Spatiotemporal ichthyofaunal dynamics in a permanently open estuary, Otago, New Zealand

Abstract

Understanding the spatial and temporal dynamics of the fish-assemblage structure of estuaries is indispensable in conservation and habitat-improvement efforts. This study reports seasonal as well as spatial dynamics of fish diversity of the Waikouaiti Estuary and indicates the key physicochemical variables that influence the ichthyofauna of the estuary. Fish were collected from upper, middle and lower reaches of the Waikouaiti Estuary monthly for 1 year, by using a seine net. In total, 15 species and 4967 individuals were collected during the study period. Distinct differences in ichthyofaunal composition, driven by spatiotemporal environmental heterogeneity, were observed between the three reaches of the Waikouaiti Estuary. Fish abundance was higher in the middle reach where the water is turbid. Whereas fish species with diadromous life history occurred more frequently in the upper reach of the estuary, marine-migrants and marine-stragglers were abundant in the lower reach. The present study indicated that salinity and turbidity were the best predictors of fish species composition in the different reaches of the Waikouaiti Estuary.

Editorial for the 70th anniversary of Marine and Freshwater Research

“…Jacob Johansen and co-authors investigated the sublethal effects of weathered oil on larval red drum (Sciaenops ocellatus) following the Deepwater Horizon oil spill in the Gulf of Mexico (Rowsey et al 2020). Fasil Taddese and Gerard Closs investigate the spatial and temporal dynamics of the ichthyofauna of a permanently open estuary (Taddese and Closs 2020). Nick Davidson led two multi-authored manuscripts, the first reviews the adequacy of reporting to the Ramsar Convention on Wetlands on change in the ecological character of wetlands (Davidson et al 2020a), and the second considers trends in the ecological character of the world's wetlands (Davidson et al 2020b).…”

Decadal changes in land-use, water quality and fish assemblages in a KwaZulu-Natal urban and non-urban estuary.

“…Environmental heterogeneity is known to increase species diversity and influence the spatial distribution of fishes (Neves et al, 2011;Taddese and Closs, 2019). These heterogeneous environmental conditions in the uMlalazi Estuary produced a more distinct distribution of species, particularly for functional guilds.…”

“…Estuaries are highly dynamic, undergoing rapid fluctuations in environmental variables and displaying distinct vertical and longitudinal gradients (Richardson et al, 2006;Medeiros et al, 2018;Connelly et al, 2020). These gradients are often more defined in estuaries with continuous freshwater and marine influences resulting from a permanent connection to the sea (Nicolas et al, 2010b;Taddese and Closs, 2019). The most common longitudinal estuary classifications revolve around salinity (e.g., The Venice system).…”

“…In addition to salinity, many researchers report turbidity as a significant factor influencing fish species distribution, with turbid water providing protection from predatory fishes (Blaber and Blaber, 1980;Cyrus and Blaber, 1987a), and greater food sources (Cyrus and Blaber, 1987a;Taddese and Closs, 2019). Estuarine temperatures generally remain relatively constant longitudinally and over tidal cycles (Kaiser et al, 2011).…”

“…Abundances of fishes in different functional groups (estuarine usage or feeding modes) may also differ along an estuary longitudinal salinity gradient (Selleslagh and Amara, 2008). In many estuaries, marine stragglers dominate the euhaline lower regions (Nicolas et al, 2010a;Taddese and Closs, 2019), whereas estuarine species are found in greater numbers in the mesohaline middle regions (Jaureguizar et al, 2003;Whitfield et al, 2012). Estuarine systems typically support few freshwater species, and these are often restricted to the riverine and upper reaches where salinities are low (Neves et al, 2011;Whitfield, 2015).…”