Competitive Species Research Articles

Comparative genomics revealed that Vibrio furnissii and Vibrio fluvialis have mutations in genes related to T6SS1 and T6SS2

The type VI secretion system (T6SS) is important for interbacterial competition and virulence in Vibrio species. It is generally agreed that T6SS provides a fitness advantage to Vibrios. Some Vibrio species possess one, while others possess two T6SSs. Even within the same Vibrio species, different strains can harbor a variable number of T6SSs. Such is the case in V. fluvialis, an opportunistic human pathogen, that some V. fluvialis strains do not harbor T6SS1. This study found that Amphritea, Marinomonas, Marinobacterium, Vibrio, Photobacterium, and Oceanospirillum species have genes encoding V. fluvialis T6SS1 homologs. The cladogram of T6SS1 genes suggested that these genes appeared to be horizontally acquired by V. fluvialis, V. furnissii, and some other Vibrio species, when compared with the species tree. Codon insertions, codon deletions, nonsense mutations, and the insertion sequence are found in many genes, such as clpV1, tssL1, and tssF1, which encode structure components of T6SS1 in V. furnissii and V. fluvialis. Codon deletion events are more common than codon insertion, insertion sequence disruption, and nonsense mutation events in genes that encode components of T6SS1. Similarly, codon insertions and codon deletions are found in genes relevant to T6SS2, including tssM2, vgrG2 and vasH, in V. furnissii and V. fluvialis. These mutations are likely to disable the functions of T6SSs. Our findings indicate that T6SS may have a fitness disadvantage in V. furnissii and V. fluvialis, and the loss of function in T6SS may help these Vibrio species to survive under certain conditions.

Contrasting patterns along tall grass dominance in mowed mountain grasslands

Semi-natural grasslands are a perfect system to study how biotic interactions influence coexistence thanks to their high species diversity in small areas resulting from millennia of anthropogenic management. Management cessation led to the increase of highly competitive tall-perennial tussock species with a marked drop of taxonomical (TD) and functional diversity (FD). The effect of highly competitive tall-perennial tussock species on plant community under management condition is largely understudied. In this study, we try to shed light on the effect of Brachypodium genuense which dominates sub-Mediterranean abandoned mountain grasslands TD and FD. For FD, we selected as traits plant height (H), specific leaf area (SLA) and leaf area (LA). We hypothesized i) TD decreases as the cover of B. genuense increases; ii): H converges towards higher values resulting from weaker competitive exclusion; iii) SLA and LA diverge resulting from limiting similarity. TD and FD were calculated using Rao's Quadratic Entropy. We computed the community weighted mean (CWM) that we analysed with fourth corner approach and built linear models using B. genuense as a predictor. We found that B. genuense ability in dominating the grassland plant community is altered by mowing in two different ways. On one hand, increase of B. genuense lead to a drop in TD whereas for FD the increase showed contrasting patterns with divergence for H and convergence for SLA. On the other, there were changes in the main dominant strategies with an overall increase in mean trait values of both H and SLA indicating species taller in size and more fast-growing. Overall, our results highlighted how tall-perennial tussock species under mowing conditions lead to a more stratified plant community convergent towards resource acquisition strategies. A multifaceted approach should be adopted to have a better understanding of the biotic drivers on different aspect of plant community.

Invasive microstegium vimineum (Japanese stiltgrass) hinders growth and biomass of hardwood seedlings regardless of light and moisture regime

Limited natural oak (Quercus spp.) regeneration in current-day, closed-canopy upland oak forests across the eastern and central United States has prompted increased use of various silvicultural practices, including prescribed fire and/or thinning, to reduce competition from shade-tolerant, often fire-sensitive species, and ultimately, restore and/or maintain oak landscapes. However, these practices create disturbances that can promote the spread of invasive plants and complicate oak restoration attempts, especially if invasion differentially impacts oaks compared to competitor species during early seedling development. To evaluate if Japanese stiltgrass (Microstegium vimineum (Trin.) A. Camus), an invasive C4 grass common in the understory of these systems, impacts growth and biomass of hardwood seedlings in different light and moisture environments, we established a shadehouse experiment in May 2020 with one-year old seedlings of white oak (Quercus alba L.) and two competitor species, red maple (Acer rubrum L.) and sweetgum (Liquidambar styraciflua L.), in the following treatments: M. vimineum (MV) presence (with/without), light (40/10 % full irradiance), soil moisture (high/low), and their interactions. Monthly, from May to October 2020, we measured seedling height growth, stem basal diameter, and MV cover and height if present. In October 2020, we harvested a subset of seedlings and measured their above- and belowground biomass and aboveground MV biomass when present. At study cessation, regardless of light or moisture treatment, red maple and sweetgum were significantly shorter when grown with MV (17.9 and 15.6 cm, respectively) than without MV (33.5 and 22.3 cm, respectively) and had smaller basal diameters (with MV: 1.03 and 0.94, respectively; without MV: 1.34 and 1.25 cm, respectively) and ∼ two times less biomass. White oak basal diameter was 1.2 times lower with MV (0.77 cm) compared to without MV (0.93 cm), but MV had no impact on white oak height growth or biomass, likely because of its conservative growth strategy and high-water use efficiency. Light and moisture treatments had little impact on MV height and cover, but MV biomass was greater with high (462 dry wt m−2) compared to low (398 g dry wt m−2) moisture treatment and ∼ 1.3 times greater when grown without vs with tree competition. Thus, MV invasion into closed-canopy upland oak forests may have species-specific effects on early seedling growth, reducing growth of competitor seedlings with non-conservative growth strategies more than that of upland oaks, but long-term studies are needed to better understand the potential legacy effects of MV on growing conditions and tree regeneration.

The effects of river regulation on diet diversity, dietary niche overlap and foraging habitat preferences of two sympatric plover species

During migration waders use a variety of microhabitats and a wide range of prey to supply their nutritional requirements. Most of them form multispecies flocks, which may result in increased competition for resources. In this study, we compare the abundance of potential prey for Ringed and Little Ringed plovers at unregulated and regulated stretches of the Vistula River. We also observed plovers and assigned them to the habitat in which they foraged and compare the diet, dietary niche overlap and foraging habitat preferences of these two plover species. The larger species, the Ringed Plover, foraged more often in invertebrate abundant habitats, yet exclusively on the three most abundant prey species, while the smaller species expanded its diet to include invertebrate species of low abundance and in suboptimal habitats. In the regulated river section, below the dam, the diet of the Little Ringed Plover was more diverse, and the dissimilarity of both plovers’ diets was much higher than in the regulated section. The unregulated river section offered richer foraging grounds and both species showed similar proportions of primary prey items in their diets here resulting in greater dietary niche overlap and weaker resource partitioning. Our study shows that river regulation increases competition for food resources due to a lower abundance of potential prey and has an influence on diet diversity and foraging habitat preferences of smaller, less competitive plover species.

The invasive Asian benthic foraminifera Trochammina hadai Uchio, 1962: identification of a new local in Normandy (France) and a discussion on its putative introduction pathways

The invasive benthic foraminifera Trochammina hadai has been found for the first time in Europe along the coast of Normandy. Its native range of distribution is in Asia (Japan and Korea), and it has also been introduced along the coasts of western North America, Brazil and Australia. Morphological and molecular assessments confirm that specimens found in Le Havre and Caen-Ouistreham harbors belong to the Asiatic type. Like in Asia, T. hadai was found in transitional waters with muddy sediments. It exhibited high relative abundances (up to about 40%) confirming that T. hadai is a highly competitive species. In the present study, it was nearly absent from natural transitional waters and very abundant in heavily modified habitats like harbors, suggesting that ballast waters may likely be the vector of introduction. It was not recorded farther north along the coast of the Hauts-de-France. It is further hypothesized that the finding of a few specimens outside the harbor may facilitate the expansion of T. hadai in the English Channel by means of propagules dispersion.

Why losing Australia's biodiversity matters for human health: insights from the latest State of the Environment assessment.

Why losing Australia's biodiversity matters for human health: insights from the latest State of the Environment assessment.

Within-host adaptation alters priority effects within the tomato phyllosphere microbiome.

To predict the composition and function of ecological communities over time, it is essential to understand how in situ evolution alters priority effects between resident and invading species. Phyllosphere microbial communities are a useful model system to explore priority effects because the system is clearly spatially delineated and can be manipulated experimentally. We conducted an experimental evolution study with tomato plants and the early-colonizing bacterium species Pantoea dispersa, exploring priority effects when P. dispersa was introduced before, simultaneously with or after competitor species. P. dispersa rapidly evolved to invade a new niche within the plant tissue and altered its ecological interactions with other members of the plant microbiome and its effect on the host. Prevailing models have assumed that adaptation primarily improves the efficiency of resident species within their existing niches, yet in our study system, the resident species expanded its niche instead. This finding suggests potential limitations to the application of existing ecological theory to microbial communities.

Bombus terrestris terrestris (Linnaeus, 1758) and hybrids with the endemic Bombus xanthopus spotted on Capraia Island (Tuscan Archipelago, Italy): some conservation management implications

Expansion of wild and managed allochthonous species leads to potential negative consequences for the endemic wildlife, such as resource competition, pathogens spread, hybridization and native species replacements. On Capraia Island, the last sighting of Bombus terrestris terrestris dates back to 1917. All subsequent surveys carried out on the island only reported the presence of B. xanthopus and B. pascuorum melleofacies with B. t. terrestris apparently no longer existing in the area. In 2021 B. t. terrestris was again detected on the island raising two main hypotheses: (i) B. t. terrestris has always been present with a low population density, such as not to be detected in previous investigations, or (ii) its presence is the result of a more recent recolonization. The recolonization event may be promoted by either intentional or unintentional introduction or it may be the result of a natural migration from the mainland or surrounding islands. Hybridization between B. t. terrestris × B. xanthopus on Capraia Island has been also ascertained by the detection of hybrid queens, workers and males. These new finding provides insight on the distribution range of B. t. terrestris in the Tuscan Archipelago and raise concern on the conservation of the endemic B. xanthopus population.

Development of red fluorescent carbon dots for optical and smartphone imaging dual-mode determination of metabisulfite and pH monitoring

A new type of red photoluminescent carbon dots (R-CDs) with high quantum yield of 46.9% was favorably developed by introducing the luminophore of resazurin into the framework. The obtained R-CDs exhibit excitation-independent behavior, advantageous dispersion and outstanding optical performance. It is worth noting that the proposed R-CDs demonstrate a particular response to S2O52- over other competitive species accompanied by a naked-eye color change from red to orange. Fluorescence quenching of R-CDs is determined to be S2O52- concentrations dependence with ultra-fast response time and low detection limit. The as-developed R-CDs is further employed in building a smartphone imaging colorimetry platform for portable recognition of S2O52- in real samples with considerable accuracy. Furthermore, the speciallyprepared R-CDs also display a significant fluorescence enhancement behavior with the increase of pH in the linear range of 5.4–6.2 with a pKa of 5.86. These findings may offer a distinctive strategy for the development of long-wavelength emission carbon dots and help to expand their application in food safety inspection.

Geobotanical study of ruderal vegetation in the geoecological monitoring program of roadside ecosystems of the Cherkasy oblast

The article is devoted to the dynamics of the spread of ruderal vegetation in phytocenoses of the roadside ecosystems of the Cherkasy oblast. Due to the high plowed area of the region, roadside field protection strips, in which, in fact, phytocenoses with the participation of ruderal plants are formed, are mostly very narrow (on average 10–15 m). Such ecotopic limitation creates extremely harsh ecological conditions in which only competitive (and sometimes aggressive) species survive. Unlike most works devoted to the formation of the phytodiversity in roadside phytocenoses, the authors follow the concept of infraecosystems presented in previous publications. The main distinguishing feature of this concept is the assumption of different states of formation of natural ecosystems on roadsides. In particular, by comparing the available phytodiversity in roadside phytocenoses with the «National Catalog of Biotopes», the degree of completeness of ecosystem formation at 19 study sites was assessed. Highways in the meridional (11 polygons) and latitudinal (8 polygons) directions were investigated within the Cherkasy oblast. Among the investigated phytocenoses at 19 polygons, only 4 phytocenoses, which spatially coincide with gas stations (Esco gas station, exit from the city of Uman, SOCAR gas station, near the village of Sharyn), or with relatively isolated settlements at the exits to the main route (Bilashki village, Rotmistrivka village). Invasive species (more than 10), which take an active part in the formation of the phytodiversity, were also found at all landfills. According to our estimates, the general trend of the formation of roadside ecosystems falls under the principle of Le Chatelier-Brown compensation, according to which the biosphere confirms its extraordinary ability to support life every time. After all, it can reduce, eliminate, and finally nullify any destructive (man-made) impact, filling existing and creating new ecological niches. Such an understanding of the geobotanical component in monitoring studies will help in the future to more correctly determine the role of man and the biosphere in the formation of anthropogenic landscapes, one of the more dynamic varieties of which are roadside landscapes. Keywords: ruderal plants, infraecosystem, phytocenosis, invasive species.

Native species can reduce the establishment of invasive alien species if sown in high density and using competitive species

Invasion of alien species is one of the main drivers of land degradation threatening both natural and managed ecosystems. Ecological restoration is crucial in controlling invasion to improve biotic resistance and avoid further land degradation. We investigated the possibility of controlling the establishment of invasive alien species (IAS) by native seed addition. We tested if trait similarity or increased propagule pressure of native species results in the suppression of IAS at the early stage of development. We set up a sowing experiment with three widespread IAS in Hungary of different life forms and functional groups (Asclepias syriaca, Conyza canadensis, Tragus racemosus) and four Pannonic sand grassland species (Festuca vaginata, Galium verum, Gypsophila paniculata, Saponaria officinalis). We found no significant differences in germination ability and seedling emergence between native species and IAS, despite the differences in thousand‐seed weight. Using univariate general linear models, we found that the seedling establishment of IAS can be reduced by adding native species at high densities but also depending on the species identity. Instead of species of similar traits, the seeding of a competitor perennial grass of sand grasslands (F. vaginata) reduced the seedling emergence of all studied IAS the most. Our results confirm that IAS can be effectively controlled by native seed addition in the early establishment stage, especially applying higher densities and competitive species. We conclude that invasion‐resistant restoration can be achieved by the combination of several factors, including high‐density sowing of native species that match IAS in the early stage of development.

Keanekaragaman Vegetasi Pada Habitat Yang Terinvasi Tumbuhan Invasif Di Hutan Kota Bukit Langkisau Painan, Sumatra Barat

The presence of invasive plants in a habitat will cause significant disturbances, especially in decreasing the abundance of biodiversity. The high competitiveness of invasive species causes native species to lose in competition. Invasive species have spread in many places, one of which is in the Bukit Langkisau City Forest. However, data on the types of weeds and vegetation types in the habitats invaded by weeds in the Bukit Langkisau City Forest are not yet available. Vegetation analysis was carried out in the Bukit Langkisau Painan City Forest, West Sumatra. The study used a survey method by laying out plots by purposive sampling, which made 15 plots at each level of vegetation. The plot is 10 x 10 m for observation of tree-level vegetation, the plot is 5 x 5 m for sapling vegetation and for understorey vegetation the plot is 2 x 2 m. The results of the vegetation analysis recorded 87 species of which there were 32 invasive species. The dominant families were found such as Fabaceae family, Meliaceae for tree level, Piperaceae for sapling level and Poaceae for understorey level. The highest Importance Value Index for tree vegetation, sapling and understorey was found in the invasive species Swietenia macrophylla (IVI = 44.69%), Piper aduncum (IVI = 85.08%), and Imperata cylindrica (IVI = 33.67%). The Vegetation Diversity Index in the Bukit Langkisau City Forest is the tree level (1.90), sapling (1.26) and understorey (1.78) which are all classified as moderate. KEYWORDSPlant invasive, urban forest, composition, structure, diversity index

Diffusion-driven instability and pattern formation in a prey-predator model with fear and Allee effect

This paper analyses a predator-prey model with Holling type II response function incorporating Allee and fear effect in the prey. The model includes intra species competition among predators. We find out the local dynamics as well as Hopf bifurcation by considering level of fear as bifurcation parameter. The condition for diffusion-driven instability and patterns are then demonstrated in relation to the system's ecological parameters and diffusion coefficients. Intra-specific competition affects the dynamics of the system and Turing pattern formation. Moreover, output of results is verified through numerical simulation. Thus, from a dynamical standpoint, the considered model seems to be relevant in the field of ecology.

Динамика живого напочвенного покрова на начальных этапах формирования лесных культур средней подзоны тайги

The growth of artificial origin stands in the clear-cut areas of the taiga zone is closely related to the development of herbaceous vegetation. The aim of the study was to study the dynamics of the species composition and structure of the ground cover of forest plantations at the early stages of formation in the conditions of the middle taiga subzone, as well as to identify the most competitive species in terms of phytocenotic activity. In the course of field studies, the taxonomic composition and ecological and coenotic structure of the living ground cover of experimental pine and spruce crops of the 1st and 2nd age classes were determined, depending on the tillage with plows PLP-135 and PLD-1.2. Species abundance ranges from 32 to 39 species in crops aged 15 years, and from 16 to 36 species in crops aged 23 years. The typological structure of the plant community naturally changes over time. The similarity coefficients for the composition of families in 15-year-old crops vary from 0,48 to 0,89 depending on tillage. Plant communities of forest crops with soil cultivation with the PLP-135 plow and reconstruction of deciduous young growth are the closest to each other in terms of family composition (R = 0,89). Plant communities of the ground cover of forest crops with tillage with the PLD-1.2 plow differ in family composition (0,48…0,58). As a result of phytocenotic analysis, we came to the conclusion that the structure of the ground cover of forest plantations naturally changes over time: the group of highly active species of the ground cover is quite numerous in 15-year-old crops and includes 15 species (33 % of the species composition of the flora). In 23-year-old forest plantations, only four species from the group of highly active plants were identified.

Competitive advantages of HAB species under changing environmental conditions in the coastal waters of the Bohai Sea, Yellow Sea and East China Sea

Harmful algal blooms (HABs) have become a severe ecological problem in coastal waters in recent decades. Under the enhanced anthropogenic disturbance, the Eastern Chinese coastal seas (ECCS), including the coastal waters of the Bohai Sea (BS), Yellow Sea and East China Sea, have been suffering environmental changes dramatically during the past 40 years. However, it is not clear how changes in coastal nutrient pollution, hydrodynamics and climate promote the succession of dominant HAB species simultaneously. In this study we used physical criteria (light availability, temperature and salinity) and chemical criteria (strategy of nutrient utilization) to quantify the competitiveness of the primary HAB species in the ECCS, i.e. Skeletonema costatum, Noctiluca scintillans, Prorocentrum donghaiense, Karenia mikimotoi, and Aureococcus anophagefferens. A risk assessment module has been developed and applied to this study based on the physical criteria of the main HAB species. Model result indicated a strong reliability on locating the potential physical habitat of blooms dominated by specific species. Imbalanced nutrient stoichiometry plays a vital role in HAB species succession in the ECCS, especially potential limitation of dissolved inorganic phosphorus. Due to long water residence time, persistence of nutrient imbalance and organic nutrient accumulation induce frequent blooms of Aureococcus anophagefferens in the BS. Observations and experiments have limitations when describing combining processes that influence HAB development, and need to be complemented with advanced mechanistic models for describing the hydrodynamics and biogeochemistry to allow for hindcasting and forecasting HAB risk under changing environmental conditions.

Microhabitat sharing for basking between squamate species in Poland

Aggregations (e.g. group basking) by snakes are usually limited to specific life cycle phases (e.g. mating) or are a consequence of drastic environmental changes (e.g. habitat destruction), high prey densities or highly limited resources within an environment (e.g. basking sites, wintering dens). Here, we report intra- and interspecific observations of four reptile species (primarily Natrix natrix and Vipera berus) sharing basking sites at the confluence of the rivers Dunajec and Poprad near the town of Stary Sącz in southern Poland. From a total of 84 records in the field between 2020–2022, there were 11 interactions from 24 July 2020 to 1 May 2022. Previous studies have indicated direct competition or interference in many species, which we did not observe. There is a noticeable lack of such observations of microhabitat sharing for basking between squamate species in scientific literature. Hence, the accumulation of such observations has the potential to reveal new insights into the behaviour and ecology of N. natrix and V. berus.

Temporal Activity Patterns of Sympatric Species in the Temperate Coniferous Forests of the Eastern Qinghai-Tibet Plateau.

Temporal niche partitioning is an important strategy for sympatric species or populations when utilizing limited resources while minimizing competition. Different resource availability across seasons may also influence the intensity of competition, resulting in a varied temporal niche partitioning pattern between species. These competitive interactions are important drivers for the formation of biodiversity patterns and species coexistence on the eastern Qinghai-Tibet Plateau. To clarify these interspecies relationships among sympatric species, we carried out a camera trap survey from 2017 to 2020. We deployed 60 camera traps in the temperate coniferous forests of the eastern Qinghai-Tibet Plateau. We analyzed the daily activity patterns of birds and mammals to reveal the temporal niches and seasonal relationships among the species-specific activity rhythms. The results are summarized as follows: (1) Eight major species, including mammals and birds, have different temporal peak activity rhythms to reduce intense competition for resources. (2) The activity rhythm of a species varies seasonally, and the competition among species is more intense in the warm season than in the cold season. (3) Among 15 pairs of competitor species, seven pairs had significantly different coefficients, with higher winter values than summer values, perhaps due to the abundance of resources in summer and the scarcity of resources in winter causing intensified competition. Among the predators and prey, the summertime coefficients were higher than those in winter, perhaps due to the need to replenish energy during the summer breeding season. The main purpose of animals in winter is to survive the harsh environment. Our results provide important information on temporal and interspecies relationships and contribute to a better understanding of species-coexistence mechanisms.

Assessment of the impact of climate change on endangered conifer tree species by considering climate and soil dual suitability and interspecific competition

Climate change results in the habitat loss of many conifer tree species and jeopardizes species biodiversity and forest ecological functions. Delineating suitable habitats for tree species via climate niche model (CNM) is widely used to predict the impact of climate change and develop conservation and management strategies. However, the robustness of CNM is broadly debated as it usually does not consider soil and competition factors. Here we developed a new approach to combine soil variables with CNM and evaluate interspecific competition potential in the niche overlapping areas. We used an endangered conifer species - Chamaecyparis formosensis (red cypress) - as a case study to predict the impact of climate change. We developed a novel approach to integrate the climate niche model and soil niche model predictions and considered interspecific competition to predict the impacts of climate change on tree species. Our results show that the suitable habitat for red cypress would decrease significantly in the future with an additional threat from the competition of an oak tree species. Our approach and results may represent significant implications in making conservation strategies and evaluating the impacts of climate change, and providing the direction of the refinement of the ecological niche model.

Functional structure and interactions within communities composed of cover crops and spontaneous species, along a cropping practices gradient

Inclusion of a cover crop is an interesting way to diversify cropping systems and support ecosystem functions and services impaired by intensified monocultures. However, pure covers are hard to obtain without substantial management, and mixed covers—wherein some spontaneous species coexist with sown cover crops—seem to be a good alternative. Greater insight into factors influencing the composition and density of the spontaneous plant community is needed to achieve relatively good control of the performances of this mixed cover. Here we addressed two questions: 1) How does the functional structure of communities with a highly competitive sown cover crop and/or high initial species diversity differ from the functional structure of communities with the opposite characteristics? 2) Can aboveground species traits explain interactions between cover crops and spontaneous species present in the same community? In a fallowed field in Guadeloupe (West French Indies), we studied communities composed of one sown cover crop species and spontaneous species growing simultaneously in the plot. The study was conducted along two unrelated experimentally-devised gradients resulting from cropping practices: a competitivity gradient of a sown cover crop species and an initial species diversity gradient resulting from an initial soil perturbation induced by the false seedbed technique. These factors (soil tillage modality before cover crop sowing and cover crop species identity) were combined in a split-plot design. Seven and twelve months after cover crop sowing, community species densities and biomasses were assessed. Leaf trait values of the 12 most present species were measured at flowering to describe the functional structure of the community using the community weighted trait means and variances, and a functional diversity index. Our results showed high functional divergence in communities with highly competitive cover crops, which suggests differentiation of functional niches between species, but no clear differences in communities with high and low initial species diversity. We also showed that the studied species were positioned along a gradient from acquisitive to conservative strategies of resource capture and use according to their leaf trait values, regardless of their type (cover crops or spontaneous species), and that cover crop species had higher trait values related to size than spontaneous species. Finally, we demonstrated that interactions between cover crops and spontaneous species could be better explained by the cover crop dynamic height or community biomasses than by the measured aboveground functional traits and that the plant growth habit had a central role. This study shed light on interactions between sown cover crops and spontaneous species, which are pivotal to the design of diversified cropping systems.

Census of potential predators and competitors of sandfish, Holothuria scabra, juveniles during floating hapa ocean nursery culture

AbstractPredation and competition are among the most important factors affecting sandfish, Holothuria scabra, growth and survival in ocean‐based production systems. In this study, the potential predators and competitors of sandfish juveniles reared at two sites in the Philippines using the floating hapa ocean nursery system were assessed. A total of 26 species of potential predators and competitors from 16 different families of fishes, molluscs and crustaceans were recorded. These taxa were dominated by the opisthobranch Stylocheilus striatus at Bolinao (north–west Luzon) and the isopod Cymodoce sp. at Maliwaliw (eastern Visayas). Highest number of potential predators and competitors that recruited and/or migrated to the inside of floating hapa nets was recorded on day 23 at Bolinao and day 30 at Maliwaliw, then decreased over the 69‐day duration of the study. Mean length, absolute growth rates (AGRs) and survival of sandfish juveniles reared in floating hapas at the two sites varied during the study. AGRs were highest at 1.17 ± 0.06 mm day−1 at Bolinao, and 1 ± 0.08 mm day−1 at Maliwaliw, by days 23 and 60, respectively. Mean lengths of sandfish juveniles reared at Bolinao and Maliwaliw by the end of the study were 46.7 ± 0.15 and 58.8 ± 2.4 mm, respectively, and survival at both sites was high at 96% by the end of the study. Negative correlations were observed between the number of individual predators and competitors, and survival and growth rates of sandfish juveniles reared at Bolinao and Maliwaliw, respectively. Our results highlight the importance of predator and competitor management measures and appropriate site selection to optimize growth performance and survival of sandfish juveniles reared in ocean‐based culture production systems.