Untersuchungen an Plattfischen und Nordseegarnelen(Crangon crangon) im Eulitoral des Wattenmeeres nach dem Übergang zum Bodenleben

In spring and early summer,Pleuronectes platessa, Platichthys flesus, Solea solea, andCrangon crangon transform to benthic postlarvae in the shallow water region of the North Frisian Wadden Sea (eastern North Sea). During the first weeks after metamorphosis, they remain in the puddles and drainage gulleys on the tidal flats that are exposed during low tide. Positive rheotaxis prompting the juveniles to swim against the ebb tide currents is an important mechanism for maintaining their position on the flats. When sunlight intensity increases, they continue their locomotory and feeding activity, even during daytime, in the pools still present at low tide. On warm, cloudless days, temperature levels in these pools may increase to lethal thresholds. Consequently, the animals attempt to escape from higher tidal flats near the shore through the drainage gulleys. Such migrations bring about changes in their distribution patterns. Plaice can scarcely be found in near-shore areas, and they are absent at both high and low tide. The responses observed were correlated to physical and chemical data recorded during the observation period. The ecological significance of tidal pools as habitats is discussed.     

Factors that affect juvenile emergence in Gammarus palustris (Bousfield, 1969)

In the laboratory, hatched juveniles of the amphipod Gammarus palustris (Bousfield, 1969) emerged from the female's brood pouch at increased rates when the mother was pipetted, fed on mussel meat, or was immersed after a period of exposure to the air. Because juveniles emerged unaided from females feeding on mussel meat, its presence appeared to stimulate the juveniles to emerge.G. palustris is typically found at the high tide mark in the intertidal zone during the reproductive season. Females experience factors similar to those tested in the laboratory only when covered by water; when the tide is out they lie quiescent under rocks and debris. It is hypothesized that in the field juveniles emerge at the greatest rate at the beginning of an incoming tide.     

Laboratory observations on the feeding behaviour, reproduction and morphology of Galeodea echinophora (Gastropoda: Gassidae)

Galeodea echinophora fed on Echinocardium cordatum in an aquarium. Every few days, each G. echinophora emerged from the sand and foraged for 1–3 h. On detecting an Echinocardium , the Galeodea stopped locomotion and attacked the buried prey from the surface of the sand. The proboscis was extended down to the prey and a small area of test was cleared of spines. A disc was cut out of the softened test, leaving a hole of about 2 mm in diameter. All flesh except the gut was removed from the prey, the entire procedure taking 50–180 min.
One Galeodea echinophora laid 120 egg capsules on the side of the aquarium. These were kept at 13^oC and hatched after 112–159 days. Within the capsule, veligers fed on the yolk cells of abortive embryos. Juveniles hatched at the crawling stage, and at first secreted strings of mucus acting as drogues, but after 1 day the juveniles crawled over the substratum. They readily attached themselves to adult Echinocardium cordatum , apparently feeding on the epithelium between the spines or tube feet. Dissection revealed entry of the acinar glands into the proboscis gland ducts, a widening of these ducts as they empty into the buccal cavity and a dorsal fold in the anterior oesophagus. Radular teeth and jaws of Galeodea differ little among species; a taxonomic review of the genus is needed.     

Ontogeny of an endogenous rhythm in Eurydice pulchra

Field catches of Eurydice pulchra (Leach) from an Isle of Man beach indicated that adult animals were active in the water column solely during spring tide periods, whereas juvenile animals swam abundantly at high tide irrespective of lunar phase. Under constant conditions in the laboratory, animals kept in actographs with sand showed a circa-tidal rhythm of spontaneous emergence and swimming activity. In adults, the activity was greatest during “expected” night-time high-waters and was expressed solely after collection during spring tide periods. The rhythm was independent of sex, season or reproductive status. Juveniles showed no such diurnal modulation of the rhythm and the pattern was expressed throughout the semi-lunar cycle. These ontogenetic differences in behaviour are discussed in the light of previous work on the rhythm, and in terms of the differing habits of the mature and immature animals.     

Juveniles stick to adults: recruitment of the tube-dwelling polychaete Lanice conchilega (Pallas, 1766)

Juveniles of the tube-dwelling polychaete L. conchilega were found attached to adult tubes at an exposed beach in South Wales (U.K.). They attached to the upper part of tubes protruding above the sediment. The aim of this study was to determine the timing of juvenile settlement on to adult tubes, their abundance and size distribution, and the time of detachment and densities in the sediment after re-settlement. Furthermore, to establish whether the sediment composition of juvenile tubes differed from those of adults and the surrounding sediment. In 1998, 1999 and 2000, tubes of adult L. conchilegawere sampled and numbers of attached juveniles were quantified and their sizes measured. Densities of solitary L. conchilega in the sediment were estimated, as well as the size distribution of solitary tubes. On average, 5–13 juveniles were attached to single adult tubes in spring, but numbers varied greatly with up to 72 juveniles on a single tube in April 1998. Availability of a hard substratum and chemical cues are discussed as potential factors triggering the attachment of juveniles to adult tubes. Juveniles started to detach and re-settle in the sediment 1 month after attachment. Once settled in the sediment, juvenile numbers decreased steeply, but the size distribution of solitary L. conchilega suggested that some juveniles survived in the population. However, the extent to which numbers of juvenile recruits contribute to the density of adults remained unclear. Juveniles used a smaller mean particle size for tube building than adults, but both actively selected particles.     

Behavioural basis of intertidal zonation in Eurydice pulchra Leach

Eurydice pulchra Leach freshly collected at neap and spring tides exhibits an endogenous circatidal rhythm of swimming when kept without sand in constant conditions in laboratory aquaria. When provided with sand in the laboratory, tidally-phased swimming may occur spontaneously at some times of the lunar month, predominantly after the times of highest spring tides but not at neaps. In these cases, therefore, there appears to be clearly demonstrated for the first time in a marine animal a circasemilunar pattern of emergence from the substratum which is coupled to a circatidal rhythm of swimming; the isopods in the laboratory emerge from the sediment only when the swimming rhythm and emergence rhythm are at their maxima. In the field at neap tides some isopods emerge to swim at high tide, dependent upon their responses to water agitation, their feeding state and responses to light. At and just after spring tides in the field large numbers of the isopods swim at high tide, triggered by the endogenous circasemilunar rhythm of emergence which in the field is probably cued by the effects of increased water agitation. The main function of the endogenous circatidal rhythm of swimming appears to be to permit the isopods to return to their preferred zone in the sand before the fall of the tide. The coupled circasemilunar rhythm of emergence which induces greater swimming at spring tides reduces the risk of animals being stranded high on the shore during neap tides.     

Population Dynamics of Heterodera glycines Life Stages on Soybean

Population fluctuations of Heterodera glycines differ in fields with high and low initial population densities. In a field with low initial numbers of nematodes, the numbers of cysts and eggs in soil remained low through 100 days from planting then increased during the remainder of the growing season. In a field with high initial nematode populations, numbers increased at 30 days, decreased to low numbers at 100 days, and then resurged to maximum populations at harvest. Numbers of juveniles were greatest at 100 days in the low initial population density field and at planting in the high initial population density field. The initial numbers of eggs in the soil gave the best correlation to soil and root nematode populations 15 and 30 days later. Juveniles in the soil at planting gave the largest correlation coefficients with nematode populations in the roots at 15 days in the field with the low initial population density. Eggs and juveniles in the soil at harvest were poorly related to numbers that overwintered.     

The energy production of juvenileArenicola marina (Polychaeta) under anoxic and hypoxic conditions

The mode of anaerobic energy production of juvenileArenicola marina (0-generation) was investigated under experimental conditions and in the biotope. Under experimental anaerobic conditions, juvenileA. marina produce energy by the pathways known from the adults and other euryoxic invertebrates with succinate and the volatile fatty acids, acetate and propionate, as main end products. However, the juvenile lugworms are less resistent to anoxia than the adults. The reasons for this might be their small glycogen stores and their limited ability to reduce the metabolic rate. Nevertheless, on the tidal flats the juveniles settle particularly in the area next to the high tide line, which offers such extreme conditions that adult lugworms cannot live there. This different behaviour can be explained by the dissimilar ability to use oxygen at very low partial pressures. Juveniles maintain an aerobic energy metabolism even at a P_{WO 2} of 15 Torr at which adults are forced to produce energy exclusively by the less effective anaerobic mode. In the field, no indications of an anaerobic energy metabolism were detected in juveniles even after an exposure of 8 hours.     

Evidence for female-biased juvenile dispersal in corophiid amphipods from a New Zealand estuary

This study examined the distribution and dispersal of corophiid amphipods (Paracorophium spp.) in a temperate New Zealand estuary. Individuals in the sediment (resident population) and those caught in bed-load (local-scale movement) and suspended-load (larger-scale movement) were counted, measured, and sexed, during two tidal cycles at 4-6 week intervals spanning 13 months. Gravid females and juveniles were present in the resident population on all sample dates suggesting near continuous reproduction. Juveniles (< 2.2 mm body length) accounted for 49.8% of individuals in the sediment, compared to 65.4% of those caught in the bed-load and suspended-load traps. For the majority of sample dates, there was a net export of juveniles from the estuary. The total number of juveniles captured in suspended-load traps was significantly greater during the ebb tide relative to the flood tide (n = 541 versus 256), whereas no significant differences were found for adults. Similarly, numbers in the bed-load traps were significantly greater for juveniles during the ebb versus the flood tide (n = 900 versus 484), and also for adult females (n = 180 versus 86). Juvenile sex ratios were female biased in the sediment (9.8:1) and in suspended-load traps (7.6:1) and both were significantly more female-biased than that recorded for juveniles caught in bed-load traps (5.8:1). By contrast, there was a significantly lower proportion of adult females to adult males found in bed-load traps (1.7:1) and in suspended-load traps (0.98:1) compared to the resident population in the sediment (3.6:1). The mean size of juvenile females caught on a flood tide was significantly larger compared to those on the ebb tide, yet juvenile males were not significantly different, suggesting that smaller females were not returning on the flood tide. We suggest that female-biased juvenile dispersal for estuarine Paracorophium spp. lowers the risk of inbreeding and reduces competition. This may have evolved in response to a polygamous breeding system with little or no social organisation where a female produces more female offspring to maximise her inclusive fitness.     

Movement Patterns and Residency of the Critically Endangered Horseshoe Crab Tachypleus tridentatus in a Semi-Enclosed Bay Determined Using Acoustic Telemetry

The horseshoe crab Tachypleus tridentatus is critically endangered in Japan due to rapidly decreasing numbers resulting from the loss of tidal flats and sandy beaches, and the deterioration of coastal environments. We monitored the year-round migratory patterns and residency of this species in a coastal embayment at Tsuyazaki, Japan, using acoustic telemetry. Total 20 adult crabs (15 males and 5 females) were tagged with ultrasonic transmitters and tracked during two periods (2006–2008; n = 10 and 2007–2009; n = 10). Adult crabs were more active during periods of higher water temperatures and their activity peaked in July, during the spawning period. Water temperature appeared to be one of the key factors influencing the movement patterns for the species. Moreover, the crabs tended to be more active at night than in the day. The nocturnal activity pattern was clearly evident before and during the reproductive period (May–August). Tracking data also showed that one pair-bond was maintained for a maximum of 17 days after the pair-bonded female had spawned. Overall, 11 males (73% of 15 individuals) remained in the bay area over winter, whereas three females (60% of 5 individuals) overwintered outside of the bay. Telemetry data showed that over 60% (13 of 20) of tagged crabs overwintered within the bay where there are sandy beaches, mudflats, and scattered seagrass beds. This year-round residence by adult T. tridentatus in the bay area identifies it as a critical habitat for the management of this species, regardless of life-stage. Not only is it a comprehensive management strategy that effectively reflects this species’ habitat use patterns but also its implementation, such as the establishment of a protected area, would contribute to its conservation.     

Substrate color preference and feeding by juvenile Chinese sturgeon <Emphasis Type="BoldItalic">Acipenser sinensi</Emphasis>s: exploration of a behavioral adaptation

Experiments were conducted in artificial stream tanks with juvenile Chinese sturgeon, Acipenser sinensis, captured in the Yangtze Estuary to test two null hypotheses (1) juveniles have no preference for white or black substrates, and (2) white or black substrate color has no effect on juvenile feeding efficiency on the barcheek goby,Rhinogobius giurinus, a dark-colored prey of wild juveniles. Juveniles strongly preferred white substrate. However, in feeding tests, feeding efficiency by juveniles was similar on white or black substrates. Thus, substrate color had no effect on feeding efficiency. Results suggest the innate preference for white substrate is not a visual adaptation for capturing prey on a contrasting background, but is an adaptation predisposing juveniles to seek light-colored sandy substrate where forage abundance is greatest.     

Periodic movement,recruitment and size-related distribution of the sea cucumber Holothuria scabra in Solomon Islands

Field studies of the sea cucumber Holothuria scabra conducted in Kogu Veke, Solomon Islands, showed monthly recruitment of newly-settled juveniles on seagrass and indicated that size distribution was a function of substratum type and depth. Adults >250 mm body length were found mainly on sand, with <5% organic matter (OM), at depths of >1–3 m. Individuals >10–250 mm were found mostly in 30–120 cm of water, on mud and muddy sand with OM content between 5 and 10%. Specimens >40–150 mm were also found in the intertidal zone, sometimes burrowed on exposed sandflats at low tide. Holothuria scabra avoided substrata of fine silt or shell and coral pebbles, and sediment with an organic content 30%. Juveniles 100 mm burrowed at sunrise and surfaced at sunset, whereas individuals >100 mm burrowed and surfaced a few hours earlier. Holothuria scabra tended to burrow when salinity decreased, whereas increased water temperatures reduced normal burrowing behaviour. Spatial distribution, observed during tank experiments, suggested that adult H. scabra aggregated prior to spawning and in response to the lunar cycle. The formation of pairs, trios or larger groups increased during the new moon and was most common just before the full moon. Newly-settled juveniles up to ca. 9 mm were found on seagrass leaves. Typically, maximum densities and smallest recruits were observed a couple of weeks after the full moon, lower densities and slightly larger recruits were found a few days later. Juveniles with a mean length around 65 mm released on sand moved less and grew faster than juveniles released in seagrass beds or on substrata of shells and crushed coral.     

Spatial configurations generated by motile benthic polychaetes

Micro-spatial patterns of five infaunal polychaete species were investigated on tidal flats in the Wadden Sea (island of Sylt, North Sea). Sediment samples were taken within plots of 4 m² at regular distances or with a multiple-cell corer composed of 144 contiguous units. Most of the configurations observed can be related to the mode of feeding. Individuals of the predatory polychaeteEteone longa do not generate discernible spatial structures.Anaitides mucosa, a carnivoruous scavanger, occurs in marked patches. Juveniles ofScoloplos armiger, a burrowing deposit feeder, live in small aggregates which in turn conglomerate to larger ones. Adults are scattered within larger clusters. High density areas of juveniles and adults do overlap. Another burrowing deposit feeder,Capitella capitata, is even more aggregated. Local attractors may cause clusters of exceptional intensity. Territoriality is exhibited by the tube-dwelling surface deposit feedingNereis diversicolor. The juveniles are restricted to interspaces left by the adults.I acknowledge a grant from the Deutsche Forschungsgemeinschaft (DFG).     

Long-Term Starvation and Posterior Feeding Effects on Biochemical and Physiological Responses of Midgut Gland of Cherax quadricarinatus Juveniles (Parastacidae)

We investigated the effect of long-term starvation and posterior feeding on energetic reserves, oxidative stress, digestive enzymes, and histology of C. quadricarinatus midgut gland. The crayfish (6.27 g) were randomly assigned to one of three feeding protocols: continuous feeding throughout 80 day, continuous starvation until 80 day, and continuous starvation throughout 50 day and then feeding for the following 30 days. Juveniles from each protocol were weighed, and sacrificed at day 15, 30, 50 or 80. The lipids, glycogen, reduced glutathione (GSH), soluble protein, lipid peroxidation (TBARS), protein oxidation (PO), catalase (CAT), lipase and proteinase activities, and histology were measured on midgut gland. Starved crayfish had a lower hepatosomatic index, number of molts, specific growth rate, lipids, glycogen, and GSH levels than fed animals at all assay times. The starvation did not affect the soluble protein, TBARS, PO levels and CAT. In starved juveniles the lipase activity decreased as starvation time increased, whereas proteinase activity decreased only at day 80. The histological analysis of the starved animals showed several signs of structural alterations. After 30 days of feeding, the starved-feeding animals exhibited a striking recovery of hepatosomatic index, number of molts, lipids and glycogen, GSH, lipase activity and midgut gland structure.     

福建及中国其他沿岸海域中国鲎资源分布现状调查

采用调访渔民、浅海底拖网、野外观测潮间带亲鲎产卵和幼鲎孵育情况等调查方法,重点调查了福建沿岸海域中国鲎(Tachypleus tridentatus)资源分布和数量,并走访调查了浙江省、广东省、海南省、广西壮族自治区和台湾地区金门岛等地代表性的中国鲎栖息地,对中国沿岸海域中国鲎资源现状作了较全面的调查。结果表明,大部分海滩已多年未见中国鲎上岸产卵,中国鲎在上岸之前已被渔民通过底拖网捕获,能见到幼鲎的海滩寥寥无几,中国鲎已经从大部分海域消失,中国鲎资源量濒临枯竭。目前尚存少量中国鲎的海域主要是东山湾和北部湾海域。金门岛海域则因为人工放流和设立了中国鲎保护区,中国鲎资源得到较好的恢复。中国鲎资源衰竭的主要原因是人类的过度捕捞、栖息地的破坏和海域环境污染等。中国鲎资源的保护迫在眉睫。建议将中国鲎列入国家级重点保护动物名录,增设中国鲎自然保护区,加强渔业管理以及人工增殖放流等措施。     

Density-dependent recruitment after winter disturbance on tidal flats by the lugworm Arenicola marina

The polychaete Arenicola marina is abundant and widespread on intertidal sand flats in K?nigshafen (island of Sylt, North Sea). Juveniles overwinter in subtidal channels and then colonize the upper tidal zone above the range of the adults. In the summers of 1995 and 1997, after a mild and a moderate winter, a distinct nursery belt fringing the shoreline was apparent. The severe winter of 1995/96 changed this pattern. Population size of the adults was halved, and in summer 1996 the juveniles were no longer restricted to an upper intertidal belt and settled over a wide range of tidal flats where adults were diminished. This spatial expansion of recruits is assumed to be a density-dependent response. An overcompensation by one-third of the previous population size did not carry over into the next year. Compared to some other species of the tidal-flat fauna, the disturbance effect by the severe winter on the lugworm population was small and brief. Received in revised form: 7 May 2001 Electronic Publication     

Post-migratory care of young by Crab Plovers Dromas ardeola

The Crab Plover Dromas ardeola is the only waterbird species known to provision offspring well after the post-reproductive migration and through overwintering. A few previous quantitative studies have reported inconclusively that juveniles begged rarely, and also indiscriminately at other juveniles. Here, we describe the feeding behaviour of adult and juvenile Crab Plovers during the first part of the wintering period. Juveniles begged frequently for food, always toward adults, and obtained 0.1 prey items/min from them. Begging birds obtained the largest prey items of those captured by the adults. When foraging alone, juveniles captured prey at the same rate as adults, but captured smaller crabs. The feeding success of adults was not altered by the presence of the begging juvenile. Juveniles depended partly on adults during the first part of the overwintering period, but were almost independent towards the end. Crab Plovers may adopt such unusually prolonged care because they need to abandon their breeding areas quickly, when environmental conditions are extreme. Large numbers of Crab Plovers overwinter in a few areas, now subject to human alteration. Isolated adults may forage on other areas such as narrow and disturbed shores, but juveniles may require wide beaches, suitable for group foraging, that should be considered as key areas for the recruitment of juveniles into the population.     

Nocturnal foraging habitats of French and bluestriped grunts,Haemulon flavolineatum and H. sciurus,at Tobacco Caye,Belize

Synopsis Nocturnal foraging habitats of Haemulon flavolineatum and H. sciurus were investigated in the backreef habitat around Tobacco Caye, Belize. Grunts leave the reef at dusk to forage in the grass beds and sand flats surrounding the reef. The hypothesis that French and bluestriped grunts use separate foraging habitats was examined by following tagged fishes from their diurnal territories or schooling sites to nocturnal foraging grounds. The tag consisted of a small, glowing Cyalume light stick sutured to the dorsal musculature of the fish, next to the first dorsal fin. Surveys of foraging habitats were done to support the tracking study. Large quadrats (225 m²) were set out over the sand flats and grass beds during the day. The numbers of French and bluestriped grunts feeding in each habitat were counted one hour after dark. Foraging French grunts used sand flats, whereas bluestriped grunts usually fed in grass beds. Repeated sightings of two French grunts and one bluestriped grunt in the same individual night-time locations support the hypothesis that nocturnal foraging sites may be used repeatedly by the same individuals.     

Feeding of grey gurnard Eutrigla gurnardus (Triglidae) in the area of the Rockall Seamount

Specific features of feeding of grey gurnard Eutrigla gurnardus depending on vertical distribution and habitat conditions in the area of the Rockall Seamount in 2000 were considered. The intensity of feeding of grey gurnard from April to September decreased by several times. The main food of this species in spring are euphausiids and that in autumn are fish. Males feed slightly more intensively than females. The intensity of feeding, distribution, and behavior of grey gurnard in different seasons and at different depths near bottom and in the pelagial noticeably differ and depend on the composition of distribution and numbers of dominant food items (euphausiids, sand eel Ammodytes marinus, fish juveniles).     

Saisonale und tidale Variation in der Nutzung von Wattfl?chen durch nahrungssuchende V?gel

Densities of feeding birds were estimated on tidal mud flats in relation to season and tide. Dunlin, Knot, Bar-tailed Godwit, Oystercatcher, Golden Plover, Common Gull, and Black-headed Gull were most abundant. Seasonal variation was significant in all species. In general, there was a correlation between bird numbers on study plots and total bird numbers in the area. Preferences for a particular sediment type and prominent occurrence at tideline in some species was explained as an adaption to differential food availability.