Within and between day variability in coral reef fish assemblages: Implications for fish community surveys

Abstract

Knowledge of the spatial and temporal variability of coral reef fish assemblages is crucial in order to implement effective monitoring and conservation measures, preserving ecosystem processes and functions (Bellwood et al., 2004;Hughes et al., 2017;Lindenmayer & Likens, 2010). This depends on robust ecological studies and monitoring programmes that detect spatial and temporal changes in fish assemblages (Goldsmith, 2012;Ormerod, 2003;Thomas, 1996).However, the spatial and temporal heterogeneity characterizing fish communities makes understanding ecological causes for changes in fish assemblage composition challenging (Levin, 1992). This requires the implementation of sampling designs that minimise sampling variance due to processes occurring at scales that are not

Impacts of coral bleaching on reef fish abundance, biomass and assemblage structure at remote Aldabra Atoll, Seychelles: insights from two survey methods

“…Restricting reef fish monitoring to indicator species, i.e., those that represent certain functions and are particularly sensitive to localised pressures or environmental changes, is practical, common practice (e.g., Reef Check: Freiwald et al, 2021, Atlantic Gulf Rapid Reef Assessments: AGGRA, 2023, programmes in the Pacific and Indian Ocean: Obura et al, 2017;Moritz et al, 2018), and may in some cases be the only option to enable surveys to be conducted at all. Despite considerable research on various aspects on fish visual census methodologies (e.g., Thompson and Mapstone, 1997;Willis, 2001;Thompson and Mapstone, 2002;Coker et al, 2017;Cheal and Emslie, 2020;Bach and Smith, 2021), no studies investigate the influence of number of target species on interpretation of results, in terms of ecosystem ecology. Since we have not done a direct comparison of methods (i.e., utilising both survey methods simultaneously in the same year), and since the extended data set only spans two years, our study cannot determine which of these methods more accurately reflects the impacts of the 2015/16 bleaching event on Aldabra's fish communities.…”

“…Although some bias is inevitable (e.g. due to varying sea conditions), efforts to reduce sampling error generally include the standardised training of observers (which cannot entirely address differences in surveyor experience; Thompson and Mapstone, 1997;Williams et al, 2006) and conducting surveys at similar tidal states and time of day (Thompson and Mapstone, 2002;Bach and Smith, 2021). For our study, training of surveyors was standardised and surveys were only done during the daytime, well after dawn and before dusk.…”

Detecting benefits of protection level on diversity facets in a sea of temporal scarcity

“…While there is evidence that TD varies over years, months and seasons, few studies, mostly marine ones, have focused on its variation on short temporal scales, displaying ambivalent results (Birt et al, 2012; Chabanet et al, 2012; Colton & Alevizon, 1981; Luise Bach & Smith, 2021; Myers et al, 2016; Santos et al, 2002; Thompson & Mapstone, 2002; Willis et al, 2006). The causes of these within‐ and between‐day variations remain uncertain but may be linked to species behaviour, for instance, to their foraging activity, which has been shown to vary at these short temporal scales (Choat & Clements, 1993; Magneville, Leréec Le Bricquir, et al, 2022; White et al, 2002).…”