Recovery in rubble fields: long-term impacts of blast fishing
Introduction
The widespread use and devastating effects of blast fishing have been well documented (Alcala and Gomez, 1987; Edinger et al., 1998; McManus et al., 1997; Pauly et al., 1989), and some researchers consider destructive fishing practices to be the largest immediate threat to coral reef ecosystems in some countries (Erdmann, 2000). However, less is known about the process of recovery once a reef has been blasted. Researchers have examined recovery from overfishing, crown-of-thorns starfish infestations, bleaching, coral mining, tourism damage, storm damage, oil spills, and ship groundings (Brown and Suharsono, 1990; Clark and Edwards, 1995; Connell et al., 1997; Done et al., 1991; Gittings et al., 1988; Gleason, 1993; Guzman et al., 1994; Hudson and Diaz, 1988; Hughes, 1994a; Rinkevich, 1995; Smith, 1988). Although recovery from blasting has been modeled (Saila et al., 1993; McManus et al., 1997), and levels of biological or economic impact have been assessed (e.g. Riegl and Luke, 1998; Guard and Masaiganah, 1997; Pet-Soede et al., 1999), few field studies of recovery from blast fishing have been conducted.
Corals are less likely to recover from chronic disturbance or disturbance that alters the physical environment than from acute disturbance that leaves the habitat intact (Connell et al., 1997). Blast fishing shatters the calcium carbonate coral skeletons and is a common and chronic occurrence on many reefs. While some broken fragments initially survive, most die after several months (Fox, personal observation). Therefore, coral larvae from neighboring intact reefs provide the primary sources for recruitment. Larval supply can vary according to coral cover of the source population, hydrodynamic variation, and connectivity between reefs (Done, 1992a; Roberts, 1997; Wallace, 1985).
Heavily disturbed or overfished sites often undergo a “phase shift” to communities dominated by soft corals and macroalgae, which limit recovery of hard coral colonies (Done, 1992a, Done, 1992b; Hughes, 1994a, Hughes, 1994b; Roberts, 1995). In Komodo National Park (KNP), large fields of the soft coral Xenia often grow on top of rubble (Fox, personal observation); it is not only a successful colonizer, with high fecundity and several dispersal modes, but also a superior competitor against hard coral (Benayahu and Loya, 1985). Soft corals also can inhibit larval recruitment of scleractinian corals via allelopathy (Maida et al., 1995). However, there are also cases where soft corals and macro algae do not invade space cleared by the death of hard corals, particularly in “sub-optimal” physical environments (Fabricius, 1997). A variety of other factors may influence coral reef recovery, including grazing intensity, sedimentation rate, larval availability and survival, and the network of source and sink populations, which is in turn dependent on ocean current patterns (Dias, 1996; Done, 1992a; Fabricus and De’ath, 1997; Gleason, 1996; McClanahan, 1997; Pearson, 1981; Roberts, 1997; Sammarco, 1996).
In order to further our understanding of reef recovery post-blasting, we have initiated a study in Indonesia that seeks to:
- 1.
Assess natural coral recruitment in rubble fields.
- 2.
Compare levels of source larvae in rubble fields at different locations within KNP and in comparison sites with greater live coral cover.
- 3.
Assess the impact of current strength on survival of small corals.
- 4.
Evaluate the effect of soft corals on hard coral recruitment.
Results from these studies will provide insights into attempts to rehabilitate damaged reefs and restore an important ecological and economic substrate (see Fox, 2002; Fox et al., 2002, for rehabilitation aspects of this study).
Section snippets
Study sites
Accurately monitoring the recovery of the reef community from anthropogenic impacts requires well-managed marine reserves that are no longer being heavily blasted. KNP, located in eastern Indonesia between the major islands of Sumbawa and Flores, fulfills this need (Fig. 1). The park encompass areas where blast fishing has occurred at varying levels since the early 1950s, declining dramatically since 1996 due to efforts by The Nature Conservancy. The diverse underwater environments within the
Natural recruitment
General characteristics of each rubble field site are listed in Table 1. Blasted sites had much lower live coral cover than reefs in similar habitats that had not been blasted. Based on line intersect transects, hard coral cover in blasted plots ranged from 0.4% to 18%, and averaged 4.7% across all nine sites. Soft coral cover ranged from 1% to 45%, and averaged 11.2%. Coral rubble was high at all sites (52–98% cover) and averaged 82.7%. The site with lowest rubble cover (52%) also had highest
Discussion
Disturbance has always been a natural structuring force in coral reef development, with storm damage and volcanic activity resulting in cycles of removal and recovery (Done, 1992a; Sousa, 1984). Stable and complex substrate and species assemblages adapted to high disturbance regimes can result in a rapid recovery of coral cover (Dollar and Tribble, 1993; Tomascik et al., 1996). In some damaged habitats extensive coral recovery has occurred as rapidly as within five years, but in many others
Acknowledgements
The authors are grateful for the assistance of the Indonesian Institute of Sciences (LIPI) and the logistical support provided by the staff of Komodo National Park and The Nature Conservancy Komodo Field Office. The majority of this work was funded by grants from The Nature Conservancy/Mellon Foundation Ecosystem Research Program, NSF grant INT98-19837, the University of California’s Pacific Rim Research Program, and the International Society for Reef Studies. M. Erdmann and P. Mous provided
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