Abstract
Sediment disturbance in marine environments is caused by activities including polychaete bait harvesting, trawling, dredging, sediment erosion and treading. These activities affect the benthic communities by changing the densities, community assemblage and diversity. The aim of this study was to evaluate the potential of nematodes as indicators of sediments disturbance following polychaete bait harvesting. The study was conducted in three sites experiencing different bait harvesting intensities in Mida Creek, Kenya. Sediment samples were collected from the mudflats during low tide, preserved in 5% formalin and transported to the laboratory for processing and identification of nematodes. The highly disturbed site recorded the lowest nematode genus richness while the less disturbed sites had the highest. Overall, the most abundant nematode genera in the non-disturbed (Dabaso) and less disturbed sites (Kirepwe) were selective deposit feeders (Spirinia and Terschellingia), while most disturbed sites (e.g. Mayonda) had predators/omnivores (Pheronus, Aporcelaimellus) and selected members of the genus Spirinia. The disturbed site was characterised by low nematode diversity (H’) and low dominance (D) while the non-disturbed and less disturbed sites had higher diversity and dominance. Clearly, nematode community assemblage, diversity and feeding guilds changed following disturbance to a low diversity that favoured higher proportions of predator/omnivore taxa.
Highlights
Mangrove forests occur within the intertidal zones and are economically and ecologically important ecosystems especially to coastal communities in developing countries
Bait harvesting and continuous disturbance of the sediment led to changes in sediment grain size distribution where the proportion of larger grain size increased over the finer ones
Sediment organic matter reduced in the disturbed station relative to the undisturbed station and a consequent change in the nematode community was observed
Summary
Mangrove forests occur within the intertidal zones and are economically and ecologically important ecosystems especially to coastal communities in developing countries. The ecosystem is important as nursery (Gajdzik et al, 2014; Sheaves et al, 2015) and feeding grounds for many offshore fish (Lugendo et al, 2007; Fry and Ewel, 2010). Mangrove ecosystems are important fishing grounds (Kihia et al, 2015), especially for artisanal fishers as the forest provides food and shelter for fish (Hutchison et al., 2014). Being close to the shoreline and accessible to humans, the ecosystem is rendered vulnerable to anthropogenic impacts such as poor harvesting methods and overexploitation of these coastal resources (Glaser et al, 2003). No regulations exist on the harvesting of non-woody products such as crabs, shrimps, fishing baits, ornamental fish etc. (Linneweber, 2002)
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