The effect of tsunamis on marine organisms
A tsunami pertains to the strong wave activity that is generated by seismic movements of the Earth’s plates. These waves are pushed inland, resulting in floods and destruction of coastal areas. One of the most recent tsunami events occurred on December 26, 2004, right after an earthquake that shook the Sumatra island of Indonesia. The tectonic activity of the earth’s plates resulted in large waves in the Indian Ocean, which in turn pushed water towards approximately 21 countries across Southeast and East Asia. According to oceanographic analysts, the December 26, 2004 tsunami is one of the most deleterious natural events in history (Hamann 26), resulting in approximately 275,000 deaths in a single day. Aside from the massive mortality, the December 2004 tsunami has also left severe damages in both infrastructure and the marine ecosystem.
The Bay of Bengal is one of several aquatic ecosystems that were reported to be severely damaged by the December 2004 tsunami. According to an intensive report by Krishnankutty (772), the tsunami brought in significant amounts of sediment from the coastal shore. The dumping of land debris into the littoral zone of the bay resulted in the mixing of organic material from the ocean floor with the sand from the coastal line, thus modifying the natural composition of the ocean floor substrate. In addition, smaller ecosystems in the bay were buried by the sudden dumping of solid material into these areas (Sampath 25). The unearthing of organic material due to the churning of the ocean floor increased the amount of nutrients in the water and this induced the growth of algae, which are known to be opportunistic organisms that thrive on nutrient resources for survival. Extensive reproduction of algae had resulted in an algal bloom and the high density of these microorganisms converted the waters from clear to murky. Unfortunately, the high density of algae in the water inhibited light from traversing the water column, resulting in aquatic organisms living in the deeper regions of the bay suffering from oxygen insufficiency.
Coral reefs, which are considered as nurseries for several fish species, have also been damaged by the December 2004 tsunami. According to Foster, (25), the December 2004 tsunami resulted in the massive movement of coral reefs. Some coral reefs were left by the strong waves in a tilted fashion, while other coral reefs were pushed to a lower level in the ocean. In other cases, the coral reefs were raised to a higher level, thus the water column of this ecosystem was smaller. It should be understood that any variations in the natural conditions of coral reefs could affect marine organisms that live in these ecosystems because the biogeochemical features of the coral reefs have changed. For example, a coral reef that is submerged after a tsunami event may receive less light from the sun, hence this new condition will result in a significantly lower amount of dissolved oxygen which is essential for photosynthetic processes of the seaweed species. Several marine vertebrates such as fishes need seaweed for nourishment and a decrease in the amount of food source may result in competition among the fish populations. The prolonged duration of scarcity in food resources can also impede the reproduction rates of the fishes, resulting in smaller fish populations.
The opposite scenario can also be observed in a coral reef that is pushed to a higher altitude relative to the water column. The coral reef in this case will receive plenty of sunlight which may be more than what is necessary for the photosynthetic processes of the seaweed population. On the other hand, the higher altitude of the coral reef will result in waters with higher temperatures which may still affect the normal physiologic processes of both plant and animal organisms living in these coral reefs. There may be particular fish species that can not tolerate higher temperatures due to the increased amount of sunlight and this may result in the death of these fishes. The ultimate result of such change is a severe alteration of the ecosystem, resulting in the loss of marine organisms.
The December 2004 tsunami event has also affected the mangrove forests in Southeast Asia. These particular ecosystems serve as habitats for crustacean and fish species because these areas are rich in nutrients. Mangrove forests are unique ecological systems because these are the areas where salt and fresh waters mix, resulting in a murky yet nutrient-rich substrate that is beneficial to mangrove organisms. There are also certain portions of the ocean wherein turtles build their nests. The force of the waves of a tsunami may destroy these nests and the turtle species may have no other place to live.
In a study conducted by Satheesh and Wesley (8), the population of phytoplankton markedly increased by two-fold while the zooplankton population decreased four-fold after the December 2004 tsunami. These variations in sizes of plankton populations are the direct result of the changes in the amounts of nutrients in the ocean, including oxygen, nitrates and phosphates which were brought about by the tsunami. The biological parameters of the water may thus affect the biodiversity of the ocean. Nutrients are important in marine ecosystems because these serve as sources for simple chemical compounds which are utilized for biogeochemical cycles. The same observation was described by other reports (Reddy 1028; Laluraj 42). Phytoplankton is an important member of marine food web as they occupy major trophic levels in the ecosystem. These organisms thrive solely on the amount of nutrients that are dissolved in the water. Phytoplankton converts inorganic nutrients into more complex organic compounds during marked reproductive periods. The concentration of dissolved oxygen has been observed to decrease after the December 2004 tsunami. Dissolved oxygen is strongly correlated to wind turbulence, as well as phytoplankton spikes in reproduction. The decrease in the amount of dissolved oxygen may possibly be due to the requirement of the microorganisms for oxygen which is used for converting decaying material to organic matter.
Marine habitats are generally complex and dynamic in terms of relationships to both biotic and abiotic factors. Marine ecosystems are generally affected by man-made activities yet the effect of natural events such as tsunamis and earthquakes are much more significant. There are major differences in the effects of human activities and natural disasters. Human activities usually result in small disturbances in marine ecosystems while natural disasters generate major changes. However, the disturbances generated by natural disasters are usually corrected over time, unlike the damages resulting from man-made influences, which are often irreversible (Kumaraguru 1731).
It has been observed that marine ecosystems have recovered from the damages of the December 2004 tsunami after at least five months. The rebuilding of marine ecosystems may vary depending on the site of the ecosystem and the severity of the damages that were inflicted. In addition, an ecosystem that has been damaged by both man-made activities and natural disasters often recover after a longer period of time and most probably, the damages generated by the tsunami are easier to remedy than those generated by human activities.
Natural disasters such as tsunamis and earthquakes are uncontrollable events that result in major changes in both land and marine ecosystems. The strong waves associated with tsunamis are thus highly destructive not only to humans but also to marine ecosystems and organisms. The oceans are very rich in marine species and any changes brought about by a tsunami may be as grave as its effect on human beings. It is thus important to understand the relationships of natural disasters and the immediate changes that may occur to the marine environment in order to possibly facilitate the healing and rebuilding of these ecosystems.
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Satheesh, S. and Wesley, S.G. “Impact Of December 26, 2004 Tsunami On The Hydrobiology Of Kudankulam Coast, Gulf Of Mannar, India.” Environmental Monitoring and Assessment, 2008, DOI 10.1007/s10661-008-0469-1.