Abundance and feeding ecology of Antarctic phaeodarian radiolarians

Phaeodarian radiolarians were sampled from the upper 200 m along a transect through the ice-edge zone in the Weddell Sea in the austral autumn (March 1986) and at several stations in the western Antarctic Peninsula region in the austral winter (June 1987). Abundances of phaeodarians reached 3 132 m^-3 and were similar to or higher than maximum abundances of polycystine radiolarians, foraminiferans, and acantharians, and similar to or less than those of the heliozoan Sticholonche sp. Phaeodarians varied in abundance and species composition both seasonally and/or geographically. In contrast to the more numerous ciliates and flagellates that were most abundant in the upper 100 m, phaeodarians were most abundant from 100 to 200 m and showed no distinct pattern related to the ice edge. Electron microscopical examination of food vacuoles showed that phaeodarians are omnivorous generalists, feeding on a variety of food ranging in size from bacteria to large protozoans in both regions and seasons. Algal cells consumed in addition to diatoms and dinoflagellates included Chlorella-like cells and members of the recently described chrysophyte order Parmales. Scales of prasinophytes were common. Phaeodarians are consumed by the non-selective particlefeeding salp Salpa thompsoni. Thus, phaeodarians link microbial food webs to macrozooplankton and increase the complexity of the Antarctic food web.     

Pelagic larval development in the brooding Antarctic brachiopod Liothyrella uva

Larvae of the Antarctic brachiopod Liothyrella uva (Broderip, 1833) were released by brooding females between 10 and 15 January 1992. They were collected and cultured for the ensuing 45 d. At release they were at the gastrula stage, and were recognisable as the usual brachiopod three-lobed larva from around 18 d after release. At 22 d post-release, larvae began to congregate under shell fragments placed in culture vessels as potential settlement substrata. However, the larvae showed no signs of settlement which, combined with the absence of many of the attributes of mature larvae seen in previous studies, was taken as evidence that these larvae had not reached fully competent stages. Previous work had shown that L. uva spawns in October, indicating that the developmental period lasts for a minimum of between 115 and 160 d. The release and subsequent development of larvae also shows that what was previously thought to be a brooding species combines a long brooding period with a free-swimming phase. If this is true of other brachiopod species, then there may need to be a recategorization of some species from brooding to combined brooding and free-swimming developmental types. Even though the development period in L. uva was likely to have been underestimated because a fully competent stage was not reached, a comparison with development rates for temperate species indicated a slowing of between 8 and 70 times. This dramatic slowing of development rate in brachiopods now joins similar data previously reported for echinoderms and nemerteans, suggesting that this is a very widespred, perhaps universal, attribute of Antarctic marine invertebrates.     

Omnivorous feeding behavior of the Antarctic krill Euphausia superba

Feeding experiments were conducted at Palmer Station from December 1985 to February 1986 to examine the potential role of copepod prey as an alternative food source for Euphausia superba. Copepod concentration, copepod size, phytoplankton concentration, the duration of krill starvation and the volume of experimental vessels were altered to determine effects on ingestion and clearance rates. Krill allowed to feed on phytoplankton and copepods in 50-litre tubs showed greatly increased feeding rates relative to animals feeding in the much smaller volumes of water traditionally used for krill-feeding studies. Clearance rates on copepods remained constant over the range of concentrations offered, but clearance rates on phytoplankton increased linearly with phytoplankton concentration. Feeding rates increased when larger copepods were offered and when krill were starved for two weeks prior to experiments. Clearance rates of krill feeding on copepods were higher than, but not correlated with, their clearance rates on phytoplankton in the same vessel. E. superba may have a distinct mechanism for capturing copepods, perhaps through mechanoreception. Although our observed clearance rate of 1055 ml krill^-1 h^-1 indicates that krill can feed very efficiently on copepod prey, such feeding would meet less than 10% of their minimum metabolic requirements at the typical copepod concentrations reported for Antarctic waters. However, substantial energy could be gained if krill fed on the patches of high copepod concentrations occasionally reported during the austral summer, or if krill and copepods were concentrated beneath the sea ice during the winter or spring months. Our results, indicating efficient feeding on zooplankton and higher clearance rates on phytoplankton than previously believed, represent a step towards balancing the energy budget of E. superba in Antarctic waters.     

Food web of an Antarctic midwater ecosystem

The diets of 93 species of plankton and micronekton taken in the upper 1000 m of Croker Passage (Gerlache Strait) in the austral fall, 1983, were examined and the principal features of the food web were characterized. Most species were small particle feeders, with phytoplankton and debris (of phytoplankton and krill) being the principal diet components. Krill remains were found in the guts of the majority of species examined, with the krill playing a greater role in the form of molts and debris than as living prey. Carcinores fed mostly on copepods, coelenterates and salps. Some of the larger species fed on live krill. No-hierarchical cluster analysis of diet information supported the concept of resource partitioning and determined the arrangement of the species into 21 feeding groups. Cluster analysis groupings tended to be along genetic lines with closely related and morphologically similar species having similar diets. These analyses were based on collections made in the austral fall (March–April, 1983) when phytoplankton standing crop was low, most zooplankton species had descended into the mesopelagic zone, and some of the more abundant species, such as Calanoides acutus, had ceased feeding. Because the trophodynamics of Antarctic ecosystems is strongly pulse-induced, it is essential to examine the food web at different periods in the seasonal cycle.     

Comparative lipid dynamics of euphausiids from the Antarctic and Northeast Pacific Oceans

To better understand the feeding and reproductive ecology of euphausiids (krill) in different ocean environments, lipid classes and individual lipid components of four different species of euphausiids from Northeast Pacific (temperate species) and Southern Ocean (Antarctic species) were analyzed in animals from multiple life stages and seasons. The dominant krill species in the Northeast Pacific Euphausia pacifica and Thysanoessa spinifera, were compared to the two major Antarctic species, Euphausia superba and E. crystallorophias. Analysis comprised total lipid and lipid classes together with individual fatty acid and sterol composition in adults, juveniles, and larvae. Antarctic krill had much higher lipid content than their temperate relatives (10–50 and 5–20% of dry mass for Antarctic and temperate species, respectively) with significant seasonal variations observed. Phospholipids were the dominant lipid class in both temperate krill species, while neutral storage lipids (wax esters and triacylglycerols for E. crystallorophias and E. superba, respectively) were the major lipid class in Antarctic krill and accounted for up to 40% of the total lipid content. Important fatty acids, specifically 16:0, 18:1ω9, 20:5ω3, and 22:6ω3, were detected in all four krill species, with minor differences between species and seasons. Detailed lipid profiles suggest that krill alter their lipid composition with life stage and season. In particular, larval Antarctic krill appear to utilize alternate food resources (i.e., sea-ice associated organisms) during austral winter in contrast to juveniles and adults (i.e., seston and copepods). Lipid dynamics in krill among krill in both systems appear closely linked to their life cycle and environmental conditions including food availability, and can provide a more complete comparative ecology of euphausiids in these environmentally distinct systems.     

Ultraviolet photosensitivity and feeding in larval and juvenile coral reef fishes

The ability of young coral reef fishes to feed using solely ultraviolet-A (UV-A) radiation during ontogeny was examined using natural prey in experimental tanks. Larvae and juveniles of three coral reef fish species (Pomacentrus amboinensis, Premnas biaculeatus and Apogon compressus) are able to feed successfully using UV-A radiation alone during the later half of the pelagic larval phase. The minimum UV radiation intensities required for larval feeding occur in the field down to depths of 90–130 m in oceanic waters and 15–20 m in turbid inshore waters. There was no abrupt change in UV sensitivity after settlement, indicating that UV photosensitivity may continue to play a significant role in benthic juveniles on coral reefs. Tests of UV sensitivity in the field using light traps indicate that larval and juvenile stages of 16 coral reef fish families are able to detect and respond photopositively to UV wavelengths. These include representatives from families that are unlikely to possess UV sensitivity as adults due to the UV transmission characteristics of the ocular media. Functional UV sensitivity may be more widespread in young coral reef fishes than in the adults, and may play a significant role in detecting zooplanktonic prey.     

Characteristics of feeding on dinoflagellates by newly hatched larval crabs

The zoeal larvae of brachyuran crabs must feed soon after hatching on a diet that includes large micro- and mesozooplankton in order to satisfy nutritional requirements. However, newly hatched larvae have been shown to ingest a variety of dinoflagellates, perhaps using microbial carbon sources to sustain them until they encounter more favored prey. Ingestion of dinoflagellates by larval crabs has been documented previously under conditions in which the larvae were exposed to algae provided in monoculture or in defined mixtures of cells. We report here on experiments conducted on the hatching stage of five crab species to determine if ingestion of dinoflagellates occurred when they were provided in combination with Artemia sp. nauplii or after a period of feeding on mesozooplankton. Quantitative measurements of chl a in the larval guts provided evidence of ingestion of algal cells. Active ingestion of the dinoflagellate Prorocentrum micans at specified intervals during an extended feeding period was determined on larvae of two crab species using fluorescently labeled cells provided for brief periods at prescribed time intervals. Stage 1 larvae of four of the five crab species ingested dinoflagellates when they were provided in combination with nauplii and larvae of all five species ingested cells after feeding solely on nauplii for 24 h. Ingestion of algal cells was first evident in the larval guts after 6 h of feeding at both low (200 cell ml⁻¹) and high (1,000 cells ml⁻¹) prey densities. Higher prey densities resulted in higher gut chl a. Larvae continuously exposed to dinoflagellates actively ingested cells at every 3 h interval tested over a 36 h period. Results confirm previous studies that larvae will ingest dinoflagellates even when they are encountered in a mixed prey field or when having previously fed. Ingestion of cells may occur on a continual basis over time.     

Remote Antarctic feeding ground important for east Australian humpback whales

Understanding the dynamics of population recovery is particularly complex when an organism has multiple, remote breeding and feeding grounds separated by one of the longest known migration routes. This study reports on the most comprehensive assessment of humpback whale (Megaptera novaeangliae) movements between remote Antarctic waters south of New Zealand and east Australia (EA), and the migratory corridors and breeding grounds of Australia and Oceania. A total of 112 individual whales were identified; 57 from microsatellites and 61 by fluke with 23 % (n = 26) matched to sites outside Antarctica. Despite large datasets from other southern regions being included in the comparison, the whales were predominantly linked to EA (n = 24). Only two matches to the Oceania catalogues directly north was surprising; therefore the primary feeding grounds of these endangered whales still remain unknown. The confirmation of the Balleny Islands as an important feeding ground for EA whales could provide an insight into reasons behind the rapid recovery of this population. Determining the feeding grounds of Oceania’s whales may explain whether prey energetics or migration length are limiting factors to their recovery and will allow an understanding of future ecosystem changes in these whales.     

Food selectivity of the rotifer Brachionus plicatilis feeding on phytoplankton

Food selectivity was examined in amictic female rotifers, Brachionus plicatilis, fed Chlamydomonas sp. and Olisthodiscus sp. Filtering and ingestion rates of the rotifers in a single food suspension were higher with Chlamydomonas sp. than with Olisthodiscus sp. In every mixture of two food species, the apparent filtering rate on Chlamydomonas sp. was much higher than that on Olisthodiscus sp. Total filtering rate and apparent filtering rate in food suspensions containing Chlamydomonas sp. decreased with increasing cell concentration of Chlamydomonas sp. Total and apparent filtering rates were calculated from the decrease in total food concentration as well as from decreases in concentrations of each of the two food algae, respectively. B. plicatilis ingested Olisthodiscus sp. at an extremely low constant rate in all mixtures. The degree of food selectivity of the rotifers fed Chlamydomonas sp. (i.e., selective filtration) from the mixture of two food algae decreased with increasing cell concentration of Chlamydomonas sp. Filtering and ingestion rates of rotifers fed senescent Chlamydomonas sp. were relatively lower than those fed Chlamydomonas sp. in the exponential phase. This indicates that Brachionus plicatilis displays selectivity in regard to condition of cells as well as type of food.     

Seasonality of feeding and nutritional status during the austral winter in the Antarctic sea urchin Sterechinus neumayeri

The seasonal pattern of food intake and tissue energy status was measured over a 2 year period for two populations of the common Antarctic echinoid Sterechinus neumayeri living on contrasting substrata at Rothera Point, Adelaide Island, Antarctica. Food intake was estimated from faecal egestion, and both tissue mass and energy content assessed. Food availability was intensely seasonal, in that water column chlorophyll content and sediment pigment content varied markedly throughout the year. In response, both urchin populations showed an extremely seasonal cycle of faecal egestion, indicating a strong seasonality of feeding activity. Urchins from North Cove living on soft sediment fed at a considerably higher rate, and had a significantly larger Aristotle's lantern, than those in South Cove, 1 km away, living on hard substrata and taking a more cosmopolitan diet. Faecal egestion in both populations was zero for a 7 month period in the austral winter of 1997, and again for a 4 month period in 1998. During the austral summer of 1997/1998, 84% of the total annual energy intake took place in the period January to March. Significant decrease in gut tissue mass provided energy for maintenance in early winter, although progressive reduction of both gonad energy content (but without a detectable change in gonad mass) and body wall organic mass provided energy during the late winter period. The mass of reproductive tissue showed large differences between the two sites, but there was no marked decrease associated with spawning. Tissue proximate composition was assessed stoichiometrically from elemental composition and also checked by direct assay; gonad tissue was richer in lipid than gut tissue, though both were dominated by protein and contained only small amounts of carbohydrate. These data suggest that the very strong seasonality of food intake does not pose a significant energetic challenge for this species.     

Food and feeding of Amphiesma stolatum (Linnaeus 1758)

The food and feeding behaviour of Amphiesma stolatum was studied. A total of 117 snakes were examined to analyse the diet composition. Ten live snakes were maintained in enclosure for evaluating the feeding habit, choice of food and rate of assimilation. The anurans constituted the major diet of the food spectrum. In captivity, fishes (fry), amphibians and reptiles were consumed by the snakes. A. stolatum exihibited Elaphe type of hunting behaviour. In most cases the snake struck the prey at its head. The assimilation rate with frog was highest.     

Hydrography and distribution dynamics of larval and juvenile fishes in the coastal waters of the Tanshui River estuary,Taiwan, with reference to estuarine larval transport

Distribution dynamics of fish larvae and juveniles in the coastal waters of the Tanshui River, Taiwan was studied fortnightly using surface horizontal tows with a larval net in daytime during the period from early April through early June 1991. Environmental factors, including water temperature, salinity, dissolved oxygen, pH, transparency and depth at sampling stations, were also monitored. A total of 10737 fish eggs and 1387 individuals, representing 43 families and 93 species, was collected during five cruises from 12 stations in the coastal waters. Most fish were estuarine-dependent marine species. Liza macrolepis, Ambassis gymnocephalus, Terapon jarbua, Mullidae and Gobiidae were the most dominant, making up 64.7% of the total catch. Early life stages, including egg, preflexion, flexion and postflexion larvae were abundant in surface samples. However, yolk-sac larvae were absent in the surface water, probably due to an ontogenetic behavioral shift as a consequence of a change in specific weight during early development. The species composition of fish larvae and juveniles was related to the microhabitats found in the coastal waters. The physico-chemical conditions, along with ontogenetic behavior, played an important role in larval fish distribution in the coastal waters.     

Diel and tidal cycles regulate larval dynamics in salt marshes and mangrove forests

Variation in the release and recruitment of larvae of estuarine invertebrates affects the distribution and abundance of adults, as well as trophic interactions in both the plankton and the benthos. Larval release and supply are often timed to environmental cycles such as the diel and tidal cycles. Here, we determined using plankton tows whether the abundance of larvae spanning salt marsh and mangrove habitats across the intertidal landscape varied with diel and tidal cycles. Using three different sampling designs across two sites and within each of two estuaries over a 12-month period, we covered a range of spatial and temporal scales. This allowed us to test the general prediction that densities of meroplankton in the water column would be greater during nocturnal ebb tides than during other phases of the diel or tidal cycle. As predicted, nocturnal ebb tides yielded the highest densities of meroplanktonic larvae and were dominated by first-stage crab zoeae and this finding was most pronounced in the salt marsh. Throughout the course of the year, greater numbers of meroplankters consistently occurred during the ebb tide compared with the flood tide. The densities of other taxa (e.g. gastropods and polychaetes) showed no clear trends with diel or tidal cycles. This study highlights the effects of these pervasive physical cycles on the timing of larval release and supply in the salt marsh–mangrove complex, and emphasises their contribution to the trophic interactions and the dynamics of benthic populations within estuaries.     

Food and feeding habits of the king crab Paralithodes camtschatica near Kodiak Island,Alaska

Stomach contents from 809 king crabs, Paralithodes camtschatica (Tilesius), from 6 areas near Kodiak Island, Alaska, and 9 sampling periods (1978–1979) were exammed quantitatively; 713 (88%) contained food. Mollusca (mainly the bivalves Nuculana spp., Nucula tenuis, and Macoma spp.) and Crustacea (mainly barnacles) were the dominant food groups in terms of percentage wet weight and frequency of occurrence; fishes were the next most important group of prey. No significant differences in feeding between sexes occurred; however, significant differences were apparent in the quantity of food consumed from different sampling periods, areas, depths, size groups, and crab molt-classes. Consumption was greater in spring and summer and in offshore locations at depths of 126 to 150 m. In addition, king crabs <140 mm carapace length (CL) consumed more food than crabs 140 mm CL. Adult, newshell (individuals that molted during the last molting period) females greater than 95 mm CL, and newshell males greater than 100 mm CL, each contained more food than did juvenile, newshell females <120 mm CL.Contribution No. 449, Institute of Marine Science, University of Alaska, Fairbanks, Alaska 99701, USA     

Food composition and feeding behavior of shallow-water crinoids at Eilat (Red Sea)

The food of 3 feather-stars, Lamprometra klunzingeri Hartlaub, 1890), Heterometra savignii (J. Müller, 1841) and Capillaster multiradiatus (Linnaeus, 1758), from the shallow water of Eilat (Red Sea) was found to be composed of planktonic and semi-benthalic organisms with a strong dominance of zooplankton. Monthly analyses of stomach contents showed seasonal changes in the participation of various systematic units in the diet. Food-comprising organisms were found to be selected according to size, and those measuring up to 400 formed 90% of the diet.This research has been sponsored partly by the Oceanic Biology Branch, Office of Naval Research, U.S.A. under contract N 62558-4556 and contract F 671052 67C 0043 between the Office of N.R. and the Tel-Aviv University. It represents part of the M.Sc. thesis of the first named author (in the framework of Red Sea investigations headed by Dr. L. Fishelson).     

Spatial assessment of fin whale hotspots and their association with krill within an important Antarctic feeding and fishing ground

Fin whale (Balaenoptera physalus quoyi) habitat use and its relationship to environmental conditions are generally unknown in the Southern Ocean, presenting challenges for predicting their seasonal occurrence and potential effects of fishing pressure and climate change on this endangered species. Using biological data collected during 14 shipboard surveys off the northern Antarctic Peninsula and oceanographic data from satellite remote sensing, we mapped the distribution of fin whale hotspots, Antarctic krill abundance (biomass from acoustics, concentrations from nets) and ocean conditions during mid- and late-summer to investigate the environmental determinants of whale hotspots. Generalized additive models (GAM) were used to test the hypothesis that intra-seasonal changes in fin whale hotspot distribution relate to sea surface temperature (SST), krill abundance and eddy kinetic energy (EKE). More whale hotspots (sightings and individuals) are observed during late- than mid-summer surveys. During mid-summer, hotspots occurred near Elephant Island while in late-summer they were distributed throughout the slope region in proximity to the mean location of the southern Antarctic Circumpolar Current Front. The spatial mean of EKE did not differ between mid- and late-summer surveys, but the spatial mean of SST was significantly warmer during late-summer. The GAM for mid-summer indicates that fin whale hotspots were positively related to SST, EKE and acoustically determined krill biomass. The GAM for late-summer indicates the hotspots were negatively related to net-based krill abundance and positively related to acoustic krill biomass and EKE. This study is important because environmental determinants of fin whale hotspots may be used as reference points for implementing future conservation plans for their recovering populations.     

Structure,composition and seasonal dynamics of the larval and juvenile fish community in the mangrove estuary of Tanshui River,Taiwan

The temporal and spatial patterns of species composition and abundance of fish larvae and juveniles in the Tanshui River mangrove estuary (Taiwan) were studied monthly using a drift bag-net in daylight. A total of 44591 individuals representing 55 families and 105 species were collected over 12 mo (August 1989 to July 1990). The community was dominated numerically by a few species. Sardinella melanura was most numerous, making up 70.15% of the total catch, followed by Stolephorus buccaneeri (19.59%), Thryssa kammalensis (2.96%), and Gerres abbreviatus (2.61%). These four species constituted ca. 95% of the total catch, the remaining 5% consisted of another 101 species. This estuary functions as a nursery and feeding area in the early life history of these fish. There was a separation in peak-immigration and seasonal utilization of the estuary by the dominant species. The abundance of fish larvae and juveniles decreased in an upstream direction.     

Food quality, competition, and parasitism influence feeding preference in a neotropical lepidopteran

We surveyed Lepidoptera found on 11 species of Inga (Fabaceae:Mimosoideae) co-existing on Barro Colorado Island, Panama, to evaluate factors influencing diet choice. Of the 47 species of caterpillars (747 individuals) recorded, each fed on a distinct set of Inga. In the field, 96% of the individuals were found on young leaves. Growth rates of caterpillars that were fed leaves in the laboratory were 60% higher on young leaves compared to mature leaves. When caterpillars were fed leaves of nonhost Inga, they grew more slowly. These data provide support for a link between preference and performance. However, among hosts on which larvae normally occurred, faster growth rates were not associated with greater host electivity (the proportion of larvae found on each host species in the field, corrected for host abundance). Growth rates on normal hosts were positively correlated with leaf expansion rates of the host, and fast expansion was associated with leaves with higher nutritional content. Detailed studies on a gelechiid leaf roller, the species with the largest diet breadth, allowed us to assess the importance of factors other than growth that could influence diet electivity. This species showed a 1.7-fold difference in growth rate among Inga hosts and faster growth on species with fast-expanding leaves. However, there was no correlation between caterpillar growth rate and abundance on different host species. Instead, abundance of the gelechiid on each Inga species was significantly correlated with the temporal predictability of food (synchrony of leaf flushing) and was negatively correlated with competition (amount of leaf area removed by species other than the gelechiid). Although rates of parasitism were high (23-43%), there were no differences among hosts. Parasitism was also not related to measures of escape, such as growth rates of caterpillars, leaf expansion rates, and synchrony of leaf production. Together, food availability, parasitism, and competition explained 84% of the variation in host preference by the gelechiid. We suggest that these ecological interactions may be particularly important in determining diet choice initially and that preferences may be reinforced by subsequent divergence in host chemistry and/or the herbivore's ability to tolerate the secondary metabolites.     

Effect of delayed first feeding on larval performance of the spider crab Maja brachydactyla assessed by digestive enzyme activities and biometric parameters

The effect of food deprivation on larval performance of the spider crab Maja brachydactyla was studied in terms of survival, moulting capacity, size, weight and enzymatic activities. Five feeding treatments that differed in the initial age of first feeding larvae (fed from hatching, 2, 4 and 6 days post-hatching and unfed) were tested for 20 days. Newly hatched larvae kept without food supply lasted for 10 days and did not moult; with 50% survival observed at 6 days post-hatching. Larvae (zoea I stage) were only able to tolerate 2 days of food deprivation after the onset of exogenous feeding without their performance being compromised. Multivariate analyses suggest that digestive enzyme activities may be good indicators of the nutritional condition of larvae.