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Ephemeral habitat supports high alpha and beta diversity during drought in a subtropical semiarid wetland

Citation

Bokhutlo, Thethela; Cunha, Eduardo R.; Winemiller, Kirk O. (2021), Ephemeral habitat supports high alpha and beta diversity during drought in a subtropical semiarid wetland, Dryad, Dataset, https://doi.org/10.5061/dryad.cjsxksn57

Abstract

Globally, the number of rivers with intermittent flow is increasing due to climate change and water abstraction for human consumption. Currently, our understanding of how hydrology in subtropical rivers with intermittent flow affects the structure and dynamics of aquatic communities is poorly understood. Here, we investigated how fish α and β-diversity patterns in intermittent channels in the lower reaches of the Okavango Delta respond to seasonal flooding and drought. Under low-flow conditions, ephemeral habitat had higher α-diversity, and this was influenced by a combination of fish aggregation and apparent transient legacy effects as habitat patches became smaller and more isolated. Investigation of changes in fish assemblage structure across different hydrological periods and habitat types showed significant species turnover when water levels fell, suggesting a strong influence from species sorting. During high-water periods, species assemblages were homogenized both at local and regional scales, suggesting a greater influence of mass effects. Our findings support hydrology as a major factor regulating diversity patterns in intermittent rivers of a major wetland in a semiarid region of subtropical Africa. We infer from these findings that maintenance of a relatively natural flow regime will be necessary for conserving aquatic ecosystem structure and function in this system.

Methods

Fish were sampled bi-monthly between August 2017 and February 2018 using a nylon multifilament gillnet. The gillnet consisted of eleven panels. 

Each panel had a length of 10 m and a depth of 2.4 m. The panels comprised of different mesh sizes: 12 mm, 16 mm, 22 mm, 28 mm, 35 mm, 45 mm, 57 mm, 73 mm, 93 mm, 118 mm, and 150 mm. Panels were randomly tied together to form one multipanel gill net. The gill net was set once at each site during each survey period for approximately 12 h between 1800 hr and 0600 hr the following day. Each site was surveyed four times (two times during the high-water season and two times during the low-water season), resulting in a total of 16-gill net samples. Although gillnets are passive gears that can select for fishes with specific morphologies and behavioral tendencies, the long duration of sets and multiple mesh sizes was effective in capturing a multitude of sizes, from small (<5 cm Total length, TL) to large (>80 cm TL) individuals of the species that are documented to be common in this system (Merron & Bruton 1995). Due to limitations of the sampling gear, small fishes were underrepresented in samples, and some species were absent. Specimens were identified to species level based on keys and illustrations in Skelton (2001) and measured for total length to the nearest 1 mm. Voucher specimens were euthanized (TAMU AUP IACUC 2017-0069), fixed in formalin, preserved in ethanol, and archived in the Biodiversity Research and Teaching Collection at Texas A&M University, College Station.

Data were rearranged to get species into columns. For the purpose of our analysis, no further processing was required.

Usage Notes

The dataset is complete.

Funding

Botswana International University of Science and Technology