Changes in nutrient content and stable isotope ratios of C and N during decomposition of seagrasses and mangrove leaves along a nutrient availability gradient in Florida Bay,USA

The decomposition of the mangrove Rhizophora mangle and the seagrass Thalassia testudinum was examined using litterbags along a natural gradient in nutrient availability. Seagrass leaves had a higher fraction of their biomass in the labile pool (57%), compared to mangrove leaves (36%) and seagrass rhizomes (29%); the overall decomposition rates of the starting material reflected the fractionation into labile and refractory components. There was no relationship between the N or P content of the starting material and the decomposition rate.

Nutrient availability had no influence on decomposition rate, and mass was lost at the same rate from litterbags that were buried in the sediment and litterbags that were left on the sediment surface. The dynamics of N and P content during decomposition varied as a function of starting material and burial state. N content of decomposing mangrove leaves increased, but seagrass rhizomes decreased in N content during decomposition while there was no change in seagrass leaf N content. These same general patterns held for P content, but buried seagrass leaves increased in P content while surficial leaves decreased. δ¹³C and δ¹⁵N changed by as much as 2‰ during decomposition.     

Mating system of the burrowing crab Neohelice granulata (Brachyura: Varunidae) in two contrasting environments: effect of burrow architecture

Few studies conducted in crustaceans have demonstrated how habitat features could shape the mating systems. Here, the burrow of Neohelice granulata was considered as a resource used for mating, and its architecture was characterized in two contrasting study sites: Mar Chiquita Lagoon (MCL), an estuary composed of muddy sediments, and San Antonio Oeste (SAO), a marine bay composed of gravel sediment. Burrow features differed between study sites and occupant gender. Large males constructed burrows with a chamber in MCL and with a widened entrance in SAO, while small males constructed the same narrow burrows as females at both study sites. Field experiments demonstrated that burrows with chambers or widened entries are places used for copulation, although successful post-copulatory guarding was displayed only in those with chambers. The intensity of the agonistic encounters and the success of males in winning resources (burrows/females) also depend on the habitat characteristics. N. granulata shows a resource defense mating system where males employ different mating strategies according to the burrow architecture to ensure mating success.     

Factors limiting distribution and activity patterns of the soldier crab Dotilla myctiroides in Phuket, South Thailand

This study was carried out between January and March 1995 on the intertidal sand flats of Tang Khen Bay, Phuket, South Thailand, where the soldier crab Dotilla myctiroides (H. Milne-Edwards) occurs in densities of up to 120 m⁻². In this bay, long, ribbon-like sand waves (wavelength 40 m, height 0.4 m) are interspersed with shallow pools, running approximately parallel to the shore. During daylight low-tides, exposure of the sand waves is followed 15 to 20 min later by the emergence of the crabs which have been buried under the sediment surface during high tide. Their subsequent burrowing and feeding activity results in the production of large numbers of sand pellets on the sediment surface. Most crabs retreat down their burrows, and some also plug the burrow entrance, prior to being covered by the incoming tide. The crab burrows have a distinct distribution on the sand waves. Burrows are most dense at the top of each sand wave, and a band of unburrowed sediment adjoins the adjacent tidal pools. Crabs are most abundant between mean high-water neap-tide level and mean low-water neap-tide level, where the median particle size of the surface sediment is ∼2 . Measurements of water-table depth below the sand waves and the exposure time of the sediment indicated that, where sediment size is suitable, the main factor controlling crab distribution is the duration of daytime exposure. This observation is in contrast to those of many previous studies, which have suggested that water-table height and sediment drainage are the main factors controlling the distribution of D. myctiroides. Received: 14 January 1998 / Accepted: 6 May 1999     

Changes in nutrient content and stable isotope ratios of C and N during decomposition of seagrasses and mangrove leaves along a nutrient availability gradient in Florida Bay, USA

The decomposition of the mangrove Rhizophora mangle and the seagrass Thalassia testudinum was examined using litterbags along a natural gradient in nutrient availability. Seagrass leaves had a higher fraction of their biomass in the labile pool (57%), compared to mangrove leaves (36%) and seagrass rhizomes (29%); the overall decomposition rates of the starting material reflected the fractionation into labile and refractory components. There was no relationship between the N or P content of the starting material and the decomposition rate.

Nutrient availability had no influence on decomposition rate, and mass was lost at the same rate from litterbags that were buried in the sediment and litterbags that were left on the sediment surface. The dynamics of N and P content during decomposition varied as a function of starting material and burial state. N content of decomposing mangrove leaves increased, but seagrass rhizomes decreased in N content during decomposition while there was no change in seagrass leaf N content. These same general patterns held for P content, but buried seagrass leaves increased in P content while surficial leaves decreased. δ¹³C and δ¹⁵N changed by as much as 2‰ during decomposition.     

Clam predation by whelks (Busycon spp.): Experimental tests of the importance of prey size,prey density,and seagrass cover

In 57 l-m² samples within a meadow of Halodule wrightii in Bogue Sound, North Carolina, USA, densities of the clams Mercenaria mercenaria and Chione cancellata were positively associated with seagrass cover. Where seagrass was experimentally removed, marked individuals of both clam species exhibited high rates of mortality in fine sand sediments during two successive experiments spanning 13 months. In the unaltered (control) seagrass meadow, M. mercenaria density remained constant over 13 months and C. cancellata density declined at a slower rate than in the unvegetated plots. Seagrass provides these clams with a refuge from whelk (Busycon carica, B. contrarium, and B. canaliculatum) predation, the major cause of mortality and population decline in experimentally unvegetated plots. In 2 factorial field experiments in unvegetated substratum in which densities of M. mercenaria and C. cancellata were varied independently, first over 5 levels (0 X, 1/2X, 1 X, 2 X, 4 X) and subsequently over 4 levels (0 X, 1/4 X, 1 X, 4 X), there was no repeatable intra- or interspecific effect of density on percent survival, or on the rate of any mortality type. Whelk predation fell preferentially on larger size classes of both species, whereas factors which contribute to clam disappearance usually acted more intensely on smaller sizes. Experimental exclusion of large predators by caging demonstrated that even in unvegetated substratum survivorship of both clam species was high in the absence of whelks and other predators. Individuals of C. cancellata live closer to the sediment surface than those of M. mercenaria, which may explain why seagrass does not serve as effectively to protect them from whelk predation. The mechanism of whelk inhibition may depend upon sediment binding by the H. wrightii root mat, which produces a demonstrable decrease in the physical penetrability of surface sediments.     

Benthic fauna of a shallow-water gaseohydrothermal vent area in the Aegean Sea (Milos, Greece)

The benthic community of shallow-water hydrothermal vents (10 m water depth) in a sandy bay on the south coast of Milos, Greece was studied. The macro- and meiofauna, as well as environmental factors such as temperature, salinity, sulfide concentration, grain size composition, ATP concentration, organic carbon, chlorophyll a and phaeopigments were evaluated. Samples were taken along transects from a seagrass meadow into a hydrothermally active area. Hydrothermally active spots were distinguished from the surrounding sediment by their black sediment coloration and an overlying white bacterial mat. For comparison, a control transect from a seagrass meadow into bare sand in a non-vent area in the same bay was studied. Overall, we found decreasing faunal diversity from the seagrass bed towards the hydrothermally active area. Along this gradient, four different zones could be distinguished. (a) The seagrass area had a relatively low diversity compared to the control stations, but much higher diversity than in the areas directly influenced by hydrothermal activity. (b) The border zone between the seagrass and the hydrothermal area, with moderate sulfide concentrations, pH values, seawater salinity and temperatures, was inhabited by an impoverished community dominated by the polychaete Capitella capitata, the nematodes Oncholaimus campylocercoides and Sabatieria sp., and an as yet undescribed chromadorid nematode (Chromadorina sp.). (c) The transition zone at the border of the hydrothermal area proper, with temperatures and sulfide concentrations higher than in the border zone, was characterized by high salinity (60‰) and low pH values. Along with the gastropod Cyclope neritea, single specimens of C. capitata and O. campylocercoides occurred. (d) The hydrothermal area proper, characterized by high sulfide concentrations, had high sediment temperatures and high salinities. The pH was as low as 6. Here, the gastropod Cyclope neritea was the only species occurring in considerable numbers. The gaseohydrothermal activity seems to largely exclude the surrounding fauna in a graded zonal pattern. The increasing hydrothermal stress entrains a change of the ambient biota towards a depauperate consortium of tolerant, opportunistic species, e.g. Capitella capitata (Polychaeta) and Oncholaimus campylocercoides (Nematoda). Although the hydrothermal area proper was characterized by a thick bacterial mat, the benthic community was characterized not by bacteria feeders but by scavenging species. Received: 13 September 1996 / Accepted: 24 October 1996     

Environmental determinants of distribution and foraging behaviour of cormorants (Phalacrocorax spp.) in temperate estuarine habitats

The distribution and behaviour of cormorants in estuarine environments was examined on the central coast of New South Wales, Australia, with respect to habitat associations at different spatial scales. No consistent variation in abundance was found for four species of cormorants (great Phalacrocorax carbo, pied P. varius, little black P. sulcirostris, and little pied P. melanoleucos) with state of tide (high and low) and time of day (early, middle, and late) at five estuarine locations. Differences in abundance were found among locations that were not confounded by short-term temporal variation (i.e. time of day and tide). Differences in abundance were detected among habitats (e.g. bays, creeks, and headlands) separated by hundreds of metres to kilometres in different estuaries. Cormorants of all species were rare on the open coast and near the entrance of estuaries. Abundances of cormorants varied greatly within and among creeks, bays, and river channels. Presence of seagrass beds explained much of this variation and most of the cormorants swimming and feeding were found near seagrass. Mapping of seagrass beds and the positions of cormorants at scales of metres to hundreds of metres showed a close relationship between the presence of swimming and roosting beds and the presence of seagrass beds for P. melanoleucos and for P. carbo. We argue that cormorants make decisions to visit particular estuarine habitats, especially those with seagrass, where many types of prey (e.g. fish and crustaceans) are probably most abundant. These choices must be interpreted in the context of decisions that cormorants make on scales of hundreds to thousands of kilometres during periodic excursions to the interior of Australia. Further, environmental threats to seagrass beds could impinge on these mobile visitors to the same extent as on more permanent residents. Received: 14 February 2000 / Accepted: 17 July 2000     

Functional burrow morphology of Biffarius arenosus (Decapoda: Callianassidae) from southern Australia

Burrows of the thalassinidean shrimp Biffarius arenosus (Poore, 1975) were investigated by in situ resin-casting on an intertidal sandflat in Western Port, southern Australia. Even though burrow casts exhibited interspecific variation, all had at least two openings, a U-shaped top and a series of tunnels and chambers. The space occupied by the burrows was deeper than it was wide; a maximal depth of 58 cm was recorded. Inhalant and exhalant shafts were restricted relative to tunnel diameter, and were often arranged in a multi-layered U-shape. Additional shafts branching from deeper sections of the burrows were occasionally observed. The main section of a burrow, extending from the base of the U, usually consisted of a downward spiral or an irregular spiral combined with some straight tunnel sections, all with a circular cross-section. The central spiral branched into further tunnels and chambers. Nearly all casts possessed peripheral chambers positioned either at the edges of horizontal lattices or in the deepest sections of the burrow. No evidence of plant material was found in peripheral chambers. Major burrow features were consistent with B. arenosus adopting a deposit-feeding trophic mode and collecting its food below the sediment surface. Received: 17 July 1998 / Accepted: 26 November 1998     

Variation in assemblages of fish associated with deep and shallow margins of the seagrass Posidonia australis

Little is known about the fish fauna of deep Posidonia australis seagrass beds in Australia. We investigated associated with the deep and shallow margins of P. australis during two surveys in Jervis Bay, New South Wales. Fish associated with deep and shallow seagrass at each of two areas within a large bed of P. australis were compared over a period of 3 mo (November 1986 to January 1987). This was followed by a larger scale survey in which we compared fish found at the two depths within three large beds of P. australis in Jervis Bay over 2 yr (September 1988 to June 1990). In the smaller scale survey there were marked dissimilarities in relative abhundance and composition of species between samples from deep and shallow P. australis. There were also significant differences in abundance between deep and shallow seagrass on most occasions for the majority of the dominant fish species. As a result of the small-scale survey, we concluded that differences in species composition of fish associated with deep and shallow P. australis may have been due to the presence of species from nearby bare substrate among the sparser leaves of the deep seagrass. The results of the smaller scale survey were not confirmed by the larger survey. The relative abundances of species in samples from deep and shallow P. australis were not dissimilar for all beds. In addition, it was rare for any of the dominant species to have significantly different abundances in deep and shallow seagrass. There was little evidence that the species composition of fish associated with deep P. australis was strongly influenced by the fauna of deep bare substrate. Rather, samples from deep P. australis were far more similar to those from shallow P. australis than to a comparable set of samples collected from deep bare substrata. This study demonstrates how the results and conclusions of small-scale survey work, a feature of many environmental impact asseesments, can be misleading when applied to larger spatial and temporal scales, even within the same bay.     

A field colonization experiment with meiofauna and seagrass mimics: effect of time,distance and leaf surface area

From a conservation point of view, it is essential to know how fast an ecosystem can recover after physical disturbance. Meiofauna and especially harpacticoid copepods are abundant in seagrass beds and are therefore useful to study ecosystem recovery after disturbance. In the western Caribbean coast, a fragmented Thalassia testudinum seagrass bed was selected to conduct a colonization field experiment by means of plastic seagrass mimics. Meiofauna colonization, with special emphasis on harpacticoid copepods, was followed in relation to: (1) colonization time (2, 4, 6, 10, 14 and 21 days); (2) distance to source of colonizers (close and far series) and (3) leaf surface area to colonize (small, medium, large). Colonization was recorded after 2 days with average meiofauna densities of 480 ind/100 cm² (close) and 1350 ind/100 cm² (far) of leaf surface area, while on average 400 ind/100 cm² were collected from the natural seagrass plants. In this early phase, the meiofauna diversity was high, with on average 8 taxa. A longer period of colonization (21 days) showed an increased meiofaunal density and diversity (average density: 3220 ind/100 cm², 13 taxa). Increasing meiofauna colonization with time is probably related to the development of a biofilm making the leaf more attractive for meiofauna. The effect of distance was not so pronounced as that of time. Total absolute densities were highest in the far series (5 m away from natural seagrass patch), mainly because of nematode densities. Meiofauna diversity was lower in the far series than in the close series (at the border of the natural seagrass patch). A larger individual leaf surface area did not affect the overall meiofauna densities but had a significant positive effect on copepod densities. Larger surface areas promoted the presence of epiphytic copepod families such as Tegastidae and Dactylopusiidae. Overall, we found a rapid recovery of meiofauna in fragmented seagrass beds with primary colonizers (both nematodes and benthic opportunistic copepods) originating from the sediment and later colonizers as epiphytic copepods and their nauplii from the local seagrass regeneration pool.     

Microbial reaction rates and bacterial communities in sediment surrounding burrows of two nereidid polychaetes (Nereis diversicolor and N. virens)

The effects of infaunal mode of life on sediment properties, microbial reaction rates, as well as abundance and composition of bacterial communities were studied in sediment surrounding burrows (mucus lining, oxidised wall, ambient anoxic and surface sediment) of two closely related, but behaviourally different, nereidid polychaete worms: the facultative suspension-feeder Nereis (Hediste) diversicolor and the obligate deposit-feeder Nereis (Neanthes) virens. Burrow sediment of the two species was collected from two adjacent (50 m distance) shallow sandy locations (Kertinge Nor, Denmark). The burrow lining and wall of both polychaete species were enriched in organic matter originating from mucous secretions by the inhabitants and phytoplankton trapped through irrigation. This was more evident for N. diversicolor that shows a significantly higher irrigation rate than N. virens. Both the organic matter mineralisation rates (based on anaerobic incubations) and bacterial abundance were higher along the burrow linings and walls. However, accumulation of porewater TCO₂ and dissolved organic carbon in sediments adjacent to burrows increased most rapidly in the presence of N. diversicolor, suggesting higher heterotrophic activity associated with this species. Surprisingly, bacterial abundance was lower around burrows of N. diversicolor than those from N. virens indicating that burrow environments from the first species harbour a more active bacterial community. Molecular fingerprints of the 16S rRNA gene from bacterial communities showed that the composition of the burrow linings and walls resembled the ambient anoxic sediment rather than the oxic sediment surface. On the other hand, the bacterial fingerprints of the sediment surrounding the burrows of the two polychaete species were markedly different suggesting either a site-specific difference in sediment parameters or a significant species-specific impact of the burrow inhabitants.     

Herbivory and detritivory among gammaridean amphipods from a Florida seagrass community

The gammaridean amphipods Cymadusa compta (Smith), Gammarus mucronatus Say, Melita nitida Smith and Grandidierella bonnieroides Stephensen from a seagrass community in the Indian River estuary of Florida (USA) fed variously upon large drift algae, small algae epiphytic on seagrasses and seagrass leaf debris and detritus. Consumption was measured in the laboratory using an index (CI) equivalent to mg ingested mg^-1 amphipod day^-1. Observations revealed that the amphipods fed by macrophagy, an attack upon large algae and seagrass debris, and by microphagy, small particle detritus feeding and scraping of plant surfaces for diatoms and other epiphytic algae. C. compta was a macrophagous feeder with a generalized diet of algae and seagrass debris, preferring epiphytic algae and drift algae at mean rates of 1.10 and 0.87 CI, respectively. Gammarus mucronatus fed upon epiphytes and seagrass debris equally at mean rates of 0.90 and 0.97 CI, respectively. The diet of M. nitida condisted primarily of epiphytes, consumed at an average rate of 1.05 CI. Grandidierella bonnieroides fed in a specialized microphagous manner, grooming plant surfaces for small particle detritus and diatoms at an approximate CI rate of 1.45. Assimilation of plants ingested, as reflected by carbon-14 uptake, varied similarly among the 4 amphipods. Epiphytic algae appeared to be most useful as food, providing means of 41 to 75% carbon-14 uptake as ingesta. Drift algae and seagrass debris were of less value, with means varying between 11 and 24 % of carbon-14 uptake by the amphipods. The data show a pattern of feeding which resembles resource partitioning of food both by size and kind. Other evidence, however, including population limitation by predators and an apparent overabundance of food, indicate that resource partitioning as seen may be an artifact, and one which has no co-evolutionary basis among the present species.Contribution No. 102 of Harbor Branch Foundation, Inc.     

Selective deposit-feeding by Lumbrineris cf. latreilli (Polychaeta: Lumbrineridae), with a new method for assessing selectivity by deposit-feeding organisms

The burrowing and feeding behaviour of an intertidal population of Lumbrineris cf. latreilli Audouin & Milne-Edwards, 1834 in Westernport Bay, Victoria, Australia was studied in 1982. Gut contents showed they were depositfeeders, ingesting predominantly sediment. Individuals were discretely motile, constructing semi-permanent burrows from which they fed upon subsurface deposits. Individuals in this population of L. cf. latreilli were selectively ingesting smaller particles. This is consistent with the predictions of optimal foraging theory modified for deposit-feeders.     

Effects of seagrasses and algae of the Caulerpa family on hydrodynamics and particle-trapping rates

The widespread decline of seagrass beds within the Mediterranean often results in the replacement of seagrasses by opportunistic green algae of the Caulerpa family. Because Caulerpa beds have a different height, stiffness and density compared to seagrasses, these changes in habitat type modify the interaction of the seafloor with hydrodynamics, influencing key processes such as sediment resuspension and particle trapping. Here, we compare the effects on hydrodynamics and particle trapping of Caulerpa taxifolia, C. racemosa, and C. prolifera with the Mediterranean seagrasses Cymodocea nodosa and Posidonia oceanica. All macrophyte canopies reduced near-bed volumetric flow rates compared to bare sediment, vertical profiles of turbulent kinetic energy revealed peak values around the top of the canopies, and maximum values of Reynolds stress increased by a factor of between 1.4 (C. nodosa) and 324.1 (P. oceanica) when vegetation was present. All canopies enhanced particle retention rates compared to bare sediment. The experimental C. prolifera canopy was the most effective at particle retention (m² habitat); however, C. racemosa had the largest particle retention capacity per structure surface area. Hence, in terms of enhancing particle trapping and reducing hydrodynamic forces at the sediment surface, Caulerpa beds provided a similar or enhanced function compared to P.oceanica and C. nodosa. However, strong seasonality in the leaf area index of C. racemosa and C. taxifolia within the Mediterranean, combined with a weak rhizome structure, suggests that sediments maybe unprotected during winter storms, when most erosion occurs. Hence, replacement of seagrass beds with Caulerpa is likely to have a major influence on annual sediment dynamics at ecosystem scales.     

Colonisation process of vegetative fragments of <Emphasis Type="Italic">Posidonia oceanica</Emphasis> (L.) Delile on rubble mounds

Seagrass colonise new areas via the dispersion of seeds or vegetative fragments. Independent of the manner of colonization, habitat requirements need to be met for the successful establishment of seagrasses. Here we report on the colonization process of Posidonia oceanica in a highly disturbed area: a gas pipeline trench at Capo Feto (SW Sicily, Italy). A trench dredged through a P. oceanica bed was back-filled with rubble added from dump barges leading to the formation of a series of rubble mounds on the seabed. Over time, these mounds became colonised with P. oceanica. I>. In order to understand the pattern of P. oceanica colonization, shoot density was quantified over 3 years (2001–2003) on different mound locations (crests, sides, valleys). Seagrass coalescence was observed only in valleys between mounds where shoot density averaged 133±50 shoots m⁻², while values for sides and crests were significantly lower (30.5±14 and 5.8±2.6 shoots m⁻², respectively). Although sediment accumulated on both crests and valleys, a significantly thicker sediment layer was recorded in the valleys (9.8±0.4 cm) than on crests (1.1±0.2). Plaster dissolution rate (an indicator of the hydrodynamic regime) tended to decrease from crests to valleys but even in the valleys, the currents were still higher than in the adjacent vegetated control location. This pattern was constant over time and depths. This is the first study to report on P. oceanica vegetative recruitment on artificial rubble after a disturbance event. It appears that the valleys between the rubble mounds are suitable for seagrass recruitment as sediment deposited between the rubble provides the necessary resources for plant settlement and growth. Once the seagrass patches are established, they may start a positive feedback of attenuation of currents, sediment accumulation and seagrass patch expansion.     

Seagrass and algal beds as nursery habitats for tiger prawns (Penaeus semisulcatus and P. esculentus) in a tropical Australian estuary

We evaluated the importance of seagrass and algae to two species of tiger prawns (Penaeus semisulcatus and P. esculentus) by detailed sampling at four sites (two seagrass, two algae) in the Embley River estuary, and through sampling 26 sites in 7 adjacent estuaries at one time of year. Samples of tiger prawns were collected in the Embley River estuary with a small beam trawl at night every 2 wk from September to May for 2 yr (1990 to 1992). The two seagrass sites, which were 11 and 13 km from the river mouth, showed less seasonal variation in salinity than the two algal sites, which were 15 and 20 km from the river mouth. The algal beds at the two upstream sites almost disappeared during the wet season, but the biomass of seagrass did not change significantly between the wet and dry seasons. The grooved tiger prawn (P. semisulcatus), the main species at all sites, comprised 88% of the total tiger prawn catch over the two years. They were found at all sites during the pre-wet season, but after the onset of the wet season, they disappeared along with the algae, from the upstream sites. The brown tiger prawn (P. esculentus) was found almost exclusively (97% of the total catch) on the seagrass sites downstream. In the study of several estuaries, juvenile P. semisulcatus were caught at all 26 sites, and P. esculentus were caught in much smaller numbers, at 16 sites. Approximately equal numbers of P. semisulcatus were caught in seagrass and algal beds in the pre-wet season. Very few individuals >10 mm carapace length of either species, were caught. The results from this study highlight the importance of algal beds during the pre-wet season as nursery areas for one species of tiger prawn (P. semisulcatus).     

Caribbean mangroves and seagrass beds as daytime feeding habitats for juvenile French grunts, Haemulon flavolineatum

Caribbean seagrass beds are important feeding habitats for so-called nocturnally active zoobenthivorous fish, but the extent to which these fishes use mangroves and seagrass beds as feeding habitats during daytime remains unclear. We hypothesised three feeding strategies: (1) fishes feed opportunistically in mangroves or seagrass beds throughout the day and feed predominantly in seagrass beds during night-time; (2) fishes start feeding in mangroves or seagrass beds during daytime just prior to nocturnal feeding in seagrass beds; (3) after nocturnal feeding in seagrass beds, fishes complete feeding in mangroves or seagrass beds during the morning. We studied the effect of habitat type, fish size, social mode and time of day on resting and feeding behaviour of large juvenile (5–10 cm) and sub-adult (10–15 cm) Haemulon flavolineatum in mangroves and seagrass beds during daytime. Sub-adults occurred in mangroves only, spent most time on resting, and showed rare opportunistic feeding events (concordant with strategy 1), regardless of their social mode (solitary or schooling). In contrast, large juveniles were present in both habitat types and solitary fishes mainly foraged, while schooling fishes mainly rested. Exceptions were small juveniles (±5 cm) in seagrass beds which foraged intensively while schooling. Large juveniles showed more feeding activity in seagrass beds than in mangroves. In both habitat types, they showed benthic feeding, whereas pelagic feeding was observed almost exclusively in the seagrass beds. In both habitat types, their feeding activity was highest during 8:00–10:30 hours (concordant with strategy 3), and for seagrass fishes, it was also high during 17:30–18:30 hours (concordant with strategy 2). The study shows that both mangroves and seagrass beds provide daytime feeding habitats for some life-stages of H. flavolineatum, which is generally considered a nocturnal feeder.     

Molecular association of Cu,Zn, Cd and 210Po in the digestive gland of the squid Nototodarus gouldi

In July 1985, very fine burrows extending at least to a sediment depth of 50 cm were found in sediments of the Vöring-Plateau, Norwegian continental slope, at depths of 1 261 to 1 969 m. Such burrows have been described from other areas of the oceans, but until now the producers have been unknown. In the box-cores from Vöring-Plateau sipunculans of the genus Golfingia, subgenus Nephasoma, were identified as inhabitants and producers of these Lebensspuren, which correspond with the fossil ichnogenus Trichichnus.     

Reproductive biology of a filter-feeding amphipod, Leptocheirus pinguis , with extended parental care

Leptocheirus pinguis (Stimpson, 1853) is a widely distributed, abundant, endobenthic amphipod that engages in extended parental care, i.e. females host their juveniles in their burrows for extended time periods. I examined reproduction and population biology of L. pinguis at mean low water (MLW) in muddy sediment in Lowes Cove, Maine, USA. Cores around individual burrows were taken monthly in 1994 and 1995, and four seasonal samples were taken at different tidal heights. During the major reproductive periods in spring/early summer and in the fall, females produced several consecutive broods and hosted growing offspring in their burrows. Juveniles remained in their mothers' burrows until they reached a length of 5 mm (approximately one-third adult size) or more. At the study site, the majority of amphipods in individual burrows were adult females. Following the main reproductive periods, subadult individuals were found in their own burrows, but densities did not increase following the reproductive period in spring/early summer 1994, probably because large numbers of L. pinguis emigrated via the water column between June and December. L. pinguis is an annual species. Many members of the cohort born in spring/early summer start reproducing in the fall, and survive until the following spring when they produce several broods. Members of the cohort born in the fall start reproducing the following spring and also produce several consecutive broods. Both the spring/early summer and fall cohorts die off after the major reproductive period in the following spring/early summer. High standing stocks of microphytobenthos occur in soft-bottoms at MLW, and I conclude that L. pinguis can engage in extended parental care there because its food is abundant year-round. The limited expandability and low stability of burrows in soft-bottoms at MLW do not permit long persistence of parent–offspring groups in L.␣pinguis. Received: 27 March 1997 / Accepted: 30 July 1997     

Adaptive behaviour of chironomid larvae (Chironomus riparius) in response to chemical stimuli from predators and resource density

Chemical-mediated effects of predatory fish on chironomid larvae behaviour have been ignored so far. Sediment-dwelling chironomid larvae inhabit protective burrows from which they extend their bodies only to feed on deposited detritus and microalgae from the surrounding sediment. Here, we performed factorial laboratory experiments to study whether fish-borne chemical cues (kairomones) are responsible for behavioural trait changes of chironomid larvae, and whether chironomid larvae are able to assess the densities of fish predators and food resources and the trade-off between them. We exposed naïve Chironomus riparius larvae to the chemical presence of zero, one, and ten predator fish (Rutilus rutilus) and offered two resource levels (low food, high food) for each treatment. Kairomones induced significant inherent behavioural trait changes in chironomid larvae. During the first 120 min after exposing chironomids to fish-conditioned water, we found a significant increase in digging activity with increasing predator density. After 3 days of exposure, the deepest chironomid burrows were found in treatments with the highest predator density. Chironomid larvae were significantly able to adjust their foraging behaviour to different predator densities and food concentrations and trade off between them; that is, when fish predators were more abundant or when more food resources were available, the foraging activities of larvae were significantly reduced. Our data suggest that chemically mediated trait changes (burrowing and foraging behaviour) may cascade through the littoral food web.