1,720,971 research outputs found
Moving towards the equator: Reverse range shifts in two subtropical reef fish species, Chromis nitida (Pomacentridae) and Pseudolabrus guentheri (Labridae)
No full textTwo reef fish species, Pseudolabrus guentheri and Chromis nitida, traditionally restricted to the central and southern Great Barrier Reef (GBR) were observed in the northern GBR. This range extension is unusual as it runs contrary to the general expectations of poleward range shifts associated with climate change
Morphological structure in a reef fish assemblage
No full textTwo key morphological traits, horizontal gape and eye diameter, were measured in a large representative group of coral reef fishes. These morphological traits were used concurrently to assess their utility in exploring abilities of coral reef fishes at an assemblage level. A total of 1,218 specimens from 181 species found on the Great Barrier Reef were examined. Cryptobenthic fishes were included to provide a broader representation of reef fish groups. In the analyses, a clear morphological distinction was found between nocturnal and diurnal fishes. Nocturnal fishes had larger relative horizontal gapes and relative eye diameters by factors of 1.6 and 1.5, respectively. A bivariate plot separated into quadrants was used to assess the implications of morphological variation. The morphological measures reflected distinct ecological traits in each quadrant. Whilst nocturnal fishes had large relative gapes and eye diameters, diurnal predators and detritivores had the same wide gapes, but small relative eye diameters. Highly selective, visual feeders such as the Chaetodontidae and Pseudochromidae had large eyes and small gapes, whilst non-selective feeders with low visual dependence such as the grazing herbivores (Acanthuridae, Siganidae, etc.) had both small eye diameters and gape sizes. The analysis proved to be robust enough to apply to a wide assemblage, but with enough subtlety to distinguish morphological differences within individual families. The methods used in this study may have broad applications to other fish assemblages, both fossil and extant
Biologically mediated sediment fluxes on coral reefs: sediment removal and off-reef transportation by the surgeonfish Ctenochaetus striatus
Get PDFOff-reef sediment transport by the surgeonfish Ctenochaetus striatus (Acanthuridae) was quantified on the reef crest at Lizard Island, Great Barrier Reef. Three independent methods were implemented to estimate sediment ingestion rates. These considered (1) the bite rate and bite volume, (2) the defecation rate and faecal pellet size, and (3) the average gut contents and throughput rate. The 3 methods provided a broad range of estimates of sediment ingestion from 8.8 ± 2.4, to 66.1 ± 14.4 g fish–1 d–1 (mean ± SE). Nevertheless, these estimates were comparable to rates of sediment ingestion by parrotfishes (Labridae), the other major sediment-moving group on reefs. Overall, 36.5% of all sediment ingested was transported from the upper reef crest into deeper water, equating to a removal rate of 28.6 ± 6.2 kg 100 m–2 yr–1 at the study site. By brushing the reef, C. striatus reduces the sediment loading in the epilithic algal matrix (EAM) while causing little damage to the algal turf. Reducing sediments in EAMs provides favourable settlement surfaces for benthic organisms and increases the palatability of the EAM to herbivorous reef fishes, thus supporting reef resilience. The ecological importance of C. striatus, which is abundant on reefs throughout the Indo-Pacific, appears to have been underestimated, particularly when considering reef sediment dynamics
Fifty million years of herbivory on coral reefs: fossils, fish and functional innovations
No full textThe evolution of ecological processes on coral reefs was examined based on Eocene fossil fishes from Monte Bolca, Italy and extant species from the Great Barrier Reef, Australia. Using ecologically relevant morphological metrics, we investigated the evolution of herbivory in surgeonfishes (Acanthuridae) and rabbitfishes (Siganidae). Eocene and Recent surgeonfishes showed remarkable similarities, with grazers, browsers and even specialized, long-snouted forms having Eocene analogues. These long-snouted Eocene species were probably pair-forming, crevice-feeding forms like their Recent counterparts. Although Eocene surgeonfishes likely played a critical role as herbivores during the origins of modern coral reefs, they lacked the novel morphologies seen in modern Acanthurus and Siganus (including eyes positioned high above their low-set mouths). Today, these forms dominate coral reefs in both abundance and species richness and are associated with feeding on shallow, exposed algal turfs. The radiation of these new forms, and their expansion into new habitats in the Oligocene-Miocene, reflects the second phase in the development of fish herbivory on coral reefs that is closely associated with the exploitation of highly productive short algal turfs
Reef-scale partitioning of cryptobenthic fish assemblages across the Great Barrier Reef, Australia
No full textOnshore to offshore gradients in marine assemblages have been well documented on coral reefs, with most studies showing a distinct separation between onshore and offshore locations. Here we use enclosed anaesthetic sampling of small, cryptobenthic reef fishes to assess changes in assemblage composition across the Great Barrier Reef continental shelf. The cryptobenthic fishes exhibited fine-scale partitioning across the shelf. Three dominant species of goby accounted for over 55% of all fishes collected, with 1 species characterising each of the 3 key shelf positions: inner-, mid- and outer-shelf. Multivariate analyses of assemblage composition revealed further separation of reefs within the inner- and mid-shelf positions, highlighting the exceptional sensitivity of cryptobenthic reef fish assemblages to shelf position, with a progressive separation of individual reef assemblages with distance from the shore. These among-reef patterns contrast markedly with other reef fish taxa which invariably show 2 broad assemblages across the continental shelf (inner-vs. a composite mid- and outer-shelf community). As a result of this exceptional sensitivity to environmental conditions, cryptobenthic reef fish communities may represent good subjects for high-resolution monitoring of disturbances on coral reefs
Fishes on coral reefs: changing roles over the past 240 million years
No full textKey morphological traits reveal changes in functional morphospace occupation of reef fish assemblages over time. We used measurements of key functional attributes (i.e., lower jaw length and orbit diameter) of 208 fossil fish species from five geological periods to create bivariate plots of functional morphological traits through time. These plots were used to examine possible function and ecological characteristics of fossil reef fish assemblages throughout the Mesozoic and Cenozoic. A previously unknown trend of increasing orbit diameter over time became apparent. The Teleostei are the principal drivers of this change. The Eocene appears to mark a dramatic increase in two previously rare feeding modes in fishes: nocturnal feeding and high-precision benthic feeding. Interestingly, members of the Pycnodontiformes had relatively large eyes since the Triassic and appear to be the ecological precursors of their later teleost counterparts and may have been among the earliest nocturnal feeding fishes. Our results highlight potential changes in the roles of fishes on coral reefs through time
Low-quality sediments deter grazing by the parrotfish Scarus rivulatus on inner-shelf reefs
No full textElevated sediment loads in the epilithic algal matrix (EAM) deter grazing by herbivorous fishes and may compromise their critical roles on coral reefs. However, the properties of sediments that drive herbivore deterrence are unknown. Binary choice trials in aquaria were used to examine the effects of three sediment attributes—sediment source, grain size and organic load—on grazing by the abundant inner-shelf parrotfish, Scarus rivulatus. Fish were presented with a choice between EAM-covered rocks treated with (a) terrigenous or reefal sediments, (b) fine or coarse sediments or (c) sediments with high or low organic loads. Scarus rivulatus did not show a preference for sediments from different sources (terrigenous vs. reefal); however, a clear preference was evident for fine-grained sediments over coarse (109 % more bites) and sediments with high organic loads over low (147 % more bites). The avoidance of coarse sediments is likely to be a key factor driving the inhibition of grazing on mid-shelf reefs, which are dominated by coarse sediments. In contrast, on inner-shelf reefs, grazing by parrotfishes may be deterred primarily by high sediment loads, which reduce the proportional organic content in EAM sediments. Our study highlights the potential impact of sediments on critical ecological processes and the threats posed by changing sediment loads on inner-shelf reefs
Evolution of long-toothed fishes and the changing nature of fish-benthos interactions on coral reefs
No full textInteractions between fishes and the benthos have shaped the development of marine ecosystems since at least the early Mesozoic. Here, using the morphology of fish teeth as an indicator of feeding abilities, we quantify changes over the last 240 million years of reef fish evolution. Fossil and extant coral reef fish assemblages reveal exceptional stasis in tooth design over time, with one notable exception, a distinct long-toothed form. Arising only in the last 40 million years, these long-toothed fishes have bypassed the invertebrate link in the food chain, feeding directly on benthic particulate material. With the appearance of elongated teeth, these specialized detritivores have moved from eating invertebrates to eating the food of invertebrates. Over evolutionary time, fishes have slid back down the food chain
The rise of jaw protrusion in spiny-rayed fishes closes the gap on elusive prey
No full textJaw protrusion is one of the most important innovations in vertebrate feeding over the last 400 million years [1 and 2]. Protrusion enables a fish to rapidly decrease the distance between itself and its prey [2 and 3]. We assessed the evolution and functional implications of jaw protrusion in teleost fish assemblages from shallow coastal seas since the Cretaceous. By examining extant teleost fishes, we identified a robust morphological predictor of jaw protrusion that enabled us to predict the extent of jaw protrusion in fossil fishes. Our analyses revealed increases in both average and maximum jaw protrusion over the last 100 million years, with a progressive increase in the potential impact of fish predation on elusive prey. Over this period, the increase in jaw protrusion was initially driven by a taxonomic restructuring of fish assemblages, with an increase in the proportion of spiny-rayed fishes (Acanthomorpha), followed by an increase in the extent of protrusion within this clade. By increasing the ability of fishes to catch elusive prey [2 and 4], jaw protrusion is likely to have fundamentally changed the nature of predator-prey interactions and may have contributed to the success of the spiny-rayed fishes, the dominant fish clade in modern oceans [5]
Sediments and herbivory as sensitive indicators of coral reef degradation
Get PDF© 2016 by the author(s). Around the world, the decreasing health of coral reef ecosystems has highlighted the need to better understand the processes of reef degradation. The development of more sensitive tools, which complement traditional methods of monitoring coral reefs, may reveal earlier signs of degradation and provide an opportunity for pre-emptive responses. We identify new, sensitive metrics of ecosystem processes and benthic composition that allow us to quantify subtle, yet destabilizing, changes in the ecosystem state of an inshore coral reef on the Great Barrier Reef. Following severe climatic disturbances over the period 2011-2012, the herbivorous reef fish community of the reef did not change in terms of biomass or functional groups present. However, fish-based ecosystem processes showed marked changes, with grazing by herbivorous fishes declining by over 90%. On the benthos, algal turf lengths in the epilithic algal matrix increased more than 50% while benthic sediment loads increased 37-fold. The profound changes in processes, despite no visible change in ecosystem state, i.e., no shift to macroalgal dominance, suggest that although the reef has not undergone a visible regime-shift, the ecosystem is highly unstable, and may sit on an ecological knife-edge. Sensitive, process-based metrics of ecosystem state, such as grazing or browsing rates thus appear to be effective in detecting subtle signs of degradation and may be critical in identifying ecosystems at risk for the future
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