Increase In Shell Length Research Articles

Temperature and salinity limits for growth and survival of some planktonic foraminifers in laboratory cultures

The biological response to extreme temperatures and salinities is investigated in the laboratory for seven species of planktonic foraminifera: Globigerinoides sacculi/er (Brady), Globigerinoides ruber (d'Orbigny), Globigerinoides conglobatus (Brady), Globigerine/la siphonifera (d'Orbigny), Orbulina universa d'Orbigny, Neogloboquadrina dutertrei (d'Orbigny) and Globorotalia menardii (d'Orbigny). When one of the vital processes, food acceptance, growth or reproduction is inhibited by a culture variable, the absolute survival limit is reached. The measured in vitro temperature ranges compare well with the global temperature distribution patterns of these species, suggesting that this parameter plays a major role in their biogeographical distribution. The salinity ranges that are tolerated in laboratory cultures exceed the range encountered in modern oceans. Thus salinity does not limit the distribution of the species investigated herein. In general, larger mean final shell sizes are attained and the total shell length increase is larger at optimum temperatures and salinities than at extreme culture conditions, but the differences were not always statistically significant. Marginal temperature and salinity conditions do not induce contained growth in expatriated specimens. Under extreme culture conditions, the relative frequency of the different shell morphologies is altered relative to normal conditions. Abnormal phenotypes are more frequent under normal conditions and the normal morphology is found more often under extreme conditions. As opposed to previous reports, the frequency of kummerform chambers generally decreases toward extreme temperature and salinity culture conditions, indicating that kummerform phenotypes are not indicative of environmental stress. The incidence of sac-like chambers in G. sacculi/er and the formation of spherical chambers in adult 0. universa decrease toward extreme temperature and salinity culture conditions, demonstrating that maturation is suppressed in stress situations. SEM investigations show that changes in shell porosity are correlated with treatment variables in culture. The highest porosities are attained at higher temperatures and lower salinities. Generally, an increase in total porosity is achieved by an increase of the pore area accompanied by a reduction of the pore density. The in vitro experiments explain the changes that occurred in the Pleistocene foraminiferal assemblages from the Red Sea around 18 thousand years ago and earlier. During glacial periods, salinity approximated or even exceeded the upper thresholds that were tolerated under laboratory conditions. Under these circumstances, species disappeared from the water column. The order of disappearance as recorded in the sediments may be explained with the upper salinity limits found in this study. Also, the recurrent shifts of dominance between G. sacculi/er and G. ruber are well documented for this fossil assemblage. The present experiments support the conclusion that salinity is the driving mechanism behind this phenomenon. Observations in modern oceans suggest that the fertility of the water mass is probably also an important factor behind the shifts of dominance between G. sacculi/er and G. ruber.

Heterozygosity and growth in transplanted mussels

Growth comparisons were made involving mussels (Mytilus spp.) collected from five different localities in Britain in 1980–1981. Two of the localities, Mumbles, South Wales, and Bude, Southwest England, have pure populations of M. edulis and M. galloprovincialis, respectively. The other three, Whitsand Bay, Southwest England, Croyde Bay, Southwest England and Robin Hood's Bay, Northeast England, have hybrid populations with both M. edulis and M. galloprovincialis ancestry. To make growth comparisons, mussels from different populations were mixed in oyster nets and transplanted to three different localities. After periods of transplantation varying between several months and one year, growth was assessed by measuring increase in shell length or dry body weight. Starch-gel electrophoresis was used to assay variation in the transplanted mussels at three allozyme loci partially diagnostic for M. edulis and M. galloprovincialis. The results provide evidence of small growth differences between populations and between allozyme genotypes within populations. These differences accounted for no more than a few percent of the total variation in growth between mussels. Statistically significant results were obtained, but were frequently found not to be reproducible. There is no clear evidence of a growth difference between M. edulis and M. galloprovincialis. Allozyme heterozygotes appear to have growth rates intermediate between allozyme homozygotes; this study thus fails to provide evidence for overdominance with respect to growth rate.

Life history of the golden ring cowry Cypraea annulus (Mollusca: gastropoda) on Okinawa Island, Japan

Two mark-recapture studies, regular population censuses, field observations, and laboratory culture were used to study the life history of the tropical marine gastropod Cypraea annulus Linnaeus, 1758 from Cape Maeda, Okinawa Island, from April 1984 to March 1986. In the field, the average rate of increase in shell length of marked juvenile snails was 1.0±0.3 mm wk-1 (N=13), with a maximum of 1.5 mm wk-1 (initial shell length 10.6 to 17.2 mm). In the laboratory, the maximum growth rate of juveniles was 3.0 mm wk-1 with food ad libitum. Snails with primordial teeth on the shells grew at a rate of 0.1 to 0.5 mm wk-1 for about 2 wk. The adults continued to grow at a similar rate for an additional 3 to 6 wk, and ceased detectable growth when some females started spawning egg masses. In the littoral zone on Okinawa Island, snails reproduced throughout the year. Egg masses brooded by three females (shell length 17.4 to 21.3 mm) in the field contained 90 000 to 133 000 ova. In the laboratory, brooding periods of three females lasted 6,8, and 9 d. The estimated average frequency of spawning was 5 egg masses female-1 yr-1. The mean shell length of adult females (20.3 mm) was significantly larger than that of adult males (19.6 mm). The life-history strategy of C. annulus is characterized by rapid growth, high fecundity, and repeated spawning throughout the year.

Food availability controls seasonal cycle of growth in Macoma balthica (L.) in San Francisco Bay, California

A 2-yr field study of growth in the bivalve Macoma balthica (L.) at four locations in San Francisco Bay, California, U.S., showed that the timing and rate of growth (increase in shell length) were related to food supply. This clam feeds on both planktonic and benthic microalgae, depending on availability. Growth was apparently food-limited during some months, during one year more than the other, and at some locations more than others. Tissue-weight changes were also related to food availability. The heaviest animals were found in that year and at those locations with the highest chl a concentrations. Tissue-weight gains usually coincided with increased shell-growth rate or with reproductive development, although some large animals showed weight gain independent of both of these factors during periods with mid-range chl a levels. Weight losses coincided with spawning or periods of low growth rate, except at one station where, during a period when most animals were reproductively ripe, food concentrations were high, and shell growth was rapid, animals lost weight. This study failed to show a relation between salinity and the timing or rate of change of either shell length or tissue weight. The mild temperatures (10–23 °C water temperature) of the area studied resulted in no growth inhibition due to low temperature, but there was some indication that the high air temperatures found in these intertidal areas limited growth rates.

Reproduction, juvenile growth, consumption and the effects of starvation upon the South China Sea whelk Hemifusus tuba (Gmelin) (Prosobranchia: Melongenidae)

The South China Sea whelk, Hemifusus tuba (Gmelin, 1791) (Melongenidae), is a predator of bivalves. This paper describes copulation, egg capsule laying, egg capsule structure, and hatchling morphology. Hatching took place 89 days post-laying at 21 ± 2°C. Hatchlings are born at a mean shell length of 5.53 mm and a total wet wt of 0.025 g and almost immediately commence feeding on living bivalve tissue. Growth of the juvenile has been followed for 62 wk post-hatching and can be divided into four phases. The first phase (Weeks 0–10) was a period of dramatic shell growth in length (from 5.53 to 28.68 mm) with some increase in wet tissue wt to 0.119 g after 8 wk and 0.750 g after 12. In Phase two (Weeks 10–20), growth proceeded at a slower rate to a shell length of 37.35 mm and the wet tissue increased to 1.489 g. In Phase three (Weeks 20–42), shell length and wet tissue weight remained relatively constant but total weight increased, suggesting that the shell was gaining weight but not length. This growth check at least in length and tissue weight appears to be endogenous. In Phase four (Weeks 42–62), growth in all parameters resumed and it is believed that following Phases 1–3 (essentially juvenile growth characteristics) adult growth will be a typical balance between somatic and gonadal growth. Adult consumption rates are ≈4% wet tissue wt · day −1. In the 4-wk old juvenile, daily consumption rates were calculated to be 36.51% wet tissue wt. Estimates of consumption ·g total wet wt. −1 for Week 2, however, were 26.89%. Using these data for an estimate of consumption/g wet tissue wt at Week 2, a figure of 92% is obtained, i.e., 2-wk-old H. tuba hatchlings ate virtually their body weight each day. Although this may be an over-estimate, it would help account for the dramatic increases in shell length up to Weeks 10–12. Following Week 2, consumption values progressively decreased to typical adult consumption rates of ≈3–4%. The effects of starvation upon H. tuba juveniles are typical, all parameters of growth declining proportionately. There was some evidence of sustained tissue weight increases but not shell growth, implying direct absorption of DOM. Surprisingly, moreover, no mortality took place until Week 27, and three animals survived 39 wk without food. In comparison with data from other predatory snails this is very long (especially for a juvenile). It is concluded that H. tuba is an opportunistic predator of shelf bivalves. The growth plan suggests urgent feeding to build up shell size, presumably to reduce predation pressure and that only later is the shell filled up and strengthened. Internal fertilization, the laying of egg capsules on the shells of others, rapid growth and an ability to survive long periods of starvation all can be used to explain the success of these whelks.

Increase in shell length as a measure of production and ingestion of Mytilus edulis L.

In short term experiments it is found that the shell growth of the mussel Mytilus edulis L. is significantly correlated to production and biodeposition and defaecation. Under constant environmental conditions the individual variation in partitioning of ingested carbon into production, respiration, excretion and defaecation is very small, and the ratios between ingestion and production and ingestion and defaecation are nearly constant. Shell growth of M. edulis may thus be used as a direct measure of production and ingestion within a short time scale.

Growth in length of Mytilus edulis L. fed on different algal diets

Mytilus edulis L. was fed on different algal diets and the increase in shell length was measured every 12–24 h. The mussels respond within 12 h to major changes in the diet. When pre-starved mussels were fed every 24 h with monocultures of Tetraselmis suecica (Kylin) Butch, there was a pronounced lag period followed by a linear increase in shell growth rate. When both pre-starved and pre-fed mussels were fed on equal rations of T. suecica with concentrations ranging from 2.5 to 10.0 × 10 7 cells · 1 −1, the growth rate levelled off at about the same rate. Within the same range of concentrations there was a linear correlation between final growth rates and algal cell concentration. Feeding with monocultures of Isochrysis galbana (Parke) or Thalassiosira pseudonana Hasle et Heimdal (Hustedt) gave approximately the same shell growth as with Tetraselmis suecica alone, while combinations of these three algal species produced significant synergistic effects. When filtrate only from T. suecica cultures was supplied to the mussels there was a rapid initial stimulation of the shell growth. Centrifugated cells of T. suecica which were resuspended in filtered sea water, homogenized and sonicated to rupture the cells, gave 13% less growth than with untreated cells ( P < 0.05). The use of the accurate laser diffraction method for length growth measurements may greatly reduce the time and effort involved in growth experiments.

Growth of Mytilus edulis in net bags transferred to different localities in a eutrophicated Danish fjord

The growth rate has been measured in Mytilus edulis transferred in net bags to seven localities in the brackish Danish fjord, Limfjorden, in which certain areas are heavily eutrophicated. The increase in shell length, shell weight and flesh body weight was measured after growth periods of 14–18 days. The increase in, e.g., flesh dry weight ranged from twice the start weight to a four-fold increase of the start weight. The net growth efficiencies were estimated to be between 54 and 73%. Algal concentration was in no case the limiting growth factor, but low growth rates were observed in areas with seasonal oxygen depletion and release of toxic H 2S from the sediments. It is suggested that measurements of actual growth in M. edulis can be a useful technique in the study of biological effects in marine recipients.

Growth and energy balance during the larval lives of three prosobranch gastropods

Larvae of most marine invertebrates postpone metamorphosis in the absence of a suitable environment for the adult stage. Larvae of three marine gastropod species, Ilyanassa obsoleta (Say), Crepidula fornicata (L.), and Bittium alternatum (Say), differed in the potential durations of their delay periods and in their ultimate fates in the absence of preferred substratum for metamorphosis in the laboratory. Experiments were conducted to test the hypothesis that differences in the delaying capabilities of the three species result from differences in the magnitude of metabolic adjustments made during the delay period. Carbon and caloric balances were calculated for larvae of Ilyanassa obsoleta before and after their attainment of competence, using data on feeding rates, respiration rates, and retention efficiencies. An excess of carbon and energy intake over expenditure was calculated in all experiments. As predicted from those calculations, but not from measurements of shell length increase, tissue biomass of I. obsoleta increases at a constant rate throughout larval life. Similarly, growth rate of larvae of Crepidula fornicata does not decline with the onset of metamorphic competence. Larvae of Bittium alternatum also show substantial growth during delay of metamorphosis. Morphological differentiation continues during the delay periods of Ilyanassa obsoleta and Crepidula fornicata. Therefore, there is no indication that changes in energy balance directly limit the potential duration of the delay period in these species. However, these data suggest a relationship between growth rate prior to the onset of competence and the potential duration of the delay period. The hypothesis is presented that there may be a program for larval development with a genetically fixed endpoint and that potential duration of the delay period may be determined by the rate at which larvae progress through this developmental program. Ecological factors potentially operating to select for differences in delay capabilities among species are discussed.

Laboratory culture of the larvae of Conus textile Linné (Gastropoda: Toxoglossa)

The larvae of the Indo-Pacific gastropod Conns textile Linné were reared in the laboratory from hatching through metamorphosis. Larvae fed a mixed phytoplankton culture of Isochrysis galbana and Phaeodactylum tricornutum grew at a rate of 0.06 mm/day and began metamorphosing 16 days after hatching. Unfed control cultures yielded no metamorphically competent larvae. Laboratory-reared larvae metamorphosed spontaneously on the walls of the fïberglass rearing tanks when their average shell length was 1.5 mm. Measurements made on field-collected Conns textile juveniles indicate that the larvae metamorphose at the same size in the laboratory as they do in nature. Rates of larval shell length increase and dry weight increase paralleled each other until metamorphosis. At this point, shell growth slowed while dry weight increased suddenly. It is suggested that this weight increase reflects calcification and strengthening of the fragile larval shell upon entering the benthic environment.