Do tabular corals constitute keystone structures for fishes on coral reefs?

Abstract

This study examined the changes in community composition of reef fishes by experimentally manipulating the availability of shelter provided by tabular structures on a mid-shelf reef on the Great Barrier Reef. At locations where access to tabular corals (Acropora hyacinthus and Acropora cytherea) was excluded, a rapid and sustained reduction in the abundance of large reef fishes occurred. At locations where tabular structure was added, the abundance and diversity of large reef fishes increased and the abundance of small reef fishes tended to decrease, although over a longer time frame. Based on their response to changes in the availability of tabular structures, nine families of large reef fishes were separated into three categories; designated as obligate, facultative or non-structure users. This relationship may relate to the particular ecological demands of each family, including avoidance of predation and ultraviolet radiation, access to feeding areas and reef navigation. This study highlights the importance of tabular corals for large reef fishes in shallow reef environments and provides a possible mechanism for local changes in the abundance of reef fishes following loss of structural complexity on coral reefs. Keystone structures have a distinct structure and disproportionate effect on their ecosystem relative to their abundance, as such the result of this study suggests tabular corals may constitute keystone structures on shallow coral reefs.

The role of the reef flat in coral reef trophodynamics: Past, present, and future

“…The two most notable effects are the loss of reef-building corals, a phenomenon that is rapidly escalating due to climate-induced bleaching (Hughes et al, 2017b), and the subsequent loss of structural complexity, which has broad flowon effects for fish communities (Graham & Nash, 2013;Pratchett et al, 2008). The loss of corals results in the loss of critical habitats for large reef fishes (Kerry & Bellwood, 2015;Khan et al, 2017;Pratchett et al, 2008) and may impact fisheries yields (Graham et al, 2007). Reefs of the future are going to be unlike anything previously encountered by humankind (Hughes et al, 2017b), with fewer corals and less three-dimensional complexity.…”

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

“…If, as predicted, climate change and ocean acidification cause a substantial decline in the availability of tabular structures on coral reefs (Pratchett et al 2008), a decline in the local abundance of large reef fishes might be expected, as shown experimentally by Kerry and Bellwood (2014). The mechanism for this is unknown but when the availability of shelter decreases those species in the higher ranks of the dominance hierarchy may establish their occupancy more forcefully, vacating or excluding subordinate fishes (Almany 2004).…”

“…Additionally, several species in the mid-to low ranks of the dominance hierarchy are predators on the sediment apron of reefs (Appeldoorn et al 2009), a role whose impact on the ecosystem is not well understood. It should be noted, however, that there may be alternate shelter options for displaced fishes, which may redistribute themselves in the event that tabular structures are only lost at small scales (Kerry and Bellwood 2014).…”

“…Multiple species of large reef fishes seek access to the Communicated by Ecology Editor Dr. Alastair Harborne understorey of these structures in shallow coral reef environments, and have been observed to leave areas where tabular structures are lost (Kerry and Bellwood 2014). This behaviour may be explained by the dependence of large reef fishes on tabular structures to avoid UV irradiance (Kerry and Bellwood 2015), which can be extreme in shallow coral reef environments, and has been shown to cause severe skin damage and melanomas on fishes (Sweet et al 2012;Zamzow et al 2013).…”

Peer Review #1 of "Diversity and abundance of conspicuous macrocrustaceans on coral reefs differing in level of degradation (v0.1)"

“…Habitat complexity is an important factor driving the abundance and diversity of associated species by facilitating niche separation and resource partitioning (Vytopil & Willis, 2001; Idjadi & Edmunds, 2006). Keystone structures (sensu Tews et al, 2004) are distinct spatial structures that create complex habitats that facilitate species' coexistence by offering food resources and shelter against predators and various environmental stressors (Bruno & Bertness, 2001; Kerry & Bellwood, 2015). In coral reefs, keystone structures are created by scleractinian corals, which provide great spatial complexity to the system and multiple shelters for other organisms in the form of crevices, holes, and branches.…”