Chilika Ecology and Biodiversity

Lagoon Ecology

As a background to defining current resource management problems within Chilika Lagoon, this section of the report describes the Lagoon ecosystem and the current status of the aquatic resources. Relevant features of the ecosystem directly supporting, or contributing to fisheries and aquaculture production, are highlighted.

High nutrient concentrations are often present in Lagoons as a result of both riverine nutrient inputs and effective nutrient recycling between the sediments and the water column. Lagoons are, therefore, often highly productive aquatic environments. A comparison of productivity land biomass estimates for lagoons around the world (Tables 4.1 and 4.2 in Barnes, 1980) clearly indicates that Lagoons are characterized by exceptionally high productivity and biomass, compared to other aquatic ecosystems. The following features provide lagoons with their distinctive characteristics.

• 1. The high degree of shelter from tidal and current action
• 2. The relatively stable salinity gradients
• The soft mud and/or sand substrates
• The well-mixed nature of the water column through wind action
• Extreme shallowness
• Organic richness in sediments
• Rapidity with which they change (over geological time scales)

in climates with seasonal rainfall, and where major inputs of freshwater exist a pronounced seasonal variation in salinity and/or water level. In comparison with estuaries, contributions of phytoplankton and submerged macrophytes in lagoons are more important in production processes. Most of the production is consumed within the system, and there is less export of nutrients and organic material due to the closed nature of lagoons and of the unimportance of tidal fluxes. Carbon sources include phytoplankton, benthic and epiphytic algae and detritus derived from macrophytes. The latter detrital source is especially important as a source of carbon.

In summary, lagoons are extremely productive environments due largely to high nutrient inputs from surrounding land drainages, as well as efficient nutrient re-cycling. This high productivity supports lagoon fisheries for both fish and shell fish. Lagoons are ephemeral environments (on geological time scales) evolving rapidly into other types of semi-aquatic, habitats (marshes, swamps). Simultaneous with this succession is a gradual shift from high salinity conditions to freshwater. Human activities within lagoon watersheds often serve to increase the succession rate of lagoons towards their ultimate terrestrial end-state. Virtually all of these general processes appear to be currently operating within Chilika Lake.

• The high degree of shelter from tidal and current action
• The relatively stable salinity gradients
• The soft mud and/or sand substrates
• The well-mixed nature of the water column through wind action
• Extreme shallowness
• Organic richness
• Rapidity with which they change (over geological time scales)
• In climates with seasonal rainfall, and where major inputs of freshwater exist, a pronounced seasonal variation in salinity and/or water level

Floral Biodiversity

Chilika is a complex ecosystem with a spatiotemporal salinity gradient and complex hydrological regime due to simultaneous connectivity with rivers and sea. The lagoon is broadly divided into four ecological sectors based on the salinity regime, i.e. northern, southern, central, and outer channel. Salinity is found to conspicuously influence the composition and distribution of the macrophytic vegetation of the lagoon. The factors that affect growth and distribution of the macrophytes are sediment texture, nutrients, and other inputs from the drainage basin along with the salinity regime.

The flora of Chilika was quite rich in terms of species content and vegetational diversity. A critical analysis of the vegetation revealed the occurrence of species that were rare, threatened, wild relatives of crop plants, economic and medicinal plants and those that were endemic to Chilika. The macrophytes encountered were classified into four broad groups, i.e. emergent, rooted floating-leaved, submerged, and free-floating. Emergent macrophytes are mostly perennial higher plants growing on periodically inundated or submerged soils with their basal portions submerged in water and tops above the water level. The rhizomes and the roots spread laterally into the deeper water to adjust with the changing water levels of the lagoon. The emergent species like Phragmites karka, Schoenoplectus littoralis, Schoenoplectus articulatus, Typha angustata, Cyperus platystylis, and Cyperus compressus were common in the eulittoral zone of the northern sector from adjoining Kalupadaghat to Mangalajodi village, extending up to the river confluence point of Daya, Bhargavi, and Luna. The western river confluence points of Kansari and Salia also supported the luxuriant growth of many emergent macrophytes.

An occurrence of 748 species of angiosperm belonging to 486 genera under 127 families were recorded and identified by the Regional Plant Resource Centre, Bhubaneswar, Odisha, India. An updated checklist of the macrophytes of Chilika Lagoon, its

uninhabited islands and shoreline has been published by Tripathy et al., 2020. Based on exhaustive and multi-seasonal survey of the lagoon, its shoreline and uninhabited islands under the Integrated Coastal Zone Management Project from 2012-2020 and earlier studies by the present authors and others, an updated checklist of 884 species of flowering plants belonging to 537 genera and 130 families has been prepared and presented in this paper. Out of this, 80 species are reported by Tripathy et al., 2020 for the first time from Chilika lagoon and its adjoining regions. For each species, correct botanical name, family, local name (wherever available), flowering and fruiting time and locality of collection have been provided in the list.