Measuring the response of the ecosystem to management using biodiversity: the case for Caribbean marine reserves

by: Marah Newman PhD and Gustavo Paredes PhD

Abstract:
The response of reef fish assemblages to protection in marine reserves depends on the initial ecological conditions of the area protected. Large reserves placed in little impacted sites harbor healthier and more diverse communities. Small reserves have a larger chance to be affected by external disturbances and may take more time to show signs of recovery.  New marine reserves should be established with more realistic objectives, taking into account the history of exploitation of local reefs and potential disturbances around the area.

Introduction
 No-take marine reserves are expected to restore fish assemblages by increasing individual fish size and total fish biomass.
 However, the recovery of fish assemblages after protection is expected to be variable as a function of the initial condition of the protected assemblages and the size of the reserve.
 We report recovery of fish assemblages inside reserves of varying size along a gradient of fishing in the Caribbean.

Study Area
We studied fish assemblages across a gradient of fishing intensity, ranging from heavily fished reefs to large marine reserves.We define three representative reef systems were to conduct the field survey: Mesoamerican Reef (Cozumel, Mexico to Belize), Florida Keys (U.S.) and Jamaican Northern coast. In 2004 the survey was conducted in the Mesoamerican reef and during 2005 we will visit the other 2 areas. Within the Mesoamerican reef we visited 3 reef areas, Cozumel, Ambergris Caye and Glover s reef where we conducted a survey to assess the health of the reef ecosystem using visual censuses and SCUBA. On each reef area we set up three to four survey sites (local reefs) where we quantified the abundances of major ecosystem components (coral, macro-algae, fishes, sea fans, sponges, sea urchins, and other invertebrates). Within each reef area up to three of the sites were located inside a marine protected areas and at least one outside the MPA for comparison purposes.

Aknowledgements. Thanks to the managers and staff of marine reserves for research permits and logistical support. This work was supported by the National Geographic Society, the Marisla Foundation Environment Program, CMBC-PADI-IGERT Mini Grants, the Wildlife Conservation Society, the Munson Foundation, the World Wildlife Fund-US,  Scripps Institution of Oceanography s (SIO) William E. and Mary B. Ritter Chair , SIO OGSR Research Grant, the International Women s Fishing Association, the PADI Foundation s Project AWARE, and the Ocean Conservancy (ISRS).  Major support for MJHN came from the National Science Foundation s Graduate Student Research Fellowship and for GAP from the Shirley Boyd Memorial Fellowship/Mexican Marine Sciences Scholarship Fund.

 

 We quantified abundance and size of reef fishes with scuba diving. We calculated biomass using length-weight relationships from the literature.
 To determine changes in fish assemblages inside reserves relative to the fished areas nearby we plotted the rank distribution of fish abundance and biomass using the Abundance/Biomass Comparison (ABC) method.
 When individuals of large bodied species are dominant (healthy community) the biomass curve lies above the abundance curve. When the biomass curve lies below the abundance curve individuals of small species dominate the reef (degraded community).
 

Results
 The biomass curve from non-protected fish communities falls below the abundance curve indicating the highly disturbed conditions of the Caribbean reef ecosystem.
  There is indication of lower disturbance conditions in large marine reserves (>10 km2) but not in very small reserves, such as the Florida Keys National Marine Sanctuary. Among those reserves we observed an increase in the average trophic level, indicating that recovery is occurring from different initial conditions.

Implications for Conservation
 The evaluation of management actions such as marine reserves should take into account the history of exploitation of the coral reefs as well as the attributes of those reserves in order to set realistic expectations for recovery. Our preliminary results show that large reserves have a better chance to protect the ecosystem from multiple disturbances and ensure ecosystem wide recovery.

Additional research:  Impacts of fishing on Caribbean Coral Reef Food Webs and Species Richness and Community Structure of the Yucatan: Marine Reserves Before and After 2005 Hurricanes.

 

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