DOI: 10.5061/dryad.cjsxksn57
title: Ephemeral habitat supports high alpha and beta diversity during drought in a subtropical semiarid wetland

description: 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.
description: 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 (&lt;5 cm Total length, TL) to large (&gt;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.
description: The dataset is complete.