Reproduction and reproductive variability in the coral Pocillopora verrucosa from the Republic of Maldives

The sexuality, reproductive mode, and timing of reproduction of Pocillopora verrucosa from the Republic of Maldives, Indian Ocean, were assessed using serial histological sections. These showed that P. verrucosa is an annual simultaneous hermaphrodite, with gonads arranged in two opposing arcs of alternating testes and ovaries, six gonads in each arc. No planulae were observed in any dissection or histological analysis carried out, therefore making brooding unlikely. Broadcast spawning is inferred from the disappearance of mature gametes from samples collected between late March and April 1991. Mean oocyte size at spawning was 53.5 m and mean potential fecundity was 7300 ooctyes cm^-2yr^-1. The reproductive pattern of P. verrucosa in the Maldives is compared to that of the same species in different locations, the short breeding season in March to April occurring earlier in the Maldives than in Red Sea populations. The maximum mean oocyte diameter found in Maldivian specimens was much smaller than elsewhere. The year-to-year variation in numbers of oocytes/polyp within single colonies, and the variation between colonies within the population was significant (p<0.01). Therefore, it is possible that fecundity is not a good variable to use when monitoring stress on coral reefs unless larger numbers of estimates can be routinely made. Some colonies contained immature oocytes at spawning that were not released and continued to grow to approximately twice the size of the spawned oocytes that were presumed to be mature. These unspawned oocytes were oosorbing, and were characterised by the presence of zooxanthellae and large numbers of vacuoles in their cytoplasm. This gradual expansion and oosorption of unspawned oocytes has not been documented previously for corals.     

Reproduction in the sea pen <Emphasis Type="Italic">Pennatula phosphorea</Emphasis> (Anthozoa: Pennatulacea) from the west coast of Scotland

Reproduction in the sea pen Pennatula phosphorea Linnaeus 1758 was investigated in a population located in southern Loch Linnhe, west Scotland. This was accomplished through analysis of trends in oocyte size-frequency distribution and fecundity over a 12-month period. Pennatula phosphorea is dioecious and the study population exhibited a sex ratio of 1:1. Oogenesis in female P. phosphorea is characterised by the maintenance of a large pool of small oocytes throughout the year of which a small proportion (<30%) mature synchronously and are broadcast-spawned during the summer months of July and/or August. Although spawning occurs annually, the duration of oogenesis exceeds 12 months. Initial oocyte generation is best described as ‘quasi-continuous’ as it may be suppressed during winter. The timing and periodicity of oogenesis and spawning may be related to seasonal environmental cues and it is proposed that annual spawning constitutes a brief and synchronous event. Fecundity is high in P. phosphorea, typically up to 50 oocytes per polyp and 40,000 oocytes per colony in medium to large colonies. Although mean polyp fecundity increased with colony size (axial rod length) there was no seasonal fluctuation in this measure of relative fecundity. Since only a small proportion of oocytes present are spawned each year, the present study advises caution when making inferences regarding the seasonal output of viable oocytes, especially on occasions where the definition of fecundity or the details of the oogenic cycle of a species are unclear. Pennatula phosphorea produces large oocytes (>500 μm), indicative of the production of lecithotrophic larvae; this may confer certain advantages with respect to larval longevity and survival.     

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     

Stereological methods applied to reproductive cycle of Tapes rhomboides

A population of Tapes rhomboides (Pennant) in the Bay of St. Malo, France, was studied for one and a half years (July 1984–October 1985) to determine spawning frequency and fecundity under natural conditions, using the techniques of qualitative histological staging, condition index calculation and quantitative stereology. Spawning took place twice a year, in late May and in July/September. There was an extended winter resting period. Gonad development and oocyte production were positively correlated with female body size. The annual fecundity in a 40 mm clam was about 5x10⁵. Stereological techniques provided accurate information on oocyte dynamics within a gonad and the relationship with atretic processes. Each oocyte generation from the onset of the cycle to the winter resting stage was spawned eventually if conditions were suitable, or the oocytes were resorbed. Atresia of oocytes was seen throughout the reproductive period, but especially after the spring spawning and at the end of the summer.     

Seasonal variations in biochemical constituents during the reproductive cycle of the female dog cockle Glycymeris glycymeris

In an attempt to describe the biochemical events associated with the main stages of the annual and reproductive cycles of the female dog cockle Glycymeris glycymeris L., we studied seasonal variations in the various stages of oocyte development of the ovaries, and the glycogen, total protein and total lipid content of five body tissues – adductor muscle, foot, tunic coat, visceral mass and mantle. From November 1991 to November 1994, microscopic examination of the ovaries and measurement of the tissue concentrations of glycogen, total proteins and total lipids in these five body tissues were made monthly on ten female dog cockles originating from the sea area around Douarnenez (south Brittany, France). Morphological studies revealed that in the population investigated the annual cycle is characterised by three major periods: a first period of vitellogenesis extending from February/March to April/May and preceding a spawning in spring; a second period of vitellogenesis extending from May/June to September/October and leading to either no spawning, a single autumnal spawning event, or to two spawning events in summer and autumn; and a third period extending from October/November to February/March and characterised by a high level of oocyte lysis. In the muscular body tissues of the dog cockle, i.e. the adductor muscles, the foot and the tunic coat (the muscular envelope containing the visceral mass), the concentrations of glycogen, total proteins and total lipids underwent very similar variations during the annual cycle. During each stage of vitellogenesis, a typical glycogen–protein–lipid sequence was observed in the muscular tissues that was characterised firstly by a peak of glycogen concentration 2 to 3 mo before spawning, followed by a peak in total proteins 1 mo before spawning, and finally by a peak in lipid content just before spawning. A similar glycogen–protein–lipid sequence was also recorded in the first half of the winter period. However, these events were followed by general atresia affecting all oocytes in the gonad. Maximum energetic value of biochemical constituents in females coincided with peaks in lipid content in the visceral mass and mantle. These biochemical events occurred principally immediately before and at the end of oocyte lysis (December/January). A drop in the total energetic value, affecting mainly the visceral mass and the mantle, was recorded each year during the period January to March, coinciding with the period of shell growth in this species. Our data clearly indicate that in female G. glycymeris all muscular tissues contribute to the storage of glycogen and proteins, and suggest that glycogen may be the source of energy triggering vitellogenesis. Biochemical and microscopic observations revealed that oocyte development takes place during the first half of winter, but that these oocytes undergo atresia in December/January. The metabolites produced from oocyte lysis could contribute to somatic growth, which occurs in late winter. Received: 3 March 1997 / Accepted: 23 July 1997     

Reproductive cycle of Golfingia margaritacea,a bipolar sipunculan,in subantarctic water

The reproductive cycle of the bipolar sipunculan Golfingia margaritacea collected from Ushuaia, Argentina (54°49 S; 68°13W) in 1986 and 1987 is reported. The population sampled showed a sex ratio of 1:1. Males, however, frequently outnumbered females. Measurements of coelomic oocytes delineated an annual reproductive cycle. Small oocytes were present in the coelom all year: a subpopulation began to increase size about the middle of spring and reached its maximum size in late summer. Spawns may occur from the end February to April. May is characterized by resorption of large oocytes. Monthy monitoring of the gonads revealed mitotic activity and a continuous release of gametocytes to the coelom. Parasites were detected in the gonads. Large coelomic oocytes were also present in the coelom during the same season in the Northern and Southern Hemispheres, but egg sizes were significantly larger in boreal populations.     

Reproductive patterns in the Antarctic brachiopod Liothyrella uva

The reproductive cycle of the Antarctic articulate brachiopod Liothyrella uva (Broderip, 1833) is described from monthly samples collected between September 1985 and July 1987 from a population at Signy Island, Antarctica. Spermatogenesis and oogenesis are described for the first time in this species. Surface dried-tissue masses for a standard individual (41 mm shell length) were calculated for the digestive diverticula, gut, lophophore and gonad from monthly dissections of 15 brachiopods. Seasonal patterns, with summer peaks, were observed in the digestive diverticula and gut. The lophophore and gonad masses did not exhibit seasonal trends. Females showed a sharp decrease in proportion of large oocytes between October and November in 1986, suggesting spawning during this period. There was no similar decrease during the same period in 1985. Mean percent spermatozoa measurements revealed a large increase in November 1985 and a rapid decline in December 1985. This suggested a large spawning event for males in 1985 which was not repeated the following year. These data indicate large inter-annual differences in reproductive activity as well as differences between males and females. They also suggest the possibility of sperm storage by females. Brood characteristics were also highly variable. The smallest brooding female was 31.5 mm in length. Some females brooded more than one developmental stage simultaneously, and variation in brood size (numbers of embryos or larvae held in the lophophore) and brood composition between individuals was high. All samples collected throughout the 2 yr period contained some females with broods. The data suggest that the reproductive strategy of L. uva is highly plastic, and that there may be three reproductive periodicities on seasonal, annual and inter-annual time scales. Received: 16 May 1997 / Accepted: 2 March 1998     

Brooding of the sub-Antarctic heart urchin, <Emphasis Type="Italic">Abatus cavernosus</Emphasis> (Spatangoida: Schizasteridae), in southern Patagonia

The reproductive cycle of the sub-Antarctic spatangoid sea urchin, Abatus cavernosus, was examined during a 2-year period in southern Patagonia, Argentina. The population studied is the northernmost known coastal population in the austral oceans, and is influenced by a greater annual range of seawater temperature than other Abatus species. The sex ratio of the overall A. cavernosus population did not differ significantly from 1:1, but was not homogeneous across size classes. A clearly defined annual reproductive cycle was found. Spawning occurred from May to July and was synchronous between sexes. Females were observed to be brooding within a 9-month period, from May to February. Juveniles were released during the austral summer, from January to February. The length at which 50% of the females were brooding occurred at a test length of 25.9 mm. A. cavernosus had a large egg size (mean diameter = 1.4 mm) and low fecundity (maximum = 57 eggs per female) compared to closely related species. The number of eggs within each brood pouch was highest in larger anterior brood pouch, which is close to two gonopores, as opposed to the other anterior and two smaller posterior pouches. Significant interannual variation was observed in gonad cycles, fecundity, and embryo development such as: brood size decreased during 2001; adjusted gonad dry weight and fecundity were higher during 2003. Hypotheses concerning the gonadal and brooding cycles and fecundity of sub-Antarctic and Antarctic Schizasteridae are discussed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Reproductive cycle of two populations of Ophionereis schayeri (Ophiuroidea) in New South Wales

Reproduction of two populations of Ophionereis schayeri (Müller and Troschel) in New South Wales was investigated from November 1991 through January 1993. The reproductive cycle was documented by histological examination of the gonads and by image analysis to determine the oocyte size-frequency distributions. Both populations of O. schayeri were mature in December and January and had a major summer spawning period between January and February. Thereafter, the condition of the gonads exhibited interindividual variability, with asynchronous low-intensity gamete release through August. O. schayeri has the potential to spawn for up to 8 mo of the year. This breeding pattern with synchronous spawning in summer and asynchronous gamete release through winter was similar in both populations. During autumn and winter, the gonads contained developing gametes and advanced gametes ready for spawning. The eggs spawned by O. schayeri during these seasons started their growth during the previous spring vitellogenic period, and continued to grow through summer. Upon reaching full size, they were stored for spawning outside the main breeding period. Spring is marked by increased spermatogenic and vitellogenic activity followed by maturation and spawning. Throughout their development, the oocytes of O. schayeri are surrounded by a follicle consisting of periodic acid-Schiff-positive (PAS+) haemal fluid and PAS+ yolk by the oocytes. In the testes, the haemal sinus projects into the centre of the spermatocyte columns, thus appearing to play a nutritive role in support of both oogenesis and spermatogenesis. Late vitellogenic oocytes of O. schayeri are firmly anchored to the germinal epithelium by an attachment complex consisting of specialised attachment cells and basophilic strands that radiate between the oolemma and the nucleus. Spawning is associated with rupture of the follicles, which remain as prominent, empty U-shaped profiles in the ovaries. O. schayeri produces copious numbers of 200 m-diam oocytes, suggesting that this species is a broadcast spawner and that it has a modified ophiopluteus or vitellaria larva.     

Reproduction,recruitment and fragmentation in nine sympatric species of the coral genus Acropora

Multispecies assemblages of the coral genus Acropora occur commonly throughout the Indo-Pacific Ocean. Nine species from such an assemblage comprising 41 species of Acropora, at Big Broadhurst Reef on the Great Barrier Reef, were studied during 1981–1983. Similarities and differences in reproductive modes and timing, oocyte dimensions and fecundity, recruitment by larvae and by fragments, and mortality were recorded. All species had an annual gametogenic cycle, were simultaneous hermaphrodites, and had the same arrangement of gonads in polyps. In six species, most colonies released gametes on the same night of the year, in early summer, during a mass spawning event involving many coral genera. A seventh species had colonies spawning at this as well as other times of the year. Another species spawned in late summer, and gametes were not observed to mature in the last species. Eggs were very large (601 to 728 m geometric mean diameter) and fecundity of polyps low, compared with other corals; no reduction in oocyte numbers occurred during oogenesis. Reef-flat species had slightly bigger and fewer eggs than reef-slope species. All species recruited by larvae, but four also multiplied by fragmentation, either year-round or during occasional rough weather. Yearround fragmenters had few larval recruits; non-fragmenters had many, and a rough-weather fragmenter had an intermediate number of larval recruits. It was concluded that larval recruitment largely determined species composition, and that reduced larval recruitment was responsible for sparse distribution of fragmenting species. Subsequent mortality in some species and increase by fragmentation in others probably determined relative abundances.     

Quantitative and ultrastructural studies on the reproductive biology of the polychaete Pholoe minuta in Galway Bay

Previous works by the present authors have identified, in a qualitative fashion, the reproductive cycle of Pholoe minuta (Fabricius) in inner Galway (53°13.5N; 9°7W). This quantitative, histological study, carried out over the period late May 1981 to late April 1982, shows that P. minuta is polytelic (two to three annual spawnings in an individual's lifespan). Individuals become sexually mature for the first time when approaching 3 yr of age. Estimates were made of the size of the reproductively active population (47 to 49%), sex ratio (1:1), duration (10 to 11 mo) and pattern (unimodal) of gametogenesis and fecundity levels (210 198 eggs m^-2). Maturation (mean oocyte size=85 m) and spawning (for 1 wk during late March through early April) were shown to be synchronised. Throughout oogenesis, follicle cells play an important role in binding together oocyte clusters, and desmosomal contacts are evident between oocyte and follicle cell plasmalemmas. No evidence for the synthesis of yolk precursors in the follicle cell cytoplasm was discovered. Oocytes are rich in Golgi apparatuses (yolk synthesising) and nuclear pores are numerous. Rough endoplasmic reticulum is distended in nature. Egg envelope development does not appear to commence until after the onset of vitellogenesis. Mature spermatozoa are of the primitive bullet-shaped type, with an unmodified acrosome. A possible method of elevation membrane formation is described.     

Sexual reproduction in solitary corals: Overlapping oogenic and brooding cycles,and benthic planulas in Balanophyllia elegans

The temperate solitary coral Balanophyllia elegans Verrill, 1864 was collected monthly between January 1977 and August 1978 off the California coast. B. elegans reproduces only sexually, is gonochoric, and broods its embryos. Males are ripe only in late summer, but oocytes and embryos (ca. 40 per female) are found throughout the year. The presence of oocytes and embryos throughout the year may be the result of very long, overlapping oocyte growth and embryonic developmental times. Large, crawling, benthic planulas are released mainly in the winter. The skeletal design of the corallum of B. elegans accommodates the brooding of unusually large embryos; this design may be indicative of brooding large embryos in other species of corals, particularly dendrophyllids.     

Reproductive biology of the holothurians from the major communities of the New Caledonian Lagoon

The reproductive biology of nine species of aspidochirote holothurians from the major communities of the New Caledonian lagoon has been analysed. The data were obtained from monthly sampling from 1978 to 1982 of their populations on reef slopes and passes for Holothuria nobilis, H. fuscogilva, H. fuscopunctata and Thelenota ananas, in the inner lagoon for Stichopus variegatus, H. scabra and H. scabra versicolor and on reef flats for Actinopyga mauritiana, A. echinites and H. atra. The morphology and anatomy of the gonads and their annual cycle are described. The reproductive cycles, composed of the five phases of gonad growth, maturing, spawning, post-spawning and resting, were determined from the changes in the sexual stages, the gonad indices and the percentage of indeterminate sex. Three main reproductive patterns are recognized, annual cycles with spawning occurring during the warm season or during the cool season and a semiannual cycle. Other population parameters, such as the size of the mature oocytes, the mean size of the individuals at first sexual maturity, and absolute and relative fecundities were calculated and related to the mean size of the species, the taxonomy and the ecology. The reproductive strategies of the species show a gradient that is probably related to the stability of the biotopes, with smaller species living in the more intrable outer reef flats and larger species in deeper lagoon floors.     

Gametogenesis in a Northumberland population of the polychaete Melinna cristata

The proliferative activity of the germinal epithelium in relation to breeding biology has been investigated in a population of the ampharetid polychaete Melinna cristata (Sars). This species is dioecious and highly gregarious, and breeds during a brief period at the end of December or beginning of January. The gonal exists in proliferative and non-proliferative states. The former begins immediately after spawning, and is maintained until September. The rate of release of gametocytes into the coelom varies during this period, with peaks in January and April. In September, DNA synthesis ceases in gonads of both males and females and no further gametocytes are released into the coelom, but primary oocytes which have completed the S phase of meiosis continue to develop and accumulate in the ovary as a population of previtellogenic oocytes which are released into the coelom immediately after spawning. This cycle of germinal epithelium activity is compared with those described in other polychaetes.     

Reproductive strategies of two deep-sea gastropod species from the Porcupine Seabight (Northeast Atlantic)

Two species of small gastropods (<6 mm in length), Amphissa acutecostata (Philippi, 1844) and Gymnobela subaraneosa (Dautzenberg and Fischer, 1896), widely distributed in the northeast Atlantic, were found in large numbers in the Porcupine Seabight (Northeast Atlantic). Except for some aspects of taxonomy and distribution, as well as some data on larval development, the biology of these species is unknown. This study describes basic aspects of the life-history strategies of both species. Histological studies showed that oocyte and sperm development in both species was similar to the gametogenetic patterns observed in other deep-sea gastropods. In females, oogonia proliferated in the germinal epithelium and developed into previtellogenic oocytes (30–40 m), which grew into vitellogenic primary oocytes. Vitellogenic oocytes were covered by a thin layer of follicle cells involved in the vitellogenic processes. The maximum size for mature oocytes was 99.06 m for A. acutecostata and 114.82 m for G. subaraneosa. In A. acutecostata most of the volume of the ovary was occupied by previtellogenic and early vitellogenic oocytes, whereas in G. subaraneosa most of the volume was filled by large vitellogenic oocytes. Both species showed quasi-continuous production of oocytes. The oocyte size-frequency diagrams suggested a continuous release of a small number of oocytes throughout the year for A. acutecostata, and asynchronous periodic spawning events for G. subaraneosa. Gonad development and gametogenesis could be strongly affected by presence of parasites in one of the populations of G. subaraneosa.Communicated by J.P. Thorpe, Port Erin     

Gonad morphology and oocyte development in<Emphasis Type="Italic"> Pseudocalanus</Emphasis> spp. in relation to spawning activity

Gonad maturation processes were studied in Pseudocalanus spp. females from Georges Bank and Cape Cod Bay (northwest Atlantic) using a combination of morphological analysis and experiments. For light microscopy of the oocytes, females of different maturation stages were preserved immediately after capture. The maturation processes during the spawning cycle were described from observations of live females which were exposed to feeding and starvation at two temperatures, 8 and 15°C, for 12 days. The gonad morphology of these females was examined in 24 h intervals, and spawning events were recorded. Both light microscopy and whole animal observation revealed that oocytes during maturation change in shape and size, in the morphology of the nucleus, and in the appearance of the ooplasm. Due to these modifications of oocyte morphology and due to oocyte migration, the morphology of the gonads changed distinctly during a spawning cycle. Five oocyte development stages were identified by light microscopy and related to a macroscopic system of four gonad development stages, that can be applied to whole animals and allows the identification of females ready to spawn. The experiment showed that food and temperature had strong effects on gonad maturation processes. High proportions of mature females were found when food was available, whereas the proportion of immature females increased shortly after exposure to starvation. Compared to 15°C, gonad maturation at 8°C was prolonged and thus spawning frequency was lower. The final maturation processes at food saturated conditions were slower than the embryonic development, and no indication was found that mature oocytes are stored in the diverticula waiting to be released. The duration of the interspawning interval would thus be determined by the duration of final oocyte maturation which is dependent on both temperature and food supply.Communicated by O. Kinne, Oldendorf/Luhe     

Age structure,growth rates,movement patterns and feeding in an estuarine population of the cardinalfish Apogon rueppellii

The biology of a population of the cardinalfish Apogon rueppellii has been studied over several years (1977–1983) in the Swan Estuary in south-western Australia, using ramples collected monthly from the shallows by beach seine and from various depths by otter trawl. While the life cycle of this species typically lasts for one year, at the end of which time the mean length is 50 to 60 mm, some individuals survive for a further year and attain lengths up to 104 mm. A. rueppellii shows a marked tendency to move offshore into deeper water during the winter months. This tendency is more pronounced in the 1+ than in the 0+ year class and in larger than smaller 0+ individuals. An inshore movement of A. rueppellii in the spring is followed by spawning and by oral brooding by the males, which leads to the recruitment of large numbers of a new 0+ year class on to the banks during the summer. The offshore movement is correlated with changes in salinity and temperature. The larger catches taken by otter trawl during the day than at night indicate that A. rueppellii exhibits a diel pattern of activity. Mean fecundity ranged from 70 in the 45 to 49 mm size class to 345 in the 90 to 94 mm size class. Measurements of fecundity and the number of oral-brooded eggs demonstrated that the majority of the eggs released by the female are collected and incubated by the males. Copepods are ingested in relatively greater amounts by small than by large A. rueppellii, whereas the reverse situation occurs with larger crustaceans, polychaetes and small fish. The presence of greater amounts of copepods in the diet during the day and of amphipods at night probably reflects the diel activity patterns of the prey.     

Growth and reproductive biology of the small penaeid shrimp Trachysalambria curvirostris in Tokyo Bay

We investigated the growth and reproductive biology of the penaeid shrimp Trachysalambria curvirostris in Tokyo Bay, Japan, by monthly bottom-trawl surveys from May 2002 to December 2004. We also examined oogenesis in T. curvirostris by histological observation of the ovary. Females grew faster and attained a larger body size for age than males. The growth rate was high in summer and low in winter and was likely to be associated with seasonal changes in water temperature. The carapace length (CL) at which 50% of females contained vitellogenic oocytes was estimated to be 17.0 mm. The reproductive season extended from May to October. Young-of-the-year appeared in October and could be traced across the months on CL histograms to the following September or October, indicating a 1-year life cycle. This extended reproductive season, together with our observation of asynchronous development of oocytes in the ovary, suggests that multiple spawning by individual females may occur during the reproductive season. Postovulated oocytes were not found among the samples we collected during the daytime, suggesting that final oocyte maturation and spawning occur at night. Cortical crypts in the cytoplasm of the oocyte, considered to be a general feature of oogenesis in penaeid shrimps, were not found in T. curvirostris, even in oocytes undergoing germinal vesicle breakdown. This result implies that the cortical reaction after spawning of T. curvirostris may be different from that of other penaeid shrimps.     

Reproduction in Amphiura filiformis (Echinodermata: Ophiuroidea): Seasonality in gonad development

The burrowing ophiuroid Amphiura filiformis (O. F. Müller) (Echinodermata: Ophiuroidea) colonises an extensive area and is a numerically dominant member of the macrofauna in Galway Bay on the west coast of Ireland. There, it has a discrete, relatively short annual breeding period, from June to September, with peak activity in the month of August. The breeding period approximates in timing those of other European populations. The oocytes of a particular year are laid down in the autumn of the previous year; they begin to develop in spring, with the period of fastest growth in May/June. Gonad growth corresponds quite closely to the annual rise in water temperature, with spawning taking place during the warmest months of the year. The species is polytelic, and it is suggested that the long-lived Galway Bay individuals may breed every year for several years. The relationship between spawning and population dynamics is discussed in the light of current, available literature concerning A. filiformis from other parts of Europe. The role of so-called ultimate factors in the process of ophiuroid maturation and spawning is discussed.     

Multi-year observations on the gametogenic ecology of the Antarctic seastar <Emphasis Type="Italic">Odontaster validus</Emphasis>

This study reports the first multi-year observations on the reproductive patterns for an Antarctic predator/scavenger, Odontaster validus (Koehler 1912). Seastars were collected monthly from a shallow site (15–20 m depth) near the British Antarctic Survey (BAS) Rothera Research Station (Adelaide Island, 67°34′S 68°08′W) from July 1997 to January 2001. Reproductive condition, oocyte size frequencies and spermatogenesis were examined in at least ten seastars each month using histological and image analysis techniques. Gonad indices (GI) and pyloric caeca indices (PI) were also examined in the same samples. Female and male GIs varied seasonally, in parallel with a reduction in the proportion of large oocytes and mature sperm in the gonad in August to mid-October following winter spawning. Despite there being remarkable consistency in the timing of spawning from year to year, differences in the reproductive condition of individuals were apparent. Patterns in the digestive tissues also varied with season, peaking in December and reaching a minimum in February in two of the three study years. This weaker annual pattern may partly reflect the varied diet of this predator/scavenger species, which is not directly dependant on the timing and magnitude of the annual phytoplankton bloom. Pooled oocyte size distributions and residual analysis suggested that oogenesis progressed over 18–24 months, with the largest of the two size classes (maximum diameter = 183 μm) being spawned annually. This pattern of oocyte growth and spawning was previously reported in the early 1960s for an O. validus population from McMurdo Sound, which lies south of Rothera by 10° latitude. The extremely catholic diet of this predator/scavenger suggests the reproductive patterns of the seastar will be less susceptible to changes in food supply compared to polar suspension feeders or deposit feeders. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.