Macroinvertebrates

Jongkar, Grinang and Brian Haessler, Delim and Lee, Nyanti and Ling, Teck Yee and Sim, Siong Fong and Tonny, Ganyai and Lee, Karen Suan Ping (2021) Macroinvertebrates. In: Life from Headwaters to the Coast, Pelagus National Park, Biodiversity Above the Rapid. Unimas Publisher, Sarawak Energy & Natural History Publications (Borneo), Sarawak, pp. 23-31. ISBN 9789672298588

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Abstract

The drainage system of the Pelagus area comprises first to sixth order streams, with slow to fast flowing water and moderate gradient channels. The tributaries are important feeder streams in sustaining hydrological functions of the main Rajang River, especially as a result of the construction of two hydroelectric dams in the upper stream, the Bakun Dam and Murum Dam. Macroinvertebrates sampling was conducted twice at 27 tributaries between 2013 and 2016. Three replicates of kick-net sampler (30 × 32 cm, 400-micron mesh size) were made for each visit, yielding a total of 162 samples. Hand collecting at night along riverbanks and forest trails was carried out for semiterrestrial crabs. Specimens caught from local fishing tools, such as castnet (‘jala’) and traps (‘bubu’) were also recorded. The multiple sampling techniques used have produced a macroinvertebrate inventory for the Pelagus area, which shows over 79 species in 52 families and 12 orders, comprising aquatic insects, crustaceans, molluscans and aquatic worms. All crabs and some taxa of aquatic insects are endemic to Borneo. Macroinvertebrates were assigned to functional feeding groups, and field observations of species occurrence on major substrate types were recorded. Analysis of functional feeding groups shows that predators and gathering-collectors are common in all stream orders. Macroinvertebrates are well represented in third order streams, which imply that the stream order is the most productive. High beta diversity (dissimilarity) between lower order stream (1st order) and higher orders (> 3rd order) suggests that conservation management of river basin should be inclusive in all stream orders. Macroinvertebrates are good indicator for stream condition in the Pelagus area. Low taxa richness of sensitive orders such as Ephemeroptera, Plecoptera and Trichoptera (EPT) may indicate that effects of logging activities persist after 30 years. EPT-values also show low adaptation to new and unstable substrates originating from the logged catchment area.Some larger species, such as shrimps, prawns (e.g., Macrobrachium rosenbergii), snails and crabs are important sources of protein for the local people.

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