Cleaner wrasse influence habitat selection of young damselfish

The presence of bluestreak cleaner wrasse, Labroides dimidiatus, on coral reefs increases total abundance and biodiversity of reef fishes. The mechanism(s) that cause such shifts in population structure are unclear, but it is possible that young fish preferentially settle into microhabitats where cleaner wrasse are present. As a first step to investigate this possibility, we conducted aquarium experiments to examine whether settlement-stage and young juveniles of ambon damselfish, Pomacentrus amboinensis, selected a microhabitat near a cleaner wrasse (adult or juvenile). Both settlement-stage (0 d post-settlement) and juvenile (~5 weeks post-settlement) fish spent a greater proportion of time in a microhabitat adjacent to L. dimidiatus than in one next to a control fish (a non-cleaner wrasse, Halichoeres melanurus) or one where no fish was present. This suggests that cleaner wrasse may serve as a positive cue during microhabitat selection. We also conducted focal observations of cleaner wrasse and counts of nearby damselfishes (1 m radius) to examine whether newly settled fish obtained direct benefits, in the form of cleaning services, from being near a cleaner wrasse. Although abundant, newly settled recruits (<20 mm total length) were rarely (2 %) observed being cleaned in 20 min observations compared with larger damselfishes (58 %). Individual damselfish that were cleaned were significantly larger than the median size of the surrounding nearby non-cleaned conspecifics; this was consistent across four species. The selection by settlement-stage fish of a microhabitat adjacent to cleaner wrasse in the laboratory, despite only being rarely cleaned in the natural environment, suggests that even rare cleaning events and/or indirect benefits may drive their settlement choices. This behaviour may also explain the decreased abundance of young fishes on reefs from which cleaner wrasse had been experimentally removed. This study reinforces the potentially important role of mutualism during the processes of settlement and recruitment of young reef fishes.     

Effects of substrata, resident conspecifics and damselfish on the settlement and recruitment of the stoplight parrotfish, Sparisoma viride

Recruitment plays an important role in the population dynamics of marine organisms and is often quantified as a surrogate for settlement. When quantified, recruitment includes settlement plus a period of time in the benthic habitat. Therefore, it is essential to determine whether post-settlement processes alter patterns established at settlement. I conducted a series of experiments on 2.0 m² patch reefs to examine the importance of pre- and post-settlement processes to the distribution and abundance of recruits of the stoplight parrotfish, Sparisoma viride, on the Tague Bay reef, St. Croix, USVI. Recruitment was higher to the coral Porites porites than to another common coral Montastrea annularis, but there was no evidence of microhabitat choice at settlement. This result, in conjunction with the examination of the size classes of recruits present on P. porites and M. annularis patch reefs in a separate experiment suggested that differences in recruitment were established after settlement. Stoplights settled in higher numbers to patch reefs that contained conspecific residents, and persistence was higher at higher recruit density. Although resident damselfish directed significant amounts of agonistic behavior towards newly stoplight recruits, damselfish presence had no effect on settlement. However, damselfish presence did reduce stoplight recruitment. These results demonstrate that both pre- and post-settlement processes influence the recruitment of stoplight parrotfish. More importantly, these results indicate that benthic processes can alter recruitment patterns from initial settlement patterns, and indicate that workers should be careful in using recruitment as a proxy for settlement.     

Predators reduce abundance and species richness of coral reef fish recruits via non-selective predation

Predators have important effects on coral reef fish populations, but their effects on community structure have only recently been investigated and are not yet well understood. Here, the effect of predation on the diversity and abundance of young coral reef fishes was experimentally examined in Moorea, French Polynesia. Effects of predators were quantified by monitoring recruitment of fishes onto standardized patch reefs in predator-exclosure cages or uncaged reefs. At the end of the 54-day experiment, recruits were 74% less abundant on reefs exposed to predators than on caged ones, and species richness was 42% lower on reefs exposed to predators. Effects of predators varied somewhat among families, however, rarefaction analysis indicated that predators foraged non-selectively among species. These results indicate that predation can alter diversity of reef fish communities by indiscriminately reducing the abundance of fishes soon after settlement, thereby reducing the number of species present on reefs.     

Impact of cyclones on hard coral and metapopulation structure,connectivity and genetic diversity of coral reef fish

Cyclones have one of the greatest effects on the biodiversity of coral reefs and the associated species. But it is unknown how stochastic alterations in habitat structure influence metapopulation structure, connectivity and genetic diversity. From 1993 to 2018, the reefs of the Capricorn Bunker Reef group in the southern part of the Great Barrier Reef were impacted by three tropical cyclones including cyclone Hamish (2009, category 5). This resulted in substantial loss of live habitat-forming coral and coral reef fish communities. Within 6–8 years after cyclones had devastated, live hard corals recovered by 50–60%. We show the relationship between hard coral cover and the abundance of the neon damselfish (Pomacentrus coelestis), the first fish colonizing destroyed reefs. We present the first long-term (2008–2015 years corresponding to 16–24 generations of P. coelestis) population genetic study to understand the impact of cyclones on the meta-population structure, connectivity and genetic diversity of the neon damselfish. After the cyclone, we observed the largest change in the genetic structure at reef populations compared to other years. Simultaneously, allelic richness of genetic microsatellite markers dropped indicating a great loss of genetic diversity, which increased again in subsequent years. Over years, metapopulation dynamics were characterized by high connectivity among fish populations associated with the Capricorn Bunker reefs (2200 km²); however, despite high exchange, genetic patchiness was observed with annual strong genetic divergence between populations among reefs. Some broad similarities in the genetic structure in 2015 could be explained by dispersal from a source reef and the related expansion of local populations. This study has shown that alternating cyclone-driven changes and subsequent recovery phases of coral habitat can greatly influence patterns of reef fish connectivity. The frequency of disturbances determines abundance of fish and genetic diversity within species.

     

Extended breeding and recruitment periods of fishes on a low latitude coral reef

The temporal dynamics of fish recruitment to equatorial Indo-Pacific coral reefs are not well known. This paper documents fish recruitment over a 2.5-year period in Kimbe Bay (PNG) and shows that it is much less seasonal than is typically described for higher latitude coral reefs. Two families, wrasses (Labridae) and damselfishes (Pomacentridae), which accounted for 90% of all non-cryptic reef fish settlers, exhibited contrasting patterns. Most wrasse species had year-round recruitment with irregular peaks in abundance between November and May. Damselfish species showed a wider range of recruitment patterns, but most had negligible recruitment during the wet season (December–February), followed by one or two recruitment peaks between May and November. Species with longer seasonal recruitment periods exhibited higher cumulative levels of recruitment. For three focal damselfish species, reproductive output was reduced during the wet season, but this alone did not account for the low recruitment at this time. The lack of damselfish recruitment during the wet season is hypothesised to be due to a combination of reduced reproductive output and increased larval mortality associated with monsoonal conditions. The results indicate that there are consistent family-wide recruitment strategies that may play a significant role in the dynamics of populations in equatorial waters.     

Structure of reef fish communities in Catalinas Islands and Ocotal beach, North Pacific of Costa Rica

The reefs are heterogeneous systems that maintain a high diversity of organisms. Fish community structure varies within and among reefs, so it would be expected that reef structure and heterogeneity should affect fish communities inhabiting reefs. Four reef patches at Catalinas Islands (Sur, La Pared, Roca Sucia and Sombrero) and one in Ocotal beach (10 degrees 28'45" N; 85 degrees 52'35" W) were studied with visual censuses (July-December 2003). The structure and composition of fishes between Catalinas islands and Ocotal beach were different, and habitat structure and composition explain most of the variance founded. The presence of the fleshy algae Caulerpa sertularioides in Ocotal, and the corals Tubastrea coccinea and Pocillopora spp. at Catalinas Island explained the variability among sites and how it affected fish community structure and composition. The butterfly fish Johnrandallia nigrirostris, damselfish Microspathodon dorsalis, and surgeon fish Prionurus punctatus were directly correlated with the ahermatipic coral Tubastrea coccinea in Roca Sucia reef, while the angel fish Holacanthus passer was associated to reefs with a major percentage of rocky substrate. Other species such as the damselfish Abudefduf troschelli and Halichoeres dispilus were more abundant at Ocotal, where the algae C sertularioides dominated. The number and abundance of reef fishes was directly correlated with the rugosity index at the reefs of Roca Sucia and Ocotal, but not at reefs of La Pared and Sombrero.     

El Niño mass coral mortality: a test of resource limitation in a coral reef damselfish population

Summary The mass mortality of reef corals in the eastern Pacific as a result of the 1982–1983 El Niño oceanographic anomaly permitted the first large scale test of resource limitation for a coral reef fish. Population densities of territorial herbivorous damselfish did not respond to the massive regional increase in space available for the cultivation of algal food following the El Niño event. The proportion of juveniles in the population was low and new recruits were uncommon, indicating that recruitment rates rather than resource supply probably control the abundance of this coral reef damselfish.     

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.     

Relationships between habitat structure and fish communities on coral

The influence of habitat structure on reef-fish communities at Bar Reef Marine Sanctuary, Sri Lanka, was investigated. The relationship between habitat characteristics and the distribution and abundance of 135 species of fishes was examined on two reef types: coral and sandstone reefs. Results suggested that the reef-fish communities were strongly influenced by various aspects of reef structure. However, relationships between habitat variables and fish communities structure, varied between the two reef types. Fish species diversity was correlated with a number of habitat variables on the sandstone reefs, although structural complexity seemed to play the dominant role. There were no correlations between habitat structure and fish diversity on the coral reefs. Total abundance was not related to any one habitat parameter on either reef type. However, abundances of some species, families and trophic groups were correlated with habitat features. These specific correlations were commonly related to food or shelter availability. For example, coral feeders were correlated with live coral cover, and pomacentrid species, which used branching corals for protection, showed a significant relationship with the density of Acropora colonies. This shows that a summary statistic such as total abundance may hide important information. Effects of habitat structure on the distribution patterns of the fish communities was further investigated using multi-dimensional scaling ordination (MDS) and the RELATE-procedure. With the MDS ordinations for both habitat and fish-community composition it was possible to show that the multivariate pattern between the two ecological components was clearly correlated.     

Habitat dynamics,marine reserve status,and the decline and recovery of coral reef fish communities

Severe climatic disturbance events often have major impacts on coral reef communities, generating cycles of decline and recovery, and in some extreme cases, community‐level phase shifts from coral‐ to algal‐dominated states. Benthic habitat changes directly affect reef fish communities, with low coral cover usually associated with low fish diversity and abundance. No‐take marine reserves (NTRs) are widely advocated for conserving biodiversity and enhancing the sustainability of exploited fish populations. Numerous studies have documented positive ecological and socio‐economic benefits of NTRs; however, the ability of NTRs to ameliorate the effects of acute disturbances on coral reefs has seldom been investigated. Here, we test these factors by tracking the dynamics of benthic and fish communities, including the important fishery species, coral trout (Plectropomus spp.), over 8 years in both NTRs and fished areas in the Keppel Island group, Great Barrier Reef, Australia. Two major disturbances impacted the reefs during the monitoring period, a coral bleaching event in 2006 and a freshwater flood plume in 2011. Both disturbances generated significant declines in coral cover and habitat complexity, with subsequent declines in fish abundance and diversity, and pronounced shifts in fish assemblage structure. Coral trout density also declined in response to the loss of live coral, however, the approximately 2:1 density ratio between NTRs and fished zones was maintained over time. The only post‐disturbance refuges for coral trout spawning stocks were within the NTRs that escaped the worst effects of the disturbances. Although NTRs had little discernible effect on the temporal dynamics of benthic or fish communities, it was evident that the post‐disturbance refuges for coral trout spawning stocks within some NTRs may be critically important to regional‐scale population persistence and recovery.     

The effect of microhabitat patch size on settlement differs among co-occurring coral reef fishes

Over small spatial scales, coral reefs represent a mosaic of suitable settlement microhabitat patches of varying size for late-stage larval reef fishes. Few studies have specifically examined how variation in patch size influences density of recently settled coral reef fishes (recruits). Using standardized units of coral rubble settlement substrate deployed on sandy bottom, we monitored the concurrent settlement of three reef fish taxa onto differently sized patches (0.28–1.68 m²) at 5-d intervals during a lunar settlement peak. We found marked differences among taxa in how recruit density scaled with patch size. Recruit density of a damselfish and a parrotfish decreased and increased, respectively, with the increase in patch size, while that of a wrasse was similar among patch sizes. Our results highlight the importance of the interaction between taxon-specific settlement behaviour and patch size in establishing initial spatial differences in density within and among coral reef fish taxa in a heterogeneous landscape.

     

Degraded Environments Alter Prey Risk Assessment

Elevated water temperatures, a decrease in ocean pH, and an increasing prevalence of severe storms have lead to bleaching and death of the hard corals that underpin coral reef ecosystems. As coral cover declines, fish diversity and abundance declines. How degradation of coral reefs affects behavior of reef inhabitants is unknown. Here, we demonstrate that risk assessment behaviors of prey are severely affected by coral degradation. Juvenile damselfish were exposed to visual and olfactory indicators of predation risk in healthy live, thermally bleached, and dead coral in a series of laboratory and field experiments. While fish still responded to visual cues in all habitats, they did not respond to olfactory indicators of risk in dead coral habitats, likely as a result of alteration or degradation of chemical cues. These cues are critical for learning and avoiding predators, and a failure to respond can have dramatic repercussions for survival and recruitment.     

To clean or not to clean: Cleaning mutualism breakdown in a tidal environment

The dynamics and prevalence of mutualistic interactions, which are responsible for the maintenance and structuring of all ecological communities, are vulnerable to changes in abiotic and biotic environmental conditions. Mutualistic outcomes can quickly shift from cooperation to conflict, but it unclear how resilient and stable mutualistic outcomes are to more variable conditions. Tidally controlled coral atoll lagoons that experience extreme diurnal environmental shifts thus provide a model from which to test plasticity in mutualistic behavior of dedicated (formerly obligate) cleaner fish, which acquire all their food resources through client interactions. Here, we investigated cleaning patterns of a model cleaner fish species, the bluestreak wrasse (Labroides dimidiatus), in an isolated tidal lagoon on the Great Barrier Reef. Under tidally restricted conditions, uniquely both adults and juveniles were part‐time facultative cleaners, pecking on Isopora palifera coral. The mutualism was not completely abandoned, with adults also wandering across the reef in search of clients, rather than waiting at fixed site cleaning stations, a behavior not yet observed at any other reef. Contrary to well‐established patterns for this cleaner, juveniles appeared to exploit the system, by biting (“cheating”) their clients more frequently than adults. We show for the first time, that within this variable tidal environment, where mutualistic cleaning might not represent a stable food source, the prevalence and dynamics of this mutualism may be breaking down (through increased cheating and partial abandonment). Environmental variability could thus reduce the pervasiveness of mutualisms within our ecosystems, ultimately reducing the stability of the system.     

Coexistence of Low Coral Cover and High Fish Biomass at Farquhar Atoll,Seychelles

We report a reef ecosystem where corals may have lost their role as major reef engineering species but fish biomass and assemblage structure is comparable to unfished reefs elsewhere around the world. This scenario is based on an extensive assessment of the coral reefs of Farquhar Atoll, the most southern of the Seychelles Islands. Coral cover and overall benthic community condition at Farquhar was poor, likely due to a combination of limited habitat, localized upwelling, past coral bleaching, and cyclones. Farquhar Atoll harbors a relatively intact reef fish assemblage with very large biomass (3.2 t ha⁻¹) reflecting natural ecological processes that are not influenced by fishing or other local anthropogenic factors. The most striking feature of the reef fish assemblage is the dominance by large groupers, snappers, and jacks with large (>1 m) potato cod (Epinephelus tukula) and marbled grouper (E. polyphekadion), commonly observed at many locations. Napoleon wrasse (Cheilinus undulatus) and bumphead parrotfish (Bolbometopon muricatum) are listed as endangered and vulnerable, respectively, but were frequently encountered at Farquhar. The high abundance and large sizes of parrotfishes at Farquhar also appears to regulate macroalgal abundance and enhance the dominance of crustose corallines, which are a necessary condition for maintenance of healthy reef communities. Overall fish biomass and biomass of large predators at Farquhar are substantially higher than other areas within the Seychelles, and are some of the highest recorded in the Indian Ocean. Remote islands like Farquhar Atoll with low human populations and limited fishing pressure offer ideal opportunities for understanding whether reefs can be resilient from global threats if local threats are minimized.     

Effect of the removal of cleaner fish on the abundance and species composition of reef fish

The ecological significance of cleaner fish on coral reefs was investigated. I removed all cleaner fish, Labroides dimidiatus, from eight small reefs, measured the subsequent effect on the abundance and species composition of all reef fish after 3 and 6 months, and compared it with eight control reefs with cleaner fish. The removal of cleaner fish had no detectable effect on the total abundance of fish on reefs and the total number of fish species at both times. Multivariate analysis by non-metric multidimensional scaling and ANOSIM pairwise tests based on 191 fish species revealed no effect of cleaners on the community structure of fish. Similar results were obtained using principal components analysis on subsets of the data using the 33 most common fish species and the 15 most abundant species (≥5 individuals per reef ) with both log10 (x + 1) transformed data and with fish numbers standardized for abundance. This study demonstrates that the removal of cleaner fish for 6 months did not result in fish suffering increased mortality nor in fish leaving reefs to seek cleaning elsewhere. Received: 28 October 1996 / Accepted: 7 February 1997     

Influence of predation risk on the sheltering behaviour of the coral-dwelling damselfish, <Emphasis Type="Italic">Pomacentrus moluccensis</Emphasis>

Predation is a key ecosystem function, especially in high diversity systems such as coral reefs. Not only is predation one of the strongest top-down controls of prey population density, but it also is a strong driver of prey behaviour and function through non-lethal effects. We ask whether predation risk influences sheltering behaviour of damselfish living in mutualism with branching corals. Host corals gain multiple advantages from the mutualistic relationship which are determined by the strength of damselfish sheltering. Distance travelled by the Lemon Damselfish Pomacentrus moluccensis away from their host colony was measured here as a proxy for sheltering strength and was expected to be shortest under highest predation risk. Predation risk, defined as a function of predator abundance and activity, turbidity and habitat complexity, was quantified at four reef slope sites in Kepulauan Seribu, Indonesia. Damselfish sheltering strength was measured using stationary unmanned video cameras. Small damselfish (< 2 cm) increased their sheltering strength under high turbidity. Predator feeding activity, but not abundance, influenced damselfish sheltering strength. Contrary to our expectations, sheltering behaviour of adult damselfish decreased under high predator activity. While these observations are in line with risk-averse behaviour by juvenile P. moluccensis, they may indicate the presence of sentinel behaviour in the adults of this species. Habitat complexity seemed to be less important as a driver of damselfish behaviour. These counterintuitive results may indicate complex social behaviour and age-specific strategies for predator avoidance.     

Responses of coral and fish assemblages to a severe but short-lived tropical cyclone on the Great Barrier Reef,Australia

Changes in reef assemblages of corals and fishes following a tropical cyclone were assessed using data sets from (1) manta tow surveys of entire reef perimeters and (2) intensive surveys of specific sites, across 11 reefs lying close to the cyclone's track. Only one of the reefs experienced an obvious and immediate decline in mean coral cover (from 24 to 8%) due to the cyclone. The abundance and species richness of adult damselfish assemblages on intensive survey sites at this reef were not affected in the short term (6-8 weeks), despite the removal of 48% of living hard coral. Assemblages of adult fishes showed a similar lack of response at three other reefs where no significant habitat changes had occurred. Eleven to twelve months later, the total abundance of damselfishes had decreased substantially at eight of the sampled reefs, while the abundance of larger mobile fishes remained stable. We infer that the effects on coral assemblages reflect the short duration and orientation of the cyclone, the history of exposure to wave energy (influencing life-form structure and therefore degree of fragility), and the degree of consolidation of the reef matrix. The lack of short-term effects of the cyclone on adult fishes shows that these fishes can endure periods of intense underwater turbulence. The lack of change in damselfish assemblages weeks after loss of coral cover implies that this resource was not limiting adult fish densities. The reasons for widespread decreases in damselfish numbers 11-12 months after the cyclone are unknown.     

Structurally complex habitats provided by Acropora palmata influence ecosystem processes on a reef in the Florida Keys National Marine Sanctuary

The disappearance of Acropora palmata from reefs in the Florida Keys National Marine Sanctuary (FKNMS) represents a significant loss in the amount of structurally complex habitat available for reef-associated species. The consequences of such a widespread loss of complex structure on ecosystem processes are still unclear. We sought to determine whether the disappearance of complex structure has adversely affected grazing and invertebrate predation rates on a shallow reef in the FKNMS. Surprisingly, we found grazing rates and invertebrate predation rates were lower in the structurally complex A. palmata branches than on the topographically simple degraded reefs. We attribute these results to high densities of aggressively territorial damselfish, Stegastes planifrons, living within A. palmata. Our study suggests the presence of agonistic damselfish can cause the realized spatial patterns of ecosystem processes to deviate from the expected patterns. Reef ecologists must therefore carefully consider the assemblage of associate fish communities when assessing how the mortality of A. palmata has affected coral reef ecosystem processes.     

Near‐term impacts of coral restoration on target species,coral reef community structure,and ecological processes

The global decline of corals has created an urgent need for effective, science‐based methods to augment coral populations and restore important ecosystem functions. To meet this challenge, the field of coral restoration has rapidly evolved over the past decade. However, despite widespread efforts to outplant corals and monitor survivorship, there is a shortage of information on the effects of coral restoration on reef communities or important ecosystem functions. To fill this knowledge gap, we examined the effects of restoration on three major criteria: diversity, community structure, and ecological processes. We conducted surveys of four restored sites in the Florida Keys ranging in restoration effort (500–2,300 corals outplanted) paired with surveys of nearby, unmanipulated control sites. Coral restoration successfully enhanced coral populations, increasing coral cover 4‐fold, but manifested in limited differences in coral and fish communities. Some restored sites had higher abundance of herbivorous fish, rates of herbivory, or more juvenile‐sized corals, but these effects were limited to individual reefs. Damselfish were consistently more abundant at restored compared to control sites. Despite augmenting target coral populations, 3 years of coral restoration has not facilitated many of the positive feedbacks that help reinforce coral success. In a time of increasingly frequent disturbances, it is urgent we hasten the speed at which reefs recover important ecological processes, such as herbivory and nutrient cycling, that make reefs more resistant and resilient if we are to achieve long‐term restoration success.