Larval abundance and recruitment of the sand dollar Dendraster excentricus in Monterey Bay,California, USA

Seasonal abundance of planktonic larvae of the sand dollar Dendraster excentricus was determined in Monterey Bay, California, USA. Larvae were counted from two offshore stations and also over a coastal sand dollar bed, and these data were compared with settlement in the sand dollar bed, with adult population structure and with adult reproductive condition. These measurements were made during the period July 1978 to October 1980 and in October 1981. Sand dollar larvae were most abundant in the plankton during the summer, a period when phytoplankton productivity tended to be high and currents were relatively slow and variable. In some years, small-scale current variations appeared to prevent many larvae in the open bay from reaching the nearshore sand dollar beds; however, in other years, massive shoreward transport of the larvae evidently did occur, since the adult population in the sand dollar bed exhibited a mode in size, indicating a large settlement. A comparison of settled individuals in 1980 and the adult size-frequency distribution in 1981 gives an estimated mortality rate of 88% yr^-1 for early juveniles of D. excentricus.     

Diverticulum sand in a miniature sand dollar Sinaechinocyamus mai (Echinodermata: Echinoidea)

Sinaechinocyamus mai (Wang) were collected from the low intertidal zone at Tunghsiao, western Taiwan, periodically from July 1990 to July 1991 and May 1993. The mean body length was 7.3±1.01 mm from 146 juveniles and adults. All individuals contained sand grains in their intestinal diverticula. The densities of sand dollars ranged from 1.2 to 2.5 mg cm^-3 and had an inverse linear relationship to the body length. The percentage of sand weight in the diverticulum to the wet body weight is inversely correlated to the body length, indicating that juveniles contain a higher proportion of sand than adults. The ratio of sand weight to body length did not change significantly during the study period. 74% of the diverticulum sand was 0.075 to 0.125 mm in diameter, whereas only 0.1% of the sand in the substrate was this size. The sand in both the diverticulum and the substratum consisted of feldspars and quartz (88.4%) and iron oxide (11.6%). The sand grains of the diverticulum were eliminated from the anus.     

An experimental analysis of lunule function in the sand dollar Mellita quinquiesperforata

Coefficients of lift and drag for fifty lunulate sand dollars [Mellita quinquiesperforata (Leske 1778)], poised over a flat, sandy surface, were determined at seven different air stream velocities. Coefficients of static friction were obtained experimentally on level sand in standing water. Critical velocity, at which a sand dollar would be dislodged, is defined as that current velocity in which the force of drag is equal to the product of residual weight (i.e. weight-lift) and the coefficient of static friction. Small individuals have lower critical velocities than large ones: 26 cm s^?1 and 43 cm s^?1 for individuals 48 and 94 mm in diameter, respectively. Measurements were repeated for 20 of the controls, their lunules smoothly filled with modelling clay, and 20 from which lunule spines were removed. In every case, blocking the lunules decreased critical velocity, by an average of 15%; this was shown to be statistically significant (P>0.01). Removal of spines, which partially occlude the lunules, significantly (P>0.01) increased critical velocity by an average of 13%. Direct measurements in a water tunnel showed that calculated values of critical velocity were slightly too high, but otherwise confirmed the role of the lunules. Allometric analysis showed that as sand dollars increase in size, the distances of the lunules from the center of the disk increase less rapidly than the radii. A principal components' analysis of profile measurements of nine species indicated that lunulate and non-lunulate sand dollars are quite different in form. Lunulate species tend to be thinedged, flat-domed and larger in diameter. Some alternative ideas of lunule function are discussed and it is shown that there are no allometric or experimental data to support any of the suggested feeding hypotheses.     

Reproductive cycle of two populations of Ophionereis schayeri (Ophiuroidea) in New South Wales

Reproduction of two populations of Ophionereis schayeri (Müller and Troschel) in New South Wales was investigated from November 1991 through January 1993. The reproductive cycle was documented by histological examination of the gonads and by image analysis to determine the oocyte size-frequency distributions. Both populations of O. schayeri were mature in December and January and had a major summer spawning period between January and February. Thereafter, the condition of the gonads exhibited interindividual variability, with asynchronous low-intensity gamete release through August. O. schayeri has the potential to spawn for up to 8 mo of the year. This breeding pattern with synchronous spawning in summer and asynchronous gamete release through winter was similar in both populations. During autumn and winter, the gonads contained developing gametes and advanced gametes ready for spawning. The eggs spawned by O. schayeri during these seasons started their growth during the previous spring vitellogenic period, and continued to grow through summer. Upon reaching full size, they were stored for spawning outside the main breeding period. Spring is marked by increased spermatogenic and vitellogenic activity followed by maturation and spawning. Throughout their development, the oocytes of O. schayeri are surrounded by a follicle consisting of periodic acid-Schiff-positive (PAS+) haemal fluid and PAS+ yolk by the oocytes. In the testes, the haemal sinus projects into the centre of the spermatocyte columns, thus appearing to play a nutritive role in support of both oogenesis and spermatogenesis. Late vitellogenic oocytes of O. schayeri are firmly anchored to the germinal epithelium by an attachment complex consisting of specialised attachment cells and basophilic strands that radiate between the oolemma and the nucleus. Spawning is associated with rupture of the follicles, which remain as prominent, empty U-shaped profiles in the ovaries. O. schayeri produces copious numbers of 200 m-diam oocytes, suggesting that this species is a broadcast spawner and that it has a modified ophiopluteus or vitellaria larva.     

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     

Sediment preferences and oil contamination in the Pacific sand lance Ammodytes hexapterus

Sand lance, Ammodytes hexapterus Pallas, forage for zooplankton in the water column and are under heavy predation from fish, marine birds and marine mammals. To avoid predation, these fish bury themselves in soft bottom sediments when not foraging and during overwintering. We collected sand lance in Sequim Bay, Washington State, USA, in 1982. In three experiments we presented the fish with: (1) four different sediment types (fine sand, coarse sand, gravel, silt) to determine their sediment preferences; (2) clean and oil-contaminated preferred sediment to determine whether the fish would avoid the contamination; and (3) clean unpreferred and oil-contaminated preferred sediment to determine whether the contamination would alter their sediment preferences. In the first experiment, sand lance preferred to bury in fine and coarse sands and avoided gravel and silt. In the second experiment, sand lance avoided sand contaminated with Prudhoe Bay crude oil (116 and 1050 ppm). In the third experiment, sand lance avoided the oiled sand (131 and 1041 ppm) and buried in clean gravel, and also avoided both oiled sand (113 and 1004 ppm) and clean silt, and chose to remain in the water column. The sediment particle size and the way it affects water flow through the sediment seemed to be responsible for the preferences. We suggest that the sediment type, the sediment distribution, the nutritional state of the fish, and the predation pressure influence how sand lance use the sediment as a refuge and how they respond to contamination of that refuge.Contribution No. 1392 of the School of Oceanography, University of Washington     

Chemical composition and effects of water extracts of petroleum on eggs of the sand dollar Melitta quinquiesperforata

Sperm and eggs of sand dollars, Melitta quinquiesperforata (Leske), were subjected to two petroleum oils, and effects determined. The oils chosen were Kuwait crude and No. 2 fuel oil, supplied by the American Petroleum Institute. Water-soluble extracts (WSF) from oil-sea water mixes were prepared and the major aromatic components in the WSF of the fuel oil were identified. WSF of No. 2 fuel oil depressed respiration, mobility of sperm, interfered with fertilization and cleavage, and retarded larval development. The effects were detectable at dilutions of 4% and less (about 0.6 ppm of WSF). Kuwait crude was much less toxic. There was no effect on water permeability of the egg membrane. Results are compared with similar studies on other marine organisms.     

Fertilisation, embryogenesis and larval development in the tropical intertidal sand dollar Arachnoides placenta in response to reduced seawater pH

We examined the response of the tropical sand dollar Arachnoides placenta to reduced seawater pH in experiments spanning ca. 50 % of the planktonic larval duration. A. placenta inhabits intertidal sandy beaches where we observed a minimum in situ pH range 0.06 pH units (pH 8.10–8.16). The responses of gametes and larvae to seawater pH were tested in vitro in ambient (pH 8.14, pCO₂ = 525.7 μatm, total alkalinity = 2,651 μmol kg soln^?1) and three reduced pH seawater treatments (7.8–7.0). Percentage fertilisation decreased significantly with decreasing pH across a range of sperm/egg ratios (4:1 up to 4,000:1). A. placenta reached the advanced pluteus stage in 4 days, and during this time, we saw no difference in survival rate of larvae between the ambient (67 %) and pH 7.79 (72 %) treatments. Four-day survival was, however, reduced to 44 and 11 % in the pH 7.65 and 7.12 treatments, respectively. Larval development and morphometrics varied among pH treatments. Embryos reared in pH 7.12 exhibited arrested development. Larvae reared at pH 7.65 showed delayed development and greater mortality compared with those reared at pH 7.79 and 8.14. When larval morphometrics are compared among larvae of the same size, differences in larval width and total arm length between pH treatments disappear. These results suggest that variation in larval size among the three highest pH treatments at a given time are likely the result of slower development and apparent shrinkage of surviving larvae and not direct changes in larval shape. There were no differences in the percentage inorganic content (a proxy for calcification) in larvae reared in either an ambient or a pH 7.7 treatment. The responses of fertilisation and development to decreased pH/increased pCO₂ in A. placenta are within the range of those reported for other intertidal and subtidal echinoid species from colder latitudes.     

Reproductive cycles of three dominant Calanus species in Disko Bay, West Greenland

This study describes the annual reproductive cycles of the three dominant Calanus species, C. finmarchicus, C. glacialis and C. hyperboreus, in Disko Bay (West Greenland) in relation to seasonal phytoplankton development. Relative abundance of females, copepodite stage V (CV) and males, and the developmental stage of the female gonad were examined from plankton samples collected at weekly to monthly intervals from May 1996 to June 1997 with a WP2 net or a pump. During spring and summer, egg production rates were determined. Females of all three species were present year round. Maximum relative abundance was reached by C. hyperboreus females at the beginning of February, by C. glacialis in mid-February, and by C. finmarchicus in April. All three species reproduced successfully in Disko Bay. Their reproductive cycles were considerably different with respect to the timing of final gonad maturation and spawning, and hence in their relation to seasonal phytoplankton development. In all three species, early gonad development took place during winter, before living food became plentiful, suggesting that these processes were largely food independent. Final gonad maturation and spawning in C. finmarchicus was related to the phytoplankton concentration, reflecting that final gonad maturation processes are food dependent in this species. C. glacialis females matured and spawned prior to the spring bloom. Our results indicate that first internal lipid stores and later ice alga grazing supplied final gonad maturation and egg production. Maximum egg production rates of C. glacialis were found in spring and summer, when the chlorophyll a concentration was high. Mature female C. hyperboreus were found from February until mid-April, when the chlorophyll a concentration was still low. In this species, reproductive activity was decoupled from phytoplankton development, and final maturation processes and spawning were solely fuelled by internal energy stores.     

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 cycles of tropical sea cucumbers (Echinodermata: Holothuroidea) in southern Taiwan

Reproductive cycles of Afrocucumis africana (Dendrochirotida), Actinopyga echinites, Holothuria leucospilota, H. cinerascens, H. difficilis (Aspidochirotida), Synaptamaculata, Opheodesoma grisea, Patinapta taiwaniensis and Polycheira rufescens (Apodida), representing three orders of intertidal holothurians in southern Taiwan, were determined by gonad index and histological examination from March 1990 through September 1991. All nine species of holothurians have annual spawning periods lasting 2 to 4 mo in spring or summer. The early spawning of H. cinerascens and P. rufescens (suspension feeders) suggests that their feeding mode is related to food resources and may influence the reproductive period. In the direct-developing dendrochirotid (suspension feeder), gonad development occurs in cool months, and gametes are released at the beginning of warm months. In indirect-developing aspidochirotid and apodid (deposit feeder), gamete release occurs in late spring or summer and appears to be correlated with summer phytoplankton growth. The holothurians in the present study display spawning periodicity and duration similar to those of temperate species. Four species of holothurians lengthened spawning season with decreased latitude.     

Seasonal and diel variation in movement rhythms of sand dollar, Peronella lesueuri (Valenciennes 1841), in Cockburn Sound, Western Australia

Rates and direction of movement in the sand dollar Peronella lesueuri were measured in summer and winter in Cockburn Sound, a large coastal embayment in south-western Australia. P. lesueuri was found to have a diurnal activity pattern throughout the year and had a greater movement rate in the summer (mean of 5.3 cm h^?1, day; 3.9 cm h^?1, night) than in the winter (mean of 2.7 cm h^?1, day; 2.0 cm h^?1, night). Seasonal change in temperature and physiological requirements by the sand dollar are the most likely reason for the seasonal differences. Reasons for diurnal variation were not clear. Direction of movement was found to be random at both times of the year. Based on these movement rates, one sand dollar can bioturbate an approximate area of 0.1 m² day^?1 and 36.4 m² year^?1. At a conservative density estimate of 0.5 sand dollars per m² it takes approximately 20 days for the sand dollars to rework the entire area of the sediments in the habitats they occupy.     

Vertical distribution,population structure and life cycles of four oncaeid copepods in the Oyashio region,western subarctic Pacific

Vertical distribution and population structure of four dominant oncaeid copepods (Triconia borealis, Triconia canadensis, Oncaea grossa and Oncaea parila) were investigated in the Oyashio region, western subarctic Pacific. Seasonal samples were collected with 0.06 mm mesh nets from five discrete layers between the surface and 2,000 m depth at seven occasions (March, May, June, August and October 2002, December 2003 and February 2004). The depth of occurrence of major populations of each species differed by species; the surface–250 m for T. borealis, 250–1,000 m for T. canadensis, 250–500 m for O. grossa and 500–1,000 m for O. parila. The ontogenetic vertical migration characterized by deeper occurrence of early and late copepodid stages, and shallower occurrence of middle copepodid stages was observed in T. canadensis and O. parila. Of the four oncaeid copepods, almost all copepodid stages occurred throughout the study period, suggesting that their reproduction continues throughout the year in the region. Nevertheless, a clear developmental sequence of stage-to-stage was traced for T. canadensis and O. grossa copepodids, implying their generation time to be 1 year. For T. borealis and O. parila copepodids, no clear seasonal succession was observed thus estimation of their generation time was uncertain. The present comprehensive results of vertical distribution and life cycle features for T. borealis, T. canadensis, O. grossa and O. parila are compared with the few published data on oncaeid species distributing in high latitude seas.     

RFLP analysis of the mtDNA control region in white shrimp (Litopenaeus vannamei) populations from the eastern Pacific

White shrimp (Litopenaeus vannamei) population genetic structure from the eastern Pacific was determined by restriction fragment length polymorphism analysis of the mitochondrial DNA control region. Four localities were surveyed with four endonucleases (Alu I, Taq I, Spe I, Ssp I) yielding 48 composite haplotypes. White shrimp showed high average within-locality haplotype (0.823) and nucleotide (5.41%) diversities and also high average nucleotide divergence between all pairs of localities (0.73%). A mismatch analysis of pairwise differences between haplotypes indicated that white shrimp does not fit the sudden population expansion model. An analysis of molecular variance showed significant geographic variation in the frequencies of haplotypes (Φ_ST=0.1382, P<0.0001). Population differentiation may be maintained by a combination of physical, oceanographic, and biological factors acting as barriers to gene flow among localities. Because of its high polymorphism, the control region might be useful as a genetic marker for monitoring genetic diversity in aquaculture stocks.     

Identification of genetic populations of the Pacific blue shrimp Penaeus stylirostris of the Gulf of California, Mexico

Species are often composed of discrete breeding units (i.e. populations or stocks) which, while not reproductively isolated from other such groups, may have limited opportunities to exchange genetic material because of geographic distance, barriers to migration, or spawning asynchrony. Low levels of gene flow between stocks may result, over time, in their genetic divergence, and species that are subdivided into morphologic or genetically distinct stocks are said to be structured. The aim of our investigation was to test whether or not Penaeus stylirostris from the Gulf of California (Mexico) was structured into genetically distinct populations. Shrimp samples were collected in 1996 from six regions of the Gulf where specimens with distinct morphologic characteristics had previously been identified. Statistical analysis of 324 RAPD loci (randomly amplified polymorphic DNA), resolved through polyacrylamide gels and scored for each of 78 specimens, permitted the quantification and comparison of between-stock genetic differences. The finding that genetically discrete stocks of P. stylirostris can be found in a small portion of the geographic distribution range of the species, disagrees with the long-held perception that this resource is panmictic in nature. This new evidence is not only of interest for selective breeding programs in the shrimp aquaculture industry, but is also relevant to the management of the Mexican shrimp fishery which, at present, is perceived and managed as a single stock. Received: 10 May 1999 / Accepted: 27 July 2000     

Temporal separation of two fin whale call types across the eastern North Pacific

Fin whales (Balaenoptera physalus) produce a variety of low-frequency, short-duration, frequency-modulated calls. The differences in temporal patterns between two fin whale call types are described from long-term passive acoustic data collected intermittently between 2005 and 2011 at three locations across the eastern North Pacific: the Bering Sea, off Southern California, and in Canal de Ballenas in the northern Gulf of California. Fin whale calls were detected at all sites year-round, during all periods with recordings. At all three locations, 40-Hz calls peaked in June, preceding a peak in 20-Hz calls by 3–5 months. Monitoring both call types may provide a more accurate insight into the seasonal presence of fin whales across the eastern North Pacific than can be obtained from a single call type. The 40-Hz call may be associated with a foraging function, and temporal separation between 40- and 20-Hz calls may indicate the separation between predominately feeding behavior and other social interactions.     

Reproductive suppression and inbreeding avoidance in wild populations of co-operatively breeding meerkats (Suricata suricatta)

Meerkats live in co-operatively breeding familial groups in which reproduction is monopolised by a dominant pair of breeders. Offspring of the breeders are behaviourally subordinate, and typically remain in their natal group as sexually mature, non-breeding helpers. In this study, we investigated the proximate factors limiting subordinate reproduction. Evidence for reproductive suppression by dominants was investigated by comparing life history, behaviour and hormonal profiles of dominants and subordinates. Baseline levels of plasma luteinising hormone (LH) were significantly higher in dominant than in subordinate females. However, following an exogenous injection of gonadotrophin-releasing hormone (GnRH), both categories had comparable concentrations of circulating LH. There were no significant differences in pre- or post-GnRH challenge LH levels in dominant or subordinate males. Reproduction in both dominant and subordinate females rarely occurred in the absence of unrelated males. Given that groups typically comprise parents and offspring, lack of suitable mates emerged as the primary constraint on subordinate reproduction. When this constraint was removed, subordinates typically bred but at a lower rate than dominants. This difference in reproduction may be attributed to intrasexual competition manifested through direct interference by dominant females through subordinate evictions, infanticide and the abandoning of subordinate litters. We argue that differences in reproductive regulation within mammalian co-operative breeding systems may be explained by differences in the mating strategy (inbreeding versus outbreeding) and the probability that subordinates in obligate outbreeding species will encounter unrelated opposite-sex partners. Received: 19 April 2000 / Accepted: 17 July 2000     

Reproductive performance in lesser snow geese: are two parents essential?

Summary The roles of male and female lesser snow geese (Anser caerulescens) in offspring care are well documented, but we know little about flexibility in these roles and how essential they are for offspring survival. We asked whether uni-parental care was adequate, which sex was required at various stages of the reproductive cycle, and what the costs and consequences were of variable amounts of parental care. We found that two parents were important in acquiring nest sites and producing clutches. Widows losing mates during the latter part of laying or in early incubation experienced similar rates of success in hatching clutches to paired females, but males losing mates during incubation experienced total nest failure. Partial clutch loss, hatch loss, intraspecific nest parasitism, duration of incubation periods and gosling weights at hatch did not differ for pairs or widows. In 1983 at La Pérouse Bay, Manitoba, Canada, widows and pairs had similar incubation behaviour, but widows were harassed more and spent more time in full alert posture while on their nests. In 1952 and 1953 at Southhampton Island, Northwest Territories, widows were significantly lighter in body weight prior to hatch than paired females. Thus while widows can bring clutches to hatch successfully, the loss of mates may result in additional physiological costs. Although all possibilities have not been tested experimentally, it appears that costs to uni-parental care up to hatch are not significant. Data collected so far on consequences of uni-parental care provided during the post-hatch period are equivocal, as in one year survival of goslings from single parent broods seemed poor and in another it did not appeart to differ from pairs. The minimum amount of parental care required to raise snow goslings from hatch to recruitment has yet to be determined.