Meiofauna And Nematode Community Assemblage As An Indicator Of Sediment Disturbance

Abstract

Meiofauna is a group of the benthic fauna mostly found in the upper centimeters (cm) of the sediments. They included: copepoda, polychaeta, nematoda among other taxa playing an important role to the environment despite their small size. Their roles are to initiate mineralization of organic matter, support the complex marine food web and many other functions. The meiofauna is however affected by environmental changes and human activities though we cannot tell the extent until we investigate on their distribution, community assemblage, diversity and abundance. This study was part of a bigger project carried out in Kirepwe, Dabaso, and Mayonda within Mida Creek, Kenya investigating the impact of bait harvesting on benthic invertebrates sampled during the wet season: November, 2013. My study focused entirely on determining the potential of nematodes as bio-indicator of sediments disturbance caused by bait harvesting. This was because bait harvesting was common albeit with different intensity in the different beaches of Mida Creek. Sediments samples were collected along two transect within the mud flat running from the mangrove forest edge to the edge of the subtidal zone. Along the transects, 1m² quadrats were placed at intervals of 20m. A replicate of 2 sediments core (3.4cm diameter, 10cm deep) were taken from each quadrat. Samples were fixed using 5% formalin, stored in plastic bottles and transported to the laboratory for processing and identification. The nematodes were used because they bring out a clear difference in their distribution, community assemblage, diversity and abundance due to sediment disturbance as compared to meiofauna. Out of the total meiofauna, a total of 3988 individual nematodes were identified to the genus level. In addition, out of all other meiofauna taxa, nematoda was the most abundant taxon. Bait harvesting through digging was more pronounced in Mayonda due to its wider mud flat width. From the result, a clear difference in the distribution, diversity and community assemblage of the nematodes was seen in all the sites. A total of 83 nematode genera were encountered. Kirepwe had 58 genera, Dabaso 46 and Mayonda 35. Mayonda had the highest nematode diversity followed by Kirepwe, and finally Dabaso. On the other hand, Dabaso had the highest nematode density, followed by Mayonda and Kirepwe. Meiofauna had a high community similarity while nematode community similarity was lower at different levels of sediment disturbances. This makes the nematodes better bio-indicators as compared to meiofauna as a group. This study therefore points out that digging out of polychaetes causes sediment disturbance. The disturbance affects the xi benthic fauna distribution, community assemblage, diversity and abundance. In the study, Terschellingia and Spirinia were distributed across all the sites although in disturbed quadrats, the numbers reduced significantly. On the other hand, Viscosia, Pontonema, Synochium, Haliplectus, and Pheronus increased in numbers in disturbed quadrats. Measures such as educating the fishermen on the effects of digging of polychaete should be emphasized to safe guard the marine biodiversity and its ecosystem. KEY WORDS: Meiofauna, Polychaete, Nematode, Bait, Sediments disturbance.