Reproduction of the commercial sea cucumber Holothuria scabra (Echinodermata: Holothuroidea) in the Solomon Islands

Over a 3-year period (1996-1998), reproduction of the commercial sea cucumber Holothuria scabra (Jaeger, 1833) was investigated in the Solomon Islands to determine the spawning pattern and whether gametogenesis is continuous or seasonal. The gonad consisted of a single cohort of tubules that developed uniformly. Macroscopic examination of the gonads revealed that mature gametes were present throughout the year. Individuals with gonads at different stages of maturity were present in most samples. Partly spawned gonads were prevalent in females, whereas mature gonads were prevalent in males. The time at which the peak gonad index was recorded differed among years. Although gametogenesis was continuous, with a potential for prolonged gamete release, a period of enhanced spawning occurred during the dry season, from September to December. Maximum gonad indices were reached prior to and during this period of enhanced spawning. Histology revealed that gametogenesis reinitiated in partly spawned gonads, resulting in the presence of gametes at different stages of development in the gonad. The uniform growth of gonad tubules indicated that H. scabra does not conform to the progressive tubule recruitment model described for holothurian oogenesis. Continuous reproduction in H. scabra and prolonged availability of mature gametes would facilitate use of this species for aquaculture.     

Reproductive cycle,development and recruitment of two geographically separated populations of the dendrochirote holothurian Aslia lefevrei

The boreo-mediterranean holothurian Aslia lefevrei (Barrois) occupies cryptic habitats from low-water mark to ca. 20 m. During the present work specimens were collected from the west coast of Ireland (February 1979 to August 1980), where A. lefevreiis a prominent element in two discrete epibenthic assemblages, and from the north-west of Spain (September 1981 to August 1982), where this holothurian is densely aggregated in association with raft cultivation of the mussel Mytilus edulis. Its reproductive cycle, spawning process, embryological development, settlement, and early growth rates have been documented by means of laboratory and field studies. Depending on geographic location, spawning in the wild occurs between January and May. Development to the gastrula takes some 3 to 4 d. Uniformly ciliated dipleurula/auricularia hatch 12 to 24 h after gastrulation. The pentactula stage is attained approximately 7 d after fertilization, following which the larva settles. Newly settled individuals utilize the five primary tentacles for both feeding and locomotion. With the advent of small numbers of podia in the ambulacral regions, two of the primary tentacles prolong their locomotory and anchorage capabilities while the remaining tentacles develop adult characteristics and function solely in feeding. Growth was followed for an estimated 30 mo period using length-frequency analyses. In the first year of life, A. lefevrei attain an average length of 3.4 cm; individuals on the sea floor can attain up to 18 cm, indicating a possible life expectancy of 10 yr or more.Contribution No. 301 from the School of Marine Sciences, University College Galway, Ireland     

The reproductive biology of a new species of sea cucumber, Holothuria (Mertensiothuria) arenacava in a Kenyan marine protected area: the possible role of light and temperature on gametogenesis and spawning

The sea cucumber Holothuria arenacava was discovered in the Mombasa marine reserve in 1997 and described by Samyn et al. (2001). The reproductive biology of this holothurian was investigated in order to (1) characterize the reproductive pattern, (2) examine the relationship among environmental parameters including temperature, light and lunar period, and (3) examine the relationship between the reproductive pattern and feeding of this new species. The gonad index method and microscopic examination of gonads was used to analyze samples collected for a period of 13 months. H. arenacava displayed an annual reproductive cycle with gametogenesis commencing in July during the south-east monsoons, when temperature and light intensity are lowest along the Kenyan coast. Gonad growth peaked in February–March at the end of the north-east monsoons when temperatures and light reach their annual maxima along the Kenyan coast. The higher correlation between light intensity and gonad growth (r=93) than temperature (r=0.71), coupled with the fact that temperatures continued to drop for a month after gametogenesis had already commenced, suggests that light intensity and not temperature is the cue for the onset of gametogenesis in this species. Spawning was synchronized between females and males and occurred during a short period between March and May (inter-monsoonal period) when both temperature and light intensity decrease along the Kenyan coast. Male and female gonad indices showed significant variation with lunar day and no lunar periodicity was observed in this sea cucumber. The sex ratio of the population of H. arenacava was skewed towards significantly more females than males, and females were significantly larger and had larger gonads and gonad indices than males. These life history strategies including spawning during a short discrete period, more and larger females that have larger gonads (i.e., typically more fecund), and spawning just prior to the peak in phytoplankton concentrations, a time that is probably more favorable for larval development, may serve to increase the reproductive success of this sea cucumber.     

Population dynamics and reproduction of Mysella bidentata (Bivalvia: Galeommatacea) in Galway Bay,Irish west coast

Mysella bidentata (Montagu) is found in high densities in an Amphiura filiformis (O. F. Müller) community in Inner Galway Bay, west coast of Ireland. As part of an ongoing investigation at one station within this community, the population dynamics and reproductive pattern of this bivalve were investigated during the period November 1978-December 1981. Monthly sampling over the 3 yr period revealed a mean population density of 745±672 individuals m^-2. Recruitment occurred during August-October and three year-classes were identified. Growth rates were assessed by analysis of length-frequency histograms and winter growth checks. Individuals from the Y1 and Y2 year-classes functioned as hermaphrodites during the 1980 and 1981 reproductive seasons. The Y0 year-class contained both males and hermaphrodites. Results are compared with available information on the same species from other locations.Contribution No. 225 from the School of Marine Sciences, University College, Galway Ireland     

Synchronous aggregated pseudo-copulation of the sea star <Emphasis Type="Italic">Archaster angulatus</Emphasis> Müller &; Troschel, 1842 (Echinodermata: Asteroidea) and its reproductive cycle in south-western Australia

Mass individual pairing or pseudo-copulation of the sea star Archaster angulatus was observed in November and December 2009, suggesting a late-spring/summer spawning period for this species on the west coast of Australia. Detailed measurements were made on the second of these occasions. Density of sea stars was 1.11 per m² and 68.5% were in mating pairs. Copulating pairs were mostly male on female, occasionally male on male. There was no difference in size between males and females in mating pairs. No evidence was found to indicate mating and spawning is coincident with lunar or tidal cycles. Females outnumbered males by more than 20%, but the difference in sex ratio was not statistically significant. Analysis of the reproductive cycle revealed that gonad indices reached their peak in October and declined from then until January. Histological sections of gonads confirmed that sea stars are in peak reproductive condition in October and November and are fully spent by January. Males have a much lower (ca. 1/3rd) gonad index than females when each are in peak reproductive condition, the second lowest recorded for any sea star. Pyloric caecae indices showed little annual variation and monthly averages of just 3–4% are among the lowest ever recorded for an asteroid. It is suggested that these characteristics are associated with the copulatory behaviour of the deposit feeding A. angulatus, enabling the species to maintain a high level of fertilisation success while also minimising the allocation of energy to gonad development in habitats with low or variable food availability. However, it is still difficult to explain why a species which ensures a high level of fertilisation by pseudo-copulation also does this en masse and synchronously. One hypothesis is that competition for males and the benefits of having eggs fertilised by multiple males favours both synchrony and aggregation.     

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

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

Effects of seasonality and population density on the reproduction of the Indo-Pacific echinoid<Emphasis Type="Italic"> Echinometra mathaei</Emphasis> in Kenyan coral reef lagoons

Reproduction in the widely distributed tropical sea urchin Echinometra mathaei (de Blainville) was examined in three Kenyan reef lagoons that differed in substrate cover and E. mathaei population density. Histological examination of the gonads and gonad index measurements for 3 years showed a seasonal reproductive cycle with gametogenesis commencing in July, when temperature and light are at their lowest, and spawning commencing in December and peaking in February to May, when temperature and light reach their annual maxima. Monthly gonad indices correlated significantly with seawater temperature and light intensity. Male urchins had mature gametes for a longer period (8 months) than females (6 months), possibly an adaptive strategy that increases the probability of fertilization. Lunar periodicity was not observed, as male and female gonads were full of gametes on all days of the lunar cycle during the period of spawning. The peak in spawning activity coincides with the peak in phytoplankton abundance, which could ensure high food availability for the planktonic larvae. Gonad weights were significantly higher relative to urchin weight at the reef having the largest mean sizes and lowest population of urchins, indicating availability of food resources for growth and reproduction. E. mathaei at the reef with the highest density had the smallest urchins and high relative gonad sizes, indicative of a tradeoff between growth and reproduction when food is limited.Communicated by O. Kinne, Oldendorf/Luhe     

Reproductive cycle of the brooding echinoid Abatus cordatus (Echinodermata) in Kerguelen (Antarctic Ocean): changes in the organ indices,biochemical composition and caloric content of the gonads

Variations in organ indices, organic levels, organic and caloric contents of the gonads of the brooding echinoid Abatus cordatus (Verrill), collected in the Morbihan Gulf (49°30′S; 70°E) were studied over a 1 yr period (March 1978 to January 1979). In both sexes, a clear annual cycle was discernable for organ indices, and for organic and caloric contents. In contrast, the protein levels in the gonads varied moderately, while the levels of lipid and carbohydrate remained almost constant. This peculiarity sets A. cordatus apart from nearly all other echinoids characterized by an annual reproductive cycle. The male and female gonad indices change synchronously. The gonad indices double during maturation, reflecting variations in the germinal tissue. In both sexes, the maximal gonad index (at the end of March) coincides with the onset of the spawning season. The average male gonad index is 50% higher than that of the female. This difference is related to the restriction of coelomic space in the female due to development of the brood pouches. At maturity, the lipid and carbohydrate levels in the ovary are 2.8 and 2.1 times greater, respectively, than the levels in the testis, the latter having a 25% higher protein level. This disparity in organic levels reflects mainly the differences in germinal tissue composition. The female reproductive effort is higher than that of the male. The spawn energy output of a standard individual is 200 cal for a male and 228 cal for a female. The unusually lower gonad index of the female is compensated for by higher lipid and carbohydrate levels, giving the ovary a 40% higher calorific value.     

Analysis of the relationship between gonads and hepatopancreas in males and females of the crab Sesarma intermedia,with reference to resource use and reproduction

At the beginning of the reproductive period in May, there was an increment in both the gonad and heaptopancreas. During the peak phase in June, with high ovary production, there was a decrease in the hepatosomatic index (HSI), particularly for the Ariake females. The minimum gonadosomatic index (GSI) of 2% in August and September for the Ariake and in September and October for the Hakata populations was inversely related to the increase of HSI. A second rise in GSI was observed in November at the 1% level as against the June peak of 5% for the Ariake and 3.5% for the Hakata females, and it remained at this level until December, while the HSI decreased to the minimum. The December minima for both GSI and HSI were about the same as the initial February values. The spermathesomatic index (SSI) had a slight increase to 0.8% in August, but remained constant at 0.5% throughout the year. Likewise, GSI for males was constant at the 0.5% level, with minor fluctuations, and did not show any clear relationship with the HSI as for female GSI. Females had higher hepatosomatic indices but the soma weighed less than males throughout the year. Again in May, medium-sized females had the highest GSI followed by large and then small-sized individuals. As the HSI steadily decreased, GSI increased with advancing egg development stages for ovigerous females. The quantitative stomach analyses showed that females had higher stomach quantity indices (SQI) in May than in September, when the breeding period had ended. Contrary results were observed for males. Also, female SQI in May was higher than that for males.     

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     

Reproductive cycle of two commercial species of sea cucumber (Echinodermata: Holothuroidea) from Caribbean Panama

The reproductive status of the holothuroid species Isostichopus badionotus (Selenka, 1867) and Holothuria mexicana (Ludwig, 1875) was studied over 16 months in Bocas del Toro (Panama), from November 1999 to February 2001. Sexual reproduction was evaluated by the gonad index method, and by histology of gonad development. In addition, population structure was assessed based on sex ratio, minimum reproductive size, and length and weight distributions of males and females. The sex ratio in both species was 1:1, with a unimodal population distribution composed mainly of mature individuals. The minimum reproductive length and weight were 13-20 cm and 150 g, respectively, for both species, although reproductive individuals 10 cm in length were also found. A consistently higher gonad index was observed in H. mexicana, due to a high proportion of mature females and males and high gonad indices in most monthly samples. Gametogenesis and spawning patterns seemed to occur throughout the year, with periods of enhanced activity. Two periods of maximum reproductive activity were tentatively identified: July-November for I. badionotus and February-July for H. mexicana, but neither species had a single, sharply defined annual spawning event. Further work on these exploited holothuroids should examine the relationships between reproduction and environmental factors and between reproductive status and recruitment.     

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.     

Reproductive periodicity in the euryalinid snake star Astrobrachion constrictum in a New Zealand fiord

The euryalinid snake star Astrobrachion constrictum (Farquhar), a normally deep-water species, exists within SCUBA diving range in New Zealand flords, and thus presents a unique opportunity for study. A population of A. constrictum in Doubtful Sound was investigated from February 1990 to July 1994 to determine the reproductive cycle. Unlike most ophiuroids, the gonads of A. constrictum are positioned along the aboral coelom in the proximal portion of the arms. The proximal 2 to 3 cm of the arms of individuals were thus removed on an approximately monthly basis for histological examination of the gonads. Image analysis was used to determine oocyte size-frequency distributions. A gonad index was calculated for each individual based on the ratio of cross-sectional area of the gonads to cross-sectional area of the arm. Maturity indices were calculated based on stage of development of the gonads of each individual. A. constrictum has a period of enhanced breeding activity in April–June, after which both the gonad and maturity indices decline. The increase in gametogenic activity during these months was correlated with rising sea temperature within the fiord. Although the females showed an annual pattern of gonad development, oogenesis was continuous throughout the year, with oocytes at different stages of development present in the gonads. Males also showed continuous spermatogenesis and, although the same annual pattern of gonad development was evident as seen in the females, it was less marked. The presence of females with large oocytes and ripe males throughout the study indicates that breeding in the Doubtful Sound population is prolonged, and possibly continuous, as found in many deep-sea ophiuroids.     

Tidal influences on the photoperiodic induction of tetrasporogenesis in Bonnemaisonia hamifera (Rhodophyta)

Photoperiodic control of tetrasporangium formation was studied in two low intertidal populations of Bonnemaisonia hamifera (Trailliella-phase) in Galway Bay, Ireland between September 1985 and February 1986. Photoperiodic induction was affected by tides, principally by the time of day at which high and low water occurred through the spring/neap cycle. High water of spring tides falling at the beginning and end of the day reduced the effective daylength for plants, and caused an early onset of reproduction. The threshold irradiance signalling light-dark transition was estimated to lie between (1-) 5 and 10 mol photons m^-2 s^-1 (400 to 700 nm). Low water of spring tides falling in the middle of the day exposed plants to high air temperatures during periods when seawater temperatures were below the lower limit for sporangium induction. This caused reproduction to be resumed. Quantitative differences between the two populations were caused by microclimatic effects (temperature, light reduction during tidal flooding) resulting from their different vertical heights on the shore.     

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     

Seasonal moulting patterns and the generation cycle of<Emphasis Type="Italic"> Calanus finmarchicus</Emphasis> in the NE Norwegian Sea,as inferred from gnathobase structures,and the size of gonads and oil sacs

The seasonal moulting pattern of Calanus finmarchicus, related to body size, oil content and depth distribution, was investigated on the Norwegian midshelf from February to October 1997. Both gonad and gnathobase development were well correlated with time, and proved to be good indices for tracing the moulting cycle. The growth and development of gonads preceded the formation of new teeth. Both gonad development and tooth formation patterns in overwintering stage V copepodites (CV) indicated that the most intensive moulting occurred in spring. In the upper 200 m layer, the proportion of copepods in premoult phases ranged from 10% at the beginning of February, 60–95% from the end of February through April, to 4–7% in mid-May. No significant latitudinally determined variations in the moulting pattern were observed. The upward migration of deep-dwelling overwintering CVs was not synchronous and was determined by the readiness to moult. In April, no CVs were found at depths >300 m, that may indicate the termination of the overwintering moulting from G_o. By the end of May, the large-sized, lipid-rich CVs of G₁ started descending to depth. The second period of moulting (i.e. most likely the formation of G₂) was only recorded to have taken place in the surface (0–200 m) component of the CV stock from July onwards. This group was estimated to make up 10–20% of CVs inhabiting the upper 200 m layer and to have originated from the smallest sized fraction of CVs. There was a consistent trend towards size-differential moulting from CVs, in both spring and summer. The large-sized CVs moulted into adults earlier in spring compared with the smaller ones. By mid-June, the large and lipid-rich CVs of G₁ disappeared from the uppermost layers, sinking to depths. In summer (July onwards), the moulting of small CVs is probably the main contributor to G₂ copepodites that completed the cycle through to CIV/CV by the end of October.Communicated by O. Kinne, Oldendorf/Luhe     

Seasonal variation in the effects of food availability on gametogenesis in the purple urchin (<Emphasis Type="Italic">Strongylocentrotus purpuratus</Emphasis>)

The amount of food and when it is available affect both the timing of reproduction and the number of gametes produced by purple sea urchins, Strongylocentrotus purpuratus. To investigate this further, the effects of food availability on feeding rates, gonad growth, and gamete development were examined in S. purpuratus collected from the Point Loma kelp forest near San Diego, California, USA (32.69° N, 117.26° W) in September (Fall) 2007, and February (Spring) and July (Summer) 2008, using laboratory mesocosms. Each seasonal laboratory feeding experiment lasted 3 months, and different levels of food availability were established with different feeding frequencies (from 1 to 7 days week⁻¹). Gonad tissues of male and female urchins were staged at the end of each experiment using histological analyses. Reduced food availability resulted in increased daily consumption rates, especially in the Fall when gamete development began. Food limitation at this time resulted in failure to produce viable gametes, suggesting there is a critical period early in gonad development when food limitation affects reproductive competency. Food limitation later in gonad development did not stop viable gamete production, although it did reduce gamete output.     

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.     

Reproduction of the commercial sea cucumber Holothuria whitmaei [Holothuroidea: Aspidochirotida] in the Indian and Pacific Ocean regions of Australia

Seasonal trends in the gonad index (GI) of two widely separated populations of black teatfish, Holothuria whitmaei (formerly included in Holothuria nobilis), were investigated between Pacific (Great Barrier Reef) and Indian Ocean (Ningaloo Reef) coral reefs of Australia. Reproductive activity followed a similar annual trend, with the GI of both populations peaking typically between April and June. Macroscopic and histological analysis of Ningaloo Reef specimens revealed that large germinal tubules, positioned centrally on the gonad basis, progressed through four maturity stages: growing (II); mature (III); partly spawned (IV); and spent (V). Growing tubules dominated the central region of the gonad basis between January and March, followed by an increase in the number of mature tubules throughout the GI peak (April–June). The progressive appearance of partly spawned and spent tubules between June and October suggests that spawning in H. whitmaei continues intermittently over an extended period throughout the austral winter. The examination of the gonad structure of sexually mature male and female specimens identified five tubule size classes in total (C₁ to C₅), each of differing physical and gametogenic status. In females, smaller C₁ tubules located at the anterior edge of the gonad basis contained pre- to early vitellogenic oocytes. Larger C₂ and C₃ tubule cohorts, positioned centrally on the gonad basis, contained mid- to late-stage vitellogenic oocytes. Smaller C₄ and C₅ tubules, located at the posterior edge, contained only relict oocytes. Similar physical and gametogenic differences were apparent between tubule cohorts in male specimens. We propose that these results, together with evidence of incomplete gonad resorption over the austral summer, indicate that gonad development in H. whitmaei conforms to the predictions of the Tubule Recruitment Model (TRM). The TRM is reported rarely among tropical aspidochirotes, and results presented here (1) provide the first direct evidence of this model in H. whitmaei, and (2) confirm that this species is one of the few winter-spawning tropical invertebrates.     

Seasonal variation in uptake and depuration of anthracene by the brackish water clam Rangia cuneata

Rangia cuneata were collected every six weeks for one year from February 1984 to January 1985 at the mouth of the Dog River, Alabama, USA and dosed with 200 ppb [9–¹⁴C] anthracene at 10, 20, and 30°C. Uptake rates of [9–¹⁴C] anthracene measured over a 15-h period were not significantly different (P>0.05), but depuration rates measured over a two-week period were significantly higher with increasing temperature. The seasonal changes in rates were related to the annual changes in biochemical composition of the clams associated with the reproductive cycle. Lipid levels were nearly constant over the year, averaging 88.0±2.0 mg/g dry wt. The level of carbohydrates peaked in July, a month before the maximal gonad index, and decreased steadily through September during spawning. The level of proteins increased from 76.6 mg/g dry wt prior to spawning to 138.3 mg/g dry wt after spawning. Uptake rates were highest in late summer during the peak of gametogenesis and decreased during spawning in the fall. Depuration rates remained low from March through August and rapidly increased to the highest levels during the fall spawning period. The results suggest that the stage of the reproductive cycle, with its associated biochemical changes, and temperature play an important role in the pattern of accumulation and release of anthracene in R. cuneata.