Low diversity of fishes in high elevation Afrotromontane streams renders them unsuitable for biomonitoring

Abstract

Most of the rivers in the Afrotropics emerge from forested uplands that are prime for human activities, including crop farming, grazing and settlement. However, streams draining these areas have a low diversity of fishes, which limits their use as indicators of water quality and ecological status. Here, we developed macroinvertebrate-and fish-based indices of biotic integrity and evaluated their responses to human activities in the Sondu-Miriu River, Kenya. Overall, water quality declined downstream because of the cumulative effects of human activities. The upper reaches had poor fish diversity with at most three species, but macroinvertebrate communities were diverse on the entire gradient of the river. Metrics that have been used to develop indices of biotic integrity in the Lake Victoria basin were selected and evaluated for responsiveness to various forms of human disturbance along the river. The poor diversity of fishes in the upper reaches limited the number of metrics that could be developed and evaluated. The fish index was only successfully applied in the middle and lower reaches where fish diversity was high. However, macroinvertebrates were diverse and sensitive to human activities on the entire gradient of the river. This study shows that for biomonitoring, macroinvertebrate communities offer a better alternative to fishes in high elevation Afromontane streams that harbour poor fish assemblages.

Longitudinal fish species diversity and distribution in a medium-sized Afro-tropical river in the Lake Victoria Basin

“…It was, however, narrower than the 0.2 to 1.7 reported in the Upper Awash River, Ethiopia [40] and much higher than the 0.04 to 0.33 range reported in River Sondu Miriu [35]. The Shannon-Weiner diversity index (H′) range of 0.54 to 1.36 observed in this study is close to those reported in studies of River Sondu Miriu (0.23 to 1.98) [35] and 0.14 to 0.80 reported in Upper Awash River, Ethiopia [35] [39]. The zero species richness, Simpson's index (D), Shannon-Weiner index (H′), and Pielou's evenness index (J) observed in the upper zone of Awach Kibuon River was also reported in the impacted Upper Awash River, Ethiopia [40].…”

“…Sondu-Miriu, and Yala rivers [25] and 0.44 to 0.78 range reported in Ganjiang River, Jiangxi, China [14]. It was, however, narrower than the 0.2 to 1.7 reported in the Upper Awash River, Ethiopia [40] and much higher than the 0.04 to 0.33 range reported in River Sondu Miriu [35]. The Shannon-Weiner diversity index (H′) range of 0.54 to 1.36 observed in this study is close to those reported in studies of River Sondu Miriu (0.23 to 1.98) [35] and 0.14 to 0.80 reported in Upper Awash River, Ethiopia [35] [39].…”

“…families reported in a study of fish diversity in River Sondu Miriu [35]. However, it is much higher than the 7 and 10 species reported in Awach Seme and Kisian rivers [27] and much lower than 41, 37, 48, 49, and 36 fish species reported in Mara, Nyando, Nzoia, Sondu-Miriu, and Yala rivers in the Lake Victoria Basin [23].…”

Drivers of species richness and beta diversity of fishes in an Afrotropical intermittent river system

“…While Amphilius grandis is reported to occur in both the Tana and Northern Ewaso Ng'iro drainages this species is found in higher elevation streams in the Tana drainage than in the Northern Ewaso Ng'iro. Recent studies have also shown that fishes in these Afrotropical higher elevation streams may not be the best indicators of ecosystem health since they are naturally species poor communities (Kleynhans, 1999; Mangadze et al, 2016; Masese et al, 2020; Raburu et al, 2022). Unfortunately, no collections were made at these localities prior to the 1990s so we are unable to determine if the low species richness in these rivers is the natural state or a result of species introductions (i.e., non‐native trout) or land use changes.…”

Bioassessment of multiple stressors in Afrotropical rivers: Evaluating the performance of a macroinvertebrate-based index of biotic integrity, diversity, and regional biotic indices

“…In addition, macroinvertebrates have many practical advantages for bioassessments, including a wide distribution in most streams and rivers, ease of sampling and identification at the family level, and the sampling equipment is relatively inexpensive (Rosenberg and Resh, 1993;Barbour et al, 1999;Bonada et al, 2006). However, in the Afrotropics, high-elevation, low-order streams have a very low diversity of fishes (Kleynhans, 1999;Mangadze et al, 2016;Raburu et al, 2022), which is the alternative bioindicator group for use in river ecosystems (Barbour et al, 1999). This low diversity of fishes makes macroinvertebrates the only best alternative available biotic group for biomonitoring headwater or high-elevation streams.…”