![]() Similarly, motile invertebrates and small fishes also remain on the reefs at night. Sessile primary producers and invertebrates do not change in abundance between day and night, and even in photosynthetically active taxa, key nutritional components (protein) are likely to remain consistent (Zemke‐White et al., 2002). Therefore, we still lack a comprehensive quantitative comparison of the relative importance of nocturnal and diurnal reef fishes in the overall community structure and, most importantly, in their relative contribution to major ecosystem functions, especially biomass production.īased on the presence of potential food resources one may hypothesize that the biomass and productivity of nocturnal feeding fishes would be comparable to their diurnal counterparts. For example, on the Great Barrier Reef, there are no quantitative comparisons of diel whole reef fish community patterns, with only a few studies focusing on commercially important fisheries target species (Cappo et al., 2004 Newman & Williams, 1995, 2001). However, despite the numerous studies characterizing reef fish community structure and/or composition (e.g., Bellwood et al., 2006 Hémery & McClanahan, 2005 Kane & Tissot, 2017 Syms & Jones, 2000), explicit evaluations of temporal partitioning of reef communities into diurnal and nocturnal communities are surprisingly rare. Because of the diverse roles they play in coral reef ecosystems, reef fishes have been a major focus of coral reef ecology (Mora, 2015 e.g., Morais, Connolly, & Bellwood, 2020 Plass‐Johnson et al., 2015 Streit et al., 2019 Tebbett et al., 2017). Reef fishes are a conspicuous, species rich, morphologically diverse, and abundant group of organisms on coral reefs (Bellwood et al., 2019 Brandl et al., 2019). ![]() Community structure offers insights into the relative importance of differing groups of organisms within the ecosystem, and is often used to quantify changes in ecosystems through time (e.g., Bellwood et al., 2006 Jackson & Blois, 2015 Stevens, 2009 Syms & Jones, 2000). Understanding community structure is one of the first steps toward a deeper understanding of ecosystem functioning. ![]() This is true even for major biological components of these high‐diversity systems, such as reef fishes (see Fox & Bellwood, 2011). Coral reefs typify this disparity resulting in a fragmentary understanding of the ecological functions performed by coral reef organisms during the nocturnal period. This diurnal research bias in ecology, likely driven by a plethora of logistical challenges, is exacerbated in submerged aquatic systems where light is naturally scarce, and where organisms must be studied in situ. This study highlights the importance of nocturnal fishes in underpinning the flow of energy and nutrients from nocturnal resources to reef communities a process driven mainly by small, cryptic fishes.ĭaytime (diurnal) ecological studies far outpace night‐time (nocturnal) studies (Gaston, 2019 Park, 1940). Taxa that overcome these constraints may thrive, as evidenced by apogonids. The substantially lower contributions of nocturnal fishes to biomass and biomass production likely indicate constraints on resource accessibility. Apogonidae dominated biomass production within the nocturnal fish assemblage, comprising 54% of total nocturnal fish productivity, which is proportionally more than any diurnal fish family. Differences in productivity were even more pronounced, with diurnal fishes contributing 163% more productivity in sheltered locations, and 558% more in exposed locations. We found that diurnal fish assemblages have a higher biomass than nocturnal fishes: 104% more in sheltered sites and 271% more in exposed sites. We combined somatic growth and mortality models to estimate rates of consumer biomass production, a key ecosystem function. We integrated a detailed dataset of coral reef fish counts, comprising diurnal and nocturnal species, in sites sheltered and exposed to wave action. In this study, we quantify and contrast the energetic dynamics of nocturnal and diurnal fishes in a model coral reef ecosystem, evaluating whether they attain similar levels of biomass production. Yet, nocturnal resources for coral reef consumers are theoretically as abundant and productive, if not more so, than their diurnal counterparts. The ecological functions of nocturnal coral reef fishes are poorly known. ![]()
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