Feeding ecology and niche segregation in oceanic top predators off eastern Australia

We examined the feeding ecology and niche segregation of the ten most abundant fish species caught by longline operations off eastern Australia between 1992 and 2006. Diets of 3,562 individuals were examined. Hook timer data were collected from a further 328 fish to examine feeding behaviour in relation to depth and time of day. Prey biomass was significantly related to predator species, predator length and year and latitude of capture. Although the fish examined fed on a mix of fish, squid and crustacea, fish dominated the diet of all species except small albacore (Thunnus alalunga) which fed mainly on crustacea and large swordfish (Xiphias gladius) and albacore which fed mainly on squid. Cannibalism was observed in lancetfish (Alepisaurus spp.). Multidimensional scaling identified three species groups based on their diet composition. One group consisted of yellowfin tuna (T. albacares), striped marlin (Tetrapturus audax) and dolphinfish (Coryphaena hippurus); a second group consisted of bigeye tuna (T. obesus), swordfish and albacore; and a third consisted of southern bluefin tuna (T. maccoyii) and blue shark (Prionace glauca). Of note was the separation of mako shark (Isurus oxyrhynchus) and lancetfish from all other predators. Prey length generally increased with increasing predator length although even large predators fed on a wide range of prey lengths including very small prey. Overall, differences in prey type and size, feeding times and depths were noted across the range of species examined to the extent that predators with overlapping prey, either in type or size, fed at different times of the diel period or at different depths. Taken together these data provide evidence for feeding niche segregation across the range of oceanic top predators examined.     

Distribution and abundance of fish larvae off the coast of West Pakistan

The material was collected during 4 different cruises on the shelf off the coast of W. Pakistan in November–December, 1964 and in March, 1967 and 1968. The hydrography as well as the zooplankton-biomass distribution are briefly described. A total of 5777 larval fish were taken in 33 positive vertical hauls by an Indian Ocean Standard Net. The number of larvae in positive hauls ranged from 2 to 1262 larvae haul^-1. The most productive area of the ichthyoplankton was the waters south of Karachi, covered during the Machera Cruise, where 828 to 1262 larvae haul^-1 were obtained. The larvae were identified to species, genera or family. Sardinella sindensis (specific identification uncertain) larvae dominated in abundance. The other abundant larvae belonged to Benthosema spp., Amentum commersonii, Vinciguerria spp. and Diaphus spp. Larval distributions and abundances are described. Aggregation and spawning of adult Sardinella (sindensis) in the waters off the coast of W. Pakistan in November/December, 1964, are discussed. Presumably, the waters south of Karachi represent good feeding grounds for s. (sindensis) larvae. Displacement volume, length and weight relationships of various larval size groups have been studied and a high rate of larval mortality (at a length of 5.0 to 8.5 mm) observed.     

Feeding ecology of herring (Clupea harengus) larvae in the turbid Blackwater Estuary

Most studies on feeding by herring larvae (Clupea harengus) have taken place in clear, open waters, but several herring stocks around the world spawn in inshore and estuarine regions. An example is the spring-spawning Blackwater Estuary (Essex, England) stock. Samples were collected in this estuary to examine prey selectivity and feeding levels in relation to biological and environmental conditions. Herring larvae negatively selected copepod nauplii, but positively selected the copepodite and adult stages of Acartia spp. Gastropod larvae were also positively selected. Particles >150 μm width were preferred, whilst particles smaller than this value were preferentially rejected. Concentrations of potential prey items in the water were in the range of 6.0 to 49.7 organisms l⁻¹ with a median concentration of 15.0 organisms l⁻¹ (n = 26). These values are towards the low end of prey concentrations quoted in the literature as being required to sustain herring larval growth and survival. However, theoretical considerations suggest that, in this environment, levels of tidally-induced turbulence enhance encounter rates between larval herring and their prey. On the other hand, turbidity is also related to tidal current speed and might reduce feeding success by decreasing underwater light levels. Measurements at two sites in the estuary confirmed that tidally-induced turbidity reduced the effective water depth in which herring larvae could visually feed by up to 50% at times of peak current speed. However, with the gut-content data available in the present study, it was not possible to discern any clear relationships between feeding success and the state of the tide. Feeding success appeared to be more strongly influenced by surface light-levels. Received: 24 June 1998 / Accepted: 17 February 1999     

Feeding ecology of juvenile rockfishes off Oregon and Washington based on stomach content and stable isotope analyses

The feeding habits of pelagic, juvenile rockfishes (Sebastes spp.) collected off Oregon in 2002, and Oregon and Washington in 2006, were examined using stomach content and stable isotope analyses. Sampling occurred along a series of transects across the shelf between Crescent City, California (Lat. 41°54.0′), and Newport, Oregon (Lat. 44°39.0′), in 2002, and off Willapa Bay, Washington (Lat. 46°40.0′), and the Columbia River, Oregon (Lat. 46°10.0′), in 2006. Species composition varied both years with distance from shore, but the predominant species were darkblotched (Sebastes crameri), canary (S. pinniger), yellowtail (2006 only; S. flavidus), and widow (S. entomelas) rockfishes. Stomach content analysis revealed that darkblotched rockfish had highly variable diets, and canary, yellowtail, and widow rockfishes exhibited a high degree of overlap in 2006. Multivariate analysis showed significant differences in diet based on distance from shore where caught, fish size, and species. Stable isotope analysis indicated that all species were feeding at about the same trophic level within each year, with a 1.5 ‰ difference in δ¹⁵N between years and regions. The difference in δ¹⁵N values may indicate a greater contribution of mesotrophic zooplankton such as euphausiids, hyperiid amphipods, and chaetognaths to fish diets in 2006. Depleted ¹³C values were indicative of diets based on primary production from a more offshore origin, suggesting that these rockfish had previously inhabited offshore waters. These results add to our understanding of some of the important environmental factors that affect young-of-the-year rockfishes during their pelagic phase.     

Feeding ecology of five fishes from the mid-slope micronekton community off southern Tasmania, Australia

We examine the feeding ecology of characteristic micronekton species inhabiting the mid-slope region (~700 to 1,500 m depths) off southern Tasmania. Five fishes, Diaphus danae, Hygophum hanseni, Lampanyctus australis (Myctophidae), Phosichthys argenteus (Phosichthyidae) and Chauliodus sloani (Chauliodontidae), were sampled by depth-stratified midwater trawling on a diel and seasonal basis. Overall, 74 prey taxa were identified from 2,132 stomachs. Euphausiids (mostly Euphausia spinifera and E. similis) and calanoid copepods (mostly Pleuromamma species) were the main prey of the three myctophids; P. argenteus ate fishes and decapods in addition to the euphausiids, while C. sloani ate only fishes. Copepods were less important in the diets of larger D. danae, L. australis and P. argenteus and were replaced by euphausiids in the myctophids and by fishes in P. argenteus. In autumn, when euphausiid biomass increased six-fold, all three myctophids and P. argenteus fed most intensively and consumed a high proportion of euphausiids. The three myctophids appeared to feed nocturnally. Differences in the timing and duration of feeding corresponded to differences in their spatio-temporal overlap with key prey. Daily rations of H. hanseni (1.93% dry-weight biomass) and L. australis (1.43%), estimated from data on stomach fullness, were typical for temperate myctophids and higher than that of the non-migratory P. argenteus (0.43%). The vertical flux of near-surface plankton production to the mesopelagic food web is based primarily on diel feeding in the upper water column (<500 m) rather than consumption of species that migrate seasonally into the deeper mesopelagic zone. Because species such as P. argenteus and C. sloani feed above the third trophic level, their predators, including the commercially important orange roughy, are feeding between levels four and five.     

Water and salt balance of halibut eggs and larvae (Hippoglossus hippoglossus)

Eggs of halibut [Hippoglossus hippoglossus (L.)] have a negative buoyancy in sea water of 35 S, in contrast to eggs of most flatfish species. The cause of this was investigated. The osmolality of the yolk is 350–420 mOsm during embryonic development. This is within the range for marine teleost serum and for yolk of pelagic eggs. Concentrations of major inorganic ions are comparable with those of pelagic plaice eggs [Pleuronectes platessa (L.)]. The values for Na⁺, K⁺ and Cl^- are 6, 85, and 64 mmol · (1 H₂O)^-1 after fertilization, and at the time of hatching the corresponding values are 17, 11, and 80. Large amounts of other inorganic constitutents are excluded for osmotic reasons. Malfunction in the regulation of osmolality or of inorganic constituents is thus unlikely to be the cause of negative buoyancy. The relative dry weight of the chorion (egg shell) in halibut eggs is less than in several pelagic egg types, excluding the chorion as the main contributor of negative buoyancy. It is concluded that a high content of organic matter in the rest of the egg is the cause of the negative buoyancy.     

Feeding and burrowing ecology of two East African mangrove crabs

The behavior and ecology of two mangrove crabs,Sesarma meinerti De Man, 1887 andCardisoma carnifex (Herbst, 1794) were investigated at the beginning of the rainy season (October–November 1988) at Mida Creek, Kenya. Both species occupy upper intertidal levels, above mean high-water neap, and completely overlap in their zonation. Each burrow lasts ca. 3 wk, with no significant difference between the species. Both are more active around dusk and dawn and also follow a similar trend in their foraging activity, but differ in that burrowing is mainly diurnal inC. carnifex and nocturnal inS. meinerti. A hierarchy of food preference, established by offeringC. carnifex andS. meinerti leaves of five mangrove species, proved similar for both, withBruguiera gymnorhiza ranking first andAvicennia marina last, but significant only forC. carnifex. A rough estimate of the amount of litter consumed by these two species and of the soil mixed up by their burrowing activity indicates that they play a role of primary importance in the ecology of East African mangroves.     

Feeding ecology and evolutionary survival of the living coelacanth Latimeria chalumnae

One concept of evolutionary ecology holds that a living fossil is the result of past evolutionary events, and is adapted to recent selective forces only if they are similar to the selective forces in the past. We describe the present environment of the living coelacanth Latimeria chalumnae Smith, 1939 at Grande Comore, western Indian Ocean and report depth-dependent cave distribution, temperature, salinity and oxygen values which are compared to the fish's distribution and its physiological demands. We studied the activity pattern, feeding behaviour, prey abundance and hunting success to evaluate possible links between environmental conditions, feeding ecology and evolutionary success of this ancient fish. Transmitter tracking experiments indicate nocturnal activity of the piscivorous predator which hunts between approximately 200 m below the surface to 500 m depth. Fish and prey density were measured between 200 and 400 m, both increase with depth. Feeding tracks and feeding strikes of the coelacanth at various depths were simulated with the help of video and laser techniques. Along a 9447 m video transect a total of 31 potential feeding strikes occurred. Assuming 100% hunting success, medium-sized individuals would obtain 122 g and large females 299 g of prey. Estimates of metabolic rates revealed for females 3.7 ml O₂ kg⁻¹ h⁻¹ and for males 4.5 ml O₂ kg⁻¹ h⁻¹. Today coelacanths are considered to be a specialist deep-water form and to inhabit, with their ancient morphology, a contemporary environment where they compete with advanced, modern fish. Received: 5 July 1999 / Accepted: 11 November 1999     

Evaluation of fatty acids as biomarkers for a natural plankton community. A field study of a spring bloom and a post-bloom period off West Greenland

An investigation of the fatty acid composition of a natural arctic plankton community was carried out over two fishing banks located between 63°N and 65°N off the West Greenland coast. Samples for fatty acid analyses, species determination and biomass assessments of the plankton community were taken at the depth of fluorescence maximum. High biomass and diatom dominance during the spring bloom and low biomass and flagellate dominance in the post-bloom period were reflected by the fatty acid profiles. The total amount of fatty acid ranged from 55 to 132 µg l^-1 during the spring bloom and from 1 to 5 µg l^-1 during the post bloom. Analysis of the fatty acids showed that when the plankton was dominated by diatoms of the genera Thalassiosira and Chaetoceros, the proportions of C16:1(n-7) and C20:5(n-3) were correspondingly high. C18s, and particularly C18:1(n-9), were more abundant when the plankton was dominated by small autotrophic flagellates, primarily haptophytes. We found a good positive correlation between the common diatom marker, C16:1(n-7)/C16:0, and the biomass percentage of diatoms (r=0.742, P<0.001), as well as between the biomass percentage of flagellates and total C18 fatty acids (r=0.739, P<0.001). This supports the use of these specific fatty acids and fatty acid ratios as general biomarkers of the plankton community. However, the fatty acids are not specific enough to sufficiently characterise the composition of the plankton community, and microscopical support is needed to verify observed trends.     

Development and drift of northern shrimp larvae (<Emphasis Type="Italic">Pandalus borealis</Emphasis>) at West Greenland

This is the first study of the West Greenland offshore population of Pandalus borealis in recent history that covers all larval stages. Shrimp larvae were sampled on the fishing banks off the west coast of Greenland from 63.5°N to 67°N in May, June and July. Abundances decreased during the summer as did cumulated mortality rates [0.06 day^–1 (ZI) to 0.04 day^–1 (ZVI)]. Modelling stage development time as a function of temperature alone by means of the Blehrádek function gave decreasing stage durations from 22.7 to 16.7 days. Drift buoys showed a northbound current with an average velocity of 0.06 m s^–1. Potential spawning grounds of shrimp larvae were located from back-calculation by coupling development times and mortality rates with current velocity. This showed larval transport of up to 500 km. The adult female shrimp abundances were estimated to 0.12–96 females per 100 m², and locations of the estimated spawning stock agreed with observations from trawl surveys.Communicated by L. Hagerman, Helsingør     

Feeding rates of the jellyfish Aurelia aurita on fish larvae

We quantified feeding rates of field caught Aurelia aurita feeding on yolk sac cod (Gadus morhua) larvae in a series of incubation experiments. A short-time (~1 h) functional response experiment with a wide range of prey concentrations (0.5–16 prey l⁻¹, initial concentration) revealed that ingestion rates increased linearly over this range, such that clearance rates were similar between the different prey concentrations. This suggests that A. aurita is capable of efficiently utilizing dense prey patches. This indication was further supported by a linear increase of prey captured by A. aurita during 2.5 h of feeding at extremely high prey concentration (>200 prey l⁻¹). Clearance rate in darkness scaled with jellyfish diameter to a power of ~1.7 for jellyfish 3.9–9.5 cm in diameter. The jellyfish did not alter their umbrella pulse frequency in response to presence of fish larvae. There were no significant differences between A. aurita feeding rates in light and darkness for yolk sac prey ages 0–7 days (at 7.5°C). Although prey vision and escape abilities of fish may develop rapidly during early larval ontogeny, these factors apparently have little impact on interactions with predators such as A. aurita during the yolk sac stage.     

Feeding ecology of benthopelagic zooplankton on an eastern tropical Pacific seamount

The gut contents of dominant deep-sea benthic boundary layer zooplankton (primarily copepods and mysids) and the vacuole contents of phaeodarians collected and preserved in situ at four depths (from 724 to 3112 m) on an eastern tropical Pacific seamount (Volcano 7; 13°23N, 102°27W) between 23 November and 4 December 1988 were analyzed using transmission electron microscopy (TEM). Suspended, and sinking plus resuspended particles, were quantitatively sampled to characterize potential food sources. The broad oxygen minimum characteristic of this region intersects the summit of the seamount and affects the feeding ecology of these organisms. Several copepods and mysids and an amphipod contained guts packed with what appeared to be gram-positive bacteria, an unusual finding. We hypothesize that the source of these bacteria-like bodies was a mat or aggregate that originated in the oxygen minimum or at its upper or lower interface. The presence of the bacteria-like bodies in 43 to 100% of the particlefeeding zooplankton that were sectioned and that had gut contents, suggests that the bacteria-like bodies are an important food source. The diverse gut and vacuole contents of other detritivores were similar among depths. Particles and microorganisms from the depths were also similar. This finding can be explained by the rapid sinking of particles and aggregates from surface waters and their relatively intact transit through the broad oxygen minimum with its reduced populations of zooplankton. The presence of algal cells in guts and vacuoles of benthic boundary-layer zooplankton suggests that these zooplankton select particles of recent surface origin for consumption. The presence of the guts filled with bacteria-like bodies shows that some deep-sea copepods and mysids that are normally generalist feeders can specialize opportunistically. The similarity of gut contents of crustaceans and vacuole contents of phaeodarians suggests that these two very different groups of particle feeders utilize similar food sources in the deep sea.     

Description of the early development of the halibut Hippoglossus hippoglossus and attempts to rear the larvae past first feeding

Rearing experiments on the halibut Hippoglossus hippoglossus (L.) were carried out using gametes from parents caught at a depth of 600 to 700 m off the Norwegian coast in February 1980. After fertilization, the average egg diameter was 3.08 mm, average dry weight 1 038 μg and neutral buoyancy was at 36.5‰ S. The eggs hatched after 20 d at 4.7°C, 18 d at 5°C and 13 d at 7°C. Survival to hatching was better when antibiotics were used. At hatching the larvae were 6.4 mm long, there were no functional eyes or mouth, but prominent neuromast organs were present. Resorption of yolk lasted 50 d at 5.3°C; the eyes and mouth were then functioning and the larva was about 11.5 mm long. The larvae were offered zooplankton as food, but with little success in initial feeding. A few larvae fed and grew in 2 500-litre plastic bags, one reaching a length of 24 mm after 90 d.     

Feeding ecology of the lanternfish Benthosema pterotum from the Indian Ocean

The feeding ecology of lanternfish Benthosema pterotum (Alcock) from the north Arabian Sea, Mozambique and the Bay of Bengal was studied. Samples were collected on cruises carried out by R.V. Dr. Fridtjof Nansen during the period 1978 to 1983. A wide variety of zooplankton organisms were identified in the diet of B. pterotum with crustanceans dominating the diet. Copepods constituted ca. 40 to 90% of the diet. Dry weight analyses of the stomach contents from the Gulf of Oman in February 1983 showed copepods to be 35 to 55% in weight (average in samples). Ontogenetic differences were observed in the diet. Prey size increased as the fish length increased, but the largest fish did not exclude the smaller prey organisms from their diet. Regional variation in diet was also shown in B. pterotum. The degree of filling and the state of digestion of stomach contents revealed that this species feeds intensively at night in the epipelagic layer. All copepods indentified were epipelagic species, providing additional evidence of diurnal pattern in the feeding chronology of B. pterotum. Identification of copepods from the Gulf of Oman in February 1983, revealed that herbivorous species dominated in biomass. Quantitative analyses show that B. pterotum probably have a daily food intake of ca. 4.5% of the body weight.     

Compartmental distribution of free amino acids and protein in developing yolk-sac larvae of Atlantic halibut (Hippoglossus hippoglossus)

Free amino acids (FAA) and protein have been measured in whole laboratory-readed halibut larvae and on dissected individuals separated into yolk and body compartments. At hatching both FAA and protein are mainly located in the yolk compartment. During the first 12 d of the yolk-sac stage more than 70% of the FAA pool disappeared from the yolk without any significant changes in the yolk protein pool. This suggests different uptake mechanisms for FAA and protein from the yolk, and a sequential utilisation of the endogeneous reservoirs of free and protein amino acids in Atlantic halibut larvae. The data suggest that in the early yolk-sac stage FAA enter the embryo from the yolk and are utilised both for energy and protein synthesis. Later on when the free pool cannot fulfil the nutritional requirements, additional amino acids are recruited from yolk protein. Of the total amino acids (free + protein amino acids) present at hatching ca. 60% will be used as precursors for body protein synthesis while the remaining 40% are used as fuel in the larval energy metabolism.     

Influence of different levels of dissolved oxygen on the success of Greenland halibut (Reinhardtius hippoglossoides) egg hatching and embryonic development

The aim of this study was to determine the influence of different levels of dissolved oxygen (DO) on embryonic development (ED) and hatching success of Greenland halibut (Reinhardtius hippoglossoides) eggs. Fertilized eggs from six females were exposed to five DO levels: severely hypoxic (10 and 20?%sat [percent saturation]), moderately hypoxic (35 and 50?%sat), and normoxic (100?%sat). Greenland halibut eggs were highly tolerant to hypoxia, with hatching occurring at levels as low as 20?%sat. In severely hypoxic conditions (10?%sat), ED was impaired and no hatching occurred. Lipid composition, during ED, changed as a function of female origin and DO levels. Phospholipids were the dominant lipid class in eggs. Although triacylglycerols were a minor lipid class in terms of abundance, they were only used under severe hypoxia. The results suggest that severe hypoxia (between 10 and 20?%sat) has detrimental effect on the early development of Greenland halibut and may result in reduced recruitment and lower population abundance if the decreasing trend in the DO levels observed in the bottom waters of the Gulf of St. Lawrence continues in the future. Other species that share similar life histories may also be at risk.     

Phytoplankton ecology and production in the Red Sea off Jiddah,Saudi Arabia

Phytoplankton species diversity was generally high throughout the year at two stations in the central Red Sea (Lat. 21°30N), and species of Mediterranean and Indian Ocean origin were represented, reflecting seasonal monsoonal influence. Low phytoplankton cell numbers accompanying high production rates suggest the significance of nanoplankton or picoplankton which were not enumerated. Production was high year-round, and averaged 390 gC m^-2 yr^-1, despite the virtual lack of nutrient additions from rainfall or land runoff or demonstrable upwelling. Highest nutrient levels followed the first seasonal peak of production. Biomass and production were seasonally bi- or tri-modal, with major peaks in December–February and June–August, 1977–1978. The first peak of production, populated by diatoms, occurred at the onset of seasonal stratification, but the second peak, populated by Trichodesmium spp., occurred at the height of seasonal stratification and lowest nutrient concentrations. There is no clear relationship between the timing of monsoon activity and the annual production cycle.     

Reproductive cycles of three dominant Calanus species in Disko Bay, West Greenland

This study describes the annual reproductive cycles of the three dominant Calanus species, C. finmarchicus, C. glacialis and C. hyperboreus, in Disko Bay (West Greenland) in relation to seasonal phytoplankton development. Relative abundance of females, copepodite stage V (CV) and males, and the developmental stage of the female gonad were examined from plankton samples collected at weekly to monthly intervals from May 1996 to June 1997 with a WP2 net or a pump. During spring and summer, egg production rates were determined. Females of all three species were present year round. Maximum relative abundance was reached by C. hyperboreus females at the beginning of February, by C. glacialis in mid-February, and by C. finmarchicus in April. All three species reproduced successfully in Disko Bay. Their reproductive cycles were considerably different with respect to the timing of final gonad maturation and spawning, and hence in their relation to seasonal phytoplankton development. In all three species, early gonad development took place during winter, before living food became plentiful, suggesting that these processes were largely food independent. Final gonad maturation and spawning in C. finmarchicus was related to the phytoplankton concentration, reflecting that final gonad maturation processes are food dependent in this species. C. glacialis females matured and spawned prior to the spring bloom. Our results indicate that first internal lipid stores and later ice alga grazing supplied final gonad maturation and egg production. Maximum egg production rates of C. glacialis were found in spring and summer, when the chlorophyll a concentration was high. Mature female C. hyperboreus were found from February until mid-April, when the chlorophyll a concentration was still low. In this species, reproductive activity was decoupled from phytoplankton development, and final maturation processes and spawning were solely fuelled by internal energy stores.     

Feeding and nutritional ecology of the sea urchin strongylocentrotus drobachiensis in Maine,USA

The sea urchin strongylocentrotus drobachiensis exhibited a high degree of food selectivity, whether foods were presented singly or in combination. Foods ranked from most to least preferred were, in summer, Laminaria longicruris, Chondrus crispus, Corallina officinalis, Ascophyllum nodosum, and Agarum cribrosum, whereas in winter A. nodosum and A. cribrosum exchanged ranks. Food preference was not correlated with caloric content but, because of higher feeding rates on preferred foods, caloric intake was positively correlated with preference. Similarly, food absorption rankings were not correlated with food preference, with the exception of gravimetric efficiencies in winter. However, the absorption of L. longicruris, the most preferred alga, was highest in all measurements. Growth and reproductive development of S. drobachiensis on single species diets were positively correlated with food preference. Highest values occurred with animals fed L. longicruris. Urchins transferred from non-preferred to preferred diets showed increased somatic and reproductive growth compared to control animals on the original, non-preferred diets. Conversely, when transferred from preferred to non-preferred diets, urchins showed reduced growth compared to controls. No combination diet tested supported significantly better gonadal growth than L. longicruris: 25% C. crispus supported slightly better somatic growth than L. longicruris alone. These data support the view that S. drobachiensis has evolved a feeding strategy resulting in the maximization of growth and reproduction.     

Feeding rates and prey selectivity of planktonic decapod larvae in the Western English Channel

Meroplankton are seasonally important contributors to the zooplankton, particularly at inshore sites, yet their feeding ecology is poorly known relative to holoplankton. While several studies have measured feeding in decapod larvae, few studies have examined the feeding rates of decapod larvae on natural prey assemblages throughout the reproductive season. We conducted 8 feeding experiments with Necora puber, Liocarcinus spp. and Upogebia spp. zoea larvae collected from the L4 monitoring site off Plymouth (50°15.00′N, 4°13.02′W) during spring–summer 2009 and 2010. This period spanned moderate-to-high food availability (0.5–1.6 µg chl-a L^?1), but a great range in food composition with small cells <20 µm dominating in 2010. Daily rations averaged 17, 60 and 22 % of body C for the 3 respective decapod species. Clearance rates differed according to prey type, and all 3 decapod genera showed evidence of selection of dinoflagellates. Importantly, small cells including nano- and pico-plankton were ingested, this being demonstrated independently by flow cytometric analysis of the feeding experiments and molecular analysis. PCR-based analysis of the haptophyte portion of the diet revealed ingestion of Isochrysis galbana by decapod larvae in the bottle incubations and Isochrysis galbana and Phaeocystis globosa by decapod larvae collected directly from the field. This study has shown that pico- and nano-sized plankton form an important supplement to the diverse and variable diet of decapod larvae.