A comparative study of the inhibitory effect of diatoms on the reproductive biology of the copepod Temora stylifera

Egg production and viability in the copepod Temora stylifera (collected in the Bay of Naples, Italy in 1992) were strongly dependent on food type. A flagellate (Isochrysis galbana) diet induced the production of good quality eggs that developed to hatching. By contrast, two diatoms (Chaetoceros curvisetum, Phaeodactylum tricornutum) resulted in poor egg quality, with hatching success as low as 20% of total egg production. With the third diatom tested, Skeletonema costatum, females produced eggs for only 3 to 4 d, after which time they either became sterile or died. These results are discussed in relation to previous findings regarding the impact of the dinoflagellate Prorocentrum minimum and the diatom Thalassiosira rotula on the hatching success of T. stylifera eggs. Low egg viability was possibly not due to an absence of remating or a deficiency of some specific essential nutrient required for egg development but to the presence of inhibitory compounds blocking cell division during early copepod embryogenesis. This questions the traditional view that diatoms are an important food item regulating copepod secondary production.     

Transfer of radioactive carbon within the copepod Temora longicornis

Standard autoradiographic techniques have been used to describe the temporal pattern in the transfer of radioactive carbon from the chlorophyte Tetraselmis suesica (Kylin) to females of the neritic copepod Temora longicornis (Müller, 1792). After 4 and 6 h exposure to labelled phytoplankton, silver grains were deposited only in the cells of the gut-wall. After 24 h exposure, grains were deposited in most tissues, with highest concentrations in cells of the gut-wall and in oocytes within the ovary. Experiments with Centropages typicus (Krøyer), Centropages hamatus (Lilljeborg), and Labidocera aestiva Wheeler demonstrated that much of the assimilated label was not turning over rapidly and that the amount of label assimilated was correlated with known food preferences of these species.     

Diet and respiration of the small planktonic marine copepod Oithona nana

The functional responses of Oithona nana (Giesbr.) to various phytoplankton and zooplankton food species are described. The food species were divided into three size categories, the seasonal abundances of which were measured in Loch Turnaig, a Scottish sea loch in 1977. The seasonal variations in feeding rates in the sea for each size class were derived. The seasonal variation in respiration rate of O. nana was measured, and metabolic requirements were claculated as between 6 and 40% of the food material estimated as being eaten. O. nana differs from other common copepods in having a wide food-particle size spectrum and a low metabolic rate. It is suggested that these adaptations constitute the strategy whereby O. nana maintains its population levels throughout the year.     

Switching between herbivory and carnivory by the planktonic marine copepod Calanus pacificus

Adult females of the omnivorous copepod Calanus pacificus, collected from the plankton off La Jolla, California, USA (June, 1978), fed disproportionately on the prey in greatest relative abundance when given mixtures of diatoms (Thalassiosira fluviatilis) and copepod (C. pacificus) nauplii as food. This switch from herbivorous to carnivorous behavior may be significant in nature during the decline of phytoplankton blooms. More generally, the widespread omnivorous habit among pelagic animals suggests a responsive and flexible trophic organization which contributes to the resiliency of planktonic communities in a dynamic physical environment.Contribution No. 1223 from the Department of Oceanography, University of Washington, Seattle, Washington 98195, USA     

Regulation of body dimethylsulfoniopropionate (DMSP) content by the copepod Temora longicornis: a test of four mechanisms

Copepods contain dimethylsulfoniopropionate (DMSP) in their tissues in addition to the DMSP in their gut contents and therefore constitute an additional pool of DMSP in the ocean. In the estuarine copepod Temora longicornis Müller, this dynamic pool of DMSP is reduced when external salinity decreases. In the present study the mechanism(s) used by T. longicornis to adjust its DMSP content were examined. Four possible mechanisms were tested in experiments conducted between July 1997 and May 1999: (1) DMSP cleavage, (2) demethylation, (3) conversion to methionine, and (4) release from the body. Tissue extracts of T. longicornis did not exhibit the ability to cleave or demethylate DMSP. In incubation experiments, when external salinity decreased, T. longicornis individuals reduced their DMSP content without increasing their methionine content. The total amount of DMSP in the incubation vials was conserved regardless of salinity. The copepods retained most of the DMSP in their tissues in 30‰ water, but when salinity was reduced to 20‰, the copepods released 41 to 55% of their body DMSP to the surrounding medium; 89 to 91% of the total DMSP was recovered. This suggests that estuarine copepods represent a reservoir of DMSP, which is released as dissolved DMSP upon salinity decline. Therefore, while osmoregulation by these copepods may have little impact on the chemical properties of DMSP, it will affect the partitioning of DMSP between particulate and dissolved phases in the water column. Received: 20 August 1999 / Accepted: 28 March 2000     

Population structure of the planktonic copepod Calanus pacificus in the North Pacific Ocean

The pelagic copepod Calanus pacificus ranges nearly continuously across temperate-boreal regions of the North Pacific Ocean and is currently divided into three subspecies—C. pacificus oceanicus, C. pacificus californicus, C. pacificus pacificus—based on subtle morphological differences and geographic location. The relation between geography and genetic differentiation was examined for 398 C. pacificus individuals sampled from six widely distributed locations across the North Pacific, including an open ocean site and coastal sites on both sides of the North Pacific basin. For each individual copepod, the DNA sequence was determined for a 421-bp region of the mitochondrial coxI gene (mtCOI). A total of sixty-three different mtCOI sequences, or haplotypes, were detected, with a sequence divergence between haplotypes of 0.2–3.1%. The number and distribution of haplotypes varied with sampling location; 12 haplotypes were distributed across multiple sampling locations, and 51 occurred at only one location. Five genetically distinct populations were detected based on F _ST values. Haplotype minimum spanning networks, nucleotide divergence and F _ST values indicated that individuals from coastal sites in the North Pacific Ocean were more closely related to each other than to individuals from the open ocean site at Station P. These results provide genetic support for the designation of two subspecies—a coastal subspecies that consists of what is currently referred to as C. p. pacificus and C. p. californicus and an open ocean subspecies C. p. oceanicus. This work also indicates that planktonic copepods with potentially high dispersal capacity can develop genetically structured populations in the absence of obvious geographic barriers between proximate locales within an ocean basin.     

Ontogenetic diel vertical migration of the planktonic copepod Calanus sinicus in the Inland Sea of Japan

The ontogenetic diel vertical migration of the planktonic copepod Calanus sinicus was investigated in the Inland Sea of Japan in June 1989, when the water column was thermally weakly stratified. Because of fewer eggs and less variation in their abundance, nocturnal spawning was not apparent. A pronounced upward migration occurred in NIII. NIII to CIII resided in the upper 20 m layer throughout the day, and from CIV on their median depths descended. CV and adult females underwent significant diel vertical migration, whereas adult males did not migrate. By integrating the results from the present study and those from our previous investigations (in August–September 1988, November 1988 and March 1989), we review seasonal variation in the ontogenetic diel vertical migration of C. sinicus. Spawning was largely nocturnal, reaching its maximum level around dawn, but spawning depth and fecundity changed seasonally. The distribution of pre-feeding stages, NI and NII, was similar to that of eggs. A pronounced upward migration always occurred in the first feeding stage, NIII, and late nauplii and early copepodites always resided in the food-rich upper layer, indicating that upward migration by NIII is feeding migration. As the stages progressed, they extended their vertical distribution range, and CV and adult females usually underwent diel vertical migration. However, the pattern and strength of this migration differed seasonally. Their day depths increased with the increase of relative biomass of planktivorous fish, indicating that predator avoidance induces their diurnal downward migration. High chlorophyll a concentrations in the upper layer (<15 m deep) relative to the lower layer (>20 m deep) amplified their diel vertical migrations. Diel vertical migration of C. sinicus is a phenotypic behavior.     

Ontogenetic diel vertical migration of the planktonic copepod Calanus sinicus in the Inland Sea of Japan

The ontogenetic diel vertical migration of the planktonic copepod Calanus sinicus was investigated in the Inland Sea of Japan in November 1988 and March 1989, when the water temperature was weakly stratified in a reversed manner. In both investigations a pronounced ontogenetic difference in vertical distribution was found. Spawning always occurred during nighttime, being confined to the upper 40 m water column in November but to the layer below 35 m in March. The distribution of pre-feeding nauplius stages, NI and NII, was more or less similar to that of the eggs. The first-feeding NIII performed a marked upward migration, and late nauplius stages (NIV to NVI) and early copepodite stages (CI and CII) continuously aggregated in the upper water column where phytoplankton was abundant. CIII to CVI (adult female and male) tended to disperse in the whole water column. In November, however, they avoided the upper 10 m strate during daytime and some individuals migrated upward to the surface during nighttime. In March, CV and CVI aggregated in the layer between 5 and 15 m deep in the daytime and migrated both upward and downward at dusk, resulting in homogeneous distributions during the nighttime.     

Toxin accumulation and feeding behaviour of the planktonic copepod Calanus finmarchicus exposed to the red-tide dinoflagellate Alexandrium excavatum

The planktonic copepod Calanus finmarchicus is a dominant member of the zooplankton community in the lower St. Lawrence Estuary in eastern Canada. Blooms of the toxic marine dinoflagellate Alexandrium excavatum which produces high cellular levels of paralytic shellfish poisoning (PSP) toxins, occur during the period of high C. finmarchicus production in summer in this region. To study the feeding behaviour of C. finmarchicus in the presence of Alexandrium spp., experiments were conducted in which female adult copepods collected from the St. Lawrence Estuary between May and September 1991 were exposed under controlled conditions to two toxic isolates of A. excavatum (Pr18b and Pr11f) from the estuary and to a non-toxic control (PLY 173) of a closely related species, A. tamarense isolated from the Tamar Estuary, Plymouth, U.K. Clearance rates on non-toxic A. tamarense cells averaged 5.5 ml ind^-1 h^-1 but were nearzero with either toxic isolate. When presented with a mixture of A. excavatum and the non-toxic diatom Thalassiosira weissflogii in varying proportions, C. finmarchicus fed upon the diatom but avoided the toxic dinoflagellate. Although feeding rates on A. excavatum were very low, toxin analysis by high-performance liquid chromatography with fluorescence detection (HPLC-FD) revealed that the PSP toxins were accumulated in copepods exposed to toxigenic dinoflagellates.The toxin composition in copepods was similar to that of the toxic dinoflagellate, but not necessarily identical, particularly after short-term (2-h) exposure, when relatively elevated levels of N-sulfocarbamoyl toxins were detected. The evidence suggests that C. finmarchicus ingests toxic dinoflagellate cells, either mistakenly or during exploratory bouts of feeding, and accumulates PSP toxins in its gut system and perhaps in other tissues.     

Food ingestion by the marine planktonic copepod Paracalanus in relation to abundance and size distribution of food

Juveniles and adult females were presented a food spectrum of three algae of different sizes (4.5, 12 and 20 m cell width). The increase in rate of ingestion of the medium-sized alga with an increase in copepod size was significantly greater than the increase in rate of ingestion of the small alga. It is hypothesized that the perception of chemical signals from the small alga by a copepod decreases as the copepod moults from stage to stage. The rate of ingestion of the large alga by copepod stage V (CV) and adult females was lower than the rate of ingestion of the medium-sized alga at mid- and high phytoplankton concentrations. The amount of nitrogen ingested when the medium-sized alga alone was offered was either higher than (stage C II) or not significantly different from that when the three algae were offered together (stage C IV). Ingestion rates are reduced when there is a multialgal food source. This implies that there is increased stability in the ocean because multiparticle food sources are more slowly depleted than unialgal foods. Weight-specific ingestion rates of copepods fed the three algae simultaneously increased from nauplius to stage C III and then decreased as adulthood approached. The contribution of the small alga to the total amount of nitrogen ingesied was greatest for naupliar stages while the contribution of the medium-sized cells was greater for later stages. The largest alga was readily ingested by stage C V and adult females but never contributed more than 25% of the nitrogen ingested. Eight to 12% of the nitrogen ingested by adult females was from the small alga. It is hypothesized that the algal cell size for maximum nitrogen ingestion in upwelled waters is relatively small, round or square and close to the size threshold below which adult females do not sense individual cells.     

Reproductive biology of deep-water calanoid copepods from the Arctic Ocean

Reproductive modes and egg production were studied in 15 species of meso- and bathypelagic copepods from nine Calanoida families in the Arctic Ocean. During shipboard incubation, females of seven species released eggs freely into the water and females of three species produced membrane-bound egg sacs. One species, Aetideopsis rostrata, produced a mass of eggs looking like an egg sac, but the “sac” lacked a membrane and disintegrated within 2 h. Females of four additional species were encountered with membrane-bound egg sacs in the preserved samples. In most families, only one reproductive mode, either egg-carrying (the Euchaetidae, Augaptilidae), or broadcast spawning (the Heterorhabdidae, Spinocalanidae, Scolecitrichidae, Tharybidae, Bathypontiidae) was observed. In contrast, different genera of the Aetideidae family demonstrated different reproductive modes, with broadcast spawning predominant in the benthopelagic species, and both broadcast spawning and egg-brooding in the planktonic species. Clutch size and egg diameter varied widely between species in both broadcast spawners and egg-brooders. In broadcast spawners, the clutch size varied from 1 to 95 eggs female⁻¹, while the average egg diameter ranged from 152 to 440 μm. The clutch size for egg brooders varied between 3 and 82, while average egg diameter varied from 258 to 732 μm. Deep-water broadcast spawners produced much larger eggs compared to surface-dwelling broadcast spawning species. This larger egg size may result in a reduction, or elimination, of feeding during naupliar stages, thereby improving the survival potential of deep-water species.     

Reproductive biology of the lanternfish Benthosema pterotum from the Indian Ocean

Samples of Benthosema pterotum (Alcock) were obtained from the Arabian Sea (1976, 1979, 1981, 1983, 1984), off Mozambique (1978) and from the Bay of Bengal (1979). The sexual maturity stages are described. For females, the size of the largest oocytes was found to be most useful for size of the largest oocytes was found to be most useful for assessing maturity. Mature and spawning fish were found in all seasons. Samples from November 1983 differed from all others in having very few mature females. A few apparently spent fish were observed in July to August 1979 and November 1983. Some females mature at 25 mm and males at 20 mm, whereas others can still be immature at 45 and 40 mm, respectively. Of the total number of stations, four had significantly more males than females, twelve significantly more females, and forty-seven displayed no difference in the sex ratios. The vertical migration of the mature and spawning fish did not differ significantly from that of other individuals. Batch fecundity ranged from ca. 200 to 3 000 eggs fish ranging from 27 to 52 mm, relative fecundity from ca. 2 000 to 7 000 eggs g^-1 maternal dry weight. There are indications that B. pterotum spawns only once, but no firm conclusions could be drawn.     

Reproductive biology in two species of deep-sea squids

Deep-sea squids, Moroteuthis ingens and Gonatus antarcticus, were collected in the slope waters off the Falkland Islands and their reproductive systems preserved and investigated onshore. Changes in oocyte length-frequencies at maturation and spawning, and their fecundity were studied. These squids, as well as many other species, are characterised by a synchronous oocyte growth and ovulation. Oviducts are not used for ripe egg accumulation and consequently the universal scale of Lipinski (1979) cannot be applied to assign female maturity. M. ingens spawns near the bottom; its fecundity is 168–297 thousand eggs. Maximum egg size is 1.8–2.7 mm. G. antarcticus spawns midwater; its fecundity is 10–25 thousand eggs. Egg size is 3.2–3.3 mm. In M. ingens spawning takes place in the austral autumn and winter, in G. antarcticus—in austral winter. Our data and the literature data show that the so-called “synchronous ovulation” probably occurs in all deepwater squids. This pattern is very rare among fish, but is quite common among benthic octopods that brood their egg masses.     

Reproductive biology of the edible jellyfish Catostylus mosaicus (Rhizostomeae)

 The reproductive biology of the jellyfish Catostylus mosaicus (Quoy and Gaimard 1824) (Scyphozoa: Rhizostomeae) was investigated in New South Wales, Australia. Medusae were gonochoristic. There was a 1:1 ratio of male and female medusae and there was no evidence of sexual dimorphism. Oocytes arose from the gastrodermis and maintained contact with the gastrodermis, via trophocytes, throughout gametogenesis. Spermatogenesis occurred within follicles that arose from invagination of the gastrodermis. Detailed sampling of gonads over a period of 3.25 yr in Botany Bay, and over 2.5 yr in Lake Illawarra, indicated that gametogenesis occurred almost continuously during the year. Oocytes were smaller, or were absent from the ovaries during 3 of the 4 winters sampled at Botany Bay and during all 3 winter periods sampled at Lake Illawarra. Comparisons were made with other locations, although these were sampled less frequently. When medusae were present at a location, similar trends were observed. The size at which medusae matured varied, but during non-winter periods and at two locations, all medusae exceeding 130 mm diam were considered mature. Received: 6 January 2000 / Accepted: 3 July 2000     

Reproductive biology of the deep-sea octocoral Drifa glomerata in the Northwest Atlantic

The present study examined the mode and timing of reproduction of poorly understood deep-water octocorals and the environmental factors that may influence their reproductive patterns. Data on reproductive characteristics of the octocoral Drifa glomerata (Alcyonacea: Nephtheidae) collected between 2004 and 2007 at ca. 100–330 m depth off Newfoundland and Labrador (eastern Canada) were compared among years, months and depth ranges. No male gonad was ever observed during the study. The ratio of fertile colonies possessing large pinkish polyps with oocytes/planulae was >50% throughout the year. The number of brooded planula larvae within a single fertile polyp varied between 1 and 10 for a total of approximately 40–3,000 in a whole colony. The size of oocytes and/or planulae was consistently greater in the polyps than in the branchlets, indicating that the development pathway of oocytes to planulae is from the branchlets to the polyps. Although larval production seemed to persist year round, the onset of major planulation events occurred in December–January of two consecutive years, when large mature planulae were released in correlation with the first increase of photoperiod and maximum temperature at 150 m. A second peak in planulation between April and early June followed the phytoplankton bloom. Seasonal trends were more apparent in colonies from <200 m, and the planula index varied among sampling depths and years. Larval release in a live colony under laboratory conditions occurred between January and June 2008, closely following predictions based on field samples.     

Etude expérimentale de la ponte chez trois espèces de copépodes pélagiques (Centropages typicus,Acartia clausi et Temora stylifera)

Egg-laying of 3 common copepod species from the Gulf of Marseilles (Centropages typicus Kröyer, Acatia clausi Giesbrecht, Temora stylifera Dana) has been studied under various trophic conditions, at different periods of the year. The role of phytoplankton abundance in the induction and importance of egg-laying is indicated. The specific quality of the algal suspension used for feeding affected also fertility. A seasonal variation in the importance of egg-laying is established. Some observations are made on egg deposition and development.     

Reproductive biology of the tiger shark (Galeocerdo cuvier) in Hawaii

The tiger shark (Galeocerdo cuvier) is the largest shark in the family Carcharhinidae and the only carcharhinid with aplacental viviparous (ovoviviparous) reproduction. Despite its size and prevalence, many details of tiger shark reproductive biology are unknown. Size at maturity and litter size have been reported by several authors, but a lack of large numbers of pregnant females has made it difficult to determine gestation period, seasonality, and timing of the female reproductive cycle. Here we analyze data from shark control program fishing and incidental catches in Hawaii (n = 318) to construct the most complete picture of tiger shark reproduction to date. Males reached maturity at approximately 292 cm total length (TL) based on clasper calcification, whereas females matured between 330 and 345 cm TL based on oviducal gland and uterus widths. Litter sizes ranged from 3 to 57 with a mean of 32.6 embryos per litter. Data from 23 litters from various months of the year indicate that tiger sharks are usually 80–90 cm TL at birth, and that the gestation period is 15–16 months. Mating scars were observed in January–February and sperm is presumably stored for 4–5 months until ovulation takes place in May–July. Gestation begins in June–July and pups are born in September–October of the following year. Our data suggest that female tiger sharks in Hawaii give birth only once every three years. This could have major implications for conservation and management of this species, as it suggests that tiger shark fecundity is 33% lower than previously thought. This could greatly reduce the ability of this species to rebound from fishing pressure.

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Reproductive biology of the commercial sea cucumber Holothuria fuscogilva in the Solomon Islands

 Reproduction of Holothuria fuscogilva (Selenka, 1867) in the Solomon Islands was investigated over a 4 yr period (1994 to 1998) by macroscopic and microscopic examination of the gonad tubules, the gonad index (GI) method, histological examination of gametogenesis, and spawning-induction trials. The gonad consisted of numerous tubules that dominated the coelom of gravid specimens. New tubules appeared in March, and grew in size and extent of branching until they reached their maximum size and maturity in August. Spawning occurred from August to October, with the majority of gametes released during October, although it was only partial in many individuals. After spawning, the tubules appeared wrinkled and resorbed into the gonad basis. A five-stage gonad maturity scale based on the macroscopic appearance of the gonad tubules corresponded with discrete stages of gametogenesis identified by histology. Gametogenesis was initiated in mid-March, with oogenesis and spermatogenesis occurring in parallel, followed by the growing stage (May to July) which was marked by active gamete development. Successful induction of spawning during the breeding period corroborated the GI and histological data. The uniform growth of gonad tubules indicated that H. fuscogilva in the Solomon Islands does not conform to the progressive tubule recruitment model described for other holothurians. An important application of this study is that the appearance of gonad tubules, removed by biopsy, can be used to determine the gonad condition of wild adults or captive broodstock. Received: 28 June 1999 / Accepted: 8 March 2000