Competition for shelter in a high-diversity system: structure use by large reef fishes

Abstract

Competition among large reef fishes for shelter beneath tabular structures provides a rare opportunity to study competition in a species-rich environment. The system permits a detailed study of localised competition with major implications for coral reefs with respect to human impacts including climate change. Using underwater video cameras, this study examined competition among 30 species of large reef fishes (from nine families) for access to shelter provided by 26 tabular structures, which may be the highest reported diversity of vertebrates competing for a single resource. Mean concentrations of fishes under tabular structures were also among the highest biomass recorded on reefs (4.71 kg m -2 ). A generated dominance hierarchy for the occupation of shelter appeared to be primarily driven by the size of fishes. In contrast to previous studies, fishes higher in the hierarchy tended to exhibit the lowest levels of aggression. However, size difference between fishes was found to be strongly negatively correlated with the proportion of aggressive interactions (R 2 = 0.971, P \ 0.0001). The strong competition for the shade provided by these corals highlights concerns about future shifts in the structure of large reef fish communities as corals are lost. This is particularly concerning given the critical functional roles played by certain species of large reef fishes that utilise tabular structure for shelter and which occupy the lower ranks of the dominance hierarchy.

The macroecology of reef fish agonistic behaviour

“…We identified all species and recorded all agonistic interaction events between them occurring in the central 10 min of each video sample (the first and last 2.5 min were discarded to remove any potential disturbance by the observers; Longo et al ). We considered an agonistic interaction as a chasing event between individual fish (Supplementary material Appendix 1 Video A2) – a behaviour that is well‐documented as representative of disputes for food resources, territory and/or mating opportunities (Robertson , Kerry and Bellwood ). We focused on species larger than 5 cm in total length because identification of smaller individuals in remote video analysis can be unprecise (Longo and Floeter ).…”

“…Contest and scramble competition among reef fishes are conspicuous – since the same local resources (e.g. food, shelter) are used by many species, territorial disputes (Munday ) and agonistic behaviour are common (Blowes et al , Kerry and Bellwood ). Competition can be so prevalent that, by influencing individual growth, reproduction and mortality of reef fishes, it can modulate their abundance and distribution across coral reef habitats (Bonin et al ).…”

Interactions between coral restoration and fish assemblages: implications for reef management

“…Increasing complexity by reintroducing intricate and table-shaped corals may produce areas of shade in which juvenile and nocturnal coral fishes can take cover (Hair et al, 1994;Kerry & Bellwood, 2016;Sheppard, 1981;Stimson, 1985). Provision of shade may effectively conceal vulnerable fishes while allowing them to better spot predatory threats (Helfman, 1981), and shade may provide protection from the damaging effects of UV light (Kerry & Bellwood, 2015b Coral density and connectivity between coral fragments may also significantly shape resident fish assemblages as clumping of coral colonies may be particularly appealing to aggregating fishes (Edwards & Gomez, 2007;Griffin et al, 2015;Huntington et al, 2017;.…”

“…The provision of shade in addition to physical shelter provided by reef crevices and holes is also likely to be a contributing factor in attracting fish assemblages to restored reefs (Spieler et al ., 2001). Increasing complexity by reintroducing intricate and table‐shaped corals may produce areas of shade in which juvenile and nocturnal coral fishes can take cover (Hair et al ., 1994; Kerry & Bellwood, 2016; Sheppard, 1981; Stimson, 1985). Provision of shade may effectively conceal vulnerable fishes while allowing them to better spot predatory threats (Helfman, 1981), and shade may provide protection from the damaging effects of UV light (Kerry & Bellwood, 2015b).…”

Contrasting distribution and foraging patterns of herbivorous and detritivorous fishes across multiple habitats in a tropical seascape

“…There is likely a trade-off between food and shelter changing throughout ontogeny in these fishes, but also between different types of shelter, provided by live coral or by microhabitat topography in the macroalgal areas. Shelter from predators is an important resource in coral reef environments (Kerry and Bellwood 2016), and can be sizespecific, as inter-structural spaces which are smaller than the potential predator width will act as shelter for a fish that fit within the space provided (Bartholomew et al 2000;Gullström et al 2011). Macroalgal areas with both soft and hard complexity in the form of fronds and coral rubble might therefore provide sufficient shelter for smaller individuals, while it is advantageous for larger fish to keep to areas with larger structures, as provided by live coral.…”