailey); where relevant, an image of a species representative of its group is depicted. Images are not drawn to scale or proportional to the group's biomass. The light grey horizontal lines and associated numbers represent trophic levels (position in the food web); lines connecting individual groups represent trophic links. Zoo = Zooplanktivorous fish; MIF = Mobile Invertebrate Feeding fish; SIF = Sessile Invertebrate Feeding fish; TurfLB = turf growing on the lava bench area; CCA = Crustose Coralline Algae; Benthic Invts = Benthic invertebrates.
  2. Develop an ecosystem model for the coastal environment off the Kona coast:
    1. Define the food web structure of the Kona region coastal system (i.e., including reef and more pelagic components of the system) through trophic modeling;
    2. Assemble catch (and effort) time series data for target species, focusing on species that are important to the recreational and commercial fisheries operating off the coast;
    3. Investigate alternative management options that combine conservation objectives (e.g., maximize ecosystem integrity) with fishing practices (e.g., maintain a given economic objective, maintain specific catch of given targeted species);
    4. Evaluate trade-offs between different sectors based on the implementation of alternative fishing strategies with differing management objectives.

The models will be developed using one of the most widely applied software in the field of ecosystem modeling, namely Ecopath with Ecosim (EwE) (Christensen & Pauly 1992; Plaganyi 2007; Walters et al. 1997). Following the original work by Polovina (1984), EwE is a unique suite of ecological modeling software in that, unlike most traditional ecological models, it allows the user not only to present an analysis on model parameters and structure at time t (Ecopath) (Christensen & Pauly 1993), but also incorporates a time dynamic aspect of ecological systems (i.e., attempts to predict ecosystem structure and function at time t+1 (Ecosim)) (Walters et al. 1997). As such, EwE allows the integration of a wide variety of information and enables the user to make predictions over a wide range of possible states of nature (Walters & Martell 2004).

The management objectives/set to be used will be based on those arrived at by relevant stakeholders during the scoping and indicator development steps of the Kona IEA process. It is expected that the outlined project will enable local management and research entities to examine alternative regulatory and conservation options, for fisheries in particular, by knowing the social and economic impacts and potential trade-offs associated with alternative conservation options.

Outcomes of this study should further facilitate the implementation of a number of identified optimal policy options for the area, thereby assisting in the reduction of conflicts among shared uses. In this regard these models would contribute to efficient coastal and marine spatial planning (CMSP), one of the nine priority objectives proposed in the Interim Report of the Interagency Ocean Policy Task Force (Interagency Ocean Policy Task Force 2009). Finally, we hope that lessons learned from the modeling component of the Kona IEA may prove valuable in fine-tuning other regional IEA efforts.

Project Contacts

Colette Wabnitz, Ph.D.
Fisheries Scientist (Aquarium trade)
Secretariat of the Pacific Community
Coastal Fisheries Science and Management Section
BP D5
98848 Noumea Cedex
New Caledonnia
Email: Colette.Wabnitz@gmail.com

Evan Howell, Ph.D.
NOAA IRC
Attn: NMFS/PIFSC/EOD/West Hawaiʻi IEA Project/Evan Howell
1845 Wasp Boulevard, Building 176
Honolulu, HI 96818
Email: Evan.Howell@noaa.gov

References

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Friedlander A, et al.
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