Analysis of lipid components for determining the condition of anchovy larvae,Engraulis mordax

It has been presumed that intertidal spawning by Limulus polyphemus minimizes the loss of egges to subtidal predators; however, this strategy involves considerable risks. Massive beach strandings of adults accompany seasonal spawning migrations of crabs along Cape May in Delaware Bay, (USA). At least 190000 horseshoe crabs, approximating 10% of the adult population, died from beach stranding along the New Jersey shore of Delaware Bay during the 1986 (May to June) spawning season. Abnormalities of the telson (which is used in righting behavior) were significantly more common among stranded crabs than among individuals actively spawning on the intertidal beach. The number of stranded crabs per day was not correlated with tidal height or environmental variables (wind speed, wave height) which characterized the conditions at spawning. A complex suite of factors, including the size of the available spawning population, tidal and weather conditions, and beach slope, influence the number stranded during the breeding season. Horseshoe crab stranding results in a large loss of gravid females from the population, and may represent a major input of organic matter to intertidal sandy beaches in certain regions of Delaware Bay.     

Utilization of partially predated snail shells by the hermit crab Pagurus longicarpus Say, 1817

The hermit crab Pagurus longicarpus was shown to inhabit shells that were partially predated from intertidal areas of Long Island, New York. Among field collections of P. longicarpus, 2.13% of the hermit crabs (46 of 2155) were found with shells with snail tissue present. Over 90% of these partially predated snail shells were occupied by male hermit crabs. Although hermit crabs were in 8 species of snail shells, only Littorina littorea and Nassarius obsoletus were found occupied by hermit crabs and containing snail tissue. In the laboratory, we found that specimens of the spider crab Libinia emarginata were able to pull off the operculum of snails, leaving damage as found in field collections. In contrast, specimens of P. longicarpus were not able to prey on live, healthy snails. When specimens of P. longicarpus were placed in communal tanks, hermit crabs preferred partially predated snail shells to empty and original shells. However, original shells and empty shells were occupied with more frequency than partially predated shells when crabs were isolated. These findings indicate P. longicarpus actively seeks shells soon after attack and abandonment by snail predators, especially in the presence of competitors.     

Potential effects of a non-indigenous predator in its expanded range: assessing green crab, <Emphasis Type="Italic">Carcinus maenas</Emphasis>, prey preference in a productive coastal area of Atlantic Canada

The non-indigenous green crab (Carcinus maenas) is an important predator on bivalve wild beds in coastal areas worldwide. This study explored size-dependent green crab prey preference on American oysters (Crassostrea virginica), blue mussels (Mytilus edulis), and soft-shell clams (Mya arenaria) in a productive coastal system of Atlantic Canada. Using two sizes of prey and three different experimental manipulations, small, medium, and large green crabs were given a choice among these three bivalves, and their daily feeding rates were monitored over the course of 3 days. For both prey sizes, green crabs showed an early feeding preference for soft-shell clams and, only as they declined in numbers, a switch toward mussels and subsequently toward oysters. We found that such changes in the timing (order) of prey preference are related to prey differences in shell thickness, a fairly reliable indicator of prey shell strength.     

Resource utilization for decorating in three intertidal majid crabs (Brachyura: Majidae)

 For three spider crabs (Tiarinia cornigera, Micippaplatipes and Pugettia quadridens quadridens), patterns of algal utilization for decorating were compared with the dynamics of algae on an intertidal rocky shore reef where the crabs co-occurred. T. cornigera and P. quadridens quadridens were most abundant from autumn to spring when the dominant algae (Boodleacoacta, Sargassum hemiphyllum, S. thunbergii and Corallina pilulifera) occurred in high coverage, while M. platipes was most abundant from spring to autumn. Monthly change of algae used for decorating was not correlated with algae growing in the crab habitat for T. cornigera, but for M. platipes, it was positively correlated for two algal species, and for P. quadridens quadridens, negatively correlated for one algal species. Each species of the spider crabs used some algal species preferentially for decoration. Decorating preference experiments conducted in the laboratory showed that M. platipes and P. quadridens quadridens exhibited similar preference to their algal utilization in the field, whereas for T. cornigera, algal preference in the experiment differed from utilization in the field. Comparisons between materials used for decoration and gut contents revealed that T. cornigera and M. platipes used algal species differently for decorating and feeding, while P. quadridens quadridens used the same algal species for both decorating and feeding. Different tactics for camouflage are discussed in terms of algal utilizations by the three majid species. Received: 25 September 1999 / Accepted: 22 June 2000     

Size-related selection of two intertidal gastropods by the reef crab Ozius truncatus

Reef crabs, Ozius truncatus H. Milne-Edwards 1834, and gastropods, Bembicium nanum (Lamarck, 1882) and Nerita atramentosa Reeve, 1855, were collected from a South Australian rocky intertidal platform in April 1981. Laboratory experiments were conducted to determine (1) the size of prey chosen, and (2) the energy gained by the reef crabs feeding on B. nanum and N. atramentosa. The time taken to break open and consume prey increased exponentially with prey shell height. Crabs with larger master claws had shorter handling times for a given prey size. When offered a range of prey sizes, crabs selected prey of a certain size, well below the maximum prey size that they could handle. The mean prey size selected by crabs did not concide with the size predicted to yield the maximum rate of energy gain. For example, one reef crab preferred B. nanum 5 to 8 mm in size, but the size class predicted to yield the greatest energy gain was 4 to 4.9 mm. The results of the laboratory prey-choice experiments are discussed in relation to the shore-level size gradients of B. nanum and N. atramentosa.     

Relationship between the habitat and diet of three species of atherinids and three species of gobies in a temperate Australian estuary

The distributions and diets of the six most abundant species of teleost in the shallows of a large south-western Australian estuary were examined from samples collected between March 1988 and February 1989. Fish were collected monthly by seine net from over bare sand and from within patchy and dense areas of the aquatic macrophyte Ruppia megacarpa. Their gut contents were compared with samples of the benthos and plankton collected from each of these three habitat types. The densities of the atherinids Leptatherina wallacei and Atherinosoma elongata and of the goby Favonigobius suppositus were greatest in dense R. megacarpa, whereas those of the atherinid L. presbyteroides and the goby F. lateralis were greatest over bare sand. The density of the goby Pseudogobius olorum was greater in patchy R. megacarpa than in the other two habitat types. The gut contents of each of the six species was dominated by crustaceans and/or polychaetes, with detritus also making a major contribution to the diet of P. olorum and F. lateralis. The relative proportions of prey items in the guts of fish in a particular habitat corresponded to the preys' relative occurrence in the environment. This indicates that the fish had been feeding predominantly in one particular habitat prior to capture. Within each habitat type, the six species partitioned the available food, the major components of the diet of each species being different. The gobiid species fed mainly on the benthos and the atherinids typically fed higher in the water column; A. elongata and P. olorum tended to be less selective as to where they foraged. There were no consistent differences in either the dietary breadth or the fullness of the guts of any species among habitat types.     

Contrasting feeding patterns among species of fish larvae from the tropical Andaman Sea

Feeding habits of tropical fish larvae were analysed in a comparative study of four species (Scorpaenodes sp., Carangoides sp., Acanthocepola sp. and Cynoglossus sp.) from the Andaman Sea. We investigated morphological characteristics and their potential influence on larval feeding, and looked for common patterns in larval prey preference. Gut contents of a total of 300 larvae were examined and compared with local zooplankton composition. The feeding habits of the investigated larvae shared a number of characteristics. During ontogeny both the preferred prey size and the number of prey in the gut increased, and across all larval size classes the relative prey size spectrum stayed constant, of approximately the same magnitude for all four species. On the other hand, larval feeding also differed in a number of aspects, especially differences in the taxonomic composition of preferred prey were apparent. Scorpaenodes sp. preferred abundant and large prey taxa, Acanthocepola sp. and Carangoides sp. preferred large, but less common prey taxa, while Cynoglossus sp., which had the relatively smallest mouth size, preferred smaller sized prey groups. Hence, the findings indicate that from an offset of common characteristics, especially related to prey size preference, larvae have their individual feeding patterns related to specific morphology and patterns of distribution.Communicated by M. Kühl, Helsingør     

Macroinfaunal structure and effects of thermal discharges in a mesohaline habitat of Chesapeake Bay,near a Nuclear Power Plant

The soft-bottom macroinfauna of the Chesapeake Bay near the Calvert Cliffs Nuclear Power Plant, Maryland, USA, was studied quarterly in 1977. A total of 42,900 organisms distributed among 55 taxa was taken in 180 Smith-McIntyre grabs. Two communities and an ecotone between these two communities were identified in association with three sediment types: sand, sand-clay, and clay. Reproductive activities of 8 numerically dominant species are described. The macroinfauna at Calvert Cliffs was largely seasonal; species richness and organism abundances were lowest in late summer. The polychaetes Scolecolepides viridis and Heteromastus filiformis and the bivalves Macoma balthica and Mya arenaria were dominant in March-June. In September-December, the polychaetes Neanthes succinea, Paraprionospio pinnata, and Glycinde solitaria and the bivalve Gemma gemma became dominant. There were clear indications of differences associated with sediment types in total number of species, total number of individuals, and abundances of the dominant species. The shallower and intermediate habitats had higher sand-clay ratios, lower organic carbon contents, and larger numbers of organisms than the deeper clay habitat. Within each depth, no apparent detrimental effects caused by the thermal discharges on total number of species, total number of individuals, abundances of the dominant species, species diversity or evenness were found. Increased abundance was observed at the discharge stations for a few species, especially for Mya arenaria and N. succinea.     

Feeding habits of the dungeness crab Cancer magister as determined by the index of relative importance

Specimens of the Dungeness crab Cancer magister, were collected subtidally and intertidally from an estuary in Washington State, USA in June and September 1980, and January, April, May and July, 1981. Gut contens of freshly collected crabs were analyzed by the Index of Relative Importance; for each prey taxon, this method measured frequency of occurrence, percentage of total biomass, and percentage of total numbers consumed. The most important higher taxon eaten was fish; however, the most important prey genus was the shrimp Crangon spp. There was greater predation on Crangon spp. at night at the intertidal site, and during winter and spring when the shrimp were most abundant there. Feeding activity, as indicated by a weight-specific gut-fullness index, showed no consistent diel pattern. There were significant ontogenetic changes in feeding patterns: first-year crabs preyed primarily on very small bivalves or small crustaceans including their conspecifics; second-year crabs preferred Crangon spp. and fish, and third-year crabs preyed less on Crangon spp. and more on fish. Such changes in feeding habits with ege could be purely due to mechanics of food handling, but might also reduce competition among age groups of crabs, possibly partitioning resources within the estuary. Findings are discussed in terms of optimal foraging and compared to other similar studies.Contribution No. 599, School of Fisheries, University of Washington, Seattle, Washington 98195, USA     

Natural food,foregut clearance-rate and activity of the crab Scylla serrata

The natural diet, rate of foregut clearance and diurnal activity of the crab Scylla serrata were determined. The gut volume is related to size of crab as gut volume (ml)=0.07e^0.033x , where x=carapace width in millimetres. Fifty per cent of crabs collected in Australia and South Africa contained molluscan remains and about 21% contained crustacean remains — chiefly grapsid crabs. Fish remains were rarely found, and it was concluded that S. serrata does not normally catch mobile forms such as fish and penaeid prawns. Gut clearance of organic tissue was rapid and almost complete after 12 h. Fish bone was retained for a mean time of 2 to 3 days, and shell for 5 to 6 days. Time-lapse photography, using infra-red light, was used to record activity. Visible light flashes reduced activity. S. serrata remained buried during the day, emerging at sunset to spend the night feeding, which occurred intermittently even when unlimited food was available. If no food was present the amount of time spent on the substrate surface was halved.     

Trophic relations of the cephalopod Martialia hyadesi (Teuthoidea: Ommastrephidae) at the Antarctic Polar Front,Scotia Sea

Samples of the squid Martialia hyadesi were collected aboard two Japanese squid-jigging vessels carrying out commercial fishing trials at the Antarctic Polar Frontal Zone, north Scotia Sea, in February 1989. The dissected stomachs of 61 specimens were classified according to fullness and the contents were examined visually. Identifiable food items included fish sagittal otoliths, crustacean eyes, the lappets on euphausiid first antennule segments and cephalopod sucker rings. The most frequent items in the squid's diet were the myctophid fishes Krefftichthys anderssoni and Electrona carlsbergi, the euphausiid Euphausia superba and a hyperiid amphipod, probably Themisto gaudichaudi. A small proportion of the sample had been feeding cannibalistically. Total lengths of the fish prey were estimated from sagittal otolith size using published relationships. All fish were relatively small; 7 to 35% of squid mantle-length. However, it is possible that some heads of larger fish are discarded by the squid and so are not represented by otoliths in the stomach contents. Over the size range of squid in the sample there was no relationship between size of fish prey and size of squid. Similarly, when the squid sample was divided into groups according to prey categories: crustaceans, crustaceans+fish, fish, cephalopod, there was no evidence that dietary preference was related to squid size. The prevalence of copepod-feeding myctophids in the diet of this squid, which is itself a major prey item of some higher predators in the Scotia Sea, suggests that a previously unrecognised food chain: copepod-myctophid-M. hyadesi-higher predator, may be an important component of the Antarctic oceanic ecosystem.     

Epibiotic community of the horseshoe crab Tachypleus gigas

Horseshoe crabs act as moving substrata for simple to complex communities of small marine organisms. Amplexed adult pairs migrate for breeding once every 2 weeks from deep waters towards nearshore waters during highest high tide. Female horseshoe crabs bury themselves to the level of the lateral eyes to deposit eggs while the male crabs fertilize them. Subsequently eggs are buried by the female. Tachypleus gigas (Müller) is the most abundant horseshoe crab species above available along the Orissa coast (India). Adults reach terminal anecdysis once sexually mature and live with their carapace for 4 to 9 years. In spite of this, epibiosis is limited. In the current investigation, differences in the epibiotic community (diatoms and macro-epibionts) present on horseshoe crabs, according to gender, were evaluated, and the macro-epibiont population from different regions of the carapace was mapped. In general, female horseshoe crabs harbored fewer epibionts than the males. Among the diatoms, Navicula spp., Nitzschia spp. and Skeletonema sp. were dominant in both sexes. However, the abundance and diversity of diatoms was greater on the carapaces of male crabs. Among the macro-epibionts, the acorn barnacle (Balanus amphitrite Darwin) and encrusting bryozoan (Membranipora sp.) were the most dominant forms. Barnacles and bryozoans were greater in abundance in the “rough” zone (cardiopthalmic region and anterior region of the opisthosoma). Mapping of the macro-epibionts from different regions of the carapace revealed differential distribution in males and females. Such differentiated distribution of the macro-epibionts can be related to factors such as changing habitat by the horseshoe crabs during breeding, mechanical abrasion and surface availability during mating and nesting periods, requirements of epizootic larvae and surface properties of the carapace (wettability and roughness). In the case of females, mechanical abrasion and surface availability played an important role in the epibiotic community structure and distribution patterns. The surface wettability measurements indicated male carapace to be slightly more hydrophobic than the female carapace. Scanning electron microscopy revealed that the male carapace was comparatively rough compared to the smooth carapace of females. A comparison of surface properties of the carapace indicated that the male carapace is more conducive for epibiosis. Received: 23 August 1999 / Accepted: 25 January 2000     

Ontogeny of diet changes in a tropical benthic carnivorous fish, Parupeneus barberinus (Mullidae): relationship between foraging behaviour, habitat use, jaw size, and prey selection

Parupeneus barberinus forages on benthic invertebrates using a wide range of foraging modes, including vigorous digging in the substratum, resulting in considerable disturbance to the benthos. Polychaetes were the most important prey item for all size classes, but fishes less than 120 mm total length consumed more small ostracods and nematodes than did larger fishes. Fishes greater than 120 mm total length consumed mostly bivalves, and fishes over 240 mm total length consumed mostly bivalves and crabs. A morphological examination of the feeding apparatus suggested that the size of important prey items consumed was determined by gape height and jaw width. Prey available to different size classes of fishes was determined by combining information on microhabitat use, foraging behaviours, and prey volumes in the substratum. Small fishes spent more time foraging on the reef flat and slope, compared with larger fishes that foraged mostly on the reef edge and base. In addition smaller fishes foraged mostly in the upper 2 cm of sediment, whereas larger fishes often foraged to depths of 10 cm. Selection ratios showed that different size classes of fishes selectively extracted different prey items from the substratum. Small fishes showed a preference for ostracods whereas large fishes selected for bivalves and crabs. Although polychaetes were the dominant prey item for all size classes, they were consistently selected against.     

Zooplankton capture by two scleractinian corals,Madracis mirabilis andMontastrea cavernosa,in a field enclosure

Capture of zooplankton by scleractinian corals has been noted for several species, yet quantitative information on rates of capture and differential capture by prey taxon has been lacking. We used field enclosures to examine prey capture for two coral species,Madracis mirabilis (Duchassaing and Michelotti) andMontastrea cavernosa (Linnaeus), on the north coast of Jamaica (Discovery Bay) in November 1989, February and March 1990, and January 1992.M. mirabilis has small polyps and a branching colony morphology (high surface/volume ratio), whereasM. cavernosa has large polyps and mounding colonies (low surface/volume ratio). Corals were isolated front potential prey, then were introduced into enclosures with enhanced zooplankton concentrations for 15- to 20-min feeding periods. Corals were fixed immediately after the experiment to prevent digestion, and coelenteron contents were examined for captured zooplankton. Plankton pumps were used to sample ambient zooplankton in the enclosures near the end of each run. Selectivity and capture rates were calculated for each prey taxon in each experiment; both indices were high for relatively uncommon large prey, and low for copepods, which were often the most common items in the plankton. Sizes of zooplankton captured by both species were generally larger than those available considering all prey taxa combined, but were almost the same for both coral species, even though the corals' polyp sizes are very different. This occurred primarily because small copepods, with low capture rates, dominated most plankton samples. For specific prey species, or group of species, there were few significant differences in size between the prey available and the prey captured.M. mirabilis, with small polyps, also captured far more prey per unit coral biomass than didM. cavernosa, with much larger polyps. We hypothesize that the large differences in capture rate of prey taxa are related to escape or avoidance behavior by those potential prey, and to the mechanics of capture, rather than to any selectivity by the corals.     

Feeding ecology of the loggerhead sea turtle Caretta caretta in the Northwestern Gulf of Mexico

Digestive tract contents collected from carcasses of 82 loggerhead sea turles (Caretta caretta) found on the south Texas coast from 1986 through 1988 were examined. Benthic invertebrates were the predominant prey. Sea pens (Virgularia presbytes), crabs, and mollusks accounted for 94% of the dry weight of the digestive tract samples. Temporal changes in the percent occurrence and percent dry weight of sea pens, crabs, and mollusks in the digestive tract samples were significant. Loggerheads fed primarily on sea pens during spring, then primarily on crabs during summer and fall. The increase of crabs in the loggerhead diet paralleled the annual increase in the abundance of crabs in the Gulf of Mexico. Sea pens were located nearshore at depths of 6 to 12 m and had a disjunct distribution. Present address: Texas A&M University, Department of Biology, College Station, Texas 77843-3258, USA     

Abundance,population structure and claw morphology of the semi-terrestrial crab <Emphasis Type="Italic">Pachygrapsus marmoratus</Emphasis> (Fabricius, 1787) on shores of differing wave exposure

Wave action is known to influence the abundance and distribution of intertidal organisms. Wave action will also determine the duration and suitability of various foraging windows (high-tide and low-tide, day and night) for predation and can also affect predator behaviour, both directly by impeding prey handling and indirectly by influencing prey abundance. It remains uncertain whether semi-terrestrial mobile predators such as crabs which can access intertidal prey during emersion when the effects of wave action are minimal, are influenced by exposure. Here, we assessed the effect of wave action on the abundance and population structure (size and gender) of the semi-terrestrial intertidal crab Pachygrapsus marmoratus on rocky shores in Portugal. The activity of P. marmoratus with the tidal cycle on sheltered and exposed shores was established using baited pots at high-tide to examine whether there was activity during intertidal immersion and by low-tide searches. Because prey abundance varies along a wave exposure gradient on most Portuguese shores and because morphology of crab chelipeds are known to be related to diet composition, we further tested the hypothesis that predator stomach contents reflected differences in prey abundance along the horizontal gradient in wave exposure and that this would be correlated with the crab cheliped morphology. Thus, we examined phenotypic variation in P. marmoratus chelipeds across shores of differing exposure to wave action. P. marmoratus was only active during low-tide. Patterns of abundance and population structure of crabs did not vary with exposure to wave action. Stomach contents, however, varied significantly between shores of differing exposure with a higher consumption of hard-shelled prey (mussels) on exposed locations, where this type of prey is more abundant, and a higher consumption of barnacles on sheltered shores. Multivariate geometric analysis of crab claws showed that claws were significantly larger on exposed shores. There was a significant correlation between animals with larger claws and the abundance of mussels in their stomach. Variation in cheliped size may have resulted from differing food availability on sheltered and exposed shores.     

Effects of Lunatia heros predation on the population dynamics of Mya arenaria and Macoma balthica in Maine,USA

The interaction between the naticid snail predator Lunatia heros and 2 iteroparous, infaunal, intertidal bivalves was investigated in Lubec, Maine, USA. The Mya arenaria population consists primarily of young, small individuals. M. arenaria survivorship is low when young (3.5% yr^-1 for the first 5 yr), then increases. M. arenaria can attain a length of 60 mm, but it is susceptible to L. heros attack only until it is 30 mm long. It delays reproduction until it is 20 mm long (3.8 yr) and diverts its resources instead into rapid early growth (4.9 mm yr^-1 for the first 5 yr). The Macoma balthica population has a larger proportion of older individuals than does that of M. arenaria. Survivorship is higher for M. balthica than for M. arenaria (76.3% yr^-1 for the first 5 yr). Unlike M. arenaria, M. balthica attains a final length of only 25 mm and all sizes are susceptible to L. heros attack. M. balthica grows slowly (2.7 mm yr^-1 for the first 5 yr) and diverts its resources into earlier reproduction at a length of 10 mm (2.9 yr). These contrasting life-history patterns and the possible relationship between bivalve resource allocation and refuges from predation are discussed.     

Leaf consumption by <Emphasis Type="Italic">Sesarma plicata</Emphasis> in a mangrove forest at Jiulongjiang Estuary,China

The feeding ecology of Sesarma plicata (Grapsidae: Sesarminae), the most abundant crab species in a mangrove forest dominated by Kandelia candel at Jiulongjiang Estuary, China, was investigated through field and laboratory experiments. Feeding preference and consumption rates were determined on mature, senescent and decomposed leaves of Kandelia candel, Bruguiera gymnorrhiza and Aegiceras corniculatum. In the laboratory, S. plicata preferred leaves of K. candel over those of B. gymnorrhiza and A. corniculatum, and consumed significantly more decomposed leaves than mature and senescent ones, irrespective of crab size. Field experiments with limited power failed to reveal detectable species preferences despite more consumption of K. candel, but decomposed leaves of each species were again preferred. Leaf characteristics associated with preference changed with plant species and leaf state. Low tannins and high water content characterized the preference for decomposed state of leaves. Species preference was significantly and negatively related to crude fibers and C:N ratios for mature leaves, and crude fiber for senescent leaves, but significantly and positively related to water content for decomposed leaves. Leaf consumption rates averaged for all leaf categories from laboratory no-choice feeding experiments were 0.101, 0.055 and 0.017 gDW ind⁻¹ d⁻¹ for large, medium and small crabs, respectively. In this forest, mean density of S. plicata was 20.5 ind m⁻² as assessed by a manual catching method. Leaf litter removal rate during neap tides by sesarmid crabs was about 1.33 gDW m⁻² d⁻¹ in April 2006. The leaves removed by crabs were grazed on the sediment surface or taken into crab burrows, shredded and stored before being eaten.     

Water flow and prey capture by three scleractinian corals, Madracis mirabilis, Montastrea cavernosa and Porites porites, in a field enclosure

Scleractinian corals experience a wide range of flow regimes which, coupled with colony morphology, can affect the ability of corals to capture zooplankton and other particulate materials. We used a field enclosure oriented parallel to prevailing oscillatory flow on the forereef at Discovery Bay, Jamaica, to investigate rates of zooplankton capture by corals of varying morphology and polyp size under realistic flow speeds. Experiments were carried out from 1989 to 1992. Particles (Artemia salina cysts) and naturally occurring zooplankton attracted into the enclosures were used as prey for the corals Madracis mirabilis (Duchassaing and Michelotti) (narrow branches, small polyps), Montastrea cavernosa (Linnaeus) (mounding, large polyps), and Porites porites (Pallas) (wide branches, small polyps). This design allowed corals to be used without removing them or their prey from the reef environment, and avoided contact of zooplankton with net surfaces. Flow speed had significant effects on capture rate for cysts (M. mirabilis), total zooplankton (M. mirabilis, M. cavernosa), and non-copepod zooplankton (M. mirabilis). Zooplankton prey capture increased with prey concentration for M. mirabilis and M. cavernosa, over a broad range of concentrations, indicating that saturation of the feeding response had not occurred until prey density was over 10⁴ items m⁻³, a concentration at least an order of magnitude greater than the normal range of reef zooplankton concentrations. Location of cyst capture on coral surfaces was not uniform; for M. cavernosa, sides and tops of mounds captured most particles, and for P. porites, capture was greatest near branch tops, but was close to uniform for M. mirabilis branches in all flow conditions. The present study confirms laboratory flume results, and field results for other species, suggesting that many coral species experience particle flux and encounter rate limitations at low flow speeds, decreasing potential zooplankton capture rates. Received: 17 September 1996 / Accepted: 22 November 1997     

Food resource partitioning by the pufferfishes Sphoeroides spengleri and S. testudineus from Biscayne Bay,Florida

Partitioning of the food resources by two coexisting pufferfishes (Sphoeroides spengleri and S. testudineus) from Biscayne Bay, Florida, USA, was investigated. Gut contents from 453 bandtail and 339 checkered puffers were analyzed. The diets of both species consisted of a variety of benthic prey, but only crustaceans and molluscs were important prey groups. While differences were found in the proportions of general prey categories eaten by these fishes, both species consumed substantial quantities of brachyuran crabs, bivalves, and gastropods. Specific identification of the prey items within these three food categories revealed additional differences in prey between the two puffer species. This partitioning of the food resources by bandtail and checkered puffers was found between both species overall, between overlapping size ranges, and between both species' most abundant size group. Differences in food habits between these two fishes illustrate that congeners with virtually identical mouth structure and complete spatial overlap can significantly partition the food resources.Contribution No. 78-58M from the U.S. Department of Commerce, NOAA, National Marine Fisheries Service, Southeast Fisheries Center, Miami Laboratory, Miami, Florida, USA.