Trophic ecology of fish community as a fundamental to management of fish resources in Segara Menyan estuary lagoon

Abstract

Estuaries areas are the complex ecosystem and provide habitat for aquatic organisms, particularly for fishes. The Segara Menyan is a semi-enclosed estuarine lagoon located within the Java Sea. Many fish species utilize estuary lagoon as feeding, nursery, and refuge area. The objectives of this study are to (1) investigate the ichthyodiversity inhabiting of various habitats, (2) describe the spatiotemporal variation in fish community distribution, (3) describe the trophic ecology of fish community, and (4) determine the strategy of fish resources management in Segara Menyan estuary. Fish samples were collected every month between January and December 2011 at three zones, i.e. coastal lagoon, lagoon, and streams. Fishes were collected using a gillnet (5 m x 85 m, three panels 2, 3, and 4 inci mesh); trammel net (2 m x 70 m, three panels 0.75; 1.5; 2.5 inci mesh); and minitrawl (6 m x 1.2 m, 4.5 mm mesh, bag 1.2m x 1.2 m). Captured fish were preserved in 10% buffered formalin in the field. In the laboratory, samples were sorted then fixed in 70% etanol for later analysis. A total of 6,254 fishes consisted of 47 families, 79 genera, and 106 species, and the most collected group of fish was Carangidae. Fish communities divided into four groups according to ecological category i.e. estuarine species from marine, marine species, resident estuarine species, and estuarine species from freshwater. The estuarine species from marine and juvenile were dominant. Based on occupied habitat, the most number of species and biomass were found at coastal lagoon zone. Spatiotemporal variation in fish density, species richness, diversity Shannon-Wiener, and dominant species were found in the three zones at Segara Menyan estuary. Multiple linear regression analysis revealed inconsistent patterns in terms of the relationships between univariate fish assemblage measures (fish density, species richness, and diversity) and environmental variables (temperature, salinity, water clarity, and dissolved oxygen). For each of 106 fish species, between 1 and 380 stomachs, were examined. The vacuity index was also different among species. Five of 106 species had a vacuity index of “0” and total number of food items consumed varied between fish species, ranging from three items to 27 items. The overall diet breadth (Bi) was relatively low among species, ranging from 0.20 to 0.78, with most of them between 0.20 and 0.48. Calanoid copepods comprised the most common food item consumed by all the fishes examined. Fishes occurring can be broadly categorized into seven different trophic guilds. The trophic level of fish communities ranged from 2.05 to 4.73. An understanding of trophic ecology of fish communities was used to determine a management and conservation of fish resources strategies. The strategy proposed were the development of recreational fisheries, regulation of capture fisheries, and management of fish habitats.