Introduction of the northern Pacific asteroid Asterias amurensis to Tasmania: reproduction and current distribution

The northern Pacific asteroid Asterias amurensis (Lütken) has been recently introduced to Tasmania and is now well-established in east and southeast Tasmania. This sea star is conspicuous throughout the Derwent River estuary and is particularly abundant in the Hobart port area. Reproduction of two populations of A. amurensis at Sullivans Cove and at Sandy Bay was investigated from August 1993 to October 1994 by gonadal histology and measurement of the gonad index (GI). An intense period of vitellogenic and spermatogenic growth started in April, with the breeding condition reached by June. In 1994, peak GI was recorded at Sullivans Cove in July and at Sandy Bay in August. Although these data indicated that the Sullivans Cove population spawned before the Sandy Bay population, histological examination revealed that major spawning activity occurred in both populations from July onwards. In the early part of the breeding season, gametogenesis proceeded in parallel with spawning, with released gametes being replaced by continual gametogenesis. Maintenance of a higher GI during the early part of the breeding season at Sandy Bay was due to prolonged gametogenic replacement at this site. Spawning continued to October 1994, resulting in a sharp decline in the GI. The cyclic expansion and regression of the genital haemal sinus coincident with germinal proliferation and growth, respectively, support the contention that haemal fluid provides nutrients for gametogenesis. In Tasmania, A. amurensis experiences temperature and photoperiod regimes similar to those experienced by endemic populations of this species in the north Pacific. Comparison of reproduction of A. amurensis in Japan and Tasmania at similar latitudes shows that gametogenesis of the northern and southern populations is 6 mo out of phase. This phase shift provides evidence for photoperiodic regulation of gametogenesis in A. amurensis. The similar trend in sea-temperature regimes associated with the stages of gametogenesis in northern and southern populations suggests that temperature also plays a modulatory role. Based on the periodicity of reproduction and the ontogeny of A. amurensis, the planktotrophic larvae of this species would be expected to be in the plankton for several months from the end of winter through summer. Considering the highly fecund, dispersive life-history of A. amurensis, the southeast Tasmanian populations have considerable potential to serve as a seed source for establishment of new populations of this asteroid elsewhere in Tasmania and in mainland Australia. Received: 18 October 1996 / Accepted: 22 October 1996     

Annual reproductive cycles of the commercial sea urchinParacentrotus lividus from an exposed intertidal and a sheltered subtidal habitat on the west coast of Ireland

Reproduction of the commercial sea urchinParacentrotus lividus (Lamarck) from contrasting habitats on the west coast of Ireland was examined from May 1986 through August 1988. Urchins were collected intertidally from an exposed rocky shore and subtidally from a protected bay. Monthly measurements of the gonad index and histological examination of the gonads demonstrated thatP. lividus has an annual reproductive cycle. Although the two populations exhibited similar reproductive patterns over three breeding seasons, there were inter-annual and inter-population differences in the amplitude of gonadal growth and in the time when spawning started. The subtidal urchins had significantly larger gonads and exhibited a longer period of reproductive maturity compared with the intertidal urchins. This difference was also evident in the histology of the ovaries at the beginning of breeding, when most of the subtidal females contained mature ovaries, whereas most of the intertidal females contained premature ovaries. An inter-annual difference in the onset of spawning was observed, with the start of gamete release differing by as much as four weeks between years. It appears that inter-annual differences in sea temperature influence the temporal variation in spawning byP. lividus and that increasing temperature may serve as an exogenous cue for gamete release. The inter-annual variability in the onset of spawning suggests that photoperiod does not cue gamete release. Gonadal growth, on the other hand, occurs during the coldest months of the year and during the period of shortest days, suggesting that temperature and photoperiod may both influence gonadal growth during the winter. Oogenesis and spermatogenesis ofP. lividus were examined histologically. During the post-spawning recovery and growth stages, the gonads gained weight through growth of the nutritive phagocytes and the accumulation of periodic acid Schiff (PAS) + droplets by these cells. The PAS + material appears to play a nutritive role in gametogenesis. For the females, the frequencies of six ovarian maturity stages was assessed at approximately monthly intervals. Small oocytes were present throughout the year and clusters of early oocytes were most apparent during the spent and recovery stages. With the onset of vitellogenesis and subsequent accumulation of ova, the nutritive phagocytes and their PAS + droplets became depleted. The ovarian condition at the onset of breeding was variable, due to differences in the number of vitellogenic oocytes, differences in the number of ova in storage, and differences in the amount of PAS + material. In general, the nutritive phagocyte tissue is reduced by the onset of spawning and is exhausted by the termination of breeding. A similar series of events occurs during spermatogenesis. The relevance of this study for the use ofP. lividus as a brood-stock organism for mariculture is discussed.     

Photoperiodic regulation of parturition in the self-fertilizing viviparous polychaete Neanthes limnicola from central California

Seasonally-changing photoperiod controls the timing of parturition in the viviparous, self-fertilizing polychaete Neanthes limnicola (Johnson, 1901) from Watsonville Slough, a central California estuary. During 1987 to 1989, worms in the field gave birth mainly in the spring. Those born in late February from field-collected parents and maintained in the laboratory under in-phase photoperiodic conditions reproduced in 12 to 13 mo, under spring light-regimes. When maintained under light conditions 6 mo out of phase,they required only about 6 to 8 mo to reproduce, giving birth in the fall, but under spring light-regimes. Worms born in the laboratory in fall and then maintained in phase reproduced in the ambient spring, at 6 to 8 mo of age; those maintained out of phase took 12 to 13 mo, giving birth the following fall under spring light-regimes. Photoperiod treatments had no consistent effect on the number of young produced, and age and fecundity were only weakly correlated. Highest fecundities were in salinities of 15 to 20,with lower fecundities at higher salinities. Worms maintained in fullstrength sea water(33 S) showed abnormal development and produced very few or no young. Salinity did not affect timing of parturition. Temperature differences of 3 to 7 C° between treatments had no effect on timing of parturition or number of young produced, and marginal effects on life span. These results indicate that photoperiod regulates the timing of reproduction in N. limnicola in central California, while salinity mainly influences fecundity.     

Effects of symbiont elimination and reinfection on the life processes of the planktonic foraminifer Globigerinoides sacculifer

Laboratory experiments were carried out to determine the influence of symbiotic dinoflagellates (zooxanthellae) on the shell growth, longevity, and reproductive potential of Globigerinoides sacculifer (Brady). Its symbionts were eliminated by 72-h treatment with a photosynthetic inhibitor (DCMU). Symbiont elimination resulted in earlier gametogenesis (shortened survival time) and smaller shell sizes of G. sacculifer when compared to untreated foraminifera grown in sea water. Individuals kept in continuous darkness in untreated sea water also exhibited early gametogenesis, short survival times and small shell sizes. Aposymbiotic foraminifera formed on the average one or two chambers fewer per individual and their rate of shell size increase is slower than symbiont-bearing foraminifera. Symbionts were lysed within perialgal vacuoles of G. sacculifer when subjected to DCMU treatment or kept in continuous darkness. One DCMU-treated group was reinfected with symbionts from crushed G. sacculifer donors. Soon after reinfection, these foraminifera resumed a shell growth rate and exhibited developmental stages that were nearly equivalent to those of untreated individuals, as deduced from their shell size, frequency of sac-like chambers, rate of gametogenesis, and survival time. Our experiments indicate that the symbionts aid in calcification and that elimination of symbionts triggers gametogenesis, thus shortening the life span of the foraminiferal host. The results imply that shell growth in symbiont-bearing planktonic foraminifera occurs mainly in the euphotic zone and that they do not survive for long periods below it.     

Selective accumulation of mycosporine-like amino acids in ovaries of the green sea urchin Strongylocentrotus droebachiensis is not affected by ultraviolet radiation

Field sampling and laboratory experiments examined whether ultraviolet radiation (UVR) affects the reproduction or the accumulation of mycosporine-like amino acids (MAAs) and ascorbic acid in ovaries of the green sea urchin Strongylocentrotus droebachiensis (Müller). Ovaries of sea urchins sampled across a depth gradient (0.5–10 m) in March 1998 did not differ in their gonadal index, or in concentrations of MAAs, or ascorbic acid. Concentrations of MAAs and ascorbic acid in ovaries were higher in sea urchins collected from a kelp bed compared with those collected from a community of crustose coralline algae. The concentrations of MAAs in ovaries varied seasonally, peaking in March, when sea urchins had high gonadal indices just before spawning. Ovaries of sea urchins maintained on controlled diets from October 1997 to April 1998 accumulated significantly higher concentrations of MAAs when fed a diet rich in MAAs than did ovaries of sea urchins fed an alga lacking MAAs, but the gonadal indices did not differ between diets. Sea urchins accumulated principally one MAA, shinorine, but not others that were available in high concentrations in their diet. Neither the gonadal index nor the ovarian concentrations of MAAs were affected by daily exposure of adult urchins to UVR for 6 months. Concentrations of ascorbic acid in ovaries did not differ among diets or UV-treatments. The percentages of nutritive phagocytes and gametic cells were not affected by diet or UVR, and did not co-vary with concentrations of MAAs or ascorbic acid in ovaries. These data support previous demonstrations that female sea urchins accumulate MAAs from their diet of macroalgae, but further show that the accumulation is selective for specific MAAs, particularly shinorine, and that adult S. droebachiensis do not accumulate MAAs in their ovaries or eggs in response to UV-exposure. These are also the first experimental studies to address whether MAAs are affected by or regulate gametogenesis, and indicate that they do not. Received: 5 May 2000 / Accepted: 29 September 2000     

Can photoperiod manipulation affect gonad development of a boreo-arctic echinoid (Strongylocentrotus droebachiensis) following exposure in the wild after the autumnal equinox?

A laboratory experiment was conducted in the winter of 2003–2004 to assess the effect of varying photoperiod regime on consumption rate, assimilation rate, absorption efficiency, and gonad development of the green sea urchin, Strongylocentrotus droebachiensis. Adult individuals were collected from the wild after they had been exposed to the ambient autumn photoperiod cue (which is the extraneous trigger thought to elicit gametogenesis in this species) and placed at ambient temperature for 12 weeks under five different photoperiod regimes: (1) 24 h light:0 h dark=“0D”, (2) 16 h light:8 h dark=“8D”, (3) 8 h light:16 h dark=“16D”, (4) 0 h light:24 h dark=“24D”, and (5) ambient photoperiod (range: 10.50–15.25 h dark). Urchins in these five treatments were fed ad libitum with bull kelp, Nereocystis luetkeana. A sixth treatment consisted of starved individuals held under 0D conditions. Various gonad factors including gonad index, percent gonad water, gonad colour (CIE lightness or L*, CIE hue or a*, and CIE chroma or b*), percent area occupation of the gonad by various cell types (nutritive phagocytes, spermatozoa, and secondary oocytes/ova), and stage of development were assessed at the beginning of the experiment and at weeks 4, 8, and 12 of the study. Consumption and assimilation rates were assessed at weeks 4 and 12 and absorption efficiency at week 12 of the experiment. Urchins were predominantly in the growing and premature stages at the beginning of the experiment, but by week 4 at least 20% of individuals in all treatments receiving food were classified as mature. Spawning occurred during all these treatments between weeks 4 and 8, as evidenced by significant decreases in spermatozoa and secondary oocytes/ova and a significant decrease in percent gonad water, but was not accompanied by major declines in gonad indices. Greater than 90% of individuals in all five of the fed treatments were in the recovering and growing stages at the end of the experiment. The 16D treatment had by far the greatest percentage of urchins in the growing stage. In contrast, individuals that were starved were predominantly in the mature stage at weeks 4, 8, and 12, with only ~30% reaching the spawning stage by the end of the experiment. Photoperiod significantly affected gonad indices at the termination of the experiment with gonad index being the highest in the 16D treatment; this was significantly greater than in the 8D and ambient treatments. Photoperiod did not significantly affect gonad percent water, gonad lightness, or gonad hue. Gonad chroma was significantly affected by photoperiod, urchins held under ambient conditions having significantly lower b* readings than individuals in any other treatment. Photoperiod had little or no affect on consumption rate, assimilation rate, or absorption efficiency. Thus, differences among treatments in regards to gonad index, gonad chroma, and stage of development cannot be attributed to variations in feeding, absorption, or assimilation. The results of this experiment indicate that once gametogenesis is initiated, photoperiod manipulation cannot prevent ultimate spawning. However, photoperiod regime can affect the rate at which urchins move through the various stages of the gametogenic cycle. Urchins placed on short days under artificial lighting (16D) moved through the spawning stage into recovering and growing stages the fastest. This photoperiod regime also produced the highest gonad index at the end of the experiment. Since the commercial urchin market prefers large gonads in the growing and premature stages (i.e. before the mature stage is reached and gonads start leaking sperm and eggs), short day-lengths under artificial lighting (16D) appear to be the best photoperiod conditions for optimizing marketability.     

Manipulation of food and photoperiod promotes out-of-season gametogenesis in the green sea urchin, Strongylocentrotus droebachiensis: implications for aquaculture

Green sea urchins, Strongylocentrotus droebachiensis OF Müller, collected off the coast of New Hampshire, USA, in late February 1995, were brought into the laboratory and fed an artificial diet ad libitum, and subjected to a photoperiod advanced by 4 months. During this study, temperatures and salinities for experimental urchins mirrored those recorded at the collection site. We examined the effects of changes in feeding regime and photoperiod on gametogenesis and compared the experimental urchins with those from the source population. During the 7-month period, experimental urchins showed no detectable changes in mean test height or diameter. Experimental urchins had a significantly higher gonad index (GI) in March, April and May (18 ± 6%) compared with field urchins in March (11 ± 3%). Subsequently, experimental urchins had a mean monthly GI of 25 to 30%, while the mean GI for field urchins was 11 to 13%. Gonial cell mitosis and gametogenesis occurred earlier in experimental male and female urchins compared with field urchins. Stereological and histological observations and stage–frequency data showed that the ovaries of experimental urchins were large because of the accelerated development of nutritive phagocytes, the volume fraction (V _v) of which was 89 to 90% of the gonad, while new vitellogenic primary oocytes occupied <1% V _v. In males, stereological and histological observations and stage–frequency data suggested a mobilization of materials from the nutritive phagocytes beginning between June and August, i.e. earlier than in females, and, by September, new gametes occupied a V _v of 49 ± 3% of the testes. Oocyte size–frequency distributions demonstrated that most primary oocytes were <80 μm in diameter between March and September, suggesting that cold temperatures may be needed for completion of vitellogenesis. We describe changes in the two principal cell types in the germinal epithelium of urchin gonads and indicate how knowledge of their population dynamics may be useful in aquaculture applications. Received: 21 February 1997 / Accepted: 3 June 1998     

Factors regulating the reproductive cycles of two northeast pacific chitons,Tonicella lineata and T. insignis

The reproductive cycles of Tonicella lineata Wood and T. insignis Reeve are examined in relation to changes in physical and biotic conditions in different locations in British Columbia, Canada, over a 3 to 4 year period. A clearly annual reproductive cycle is displayed by both species, and in any one location and year reproductive events in the two species are similar. There is a progressive increase in the size of the gonads starting in the summer and continuing to mid-winter. Although no one environmental factor is likely to be correlated with this prolonged period of gonadal development, various phases of the annual temperature and photoperiod cycles do appear to coincide with particular phases of gametogenesis (such as gonial proliferation, vitellogenesis and gonadal maturation), and thus could act as external cues. There isa synchronous drop in gonadal size in T. lineata and T. insignis in the spring, as a result of spawning. The exact timing and abruptness of this event in different years can not be accounted for on the basis of temperature. However, new correlative data are presented to add further support to the hypothesis previously presented that the spring phytoplankton is the cue for natural spawning (Himmelman, 1975). Temperature may inhibit spawning in T. lineata if conditions are unseasonably cold.     

Control and coordination of reproduction and molting in the spiny lobster Panulirus argus

Behavioral and physiological correlates of vernal reproduction and molting were investigated experimentally in laboratory-held spiny lobsters (Panulirus argus Latreille) from Florida to determine their control by photoperiod and temperature. Behavioral measures included courtship, copulation and aggression; physiological measures included the timing and frequency of ecdysis, spermatophore emplacement, oviposition, egg hatching, and setal (pleopod) and gonadal development. Behavior resembled that observed in nature, as evidenced in the expression of complete reproductive cycles. Long daylengths and warmer temperatures enhanced courtship, spawning frequencies, and female gonadal development, although gonadal recrudescence occurred in large females irrespective of photoperiod. A significant interaction effect between photoperiod and temperature indicated a need to examine joint, non-independent factor effects upon reproductive parameters. Photoperiod and temperature did not significantly influence aggression and male gonadal development. Photoperiod did not affect molting rates significantly. However, warm temperatures enhanced molting and growth such that sub-adult and young adult lobsters (both sexes) had highest molting rates, followed by large adult males, which in turn had higher rates than reproductively active females. Female setal development correlated positively with female size, and changed abruptly at ecdysis. Although setal lengths were highly variable, setae of 9 mm or more signified sexual maturity. Reproduction and molting were size-dependent: the largest adults mated or spawned, the smallest molted, and intermediate-sized ones either mated, or molted before mating. Spiny-lobster reproductive and molting patterns were influenced by photoperiod and temperature in a complex manner depending upon sex, season, size and developmental state.     

Time-lapse cinematography of feather stars (Echinodermata: Crinoidea) on the Great Barrier Reef,Australia: demonstrations of posture changes,locomotion, spawning and possible predation by fish

Aspects of feather star behavior and ecology were recorded by time-lapse cinematography approximately 1 frame min^-1 on the Great Barrier Reef, Australia over a 1 mo period in 1983. The current regime influenced body postures of most species studied, whether nocturnal or not. Moreover, feather stars of several species crawled on the substratum with their arms; each crawling episode lasted roughly 10 min, and the maximum speed attained was about 1 arm length min^-1. Nocturnal feather stars crawled to their nighttime feeding perches around dusk and crawled back to their daytime hiding places around dawn. Surprisingly, some species of feather stars living on the reef surface both day and night also crawled around at dawn and dusk for reasons that are not known. In the time-lapse films, and individual of Comanthus bennetti (sex undetermined) spawned for about 2 min just after dark on 5 July 1983. Another film showed possible predation on a feather star (Himerometra robustipinna) by a saddled coralfish (Chaetodon ephippium).     

Reproduction and growth of Isostichopus fuscus (Echinodermata: Holothuroidea) in the southern Gulf of California, México

The reproduction and growth of Isostichopus fuscus (Ludwig, 1875) at Isla Espíritu Santo, Baja California Sur, México from July 1992 to September 1993 and from August 1996 to July 1997 were analyzed. The reproductive cycle was monitored by using histological analysis. Five gonadal stages were described according to cell types present in the gonad; undetermined, gametogenesis, maturity, spawning and post-spawning. This holothurian reproduces annually during summer (July to September), when sea surface temperature reaches 27 °C. The gonad index is related to the gonadal stages. The first sexual maturity for I. fuscus was calculated at 367 g (4 to 5 years old) according to the von Bertalanffy equation, and nearly all the specimens at Isla Espíritu Santo were 5 to 7 years old (including some individuals over 35 years old). Data of the length–weight relationship showed that I. fuscus grows allometrically at the studied site (b = 1.83). The mortality rate was relatively high (M = 0.51), indicating that in a typical cohort, 40% of the recruits does not survive the first year, and less than 20% reaches maturity. Received: 15 July 1998 / Accepted: 19 August 1999     

A new quantitative analysis of ovarian development in echinoderms: the maturity stage index

This study developed an objective quantitative method for detecting small-scale temporal or spatial differences in gametogenesis in echinoderms. The method was applied to conventional monthly samples of the planktotrophic brittle star, Ophiopholis aculeata, collected at a single site in Newfoundland (eastern Canada) at 10–15 m depth. The samples were analysed to determine gonad index, oocyte size and gonadal stage using histology. The maturity stage index (MSI) was developed to integrate a measure of brittle star size (disc diameter), oocyte size and oocyte density. The MSIs ranged from 0 to 800 and had significantly different means among the four gametogenic stages (early growth, growth, mature and spent). The MSI was more sensitive in revealing significant differences between consecutive stages than any of its individual constituents. The MSI was also applied to gametogenic data from the lecithotrophic holothuroid, Mesothuria lactea, again revealing significant differences between successive oogenic stages. This method is expected to be useful in field and experimental studies of gametogenesis in echinoderms (and possibly other taxa), where it is important to detect not just the timing of annual peaks in reproduction but small differences in reproductive status among individuals or populations (e.g. from different habitats or feeding regimes).     

Rates of fission, somatic growth and gonadal development of a fissiparous sea star, Allostichaster insignis, in New Zealand

Seasonal changes in population structure and incidence of fission were measured in intertidal and subtidal populations of Allostichaster insignis, a fissiparous sea star. Population size structure was stable over the course of the 1-year study. Sea stars in the subtidal zone attained greater maximum size (mean arm length, R = 35 mm) than those in the intertidal population (20 mm). Fission rates were greatest among small individuals (R < 20 mm). The frequency of fission ranged from 5 to 32% with peaks in early austral summer in the intertidal zone, and in autumn and winter in the subtidal zone. Sexual reproduction occurred in early spring in sea stars larger than 12 mm. The populations were heavily biased toward males. In the laboratory, A. insignis of three size classes (small, R = 9–13 mm; medium, 19–21 mm; and large, 29–31 mm) were fed mussels ad libitum or starved (not fed macroscopic food) for ∼1 year in a 3 × 2 factorial experiment. Small and medium-sized sea stars divided throughout the experiment and the ramets of most individuals regenerated sufficiently to divide again after 6–9 months. Unfed sea stars did not undergo fission (with one exception), had a higher mortality rate, and did not grow. Small, fed sea stars grew significantly faster than medium-sized or large individuals. At the end of the experiment, the pyloric caeca index (a measure of nutritional condition) was greater in fed than in unfed animals. Gonads (only testes were observed) developed in medium-sized and large, fed sea stars. Our field and laboratory results indicate that asexual reproduction in A. insignis predominantly occurs in small, well-nourished individuals. Ramets grow gradually through repeated fission and regeneration to a size (mean length of regenerating arms, R _r ∼ 20 mm) at which they begin to switch to sexual reproduction as the dominant reproductive mode.     

Feeding aggregations of sea stars (<Emphasis Type="Italic">Asterias</Emphasis> spp. and <Emphasis Type="Italic">Henricia sanguinolenta</Emphasis>) associated with sea urchin (<Emphasis Type="Italic">Strongylocentrotus droebachiensis</Emphasis>) grazing fronts in Nova Scotia

Migrating feeding aggregations (or fronts) of sea urchins can dramatically alter subtidal seascapes by destructively grazing macrophytes. While direct effects of urchin fronts on macrophytes (particularly kelps) are well documented, indirect effects on associated fauna are largely unknown. Secondary aggregations of predators and scavengers form around fronts of Strongylocentrotus droebachiensis in Nova Scotia. We recorded mean densities of the sea stars Asterias spp. (mainly A. rubens) and Henricia sanguinolenta of up to 11.6 and 1.7 individuals 0.25 m⁻² along an urchin front over 1 year. For Asterias, mean density at the front was 7 and 15 times greater than in the kelp bed and adjacent barrens, respectively. There was strong concordance between locations of peak density of urchins and sea stars (Asterias r = 0.98; H. sanguinolenta r = 0.97) along transects across the kelp–barrens interface, indicating that sea star aggregations migrated along with the urchin front at rates of up to 2.5 m per month. Size–frequency distributions suggest that Asterias at the front were drawn from both the barrens (smaller individuals) and the kelp bed (larger individuals). These sea stars fed intensively on mussels on kelp holdfasts and in adjacent patches. Urchin grazing may precipitate aggregations of sea stars and other predators or scavengers by incidentally consuming or damaging mussels and other small invertebrates, and thereby releasing a strong odor cue. Consumption of protective holdfasts and turf algae by urchins could facilitate feeding by these consumers, which may obtain a substantial energy subsidy during destructive grazing events.     

The effect of depth on the reproductive cycle ofBrissopsis lyrifera (Echinoidea,Echinodermata) in the Gulf of Lions,Mediterranean Sea

A sample of 227Brissopsis lyrifera were collected in the Gulf of Lions in the Mediterranean Sea between 60 and 1000 m depth over a 21/2-yr period (June 1983 to November 1985). Males and females were sexually mature at the end of summer. After a period of gonadal inactivity during winter, gametogenesis resumed at the beginning of spiring. The cycle was synchronous over the entire bathymetric range studied. Variations in environmental conditions may be one factor inducing gametogenesis.     

Effect of photoperiod and temperature on testicular regression in Channa punctatus

In Channa punctatus testicular regression commonly observed during spawning and postspawing phases of reproductive cycle. In the present study testicular regression was frequently noticed in fish maintained under both long photoperiod-warm temperature (LD 16 : 8-30 degrees C) and short photoperiod-warm temperature (LD 8 : 16-30 degrees C) regimes. Testicular regression was characterized by distortion of cellular boundary of lobules and formation of collagenous capsules containing degenerating germ cells, blood cells and colloidal mass within the lobules. The magnitude of testicular regression was more in fish exposed to short photoperiod regime (R-73.33%, SP-41.67%) than long photoperiod regime (R-50.83%, SP-19.16%) and control group (R-20.83%, SP-16.67%) in both resting (R) and spawning (SP) phases. Further the frequency of testicular regression during resting phase was 73.33% (short photoperiod), 50.83% (long photoperiod) and 20.83% (control) whereas during spawning phase was 41.67% (short photoperiod) 19.16% (long photoperiod) and 16.67% (control). In the present study occurrence of more testicular regression during resting phase than spawning phase may be due to change in the endogenous condition of the fish.     

Population structure and energetics of the shallow-water antarctic sea star Odontaster validus in contrasting habitats

Individuals and populations of Odontaster validus Koehler differed markedly among different habitats, as revealed in a study from October 1984 through January 1986 in McMurdo Sound, Antarctica. At McMurdo Station, individual sizes (wet weight) and population biomass (g wet wt m^-2 and kJ m^-2) decreased significantly with increasing depth. Individuals from shallow (10 to 20 m) habitats were in superior nutritional condition to those from deeper water (30 and 165 m), as shown by higher gonad and pyloric cecum indexes, and by higher lipid and energetic levels in the pyloric ceca. Moreover, gonadal output (reproductive output) was higher in shallow-water individuals. Higher levels of chlorophyll in the pyloric ceca and richer yellow to red coloration of the body wall in the shallow-water individuals indicate that they utilize the higher levels of primary production at shallow depths. At East Cape Armitage, where nearly permanent, thick, snow-covered ice most of the year resulted in very low levels of benthic primary production, the lowdensity sea stars were all very small and nutritionally similar to the deep-water individuals at McMurdo Station. At Cape Evans, where the generally snow-free sea-ice that broke up in mid-summer resulted in a luxurient benthic cover of diatoms and macroalgae, the sea stars were smaller than at McMurdo Station at comparable depths, but population densities were higher, resulting in 4 to 9 times greater biomass. Growth rates of sea stars fed in the laboratory were very low, especially compared to laboratory-reared temperate and tropical species; well-fed individuals need about 9 yr to reach 30 g wet weight, near the mean size of shallowwater individuals at McMurdo Station. No growth was detected in individuals caged at McMurdo Station for one year, suggesting even lower growth rates in the field. The stable size-frequency distributions at the different sites and depths throughout the year-long study suggest highly stable populations with low temporal variability in recruitment, migration and mortality. These data indicate that individuals and populations of O. validus quantitatively and qualitatively reflect the general level of productivity of a habitat. Differences noted in size, coloration, nutrition, and reproductive effort may be the result of long-term integration of local levels of primary production. These ubiquitous sea stars may serve as a biotic indicator of productivity in localized habitats around the continental shelf of Antarctica.     

The reproductive ecology of the invasive ascidian, <Emphasis Type="Italic">Styela clava,</Emphasis> in Auckland Harbour,New Zealand

The ascidian Styela clava, native to the north-west Pacific, is an invasive species affecting New Zealand’s marine ecosystems, biodiversity and aquaculture operations. To provide detailed information on the reproductive biology of S. clava in New Zealand for post-border biosecurity management, long-term seasonal patterns of gametogenesis were determined from May 2006 to May 2008 in Auckland’s Waitemata Harbour (36°49′20″S, 174°45′85″E). Of particular interest was whether the critical 15°C threshold spawning temperature for reproduction observed in the Northern Hemisphere applied here to the first Southern Hemisphere study. S. clava gametogenesis followed a regular seasonal cycle with ripe gametes appearing as early as September and persisting to June; this time frame corresponds to the period when sea surface temperatures in the region first reach 15°C and with spawning occurring mainly during late summer to early autumn. From photoperiod manipulation, it was determined that spawning occurred at approximately 18:20. The extended reproductive period and a short generation time in the Waitemata Harbour provides a lengthy opportunity for S. clava to spread. Findings are discussed in relation to S. clava’s post-border management.     

Chemical mediation of invertebrate defensive behaviors and the ability to distinguish between foraging and inactive predators

When the predatory sea star Pycnopodia helianthoides was placed upstream, the sea urchin Strongylocentrotus purpuratus responded defensively by extending and opening its globiferous pedicellariae. No pedicellaria response was given in control seawater or when the sea star was downstream. The snail Tegula funebralis responded by moving up vertical surfaces when Pycnopodia helianthoides or when Pisaster ochraceus were placed upstream. When these sea stars were introduced downstream, the snail's response was not significantly different from that in control seawater. Water collected from an aquarium containing a single sea star was sufficient to trigger the response of S. purpuratus and T. funebralis; the physical presence of the sea star was not essential. This indicated that a chemical stimulus was involved, and the lack of responses when sea stars were downstream argued strongly against the possible additional involvement of visual or vibrational stimuli. S. purpuratus gave stronger pedicellaria responses to water flowing over an active Pycnopodia helianthoides than to water flowing over the same sea star when it was inactive. The significance of the ability to distinguish between actively foraging and inactive predators is discussed, and a mechanism is proposed to explain differences in the amount of stimulatory chemicals released by active and inactive sea stars.     

Effects of food ration and feeding regime on growth and reproduction of the sea urchin Strongylocentrotus droebachiensis

To determine the effects food ration and feeding regime on growth and reproduction of Strongylocentrotus droebachiensis (Müller), sea urchins in laboratory aquaria were fed kelp (Laminaria longicruris) supplied at either a high (H, ad libidum daily) or a low (L, ad libidum 1 d wk⁻¹) ration in two successive 12-wk intervals during the reproductive period. After 24 wk, urchins fed the high ration continuously (HH) or for the last 12 wk only (LH) had a significantly greater mean gonad index [(gonad weight/total body weight) × 100] and body weight than urchins fed the low ration continuously (LL) or for the last 12 wk only (HL). Urchins in the HL treatment had a significantly greater gonad index than those in the LL treatment; there was no significant difference in gonad index between the LH and HH treatments. Females had a greater gonad index than males in the low ration (LL and HL) treatments at the end of the experiment; there was no significant difference between sexes in the high ration (LH, HH) treatments. Gametogenesis proceeded to maturation in all treatments and some individuals spawned at the end of the experiment. Females in the high ration (HH and LH) treatments had a greater proportion of nutritive phagocytes in their ovaries than females in the low ration treatments, but there was no effect of feeding treatment on oocyte or ovum size. Feeding treatment had no effect on the relative abundance of nutritive phagocytes in the testes, although the proportion of spermatocytes was higher (and that of spermatozoa lower) in the high ration than in the low ration treatments. Urchins in the high ration treatments had a lower mean jaw height index [(jaw height/test diameter) × 100] and greater mean test diameter than those in the low ration treatments at the end of the experiment, although these differences were not statistically significant. Feeding rate on kelp at the end of the experiment was significantly greater for urchins in the low ration than in the high ration treatments. Our experimental results show that even relatively low rations of kelp support somatic and gonadal growth in S. droebachiensis. Increasing the supply of kelp, particularly during the period of active gametogenesis, results in maximal rates of growth and reproduction. These results suggest that populations of S. droebachiensis in barrens may derive a substantial proportion of their nutrition from drift kelp, which may contribute to their persistence in these habitats. They also explain the large body size, high reproductive effort and fecundity of urchins grazing on kelp beds. These findings have important implications for understanding the dynamics of natural populations of S. droebachiensis and for development of effective aquacultural practices. Received: 17 February 1997 / Accepted: 5 March 1997