Patterns of gamete incompatibility between the blue mussels<Emphasis Type="Italic"> Mytilus edulis</Emphasis> and<Emphasis Type="Italic"> M</Emphasis>.<Emphasis Type="Italic"> trossulus</Emphasis>

Previous research on gametic incompatibility in marine invertebrates suggests that for highly dispersive marine invertebrate species, barriers to fertilization among closely related taxa are often incomplete and sometimes asymmetric. The nature of these barriers can dramatically affect the patterns of gene flow and genetic differentiation between species, and thus speciation. Blue mussels, in the genus Mytilus, are genetically distinct in allopatry yet hybrids are present wherever any two species within the group co-occur. The present study sampled M. edulis (L.) and M. trossulus (Gould) in May and June 2001 from the East Bay section of Cobscook Bay, Maine, USA (latitude 44°56′30″N; longitude 67°07′50″W), where the two species are sympatric. Gamete incompatibility was investigated in a series of laboratory fertilizations carried out in July 2001. The proportion of fertilized eggs typically exceeded 80% at sperm concentrations of 10³–10⁴ ml^?1 among intraspecific matings (n=18), but was <30% even at sperm concentrations in excess of 10⁵–10⁶ ml^?1 for interspecific matings (n=13). Further analysis indicated that approximately 100- to 700-fold higher sperm concentrations were required to achieve 20% fertilization in interspecific matings relative to intraspecific matings, indicating strong barriers to interspecific fertilization. The proportion of fertilized eggs did not follow this general pattern in all matings, however. The eggs from two (out of five) M. edulis females were almost as receptive to M. trossulus sperm as they were to M. edulis sperm. In contrast, the eggs from all M. trossulus females (n=3) were unreceptive to M. edulis sperm, suggesting that fertilization barriers between these species may be asymmetric. Given the experimental design employed in this study, the results are also consistent with a strong maternal or egg effect on the level of interspecific gamete compatibility in M. edulis.     

The reproductive cycle of <Emphasis Type="Italic">Scolelepis goodbodyi</Emphasis> (Polychaeta,Spionidae)

The aim of this study was to examine the reproductive and gametogenic cycle of the spionid polychaete Scolelepis goodbodyi (Jones). Every 15 days, in the upper level of the intertidal zone on Barequeçaba Beach in southeastern Brazil, a 100 m² area was delimited and within it three points were selected and sampled using a core sampler 0.01 m² in area × 0.2 m long. Each sample was divided into three sub-samples: surface (2 cm) and middle (8 cm), which were sieved through 0.5, 0.25 and 0.125 mm mesh sieves; and lower (10 cm), sieved through 1.0 and 0.5 mm mesh sieves. Males, females and undetermined individuals were separated, and the width of the third setiger was measured. The gonadal development of each individual was classified based on external features of the gametogenic setigers. Ten to 20 adults from each sampling period were classified according to their gonadal development stage and then analyzed histologically for gametogenic studies, for comparison with the former classification. Some of the ripe females were used for fecundity evaluation. The diameters of the oocytes were measured prior to spawning. Eight hundred and twenty-eight females (29.70%), 848 males (30.42%) and 1,112 undetermined individuals (39.89%) were analyzed. The sex ratio did not differ significantly from unity (χ² = 0.24; df = 1; P < 0.05). Males and females were more abundant in May 2002 (ca. 80%) and between November 2002 and May 2003 (between 77 and 90%); the proportion of undetermined individuals did not represent recruitment alone, but also a high incidence of adults with recovering gonads. Fecundity varied from 134 oocytes in a 0.54 mm W3 individual to 289 oocytes in a 0.4 mm W3 individual, with a mean of 220 (SD = 57) oocytes per female and 19 (SD = 5) oocytes per gametogenic setiger. Oocytes were ellipsoid, and ranged in size from 150 × 80 (to 220 × 120 μm (mean ± SD = 173 × 113 ± 15 × 11 μm). Neither a well-defined gametogenic cycle nor synchrony in the reproductive period was observed, because many gonadal development stages occurred in each month. Nevertheless, peaks of maturity were observed between October–December 2002 and April–May 2003.     

Comparative life-history study on sympatric hyperiid amphipods (<Emphasis Type="Italic">Themisto pacifica</Emphasis> and <Emphasis Type="Italic">T</Emphasis>. <Emphasis Type="Italic">japonica</Emphasis>) in the Oyashio region,western North Pacific

Life-history features of the sympatric amphipods Themisto pacifica and T. japonica in the western North Pacific were analyzed based on seasonal field samples collected from July 1996 through July 1998, and data from laboratory rearing experiments. T. pacfica occurred throughout the year, with populations peaking from spring to summer. In contrast, T. japonica were rare from autumn to early winter, but became abundant in late winter to spring. Mature T. pacifica females and juveniles occurred together throughout the year, indicating year-round reproduction. Mature T. japonica females were observed only in spring, and juveniles occurred irregularly in small numbers, suggesting limited, early-spring reproduction in this study area. Size composition analysis of T. pacifica identified a total of eight cohorts over the 2 years of the study. Due to the smaller sample size and rarity of mature females (>9.6 mm) and males (>7.1 mm), cohort analyses of T. japonica were not comparable. Laboratory rearing of specimens at 2°C, 5°C, 8°C and 12°C revealed that a linear equation best expressed body length growth by T. pacifica, while a logistic equation best expressed body length growth by T. japoncia. Combining these laboratory-derived growth patterns with maturity sizes of wild specimens, the minimum and maximum generation times of females at a temperature range of 2–12°C were computed as 32 days (12°C) and 224 days (2°C), respectively, for T. pacifica, and 66 days (12°C) and 358 days (2°C), respectively, for T. japonica. The numbers of eggs or juveniles in females marsupia increased with female body length and ranged from 23 to 64 for T. pacifica and from 152 to 601 for T. japonica. Taking into account the number of mature female instars, lifetime fecundities were estimated as 342 eggs for T. pacifica and 1195 eggs for T. japonica. Possible mechanisms for the coexistence of these two amphipods in the Oyashio region are also discussed.Communicated by O. Kinne, Oldendorf/Luhe     

A histological study of reproduction in the serpulids<Emphasis Type="Italic"> Pomatoceros triqueter</Emphasis> and<Emphasis Type="Italic"> Pomatoceros lamarckii</Emphasis> (Annelida: Polychaeta)

The reproductive cycles of the serpulid polychaetes Pomatoceros lamarckii (Quatrefages, 1865, as Vermilia) and P. triqueter (Linnaeus, 1767, as Serpula triquetra) were studied by histological examination during 1999 and 2000 at Bantry Bay, south-west Ireland. Gametogenesis, sex ratios and hermaphroditism were also investigated. The male/female ratio in P. lamarckii was approximately equal, but in P. triqueter it deviated significantly in favour of females. There was no significant variation in the sex ratios throughout the year in either species. Results confirm that the species are protandric hermaphrodites. In P. lamarckii, but not in P. triqueter, sexual dimorphism was exhibited in body size, the females being larger than the males of the same species. In both species, the proportion of females increased with increasing body size. Simultaneous hermaphroditism was recorded in P. lamarckii, but not in P. triqueter. There was no clearly defined annual gametogenic cycle in either species. Both species appear to have an extended reproductive season, with numerous small-scale peaks in reproductive maturity that can vary annually. Spawning was broadly synchronous between sexes. Visual observation alone (i.e. without histology) was insufficient to accurately assess reproductive condition in individuals not in, or close to, a ripe state.     

Reproductive cycle of<Emphasis Type="Italic"> Bispira volutacornis</Emphasis> (Polychaeta: Sabellidae) on the west coast of Ireland

The reproductive cycle of Bispira volutacornis, a dioecious polychaete, was followed over two spawning periods in Lettercallow Bay, on the west coast of Ireland. In the younger generation of sexually mature adults, gender can be determined on the basis of colour, the dorsal aspect of the males being cream at maturation, whilst the females are pink at the previtellogenic stage and an olive green at maturation. An annual reproductive cycle of 12 months shows that oocyte/sperm maturation is extraovarian. The male reproductive cycle proceeded at a more rapid pace than that of the female cycle, with sperm maturing earlier. Spawning in B. volutacornis occurred between late July and early September. B. volutacornis is a polytelic species, surviving spawning and releasing all gametes in a single batch, with a mean spawned oocyte diameter of 118 m. The reproductive cycle appears to be regulated by a seasonal change in water temperature, and spawning is timed to produce larvae during the autumnal planktonic bloom in Lettercallow Bay.Communicated by J.P. Thorpe, Port Erin     

Genetic analysis of tuna populations,<Emphasis Type="Italic"> Thunnus thynnus thynnus</Emphasis> and<Emphasis Type="Italic"> T</Emphasis>.<Emphasis Type="Italic"> alalunga</Emphasis>

The genetic population structures of Atlantic northern bluefin tuna ( Thunnus thynnus thynnus) and albacore ( T. alalunga) were examined using allozyme analysis. A total of 822 Atlantic northern bluefin tuna from 18 different samples (16 Mediterranean, 1 East Atlantic, 1 West Atlantic) and 188 albacore from 5 samples (4 Mediterranean, 1 East Atlantic) were surveyed for genetic variation in 37 loci. Polymorphism and heterozygosity reveal a moderate level of genetic variability, with only two highly polymorphic loci in both Atlantic northern bluefin tuna ( FH* and SOD- 1*) and albacore ( GPI- 3* and XDH*). The level of population differentiation found for Atlantic northern bluefin tuna and albacore fits the pattern that has generally been observed in tunas, with genetic differences on a broad rather than a more local scale. For Atlantic northern bluefin tuna, no spatial or temporal genetic heterogeneity was observed within the Mediterranean Sea or between the East Atlantic and Mediterranean, indicating the existence of a single genetic grouping on the eastern side of the Atlantic Ocean. Very limited genetic differentiation was found between West Atlantic and East Atlantic/Mediterranean northern bluefin tuna, mainly due to an inversion of SOD- 1* allele frequencies. Regarding albacore, no genetic heterogeneity was observed within the Mediterranean Sea or between Mediterranean and Azores samples, suggesting the existence of a single gene pool in this area.     

Feeding selectivities of the marine cladocerans<Emphasis Type="Italic"> Penilia avirostris</Emphasis>,<Emphasis Type="Italic"> Podon intermedius</Emphasis> and<Emphasis Type="Italic"> Evadne nordmanni</Emphasis>

We conducted grazing experiments with the three marine cladoceran genera Penilia, Podon and Evadne, with Penilia avirostris feeding on plankton communities from Blanes Bay (NW Mediterranean, Spain), covering a wide range of food concentrations (0.02–8.8 mm³ l^–1, plankton assemblages grown in mesocosms at different nutrient levels), and with Podon intermedius and Evadne nordmanni feeding on the plankton community found in summer in Hopavågen Fjord (NE Atlantic, Norway, 0.4 mm³ l^–1). P. avirostris and P. intermedius showed bell-shaped grazing spectra. Both species reached highest grazing coefficients at similar food sizes, i.e. when the food organisms ranged between 15 and 70 µm and between 7.5 and 70 µm at their longest linear extensions, respectively. E. nordmanni preferred organisms of around 125 µm, but also showed high grazing coefficients for particles of around 10 µm, while grazing coefficients for intermediate food sizes were low. Lower size limits were >2.5 µm, for all cladocerans. P. avirostris showed upper food size limits of 100 µm length (longest linear extension) and of 37.5 µm particle width. Upper size limits for P. intermedius were 135 µm long and 60 µm wide; those for E. nordmanni were 210 µm long and 60 µm wide. Effective food concentration (EFC) followed a domed curve with increasing nutrient enrichment for P. avirostris; maximum values were at intermediate enrichment levels. The EFC was significantly higher for P. intermedius than for E. nordmanni. With increasing food concentrations, the clearance rates of P. avirostris showed a curvilinear response, with a narrow modal range; ingestion rates indicated a rectilinear functional response. Mean clearance rates of P. avirostris, P. intermedius and E. nordmanni were 25.5, 18.0 and 19.3 ml ind.^–1 day^–1, respectively. Ingestion rates at similar food concentrations (0.4 mm³ l^–1) were 0.6, 0.8 and 0.9 g C ind.^–1 day^–1.Communicated by O. Kinne, Oldendorf/Luhe     

Characterization of urease activity in three marine phytoplankton species,<Emphasis Type="Italic"> Aureococcus anophagefferens</Emphasis>,<Emphasis Type="Italic"> Prorocentrum minimum</Emphasis>, and<Emphasis Type="Italic"> Thalassiosira weissflogii</Emphasis>

The availability of different forms of nitrogen in coastal and estuarine waters may be important in determining the abundance and productivity of different phytoplankton species. Although urea has been shown to contribute as much as 50% of the nitrogen for phytoplankton nutrition, relatively little is known of the activity and expression of urease in phytoplankton. Using an in vitro enzyme assay, urease activities were examined in laboratory cultures of three species: Aureococcus anophagefferens Hargraves et Sieburth, Prorocentrum minimum (Pavillard) Schiller, and Thalassiosira weissflogii (Grunow) Fryxell et Hasle. Cultures of P. minimum and T. weissflogii were grown on three nitrogen sources (NO₃^m, NH₄⁺, and urea), while A. anophagefferens was grown only on NO₃^m and urea. Urease was found to be constitutive in all cultures, but activity varied with growth rate and assay temperature for the different cultures. For A. anophagefferens, urease activity varied positively with growth rate regardless of the N source, while for P. minimum, urease activity varied positively with growth rate only for cultures grown on urea and NH₄⁺. In contrast, for T. weissflogii, activity did not vary with growth rate for any of the N sources. For all species, urease activity increased with assay temperature, but with different apparent temperature optima. For A. anophagefferens, in vitro activity increased from near 0-30°C, and remained stable to 50°C, while for P. minimum, increased in vitro activity was noted from near 0-20°C, but constant activity was observed between 20°C and 50°C. For T. weissfloggii, while activity also increased from 0°C to 20°C, subsequent decreases were noted when temperature was elevated above 20°C. Urease activity had a half-saturation constant of 120-165 wg atom N l^у in all three species. On both an hourly and daily basis, urease activity in A. anophagefferens exceeded nitrogen demand for growth. In P. minimum, urease activity on an hourly basis matched the nitrogen demand, but was less than the demand on a daily basis. For T. weissflogii, urease activity was always less than the nitrogen demand. These patterns in urease activity in three different species demonstrate that while apparently constitutive, the regulation of activity was substantially different in the diatom. These differences in the physiological regulation of urease activity, as well as other enzymes, may play a role in their ecological success in different environments.     

Auditory defence in the peacock butterfly (<Emphasis Type="Italic">Inachis io</Emphasis>) against mice (<Emphasis Type="Italic">Apodemus flavicollis</Emphasis> and <Emphasis Type="Italic">A. sylvaticus</Emphasis>)

Morphological and behavioural traits can serve as anti-predator defence either by reducing detection or recognition risks, or by thwarting initiated attacks. The latter defence is secondary and often involves a ‘startle display’ comprising a sudden release of signals targeting more than one sensory modality. A suggested candidate for employing a multimodal defence is the peacock butterfly, Inachis io, which, by wing-flicking suddenly, produces sonic and ultrasonic sounds and displays four large eyespots when attacked. The eyespots make small birds retreat, but whether the sounds produced thwart predator attacks is largely unknown. Peacocks hibernate as adults in dark wintering sites and employ their secondary defence upon encounter with small rodent predators during this period. In this study, we staged predator–prey encounters in complete darkness in the laboratory between wild mice, Apodemus flavicollis and Apodemus sylvaticus, and peacocks which had their sound production intact or disabled. Results show that mice were more likely to flee from sound-producing butterflies than from butterflies which had their sound production disabled. Our study presents experimental evidence that the peacock butterfly truly employs a multimodal defence with different traits targeting different predator groups; the eyespots target birds and the sound production targets small rodent predators.     

Disinfection efficacy on cyst viability of<Emphasis Type="Italic"> Artemia franciscana</Emphasis> (Crustacea),<Emphasis Type="Italic"> Hexarthra fennica</Emphasis> (Rotifera) and<Emphasis Type="Italic"> Fabrea salina</Emphasis> (Ciliophora)

Resting stages (cysts) of Artemia franciscana, Hexarthra fennica and Fabrea salina were exposed for two periods (acute and chronic exposures) to different concentrations of five aquaculture disinfectants (formalin, sodium hypochlorite, potassium permanganate, organic iodine, copper sulphate). The effects of chemical treatments were ranked according to their action on cyst hatching: total inhibition (no cyst hatching), heavy inhibition (significant decrease of cyst hatching), alteration of hatching synchrony, and occurrence of anomalous hatching (death of emerging individuals or birth of malformed organisms). Resting-stage viability was not completely impaired by disinfectant exposures at the ordinary doses used in aquaculture, so that usual treatments are possibly ineffective against the protist and metazoan cysts potentially present in breeding systems. On the other hand, the high resistance shown by cysts suggests the possibility of using these chemicals in live-feed disinfection.     

Competition and facilitation between germlings of<Emphasis Type="Italic"> Ascophyllum nodosum</Emphasis> and<Emphasis Type="Italic"> Fucus vesiculosus</Emphasis>

Competitive interactions between germlings of Ascophyllum nodosum (L) Le Jolis and Fucus vesiculosus L. were studied both in the laboratory and on a shore of the Isle of Man, in the Irish Sea. Both intra- and interspecific competition were investigated by comparing the performance of algal germlings both in monocultures and mixed populations of the two species. The growth of germlings of both species reduced with increasing density. F. vesiculosus always grew faster than Ascophyllum and did best in mixed cultures, whereas Ascophyllum did least well when mixed with Fucus germlings. Clearly the adverse effects of F. vesiculosus on A. nodosum were greater than those of Ascophyllum cohorts. At the same total density, the survival and growth of Ascophyllum declined with an increasing proportion of Fucus germlings, implying that poor recruitment of A. nodosum results from strong competition with F. vesiculosus. However, under desiccation stress on the shore, F. vesiculosus enhanced the survival of A. nodosum at the early germling stage even though competition may occur again at the late stage. Thus, whether interactions between germlings take the form of competition or facilitation depends on the environmental conditions.Communicated by O. Kinne, Oldendorf/Luhe     

Movements and site fidelity of grass shrimp (<Emphasis Type="Italic">Palaemonetes pugio</Emphasis> and <Emphasis Type="Italic">P. vulgaris</Emphasis>) in salt marsh intertidal creeks

Grass shrimp are abundant residents of shallow-water habitats in US Atlantic and Gulf coast estuaries. Mark-recapture events determined the extent and direction of their movements in meso-tidal salt marsh creeks at North Inlet, South Carolina. Microwire-tagged Palaemonetes vulgaris demonstrated high fidelity for a dock in a subtidal channel. In the 48 days following release, 11 % of the 422 tagged shrimp were recaptured and 99 % of all recaptures were made there an average of 14 days post-release. Palaemonetes pugio, which favored the use of shallow intertidal areas, exhibited moderate fidelity for pools within creek beds with 53 % of the recaptured shrimp collected at the release site. Higher fidelity was observed for confluences of intertidal creeks and the subtidal channels. Of the 5565 shrimp released with coded microwire tags, 7.5 % were recaptured and 98 % of those recaptures were at release sites up to 53 days later. During another event, P. pugio released 235 m from their origin demonstrated relatively low fidelity for the new site and a lack of homing behavior. Of the 544 tagged shrimp, 3 % were recaptured; only 40 % of those recaptured were from the release site. Site fidelity is a mechanism by which previously discovered large and consistent differences in grass shrimp use of neighboring intertidal creek basins can be sustained over weeks, seasons, and years. Spatial variations and the tendency of these keystone organisms to resist relocation by tidal currents and occupy certain areas for extended periods should be considered in decisions about proposed alterations to creeks and shorelines.     

Intraspecific competition in<Emphasis Type="Italic"> Fucus serratus</Emphasis> and<Emphasis Type="Italic"> F</Emphasis>.<Emphasis Type="Italic"> evanescens</Emphasis> (Phaeophyceae: Fucales) germlings: effects of settlement density,nutrient concentration,and temperature

Survival and growth of early post-settlement stages are critical for the development of seaweed populations. Fucoid germlings commonly settle in dense monospecific aggregates, where intraspecific competition and environmental variables (e.g. nutrient concentration and temperature) may affect survival and growth. Using factorial experiments, we determined the effects of settlement density (~10, ~50 and ~250 germlings cm^–2), nutrient enrichment (from ~10 to ~40 µM N and from ~0.5 to ~2.5 µM P), and temperature (7°C and 17°C) on Fucus serratus and F. evanescens germlings in laboratory cultures over 3 months. Settlement density, nutrient concentration and temperature interactively affected growth of germlings, and the magnitude of this interaction varied between the two species. This represents the first record of such factorial interactions in Fucus spp. germlings. Intraspecific competition, estimated as the relative reduction in germling growth and survival from low to high densities, increased with decreasing nutrient concentration and increasing temperature in both species. While temperature and nutrient concentration had little effect on germling size distributions, size inequality and skewness generally increased with germling density, indicating that a few large individuals gained dominance and suppressed many smaller ones at high density. Self-thinning increased with settlement density and depended on nutrient concentration and species at high density. At high density, self-thinning increased with decreasing nutrient levels in F. evanescens, but not in F. serratus. At low density, nutrient enrichment increased germling growth in F. evanescens, but not in F. serratus, whereas growth in both species was stimulated by nutrient enrichment at higher densities. These results suggest that germling growth and self-thinning are more sensitive to variation in nutrient concentration in F. evanescens than in F. serratus. The potential implications of our findings for the understanding of eutrophication-related abundance changes in both species in southern Norway are discussed.Communicated by L. Hagerman, Helsingør     

Reproductive isolation among morphotypes of the Atlantic seastar species<Emphasis Type="Italic"> Zoroaster fulgens</Emphasis> (Asteroidea: Echinodermata)

Zoroaster fulgens is a slope-dwelling seastar species that is distributed throughout the Atlantic Ocean. Studies into the population structure and systematics of marine animals have increasingly found that species with a reported cosmopolitan distribution are, in fact, collections of closely related cryptic or sibling species. In the Porcupine Seabight, three morphotypes of Z. fulgens can be found that have a distribution that is stratified by depth. This study investigates the genetic divergence between these morphotypes using sections of the cytochrome oxidase 1 (COI) and 16S regions of the mitochondrial genome. Bathymetrically separated morphotypes of Z. fulgens are reproductively isolated over distances of approximately 1 km while gene flow occurs among morphotypes, along isobaths, over distances of approximately 900 km. Reproductive isolation on the continental slope may have occurred as a result of selection exerted by gradients of depth-correlated physical factors, such as pressure and temperature. However, allopatric speciation with subsequent range expansion may also explain the observed patterns of genetic divergence. Further investigation of radiation within this group may provide important information on the evolution of slope species. Taxonomic revision of the genus is required.Communicated by J.P. Thorpe, Port Erin     

A commensal relationship between the scyphozoan medusae<Emphasis Type="Italic"> Catostylus mosaicus</Emphasis> and the copepod<Emphasis Type="Italic"> Paramacrochiron maximum</Emphasis>

The copepod Paramacrochiron maximum was found in high numbers (up to 5,675 copepods/medusa) on the oral arms of the scyphozoan Catostylus mosaicus. This association was considered to be commensalism for the following reasons: P. maximum (Lichomolgidae) was abundant on the medusae (approximately 805 copepods/kg of medusae) and very rare in the water column (approximately 5.99×10^-4 copepods/kg of water); copepodites and adults of the symbiont were present on the host; the copepods were on the medusae both day and night, at different times (nine occasions between March 1999 and May 2000) and different locations (Botany Bay and Lake Illawarra, NSW, Australia). Over 40 taxa of plankton were found on the oral arms of C. mosaicus (including protists, cnidarians, polychaetes, molluscs, a wide range of holoplanktonic and meroplanktonic crustaceans, chaetognaths and fish eggs). These taxa were abundant in the water column and we concluded that they were prey. Symbiotic amphipods and carangid fishes were found with medusae. We conclude that there is a symbiotic association between P. maximum and C. mosaicus and care should be taken not to confound these copepods with the prey of C. mosaicus. Poecilostomid copepods are well known for consuming mucus and feeding is likely to be a major reason for the association.Communicated by G.F. Humphrey, Sydney     

Karyotype and sex determination in <Emphasis Type="Italic">Dinophilus gyrociliatus</Emphasis> (Polychaeta: Dinophilidae)

The study of the male and female karyotypes of the polychaete Dinophilus gyrociliatus was performed with the aim of ascertaining the diploid number of chromosomes and confirming the existence of karyological differences between the two sexes. Our results evidenced that the female karyotype of D. gyrociliatus consists of 2n=24 chromosomes, while the male karyotype has 2n=23 chromosomes. X chromosomes are subtelocentric and much bigger than the autosomes. The size of the D. gyrociliatus chromosomes, which in the female embryos vary in length from little more than 2.8 wm to less than 0.7 wm, are relatively small by comparison with those of other polychaetes. The existence of maternal and environmental factors able to influence the sex ratio of D. gyrociliatus and chromosomal differences between the sexes confirms that: (1) sex determination is chromosomal and syngamic of the XX-X0 type and (2) control of the sex ratio is progamic and depends on genetic and environmental factors.     

Movements of <Emphasis Type="Italic">Ilyanassa obsoleta</Emphasis> (Gastropoda) on an intertidal sandflat

The gastropod Ilyanassa obsoleta (Say) is native to the east coast of North America where it is locally abundant on sandflats, mudflats, and in saltmarsh creeks. The local disturbances created by snails and their movements affect soft-sediment community composition. Movements of individually marked snails were followed on an intertidal sandflat on Cape Henlopen, Delaware, U.S.A. In June 1991, 1,200 snails that had tested as trematode-uninfected were released and over 5 months 554 were sighted 971 times. Mean daily net distance moved was 1.7 m, but snails often moved 10–20 m day⁻¹ and one snail was 180 m distant after 130 days. Net dispersal of the released population was attained in ≈10 days, by which time, a typical distance from release was 15–20 m. Snails were not found crossing sandbars and most moved away from shore into a tidal gully. In June 1993, 500 snails, both uninfected and trematode-infected, were released at the same position and over 6 months, 350 snails were sighted 949 times. Sandbars were again barriers to movement, but their changed positions allowed wider dispersal. Net dispersal was complete in ≈20 days by which time a typical distance from release was 30–40 m. Mean daily net distance moved was 2.2 m, but within 10 days snails had moved 50–100 m. In both years, following initial dispersal, snails (infected or not) took up random directions from move to move. Infected and uninfected snails dispersed equal distances, but had different mean final dispersal directions. Dispersal of I. obsoleta individuals was extensive and affected by shifting sandbar positions and parasitism. Recognizing this will be important in appreciating the ecological dynamics of this gastropod and in determining its effects on soft-bottom communities.Electronic Supplementary Material Supplementary material is available for this article at     

Coexistence and reproductive isolation of the sympatric echinoids<Emphasis Type="Italic"> Diadema savignyi</Emphasis> Michelin and<Emphasis Type="Italic"> Diadema setosum</Emphasis> (Leske) on Kenyan coral reefs

The sympatric echinoids Diadema savignyi and D. setosum coexist in shallow reef lagoons throughout East Africa. The reproductive strategies of these echinoids were studied to investigate reproductive isolation as a possible mechanism for maintaining the coexistence of these closely related species. The annual reproductive cycle and lunar periodicity were determined by gonad index measurements, histological examination of gametogenesis, and induction of spawning with injections of KCl. The peak reproductive period of D. savignyi coincided with the north-east monsoon period (when light and temperatures are high) as gonad indices were high (>8%) beginning in February and peaked at 9.7% in May. Gonad indices subsequently rapidly decreased (by 26%) in June at the beginning of the cooler south-east monsoon period. However, the presence of sperm and ova in most months of the year indicates continuous gametogenesis with reduced reproductive effort during the cooler months. The annual cycle for D. setosum showed less of a seasonal trend as gonad indices remained above 7% throughout much of the year but tended to be highest when temperatures were lower. This is the first confirmation of continuous reproduction in these two species at the equator. The reproductive patterns of both species remained consistent over 2 years of sampling. Both species exhibited a synchronized lunar spawning periodicity during the 3 months sampled, with D. setosum spawning on lunar days 8–10 and D. savignyi spawning after the full moon (lunar days 17–18). Whereas spawning in D. savignyi was very tightly synchronized, 20% of D. setosum individuals still spawned after the peak spawning period. The coexistence of these closely related species appears to be maintained by temporal reproductive isolation during the lunar spawning period reinforced by seasonal differences in reproductive effort.Communicated by O. Kinne, Oldendorf/Luhe     

Histological investigation of the reproductive cycles of the limpets <Emphasis Type="Italic">Patella </Emphasis><Emphasis Type="Italic">vulgata</Emphasis> and <Emphasis Type="Italic">Patella ulyssiponensis</Emphasis>

This study devised a staging system for, and monitored, the gonad development of the limpet species Patella vulgata and Patella ulyssiponensis on the South West coast of Ireland using histological techniques. Maturation began in the males of both species in January and in the females it began in March. There was no statistical difference in gonad development between sexes and between species. Spawning in the male P. vulgata occurred from September to December 2003 and in September and October 2004. In female P. vulgata spawning occurred from October to December 2003, no spawning of females was observed in 2004. In male P. ulyssiponensis spawning occurred in November and December 2003 and from September 2004 to December 2004. Spawning was observed from November 2003 to January 2004 and in September 2004 in female P. ulyssiponensis. Sex ratios also varied between the species and between months sampled. Nevertheless more males were observed in both species.     

Effect of sexual maturation on the tissue biochemical composition of<Emphasis Type="Italic"> Octopus vulgaris</Emphasis> and<Emphasis Type="Italic"> O</Emphasis>.<Emphasis Type="Italic"> defilippi</Emphasis> (Mollusca: Cephalopoda)

Changes in the protein, lipid, glycogen, cholesterol and energy contents, total amino acid and fatty acid profiles of Octopus vulgaris and O. defilippi tissues (gonad, digestive gland and muscle) during sexual maturation (spermatogenesis and oogenesis) were investigated. Both species showed an increase of amino acids and protein content in the gonad throughout sexual maturation (namely in oogenesis), but allocation of these nitrogen compounds from the digestive gland and muscle was not evident. The major essential amino acids in the three tissues were leucine, lysine and arginine. The major non-essential amino acids were glutamic acid, aspartic acid and alanine. With respect to carbon compounds, a significant increasing trend (P<0.05) in the lipid and fatty acid contents in the three tissues was observed, and, consequently, there was also little evidence of accumulated lipid storage reserves being used for egg production. It seems that for egg production both Octopus species use energy directly from food, rather than from stored products. This direct acquisition model contrasts with the previous model for Octopus vulgaris proposed by ODor and Wells (1978: J Exp Biol 77:15–31). Most of saturated fatty acid content of the three tissues was presented as 16:0 and 18:0, monounsaturated fatty acid content as 18:1 and 20:1 and polyunsaturated fatty acid content as arachidonic acid (20:4n-6), eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3). Though cholesterol is an important precursor of steroid hormones, this sterol content exhibited variations that do not seem to be related with the maturation process. Moreover, significant differences (P<0.05) were obtained between genders, suggesting that perhaps there is a greater physiological demand for cholesterol during spermatogenesis than oogenesis. If the component sterols of octopus are of a dietary origin, considerable variation in the cholesterol content between species might be expected on the basis of the sterol composition of their prey. The glycogen reserves increased significantly in the gonad and decreased significantly (P<0.05) in the digestive gland and muscle of O. vulgaris (these trends were not evident in O. defilippi). Glycogen may play an important role in the maturation process and embryogenesis of these organisms, because carbohydrates are precursors of metabolic intermediates in the production of energy. It was evident that sexual maturation had a significant effect upon the gonad energy content, but the non-significant energy variation (P>0.05) in the digestive gland and muscle revealed no evidence that storage reserves are transferred from tissue to tissue. The biochemical composition of digestive gland and muscle may not be influenced by sexual maturation, but rather by other biotic factors, such as feeding activity, food availability, spawning and brooding.Communicated by S.A. Poulet, Roscoff