Responses of the chaetognath, Sagitta elegans, and larval Pacific hake, Merluccius productus, to spring diatom and copepod blooms in a temperate fjord (Dabob Bay, Washington)

As part of a broader field study examining the potentially deleterious effects of diatoms on planktonic food webs, we examined the abundance, stage composition, diet, and feeding success of the chaetognath, Sagitta elegans, and the abundance and morphometric condition of larval Pacific hake, Merluccius productus. Our objective was to look for a relationship between spring phytoplankton blooms and planktonic predators, as mediated by their copepod prey, with special reference to possible deleterious effects of diatoms. Zooplankton were collected weekly during February–May and in mid-summer of 2002 and 2003 in Dabob Bay, Washington State, USA. S. elegans abundance was high in summer of both years and was higher in spring 2003 than spring 2002. Larval chaetognaths dominated the population in early spring and remained present throughout sampling. S. elegans consumed mostly copepods. The abundance of larval S. elegans was correlated with the abundance of copepodites, although no relationship between chaetognath feeding success and prey abundance was found. Larval Pacific hake abundance was high (1200 larvae per square meter) in late February and early March of 2002 and 2003 and decreased rapidly in late spring. The morphometric condition of M. productus was not significantly related to copepod abundance. These results indicate that any deleterious effects of diatoms on copepod abundance, at the scale seen during spring 2002 and 2003 in Dabob Bay, did not greatly affect the next higher trophic level.     

Predatory Promesostoma species (Plathelminthes, Rhabdocoela) in the Wadden Sea

Laboratory experiments were performed on the food ecology of four congeneric species of free-living plathelminths, Promesostoma caligulatum, P. marmoratum, P. rostratum, and P. meixneri, all inhabiting an intertidal sandflat near the island of Sylt (North Sea). Their prey spectrum is within the microcrustaceans: P. caligulatum preferred ostracods, while the other three species favoured copepods, with species-specific differences for copepod species and size classes. Daily consumption of prey species varied with the size of both the predator and the prey. On average, P. marmoratum consumed 0.76 Harpacticus flexus per day while this rate decreased to 0.06 in P. meixneri, the smallest predator. When these Promesostoma species were fed with Tachidius discipes, a smaller prey species, their predation rates were about 25% higher. While the larger predators preferred the larger harpacticoids as prey, the small P. meixneri preferred small cyclopoids over larger harpacticoids. In terms of biomass, P. marmoratum's mean consumption of T. discipes per day was about half the predator's own weight. This average varied with prey density and temperature. A comparison of these consumption rates with the field densities of the predators and their prey shows that the plathelminth predators may consume as much as 10% per day of their copepod prey populations, thus strongly influencing these prey populations on these sandflats. The predation pressure of P. caligulatum on ostracods was about 1% per day of the prey population. Since ostracods usually have fewer generations per year, the total effect on the population dynamics may be similar to that on copepods. Therefore, nocturnal swimming of copepods in the water column may be interpreted as an attempt to escape plathelminth predators.     

Groupers of the World: A Field and Market Guide

The diet of Chrysaora hysoscella was investigated from 55 specimens caught near the surface throughout 24h in Walvis Bay Lagoon, Namibia, during September 2003. The diet was diverse, ranging from dinoflagellates to carideans, and included abundant benthic species (adults and larvae). There was no clear overall relationship between medusa size and either the number or type of prey ingested, although aspects of both measures were significantly related to size when analyses were confined to the nocturnally collected data. Whereas there was a significant difference in the diet of medusae collected by day and night, principally because of an increase in the abundance of benthic prey items, it was not possible to partition this between the vertical migration of predator (downwards) or prey (upwards) owing to a lack of information on the ambient prey environment. Regardless, the abundance of benthic prey in the diet could help explain the predominance of medusae off Namibia, where there has been an increased flow of surface production to the benthos since the collapse of the pelagic fisheries.     

Cross-shelf distribution of copepods and the role of event-scale winds in a northern California upwelling zone

Cross-shelf distribution and abundance of copepod nauplii and copepodids were measured during three summer upwelling seasons (2000–2002) in a coastal upwelling zone off northern California. These 3 years varied considerably in the intensity of winds, abundance of chlorophyll, and water temperature. The cruises in 2000 were characterized by relaxation conditions, with generally high levels of chlorophyll and high water temperature. The cruises in 2001 and 2002 were dominated by strong and persistent upwelling events, leading to lower chlorophyll and water temperatures. The copepod assemblage was dominated by Oithona spp., Acartia spp. and Pseudocalanus spp., with Metridia pacifica (lucens), Microsetella rosea, Oncaea spp. and Tortanus discaudatus also common during all 3 years. The cross-shelf distribution of copepods was generally shifted offshore during upwelling and onshore during relaxation events, although some variability between species occurred. Abundance of all life stages generally exhibited a negative correlation with cross-shelf transport averaged over at least 1–4 days and lagged by 0–3 days, indicating lower abundances during and immediately after active upwelling. However, copepod nauplii seemed to respond positively to wind events lasting 1–5 days followed by a period of relaxation lasting 6 or 7 days. These rapid rates of change in abundance are probably too great to be due to in situ growth and reproduction alone; physical processes must also play a role. These results suggest a highly dynamic relationship between copepods and upwelling events off northern California, with species-specific responses to upwelling to be expected.     

Population biology and recruitment of a vulnerable sea cucumber,Stichopus herrmanni,on a protected reef

Populations of tropical sea cucumbers, harvested for bêche‐de‐mer, are in a perilous state of conservation, yet there remains a paucity of information on the biology of many harvested species. We examined the population biology of the commercially important curryfish, Stichopus herrmanni, across 2 years on Heron Reef, a protected zone in the Great Barrier Reef (GBR) Marine Park. Stichopus herrmanni, a species recently listed as vulnerable to extinction, is a major target species for the fishery operating in the GBR. The size class distribution and density of S. herrmanni were documented for six sites across Heron Reef. There was distinct spatial variation in the size and density of S. herrmanni across sites, with no significant difference between the 2 years. The smallest individuals found were 10 cm long, some of the only juvenile S. herrmanni documented in nature. Juvenile and sub‐adult populations were found along the leeward reef edge of Heron Reef, a habitat characterized by shallow channels of sand between inter‐tidal coral reef and crustose coralline algae (CCA). Juvenile nurseries of sea cucumbers are rarely observed in nature, making this an important observation for understanding the recruitment and population biology of S. herrmanni. The presence of juveniles in the consolidated CCA habitat each year in autumn following the summer spawning period, and the absence of small individuals several months later in spring, suggests an ontogenetic migration or displacement of these individuals to adult habitat. The distribution of larger S. herrmanni suggests intra‐reef connectivity and migration into deeper lagoon areas. This study contributes to understanding the population dynamics of this vulnerable species, a consideration for fisheries management in light of increasing global harvest.     

Diel Changes in Vertical Distribution and Feeding Conditions of the Chaetognath Parasagitta elegans (Verill) in the Subarctic Pacific in Summer

Diel changes in vertical distribution and feeding conditions of the chaetognath Parasagitta elegans (Verill) were observed in three regions of the subarctic North Pacific in the summer of 1997. Samples were collected by repeated vertical hauls with a Vertical Multiple Plankton Sampler (VMPS) for 15–45 hours by demarcating the 0–500 m water column into four sampling layers. Integrated abundance through the entire water column and the proportion of juveniles were higher in the Bering Sea than the western and eastern subarctic Pacific. Juveniles always inhabited the surface layer in the western subarctic Pacific and Bering Sea, but they inhabited the underlying layer in the eastern subarctic Pacific. Stages I–III concentrated into the upper 150 m in the western subarctic Pacific but were distributed widely from 20–300 m in the Bering Sea. Among them, Stages II and III migrated rather synchronously over a wide vertical range in the eastern subarctic Pacific. The feeding rate of P. elegans was calculated to be 0.18 prey/chaetognath/day in the western subarctic Pacific, 0.27 prey/chaetognath/day in the Bering Sea and 0.07 prey/chaetognath/day in the eastern subarctic Pacific.     

Dietary separation between co-occurring copepods in a food-limited tropical coral reef of the Sanya Bay

Food differentiation among coexistent species in the field is important strategy for copepods to acquire materials and maintain population stabilization.In situ diet analysis of co-occurring six copepod species in coral waters of the Sanya Bay was conducted using a PCR protocol based on 18 S ribosomal gene.Various prey organisms were uncovered,including dinoflagellate,diatom,green algae and plant,protozoa and metazoan.All these spatially coexisting six species showed different dietary diversity,with the food niche breadth(B)ranging from 1.00(Temora turbinate in morning)to 10.68(Calanopia elliptica in night).While food overlap between all these copepods were low,with the average value of the diet niche overlap index being approximately 0.09.Even temporally co-existing species sampled from the same time point fed on different groups of prey items with the food overlap index of 0.04 to 0.07 in midday and night but 0 in morning.As the most important dominant copepod in the Sanya Bay,Subeucalanus subcrassus seems to be capable to regulate its feeding,by exhibiting a rhythm of herbivorous feeding in midday and carnivorous feeding in morning and night,to better coordinate with other competitors for utilization of food resources.For most copepods,none of the prey items belonged to the dominant phytoplankton in the ambient water,indicating that copepod can better their survival by widening the choice of potential food resources in food limited environment.The dietary separation observed here might be important strategy for copepod to maintain population stabilization and thriving in the Sanya coastal waters.     

Observations on the predatory behaviour of the sevengill shark Notorynchus cepedianus

Studies on the feeding behaviour of large predatory sharks are inherently problematic because of the size of the animals, the difficulty in observing and handling them and the risks to the investigator. Observations on the feeding behaviour of the sevengill shark Notorynchus cepedianus over a seven-year period revealed this species to display at least four distinct foraging strategies. A particular strategy, or a combination of two or more, was employed depending on the size and type of prey being subdued. The four primary factors that appear to influence prey selection were prey size, availability and density, and scavenging. The behaviour of a prey species influences the predator's foraging and hunting behaviour. The success of the sevengill shark as an apical predator can be attributed, in part, to the feeding strategies it employs to subdue prey.     

Clam community composition and prey shell size impacts moon snail (Gastropod: Naticidae) drilling frequencies in South Carolina,USA

Moon snail predation on clams is a common model system of predator–prey interactions. In this system, the predator bores through the shell of its prey, leaving a distinct and identifiable hole. Some paleoecological and behavioral research on moon snails suggests a trend in predation preference directed toward clams with small shells. Rarely, however, have studies tested relative drilling frequencies across species and size ranges in natural assemblages of clam communities. We examined the clam community composition at two beaches in South Carolina, USA, and we then tested moon snail predator preferences for (a) clam prey species and (b) whether their selection is related to prey shell size. We collected a total of 1,879 clam shells, identified each shell to species and recorded their anteroposterior length. The species composition of clams differed significantly between the two beaches; Anadara ovalis was dominant at both sites, but three of ten total species were only collected at one beach. Folly Beach had nearly a 60% higher the overall drilling frequency (34.6%) versus Edisto Beach (21.8%), and this may be linked to the differences in clam community compositions at the sites. For A. ovalis and Mulinia lateralis, shells with larger lengths have lower probabilities of being bored by a moon snail. Anadara brasiliana, which generally is a thinner‐shelled clam species, had the highest total drilling frequency (77.2%), and Noetia ponderosa, a thicker‐shelled clam, had a considerably lower drilling frequency (12.0%). We conclude that both community level factors (species composition) and population characteristics (shell size distributions) may influence the local drilling frequency by moon snails.     

Limpets as prey: Lipophrys pholis choice for size

Patellid limpets are key species on rocky shores, structuring intertidal assemblages through their grazing. Their role as prey for fish is, however, often overlooked in studies of intertidal ecosystem functioning. The shanny Lipophrys pholis is a common predator of limpets on rocky shores in Northern Europe and, in this study, we examined the characteristics of its predation on limpets based on prey size. The limpet size range that adult L. pholis (10–12.5 cm) can eat was examined in the laboratory using Patella depressa in 0.2 cm classes, varying between 0.5 cm and 3.0 cm in maximum shell length. There was a limpet size refuge above 1.8 cm, while all smaller sizes were readily consumed by the shanny. The predator attacking behaviour was also examined and found to vary with prey size. Limpets up to 0.8 cm were crushed by the jaw‐constricting force and eaten whole, whereas larger prey were prised from the substratum and the body subsequently separated from the shell. To examine whether there was a L. pholis preference for P. depressa size, a two‐stage laboratory experiment was done using two size classes defined as small (0.7–0.8 cm maximum shell length) and large (1.5–1.6 cm maximum shell length). In the first stage, the predator was given each limpet size class separately. In the second stage, the fish was given a choice between the two classes. Lipophrys pholis was shown to have a preference for the large size class (1.5–1.6 cm). The average number of limpets consumed by the shanny was examined for the duration of one high‐tide typical of the central region of Portugal (≈ 4 h). On average, approximately five limpets (up to an eight limpet maximum) were consumed. The present study shows that L. pholis has a feeding preference based on limpet size, which suggests that the limpet population structure and intra‐ and inter‐specific interactions may be influenced by the shanny predation.     

Feeding of a pelagic chaetognath,Sagitta nagae Alvariño in Suruga Bay,Central Japan

The feeding ofSagitta nagae, the most predominant chaetognath species in Suruga Bay, was studied. Specimens were collected with ORI-100 net (1.0 mm in mesh aperture) and MTD net (0.35 mm in mesh aperture) and were fixed with neutralized formalin. The main food organisms ofSagitta nagae were the copepods,Candacia bipinnata, Calanus pacificus andPareuchaeta russelli. The food-containing ratio (P/T, %) was higher at night and lower in the daytime. Here, P is the number ofSagitta containing food organisms in the gut and T is the total number ofSagitta examined. P/T was almost constant vertically in the upper 100 m layer. P/T was generally influenced neither by food density nor by the copepod numbers perSagitta in this study.Sagitta nagae took food throughout life. Food ingested bySagitta per day was calculated as 37.6% ofSagitta in dry weight.     

Feeding ecology of the banded wrasse Notolabrus fucicola (Labridae) in southern New Zealand: Prey items,seasonal differences,and ontogenetic variation

Notolabrus fucicola Richardson, a large common labrid inhabiting shallow waters around New Zealand and southern Australia, were collected monthly (December 1996‐February 1998) around Kaikoura on the east coast of the South Island, New Zealand. Their diet, temporal variation in prey and gut fullness, and ontogenetic differences were examined. N. fucicola is a generalist predator, the major prey items being bivalves, amphipods, and crabs, which varied temporally in their diet. There were size specific changes in their diet. Small fish (100–180 mm) ate mostly amphipods and isopods, whereas larger fish (> 180 mm) ate mainly bivalves, crabs, and gastropods. There was a temporal variation in gut fullness but no significant difference between sexes.     

Feeding ecology of whelks on an intertidal sand flat in north‐eastern New Zealand

The dispersion patterns and feeding behaviour of intertidal whelks were investigated in north‐eastern New Zealand. Aggregations of whelks feeding on clams occurred regularly, with an average of 15–20 individuals per aggregation. Death of clams was attributable to predation in up to 50% of the aggregations, although scavenging of dead and moribund animals was the main activity of whelks. Laboratory and field studies showed that Lepsiella scobina (generally not considered a soft shore species) was the main whelk predator at Lews Bay, Whangateau Harbour, drilling a small neat hole through the clam shell. The distinction between Cominella spp. as predators or scavengers is not so clear. Reseeding of intertidal clams, Austrovenus stutchburyi, has been proposed as a technique for reestablishing populations in some degraded New Zealand estuaries. The impact of whelk predation has many implications for A. stutchburyi reseeding. Both L. scobina and Cominella adspersa may potentially prey on newly reseeded clams as they preferentially attacked small clams in the laboratory. On‐growing to a larger size before reseeding may be advantageous although large size was not found to protect prey from predation. Additionally, no seasonal trend in whelk activity was found.     

Effects of the oophagous bivalve Acesta oophaga on the morphology and fecundity of its deep‐sea tubeworm host,Lamellibrachia luymesi

The deep‐sea bivalve Acesta oophaga lives attached to the anterior end of the vestimentiferan tubeworm, Lamellibrachia luymesi, at cold methane seeps. The bivalve is found almost exclusively on female tubeworms, where it consumes the lipid‐rich eggs of L. luymesi that are spawned year round (Biological Bulletin, 209, 2005, 87). It is apparent that A. oophaga benefits directly from this close association, but the consequences for the tubeworm host may be more complicated than just a simple predator–prey interaction. Since A. oophaga completely surrounds the tube opening and plume of the worm, it is likely that its presence would limit oxygen uptake by L. luymesi, thereby inhibiting worm growth and reproduction. We hypothesized that occupied tubeworms would compensate for this by growing larger plumes for oxygen uptake. To explore the effects of bivalve presence/absence on female tubeworms, several morphological features, including body size, plume length, tube diameter, and tube segment length, as well as instantaneous fecundity, were compared. Results suggest that the mere presence of A. oophaga has a significant impact on the morphology of its host worm, as all measures of worm size, except for tube segment length, were significantly greater with clams present. Additionally, instantaneous fecundity was 3.5 times higher in occupied worms, implying that tubeworms are not oxygen‐deprived or energy limited as a result of bivalve presence. Our findings suggest that the association between these two deep‐sea organisms may be a more complex form of symbiosis than the simple predator–prey relationship, as previously thought.     

The contribution of microzooplankton to the diet of mesozooplankton in an upwelling filament off the north west coast of Spain

Incubation experiments were carried out daily during a Lagrangian experiment within an upwelled filament off the Galician coast to determine the importance of microzooplankton in the diet of calanoid copepods. Despite low chlorophyll concentrations the microzooplankton formed the minor component of the diet of the copepod community (7 to 15% of carbon ingested through autotrophic and heterotrophic prey). Ingestion of ciliates was greater than that of heterotrophic dinoflagellates, which reflected a higher abundance of ciliates in the water column. Heterotrophic nanoflagellates appeared also to be consumed by the copepods, although the very small size fraction (2–5μm) was probably not grazed by the larger copepods of Calanus spp. Grazing pressure by the copepods enumerated in the net samples was not sufficient to impact significantly the microzooplankton populations (2 to 51% of daily microzooplankton production was removed). Allometric relationships of grazing on microzooplankton for a range of numerically dominant copepod species are developed from the experimental results. The grazing pressure of the whole copepod community is estimated from these relationships. By considering the total mesozooplankton community we suggest that microzooplankton growth was probably restricted by metazoan grazers.     

Resource Partitioning Among Planktivorous Fish Larvae and Fry in a Mediterranean Coastal Lagoon

Resource partioning among the planktivorous stages of eight fish species occurring in a Mediterranean coastal lagoon was studied. Five species were migratory mullets that spawned in the sea (Liza ramada, L. aurata, L. saliens, Chelon labrosusandMugil cephalus), while the other three species were resident and spawned in the lagoon (Atherina boyeri, Cyprinus carpioandGambusia holbrooki).Mullet fry exhibited similar diets, based on the consumption of zooplanktonic Crustacea such as copepods and cladocerans, although adult chironomids were also important.Gambusia holbrookiandA. boyerifed on small prey such as copepod nauplii, copepodites and rotifers, whileC. carpioconsumed larger prey preferentially (cladocerans and copepods).According to the trophic overlap and niche width results, seven species pairs could be competing in the estuary, although further experimental evidence is still required.     

Distribution of chaetognaths in the central part of the Drake Passage

The mesoscale distribution of two chaetognath species, Eukrohnia hamata and Sagitta gazellae, found in the Drake Passage in October and November of 2008 was studied using a stationary grid in the area of the Antarctic Polar Front. The distance between the stations was around ten miles. The most abundant chaetognath species was Eukrohnia hamata, which accounted for 86.7% of all the individuals collected. In the upper 200 m, the average abundance of chaetognaths decreased from 2.1 to 0.8 ind./m³, and their average biomass decreased from 1.25 to 0.25 mg/m³ over the transition through the front from the north to the south. The high heterogeneity of the spatial chaetognath distribution in the area was demonstrated: the abundance of the chaetognaths could increase or decrease over 20 miles by a factor of 45 (6.8 and 0.15 ind./m³). In addition, two peaks were revealed in the size structure of the E. hamata population, probably indicating two periods of reproduction in this species in the Drake Passage.     

南黄海和渤海近海海域中华哲水蚤的现场摄食研究

桡足类是海洋生态系统中初级生产者和较高营养级消费者之间的关键联系环节,掌握桡足类的现场食物组成对于准确评估海洋食物网中的营养关系和能量转移至关重要。本研究中,我们以中华哲水蚤这一在中国、日本以及韩国近海具有重要生态地位的大型哲水蚤属桡足类为研究对象,应用之前开发的基于PCR的克隆技术,通过分析中华哲水蚤所摄食生物的18S rDNA序列,研究了中华哲水蚤的现场食物组成。结果揭示了南黄海（Y19站位）和渤海（B49站位）中华哲水蚤食物组成的多样性。共检测出43个操作分类单元（OTUs）,分别隶属于13个类群：硅藻（Bacillariophyta）、甲藻（Dinoflagellata）、硅鞭藻（Dictyochophyceae）、金藻（Chrysophyta）、Katablepharidophyta、浮生藻（Pelagophyceae）、无根虫（Apusozoa）、水螅水母（Hydrozoa）、栉水母（Ctenophora）、棘皮动物（Echinodermata）、被囊动物（Tunicata）、毛颚动物（Chaetognatha）以及海洋真菌。结果还表明,当发生藻类暴发时,中华哲水蚤可以摄食引发藻类暴发的藻种。当周围海域浮游植物的丰度相对较低时,中华哲水蚤可以选择摄食各种后生动物尤其是水螅水母和栉水母的卵、幼虫或者有机碎屑。我们的研究结果表明中华哲水蚤是一种杂食性桡足类,它对食物的选择依赖其生活海域中食物的可获得性。     

Predatory impact of an epiphytic hydrozoan in an upwelling area in the Bay of Coliumo (Dichato, Chile)

The natural diet of the epiphytic hydrozoan Obelia geniculata has been studied in an upwelling area in the Bay of Coliumo (Dichato, Chile) during two 24-h cycles. Number of prey per predator and predatory density have been measured. In both cycles more than 78% of the diet consisted of eggs of invertebrates and faecal pellets. Compared with other species of hydrozoans studied in a similar way, O. geniculata had a heterogeneous diet and a capture rate which was scarcely related to the peaks of abundance of its prey. This catch rate was between 632×10³ and 10 393×10³ prey m⁻² day⁻¹, which corresponds to a mean ingestion rate of 113% of the hydranth biomass per day. These results indicate the importance of small-sized benthic suspension feeders in upwelling systems.     

Scales of predator detection behavior and escape in Fissurella limbata: A field and laboratory assessment

The consumptive effects of predators are widely acknowledged, but predation can also impact prey populations through non‐consumptive effects (NCEs) such as costly antipredator behavioral responses. The magnitude of antipredator behavioral responses by prey is determined by an assessment of risk using sensory cues, which in turn is modulated by the environmental context. We studied the detection behavior and escape response of the keyhole limpet Fissurella limbata from the predatory sea star Heliaster helianthus. Through laboratory and field experimental trials, we quantified the distance and time of predator detection behavior by the prey, and measured their active escape responses when elicited. We found that predator detection by the limpet was chiefly mediated by distance, with experimental individuals capable of detecting predator presence effectively up to distances of at least 50 cm in the field and 70 cm under laboratory conditions. Our results indicate that this prey species is able to evaluate the proximity of its predator and use it as an indication of predation risk; therefore, predator–prey distance appears to be a primary predictor of the magnitude of the antipredator response. Given the tight relationship between predator distance and prey movement and the important role herbivores can play, particularly in this ecosystem, we expect that NCEs will cascade to the patterns of abundance and composition of rocky shore communities through changes in prey foraging behavior under risk.