Satellite view of the Indus River delta and surrounding coastline in Pakistan and India. (Photograh by National Geographic Society)

The Indus River Delta-Arabian Sea mangroves ecoregion represents a mangrove habitat that is adapted to some of the most extreme temperatures and salinity conditions in the Indo-Pacific region. As a transition from the marine to freshwater and terrestrial systems, mangroves provide critical habitat for numerous species of fishes and crustaceans that are adapted to live among the tangled mass of pneumatophores, the roots that reach up from the muddy, anaerobic substrate to obrain the supply of oxygen for the mangrove trees.

Location and General Description

This ecoregion lies at the delta of the Indus River, which originates in the Tibetan Plateau and flows through the northwestern part of India and into the arid Thar Desert in Pakistan before finally emptying into the Arabian Sea. There are high salinity levels in the sloughs because of the high evaporation rates and the salts that are washed down by the river, which flows through a highly saline area. Climatic conditions are extreme. Ambient temperatures range from near-freezing temperatures in the winter to higher than 50 degrees Celsius during the summer. All rainfall is associated with the July to September southwest monsoon, which brings a mere 100 to 500 millimeters (mm) of precipitation.

Mangroves in general are not diverse compared with most other terrestrial ecosystems, and undisturbed mangrove forests have a dense canopy with little stratification and an undergrowth made up of seedlings and saplings from the canopy trees. The Indus River mangroves are even less diverse, being composed of nearly monospecific stands of Avicennia marina, a species that is highly resistant to high salinity levels and capable of surviving the region's extreme conditions. Other species that are sometimes associated with the Avicennia include Rhizophora apiculata and Acanthus ilicifolius, with occasional smaller patches of Rhizophora mucronata and Ceriops tagal scattered throughout. The former usually is closer to creeks.

Biodiversity Features

This mangrove ecoregion provides important habitat for fish and invertebrates and serves as critically important spawning grounds and nurseries for fishes and aquatic crustaceans. There are 123 bird species known from this ecoregion, although none are considered endemic.

Current Status

Although this ecoregion has been heavily degraded, and more than 85 percent of the habitat has been destroyed, several patches of intact habitat still exist. There are three protected areas that cover about 820 square kilometers (km²⁾, or 16 percent of the ecoregion (table 1), but even these protected areas are degraded.

Table 1. Protected Areas That Overlap with the Ecoregion.

Types and Severity of Threats

Threats to this mangrove ecoregion stem from several sources. Mangroves are cut for fuelwood by local peoples, this being the major source of firewood for the more than 10,000 people who live in the area, and for fodder to feed the domestic livestock, which include camels.

Other threats stem from industrial water pollutionfrom the city of Karachi, oil spills and discharges from the ships that anchor in the city's harbour, and increased salinity levels caused by flow diversions in the Indus River. Seasonal fishermen live in the mangrove forests and cut and clear the forests while setting up camps.

Additional information on this ecoregion

• For a terser summary of this entry, see the WWF WildWorld profile of this ecoregion