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     

Distribution and relative abundance of Pseudocalanus moultoni and P. newmani (Copepoda: Calanoida) on Georges Bank using molecular identification of sibling species

The sibling species, Pseudocalanus moultoni (Frost, 1989) and P. newmani (Frost, 1989), occur sympatrically on Georges Bank. Taxonomic discrimination of the species relies on subtle morphological characteristics, making routine identification of the species very difficult. DNA sequence variation of two mitochondrial genes, 16S rRNA and cytochrome oxidase I (COI), reliably discriminated P. moultoni and P.␣newmani. Levels of DNA sequence variation for both genes were consistent with those between species of calanoid copepods. A molecular systematic protocol (based on allele-specific PCR amplification) was designed from the COI sequences and used to discriminate females of the two species. The distributions and relative abundances of the two species were mapped for April 1996 based on samples of 15 to 30 females from 12 collections across Georges Bank. The results of this study indicated that P. moultoni females predominated along the northern flank of Georges Bank, while P. newmani females were common on the southern flank, deeper than the 60-m isobath. Received: 16 May 1997 / Accepted: 26 April 1998     

Effects of Trichodesmium spp. blooms on penaeid prawn larvae

The effects of blooms of the cyanobacterium Trichodesmium spp. on penaeid prawn larvae were examined using in situ and laboratory rearing experiments and plankton surveys in Albatross Bay, Gulf of Carpentaria, Australia. The in situ experiments demonstrated that, during a bloom of Trichodesmium spp., larvae of the prawn Penaeus merguiensis did not develop beyond the first protozoea stage, and survival was low compared with times when diatoms were dominant in the same study area. Laboratory experiments confirmed the in situ results. None of the prawn larvae fed Trichodesmium sp. in laboratory experiments developed beyond the first protozoeal stage. In contrast, 94% of prawn larvae fed the green flagellate Tetraselmis suecica successfully developed to the second protozoea stage. Electron microscopy of larvae gut-contents revealed that Trichodesmium spp. were ingested by larvae but were of no nutritional value, resulting in starvation. A 7 yr plankton survey, from 1985 to 1992, showed that minimum abundance of prawn larvae occurs during the annual summer blooms of Trichodesmium spp. and that maximum abundance of prawn larvae generally occurs just after the bloom. There was a negative correlation between the abundance of larvae and the abundance of Trichodesmium at individual sites, one offshore and one inshore, indicating that the blooms affect the survival of larvae. We conclude that variations in both timing and magnitude of Trichodesmium blooms are important determinants of prawn larvae abundance in Albatross Bay. Received: 28 April 1997 / Accepted: 2 April 1998     

Population biology of Dyopedos monacanthus (Crustacea: Amphipoda) on estuarine soft-bottoms: importance of extended parental care and pelagic movements

The suspension-feeding amphipod Dyopedos monacanthus (Metzger, 1875) is a common epibenthic amphipod that lives on self-constructed “mud whips” (built from filamentous algae, detritus and sediment particles) in estuaries of the northern North Atlantic Ocean. The population biology of D. monacanthus at a shallow subtidal site in the Damariscotta River Estuary (Maine, USA) was examined between July 1995 and July 1997. The resident population at the study site was dominated by adult females during most months of the year. High percentages of subadults were found in late summer/early fall. Often, between 10 and 20% of the adult females were paired with males, and the percentage of ovigerous females varied between 40 and 100%, indicating continuous reproduction. The percentage of parental females varied between 40 and 80% during most months, but dropped to levels below 20% during summer/early fall. The average size of amphipods on their own mud whips was ∼4 mm during the summer/early fall, after which it increased continuously to >7.0 mm in March or April, and then dropped again. In March and April, the average number of eggs and juveniles female⁻¹ was ∼100 eggs and 55 juveniles, while during the summer/early fall the average number of eggs female⁻¹ was <20 and that of juveniles female⁻¹ was <10. Many juveniles grew to large sizes (>1.4 mm) on their mothers' whips in winter/early spring but not in the summer/fall. The average number of amphipods at the study site was low in late summer/early fall (<50 individuals m⁻²), increased steadily during the winter, and reached peak densities of >3000 individuals m⁻² in April 1996 (>1600 individuals m⁻² in May 1997), after which densities decreased again. The decrease of the D.␣monacanthus population at the study site coincided with a strong increase of amphipods found pelagic in the water column. This behavioural shift occurred when temperatures increased and benthic predators became more abundant and active on shallow soft-bottoms, suggesting that D. monacanthus at the study site is strongly affected by predation. The effects are direct (by predation on amphipods) and indirect (by reducing duration of extended parental care and enhancing pelagic movements). Both extended parental care and pelagic movements are important behavioural traits of D.␣monacanthus (and other marine amphipods), and significantly affect its population dynamics. Received: 18 January 1998 / Accepted: 27 May 1998     

Karyotypic characterization of the great sturgeon, Huso huso, by multiple staining techniques and fluorescent in situ hybridization

A karyotype analysis by several staining techniques was carried out on the great sturgeon, Huso huso (Linnaeus, 1758). The karyotype (2n = 118 ± 2) was composed of 42 pairs of meta-/submetacentric chromosomes and 17 pairs of acrocentrics/microchromosomes. Constitutive heterochromatin was mainly located at the centromeric regions of the acrocentric chromosomes. The biarmed chromosomes showed weak C-bands. Fluorescent staining with GC-specific chromomycin A₃ showed clearly recognizable fluorescent regions, whereas a more uniform base composition was revealed by the AT-specific 4,6-diamidino-2 phenylindole. After Ag-staining, nucleolar organizer regions could be observed on the short arms of two medium-sized submetacentrics and on two acrocentrics. Digoxigenated 28S and 5S rDNA probes, prepared from Acipenser naccarii DNA and hybridized to metaphase chromosomes, showed signals on six and two chromosomes, respectively. The telomeric sequence (TTAGGG) _n detected by FISH was located at both ends of each chromosome. Results are discussed in relation to karyotype organization and evolution in sturgeons. Received: 1 April 1998 / Accepted: 21 July 1998     

Effects of UV radiation of different wavebands on pigmentation, 15N-ammonium uptake, amino acid pools and adenylate contents of marine diatoms

Three marine diatoms Lauderia annulata Cleve, Odontella sinensis (Greville) Grunow and Thalassiosira rotula Meunier were exposed to ultraviolet (UV) radiation of different wavebands under controlled laboratory conditions (0.035 vol% CO₂, 18 °C). Several changes in the patterns of pigments in these organisms were seen depending on the waveband of UV radiation and species examined. UV-B and UV-B plus UV-A radiation led to a reduction in the overall pigment content of all three diatoms. The uptake of ¹⁵N-ammonium was less affected by 5-h UV-A (WG 320) but significantly reduced after UV-B and UV-B plus UV-A exposure. The pattern of free amino acid pools varied depending on the applied UV wavebands and the tested diatom. The main protein-bound amino acids of T. rotula decreased after 5-h UV irradiance except leucine. Contents of adenosine 5′-mono-, di-, and triphosphate (AMP, ADP and ATP) were affected differently by UV radiation; ATP values increased at the end of UV-B and UV-B plus UV-A exposure. These results have been discussed with reference to the impact of the different UV sources and the influence on the nitrogen metabolism in connection to pigments and supply with energy. Received: 13 May 1997 / Accepted: 11 October 1997     

Genetic protein variation in red mullet (Mullus barbatus) and striped red mullet (M. surmuletus) populations from the Mediterranean Sea

Starch-gel electrophoresis of allozymes was used to differentiate the two red mullet species (Mullus barbatus L. and M. surmuletus L.) in the Mediterranean Sea and, further, to investigate the genetic stock structure of M. barbatus in the eastern Mediterranean area. Twenty putative enzyme-coding loci were examined in eight M. barbatus samples caught in the Aegean and Ionian Seas (Greece) and in the Gulf of Lion (France), and two M. surmuletus samples caught in the Aegean and Gulf of Lion. A high degree of genetic polymorphism was found in both species. Species-specific electrophoretic patterns were found in PGI* and PGM*. Estimates of variance of allele frequencies among samples (F _ST) and ² analyses both revealed significant differences (P < 0.05) among the M. barbatus samples. Most of the genetic variation was among samples regardless of region. The mean value of Nei's genetic distance between the two species was 0.329. Genetic distance among M. barbatus samples was low (maximum Nei's D = 0.012), with the sample from Platania differing most from other M. barbatus samples. This is probably be due to founder effects existing at this area. These results suggest that allozyme analysis may provide important information on the genetic structure of the red mullet to ensure sustainable management of this species. Received: 7 May 1997 / Accepted: 13 October 1997     

Semi-parametric statistical approaches for space-time process prediction

The problem of estimation and prediction of a spatial-temporal stochastic process, observed at regular times and irregularly in space, is considered. A mixed formulation involving a non- parametric component, accounting for a deterministic trend and the effect of exogenous variables, and a parametric component representing the purely spatio-temporal random variation is proposed. Correspondingly, a two-step procedure, first addressing the estimation of the non- parametric component, and then the estimation of the parametric component is developed from the residual series obtained, with spatial-temporal prediction being performed in terms of suitable spatial interpolation of the temporal variation structure. The proposed model formula-tion, together with the estimation and prediction procedure, are applied using a Gaussian ARMA structure for temporal modelling to space-time forecasting from real data of air pollution concentration levels in the region surrounding a power station in northwest Spain.