Abstract

When operating in sensitive environments, mangroves and other areas with high biodiversity require broad environmental assessments that consider the full range of habitats as well as ecological processes and functions. The objective of this paper is to provide site managers and other environmental management professionals a method for mangrove assessment that follows the international guidelines of the World Bank, the Convention on Biodiversity, and the Energy and Biodiversity Initiative set forth by Conservation International.These guidelines emphasize the need to incorporate an ecosystem approach so that environmental assessment is broad and considers both long-term and cumulative secondary impacts as well as more immediate primary impacts. In order to accomplish this, mangroves should be assessed at three levels:landscape, habitat, and species health.

Landscape level assessment is necessary to identify historical trends in habitat loss or expansion, fragmentation, or degradation of mangrove over time. Various types of optical satellite imaging (Landsat TM, MSS and Spot XC), radar satellite imaging (ERS-1, JERS-1, and Radarsat), and aerial photography are used to characterize the expansion and contraction of mangrove communities over time.

Habitat level assessments take place in the field and should be designed to yield information about ecosystem or species functioning.Indicators that are discussed include species distribution and abundance, percent canopy cover, seedling densities, faunal biodiversity, hydrology, and soil and water quality.

Species level assessments consider impacts that range in magnitude from localized individuals to entire populations.These assessments use indicators aimed at individual mangrove trees and include diameter at breast height, lenticel densities, leaf morphometrics and chlorophyll concentrations, and the presence or absence of adventitious roots, pneumathodes, and other morphological adaptations that can be used to track both the structural and functional responses of mangrove trees.

Introduction

Oil and gas exploration has been conducted in sensitive environments throughout the world for over a century.Various organizations such as the International Petroleum Industry Environmental Conservation Association (IPIECA) and the Energy and Biodiversity Initiative (EBI) within the industry are continuously improving technology and environmental management systems to minimize impacts associated with operations.

One type of sensitive ecosystem often encountered during exploration is mangrove. The term "mangrove" refers to a tidally influenced wetland complex that consists of mangrove forest, tidal flats, salt flats, and other associated habitats within the intertidal zone. Approximately 60 species of mangrove trees occur exclusively in this habitat. In recent years, there have been increased efforts worldwide by governments, non-governmental organizations (NGOs), and local communities to conserve and manage mangroves.

The objective of this paper is to provide site managers and other environmental management professionals a method for mangrove assessment that follows the guidelines of the World Bank, the Convention on Biodiversity, and industry organizations such as IPIECA and EBI.These guidelines emphasize the need to incorporate an ecosystem approach so that environmental assessment is conducted at three levels:landscape, habitat, and species.

Ecology of Mangroves. Mangroves exist in a constantly changing environment. They have adapted to tidal fluctuations in water depth, temperature, and salinity and dominate tropical and subtropical marine and estuarine shorelines due to:

  1. tolerance of a wide range of salinities;

  2. ability to live in anoxic soil;

  3. ability to stabilize their structures (trunks, roots, and limbs) in soft sediments; and

  4. production of seeds for long distance dispersal.

Different mangrove species have different requirements.Some mangrove species are more tolerant of salt than others.Additional factors that affect their distribution include wave energy, soil oxygen levels, drainage conditions and nutrient levels.When one species finds its preferred conditions - or conditions tolerated better than other plants - it tends to become dominant.

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