Individual Predators Research Articles

Determining selectivity of isocycloseram and afidopyropen and their compatibility with conservation biological control in Arizona cotton.

Selective tools, including selective insecticides and transgenic cotton, have been crucial in reducing insecticide usage within the integrated pest management (IPM) plan for Arizona cotton. To guide growers effectively, cotton field trials evaluated the effects of the novel insecticides, isocycloseram and afidopyropen against our primary pests, Bemisia argentifolii and Lygus hesperus, and their impacts on nontarget arthropods, including key predators: Collops spp., Orius tristicolor, Geocoris spp., Misumenops celer, Drapetis nr. divergens and Chrysoperla carnea s.l. Assessments involved over 27 arthropod taxa through community analyses, individual predator abundance, and biological control function via predator to prey ratios and a sentinel prey method. Comparisons were made with an untreated check, a proven fully selective insecticide (flonicamid) and acephate-treated positive controls. Overall, relative to the untreated check, afidopyropen showed no significant differences, whereas isocycloseram exhibited some negative impacts, primarily reducing M. celer and Geocoris spp. nymphs, yet it was less detrimental compared with the positive control, acephate, and it did not affect four of the six key predators and most nontarget arthropods. Afidopyropen was classified as a fully selective insecticide and isocycloseram as a partially selective insecticide. Their fit for conservation biological control in Arizona cotton IPM and similar systems is discussed. © 2024 Society of Chemical Industry. Published by John Wiley & Sons Ltd.

Modeling the structure changes of cold-water copepods Calanus euxinus population under the influence of the black sea depths deoxygenation

The paper presents the results of modeling the possible changes in the structure of the population of Calanus euxinus Hulsemann, 1991 copepods in the Black Sea under the influence of deoxygenation that began in the late 1980s. Over the past 50 years, the depth of oxygen penetration in the deep sea has decreased by almost 50 m. The lower “life limit” of zooplankton in the Black Sea corresponds to the upper boundary of the suboxic layer, where intense copepod aggregation occurs at an oxygen concentration of 10 μM /L. In 1955–1976, this boundary was 130–140 m across the sea, but due to eutrophication and climate change since late 1980s, it has risen in deep water areas to 70–80 m. As a result, the dense copepod layers near the redoxcline and especially their reserve population stock, consisting of non-migrating individuals in diapause, may have been subjected to intensive eating by the Black Sea sprat, which lives to a depth of 100 m and can tolerate hypoxia. To explore this process, we created a new population dynamics model for C. euxinus, which makes it possible to assess changes in the abundance and structure of the population under conditions of a quasi-stationary state and during intensive predation of individuals in diapause. The model describes the dynamics of the Сalanus population based on a statistical description of the relationship between the growth of individuals, their fecundity, the duration of diapause, mortality, and environmental conditions: the concentration of food suspension and temperature in the layer of vertical migration. We put forward the hypothesis that the access of small pelagic fish to the concentration layers of copepods in diapause has a key effect on significant changes in the Black Sea ecosystem, associated with a decrease in the supply of forage plankton and fluctuations in the abundance of pelagic fish.

To pool or not to pool: Pooled metabarcoding does not affect estimates of prey diversity in spider gut content analysis

Abstract Gut content metabarcoding has provided important insights into the food web ecology of spiders, the most dominant terrestrial arthropod predators. In small invertebrates, like spiders, gut content analysis is often performed on whole body DNA extracts of individual predators, from which prey sequences are selectively enriched and sequenced. Since many spider species are generalist predators, large numbers of samples comprising individual spider specimens must be analysed to recover an exhaustive image of a spider species' prey spectrum, which is costly and time‐consuming. Pooled processing of bulk samples of multiple specimens has been suggested to reduce the necessary workload and cost while still recovering a representative estimate of the prey diversity. However, it is still unclear if pooling approaches lead to bias in recovering the prey spectrum and if the results are comparable with data from individually processed spiders. Here, we test the effects of metabarcoding pooled spider gut content on the recovered taxonomic diversity and composition of prey. Using a newly adapted primer pair, which efficiently enriches COI barcode sequences of diverse arthropod prey groups while suppressing spider amplification, we test if pooling leads to reduced taxonomic diversity or skewed estimates of prey composition. Our results show that pooling and individual processing recover highly correlated taxonomic diversity and composition of prey. The only exception are very rare prey items which were less well recovered by pooling. Our results support pooling as a cost‐effective and time‐efficient approach to recover the diet of generalist predators for population‐level studies of spider trophic interactions.

Predatory Potential of Nymphal Odonates on Aedes aegypti Developing in Freshwater and Brackish Water Habitats.

Aedes aegypti, the primary vector of dengue, undergoes preimaginal development in brackish water (BW). However, dengue vector control exclusively targets freshwater (FW) habitats. The present study evaluated the predatory efficacy of nymphal odonates that can develop in both FW and BW. Nymphs of three damselfly and three dragonfly species from FW and BW habitats were identified and acclimatized to FW (<0.5 gL-1 salt) and BW (10 gL-1 salt) mesocosm conditions. The experiment was repeated nine times with nine different individual predators per species under both salinity conditions. One hundred L3 Ae. aegypti from FW and BW laboratory colonies were introduced to determine the predatory rate (PR) and clearance rate (CR) after 24, 48, and 72 h, and one hundred L3 larvae were introduced every 24 h. The dragonfly nymph Hydrobasileus croceus and the damselfly nymph Paracercion hieroglyphicum showed the highest PR and CR under both rearing conditions at all times. However, damselfly and dragonfly nymphs significantly (p < 0.05) differed in their CR under both FW and BW conditions. Thus, all six odonate species have predatory potential and this suggests that they could be used as biological control agents to eliminate preimaginal stages of Ae. aegypti developing in both FW and BW habitats.

Different patterns of coupled predator-prey dynamics when the same species interact in different locations.

Individual predator and prey species exhibit coupled population dynamics in simple laboratory systems and simple natural communities. It is unclear how often such pairwise coupling occurs in more complex communities, in which an individual predator species might feed on several prey species and an individual prey species might be attacked by several predators. To examine this problem, we applied multivariate autoregressive state-space (MARSS) models to 5-year time-series of monthly surveys of a predatory fish, the eastern mosquitofish (Gambusia holbrooki), and its littoral zone prey species, the least killifish (Heterandria formosa), in three locations in north Florida. The MARSS models were consistent with coupled predator-prey dynamics at two of the three locations. In one of these two locations, the estimated densities of the two species displayed classic predator-prey oscillations. In the third location, there was a positive effect of killifish density on mosquitofish density but no detectable effect of mosquitofish density on killifish density. In all three locations, increased submergent vegetation cover was associated with increased prey density but not increased predator density. Eigenvalues analyses for the joint predator-prey dynamics indicated that one of the cyclic locations had more stable dynamics than the other locations. The three different patterns demonstrate that the dynamics of a pairwise predator-prey interaction emerge not only from the characteristics of the prey and the predator, but also those of the habitat and trophic web in which the predator and prey are embedded.

Validation of a new acoustic telemetry transmitter for the study of predation events in small fishes.

Acoustic telemetry has emerged as an important tool for studying the movement and behavior of aquatic animals. Predation-sensing acoustic transmitters combine the functions of typical acoustic transmitters with the added ability to identify the predation of tagged animals. The objective of this paper was to assess the performance of a newly miniaturized acid-based predation-sensing acoustic transmitter (Innovasea V3D; 0.33 g in air). We conducted staged predation events in the laboratory where acoustically tagged rainbow trout (Oncorhynchus mykiss) were fed to largemouth bass (Micropterus nigricans) at 3.3-7.0, 9.0-10.8, 16.0-20.0, and 22.0-25.8°C. We also conducted false-positive tests where tagged rainbow trout were held at 10.0 and 16.8°C without the risk of predation. Predation events were successfully identified in 92% of the staged predation trials. Signal lag (i.e., the time required for a predation tag to indicate that predation occurred) ranged from 0.11 to 6.29 days and decreased strongly with increasing water temperature and increased with increasing body mass of the tagged prey. Tag retention in the gut of the predator was much more variable than signal lag and was influenced by water temperature and individual predators but not by prey mass. No false positives were detected after 60 days at either temperature (n = 27 individuals). Although the relationships between water temperature, signal lag, and retention time are likely species-specific, the data reported here provide useful information for the use of these transmitters to study predation in wild fishes, especially for temperate, freshwater fish.

Functional response and predation rate of Cryptolaemus montrouzieri (Coleoptera: Coccinellidae) to Paracoccus marginatus (Hemiptera: Pseudococcidae) at different temperatures.

The ladybug, Cryptolaemus montrouzieri (Mulsant) (Coleoptera: Cocccinellidae)(Mulsant)(Coleoptera: Cocccinellidae), is a highly efficient predator in controlling mealybug populations and is considered an effective agent for controlling the papaya mealybugs (Paracoccus marginatus) (Williams & Granara de Willink) (Hemiptera: Pseudococcidae). Various criteria have been proposed for evaluating predator effectiveness, with the consumption rate of prey by individual predators, specifically the functional response, emerging as a common and crucial metric. This study evaluated the functional responses of third- and fourth-instar larvae, as well as male and female adults (<48 h old) of C. montrouzieri to adult females of P. marginatus at 3 different temperatures (22 °C, 28 °C, and 35 °C) with 70% ± 5% RH and a 12L:12D h photoperiod. Prey densities were 2, 4, 8, 16, 32, 45, or 60 papaya mealybugs per predator for all tests. The response to prey density by third- and fourth-instar larvae or both sexes of adult C. montrouzieri was a type II at all temperatures. The highest attack rate and lowest handling time were estimated at 28 °C in males and 35 °C in females, respectively. The highest daily prey consumption rate occurred at 35 °C in both the immature and adult stages of C. montrouzieri. These findings support the potential of C. montrouzieri in controlling the papaya mealybug, especially in tropical and subtropical regions, given its search efficiency at high temperatures tested in this study. However, additional field investigations are needed to ascertain the control efficacy of C. montrouzieri for this mealybug in biocontrol programs.

Phenotypes of predator individuals underpin contrasting ecosystem effects

Abstract Intraspecific variability has implications for our understanding of ecosystem functioning. Yet, beyond ontogenetic variation in body size, we know little about how phenotypic differences between individuals modulate ecosystem functioning. We addressed this question empirically within a forested stream, by studying the ecosystem effects triggered by conspecific predatory dragonfly larvae that varied in sex, body shape, behaviour and growth rate. With the help of stream enclosures, we were able to evaluate how different predator phenotypes drive cascading effects on litter‐dwelling prey, fungal biomass and leaf litter decomposition, in uncontrolled natural conditions. Some individual predators increased leaf litter standing stocks and fungal biomass compared to controls (without dragonfly larvae added), but others had the opposite effect. These contrasting effects were repeatable between the two runs of our experiment. Phenotypic effects were related to the sex and the position of individuals along a life history—behavioural continuum, and were possibly mediated by differential top‐down control of prey, or by inter‐individual variability in non‐consumptive effects. Several phenotypic dimensions are likely to mediate individual variability in predator effects on ecosystem processes, even in a complex and stochastic natural context such as a forested stream. We invite further investigations that seek to understand the mechanisms (e.g., non‐consumptive effects) driving individual variability in predator effects on ecosystem processes.

Social attributes shape antipredator behavior strategies in the ruddy ground-dove

The cost-benefit of social behavior depends on group size and the social interaction. As group size increases, competition for resources increases, while individual vigilance may decrease due to the lower probability of individual predation or increased competition for resources. To test predictions of the “many eyes hypothesis” and the “competition hypothesis”, we investigated the effects of social attributes on the vigilance, foraging, direct conflict and sex on social groups of ruddy ground-doves (Columbina talpacoti) in an urban area. We observed that the number of conspecifics did not influence individual foraging behavior, instead, the vigilance decreased as flock size increased. Moreover, the number of conflicts within the flock negatively affected individual vigilance. However, larger flocks exhibited more direct conflicts, and males were more frequently involved in social conflicts, regardless of the sex ratio of the flock. Finally, the investment in both vigilance and foraging was not influenced by the sex of the focal individual or the sex ratio of the flock. Our findings indicate that conspecific numbers and flock social organization significantly influence the cost-benefit dynamics of flocking behavior. Larger flocks enhance vigilance for predator detection but come at an individual cost due to increased resource competition and conflicts.

Numerical response of predator to prey: Dynamic interactions and population cycles in Eurasian lynx and roe deer

AbstractThe dynamic interactions between predators and their prey have two fundamental processes: numerical and functional responses. Numerical response is defined as predator growth rate as a function of prey density or both prey and predator densities [dP/dt = f(N, P)]. Functional response is defined as the kill rate by an individual predator being a function of prey density or prey and predator densities combined. Although there are relatively many studies on the functional response in mammalian predators, the numerical response remains poorly documented. We studied the numerical response of Eurasian lynx (Lynx lynx) to various densities of its primary prey species, roe deer (Capreolus capreolus), and to itself (lynx). We exploited an unusual natural situation, spanning three decades where lynx, after a period of absence in central and southern Sweden, during which roe deer populations had grown to high densities, subsequently recolonized region after region, from north to south. We divided the study area into seven regions, with increasing productivity from north to south. We found strong effects of both roe deer density and lynx density on lynx numerical response. Thus, both resources and intraspecific competition for these resources are important to understanding the lynx population dynamic. We built a series of deterministic lynx–roe deer models, and applied them to the seven regions. We found a very good fit between these Lotka–Volterra type models and the data. The deterministic models produced almost cyclic dynamics or dampened cycles in five of the seven regions. Thus, we documented population cycles in this large predator–large herbivore system, which is rarely done. The amplitudes in the dampened cycles decreased toward the south. Thus, the dynamics between lynx and roe deer became more stable with increasing carrying capacity for roe deer, which is related to higher productivity in the environment. This increased stability could be explained by variation in predation risk, where human presence can act as prey refugia, and by a more diverse prey guild that will weaken the direct interaction between lynx and roe deer.

Combining stable isotope ratios with elemental concentrations to improve the estimation of terrestrial carnivore diets

Stable isotopes of animal tissue have been used to estimate diet for many consumer species and places, but the ability to assign contributions to all food items is limited by the number of tracers used, and the separation of the tracer data among the dietary sources. We tested whether we could detect caribou (Rangifer tarandus) in the diet of individual predators in southwest Canada, where caribou are endangered. The separation between caribou tissue and that of other common prey was minimal using C13 and N15 isotope ratios and our confidence in assigning the caribou diet fraction correctly was low despite testing several fractionation values and priors. We measured the concentration of a suite of elements in the tissue of lichen, large prey and predators to investigate whether we could use an elemental concentration as a diet tracer and better assign the caribou diet fraction, because several of these elements were known to be more abundant in lichen, a major food for caribou in winter. Strontium and cesium had higher concentrations, when normalized by a common salt (we chose calcium), in caribou tissue than the other prey species we measured; this was also true for strontium isotope ratios. The elemental tracers appeared to overestimate caribou in the diet however, we suggest that the addition of either cation could yield finer and more accurate estimates of diet for large terrestrial predators after further investigation. The addition of a strontium isotope ratio tracer to a diet investigation may be equally informative and require less pre-work, because one ratio (Sr87/Sr86) has already been well studied.

Mesopelagic fishes are important prey for a diversity of predators

Through daily vertical movements, mesopelagic fishes contribute to global carbon export and, when eaten, link primary consumers to higher trophic level predators. Although the importance of mesopelagic fishes as prey to individual predator species has been explored, a comprehensive assessment of mesopelagic fishes as prey at the scale of a large marine ecosystem would advance our observing, modeling, and predicting of biodiversity and ecosystem function. We use diet samples from over 105,000 individual predators from 143 taxa in the California Current Ecosystem (CCE) to quantify and evaluate the role of mesopelagic fishes as prey. For 11 predator taxa, including protected mammal species, pelagic squids, a shelf-edge-associated rockfish and highly migratory species, mesopelagic fishes occurred in greater than 25% of all diet samples, likely comprising an important source of prey. Of the 143 taxa represented, individuals from 36 taxa, or 25% percent of all predator taxa in the database, consumed at least one mesopelagic fish species, including economically important fishery species such as Bluefin tuna (16% of all non-empty diet samples), Albacore (19%), Swordfish (50%), Humboldt squid (52%), and Pacific hake (4%). Compared with coastal pelagic fish species (essential prey in the CCE), mesopelagic fish were more frequently encountered in the diets of 21 predator taxa. Lanternfish (family Myctophidae) were the most common prey and consumed by the greatest diversity of predators (32 taxa), but an additional 16 families of mesopelagic fishes were also consumed by predators, highlighting the diversity of organisms inhabiting mesopelagic depths. Mesopelagic fishes were found in the diets of predators collected from shelf depths to well offshore, accentuating the role of mesopelagic fishes as prey across habitats, especially for predators foraging over the slope and further offshore. Our work illuminates the importance of mesopelagic fishes as prey to a diversity of economically valuable and protected species, underscoring the need to incorporate mesopelagic fishes more comprehensively into food web models, global carbon budgets and ultimately our understanding of ecosystem function.

A multi-predator trophic database for the California Current Large Marine Ecosystem

The California Current Trophic Database (CCTD) was developed at NOAA Southwest Fisheries Science Center in collaboration with numerous diet data contributors. We compiled the CCTD from twenty-four data sets, representing both systematic collections and directed trophic studies. Diet composition data, including stomach and scat samples, were obtained from 105,694 individual predators among 143 taxa collected throughout the California Current Large Marine Ecosystem (CCLME) from 1967–2019. Predator taxa consist of squids (n = 5), elasmobranchs (n = 13), bony fishes (n = 118), and marine mammals (n = 7). Extensive time series are available for some predators (e.g., California Sea Lion, Pacific Hake, Chinook Salmon). The CCTD represents the largest compilation of raw trophic data within the CCLME, allowing for more refined analyses and modeling studies within this region. Our intention is to further augment and periodically update the dataset as additional historical or contemporary data become available to increase its utility and impact.

Ecological uncertainty and antipredator behaviour: an integrative perspective

Due to its unforgiving nature, predation pressure exerts strong selection pressure on the behaviour of prey animals. As a result, prey are forced to balance the conflicting demands of successfully detecting and avoiding predators and the need to engage in other fitness-related activities such as foraging, mating and social behaviour. Here, we provide an overview of the role that individual predator avoidance decisions plays in constraining behavioural phenotypes and how past experience with risks shapes current (and future) trade-offs, physiological and life history investments. Critically, access to reliable risk assessment information allows prey to respond to spatially and temporally variable predation risks. Uncertainty of predation risks is expected to limit the ability of prey to make short- and longer-term adjustments responses to predation threats, potentially increasing the indirect costs of predation. We describe a ‘landscape of information’ in which prey rely on publicly available risk assessment information to reduce the uncertainty of predation risks associated with variable threats and the potential impact of natural and anthropogenic environmental factors which may limit information availability. Despite a long tradition of research into the antipredator trade-offs made by prey animals, there remain a number of important unanswered questions.

Modulation of prey size reveals adaptability and robustness in the cell cycle of an intracellular predator

Despite a remarkable diversity of lifestyles, bacterial replication has only been investigated in a few model species. In bacteria that do not rely on canonical binary division for proliferation, the coordination of major cellular processes is still largely mysterious. Moreover, the dynamics of bacterial growth and division remain unexplored within spatially confined niches where nutrients are limited. This includes the life cycle of the model endobiotic predatory bacterium Bdellovibrio bacteriovorus, which grows by filamentation within its prey and produces a variable number of daughter cells. Here, we examined the impact of the micro-compartment in which predators replicate (i.e., the prey bacterium) on their cell-cycle progression at the single-cell level. Using Escherichia coli with genetically encoded size differences, we show that the duration of the predator cell cycle scales with prey size. Consequently, prey size determines predator offspring numbers. We found that individual predators elongate exponentially, with a growth rate determined by the nutritional quality of the prey, irrespective of prey size. However, the size of newborn predator cells is remarkably stable across prey nutritional content and size variations. Tuning the predatory cell cycle by modulating prey dimensions also allowed us to reveal invariable temporal connections between key cellular processes. Altogether, our data imply adaptability and robustness shaping the enclosed cell-cycle progression of B.bacteriovorus, which might contribute to optimal exploitation of the finite resources and space in their prey. This study extends the characterization of cell cycle control strategies and growth patterns beyond canonical models and lifestyles.

KAPASITAS POTENSI PARASITISME Trichogramma sp. (Hymenoptera: Trichogrammatidae) TERHADAP Corcyra sp.

Parasitism research Trichogramma sp. (Hymenoptera: Trichogrammatidae) has been carried out with the aim of studying the functional response of the parasitoid Trichogramma sp. Functional response is one measure to determine the effectiveness of a predator or parasitoid as an agent in biological control, so that it can express a change in the number of preys attacked by individual predators. Temperature is one of the most important host-parasitoid interactions in functional responses. The method used in the parasitoid parasitism Trichogramma sp. on the host Corcyra sp. using four levels of egg density Corcyra sp. with two different temperature treatments (27OC and room temperature). The results show the functional response model of the parasitoid Trichogramma sp. against its host Corcyra sp. described in the type I model. Parasitization level of Trichogramma sp. showed the same results for both temperature treatments, however, it also shows differences in the speed of predation. It also showed linearity between the parasitoids Trichogramma sp. with the host Corcyra sp. Parasitism rates are still increasing, along with an increase in host density. This research can be a starting point to improve the control of Corcyra sp. using the parasitoid Trichogramma sp. in the field.

Mass mortality of the invasive alien echinoid Diadema setosum (Echinoidea: Diadematidae) in the Mediterranean Sea.

The sea urchin Diadema setosum is an ecological key species across its range, particularly on coral reefs. In 2006 D. setosum was first observed in the Mediterranean Sea, and since, it has proliferated to occupy the entire Levantine Basin. Here we report the mass mortality of the invasive D. setosum in the Mediterranean Sea. This is the first report of D. setosum mass mortality. The mortality spans over 1000 km along the Levantine coast of Greece and Turkey. The current mortality shows similar pathologies to previously reported Diadema mass mortality events, suggesting pathogenic infection as the cause of mortalities. Maritime transport, local currents, and fish predation of infected individuals may distribute pathogens at varying geographical scales. Due to the proximity of the Levantine Basin to the Red Sea, the risk of pathogen transport to the native Red Sea D. setosum population is imminent-with potentially catastrophic consequences.

Understanding species responses in a changing world by examining the predatory behaviour of southern calamari to changes in temperature

Predator–prey interactions are key drivers in structuring communities, with the potential to substantially impact the whole ecosystem when important predators and prey are involved. Squid are voracious predators and also important prey for other top predators. To date, the available data suggests that under current and projected ocean warming, the behaviour of ectotherms could be modified (for example, through individual movement, predator avoidance and escape speed), yet little is known of the influence of temperature on the predatory behaviour of cephalopods. Here, the predatory behaviour of adult southern calamari (Sepioteuthis australis) under different thermal scenarios was examined demonstrating that squid exhibited different behaviour and performance capabilities across temperature treatments. Overall, attempts of squid to capture prey were faster and more persistent at higher temperature treatments (25°C), suggesting that individuals need to increase their food consumption rate, presumably associated with the higher energetic costs of living at elevated temperatures. However, we also observed a possible decrease in capture efficiency and increased prey handling time at higher temperatures suggesting that implications for energetic balance are not straightforward and that trade-offs need to be carefully explored. As cephalopods are ecologically important species acting as key links in food webs around the world, the results here could have important implications for the dynamics of many marine ecosystems in future.

The Effects of Intraguild Predation on Phytoplankton Assemblage Composition and Diversity: A Mesocosm Experiment.

Intraguild predation (IGP) can have a significant impact on phytoplankton biomass, but its effects on their diversity and assemblage composition are not well understood. In this study, we constructed an IGP model based on the common three-trophic food chain of "fish (or shrimp)-large branchiopods (Daphnia)-phytoplankton", and investigated the effects of IGP on phytoplankton assemblage composition and diversity in outdoor mesocosms using environmental DNA high-throughput sequencing. Our results indicated that the alpha diversities (number of amplicon sequence variants and Faith's phylogenetic diversity) of phytoplankton and the relative abundance of Chlorophyceae increased with the addition of Pelteobagrus fulvidraco, while similar trends were found in alpha diversities but with a decrease in the relative abundance of Chlorophyceae in the Exopalaemon modestus treatment. When both predators were added to the community, the strength of collective cascading effects on phytoplankton alpha diversities and assemblage composition were weaker than the sum of the individual predator effects. Network analysis further showed that this IGP effect also decreased the strength of collective cascading effects in reducing the complexity and stability of the phytoplankton assemblages. These findings contribute to a better understanding of the mechanisms underlying the impacts of IGP on lake biodiversity, and provide further knowledge relevant to lake management and conservation.

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.