Macroalgae removal on coral reefs: realised ecosystem functions transcend biogeographic locations

Coral reef ecosystems are at the forefront of biodiversity loss and climate change-mediated transformations. This is expected to have profound consequences for the functioning of these ecosystems. However, assessments of ecosystem function on reefs are often spatially limited, within biogeographic realms, or rely on presumed proxies such as traits. To address these shortcomings and assess the effects of biogeography and fish presence on the critical ecosystem function of macroalgal removal, we used assays of six algal genera across three reef habitats in two biogeographically distinct locations: Little Cayman in the Caribbean and Lizard Island on the Great Barrier Reef (GBR). Patterns of fish feeding and realised ecosystem function were strikingly similar between the two geographic locations, despite a threefold difference in the local diversity of nominally herbivorous fishes, a 2.4-fold difference in the diversity of fishes feeding and differences in the biogeographic history of the two locations. In both regions, a single species dominated the function: a surgeonfish, Naso unicornis, at the GBR location and, surprisingly, a triggerfish, Melichthys niger, at the Caribbean location. Both species, especially M. niger, were relatively rare, compared to other nominally herbivorous fishes, in censuses covering more than 14,000 m(2) at each location. Our study provides novel insights into the critical function of macroalgal removal in hyperdiverse coral reef ecosystems, highlighting: (a) that function can transcend biogeographic, taxonomic and historical constraints; and (b) shortcomings in our assumptions regarding fish presence and realised ecosystem function on coral reefs

The contribution of macroalgae-associated fishes to small-scale tropical reef fisheries

Macroalgae-dominated reefs are a prominent habitat in tropical seascapes that support a diversity of fishes, including fishery target species. To what extent, then, do macroalgal habitats contribute to small-scale tropical reef fisheries? To address this question we: (1) Quantified the macroalgae-associated fish component in catches from 133 small-scale fisheries, (2) Compared life-history traits relevant to fishing (e.g. growth, longevity) in macroalgal and coral-associated fishes, (3) Examined how macroalgae-associated species can influence catch diversity, trophic level and vulnerability and (4) Explored how tropical fisheries change with the expansion of macroalgal habitats using a case study of fishery-independent data for Seychelles. Fish that utilised macroalgal habitats comprise 24% of the catch, but very few fished species relied entirely on macroalgal or coral habitats post-settlement. Macroalgal and coral-associated fishes had similar life-history traits, although vulnerability to fishing declined with increasing contribution of macroalgae association to the catch, whilst mean trophic level and diversity peaked when macroalgal-associated fish accounted for 20%-30% of catches. The Seychelles case study revealed similar total fish biomass on macroalgal and coral reefs, although the biomass of primary target species increased as macroalgae cover expanded. Our findings reinforce that multiple habitat types are needed to support tropical fishery stability and sustainability. Whilst coral habitats have been the focus of tropical fisheries management, we show the potential for macroalgae-associated fish to support catch size and diversity in ways that reduce vulnerability to overfishing. This is pertinent to seascapes where repeated disturbances are facilitating the replacement of coral reef with macroalgal habitats

Habitat Associations of Juvenile Fish at Ningaloo Reef, Western Australia: The Importance of Coral and Algae

Habitat specificity plays a pivotal role in forming community patterns in coral reef fishes, yet considerable uncertainty remains as to the extent of this selectivity, particularly among newly settled recruits. Here we quantified habitat specificity of juvenile coral reef fish at three ecological levels; algal meadows vs. coral reefs, live vs. dead coral and among different coral morphologies. In total, 6979 individuals from 11 families and 56 species were censused along Ningaloo Reef, Western Australia. Juvenile fishes exhibited divergence in habitat use and specialization among species and at all study scales. Despite the close proximity of coral reef and algal meadows (10's of metres) 25 species were unique to coral reef habitats, and seven to algal meadows. Of the seven unique to algal meadows, several species are known to occupy coral reef habitat as adults, suggesting possible ontogenetic shifts in habitat use. Selectivity between live and dead coral was found to be species-specific. In particular, juvenile scarids were found predominantly on the skeletons of dead coral whereas many damsel and butterfly fishes were closely associated with live coral habitat. Among the coral dependent species, coral morphology played a key role in juvenile distribution. Corymbose corals supported a disproportionate number of coral species and individuals relative to their availability, whereas less complex shapes (i.e. massive & encrusting) were rarely used by juvenile fish. Habitat specialisation by juvenile species of ecological and fisheries importance, for a variety of habitat types, argues strongly for the careful conservation and management of multiple habitat types within marine parks, and indicates that the current emphasis on planning conservation using representative habitat areas is warranted. Furthermore, the close association of many juvenile fish with corals susceptible to climate change related disturbances suggests that identifying and protecting reefs resilient to this should be a conservation priority

Small cryptic fishes on coral reefs : a new perspective on reef fish ecology and life histories

Small cryptic fishes represent over 50% of fishes on coral reefs. Yet our knowledge of them lags far behind that of larger species and their significance to coral reef ecosystems remains unclear. Vastly different in their ecology due to their small size, this thesis examines their community structure and identifies key life history features that highlight their unique ecological status. These results are combined to model the relative contribution of small cryptic fishes to reef fish assemblages and define their significance to coral reef ecosystems. Small-scale clove oil samples (0.4m2) were used to quantify the spatial distribution of small (< 10cm) cryptic fishes across reef zones and microhabitats at both exposed and sheltered reefs. Marked variation in abundance, species numbers, size-class distribution and community composition were found among reef zones at exposed sites; in contrast, comparatively little among-zone variation was found at sheltered sites. At exposed sites, there was a strong trend of declining abundance, species numbers and larger body sizes with increasing wave energy; whereas at sheltered sites, microhabitat type played a more important role. There was little taxonomic overlap between sheltered and exposed reefs even of highly abundant species. Overall, wave energy was found to play a pivotal role in the spatial distribution of this community with microhabitat type playing a significant, yet secondary role. Contrasting the life history (LH) characteristics of the most abundant genus (Eviota: 3 species of Gobiidae) at the two study sites with those of existing coral reef fishes in a meta-analysis revealed vastly different LH features. Otolith analysis revealed rapid linear growth trajectories and extremely short maximum life spans of < 100 days (E. queenslandica 99 days; E. melasma 97 days and E. sigillata at 59 days - the shortest recorded lifespan for any vertebrate). Although settlement marks on otoliths disclosed unremarkable pelagic larval durations (PLDs) of 24 - 26 days, this represented 24 - 42% of their total lifespan. The complete lack of response in shortening PLDs to compensate for such short life spans suggests that developmental constraints may be the primary determinant of PLDs in coral reef fishes. Histological examinations indicated that Eviota mature at an earlier than expected size and showed a strong female bias in their sex ratios (1 ♂:1.4 - 1.7 ♀) indicating the possibility of protogyny or harem keeping by males. A field tagging study indicated remarkably high daily mortality rates of 7- 8% which closely matched otolith-based estimates of 4-7% d-1. An experimental breeding study using E. sigillata revealed a frequent semi-lunar spawning pattern and batch sizes of 108-163 eggs. Although small in comparison to those of larger species, the frequency of spawning events coupled with generational turnover rates of 47 days indicated potential annual offspring production to be orders of magnitude higher than that of much larger reef fish species. Collectively, these LH attributes revealed how the smallest of reef fish size-classes respond to their vastly different ecological environments and highlight the extensive range and versatility of coral reef fish evolutionary strategies. The relative contribution of the small cryptic group to reef fish assemblages was examined using visual censuses of 14 coral reef fish families. In total, data on 58,944 fish were utilized over five reef zones providing 86g m-2 of biomass. The clear trend among size-class distributions was one of rapidly decreasing densities with increasing size. Small cryptic fishes represented 45-90% of the numbers of individuals across reef zones with a reef average contribution of 67%. Among families, the numerical dominance of the Gobiidae was evident (11m-2 ± 1.4SE) with significant contributions made by the Pomacentridae, Apogonidae, Blenniidae, Labridae and Tripterygiidae. For biomass, the Acanthuridae made the largest contribution (35g m-2 ± 11.6SE) followed by the Pomacentridae, Scaridae and Serranidae. Small cryptic families made up < 3%. To examine the implications of taxa-specific growth rates in the energy dynamics of coral reef systems, a community growth model was produced. Sizespecific growth estimates for all genera censused were calculated over a 7-day period. Overall, small cryptic fishes contributed 79.5% to reef fish assemblage patterns of growth in length and 14% to the period’s total weight accumulation in grams. This cryptic contribution stands in marked contrast to the static biomass estimate presented above and highlights the significance of LH’s in defining community and ecosystem energetics. Overall, small cryptic fishes make a substantial contribution to coral reef communities but differ considerably from their larger counterparts in the way they achieve this. Demographic evidence of drastically shortened life spans, rapid linear growth and high turnover rates, coupled with high average abundances and rates of mortality suggests they play a significant role in the energetics of coral reefs. This addition of demographic information on small cryptic reef fishes emphasized this role, uncovered new extremes in vertebrate biology and showcases the rich potential for coral reef fishes to test general life history theory

Spot the difference: mimicry in a coral reef fish.

Eyespots on the body of many animals have long been assumed to confer protection against predators, but empirical evidence has recently demonstrated that this may not always be the case and suggested that such markings may also serve other purposes. Clearly, this raises the unresolved question of what functions do these markings have and do they contribute to an individual's evolutionary fitness in the wild. Here, we examined the occurrence of eyespots on the dorsal fin of a coral reef damselfish (Pomacentrus amboinensis), where these markings are typical of the juvenile stage and fade away as the fish approaches sexual maturation to then disappear completely in the vast majority of, but not all, adult individuals. By exploring differences in body shape among age and gender groups, we found that individuals retaining the eyespot into adulthood are all sexually mature males, suggesting that these eyespots may be an adult deceptive signal. Interestingly, the body shape of these individuals resembled more closely that of immature females than mature dominant males. These results suggest that eyespots have multiple roles and their functional significance changes within the lifetime of an animal from being a juvenile advertisement to a deceptive adult signal. Male removal experiments or colour manipulations may be necessary to establish specific functions

The role of cryptobenthic reef fishes in coral reef trophodynamics

An examination of the trophic status of a cryptobenthic reef fish community from the central Great Barrier Reef was carried out to evaluate the potential role of cryptobenthic fishes in coral reef ecosystems. Using frequency of occurrence data, dietary analyses revealed a diverse range\ud of trophic groups, although detritivory (in 10 out of 16 species and 39.3% of individuals) and carnivory (5 of 16 species and 40.5% of individuals) clearly dominate as trophic modes. Herbivory (1 species; 2.4% of individuals) is only a minor component in the community trophic structure. Of the 18 dietary categories identified, detritus and copepods were the only constituents represented in all 16 species examined. Although the degree of dietary specialization varied among taxa, the 2 most\ud abundant species, Eviota queenslandica and Istigobius goldmanni, utilised the broadest range of dietary items. Morphology reflected the trophic partitioning among fishes: carnivores were invariably <28 mm total length (TL) and had gut-length ratios (GLRs) of <0.5; detritivores were all >38 mm TL with GLRs generally exceeding >1.0. The trophic composition and numerical strength of the cryptobenthic fish fauna suggests that cryptobenthic reef fishes have the potential to make a significant contribution to reef trophodynamics along a number of trophic pathways. This prompts a re-evaluation of the roles of reef fishes in the functioning of coral reefs, particularly those related to\ud the recycling of primary production through detrital pathways

Wave energy and spatial variability in community structure of small cryptic coral reef fishes

The distribution and abundance of small cryptic reef fishes were quantified among microhabitats and reef zones at both exposed and sheltered sites at Lizard Island, Great Barrier Reef. A total of 1042 individuals from 44 species in 8 families were sampled. Marked variation in abundance, species numbers, size-class distribution and species composition were displayed among reef zones at exposed sites; in contrast, comparatively little variation was found in sheltered sites. The exposed, wave-swept front flat reef zone was clearly the most depauperate and species-poor zone with calmer back reef, lagoonal and reef base zones containing the highest numbers of individuals and species. Larger, heavier individuals predominated in exposed wave-swept reef zones whereas smaller, lighter individuals were commonly found in calmer waters. Sheltered sites exhibited little variation among zones. In these sites, microhabitat appeared to play a much greater role in shaping community composition. Overall, 68.5% of all individuals (70.1% at exposed and 65.4% at sheltered sites) were collected from sand/rubble microhabitats as opposed to 31.5% from open reef microhabitats. Assemblages at exposed and sheltered sites exhibited little taxonomic overlap, even of highly abundant species. These results indicate that wave energy plays a significant role in structuring small cryptic coral reef fish communities, with microhabitat type playing a key role in the absence of wave energy

Comparison of the body shape of <i>P. amboinensis</i> belonging to different age and gender groups.

<p>Results of a canonical discriminant analysis are displayed with treatment centroids and 95% confidence clouds plotted together with the direction and importance (as indicated by the length of the vector) of trends in statistically significant shape descriptors.</p