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.     

Adaptations of subtropical Venus clams to predation and desiccation: endurance of<Emphasis Type="Italic"> Gafrarium tumidum</Emphasis> and avoidance of<Emphasis Type="Italic"> Ruditapes variegatus</Emphasis>

Intertidal endobenthic bivalves are often dislodged from sediments by hydrodynamic forces. As a result, they encounter the dangers of predation and desiccation, which are generally harsh near the sediment surface. To cope with such dangers, the bivalves possibly possess: (1) a strong body to endure predation and desiccation stress, (2) quick mobility to avoid the stresses, or (3) a high growth rate for attaining a size refuge. The present study examined which of these modes are adopted by the subtropical cobbled-shore Venus clams Gafrarium tumidum (Röding, 1798) and Ruditapes variegatus (Sowerby, 1852), revealing the following interspecific differences. (1) G. tumidum survived better than R. variegatus did in harsh experimental conditions, namely: the experimental cages exposed to predation and desiccation on a cobbled shore; a laboratory aquarium with a predatory crab Scylla serrata; and ovens with high temperatures (27°C and 34°C). (2) R. variegatus was more mobile than G. tumidum was, digging into the sediment on a cobbled shore more rapidly at both high and low tides. (3) The two species with shell lengths 20–30 mm showed similar growth rates (median: –0.2 to 44.5 m day^–1) in seasonal mark–recapture surveys over 2 years. Overall, to cope with the dangers of predation and desiccation G. tumidum appears to have a strong body, while R. variegatus displays rapid mobility, and neither species seems to attain a size refuge through rapid growth. Such species-specific modes are discussed in relation to the interspecific differences found in shell morphology.Communicated by T. Ikeda, Hakodate     

Predation on egg capsules of <Emphasis Type="Italic">Zidona</Emphasis><Emphasis Type="Italic">dufresnei</Emphasis> (Volutidae): ecological implications

Among the diverse patterns of energy allocation to the offspring of gastropods, the presence of egg capsules to protect embryos is common. Females of the edible snail Zidona dufresnei attach egg capsules to hard substrates in shallow Argentine Patagonian waters (40°45′S, 64°56′W) during spring-summer. Embryonic development takes about 30 days at 22°C. In this study, three likely capsule predator species and the marks left by each on egg capsule walls were identified in laboratory experiments in February 2010. Abundances of predators and egg capsules with evidence of predation were assessed in the field in the summers of 2010 and 2011. Under laboratory conditions (N = 10 replicates per treatment and control), the predation rate by the chiton Chaetopleura isabellei was the highest (up to 90%), followed by the gastropod Tegula patagonica and the crab Neohelice granulata (~20% each). Nearly 60% of 41 capsules found in the field showed signs of predation. According to the marks identified in the laboratory, C. isabellei was responsible for 79% of this predation, and T. patagonica for the rest. Predation appears to be important during the encapsulated early life and could be an agent for selecting for resistant capsule walls and a relatively shorter development time.     

A morphological and structural study of the larval shell from the abalone <Emphasis Type="Italic">Haliotis tuberculata</Emphasis>

The larval shell of the marine gastropod Haliotis tuberculata was investigated by polarised light microscopy, scanning electron microscopy, Raman microspectroscopy and infra-red spectroscopy. Trochophore and veliger larval sections were used for histological examination of the growing shell and each larval stage was related to the shell development and the appearance of calcified formations. We determined the stage of initial calcification by specific staining combined with polarised light examination. The shell of 30-h-old pre-veliger larvae was found to be mineralized, confirming that calcification occurred before larval torsion. Using both infra-red and Raman spectroscopy, we showed that CaCO₃ deposition occurred at the pre-veliger stage and that the mineral phase initially deposited was essentially composed of aragonite.     

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     

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.     

Sand and wave induced mortality in invasive (<Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis>) and indigenous (<Emphasis Type="Italic">Perna perna</Emphasis>) mussels

The ability of an invasive species to spread in a new locality depends on its interaction with the indigenous community and on variation in time and space in the environment. The Mediterranean mussel Mytilus galloprovincialis invaded the South African coast 30 years ago and it now competes and coexists with the indigenous mussel Perna perna. The two species show different tolerances to wave and sand stress, two of the main environmental factors affecting this intertidal community. P. perna is more resistant to hydrodynamic stress than M. galloprovincialis, while the invasive species is less vulnerable to sand action. Our results show that mortality rates of the two species over a period of 6 months had different timing. The indigenous species had higher mortality than M. galloprovincialis during periods of high sand accumulation in mussel beds, while the pattern reversed during winter, when wave action was high. A negative correlation between sand accumulation and attachment strength of the two mussels showed that sand not only affects mussel mortality through scouring and burial, but also weakens their attachment strength, subjecting them to a higher risk of dislodgement. Here we underline the importance of variations in time and space of environmental stress in regulating the interaction between invasive and indigenous species, and how these variations can create new competitive balances.     

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.     

Reproductive parameters of female Hawaiian damselfish<Emphasis Type="Italic"> Dascyllus albisella</Emphasis> with comparison to other tropical and subtropical damselfishes

The reproductive ecology of female Hawaiian damselfish Dascyllus albisella (Gill) was studied at Kaneohe Bay, Oahu, Hawaii (21°27'N; 157°47'W) during two peak reproductive seasons (June–September 1997, July–August 1998). In both years, spawning occurred cyclically every 5–7 days, with all spawning in the study area in each cycle concluding within 2–3 days. The study period encompassed 16 spawning cycles in 1997 and 10 cycles in 1998. Some females spawned in almost all cycles, whereas others spawned in as few as one. Mean spawning interval of individual females ranged from 6.4 to 11.7 days in 1997 and from 5.5 to 29.0 days in 1998. Batch fecundity increased exponentially with body length, and ranged from 23,100 to 52,800. Spawning duration increased linearly with body length and ranged from 20 to 286 min. On a single day, large females spawned earlier than small females. Females mated with several different males over a season, but typically mated with only one male on a single spawning day. Female spawning frequency and interval, spawning duration, batch fecundity, as well as diel timing of spawning in D. albisella were comparable to those reported for other large, planktivorous, non-territorial damselfishes.     

<Emphasis Type="Italic">Symbiodinium</Emphasis> sp. associations in the gorgonian<Emphasis Type="Italic"> Pseudopterogorgia elisabethae</Emphasis> in the Bahamas: high levels of genetic variability and population structure in symbiotic dinoflagellates

Little is known concerning the fine-scale diversity, population structure, and biogeography for Symbiodinium spp. populations inhabiting particular invertebrate species, including the gorgonian corals, which are prevalent members of reef communities in the Gulf of Mexico, the Caribbean, and the western Atlantic. This study examined the Symbiodinium sp. clade B symbionts hosted by the Caribbean gorgonian Pseudopterogorgia elisabethae (Bayer). A total of 575 colonies of P. elisabethae were sampled in 1995 and 1998–2000 from 12 populations lying along an ~450 km transect in the Bahamas and their Symbiodinium sp. clade B symbionts genotyped at two polymorphic dinucleotide microsatellite loci. Twenty-three unique, two-locus genotypes were identified in association with these P. elisabethae colonies. Most colonies hosted only a single Symbiodinium sp. clade B genotype; however, in some instances ( n=25), two genotypes were harbored simultaneously. For 10 of the 12 populations, 66–100% of the P. elisabethae colonies hosted the same symbiont genotype. Added to this, in 9 of the 12 populations, a Symbiodinium sp. clade B genotype was either unique to a population or found infrequently in other populations. This distribution of Symbiodinium sp. clade B genotypes resulted in statistically significant ( P<0.05 or <0.001) differentiation in 62 of 66 pairwise comparisons of P. elisabethae populations. Tests of linkage disequilibrium suggested that a combination of clonal propagation of the haploid phase and recombination is responsible for maintaining these distinct Symbiodinium sp. clade B populations.     

Influence of environmental factors and female size on reproductive output in an invasive temperate marine gastropod <Emphasis Type="Italic">Rapana</Emphasis><Emphasis Type="Italic">venosa</Emphasis> (Muricidae)

Life history and reproductive strategies influence population dynamics at the inter- and intra-specific level. Environmental conditions suitable for gonad development and spawning, the reproductive range, may be a smaller portion of the broader species distribution. The only known breeding population of veined rapa whelks (Rapana venosa) in North America is in Chesapeake Bay, USA. There is considerable interest in the potential reproductive range of this non-indigenous species given the rapa whelk’s negative impacts on commercial shellfish species in both its native and introduced ranges. Weight-specific reproductive output is described for wild caught Chesapeake Bay rapa whelks maintained in flow-through mesocosms for 2 years. Measured reproductive output within and between egg capsule deposition seasons (years) in relation to water temperature, salinity, daylength, and female size is used to describe the rapa whelk’s reproductive range. Egg capsule production is influenced by seasonal and absolute water temperatures as well as seasonal daylength cycles. Egg capsule deposition by Chesapeake Bay rapa whelks begins at water temperatures of approximately 18°C and continues for 11–15 weeks. Forty to 70% of female whelks deposited egg capsules in most weeks during this season, producing 150–200 egg capsules female⁻¹ week⁻¹. Water temperatures >28°C caused reduced egg capsule production relative to temperatures of 20–25°C. Egg capsule production was positively related to seasonal changes in daylength, and two peaks of egg capsule deposition were observed in the 2001 and 2002 deposition seasons. The combination of declining daylength and higher water temperatures in late summer was associated with the cessation of egg capsule deposition. A lower average weight specific reproductive output in 130–145 mm SL rapa whelks (average 12 ± 1%) than in 90–106 mm SL rapa whelks (average 22 ± 1% of body weight) may reflect a life history that balances the physiological costs of maintaining a large body mass with the production of many planktonic larvae from multiple clutches of egg capsules per breeding season over a 10–15-year lifespan. Estimates of the cumulative day-degree requirements corresponding to the annual initiation of egg capsule deposition were 238 and 236 for 2001 and 2002, respectively. Reproductive output and day-degree requirements for Chesapeake Bay rapa whelks were similar to values calculated from previous studies of native muricids (Eupleura caudata and Urosalpinx cinerea). A latitudinal range of 30–41° (N and S) is predicted as the realized reproductive range for rapa whelk populations on the basis of the day-degree requirements for native whelks and reproductively active invasive rapa whelk populations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Relation of growth and condition with the <Emphasis Type="Italic">Pan</Emphasis> I locus in Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis> L.) around Iceland

Growth and condition (both somatic and hepatosomatic index) of Atlantic cod spawning at different locations around Iceland was studied in relation to the Pan I locus. South of Iceland cod carrying the Pan I^AB and Pan I^BB genotypes were more frequent while cod carrying the Pan I^AA genotype was more frequent north of Iceland. Differences in growth were detected between cod spawning at different areas around Iceland. Cod spawning south of Iceland grew faster than cod spawning north of Iceland. Differences in growth rate were also observed among cod carrying different Pan I genotypes within a spawning area. The least frequent Pan I genotype expressed the highest growth in both south and north of Iceland. Cod carrying the Pan I^AA grew fastest at spawning locations south of Iceland, while cod carrying the Pan I^BB genotype grew fastest in north of Iceland. A consistent relationship between condition and the different Pan I genotypes was also observed in all the areas. Cod carrying the Pan I^AA expressed the highest somatic condition and the lowest hepatosomatic index. Together, these results indicate that the relation of growth and condition with the Pan I locus is more complicated than earlier thought and is likely to be influenced by other factors, like size-selective fishing and food supply.     

Phylogeographic differentiation of storm petrels (<Emphasis Type="Italic">Hydrobates pelagicus</Emphasis>) based on cytochrome<Emphasis Type="Italic"> b</Emphasis> mitochondrial DNA variation

We evaluated mitochondrial DNA (mtDNA) sequence variation in a 910 bp region of the cytochrome b gene of the storm petrel, Hydrobates pelagicus. Samples from birds collected from five populations in the North Atlantic Ocean and the Mediterranean Sea were investigated. Genetic differentiation within the Mediterranean basin was low but high in the Atlantic. Strong differences were noted between the Atlantic and the Mediterranean populations, confirming the distinction of the subspecies H. p. pelagicus and H. p. melitensis for the Atlantic and Mediterranean seabirds, respectively. Divergence between the two subspecies probably resulted from paleogeographic changes in the Strait of Gibraltar, which was likely the route used by H. pelagicus to invade the Mediterranean Sea. Current and past demography and ecology of the storm petrel is regarded as an explanation for the level of differentiation observed within each oceanic basin. We compare the phylogeographic pattern of the storm petrel to other seabirds that breed in the same regions.Communicated by S. A. Poulet, RoscoffC.C. and L.B. contributed equally to this paper.     

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     

In vitro reproduction of the turbellarian<Emphasis Type="Italic"> Urastoma cyprinae</Emphasis> isolated from<Emphasis Type="Italic"> Mytilus galloprovincialis</Emphasis>

Urastoma cyprinae is a species infecting the gills of several marine bivalves. Although there is some literature on this turbellarian, its life cycle remains unknown. In our work we have demonstrated that reproduction of U. cyprinae can be completed out of its host. More than 50% of turbellarians isolated from mussels (Mytilus galloprovincialis) secreted and cemented a cocoon to the well bottom during the first 72 h of incubation in seawater (34 salinity) at 14°C. Oviposition started at days 1–18 (average 4.8 days) and occurred in most cases inside the protective cocoon. Each Urastoma laid an average of 2.9 egg capsules (range 1–10) and 3.9 embryos were developed inside each egg capsule (range 1–11). Hatching started at days 20–43 (average 24 days). An average of 12.8 juvenile forms (range 1–64) escaped from the cocoon after hatching. The free-swimming juveniles showed a positive phototactic response and survived about a month after hatching. On the basis of our results, we propose a life cycle for U. cyprinae involving a sexual maturation parasitic period in the bivalve gills and a reproduction period including cocoon secretion, egg laying, and hatching that is entirely completed in the external environment.Communicated by S.A. Poulet, Roscoff     

Reproduction and sex reversal of the solitary vermetid gastropod<Emphasis Type="Italic"> Serpulorbis arenarius</Emphasis>

The reproductive biology of the Mediterranean vermetid gastropod Serpulorbis arenarius, a subtidal sessile solitary species that lives in shady rocky communities, was studied at two localities south-east of the Iberian Peninsula. Its population density is usually low, with specimens sometimes sparsely distributed. Its shell often appears to be covered by epibiotic organisms. The sex ratio is biased toward males (63%) in the populations of SE Spain, and the results point towards hermaphroditism with alternating sexuality. The results obtained suggest that all specimens are first males, change to females under some as yet unknown condition and, after the ovogenesis cycle has been completed, revert to the original sexual state (male). The possible adaptive forces that favour hermaphroditism in this species are discussed, and we hypothesise that the seizure of a spermatophore by males may stimulate sex change to female. Brooding females (51% of females studied) were found from March to December. In males, histological study of testes revealed that spermatogenesis seems to occur throughout the year. Females brooded between 5 and 28 (=15) egg capsules, which were attached by stalks to the inner surface of the shell. It is noteworthy that the gonads of two of the specimens brooding egg capsules were developing testes. The newly laid egg capsules were filled with an organic intracapsular matrix, in which 40–153 (=94) eggs were embedded. The mean diameter of the uncleaved ova was 352.5 µm. The organic intracapsular matrix and some nurse eggs were used as an extra-embryonic food source. Hatching occurred at an advanced veliger stage, immediately followed by metamorphosis. Therefore, the larval development of S. arenarius is of a lecithotrophic intracapsular type, with a short, free-swimming/crawling phase.Communicated by O. Kinne, Oldendorf/Luhe     

Acrosome differentiation and the acrosome reaction in ascidian spermatozoa:<Emphasis Type="Italic"> Ascidiella aspersa</Emphasis> and<Emphasis Type="Italic"> Ascidia mentula</Emphasis> with some implications for tunicate phylogeny

The spermatozoa of both Ascidiella aspersa and Ascidia mentula have architectural features characteristic of ascidian spermatozoa that have previously been described. They have an elongated head (7 µm long for A. aspersa and 4 µm long for A. mentula), a single mitochondrion that is applied laterally to the nucleus and lacks a midpiece. The acrosome of A. aspersa spermatozoa is a flattened vesicle, about 200 nm×100 nm×40 nm (length, width and height). The acrosome of A. mentula spermatozoa consists of multiple vesicles; they are about 50 nm×50 nm×40 nm (length, width and height). During spermiogenesis in both species, several proacrosomal vesicles (50–70 nm in diameter) appear in a blister at the future apex of the spermatid. In A. aspersa, these vesicles fuse with each other to form a single acrosomal vesicle, while in A. mentula these vesicles do not fuse with each other, and form multiple acrosomal vesicles. In A. aspersa spermatozoa, calcium ionophore A23187 induces the acrosome reaction in which membrane fusion between the acrosomal apical membrane and the overlying sperm plasma membrane occurs along the peripheral margin of the acrosome, resulting in the release of a hybrid, membrane-bound, small vesicle. In A. mentula, multiple acrosomal vesicles disappear by releasing small vesicles after treatment with the calcium ionophore A23187; this also appears to be an acrosome reaction. This paper discusses the way in which acrosome structure and function may have changed during the evolution of the Tunicata.Communicated by T. Ikeda, Hakodate     

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     

Pair formation,pre-spawning waiting,and protandry in kokanee,<Emphasis Type="Italic"> Oncorhynchus nerka</Emphasis>

The timing of arrival to breeding areas can have profound effects on reproductive success. Under some conditions (restricted breeding seasons and mating systems characterized by a longer period of mating among males than females), the maximization of mating opportunities by males theoretically selects for the earlier arrival of males than females (a phenomenon called protandry). This study quantifies the relationship between the arrival timing and spawning success of male kokanee (non-anadromous Oncorhynchus nerka). The spawning behavior of kokanee was observed in a large pen and the spawning success of each male was estimated as the number of spawning events he participated in. A male's spawning success depended primarily on his success at pairing with and mate-guarding females, and less on participation in spawning events while unpaired. Males who paired earlier in the season had higher spawning success than males who paired later in the season because they experienced more opportunities to pair with new females. Among males who eventually paired (some males never did), arriving early was correlated with pairing early. However, selection for protandry was weak, largely because early arrival did not guarantee that a male would pair. Pre-spawning waiting by females also weakened the correlation between arrival day and pairing day. The random probability of pairing with respect to arrival day and pre-spawning waiting by females likely explains the weak selection for protandry in kokanee and the low amount of protandry observed in other sockeye salmon (anadromous O. nerka) populations.     

Predator avoidance behaviour of Baltic littoral mysids<Emphasis Type="Italic"> Neomysis integer</Emphasis> and<Emphasis Type="Italic"> Praunus flexuosus</Emphasis>

The predator avoidance behaviours of two littoral mysid species, Neomysis integer (Leach) and Praunus flexuosus (Müller), were studied experimentally. In ingestion experiments, mysids responded to a combination of chemical and visual signals of perch (Perca fluviatilis), but not to each stimulus alone. In the presence of the combined visual and chemical predator signal the swimming activity and choice of habitat (open vs. artificial vegetation, the Charophyte Chara tomentosa or the brown alga Fucus vesiculosus) were also influenced. The two mysid species behaved differently when perceiving predation risk: N. integer reduced swimming activity, whereas P. flexuosus increased their use of the vegetation. The different antipredator strategies of the two mysid species reflect their different lifestyles, N. integer being a swarm-forming species and P. flexuosus living in association with aquatic macrophyte vegetation.Communicated by L. Hagerman, Helsingør