The Arabian Sea


      The Arabian sea borders Asia and Africa.  There is high productivity around it's coast line and it is home to a large number of ecosystems and commercial trade routes.  Fisheries and aquaculture are extremely important to the surrounding populations especially India where over 70% of the population is dependent on a fish based diet.  Oil spills and aerosol pollution are abundant and are environmental issues of increasing importance.   
                                          Table of Contents:

1. General Information
2. Historical Use
3. Productivity
4. Habitat Changes
5. Biodiversity & Ecosystems
      Coral Reefs
      Sea grass beds
      Food web
      Introduced Species
6. Fisheries
      Major fisheries
6. Environmental Concerns
      Acidification and Foraminifera
      Oil Spills
      Fishery Problems
      Aerosol Pollution (region specific)
7. Solutions

                                                                                 General Information

The Arabian Sea in the NW Indian Ocean [1]
The Arabian Sea is located in the north western region of the Indian Ocean.  It borders Yemen, Oman, United Arab Emirates, Pakistan, Kuwait, India, Iran, Kuwait, Bahrain, and Qatar.  The largest rivers emptying into the sea are the Indus River the Mahi, the Tapti, and the Shatt al Arab river system.  It's surface area is 3,950,000 km^2, average surface temperature is 22.5 - 28.5 C, and maximum depth is 4,652 m.  The highest salinity is found in the northern part of the Arabian Sea as a result of high evaporation rates and input of salty water from the Persian Gulf.

         Historical Use

Historical trade routes on the Arabian Sea [2]
The Arabian sea plays host to a vast network of trade routes dating back to 250 A.D.  These trade routes are primarily dominated by the oil industry and as a result there have been numerous oil spills over the years.  The largest happened in 1994 when a Panamanian-flagged Seki collided with a United Arab Emirate tanker dumping 15,900 tons of oil into the sea. 


Productivity in the Arabian Sea [3]
Productivity is highest in the northern region of the Arabian Sea.  In figure 3 red is the highest productivity and blue is the lowest.  The sea's productivity is subject to seasonal fluctuations.  In the spring intermonsoon season there is a shallow mixed layer with low nutrient yielding low productivity.  In the summer monsoon season winds drive waters away from the coast causing upwelling that brings cold nutrient rich waters to the surface.  As a result there is high productivity in the summer.  In the winter there is a deep mixed layer and convective mixing the injects nutrient rich waters from the subsurface to the surface promoting high productivity.

Habitat Changes

    In the mid Pleistocene there was a mass extinction of foraminifera in the Arabian Sea. Sixty three species of foraminifera vanished according to the fossil record most likely due to decreased oxygen levels caused by decomposition of increased organic matter input.  This extinction effected various organisms as foraminifera provide food for snails, sand dollars, scaphopods, and small fish.  They eat algae, bacteria, other foraminifera and organic matter through sediment.
    Climate change has altered the monsoon cycle causing increased precipitation in premonsoon season and decreased precipitation during the monsoon season.  Anthropogenic influences include excess nutrient input resulting in eutrophication, anoxic conditions and fish kill events.  Dams play a large role in shaping estuarine habitat.  Along the Indus river dams have destroyed thousands of acres of riparian zone which in turn effects the quality of discharge in to estuaries.  Overfishing and destructive fishing practices have taken a large toll on the populations of fish, especially the grouper and yellow fin tuna populations. 

Biodiversity & Ecosystems

                         Coral Reefs

Lakshadweep Islands off the coast of India [4]
The majority of the coral reefs in the Arabian sea are located at the Lakshadweep Island archipelago off the coast of India.  The island are formed by the coral and are surrounded by 32 km^2 of reefs.  There are over 300 species of coral, 500 species of mollusks, 200 species of crabs, 1,200 species of fish and 20 marine mammals.  Primary productivity is driven by corals, algae and phytoplankton. Prominent bird species found on the islands include the sand piper, golden clover, and green and red shanks.  Some important fish in the surrounding sea are skip jack, yellow fin, and the rainbow fish. 


Mangrove distribution [5]
Most of the mangrove forests in the Arabian Sea are located at the Indus River Delta and along the coast of the Persian Gulf as seen in Fig. 4.  Diversity of flora ranges from about 150 to 250 species at sites on the Indus delta.  Some abundant species of fauna include fiddler crabs, ghost crabs and mud snails.  The trees are the key carbon stores driving production and provide habitat supporting over 60 birds.  Stands usually do not exceed 6 meters in height however, they may grow to as much as 150 years old.    

                  Sea Grass Beds

Sea grass beds [6]
Species richness of sea grass beds is highest along the coasts of India and Yemen.  There are 8 species of sea grasses found in Yemen  beds and 12 along the Indian coast.  Sea grasses provide nursery habitat for countless species of invertebrates and small fish.  One acre of sea grass bed can support some 4,000 fish and 50 million invertebrates.  Sea turtles and dugongs are both dependent on sea grass beds for grazing purposes.

Food Web

From left to right: Zooplankton, Humback whale, Fiddler crab, Rainbow fish, Sand piper, Sea turtle, Tuna [7]

General food web with species from all mentioned ecosystems [7]

                                                                                Introduced Species

Paradella dianae [8]
There is very little information available about introduced species in the Arabian sea.  Paradella dianae is a species of crustacean native to the coast of North America.  They are a dorso-ventrally flattened, brown and yellowinsh sphaeromatid isopod.  Paradella has been introduced all over the world including the coasts of Australia, the Meditteranean sea, China, Brazil, and the Arabian Sea.  They hitch rides on the hulls of ships in fouling communities or are carried in ballast water.  Their success at traveling the world can be attributed to the fact that they can survive in a wide range of salinity.  Impacts of P. dianae has only been observed at high concentrations off the coast of Florida.  It has been noted as a significant competitor of other native grazing species for food and space.


                   Major Fisheries

Indian Oil Sardines on ice [9]
The major species of fish caught in the Arabian Sea are the Indian Oil Sardine, Drums, Croakers and the Bombay Duck.  Other important fish caught in the area are anchovies, mackerel, and various crustaceans including the spiny lobster.  Major fishing techniques used in the Arabian Sea are gillnets, trawls, longlines and purse seines. 


Rajitha Senaratne, Minister of Fisheries, IOTC [10]
Ten countries share exclusive economic zones in the Arabian sea.  India's is the largest followed by Oman.  Fish landing trends presented by the National Institute of Water and Atmospheric Research showed a 5,000 metric ton increase from 1995 to 2005 and a 8,000 metric ton increase in small pelagic fish.  In a general survey the FAO found an increase from 1.9 million tons of fish caught in 1990 to 2.2 million tons in 1999.  The hope is that the data collected by these two organizations will help in creating proper management procedures for fisheries in the future.  The main company regulating fisheries in the Arabian Sea is the Indian Ocean Tuna Commission (IOTC).  They are mainly in charge of pelagic longline, purse seines, and artisinal gillnet fisheries.  The IOTC encourages reporting bycatch and has attempted to decrease tuna predation.


Carp farm on the coast of India [11]
Major farmed fish in the Arabian sea are tilapia, carps, groupers, the sea bream, shrimps, prawns and mullets.  In addition to farms where fish are cultured from birth, there are also fish fattening farms where fish are caught in the wild and brought back to a farm off shore where they are fed extra in attempts to make them more profitable on the market.  This is primarily done with the yellowfin tuna and small finfish.

Environmental Concerns

                                                                         Acidification and Foraminifera

Foraminifera fossil [12]
The acidification of the ocean means the there is increased hydrogen ion availability.  As a result carbonate is converted to bicarbonate molecules.  This means that there is less calcium available for shell forming creatures, such as foraminifera.  Foraminifera are a large group of protists that produce a shell consisting of calcium carbonate.  They are used in determining where oil deposits are, historical climate characteristics, and rock dating. In study by Moel et al. fluctuations in shell thickness was correlated to seasonal nutrient availability.  It was determined that not all of the thinning of foraminifera shells could be accounted for by seasonal changes.  The conclusion was that ocean acidification was causing thinner foraminifera shells as a result of decreased calcium availability.

                       Oil Spills

Oil-stained foot near the Arabian Sea shore in Mumbai, India [12]
There have been many oil spills in the Arabian Sea.  The most recent reported spill happened on August 7, 2010 near Mumbai.  Two Panamanian cargo ships collided off the coast of Mumbai dumping 400 tons of oil into the sea.  This particular spill occurred next to the Mahim Bay estuary system that provides countless ecosystem services to populations up and down the adjacent coastlines. 

                                                                                     Fishery Problems

Bottom trawl scars [14]
There are various problems caused by fisheries in the Arabian Sea.  Overfishing has exploited numerous fish stocks including the yellowfin tuna and the hammour (grouper).  Improvements in fishing technologies have caused increases in the amounts of bycatch.  Sea turtles, dugongs, and dolphins have all been reported as bycatch in gillnet and trawl fisheries.  Seabirds have also been caught on long line fisheries as they attempt to prey on the baited hooks.

   Aerosol Pollution (Region Specific)

Aerosol albedo effect [15]
    Aerosols are particulate matter that has become airborne. They can decrease the amount of light that reaches and is reflected of the earth, alter cloud densities, and enhance or supress chemical reactions in the atmosphere.  Anthropogenic sources include car emissions and power plants.  Natural sources include fires, dust storms and volcanoes.  Secondary sources of carbon are compounds that undergo photodissociation which is where high energy ultra violet light breaks molecules apart in the atmosphere.  The most well known aerosol is black carbon highlighted in the study: Effects of Black Carbon on the Indian Monsoon (Meehl et. al 2008).  China and india account for over 35% of worldwide black carbon emissions.
    Because aerosols are so small, water in clouds accumulate around aerosols instead of forming normal sized rain drops.  As a result, precipitation in areas of high aerosol is reduced.  Meehl et. al found that aerosol concentrations caused higher precipitation before the monsoon season and reduced precipitation during the monsoon.  Much of the aerosol pollution influencing the monsoon comes from China's cheap, soft coal power plants.
   The monsoon  occurs as a result of radiation from the sun being reflected off the land in India.  The radiation heats the air above the land which then rises.  Cold, moist air from the ocean rushes in to take its place.  This causes winds to blow northeast along the coasts of Yemen Oman and Pakistan.  Due to the Coriolis effect, Ekman transport pushes water away from the coast causing cold, nutrient rich waters to be upwelled along the coast.  This upwelling event promotes the large rates of primary production observed in this region.
    Aerosols reduce the amount of radiation that is reflected off the earth deacreasing the amount of hot air that rises over India.  This diminishes the magnitude of wind currents blowing along the northern coastline.  Diminished winds cause reductions in the monsoon driven upwellings that bring nutrients to the surface and thus reduce primary productivity rates.   

Solutions (ITC's)

    There is really only one solution to the problems caused by fossil fuel extraction and combustion: Stop.  It is past time to invest in alternative energy sources.  The primary need is for governmental institutions to place beneficial investment tax credits on wind or wave farm production.  Firms investing in wind or wave power infrastructure will the reap benefits of the investment credits now and the entire world will be experience the repercussions of switching to non polluting power plants at a later time.  Once a stable base of renewable energy generating infrastructure is in place cars can go electric.  As a result, energy demand will increase towards the already thriving renewable economy and away from the fossil fuel industry.  Electric cars will dramatically reduce aerosol emissions as well as green house gases that are driving acidification of the oceans.
    Fishery problems may be solved in a similar fashion.  Reduced aerosol emissions as a result of the renewable revolution will enhance primary productivity that drives ecosystem support of various fisheries.  Fishing regulations will need to be adjusted to meet new distributions of fisheries and still support the vast populations of humans on the surrounding coastlines.  Technological advances will be needed to reduce destructive fishing practices.   

Image Sources

Other Sources

    General Information:
    Historical Use:
    Habitat Changes:
Kawagata S., Hayward B. W., Gupta A. K. 2006. Benthic foraminiferal extinctions linked
     to late pliocene- pleistocene deep-sea circulation changes in the Northern Indian
     Ocean (OPD sites 722 and 758). Marine Micropaleontology Vol. 58, Issue 3: 219 -
    Coral Reefs:
    Introduced Species:
Madhupratrap M., Nair., K. N. V., Gopalakrishnan T. C., Harida P., Nair K. K. C., Gauns
     M. 2001. Arabian sea oceanography and fisheries of the west coast of India. Current
     Science Vol. 81 no 4: 355 - 361.
    Ocean Acidification:
Moel H., Ganssen G. M., Peeters F. J. C., Jung S. J. A., Brummer G. J. A., Kroon D., and
     Zeebe R. E., 2009. Planktic foraminifera shell thinning in the Arabian Sea due to
     anthropogenic ocean acidification? Biogeosciences, Discussions 6: 1811 - 1835.
    Oil Spills:
    Aerosol Pollution
Meehl G. A., Arblaster J. M., Collins W. D. 2008. Effects of black carbon aerosols on the
     Indian monsoon. Journal of Climate Vol. 21: 2869 - 2882.

Created by: Anthony Maddox          Last modified: December 7, 2010