Human Impacts on Mangrove Forests

By Stephen Holle

Originally published at ScientificAmerican.com

As the global human population continues to increase, many organisms have had to adapt to the loss and fragmentation of their habitat by development. Not surprisingly, global biodiversity has steadily declined, and as Anthony Barnosky, a Professor of Integrative Biology at UC Berkeley suggests, “we are witnessing a collision of human impacts and climatic changes that caused so many large animal extinctions toward the end of the Pleistocene.” Many of the impacts that ecosystems experience today are not “natural” occurrences. Rather, they are the result of our lust for modernization and development.[1]

Satellite image of Sasa Bay Marine Preserve, Apra Harbor Guam, which suggests some of the threats from human development and encroachments. Image: Google Earth

Such is the case for mangrove forests, which are one the most biologically diverse ecosystems on earth. Yet, on a global scale, more than 35% of these habitats have been lost over the last two decades due to human activities and climate stressors.[2] Often referred to as a foundation species, mangroves provide an important refuge for both juvenile and adult organisms (marine and terrestrial alike), and are amongst one of the greatest carbon sinks on Earth.[3]

One of the greatest threats to mangrove habitat is human development, which in many regions of the world creeps ever closer these critically sensitive ecosystems. For example, terrestrial runoff (e.g., sedimentation, contaminants, nutrients) has a significant impact on the architecture and function of mangrove root systems that ultimately will lead to a decline on productivity and growth over time. [1]

Red mangroves in Sasa Bay Marine Preserve. Photo by David Burdick (Courtesy of NOAA)

Within the Marianas, the island of Guam is unique in that it sustains a relatively healthy and intact mangrove ecosystem. Almost entirely contained within the Sasa Bay Marine Preserve, this area is recognized by local scientists and the Government of Guam as critically sensitive habitat. Unfortunately, “designated sanctuaries are not immune to external forces such as oil spills and nearby dredge spoils,”[4] and runoff from nearby watersheds.

Although such protected areas are in place to conserve coastal resources, ongoing ecosystem monitoring and enforcement are limited. Coastal management exists to protect environmental resources for both economical and ecological value. Although section 302 of the Coastal Zone Management Act suggests that “important ecological, cultural, historic, and esthetic values in the coastal zone which are essential to the well-being of all citizens are being irretrievably damaged or lost”, competing demands often sacrifice the intrinsic value of nature for human development.

Works Cited:

Hannah, L. (2012) “As Threats to Biodiversity Grow, Can we Save the World’s Species?

Feller, I.C. et al. (2010) Biocomplexity in Mangrove Ecosystems. Annual Review of Marine Science 2: 395-417

Bouillon, S (2008) Mangrove production and carbon sinks: A revision of global budget estimates. Global Biogeochemical Cycles Vol 22: GB2013

Guam’s Coral Reef Management Priorities (2010-15). NOAA Technical Report

Author photo by Jim Haw.

About the Author: Stephen Holle is a senior working toward a bachelor’s degree in environmental studies at USC Dana and David Dornsife College of Letters, Arts and Sciences. With his ENST scientific diving experience he hopes to move on to a career focused on policy and natural resource management.

Editor’s note: Scientific Research Diving at USC Dornsife is offered as part of an experiential summer program offered to undergraduate students of the USC Dana and David Dornsife College of Letters, Arts and Sciences. This course takes place on location at the USC Wrigley Marine Science Center on Catalina Island and throughout Micronesia. Students investigate important environmental issues such as ecologically sustainable development, fisheries management, protected-area planning and assessment, and human health issues. During the course of the program, the student team will dive and collect data to support conservation and management strategies to protect the fragile coral reefs of Guam and Palau in Micronesia.

Instructors for the course include Jim Haw, Director of the Environmental Studies Program in USC Dornsife, Environmental Studies Lecturer Dave Ginsburg, SCUBA instructor and volunteer in the USC Scientific Diving Program Tom Carr and USC Dive Safety Officer Gerry Smith of the USC Wrigley Institute for Environmental Studies.

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