Chemical composition of sergestid shrimps (Decapoda: Natantia) collected near Bermuda

Chemical composition was determined for Sergestes corniculum, S. grandis, S. japonicus, S. robustus and S. splendens collected in December, April and September. Protein content expressed as percent of dry weight varied from 65.7% in S. splendens to 46.8% in S. japonicus. Significant differences were noted among species in Apria and September, with highest protein values in April in S. corniculum, s. robustus and S. splendens. Lipid content expressed as percent dry weight ranged from 12.6% in S. robustus to 8.3% in s. splendens. Differences in percent lipid among species were significant in December and September with highest values in s. robustus and lowest values in S. splendens. Carbohydrate content varied from 1.0% in S. grandis to 2.5% in S. splendens. Ash and chitin were only determined for S. corniculum, S. grandis and S. splendens. Although protein and lipid content were correlated with size of shrimp analyzed, protein and lipid values in S. splendens, a species known to occur near the surface only at night, appeared to be related to seasonal zooplankton abundance in near-surface waters. Differences in lipid and protein content among species suggest that higher lipid and lower protein content occurs in species with shorter ranges of diel vertical migration.     

Preliminary rearing experiments on the larvae of Sergestes lucens (Penaedia,Natantia, Decapoda)

Sergestes lucens Hansen, a mesopelagic shrimp fished commercially in Suruga Bay, Japan, was successfully reared from egg to post-larval stage V under laboratory conditions. Chaetoceros ceratosporum and Artemia nauplii were found to be satisfactory food in the laboratory during rearing. Growth, mortality, food preference, and feeding and swimming activities during the various developmental stages were investigated. Temperature changes greatly affected the speed of development and the mortality of the larvae. The optimum temperature range for larval development was 18° to 25°C. The growth rate (length) of larval stages was as rapid as 0.16mm/ day at 20 °C and 0.21 mm/day at 23 °C. The larvae first started feeding on phytoplankton at elaphocaris stage I, and then gradually became predators in the post-larval stages. It is suggested that the critical period for the species occurs in the elaphocaris stages. Environmental data, vertical distribution of the species, and data obtained from laboratory experiments suggest that the fluctuation in the abundance of S. lucens is greatly influenced by the water temperature at around 50 m from June to August. Feeding mechanisms observed in the post-larval stages are described.     

Natural tracers in dietary studies: data for 210Po and 210Pb in decapod shrimp and other pelagic organisms in the Northeast Atlantic Ocean

Measurements of the concentrations of the naturally-occurring radioactive nuclides ²¹⁰Po and ²¹⁰Pb in a large number of pelagic organisms from the Atlantic Ocean made in the spring/summer of 1984 and 1985 are reported. Marine shrimp are particularly well represented, and in many cases data were obtained for shrimp hepatopancreas, stomach-contents, and posterior intestine plus contents, as well as for whole individuals. The wide ranges found in ²¹⁰Po concentrations group into categories: the shrimp, for example, divide into four categories, two penaeid and two carid. These groupings are explained on the basis of variations in diet between the different categories. A clear difference was also observed between the ²¹⁰Po levels in shrimp of similar species and size from opposite sides of an oceanographic front; this difference too can be explained plausibly in terms of a change in certain penaeid shrimp, and attention is drawn to the need for investigation of cytological and/or genetic effects which could possibly be caused by the very high natural radiation doses to which such organisms are exposed.     

Genetic comparison of two populations of the deep-sea vent shrimp Rimicaris exoculata (Decapoda: Bresiliidae) from the Mid-Atlantic Ridge

Allozyme data are presented for populations of the bresiliid shrimp Rimicaris exoculata from two hydrothermal vent fields, Trans-Atlantic Geotraverse (TAG) and Broken Spur, located along the Mid-Atlantic Ridge. These indicate that all morphotypes of R. exoculata examined, including those previously interpreted as representing separate species, are conspecific. Conversely, genetic identity between a single specimen of Chorocaris sp. and R. exoculata was high for intergeneric comparisons. Genetic variation in the populations of R. exoculata (H _o =0.034 to 0.056) was in the lower range of that estimated for other vent organisms, but similar to values obtained for other species of caridean shrimps in previous genetic studies. F-statistics were used to examine the population structure of R. exoculata. Estimates of variance of allele frequencies among populations (F _ST ) between TAG and Broken Spur were very low (mean F _ST =0.001), indicating no significant genetic differentiation between these populations although they were separated by 370 km. The number of migrants per generation was estimated from F _ST and by a private-alleles method, and indicates that migration between the two fields exceeds 100 individuals per generation. This may be because of efficient larval or adult migration or a combination of both. Estimates of the correlation between homologous alleles between individuals within local populations (F _IS ) of R. exoculata were high at two enzyme loci and indicate a heterozygote deficiency which caused a significant deviation from genotype frequencies expected under Hardy-Weinberg conditions. This deficiency was caused by the occurrence of rare homozygous genotypes in small individuals. In large individuals, rare alleles decreased in frequency or disappeared completely. This is discussed in relation to previous genetic investigations on other vent and nonvent organisms.     

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

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

Latitudinal variation in the reproductive biology of the burrowing ghost shrimp Callianassa filholi (Decapoda: Thalassinidea)

Population structure and reproductive ecology of the burrowing ghost shrimp Callianassa filholi Milne-Edwards, 1878 were studied in populations along a latitudinal gradient throughout New Zealand during the breeding season. Size-frequency distributions revealed unimodal populations, with predominantly sexually mature shrimp. All populations showed an unbiased sex-ratio, and there appeared to be no significant difference in size (carapace length, CL) between sexes. At the same time, CL and size at maturity differed significantly between populations; however, a general increase in sizes from north to south was not consistent throughout the latitudinal range studied. The timing of the breeding cycle differed significantly between populations, and breeding started earlier in southern populations. Number of embryos (fecundity) increased linearly with female CL at each location, but rates differed significantly between populations. Embryo size was not related to number of embryos, and the former increased significantly with latitude. With the exception of embryo size, observed differences in body size/size at maturity and reproductive timing between C. filholi populations are thought to be determined by food availability rather than temperature. Thus, further study is suggested on these aspects of thalassinid reproductive biology. Received: 17 June 1999 / Accepted: 8 January 2000     

Reproductive biology of the common shrimp Crangon crangon (Decapoda: Crangonidae) in the central Irish Sea

Aspects of the reproductive biology of the common shrimp Crangon crangon (L.) were studied in Port Erin Bay, Isle of Man, Irish Sea. Size at sexual maturity was determined from the proportions of ovigerous females and of females with maturing ovaries. The size at which 50% of females are mature is estimated (±95% confidence intervals) as 12.5±0.48 mm carapace length. Based on the proportions of ovigerous females and of mature females, the main breeding season was from January to June. Mean ovarian dry weights indicated two broods (winter and summer), with females bearing winter broods (WB) having higher gonad indices than those with summer broods (SB). WB females with non-eyed eggs and with eyed eggs differed in the regression of ovarian dry weight on carapace length, indicating preparation for laying a second brood. In both broods the moult stages of berried females were related to egg stage. Moulting will occur following the release of the brood. During embryonic development, mean egg length and egg volume were larger in all stages, and the mean dry weight of individual eggs of all stages heavier, in WB than in SB; there was no difference in egg number, however. Consequently, reproductive investment, the proportion of female weight devoted to egg production, was 67% higher in WB (0.20±0.04) than in SB (0.12±0.03). There is a significant effect of egg volume on brood weight, but not on egg number. In both broods, egg number was a negatively allometric function of female body size in non-eyed eggs and an isometric function of female body size in eyed eggs. Brood mortality during incubation was higher in SB (17%) than WB (10%). Differences in the reproductive variables and investment between the two broods of C. crangon are discussed in the light of reproductive strategies and life history.Communicated by J.P. Thorpe, Port Erin     

Facultative lecithotrophy during larval development of the burrowing shrimp Callianassa tyrrhena (Decapoda: Callianassidae)

Survival, developmental and consumption rate (Artemia nauplii ingested per day) as well as predation efficiency (ingested per available Artemia nauplii) were studied during the larval development of the shallow-water burrowing thalassinid Callianassa tyrrhena (Petagna, 1792), which exhibits an abbreviated type of development with only two zoeal stages and a megalopa. The larvae, hatched from berried females from S. Euboikos Bay (Aegean Sea, Greece), were reared at 10 temperature–food density combinations (19 and 24 °C; 0, 2, 4, 8 and 16 Artemia nauplii d⁻¹). Enhanced starvation resistance was evident: 92 and 58% of starved zoeas I molted to zoea II, while metamorphosis to megalopa was achieved by 76 and 42% of the hatched zoeas at 19 and 24 °C, respectively. The duration of both zoeal stages was affected by temperature, food density and their interaction. Nevertheless, starvation showed different effects at the two temperatures: compared to the fed shrimp, the starved zoeae exhibited accelerated development at 19 °C (8.4 d) but delayed metamorphosis at 24 °C (5.9 d). On the other hand, both zoeal stages were able to consume food at an increased rate as food density and temperature increased. Predation efficiency also increased with temperature, but never exceeded 0.6. Facultative lecithotrophy, more pronounced during the first zoeal stage of C.tyrrhena, can be regarded as an adaptation of a species whose larvae can respond physiologically to the different temperature–food density combinations encountered in the wide geographical range of their natural habitat. Received: 28 February 1998 / Accepted: 21 October 1998     

Factors influencing the association patterns of Hippolyte zostericola and Palaemonetes intermedius (Decapoda: Natantia) with seagrasses of the Indian River Lagoon, Florida

The ecological role and the association of Hippolyte zostericola (Smith, 1873) (Decapoda: Natantia) with different seagrass species in the Indian River Lagoon (Florida, USA) were investigated through field sampling and the analysis of diet, size–frequency distributions and laboratory experiments. Gut contents suggested that H. zostericola is a mesograzer which may be important in the transfer of primary production to higher trophic levels. Population size–frequency distributions showed a polymodal pattern variable according to the site. Preference experiments indicated that choice of seagrass species is not influenced by the available surface area of seagrass blades, nor by the presence of epiphytic food. Significant responses of the shrimp to the ambient light field, mediated by the seagrass canopy, were detected. A clear negative phototropism was observed for H. zostericola which may be an adaptive response to improve avoidance of visual predators. Received: 1 February 1998 / Accepted: 21 December 1998     

Mineral concentration in tissues during ovarian development of the white shrimp Penaeus vannamei (Decapoda: Penaeidae)

Levels of calcium, magnesium, zinc, copper, iron, and manganese were examined in the muscle, hepatopancreas, and gonad of white shrimp, Penaeus vannamei, females at different stages of ovary maturation. Eyestalk-ablated shrimp were sampled during the intermolt stage and classified using the following maturation stages evaluated histologically: cortical stage, vitellogenesis, previtellogenesis, and without gonadic development. In muscle, the copper concentration was significantly lower in the vitellogenic stage than in other stages of ovary development. In the hepatopancreas, manganese levels were higher in the cortical and vitellogenic stages than in animals in previtellogenesis and without gonadic development. No other influence of ovary maturation on muscle and hepatopancreas mineral content was found. In contrast, in the ovary, significant differences of some mineral concentrations were detected. Zinc, iron, and magnesium concentrations were significantly increased in the cortical stage compared to the vitellogenic and previtellogenic stages. Our results indicate that these elements are selectively accumulated during ovary development, especially when the ovaries reach the cortical stage. Received: 14 March 2000 / Accepted: 30 November 2000     

Allozyme and mitochondrial DNA variation in Cuban populations of the shrimp Farfantepenaeus notialis (Crustacea: Decapoda)

We investigated the genetic diversity among populations of the shrimp Farfantepenaeus notialis, the most abundant penaeid species around Cuba. A total of 25 allozyme loci were analyzed in samples of shrimps from seven localities at the south central platform of the island (Ana María Gulf). Samples from three of these localities and from Batabanó Gulf and Guacanayabo Gulf at the south west and south east platforms of the island, respectively, were also characterized at the mtDNA level through sequence variation of a 2027 bp segment including part of the COI and COIII genes. Of the 25 allozyme loci studied 9 were polymorphic: Akp2, Akp3, AmyB, Est3, Gdh, GP7, and Per1, 2 and 3. In contrast to mtDNA, the pattern of allozyme variation among localities revealed strong population structuring at Ana María Gulf, with significant F _st in all pairwise comparisons. The magnitude of F _st estimates as well as the grouping pattern obtained by a UPGMA analysis based on a distance matrix indicated that the level of differentiation was concordant with the geographical position of the localities and the hydrographic regime. Homogeneity of mtDNA suggested that differentiation of allozyme loci might be due to more recent events rather than historical isolation of the sampled populations. Ana María and Guacanayabo Gulf populations were differentiated by mtDNA from Batabanó Gulf, at the southwestern end of the island. The analysis showed three restriction site differences among them, suggesting genetic isolation of the two regions. The present results also suggest that an artificial introduction of larvae from Tunas de Zaza into Batabanó Gulf, in an effort to repopulate this fishing region, may have been ineffective. Received: 13 December 1999 / Accepted: 2 October 2000     

Effect of hypophyseal gonadotropins (FSH and LH) on the ovaries of the sand shrimp Crangon crangon (Crustacea: Decapoda)

The effect of purified preparations of ovine hypophyseal gonadotropins NIH-FSH-S12 and NIH-LH-S19 on the histological structure of the ovaries of the sand shrimp Crangon crangon (L.) (Crustacea: Decapoda) was studied. All experiments were carried out on sexually mature females, out of the breeding season. The individuals treated with the gonadotropins included intact females as well as those in which the eyestalks were ligated to eliminate a source of gonad-inhibiting hormone (GIH). The results obtained indicate that both FSH and LH have a stimulating effect on the ovaries of the common shrimp, FSH causing growth in the number of somatic cells of the ovary, and LH — meiosis in the sex cells. The effect of each of the 2 gonadotropins was similar in intact and eyestalkless females which indicates its independence from the presence or absence of GIH. The response of crustacean ovaries to mammalian FSH and LH indicates that gonadotropins may act upon invertebrates.     

Influence du niveau sonore de bruit ambiant sur le métabolisme de Crangon crangon (Decapoda: Natantia) en élevage

The influence of ambient noise on the metabolism of the sand-shrimp Crangon crangon L. was estimated from NH₄ excretion and O₂ consumption rates. Two ambient noise levels were compared: the first (+32 dB bar⁺¹) was that present under usual rearing conditions, the second (+5 to 0 dB bar⁺¹) was the level in a soundproof rearing tank. Over a 24 h period, NH₄ excretion and O₂ consumption rates were higher by 1.4 times and 1.2 to 1.4 times, respectively, under the noisy conditions than in the sound-proof tank. The influence of ambient noise level on the shrimp's metabolic level appears to be long-lasting(>1 month). When the acoustic pressure of the environment was increased abruptly, the excretion rate was strongly enhanced but oxygen consumption was reduced; these stress-effects usually disappeared within 3 h. The influence of ambient noise on the metabolic level of this shrimp should be taken into consideration during physiological studies as well as rearing experiments in the laboratory.     

Photographic and acoustic tracking observations of the behaviour of the grenadier Coryphaenoides (Nematonurus) armatus the eel Synaphobranchus bathybius,and other abyssal demersal fish in the North Atlantic Ocean

Using an autonomous free-fall vehicle (AU-DOS), observations were made of demersal fish attracted to baits and baited acoustic transmitters at two stations in the North Atlantic Ocean. A comparison was made between Station PAP (48°50N; 16°30W), 4800 m deep on the Porcupine Abyssal Plain which is relatively eutrophic, and Station MAP (31°N; 20°W), 4900 m deep on the Madeira Abyssal Plain, which is oligotrophic. Experiments were conducted during summer, in 1989 and 1990. Four species of fish were observed at Station MAP, the grenadier, Coryphaenoides (Nematonurus) armatus, the eel, Synaphobranchus bathybius, and the ophidiids Spectrunculus grandis, and Barathrites sp. At Station PAP, C. (N.) armatus and H. (S.) bathybius were attracted to bait on all deployments and only two other individuals of different species, probably ophidiids, were seen. The mean first grenadier arrival time was 30 and 138 min at Stations PAP and MAP, respectively. Mean first eel arrival time was 29 and 151 min at Stations PAP and MAP, respectively. Estimated population densities of fish were 167 grenadiers km^-2 and 180 synaphobranchid eels km^-2 at Station PAP and 8 grenadiers km^-2 and 7 eels km^-2 at Station MAP. Only the grenadier C. (N.) armatus definitely ingested transmitters, and this species dominated fish activity around the baits. Mean time of departure of grenadiers with transmitters in their stomachs across an acoustic horizon at 1000 m range was 371 and 488 min at Stations PAP and MAP, respectively. Grenadiers had a longer mean staying time at the food source at the more oligotrophic Station MAP (364 min) than at Station PAP (141 min). This corresponds with predictions of optimal foraging theory.     

Interception and dispersal of artificial food falls by scavenging fishes in the abyssal Northeast Atlantic: early-season observations prior to annual deposition of phytodetritus

The hypothesis that the behaviour of deep-sea scavenging fishes is influenced by seasonal input of organic matter from the ocean surface was investigated by observing responses to baits placed on the sea floor at 4800 m depth in the NE Atlantic (48°50′N; 16°30′W) during spring (April 1994). Data from the present study are compared with those from previous studies of the same location made in summer 1989. The first fishes to arrive at baits were the grenadier Coryphaenoides (Nematonurus) armatus and the eel Histiobranchus bathybius, after delays of 28 and 29 min, respectively; these results are not significantly different from those of summer 1989. Similarly, other indices of activity (staying time and swimming speed) showed no evidence of differences between years/seasons. However, the rate of radial dispersal of bait (0.009 m s⁻¹) by C. (N.) armatus was much slower than in all previous studies. A change in the size distribution of C. (N.) armatus to smaller individuals in spring 1994 was also evident. It is suggested that the fish on the abyssal plain may not comprise a steady-state population and that major episodic or seasonal migrations may occur. Received: 18 October 1996 / Accepted: 20 December 1996     

Geographic variation in Loligo forbesi in the Northeast Atlantic Ocean: analysis of morphometric data and tests of causal hypotheses

Geographic variation in the squid Loligo forbesi was investigated using multivariate analysis of morphometric and meristic characters in samples of squid taken from 13 localities in the Northeast Atlantic Ocean. Two character sets, body morphometrics and beak morphometrics, indicated similar patterns of variation, with squid from the Azores differing markedly from those on the continental shelf. No consistent pattern was apparent in meristic data. Partial Mantel tests indicated that similarity matrices for morphological data were significantly correlated with distance matrices for (a) geographic proximity, (b) whether the capture site was on the continental shelf or the Azorean bank, and (c) (beak data only) average seasurface temperature at site of capture. Partial Mantel tests on allozyme data for the same individuals support hypothesis (b). The results suggest that L. forbesi in the Azores may reasonably be regarded as a distinct stock, differing significantly from L. forbesi on the continental shelf.     

Genetic variation in the neritic squid Loligo forbesi (Myopsida: Loliginidae) in the northeast Atlantic Ocean

Horizontal starch gel electrophoresis was employed to investigate levels of genetic differentiation between 13 samples of the neritic squid species Loligo forbesi Steenstrup obtained from throughout the majority of its known geographical range. Six enzyme loci identified in a preliminary study as being polymorphic were screened for variation between samples. No significant differences in allele distribution were detected between any of the samples obtained from the Faroe Bank in the north to Lisbon in the south, suggesting that squid throughout this range in the vicinity of the continental shelf are able to maintain panmixia, and effectively belong to a single population sharing a common gene pool. No clinal variation in allele distribution was detected throughout this range, a result which complements the findings of a detailed morphological companion study of the same individuals. Comparison of this homogenous European continental shelf population with squid from the Azores revealed highly significant (P<0.01) differences in allele distribution at five of the six polymorphic enzyme loci studied. A genetic identity value (I) equivalent to 0.93 over 33 loci was obtained. Analysis of F-statistics suggested migration rates between sites to be as low as one individual per five generations, a rate deemed insufficient under most models to prevent divergence by random genetic drift. The large distance and oceanic depths separating the Azores from continental Europe seem to present an effective barrier to gene flow to L. forbesi, a squid belonging to a family considered to be confined in distribution to relatively shallow, near coastal waters. The two populations of squid in the Azores and along the European continental shelf currently both ascribed to L. forbesi should therefore probably best be regarded as relative subspecies.