Assembly rules of coral reef fish communities along the depth gradient

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Disturbance and the structure of coral reef fish communities on the reef slope

Three levels of physical disturbance were applied to corals in permanent 10x10 m quadrats along a section of fringing reef at Lizard Island on the Great Barrier Reef to investigate the response of fish assemblages. Tabular and corymbose corals were overturned and left in situ, reducing total hard coral cover from ˜55% to ˜47%, ˜43%, and ˜34%. Despite pre-existing associations with benthic cover, all fish groups examined (pomacentrids, labrids, chaetodontids, and acanthurids) were resistent to benthic disturbances at the level and scale at which they were applied. Partial Mantel's tests, in combination with partial Canonical Correspondence Analysis enabled spatial and temporal variation to be factored out from experimental effects. Most of the variation in the fish community could be assigned to spatio-temporal variables, indicating that spatial structure over the reef landscape may moderate localised disturbance effects. This study indicates that coral reef fish assemblages may be more resistant to disturbance than many correlative studies would suggest, and highlights a need for further information on levels and scales of natural habitat disturbance in order to apply a structured approach to the experimental investigation of the importance of habitat in structuring coral-reef fish assemblages.     

Long-term effects of the cleaner fish Labroides dimidiatus on coral reef fish communities

Cleaning behaviour is deemed a mutualism, however the benefit of cleaning interactions to client individuals is unknown. Furthermore, mechanisms that may shift fish community structure in the presence of cleaning organisms are unclear. Here we show that on patch reefs (61–285 m²) which had all cleaner wrasse Labroides dimidiatus (Labridae) experimentally removed (1–5 adults reef⁻¹) and which were then maintained cleaner-fish free over 8.5 years, individuals of two site-attached (resident) client damselfishes (Pomacentridae) were smaller compared to those on control reefs. Furthermore, resident fishes were 37% less abundant and 23% less species rich per reef, compared to control reefs. Such changes in site-attached fish may reflect lower fish growth rates and/or survivorship. Additionally, juveniles of visitors (fish likely to move between reefs) were 65% less abundant on removal reefs suggesting cleaners may also affect recruitment. This may, in part, explain the 23% lower abundance and 33% lower species richness of visitor fishes, and 66% lower abundance of visitor herbivores (Acanthuridae) on removal reefs that we also observed. This is the first study to demonstrate a benefit of cleaning behaviour to client individuals, in the form of increased size, and to elucidate potential mechanisms leading to community-wide effects on the fish population. Many of the fish groups affected may also indirectly affect other reef organisms, thus further impacting the reef community. The large-scale effect of the presence of the relatively small and uncommon fish, Labroides dimidiadus, on other fishes is unparalleled on coral reefs.     

Larval mortality and the composition of coral reef fish communities

Research over the past decade shows that fish populations on coral reefs can vary enormously, both spatially and temporally. Nonetheless, predictable patterns in structure are present at both small and regional scales. These have usually been interpreted as resulting from processes acting after settlement of fishes from the plankton. However, current research now suggests that planktonic processes could also result in deterministic patterns of community structure.     

Do cleaning stations affect the distribution of territorial reef fishes?

We investigated the role of cleaning stations in determining the distribution of territorial reef species. Cleaner fish reduce their clients' ectoparasite loads and, therefore, proximity to cleaning stations should be advantageous for territorial fish. We focused on five damselfish species which hold permanent territories and cleaning stations occupied by cleaning gobies (Elacatinus spp.) on a Caribbean reef. Contrary to our predictions of higher densities near cleaning stations, we found that bicolor damselfish were less abundant near cleaning stations than at ecologically similar points without cleaning gobies whereas no effects were seen for longfin, dusky, yellowtail, and threespot damselfish. In addition, although damselfish densities were higher in the immediate vicinity of cleaning stations than 1.5-3 m away for most species, this was also the case at points without cleaners. Because cleaning stations are usually located on prominent coral heads or sponges, the overall significant attraction of damselfish to such structures, whether occupied by cleaning gobies or not, could reflect attraction to past or potential cleaning stations. However, it is more likely that interspecific competition and/or the low benefits of being cleaned at our study site prevent aggregation around cleaners. Cleaning stations may play only a minor role in determining the distribution of territorial reef fishes.     

Effects of marine reserves versus nursery habitat availability on structure of reef fish communities

No-take marine fishery reserves sustain commercial stocks by acting as buffers against overexploitation and enhancing fishery catches in adjacent areas through spillover. Likewise, nursery habitats such as mangroves enhance populations of some species in adjacent habitats. However, there is lack of understanding of the magnitude of stock enhancement and the effects on community structure when both protection from fishing and access to nurseries concurrently act as drivers of fish population dynamics. In this study we test the separate as well as interactive effects of marine reserves and nursery habitat proximity on structure and abundance of coral reef fish communities. Reserves had no effect on fish community composition, while proximity to nursery habitat only had a significant effect on community structure of species that use mangroves or seagrass beds as nurseries. In terms of reef fish biomass, proximity to nursery habitat by far outweighed (biomass 249% higher than that in areas with no nursery access) the effects of protection from fishing in reserves (biomass 21% lower than non-reserve areas) for small nursery fish (≤ 25 cm total length). For large-bodied individuals of nursery species (>25 cm total length), an additive effect was present for these two factors, although fish benefited more from fishing protection (203% higher biomass) than from proximity to nurseries (139% higher). The magnitude of elevated biomass for small fish on coral reefs due to proximity to nurseries was such that nursery habitats seem able to overrule the usually positive effects on fish biomass by reef reserves. As a result, conservation of nursery habitats gains importance and more consideration should be given to the ecological processes that occur along nursery-reef boundaries that connect neighboring ecosystems.     

Biogeography and the structure of coral reef fish communities on isolated islands

Aim To determine the applicability of biogeographical and ecological theory to marine species at two remote island locations. This study examines how biogeography, isolation and species geographic range size influence patterns of species richness, endemism, species composition and the abundance of coral reef fishes. Location Christmas Island and the Cocos (Keeling) Islands in the tropical eastern Indian Ocean. Methods Published species lists and underwater visual surveys were used to determine species richness, endemism, species composition and abundance of reef fishes at the islands. These data were statistically compared with patterns of species composition and abundance from the neighbouring ‘mainland’ Indonesian region. Results The two isolated reef fish communities were species‐poor and contained a distinct taxonomic composition with an overrepresentation of species with high dispersal potential. Despite low species richness, we found no evidence of density compensation, with population densities on the islands similar to those of species‐rich mainland assemblages. The mix of Indian and Pacific Ocean species and the proportional representations of the various regional faunas in the assemblages were not influenced by the relative proximity of the islands to different biogeographical provinces. Moreover, species at the edge of their range did not have a lower abundance than species at the centre of their range, and endemic species had substantially higher abundances than widespread species. At both locations, endemism was low (less than 1.2% of the community); this may be because the locations are not sufficiently isolated or old enough to promote the evolution of endemic species. Main conclusions The patterns observed generally conform to terrestrial biogeographical theory, suggesting that similar processes may be influencing species richness and community composition in reef fish communities at these remote islands. However, species abundances differed from typical terrestrial patterns, and this may be because of the life history of reef fishes and the processes maintaining isolated populations.     

Effects of territorial damselfish on an algal-dominated coastal coral reef

Territorial damselfish are important herbivores on coral reefs because they can occupy a large proportion of the substratum and modify the benthic community to promote the cover of food algae. However, on coastal coral reefs damselfish occupy habitats that are often dominated by unpalatable macroalgae. The aim of this study was to examine whether damselfish can maintain distinctive algal assemblages on a coastal reef that is seasonally dominated by Sargassum (Magnetic Island, Great Barrier Reef). Here, three abundant species (Pomacentrus tripunctatus, P. wardi and Stegastes apicalis) occupied up to 60% of the reef substrata. All three species promoted the abundance of food algae in their territories. The magnitudes of the effects varied among reef zones, but patterns were relatively stable over time. Damselfish appear to readily co-exist with large unpalatable macroalgae as they can use it as a substratum for promoting the growth of palatable epiphytes. Damselfish territories represent patches of increased epiphyte load on macroalgae, decreased sediment cover, and enhanced cover of palatable algal turf.     

Regional biogeography of shallow reef fish and macro-invertebrate communities in the Galapagos archipelago

Aim To delineate biogeographical patterns in Galapagos shallow‐water reef fauna at regional scales. Location Galapagos Islands. Methods Fishes and macro‐invertebrates were quantitatively censused using underwater visual techniques along more than 500 transects at defined depth strata across the Galapagos archipelago. Data were analysed using multivariate techniques to define regional patterns and identify species typical of different regions. Results Subtidal communities of fishes and macro‐invertebrates on shallow reefs differed consistently in species composition across the Galapagos archipelago, with three major biogeographical groupings: (1) the ‘far‐northern area’ containing the islands of Darwin and Wolf, (2) the ‘central/south‐eastern area’, including the east coast of Isabela, and (3) the ‘western area’, encompassing Fernandina and western Isabela. In addition, the northern islands of Pinta, Marchena and Genovesa form a separate region in the central/south‐eastern area, and Bahia Elizabeth and Canal Bolivar separate from other parts of the western area. The far‐northern bioregion is characterized by high fish species richness overall, including a high proportion of species of Indo‐Pacific origin. However, very few endemic fishes or species with distributions extending south from Ecuador (‘Peruvian’ species) are present, and the bioregion also possesses relatively low species richness of mobile macro‐invertebrate taxa. By contrast, the ‘western’ bioregion possesses disproportionately high numbers of endemic fish taxa, high numbers of cool‐temperate Peruvian fish species, and high invertebrate species richness, but very few species of Indo‐Pacific origin. The Bahia Elizabeth/Canal Bolivar bioregion possesses more endemic species and fewer species with Peruvian affinities than coasts within the western bioregion. The northern bioregion of Pinta, Marchena and Genovesa represents an overlap zone with affinities to both the far‐northern and south‐eastern islands. The south‐eastern bioregion includes species from a variety of different sources, particularly ‘Panamic’ species with distributions extending north to Central America. Main conclusions On the basis of congruent divisions for reef fish and macro‐invertebrate communities, the Galapagos archipelago can be separated into three major biogeographical areas, two of which can be further subdivided into two regions. Each of these five bioregions possesses communities characterized by a distinctive mix of species derived from Indo‐Pacific, Panamic, Peruvian and endemic source areas. The conservation significance of different regions is not reflected in counts of total species richness. The regions with the lowest overall fish species richness possess a temperate rather than tropical climate and highest levels of endemism.     

Effects of alternate reef states on coral reef fish habitat associations

The present study describes ontogenetic shifts in habitat use for 15 species of coral reef fish at Rangiroa Atoll, French Polynesia. The distribution of fish in different habitats at three ontogenetic stages (new settler, juvenile, and adult) was investigated in coral-dominated and algal-dominated sites at two reefs (fringing reef and inner reef of motu). Three main ontogenetic patterns in habitat use were identified: (1) species that did not change habitats between new settler and juvenile life stages (60% of species) or between juvenile and adult stages (55% of species—no ontogenetic shift); (2) species that changed habitats at different ontogenetic stages (for the transition “new settler to juvenile stage”: 15% of species; for the transition “juvenile to adult stage”: 20% of species); and (3) species that increased the number of habitats they used over ontogeny (for the transition “new settler to juvenile stage”: 25% of species; for the transition “juvenile to adult stage”: 25% of species). Moreover, the majority of studied species (53%) showed a spatial variability in their ontogenetic pattern of habitat use according to alternate reef states (coral reef vs algal reef), suggesting that reef state can influence the dynamics of habitat associations in coral reef fish.     

Perception,pattern, chance and the structure of reef fish communities

The recent history of attempts to understand the ecology of fish on coral reefs is surveyed as an example of the way in which science progresses. Scientists are trapped, both by their sensory equipment and by their preconceptions, into viewing the world in certain ways. Paradigms fall only slowly. Scientists are trained to seek pattern in their data, yet in some cases the largely stochastic variation of a system around its mean condition is the more important key to understanding its ecology. The reef fish assemblage provides such a case. It is unlikely that our present understanding of the nature of reef fish communities will survive unchanged by future research. And it is also unlikely that reef fish ecologists are the only ecologists who have difficulty discovering truth! Editorial     

Structure and temporal dynamics of macroinfaunal communities of a sandy reef flat in the northwestern Philippines

Temporal variation in macroinfaunal community structure wasassessed from monthly monitoring of the sandy substrate of theLucero reef flat in Bolinao, Pangasinan (northwesternPhilippines)between November 1990 and November 1991. The community wascomposedof 98 taxa from 10 phyla and was consistently dominated by thepolychaete family Syllidae (19–33% of monthly totalabundance).Five polychaete and crustacean taxa co-dominated with thesyllidsand exhibited monthly shifts in dominance ranks. Overall,there wasno significant change in the composition of the communityafter ayear.Results of the study show that the temporal dynamics of thecommunity was a function of the seasonality in salinity and oftherelatively consistent nature of the substrate. Abundances ofmacroinfaunal crustaceans, chaetognaths, and molluscsfluctuatedsignificantly over 12 months, and corresponded to the seasonalfluctuation in salinity. Total and polychaete abundances didnotshow significant monthly variation, but tended to beinfluenced bysalinity changes. Densities of turbellarians, nemerteans, andechinoderms appeared homogeneous across 12 months, andcorrelatedwith the consistency of substrate structure in the reef flatoverthe experimental period. In addition, sipunculid numbersseemed tobe supported by the stable amount of organic matter in thesandysubstrate.     

Influence of depth on sex-specific energy allocation patterns in a tropical reef fish

The effect of depth on the distribution and sex-specific energy allocation patterns of a common coral reef fish, Chrysiptera rollandi (Pomacentridae), was investigated using depth-stratified collections over a broad depth range (5–39 m) and a translocation experiment. C. rollandi consistently selected rubble habitats at each depth, however abundance patterns did not reflect the availability of the preferred microhabitat suggesting a preference for depth as well as microhabitat. Reproductive investment (gonado-somatic index), energy stores (liver cell density and hepatocyte vacuolation), and overall body condition (hepato-somatic index and Fulton’s K) of female fish varied significantly among depths and among the three reefs sampled. Male conspecifics displayed no variation between depth or reef. Depth influenced growth dynamics, with faster initial growth rates and smaller mean asymptotic lengths with decreasing depth. In female fish, relative gonad weight and overall body condition (Fulton’s K and hepato-somatic index) were generally higher in shallower depths (≤10 m). Hepatic lipid storage was highest at the deepest sites sampled on each reef, whereas hepatic glycogen stores tended to decrease with depth. Depth was found to influence energy allocation dynamics in C. rollandi. While it is unclear what processes directly influenced the depth-related patterns in energy allocation, this study shows that individuals across a broad depth gradient are not all in the same physiological state and may contribute differentially to the population reproductive output. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Communication in coral reef fish: the role of ultraviolet colour patterns in damselfish territorial behaviour

Many coral reef fish possess ultraviolet (UV) colour patterns. The behavioural significance of these patterns is poorly understood and experiments on this issue have not been reported for free-living reef fish in their natural environment. The damselfish Pomacentrus amboinensis has UV facial patterns, and spectroradiometric ocular media measurements show that it has the potential for UV vision. To test the potential behavioural significance of the UV patterns, I studied the response of males, in natural territories on the reef and in aquaria, to two conspecific intruders, one presented in a UV-transmitting (UV+) container and the other in a UV-absorbing (UV−) one. Territory owners attacked intruders viewed through UV+ filters significantly more often and for longer than intruders viewed through the UV− filter. In general, the results of the field experiment confirmed those of the laboratory experiment. The results support the hypothesis that P. amboinensis males are sensitive to UV light and that reflectance patterns, which appear in high contrast only in UV, modulate the level of aggressive behaviour. A recent survey showed that many predatory fish may not have UV vision and the use of UV colours in select species of reef fish may therefore serve as a ‘private communication channel’.     

Phosphorus metabolism in coral reef communities: exchange between the water column and bottom biotopes

Exchange of phosphate between components of the reef bottom and the water column were studied on reefs around Heron Island (Great Barrier Reef), both in aquaria and in in situ enclosures, using radioactive phosphorus (³²P) as a tracer. Living corals, dead corals, coral rubble overgrown with periphyton, and soft sediments of coral sand were used in experiments. In all of these components of bottom reef biotopes, two opposite flows of inorganic phosphate were recorded and measured, i.e. the rate of PO₄-P uptake from water (A_c), and its release (A_e). At ambient PO₄-P concentrations in water of 0.1– 0.3 µmoll^–1, both flows varied in living corals and coral rubble between 10 and 70 µg P kg^–1 h^–1, 3–10 mg P m^–2 day^–1, and in coral sand between 10 and 30 µg P kg^–1 h^–1, or 2–7 mg P m^–2 day^–1. Under the latter concentration range (which is typical for coral reef areas), the reciprocal PO₄-P flows almost balanced each other, so that net uptake (A_t) was very low. Often it approached zero or was positive, showing that a net PO₄-P release had taken place. The uptake flow (A_c) in living coral was much more dependent on the PO₄-P content in overlying water than was the release flow (A_e). The influence of conditions of illumination upon the values of A_c and A_e was comparatively low. The data obtained are used to discuss problems of phosphorus balance and dynamics in coral reef ecosystems.     

典型气候事件对浙江近海底层鱼类时空分布的影响

气候变化对海洋生态系统产生多方面的影响,作为海洋生物中的主体,鱼类对气候变化的响应机制研究是探索典型气候事件对海洋生态系统影响的关键。根据2013-2022年浙江近海底拖网渔业资源调查数据,结合尼诺指数(Ocean Nino Index, ONI)、海表温度 (Sea Surface Temperature, SST)、海表温度距平 (Sea Surface Temperature Anomaly, SSTA)、叶绿素a浓度(Chlorophyll a, Chl-a)等海洋环境数据,采用小波函数、相关性分析等探究典型气候事件厄尔尼诺、拉尼娜对浙江近海底层鱼类生物量及其时空分布的影响。结果表明,浙江近海底层鱼类生物量与SST及Chl-a呈极显著正相关(P ＜ 0.01)。厄尔尼诺与拉尼娜发生时期春、秋季生物量均小于正常年份,正常年份及拉尼娜事件期间春季生物量具有显著性差异(P ＜ 0.05);正常年份及厄尔尼诺事件期间秋季生物量具有极显著性差异(P ＜ 0.01)。对ONI与海洋环境因子指数进行交叉小波发现,浙江近海SST、Chl-a对于典型气候事件均存在不同的频域同步及相关性:ONI与SST在时间局部存在2-3.9个月频域同步,SST滞后ONI3个月;ONI与 Chl-a存在1.7-3个月频域同步,Chl-a与ONI呈正相关;ONI与生物量存在3-3.6个月频域同步,生物量滞后于ONI3个月;ONI与SSTA在研究期间不存在明显的频域同步。春季,相较于正常年份,厄尔尼诺期间鱼类整体分布偏北;秋季厄尔尼诺发生期间鱼类整体向南移动,拉尼娜期间则向北移动。厄尔尼诺及拉尼娜事件不仅对鱼类群落在纬度上的分布产生影响,还会对鱼类向近岸洄游的快慢产生影响。两种典型气候事件通过影响浙江近海SST等环境进而对浙江近海底层鱼类时空分布产生影响。     

The effect of patch reef size on fish species richness in a shallow coral reef shore zone where territorial herbivores are abundant

Small patch reefs can harbor many reef fishes because most fishes have a drifting larval phase to randomly disperse over patchy habitats. We examined the species–area relationship (SAR) of damselfish (Pomacentridae) assemblages over 84 small patch reefs (0.05–45.4 m²) using an enlarged section of a high-resolution color aerial photograph as a field map (1/2500) in a shallow coral reef shore zone (<2 m deep, 3.6 ha, Shiraho Reef, Ishigaki Island, Japan). This study confirmed that the logarithmic function is better than other functions (including the power function) to explain the SAR in this scale. Actual species richness (24) over the entire study site was much higher than the species richness (15.4) extrapolated from the regression line in semi-log space. Better estimates were obtained using random placement models and computer simulations. These results suggest that several small patch reefs are likely to have higher species richness than a single large reef of equivalent area at the study site. The total number of individuals of the four most abundant territorial herbivores increased almost linearly with patch reef area, but that of other species roughly increased with the square root of the area. While no territorial species were found in the smallest reefs, the large territorial herbivore, Hemiglyphidodon plagiometopon, was abundant and had negative effects on species richness in large reefs. Although the well-known single-large-or-several-small (SLOSS) debate has largely been settled, this dichotomy can be important in places where territorial herbivores do not occupy the smallest reefs.