Coastal ecosystem too vulnerable to sea level rise

Salt water intrusion into fresh water ecosystem of Bangladesh coastal area.

Climate change affects all aspects of biodiversity; however, the changes have to be taken into account vis-a-vis the impacts from the past, present, and future human activities, including increasing atmospheric concentration of carbon dioxide. For the wide range of IPPC emission scenarios, the Earth's mean surface temperature has been projected to warm 1.4 to 5.8º C by the end of the 21st century, with land areas warming more than the oceans and the high altitudes more than tropics. Then globally, by the year 2080, about 20% of the coastal wetlands could be lost due to sea level-rise. The associated sea-level rise is supposed to be 0.09 to 0.88m.
So far the impact of climate change on biodiversity is concerned, it is to affect individual organisms, populations, species distributions, and ecosystem composition and function both directly (through increase in temperature and changes in precipitation and in the case of marine and coastal ecosystems also changes in sea-level and storm surges) and indirectly (through climate change the intensity and frequency of disturbances on species assemblage).
Climate change impact on plants, animals and humans is enormous in volume and it is more or less everywhere of the world. But the impacts of climate change on sea-level-rise and its consequent effects on coastal ecosystems are exceptionally significant. These impacts are equally devastating to the biodiversity and to the people in the different areas of the ecosystem. A coastal ecosystem provides high species assemblage and at the same time human need-resources. Human need-resources are available in the coastal ecosystems from different dimensions and different formations.
Coastal ecosystems are affected by both anthropogenic activities and climate change variability. Coastal developments, tourism management, land clearance, pollution, exploitation of species, habitat degradation, and depletion of coral reefs, mangroves, sea grasses, coastal wetlands and loss of beaches are due to anthropogenic activities. Climate change impacts affect physical, biological, and biochemical characteristics of the ocean and coastal ecosystems at different time and space scales. These modify their ecological structure and functions.
As it is told that, when sea surface temperatures will increase by more than 1°C, coral reefs will be impacted upon detrimentally. It is already reported that many coral reefs occur at or close to temperature tolerance thresholds. Over the past several decades, increasing sea-surface temperatures have been recorded in much of the tropical oceans. Coral reefs have been adversely affected by rising sea surface temperatures. Many coral reefs have undergone major, although often partially reversible, bleaching episodes when sea surface temperatures have risen 1°C above the mean seasonal sea-surface temperatures in any one season, and extensive mortality has occurred in a 3°C rise. The coral bleaching events of 1997-1998 were the most geographically widespread -- with coral reefs throughout the world being affected leading to death of some corals.
If sea-surface temperatures increase by 3°C in short term, and if this increase is sustained over several months, it will cause extensive mortality of corals. In addition, an increase in atmospheric CO2 concentration and hence oceanic CO2 affects the ability of the reef plants and animals to make limestone skeletons (reef calcification); a doubling of atmospheric CO2 concentration could reduce reef calcification and reduce the ability of the coral to grow vertically and keep pace with rising sea level. The over all impact of sea-surface temperature increase and elevated CO2 concentration could result in reduced species diversity in coral reefs and more frequent outbreaks of pests and diseases in the reef system. The effects of reducing productivity of reef ecosystems on mollusks, echinoderms, crabs, birds and marine mammals are expected to be substantial.
When climate changes and sea-level rises, the situation erodes beaches and barriers of the coastal areas. Coastal erosion, which is already a problem on many coastlines for reasons other than accelerated sea-level rise, is likely to be exacerbated by sea-level rise and adversely affect coastal biodiversity. A 1-meter increase in sea-level is projected to cause the loss of 14% of the land mass of Tongatapu island, Tonga, and 80% of Monjuro Atoll, Marshall Islands, with consequent changes in overall biodiversity. Similar processes are expected to affect endemic plant species in Cuba, endangered and breeding bird species in Hawaii and other islands, and the loss of important pollinators such as flying foxes in Samoa.
It is anticipated that globally about 20% of coastal wetlands could be lost by the year 2028 due to sea-level rise, with significant regional variations. Such losses would reinforce other adverse trends of wetland loss resulting primarily from other human activities.
Climate change has negative impacts on the abundance and distribution of marine biota as a whole. The impact of climate change will affect dynamics of fish and shell fishes. Climate change impacts on the ocean system include sea-surface temperature-induced shifts in the geographic distribution of marine biota and compositional changes in biodiversity, particularly at high latitudes. The degree of the impact is likely to vary within a wide range, depending on the species and community characteristics and the region-specific conditions.
It is not known how projected climate change will affect the size and location of the warm pool in the western and central Pacific but, if more El Nino-like conditions occur, an easterly shift in the centre of tuna abundance may become more persistent. The warming of the north Pacific Ocean will compress the distribution of sockeye salmon, essentially sequencing them out of the north Pacific and into the Bering Sea. There are clear linkages with the intensity and position of the Aleutian Low Pressure system in the Pacific Ocean and the production trends of many of the commercially important fish species.
Sea-level rise with many other factors could affect a range of fresh water wetlands in low-lying regions. In tropical regions, low-lying floodplains and associated swamps could be displaced by saltwater habitats due to the combined actions of sea-level rise, more intense monsoonal rains, and larger tidal or storm surges. Saltwater intrusion into freshwater aquifers is also potentially a major problem.
Scientists are concerned with a fact that, everybody anticipates sea-level-rise impact and associated climate change impact on Bangladesh coastal areas. It is already reported that about 18% of Bangladesh's land will be submerged if the sea-level rises by one meter.
In Bangladesh, sea-level-rise is colossally affecting coastal areas. Of the severely affected coastal districts, most affected ones are Satkhira and Bagerhat. Ten years ago in the districts of Bagerhat and Satkhira, rice production was very common almost in all areas. Now almost entire area of the Satkhira district and 80% of the Bagerhat district have gone under sea-level-rise impacts. An area of 80km long and 40km wide has lost rice production capability and has been taken under shrimp culture projects in the Bagerhat district. In the Satkhira district, shrimp culture is prevailing throughout the entire district. Rice cultivation has been reduced by 8 times during the last 10 years in these two districts.
We must remember that impact of climatic change anywhere in an ecosystem (especially in the tropics and subtropics) is first and most sensitively received by plant phenology and by the life stages of animals (especially of phytophagous animals). Plant-animal relation in an ecosystem is biotic-biotic interaction. Sequence and or occurrence of biotic-biotic relation is the key factor for species assemblage/ species richness in an ecosystem. This species richness is the healthiness of biodiversity in a region of the biosphere. Healthiness of biodiversity is the sustenance of integration of biotic-biotic and abiotic-biotic interactions. This sustenance of integration never stands in proper 'functioning' condition when phenological stages of the plant and life stages (especially developmental stages) of animals are affected by climatic changes or any other anthropogenic activities.
Bangladesh is a natural laboratory and the place of highest species assemblage as well as species richness in the world, especially the southwestern coastal areas of the country. This area functions both as terrestrial and aquatic ecosystems ensemble. This situation is presented by mangrove vegetation as the aquatico-terrestrial condition and estuarine ecosystem as the highest productive area of marine and riverine ecosystem. Here is the secret of containing highest integration of biotic-biotic and biotic-abiotic interactions; and then for the maintenance of the highest species assemblage in the world. These interactions of the biological processes in such fertile ecosystems are very vulnerable to climatic changes.

Dr MA Bashar is professor, EBBL, Department of Zoology, University of Dhaka.