Diel patterns in sea urchin activity and predation on sea urchins on the Great Barrier Reef

Understanding diel patterns in sea urchin activity is important when assessing sea urchin populations and when interpreting their interactions with predators. Here we employ a combination of surveys and a non-invasive tethering technique to examine these patterns in an intact coral reef system on the Great Barrier Reef (GBR). We also assess local scale variation in relative diurnal predation pressure. Surveys revealed that sea urchins were active and exposed at night. Echinometra mathaei and Echinothrix calamaris were the most abundant species with significantly higher night densities (0.21 and 0.03 ind. m⁻², respectively), than daytime densities (0.05 and 0.001, respectively). Bioassays revealed that exposed adult E. mathaei (the most abundant sea urchin species) were 30.8 times more likely to be eaten during the day than at night when controlling for sites. This observation concurs with widely held assumptions that nocturnal activity is a risk-related adaptive response to diurnal predation pressure. Despite relatively intact predator communities on the GBR, potential predation pressure on diurnally exposed E. mathaei assays was variable at a local scale and the biomass of potential fish predators at each site was a poor predictive measure of this variation. Patterns in predation appear to be more complex and variable than we may have assumed.     

Fish predators and scavengers of the sea urchinEchinometra mathaei in Kenyan coral-reef marine parks

Synopsis Predation on 120 adult sea urchins of the speciesEchinometra mathaei was observed during daylight in shallow-water coral reefs (0.5 to 3 m deep) in a variety of sites in 3 Kenyan marine parks. The predators were few (8 species) and dominated by the triggerfishBalistapus undulatus (65 % of all observations) followed by terminal-male wrassesCoris formosa, C. aygula andCheilinus trilobatus, and lastly the scavengerLethrinus mahsena. Those species that attempted, but failed, to prey onE. mathaei were slightly more numerous (11 species), while scavengers of opened carcasses were the most speciose (20 species). Based on these observations, it is suggested thatB. undulatus is a keystone predator and that fishery regulations that protect this species may be necessary in order to reduce the detrimental consequences of high sea urchin abundance — such as high reef substrate erosion and competitive exclusion of fishes.     

Consumers of sea urchins,<Emphasis Type="Italic"> Paracentrotus lividus</Emphasis> and<Emphasis Type="Italic"> Arbacia lixula</Emphasis>, in shallow Mediterranean rocky reefs

Underwater observations on fish and asteroid consumers (i.e. predators and scavengers) of sea urchins, Paracentrotus lividus and Arbacia lixula, were carried out at several locations in shallow Mediterranean rocky reefs. Observations conducted in the marine reserve of Torre Guaceto (Adriatic Sea) revealed that sparid fishes, Diplodus sargus and D. vulgaris, are the main fish predators of small (<1 cm in test diameter) and medium (1–4 cm) sea urchins, whereas the labrids Coris julis and Thalassoma pavo preyed only upon small sea urchins. Large D. sargus were able to prey upon small and medium, and occasionally large (>4 cm) sea urchins, whereas medium and small Diplodus preyed mainly upon small sea urchins. The number of sea urchins preyed upon by fishes was negatively related to sea urchin size for both species. P. lividus appeared to be subject to higher predation levels than A. lixula. The scavenger guild comprised 11 fish species, with D. sargus, D. vulgaris, Coris julis and Chromis chromis accounting for about 80% of scavenger fishes. Observations performed at several locations in the Mediterranean on the predatory asteroid Marthasterias glacialis revealed that only 3% of the detected individuals were preying upon sea urchins. Due to the importance of sea urchins for assemblage structure and functioning of Mediterranean rocky reef ecosystems, these results may have also important implications for management of fishing activities.Communicated by H.-D. Franke     

Predation cues rather than resource availability promote cryptic behaviour in a habitat-forming sea urchin

It is well known that predators often influence the foraging behaviour of prey through the so-called “fear effect”. However, it is also possible that predators could change prey behaviour indirectly by altering the prey’s food supply through a trophic cascade. The predator–sea urchin–kelp trophic cascade is widely assumed to be driven by the removal of sea urchins by predators, but changes in sea urchin behaviour in response to predators or increased food availability could also play an important role. We tested whether increased crevice occupancy by herbivorous sea urchins in the presence of abundant predatory fishes and lobsters is a response to the increased risk of predation, or an indirect response to higher kelp abundances. Inside two New Zealand marine reserves with abundant predators and kelp, individuals of the sea urchin Evechinus chloroticus were rarer and remained cryptic (i.e. found in crevices) to larger sizes than on adjacent fished coasts where predators and kelp are rare. In a mesocosm experiment, cryptic behaviour was induced by simulated predation (the addition of crushed conspecifics), but the addition of food in the form of drift kelp did not induce cryptic behaviour. These findings demonstrate that the ‘fear’ of predators is more important than food availability in promoting sea urchin cryptic behaviour and suggest that both density- and behaviourally mediated interactions are important in the predator–sea urchin–kelp trophic cascade.     

Predation of the sea urchin Heliocidaris erythrogramma by rock lobsters (Jasus edwardsii) in no-take marine reserves

The formation of sea urchin ‘barrens’ on shallow temperate rocky reefs is well documented. However there has been much conjecture about the underlying mechanisms leading to sea urchin barrens, and relatively little experimentation to test these ideas critically. We conducted a series of manipulative experiments to determine whether predation mortality is an important mechanism structuring populations of the sea urchin Heliocidaris erythrogramma in Tasmania. Tethered juvenile and adult sea urchins experienced much higher rates of mortality inside no-take marine reserves where sea urchin predators were abundant compared to adjacent fished areas where predators were fewer. Mortality of tagged (but not tethered) sea urchins was also notably higher in marine reserves than in adjacent areas open to fishing. When a range of sizes of sea urchins was exposed to three sizes of rock lobsters in a caging experiment, juvenile sea urchins were eaten more frequently than larger sea urchins by all sizes of rock lobster, but only the largest rock lobsters (> 120 mm CL) were able to consume large adult sea urchins. Tagging (but not tethering) juvenile and adult sea urchins in two separate marine reserves indicated that adult sea urchins experience higher predation mortality than juveniles, probably because juveniles can shelter in cryptic microhabitat more effectively. In a field experiment in which exposure of sea urchins to rock lobster (Jasus edwardsii) and demersal reef fish predators was manipulated, rock lobsters were shown to be more important than fish as predators of adult sea urchins in a marine reserve. We conclude that predators, and particularly rock lobsters, exert significant predation mortality on H. erythrogramma in Tasmanian marine reserves, and that adult sea urchins are more vulnerable than smaller cryptic individuals. Fishing of rock lobsters is likely to reduce an important component of mortality in H. erythrogramma populations.     

Size-dependent trait-mediated indirect interactions among sea urchin herbivores

Despite their importance in community interactions, nonlethalindirect effects of predators are not well understood in manymarine food webs. In this study, I found that within a guildof herbivorous sea urchins, small urchins (Strongylocentrotusdroebachiensis and small Strongylocentrotus franciscanus) alteredgrazing rates in the presence of the predatory sea star (Pycnopodiahelianthoides) and were highly preferred by the predator. Incontrast, large urchins (adult S. franciscanus) did not significantlyalter grazing in the presence of cues from the sea star and,when immobile, were less frequently attacked by the predator.However, the sea star's preference (active predator choice)was obscured by sea urchin mobility, that is, small S. franciscanuswas only most preferred when unable to escape. These resultssuggest that by identifying the relative threat of predationfacing guild members and the degree to which individuals transmittrait-mediated indirect interactions, these indirect effectsmay be predictably incorporated in community interactions.     

Evaluation of indicators of nitrogen limitation in deep prairie lakes with laboratory bioassays and limnocorrals

A comparison of Kenyan reefs of different historical and observed levels of fishing exploitation showed that more exploited reef lagoons had greater sea urchin densities and sizes, fewer and smaller fish and less coral cover. In the most exploited lagoon the biomass of the burrowing sea urchin Echinometra mathaei increased five fold during the previous 15 years. An ecological study of the three most common omnivorous sea urchin species inhabiting hard substrate within these reef lagoons (E. mathaei, Diadema savignyi and D. setosum) suggests that they are ecologically separated by predation and avoid predators and competitors by occupying different size burrows or crevices within the lagoon. Predator removal through fishing activities may result in ecological release of the sea urchins and result in competitive exclusion of weaker competitors. The most exploited reef had a nearly monospecific barren of E. mathaei living outside burrows suggesting that E. mathaei may be the top competitor. Its ecological release appears to lead to a decrease in live coral cover, increased substrate bioerosion and eventually a loss of topographic complexity, species diversity, fish biomass and utilizable fisheries productivity. Data from the outer reef edge were more difficult to interpret but may indicate similar patterns. Within this area, physical stresses such as waves and currents may be a greater controlling force in regulating fishing activities and coral reef community structure.     

Environmental factors influencing urchin spatial distributions on disturbed coral reefs (New Caledonia, South Pacific)

Few works have examined the relative contributions of habitat variables to the distribution of coral reef urchins. In the present study, the spatial distribution of two common urchin species (Diadema setosum and Echinometra mathaei) was studied in the fringing reefs of two urban bays in New Caledonia (South Pacific). Urchins were surveyed at 105 stations with contrasted habitat structure/anthropic disturbance levels; 32 environmental variables (water/sediment characteristics, reef structuring species) were considered. Moderate densities were generally observed at station scale (mean 0.5 individuals m^− 2). The combination of univariate and multivariate techniques highlighted patchy distributions for Diadema as well as Echinometra, with distinct species/habitat associations; environmental gradients occurring within the bays did not seem to influence the species patterns. For Diadema, the spatial variability was better explained by sediment type than by biotic cover; increasing densities occurred across habitats with larger sediment sizes and decreasing coral complexity/macrophytes cover. In contrast, the distribution of E. mathaei exhibited weak relationships with habitat variables. In coral reefs, small-scale heterogeneity may thus be responsible for most of urchins spatial variability.     

Can multitrophic interactions and ocean warming influence large‐scale kelp recovery?

Ongoing changes along the northeastern Atlantic coastline provide an opportunity to explore the influence of climate change and multitrophic interactions on the recovery of kelp. Here, vast areas of sea urchin‐dominated barren grounds have shifted back to kelp forests, in parallel with changes in sea temperature and predator abundances. We have compiled data from studies covering more than 1,500‐km coastline in northern Norway. The dataset has been used to identify regional patterns in kelp recovery and sea urchin recruitment, and to relate these to abiotic and biotic factors, including structurally complex substrates functioning as refuge for sea urchins. The study area covers a latitudinal gradient of temperature and different levels of predator pressure from the edible crab (Cancer pagurus) and the red king crab (Paralithodes camtschaticus). The population development of these two sea urchin predators and a possible predator on crabs, the coastal cod (Gadus morhua), were analyzed. In the southernmost and warmest region, kelp forests recovery and sea urchin recruitment are mainly low, although sea urchins might also be locally abundant. Further north, sea urchin barrens still dominate, and juvenile sea urchin densities are high. In the northernmost and cold region, kelp forests are recovering, despite high recruitment and densities of sea urchins. Here, sea urchins were found only in refuge habitats, whereas kelp recovery occurred mainly on open bedrock. The ocean warming, the increase in the abundance of edible crab in the south, and the increase in invasive red king crab in the north may explain the observed changes in kelp recovery and sea urchin distribution. The expansion of both crab species coincided with a population decline in the top‐predator coastal cod. The role of key species (sea urchins, kelp, cod, and crabs) and processes involved in structuring the community are hypothesized in a conceptual model, and the knowledge behind the suggested links and interactions is explored.     

Will pre‐adaptation buffer the impacts of climate change on novel species interactions?

Species are expected to alter their ranges as climates change. Climate‐induced range expansions of predators could threaten evolutionarily naïve prey populations, leading to high mortality at the invasion front. If prey can apply existing defenses against local predators to novel predation threats induced by climate change, mortality threats will be less than expected. Here, we examine if spotted salamander larvae Ambystoma maculatum from populations that coexist with native red‐spotted newts Notophthalmus viridescens survive better when exposed to a novel predator, the marbled salamander Ambystoma opacum. We show that regional mean winter temperatures warmed 2.0°C over 116 yr in the region, and that A. opacum survival increases in ponds with higher winter temperatures. Hence as winters continue to warm, this apex predator will likely colonize ponds north of their current range limit. Next, we performed common garden experiments to determine if local adaptations to native N. viridescens and exposure to A. opacum or N. viridescens kairomones (predator chemical cues) altered A. maculatum survival in predation trials. We did not find evidence for local adaptation to N. viridescens. However, A. maculatum from high‐N. viridescens ponds that were reared with A. opacum kairomones suffered significantly higher mortality from the native predator N. viridescens. This outcome suggests an unanticipated interaction between local adaptation and plastic responses to novel kairomones from a potentially range‐expanding predator. Current projections of biodiversity losses from climate change generally ignore the potential for eco‐evolutionary interactions between native and range‐expanding species and thus could be inaccurate.     

Geotaxis and leaf-surface preferences mitigate negative effects of a predatory mite on an herbivorous mite

Reproductive success and population growth of an herbivorous mite are limited by activities of phytoseiid predators. However, occurrences on upper versus lower leaf surfaces are sometimes mismatched between these prey and predators. The mismatch potentially mitigates predation risk for the prey species. We assessed factors that affect mite distributions on leaf surfaces, testing whether the presence of the phytoseiid mite Phytoseius nipponicus alters the leaf-surface distribution and reproductive success of the herbivorous false spider mite Brevipalpus obovatus. The host plant was Viburnum erosum var. punctatum (Adoxaceae). Leaves were set in natural (TRUE) and reversed (upside down; INVERTED) orientations using experimental devices. Both surfaces were accessible to mites. We detected lower and abaxial leaf-surface preferences in P. nipponicus. In contrast, upper and adaxial surfaces were preferred by B. obovatus. Thus, prey and predatory mites accumulated on different sides of leaves. Presence of the predator also indirectly decreased egg production in B. obovatus. Brevipalpus obovatus females actively avoided leaf surfaces with elevated predator numbers; these females shifted their distributions and changed oviposition sites to leaf surfaces with fewer predators. In consequence, B. obovatus eggs on the upper sides of leaves were less frequently preyed upon than were those on lower sides. We suggest that upper leaf-surface exploitation in this particular herbivorous mite species mitigates predation risk from phytoseiid mites, which prefer lower leaf surfaces.     

Intraguild predation by the generalist predator Orius majusculus on the parasitoid Encarsia formosa

Intraguild predation of Orius majusculus (Reuter) (Heteroptera: Anthocoridae) on Encarsia formosa (Gahan) (Hymenoptera: Aphelinidae), both natural enemies of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), was studied under laboratory conditions. The experiments quantified prey consumption by 5th instar nymphs and adults of O. majusculus offered unparasitised 3rd, early 4th or 4th instar B. tabaci nymphs or parasitised nymphs containing 2nd or 3rd larval instar or pupal parasitoids. In addition, prey preference of the two stages of O. majusculus for parasitised or unparasitised whitefly nymphs was studied using nine different prey combinations. Both predator stages readily preyed upon on both unparasitised and parasitised B. tabaci. In no-choice experiments, predation on 3rd instar E. formosa by adult predators was the highest, while predator nymphs preyed most on unparasitised 3rd instar B. tabaci and 2nd instar parasitoids. Predation of predator stages was lowest on 4th instar B. tabaci and E. formosa pupae. In all prey combinations, both stages of O. majusculus showed a significant preference for parasitised over unparasitised whitefly nymphs except for the combination of 5th instars of O. majusculus with early 4th instar whiteflies and E. formosa pupae. The results indicate that intraguild interactions between O. majusculus and E. formosa may have negative effects on biological control of B. tabaci.     

Does concentrating chemical defenses within specific regions of marine sponges result in enhanced protection from predators?

Chemical defenses are an effective mode of predator deterrence across benthic marine organisms, but their production may come with associated costs to the organism as limited resources are diverted away from primary processes like growth and reproduction. Organisms concentrating ecologically relevant levels of these defenses in tissues most at risk to predator attack may alleviate this cost while deterring predators. We addressed this hypothesis by investigating the deterrence of chemical extracts from the inner and outer regions of the sponges Aplysina fulva, Ircinia felix, and I. campana from a temperate hard-bottom reef in the South Atlantic Bight. Assays were conducted using natural fish assemblages and sea urchins. Although, A. fulva and I. felix have higher concentrations of defensive metabolites in the outer and inner regions, respectively, extracts from these regions did not display enhanced deterrency against fish or mobile invertebrate predators. Likewise, extracts from both regions of the sponge Ircinia campana, which has a uniform distribution of defensive chemicals throughout, did not differ in their ability to deter either group of predators. Since chemical defenses were effective deterrents at lower concentrations, secondary metabolite allocation patterns observed among these sponges are likely not driven by predation pressure from generalist fish and mobile invertebrate predators on these reefs. Alternatively, these patterns may be driven by other ecological stressors, another suite of predators, or may be more effective at deterring predators when combined with structural defenses.     

Coexistence in a sea urchin guild and its implications to coral reef diversity and degradation

Summary Coexistence between the coral reef inhabiting sea urchins Echinometra mathaei, Diadema savignyi and D. setosum was studied by comparing differences in body morphology, distribution, diet, susceptibility to predators, intra- and interspecific competition and settlement. The three species share similar diets and broad within-habitat distributions but differ in their microspatial preferences. E. mathaei is the smallest species, has the highest settlement rates and lives territorially within small burrows or crevices. D. savignyi is intermediate in size and lives frequently in intermediate size crevices or occassionally in social groups. D. setosum is the largest species and occassionally lives in large crevices or more frequently in social groups. Both Diadema have similarily low settlement rates. Competition experiments showed that E. mathaei was consistently the top competitor for crevice space. Diadema species shared larger crevices but competition occured within smaller crevices and was frequently won by the largest individual, regardless of species. D. savignyi may be the top competitor for crevice space between the Diadema species due to a reduced spine length/test size ratio which gives it a larger test for the same crevice size requirement. Predation rates were high for E. mathaei and low for both Diadema species. Coexistence is mediated by predation on the competitive-dominant while predation coupled with different body morphologies and behavior allows spatial resource partitioning of the reef's variable topography. Consequently, the three variables of predation, topographic complexity and differing body shapes create the observed species diversity. A reduction in predators due to stochastic fluctuations or from fishing pressure can lead to E. mathaei population increases and competitive exclusion of Diadema.     

Effects of Covering Behavior and Exposure to a Predatory Crab Charybdis japonica on Survival and HSP70 Expression of Juvenile Sea Urchins Strongylocentrotus intermedius

Predation is a complex process among predator, prey and environment. Juvenile sea urchins are more susceptible to predators than adults, which affects community structure. Behavior is involved in anti-predator responses by changes in the expression of anti-predator responsive genes. Here, we investigated the effects of exposure to a predatory crab Charybdis japonica and covering behavior on survival and HSP70 expression of juvenile sea urchins Strongylocentrotus intermedius. C. japonica consumed large numbers of juvenile S. intermedius in 12 hours with a mortality of 34.17±11.43%. Covering behavior did not significantly reduce predation. Exposure to C. japonica did not significantly upregulate HSP70 expression of juvenile S. intermedius in 12 hours. Covering behavior showed no significant regulative effect on the gene expression of HSP70 of juvenile S. intermedius exposed to C. japonica for 12 hours. The results indicate that the anti-predator function of covering behavior is limited and that HSP70 expression does not appear to play an important role in the anti-predator process of S. intermedius.     

Studies on predation of the mosquito Culex fatigans by Rana tigrina tadpoles

Satiated predation, predation rate and prey preference of different weight groups of Rana tigrina (Daud) tadpoles on different larval and pupal stages of Culex fatigans were studied. Irrespective of the prey and predator size, the satiation time remained more or less equal. There exists a mass-dependent predation: Calculated predation rates or predatory constants (Kpr) showed that I instar prey was preyed upon at about equal rate, while other instars and pupa showed an increasing trend with increasing body weight of the predator. The prey preference assessed using the Kpr, revealed that prey size is an important parameter in predation. The R. tigrina tadpole is a more efficient pupal predator than other mosquito predators.     

Nature and role of newly described symbiotic associations between a sea anemone and gastropods at bathyal depths in the NW Atlantic

The hormathiid sea anemone Allantactis parasitica was found living as an epibiont on numerous species of gastropods at depths of 725-1100 m along the continental slope of eastern Canada. The proportion of bathyal gastropods hosting 1-6 sea anemones reached 72.5% in a single trawl. Although A. parasitica was occasionally found on other substrata (i.e. empty shells, pebbles), laboratory trials confirmed that they preferably associate with living gastropods. Settlement of planula larvae occurred significantly more often on the shells of live bathyal gastropods than on all other substrata present in the tanks. Juvenile sea anemones (∼ 1 mm diameter) readily moved from the mud or other inert substrata onto shells of burrowed bathyal gastropods. Conversely, larvae, juveniles and adults of A. parasitica never associated with any shallow-water gastropods when given the opportunity. Trials exposing predatory sea stars (Leptasterias polaris) from shallow and bathyal depths to bathyal gastropods (Buccinum undatum) with epibiotic A. parasitica, and to asymbiotic bathyal and shallow-water B. undatum, revealed adaptive behaviours in both prey and predator. Shallow-water gastropods (devoid of epibionts) reacted defensively to L. polaris, whereas bathyal gastropods relied mostly on their epibionts to protect them, thus falling prey to L. polaris when the epibionts were removed. L. polaris from bathyal depths typically ignored symbiotic gastropods, but they consistently preyed on asymbiotic ones, while L. polaris from shallow areas initially attempted to prey on all gastropods, but learned to avoid those harbouring sea anemones. Furthermore, living as epibionts afforded sea anemones a means to escape one of their own predators, the sea star Crossaster papposus. The mutualistic relationship between hormathiid sea anemones and bathyal gastropods from the NW Atlantic may have evolved in response to predation pressure.     

Global patterns in the effects of predator declines on sea urchins

Latitudinal gradients in the strength of biotic interactions have long been proposed, but empirical evidence for the expectation of more intense predation, herbivory and competition at low latitudes has been mixed. Here, we use a meta‐analysis to test the prediction that predation pressure on sea urchins, a group of consumers with a particularly strong influence on community structure in the world's oceans, is strongest in the tropics. We then examine which biotic and abiotic factors best correlate with biogeographic and within habitat patterns in sea urchin responses to predation. Consistent with expectations, predator impacts on sea urchins were highest in tropical coral reefs and decreased towards the poles in rocky reef habitats (> 25° absolute latitude). However, latitude and temperature were weakly correlated with effect sizes, and the strongest predictor of predator impacts was sea urchin species. This suggests an important role of prey identity (i.e. traits including behaviour, physical, and chemical defences) rather than large scale abiotic factors in determining variation in interaction strengths. Ecosystem‐shaping sea urchins such as Tripneustes gratilla, Diadema savignyi and Centrostephanus rodgersii were strongly impacted by consumers, indicating a tight coupling between predators of these species and their boom and bust prey. Anthropogenic activities such as over‐fishing, climate change and habitat destruction are causing rapid environmental change, and understanding how predation pressure varies with temperature, across habitats and among prey species, will aid in predicting the likelihood of ecosystem wide effects (via trophic cascades).     

Natural born killers: an invasive amphipod is predatory throughout its life-history

Introduced predators can have profound impacts on prey populations, with subsequent ramifications throughout entire ecosystems. However, studies of predator–prey interaction strengths in community and food-web analyses focus on adults or use average body sizes. This ignores ontogenetic changes, or lack thereof, in predatory capabilities over the life-histories of predators. Additionally, large individual predators might not be physically capable of consuming very small prey individuals. Both situations are important to resolve, as native prey may or may not therefore experience ontogenetic or size refuges from invasive predators. Here, we find that the freshwater amphipod invader, Gammarus pulex, is predatory throughout its development from juvenile through to adult. All size classes collected in the field had a common prey, nymphs of the mayfly Baetis rhodani, in their guts. In an experiment with predator, prey and experimental arenas scaled for body size, G. pulex juveniles and adults consumed B. rhodani in all size-matched categories. In a second experiment, the largest G. pulex individuals were able to prey on the smallest B. rhodani. Thus, the prey do not benefit from any ontogenetic or size refuge from the predator. This corroborates with the known negative population abundance relationships between this invasive predator and its native prey species. Understanding and predicting invasive predator impacts will be best served when interactions among all life-history stages of predator and prey are considered.     

Diel variation in predator abundance, predation risk and prey distribution in shallow-water estuarine habitats

Predation by visual predators is often affected by light conditions and may therefore exhibit strong diel variation. The dominant predators on grass shrimp, Palaemonetes pugio, are finfish predators that are thought to locate their prey by visual cues. We examined the response of grass shrimp to diel variation in predation risk in the nearshore shallow waters of the Chesapeake Bay. We used diel shoreline seines to assess the relative abundance of predators. We assessed the relative risk of predation with shrimp tethered at refuge (30 cm) and nonrefuge (60 cm) depths. To measure grass shrimp response to predation risk, we used dipnets to monitor habitat use. Four predominantly visual predators dominated the shoreline seine catches, Fundulus heteroclitus, Micropogonias undulatus, Morone americana and Morone saxatilis. Total predator abundance had a diel component, with dramatic nighttime decreases in total abundance, whereas guild composition and relative abundance remained unchanged. Relative predation risk for tethered shrimp exhibited significant time by habitat interaction. During the day, depth negatively affected survivorship of tethered shrimp while at night overall survivorship increased and there was no effect of depth. Shrimp habitats use reflected diel predation risks. Abundances in the near shore were highest during the day with decreased abundances at night. Together, the seine and tethering data highlight the importance for a refuge (e.g., shallow water) from predation during the daytime and a relaxation of predation pressure at night.