Composition and Distribution of aquatic insect communities in selected tributaries of Tasik Kenyir, Terengganu

Summary by Wahizatul, A.A. and Hoon, A.G. (contact: Wahizatul@umt.edu.my)

Tasik Kenyir supports a wide range of aquatic insects and other benthic invertebrates. As the diversity and distribution of aquatic insects in Taman Negara Tasik Kenyir has not yet been reported in the literature, UMT has been sampling aquatic insects with the aim of documenting the composition and distribution of kenyir’s aquatic insect communities. The project started in 2010 with a team surveying two selected tributaries (Sungai Cacing and Sungai Perpek) of Tasik Kenyir, Terengganu (Fig. 1).

Figure 1. Staff and students of the Department of Biological Sciences, Faculty of Science & Technology that were involved in the expedition of Tasik Kenyir from 14-17 October 2010.

A total number of 290 individuals of aquatic insects representing 21 families from six orders were collected using disturbance-removal sampling technique. Total abundance of aquatic insects was significantly higher in Sungai Perpek (198 individuals) compared with Sungai Cacing (92 individuals). In terms of taxon richness, a slightly more diverse and richer fauna was recorded in Sungai Perpek (16 families), compared to Sungai Cacing (11 families). Philopotamidae (Order: Trichoptera) was the most dominant family recorded in Sungai Perpek, whereas the most abundant family collected in Sungai Cacing was Perlidae (Order: Plecoptera) (Fig. 2). A relatively high abundance of Heptageniidae (Order: Ephemeroptera) was also found in both streams.

Figure 2. Perlidae (Order: Plecoptera) nymphs were found in abundance in Sungai Cacing.

It was apparent that the diversity and abundances of aquatic insect communities in this study were closely related to the existence of microhabitats, hydrological characteristics and land use surrounding land use. For example, the high abundance of Perlidae in Sungai Cacing was probably due to the hydrological characteristics of the stream. In general, Sungai Cacing is deeper than Sungai Perpek, typically of hilly types with sands, gravels, cobbles and boulders substrates, highly exposed to the sunlight as most of the stretches were sparsely canopied and almost crystal clear water. Perlidae nymphs require high concentration of dissolved oxygen, relatively clean water and restricted to lotic water. Their presence with a high diversity of other aquatic species indicates clean water quality (Sivec and Yule 2004).

The high abundance of philopotamids and baetids (Fig. 3) in Sungai Perpek is likely to be realted to the composition of the substrate which generally consists of pebbles and gravels; suitable habitat for these organisms. Both families like to live and feed on the sides or bottoms of rocks with their protected shelter made of silk and debris (Morse 2004).

Figure 3. Philopotamidae (left) and Hydropsychidae (right) (Order: Trichoptera); the most dominant caddisfly nymphs recorded in Sungai Perpek.

Sungai Cacing and Sungai Perpek had relatively high abundances of mayfly nymphs. As both streams were quite fast-flowing, they supported high numbers of Heptageniidae which live among crevices in relatively stable substrates such as stones and rocks in moderately fast-flowing streams (Khoo 2004). In general, this family is considered as an indicator species for clean water ecosystems and most sensitive to environmental disturbance as they strictly inhabit clean, fast flowing and running water habitats (Merritt and Cummins 1996).

Aquatic insects that were exclusively found in Sungai Perpek. Top left: Ptychopteridae, Top right: Tipulidae, Bottom left: Ocontericidae, Bottom right: Ephemeriliidae.

Odonate nymphs and chironomids (Fig. 5&6) were  almost entirely confined to slow moving water and soft streambeds. Their morphology and behaviour appear to depend partly upon the particle size of the substrates in which they inhabit; either in sand, grit, silt or debris in streams, rivers, lakeshores and ponds.

Some of dragonfly nymphs (Order: Odonata) found in both streams. Top left: Aeshnidae, Top right: Libellulidae, Bottom: Lestidae.

The presence and abundance of Chironomidae larvae, often associated with water pollution, in Sungai Perpek may indicate that visiting houseboats are having a detrimental effect on aquatic habitat in this area.

Chironomidae larvae were found in the lower Sungai Perpek. These are commonly used as a bioindicator for unhealthy aquatic systems.

This study is important to document the current diversity of aquatic insects in Taman Negara Tasik Kenyir and the characterization of their habitats will ensure that threatened habitat can be protected. As aquatic insects are particularly sensitive to human disturbance, it is necessary for us to preserve these unique creatures for future generations to enjoy.

References

Khoo, S.G. 2004. Insecta: Ephemeroptera. InYule, C.M. and Yong, H.S. Eds. Freshwater invertebrates of the Malaysian Region. Malaysia: Academy of Sciences Malaysia, pp 394-408.

Merritt, R.W. and Cummins, K.W. 1996. An introduction to the aquatic insects of North America. Iowa: Kendall/Hunt Publishing Company.

Sivec, I. & Yule, C.M. 2004. Insecta: Plecoptera. In Yule, C.M. and Yong, H.S. Ed. Freshwater invertebrates of the Malaysian Region. Malaysia: Academy of Sciences Malaysia, pp 443-456.