Body size and mortality rates in coral reef fishes: a three-phase relationship

Tebbett

et al. 2018

Ecology and Evolution

The reef flat is one of the largest and most distinctive habitats on coral reefs, yet its role in reef trophodynamics is poorly understood. Evolutionary evidence suggests that reef flat colonization by grazing fishes was a major innovation that permitted the exploitation of new space and trophic resources. However, the reef flat is hydrodynamically challenging, subject to high predation risks and covered with sediments that inhibit feeding by grazers. To explore these opposing influences, we examine the Great Barrier Reef (GBR) as a model system. We focus on grazing herbivores that directly access algal primary productivity in the epilithic algal matrix (EAM). By assessing abundance, biomass, and potential fish productivity, we explore the potential of the reef flat to support key ecosystem processes and its ability to maintain fisheries yields. On the GBR, the reef flat is, by far, the most important habitat for turf‐grazing fishes, supporting an estimated 79% of individuals and 58% of the total biomass of grazing surgeonfishes, parrotfishes, and rabbitfishes. Approximately 59% of all (reef‐wide) turf algal productivity is removed by reef flat grazers. The flat also supports approximately 75% of all grazer biomass growth. Our results highlight the evolutionary and ecological benefits of occupying shallow‐water habitats (permitting a ninefold population increase). The acquisition of key locomotor and feeding traits has enabled fishes to access the trophic benefits of the reef flat, outweighing the costs imposed by water movement, predation, and sediments. Benthic assemblages on reefs in the future may increasingly resemble those seen on reef flats today, with low coral cover, limited topographic complexity, and extensive EAM. Reef flat grazing fishes may therefore play an increasingly important role in key ecosystem processes and in sustaining future fisheries yields.

Section: Discussionmentioning

confidence: 99%

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

Tebbett

et al. 2018

Ecology and Evolution

“…Note that all three plots are plotted on a log–log scale. Data were gathered from (A) Barneche et al () and additional primary sources [see raw data on Figshare ( https://figshare.com/s/cb081b58304eef6269e7)], (B) Goatley & Bellwood () and sources within, and (C) Kasimatis & Riginos ().…”

Section: Ecology and Functional Role Of Crfsmentioning

confidence: 99%

“…In both of these families, it appears that larger-bodied species are more likely to be consumers of primary producers (e.g. genera Amblygobius, Ophioblennius; Kotrschal & Thomson, 1986;Wilson, 2000;Hernaman et al, 2009;Hundt, Nakamura & Yamaoka, 2014;Hundt et al, 2017), suggesting that even slight increases in body size relax nutritional limits associated with marine herbivory and the trade-off between constant grazing and vulnerability to predation (Goatley & Bellwood, 2016;Goatley et al, 2017).…”

Section: (A) Feedingmentioning

confidence: 99%

The hidden half: ecology and evolution of cryptobenthic fishes on coral reefs

et al. 2018

Self Cite

Teleost fishes are the most diverse group of vertebrates on Earth. On tropical coral reefs, their species richness exceeds 6000 species; one tenth of total vertebrate biodiversity. A large proportion of this diversity is composed of cryptobenthic reef fishes (CRFs): bottom-dwelling, morphologically or behaviourally cryptic species typically less than 50 mm in length. Yet, despite their diversity and abundance, these fishes are both poorly defined and understood. Herein we provide a new quantitative definition and synthesise current knowledge on the diversity, distribution and life history of CRFs. First, we use size distributions within families to define 17 core CRF families as characterised by the high prevalence (>10%) of small-bodied species (<50 mm). This stands in strong contrast to 42 families of large reef fishes, in which virtually no small-bodied species have evolved. We posit that small body size has allowed CRFs to diversify at extremely high rates, primarily by allowing for fine partitioning of microhabitats and facilitation of allopatric reproductive isolation; yet, we are far from understanding and documenting the biodiversity of CRFs. Using rates of description since 1758, we predict that approximately 30 new species of cryptobenthic species will be described per year until 2050 (approximately twice the annual rate compared to large fishes). Furthermore, we predict that by the year 2031, more than half of the described coral reef fish biodiversity will consist of CRFs. These fishes are the 'hidden half' of vertebrate biodiversity on coral reefs. Notably, global geographic coverage and spatial resolution of quantitative data on CRF communities is uniformly poor, which further emphasises the remarkable reservoir of biodiversity that is yet to be discovered. Although small body size may have enabled extensive diversification within CRF families, small size also comes with a suite of ecological challenges that affect fishes' capacities to feed, survive and reproduce; we identify a range of life-history adaptations that have enabled CRFs to overcome these limitations. In turn, these adaptations bestow a unique socio-ecological role on CRFs, which includes a key role in coral reef trophodynamics by cycling trophic energy provided by microscopic prey to larger consumers. Although small in body size, the ecology and evolutionary history of CRFs may make them a critical component of coral-reef food webs; yet our review also shows that these fishes are highly susceptible to a variety of anthropogenic disturbances. Understanding the consequences of these changes for CRFs and coral reef ecosystems will require us to shed more light on this frequently overlooked but highly diverse and abundant guild of coral reef fishes.

“…Settling fishes experience extraordinarily high predation rates on coral reefs (Almany and Webster 2006), with an average of 50% mortality in their first 48 h on the reef (i.e., a 'predation gauntlet'). This effect of predators declines rapidly with increases in prey body size (Sogard 1997;Goatley and Bellwood 2016). Thus, increases in mesopredator abundance have the capacity to drive major shifts in the abundance and biodiversity of coral-reef fish communities by amplifying the intensity of the predation gauntlet.…”

Section: Introductionmentioning

confidence: 99%

Biodiversity effects of the predation gauntlet

et al. 2017

The ubiquity of trophic downgrading has led to interest in the consequences of mesopredator release on prey communities and ecosystems. This issue is of particular concern for reef-fish communities, where predation is a key process driving ecological and evolutionary dynamics. Here, we synthesize existing experiments that have isolated the effects of mesopredators to quantify the role of predation in driving changes in the abundance and biodiversity of recently settled reef fishes. On average, predators reduced prey abundance through generalist foraging behavior, which, through a statistical sampling artifact, caused a reduction in alpha diversity and an increase in beta diversity. Thus, the synthesized experiments provide evidence that predation reduces overall abundance within prey communities, but-after accounting for sampling effects-does not cause disproportionate effects on biodiversity.