Feeding grounds for waders in the Bay of the Mont Saint-Michel (France): the Lanice conchilega reef serves as an oasis in the tidal flats

The tube-building polychaete Lanice conchilega can form dense populations, often called reefs, which promote benthic community change and constitute feeding grounds for secondary consumers. The aim of this study was to quantify the role of the L. conchilega reef of the Bay of the Mont Saint-Michel (BMSM) for feeding waders, by combining macrobenthos data, bird counts and bird diet information. Wader densities in the reef were on average 46.6 times higher than in non-reef areas. According to faecal analyses, waders in the reef mainly selected the accompanying fauna and especially crustaceans. The attractiveness of the reef to feeding birds may be largely explained by the high abundance, richness and biomass of macrobenthic species in the reef compared with the rest of the BMSM.     

Anchorage of embryos in Spirorbinae (Polychaeta)

Methods of incubation are taxonomically important in Spirorbinae. About half of the known species incubate in the operculum, but the remainder are usually described simply as incubating within the tube. Studies of tube incubation show that the embryos are anchored in various ways. They form an egg string, which is attached to the tube by a posterior filament in Spirorbis and Spirorbella; they adhere more generally to the tube wall in Circies and Paradexiospira; they are attached to specialised thoracic stalks in Protolaeospira, Helicosiphon and Romanchella; they adhere to the body surface in Metalaeospira and probably in Eulaeospira; they are not attached to either body or tube in Paralaeospira. Tube incubation is found predominantly in temperate or cold waters. In most species from the southern hemisphere, embryos are anchored to the bodies of the parents, but in most species from the northern hemisphere, embryos are fixed to the walls of the parent tubes.     

Gametogenesis in Harmothoe imbricata (Polychaeta: Polynoidae)

The processes of gametogenesis in Harmothoe imbricata are described and illustrated. For most of their development the gametes are attached to the walls of segmental blood vessels. In males, only meiosis and sperm differentiation occur while the cells are free in the coelom. In females, oocytes are only released into the coelom briefly, after vitellogenesis has been completed. H. imbricata thus differs from most polychaete species so far described — where in males the spermatogonia divide mitotically to form rosettes after they have been released into the coelom, and in females the whole of vitellogenesis occurs after release of oocytes into the coelom. The oocytes of H. imbricata enter the first metaphase of meiosis before they are shed at spawning. The elongated head of the sperm in H. imbricata is atypical of polychaetes in general.     

Feeding preferences and the relationships between food choice and assimilation efficiency in the herbivorous marine snail Lithopoma undosum (Turbinidae)

Preference rankings for 13 macrophytes were established for the subtidal herbivorous snail Lithopoma undosum using two-choice laboratory experiments and consumption rates. L. undosum did not discriminate among three kelp foods (Egregia menziesii, Eisenia arborea and Macrocystis pyrifera) but ate kelp preferentially and more rapidly over all but Ulva spp. among tested macrophytes. Secondary preferences were established for the red alga Pterocladiella capillacea, followed by the coralline Lithothrix aspergillum, whereas the brown seaweeds Zonaria farlowii and Halidrys dioica and the seagrass Phyllospadix torreyi were the least preferred macrophytes. Fastest consumption rates (1.91 g day⁻¹) were measured in trials consisting only of kelp foods. These results indicate that L. undosum exhibits clear feeding preferences even when given less-preferred, non-kelp macrophytes. Using an ash-marker technique, we determined total organic, carbon, and nitrogen assimilation efficiencies (AE%) for six macroalgae used in preference trials. Tested macrophytes were assimilated at different efficiencies but a pattern was not detected between AE (%) and a macrophyte’s position in L. undosum’s preference hierarchy. Highest total organic AEs were found for P. capillacea (61.2%) and H. dioica (59.4%); lowest AEs were detected for E. menziesii (34.9%), a preferred dietary item. Nitrogen was assimilated from red algae with higher efficiencies (74.9–84.3%) than from brown or green algae. These data suggest that the digestive capabilities of L. undosum are better suited for assimilating organic material and nitrogen from less-preferred, non-kelp foods. This supports the hypothesis that factors besides nutritional composition and digestive optimization have played a role in the evolution of feeding preferences in L. undosum and probably other herbivorous snails associated with northeastern Pacific kelp beds.     

Ovary structure and oogenesis in Cirratulus cirratus (Polychaeta: Cirratulidae)

Oogenesis in polychaetes has, in most species, two main phases: a coelomic phase during which vitellogenesis occurs, and an ovarian phase. Details of the latter are known in very few species. Efficient reproduction requires coordination between these two phases of oocyte differentiation. The ovaries of Cirratulus cirratus (O. F. Müller) occur 2/segment throughout the fertile region of the body; 5 main stages of oocyte differentiation can be recognised on them: stem cells, oogonia, premeiotic oocytes, early oocytes and terminal oocytes. A quantitative study of the composition of the ovary throughout the reproductive cycle shows that the ovary size is approximately constant, but that the percentage of cells in the terminal oocyte stage is reduced to zero prior to spawning. This stage in oocyte differentiation is therefore a critical one, at which oogenesis may be arrested. The ovary alternates between a proliferative phase when the terminal oocytes are present, and a non-proliferative phase when they are absent. The overall rate of germ cell production for each ovary is low, less than 1 cell/ovary/day, and the, ovary tissue turnover time is greater than 2 years. A qualitative model describing the production of oocytes is presented, and the implications of the low rate of germ cell production are discussed. A low rate of germ cell proliferation, as in Cirratulus cirratus, implies that the rate of oocyte output into the coelom will be controlled by factors influencing the later stages of ovarian oocyte differentiation.     

Fecundity and reproductive effort in Ophryotrocha labronica (Polychaeta: Dorvilleidae)

Reproductive effort in terms of fecundity and energy allocation was studied in Ophryotrocha labronica La Greca and Bacci, 1962 a small, semicontinuous iteroparous species. In O. labronica fecundity is more or less constant throughout life, and the total fecundity of the 64 couples examined in this experiment only declined by 12% from the first to the last spawning. No linear relationship was found between fecundity and body size.␣The energy content of germinal and somatic tissues was determined by differential scanning calorimeter. The␣reproductive effort and a reproductive index based on the fifth spawning were evaluated to compare the␣patterns of energy allocation of a semicontinuous iteroparous species with semelparous and annual iteroparous species. The reproductive index ranged from 0.20 to 0.77, with an average of 0.480. The average reproductive effort was 0.840, ranging from 0.60 to 0.96. These figures highlight the enormous amount of energy that O. labronica allocates to reproductive tissues. Received: 23 July 1997 / Accepted: 20 October 1998     

Reproductive behaviour ofNereis diversicolor (Annelida: Polychaeta)

Nereis diversicolor O. F. Müller, collected on the tidal flats of the Jadebusen (North Sea, FRG) in autumn 1987 and 1988, was exposed to different temperatures in the laboratory. Results indicated that maturation was induced by temperatures above 6°C; spawning in early spring was synchronized by raising temperatures after a period of low temperatures in winter, and occurred mainly at new and full moon. During reproduction the female stays inside the burrow; the male releases sperm in front of it; the resultant larvae remain in the tube for 10 to 14 d protected by the female.     

Population dynamics and secondary production in Melinna palmata (Polychaeta: Ampharetidae)

A Southampton Water (England) population of Melinna palmata Malmgren was studied from July 1978 to March 1980. M. palmata is a gregarious sedentary polychaete living in muddy substratum. The distribution of the polychaete in Southampton Water was related to the silt content of the sediment. The species occurs in sediments of <60% silt, it is dioecious, and the gametes are shed during a prolonged breeding season throughout the year, with peaks in March and July. Mature oocytes measure between 180 and 240 m in diameter at spawning, and fertilization is external. Unshed oocytes are resorbed. Annual secondary ary production was 0.42 gC m^–2yr^–1 and the P:B ratio was 2.19.     

Tube-worm-sediment relationships of Diopatra cuprea (Polychaeta: Onuphidae)

Diopatra cuprea (Bosc) builds a long, nearly vertical parchment tube in sediments, which is reinforced with bits of shell, sediment or debris. The tube can be divided on the basis of structure into reinforced sections built at or above the sediment surface, and unreinforced sections built below the sediment surface. If sediment accumulates faster than the worm can build reinforced tube, an unreinforced section results. When this occurs, D. cuprea builds reinforced tube at the new sediment surface, and then pulls it down into the substratum until it joins the next lower reinforced section, or until the worm can no longer overcome sediment resistance. In the latter case, the unreinforced section occurs between two reinforced sections. The tube cap is trimmed as sediment is eroded from around it. Selection for reinforcing materials occurs only in the transitional zone from unreinforced to reinforced tube. The exposed portion of the tube (the tube cap) extends from 1 to 6 cm above the sediment surface as an inverted J. The tube mouth is oriented perpendicularly to the direction of current flow. Tube maintenance continues at temperatures below feeding-response blockage (5° to 10°C), but ceases below about 1.8°C.     

Ammonium regeneration and assimilation in eelgrass (Zostera marina) beds

Regeneration and assimilation of ammonium in the water column and in sediments of eelgrass (Zostera marina L.) beds of Izembek Lagoon and Crane Cove, Alaska, USA and Mangoku-Ura, northeastern Japan, were investigated by using a ¹⁵N isotope dilution technique. In the water column of Mangoku-Ura, ammonium was regenerated at a rate of 12 nmol l^-1 h^-1 and assimilated at a rate of 74 nmol l^-1 h^-1. The ammonium regeneration rate in sediments ranged from 2 to 150 nmol g^-1 h^-1, and with one exception, exceeded ammonium assimilation in sediments (0.3 to 77 nmol g^-1 h^-1). The ammonium regeneration in the water column was of little significance for the nitrogen supply to the eelgrass bed ecosystem. Net ammonium production (regeneration minus assimilation) in the sediment of Izembek Laggon met nitrogen demand for eelgrass growth, suggesting that ammonium regeneration in the sediments was very important for the nitrogen cycle in the eelgrass bed ecosystem.     

Life history and population dynamics ofKinbergonuphis simoni (Polychaeta: Onuphidae)

The relationship between life-history characteristics and population dynamics were investigated in the onuphid polychaeteKinbergonuphis simoni (Santos, Day and Rice) between 1982 and 1987. The studied population is located in Upper Tampa Bay, Florida, USA. This worm attains sexual maturity at 5 to 10 mo of age, depending on temperature. Several consecutive broods are produced during a female's life time, with 7 to 26 young per brood. Adults die in June–July after the breeding season. Generations of breeding individuals do not overlap and the replacement of generations occurs in July–August. Only one extended breeding season is experienced per life time. Life span does not exceed 2 yr. Field population density in 1982 was high in fall and spring (2000 to 9000 individuals/m²), low in summer (1600 individuals/m²), and slightly depressed in winter (2500 to 4000 individuals/m²). Changes in population density may be explained by seasonal, temperature-controlled changes in instantaneous birth and death rates. Birth rates are high in fall and spring, while death rates are high in early summer. Death of juveniles contributes to the winter density decrease.     

Reproduction and larval development of Marenzelleria viridis (Polychaeta: Spionidae)

The pelagic larvae of the polychaete Marenzelleria viridis (Verrill, 1873) are newcomers among the meroplankton of the Baltic Sea, where they sometimes achieve an abundance of up to 21x10⁶ ind m^-3 near the coast, especially in late autumn and even in winter. Benthos samples were collected in the Darss-Zingst bodden chain from April 1992 to 1993 and used to ascertain the reproductive stages of individuals. Development from fertilized egg to benthic juvenile is described on the basis of field material. Details of the morphology of various pelagic stages and the young benthic worm are presented as drawings and scanning electron microscope photographs. In 1992, development of the gametes started in mid-May. The individuals reached maturity in late September after about 20 wk. The first planktonic stage was the fertilized egg. The larvae have initially one and later two pairs of black eyes and, in the 2nd segment, a ciliated pit. Gastrotrochs are present on the third and thereafter every alternate segment. Neuropodial setae develop once the 7-setiger stage is reached. Palps appear at the 10-setiger stage, and neuropodial bidentate hooks from the 10th to 11th setiger on. Metamorphosis into the juvenile benthic stage takes place at the earliest when the 15-setiger stage has been reached. The reproductive seasons of various populations of M. viridis and the developmental patterns of their larvae are discussed, and differences are compared with relevant findings for the spionids.     

Sex ratio and sex change in wild and laboratory populations ofTyposyllis prolifera (Polychaeta)

Sex determination and sex differentiation in three local Istrian (Yugoslavia) populations of the polychaeteTyposyllis prolifera were studied both in the field and the laboratory. Significant differences in sex habits were revealed among the populations, the biological significance of which is unknown. (1) Sex ratios (% ) in natural populations from the Adriatic Sea amounted to 50% (Rovinj), 62% (Pore) and 77% (Pula). In the Pula-(but not in the Rovinj-)population, a correlation was found between population density on individualHalopteris scoparia thalli (the favorite habitat ofT. prolifera) and the respective sex ratio: The mean male protion was only a little more than 50% in densely populated thalli, and increased to more than 80% in sparsely populated thalli. Laboratory studies provided the information necessary to explain these field findings. (2) Laboratoryraised progenies showed an overall 1:1 primary (first sexual phase) sex ratio, independent of the local origin of the material and of whether worms were raised singly or under conditions of social contact. Nevertheless, the studied populations may differ with respect to the genetic mechanisms of sex determination: In the Pore- and Pulapopulation individual progenies often departed significantly from the 1:1 sex ratio, whereas individual progenies in the Rovinj- population never did so. (3) The populations proved to be partially protogynous. Sex differentiation in that half of the individuals which differentiated into males (primary males) was absolutely stable during sequential sexual phases. Worms which differentiated into females, however, often changed sex at an earlier or later stage of their life cycle (secondary males). Sex change was irreversible. As to the degree of lability of female differentiation under conditions of isolation, the findings suggest a genetic divergence among both populations and individuals of the same population. Female differentiation in the Rovinj-population was virtually stable, but Pula-females underwent rapid and complete masculinization. Pore-females were between these extremes. (4) In addition to genetic factors, exogenous conditions affected the incidence and time of sex change (Pula-population): Under conditions of social contact, sex change was delayed or suppressed as compared with isolated individuals. The degree of delay or inhibition was independent of the sex of the social partners, yet increased (to the point of saturation) with population density.     

Secondary production ofPrionospio caspersi (Annelida: Polychaeta: Spionidae)

The annual somatic production ofPrionospio caspersi Laubier was estimated, between July 1986 and 1987, at a sandy shallow-bottom station in the area facing the Po River Delta, Italy, where this species is one of the most abundant. Primary recruitment occurs in summer, and maturation of gametes the following spring. Body sizes were estimated from the surface area of the anterior end of worms, projected onto a monitor and recorded using a digitizer tablet. Measurements, to the tenth setiger, were correlated with total length, total body surface area and AFDW. The annual production was 8.06 g m^–2 yr^–1 (AFDW) and the production:biomass (P:B) ratio 4.09. The results are discussed in relation to some physical and chemical features of the environment, stressing differences with the life cycle of other coexisting populations.     

Zur sexuellen Differenzierung von Ophryotrocha puerilis (Polychaeta: Eunicidae)

Intact young males of Ophryotrocha puerilis Clap. Mecz. which are about to reach the female phase are capable of producing oocytes even under conditions of fasting. Intact isolated females may change sex under fasting conditions; their oocytes are not shed but resorbed. Decerebrated males which are about to reach the female phase at the moment of decerebration are unable to develop oocytes. Decerebrated females begin earlier with the production of spermatozoa than females under fasting conditions. The oocytes of decapitated females are either resorbed (young females with oocytes ranging in diameter up to 60 μm), or shed in egg masses capable of development after fertilization (older females with oocytes of 90 μm diameter or more). The effect of decerebration on females is compensated completely by implantation of isolated prostomia from female donors. Decerebrated males with implanted isolated prostomia from female donors immediately start oocyte production; these oocytes are not shed. In the majority of cases, decerebrated females change to the male phase after implantation of prostomia isolated from male donors. The mutual influence of a pair depends on direct contact of the partners. In isolated females, anterior fragments, consisting of prostomia and some segments, may induce change of sex and shedding of oocytes. On the other hand, intact females may induce sex reversal in anterior fragments. Even isolated prostomia from female donors may induce change of sex in intact females. A possible influence of intact females upon isolated prostomia was not found. Intact females and decerebrated females with implanted prostomia from female donors exhibit no mutual influence when placed together.     

Functional morphology and feeding behavior of Paraprionospio pinnata (Polychaeta: Spionidae)

The functional morphology and feeding behavior of Paraprionospio pinnata (Ehlers) were studied. The tentacular feeding palps of P. pinnata possess four groups of cilia: laterals, latero-frontal cirri, frontals and basal transverse rows. The lateral cilia beat in metachronal waves creating in current that flows toward the frontal surface of the palp. The latero-frontal cirri deflect suspended particles onto the frontal surface and potentially resuspend deposited particles. The frontal cilia line the groove of the palp and transport particles to the ciliated pharynx. The basal transverse cilia also beat in metachronal waves and together with the frontal cilia of the branchiae produce a U-shaped current that removes particles rejected by the pharynx from the burrow. The significance of particle selection at the site of the pharynx in spionid polychaetes is hypothesized to be constrained by the interaction of specific morphologies and behaviors that reduce the effects of epifaunal predation and browsing. The relationship between sediment permeability and type of respiratory or ventilation current is hypothesized to be a potentially important factor in understanding the distribution of spionid polychaetes.     

Life-history evidence for sibling species in Axiothella rubrocincta (Polychaeta: Maldanidae)

Individual Axiothella rubrocincta Johnson on the Californian coast live in U-shaped tubes, feed on the surface of the sediment, attain densities of 100 m^-2, attain lengths of 140 mm, have maximum oocyte diameters of 220 μm and produce demersal larvae. Individuals from Washington populations live in vertical tubes, feed 10–15 cm below the sediment surface, reach densities of 5000 m^-2, attain lengths of 60 mm, have maximum oocyte diameters of 385 μm and brood their young in their tubes to at least the 7-setiger stage. Individuals from California have a scalloped posterior margin of the cephalic plate, while individuals from Washington have entire margins. There are no other consistent morphological differences between populations. The population from Eagle Cove, Washington has individuals similar in size and oocyte diameter to individuals from California, but which maintain vertical tubes. A. rubrocincta represents a sibling species complex.     

Functional morphology and feeding behavior of Scolelepis squamata (Polychaeta: Spionidae)

Functional morphology and feeding behavior of Scolelepis squamata (Müller) were studied. Gut contents consisted of unconsolidated sedimentary particles, fecal pellets of other species, and a wide variety of embryos, larvae, and juveniles. Unlike other spionid polychaetes the palps of S. squamata lack a median, ciliated groove. Particles captured by the palps were brought to the pharynx by a complete contraction of the palp. In the presence of a current, S. squamata helically coiled their palps, and fed almost exclusively on suspended and resuspended particles. In contrast to most spionid polychaetes the palps of S. squamata are not deciduous. Various aspects of the morphology and feeding behavior of S. squamata are discussed in terms of their functional and ecological significance.     

Rates of seasonal sediment reworking in Axiothella rubrocincta (Polychaeta: Maldanidae)

Sediment reworking rates of Axiothella rubrocincta (Johnson, 1901) (Polychaeta: Maldanidae) were measured in situ in Tomales Bay, California (USA), from August, 1969 through July, 1970. On the average, each adult worm (approximate fresh weight=1 g) reworks about 5 g dry sediment d^-1 at a mean temperature of 13.4°C and a mean salinity of 31.8.Reworking rates are positively correlated with temperature and salinity, and negatively with sediment organic carbon, sedimentation rates and grain size. An inverse correlation exists between sediment reworking rates (g dry sediment g^-1 wet wt of worm d^-1) and g wet weight of worm. Sediment parameters deseribing unworked sediments are not significantly different from those for fecal sediments. Although these data suggest this species to be a non-selective deposit-feeder, it is more likely that it is faculatively selective.     

The maturation and breeding biology of Harmothoë imbricata (Polychaeta: Polynoidae)

The embryos of Harmothoë imbricata (L.) are protected during their early development as a mass under the scales of the female parent. Eggs are shed into the space under the scales through nephridial papillae which elongate and turn dorsally as the female matures. The mass is held together by an adhesive layer surrounding each egg. Maturation begins in September and breeding occurs during March and April, when each female spawns twice in succession. Males contain mature sperm throughout the breeding season and shed only a small proportion at each spawning. As the polychaetes mature, pairs are formed with the male resting on the dorsal surface of the female. When the female spawns, the male sheds sperm over the egg mass and the two animals then separate. The sperm has a long acrosome to penetrate the adhesive layer around the egg. Embryo-protecting species in other groups of polychaeces show parallel specialization in sperm structure and in breeding behaviour. A chronology has been established for the development of embryos up to their release from the parent, and this can be used to estimate the spawning date of females with embryo masses collected on the shore. Individuals grow at widely varying rates after settlement on the shore, and no year classes could be detected in the population. All individuals spawn in the first spring after settlement, and at least some survive to spawn again in one or more subsequent springs.