Ovarian development and spawning in relation to the moult cycle in Northern krill, Meganyctiphanes norvegica (Crustacea: Euphausiacea), along a climatic gradient

Adaptive processes linked to reproduction were studied comparatively for three populations of Northern krill, Meganyctiphanes norvegica (M. Sars, 1857), sampled during winter and summer cruises in the Clyde Sea (W Scotland), the Kattegat (E Denmark), and the Ligurian Sea (NW Mediterranean). The aim was to investigate the functional relationship between egg production and moulting under contrasted climatic and environmental conditions. A staging system for female sexual development established for live krill was complemented by a histological study of the ovary at various developmental steps. During the reproductive season, all adult female krill were engaged in cyclical egg production. During experiments, female krill released one batch of mature oocytes in one or two spawning events. The ovary of postspawn female krill still contained developing oocytes for another egg batch. In the non-reproductive period, all female krill had a resting ovary. Ovarian structure and pattern of egg production were identical in the three populations, but seasonal timing of egg production was different. The model proposed for the Ligurian population of the annual cycle of ovarian development can be extended to the other two populations, taking into account the seasonal characteristics of each site. Random field samples were staged simultaneously for moult cycle and for sexual development. Moult stages and the seasonal variation of the intermoult period were studied for the Kattegat population using multi-year data and compared to data obtained during summer/winter cruises in the Clyde and the Ligurian Sea. At the three sites, intermoult period was shorter and temperature-dependent during the reproductive period, concurrent with the season of greatest food availability. During most of the year and the period of sexual rest, moulting activity was reduced. The relationship between spawning and the moult cycle was studied comparatively for the three populations. Eggs were released during the premoult phase of a “spawning moult cycle”, in one or two spawnings associated with apolysis and Moult Stage D1, respectively. Yolk accumulation for the next egg batch was completed during an alternating “vitellogenic moult cycle”. A model for the timing of cyclical egg production in relation to moulting, as proposed for the Kattegat, can be extended to the other populations, taking into account intermoult period variation with temperature. Temperature appeared to be the principal environmental factor controlling growth (through moulting) and egg production during the reproductive season, in connection with favourable trophic conditions. Received: 22 December 1997 / Accepted: 29 August 1998     

Laboratory observations on spawning,brood size and egg hatchability of the Antarctic krill Euphausia superba from Prydz Bay,Antarctica

Forty-three female Euphausia superba were collected from three sites in Prydz Bay, Antarctica in January 1985. Most gravid females took 3 to 14 d to spawn after capture and some less mature females released eggs after 21 d. Most females spawned only once; overall mean brood size was 2 809 eggs and mean hatchability for eggs from the premoult females was 69.7%. For seven females spawning a second time, overall mean brood size was 597 eggs. Mean hatchability for second-spawn eggs from five premoult females was 67.1%. Possible origins of the second-spawned eggs were small numbers of matured eggs left in the ovaries after the first spawning or eggs developed from those of peripheral nucleolus and vitellogenic stages. Throughout the 8 wk of observations, there was no apparent development of eggs in females which had released all their eggs at one spawning.     

Moult in relation to some aspects of reproduction and growth in swarms of Antarctic krill,Euphausia superba

In a 14-d period 38 swarms of Antarctic krill,Euphausia superba Dana, were sampled in an area 55.5 x 55.5 km to the southwest of Elephant Island, at the north of the South Shetland Islands. Moult stage, maturity stage, and size of ca. 100 krill from each swarm were measured. Each of the characteristics varied greatly between swarms. Moulting krill were found in most swarms, but in one swarm all of the krill were just about to moult. Ways in which moulting may act as a possible sorting mechanism are discussed. Data for all the analysed krill (ca. 3000 specimens) were used to investigate the interdependence of moult rate, sexual maturation and growth. While all immature krill moulted at approximately the saine rate in the study, there were significant differences in the moulting rates of mature male and female krill. Gravid female krill continued to moult, although less frequently than mature males. As a consequence males had to attach spermatophores to females after each moult. It is likely that variation in moult rate of females and males was related to the energy expenditure required for ovary development in females and spermatophore production and searching behaviour in males. Spawning and moulting were only partly coupled in gravid females. Spawning appeared to take place predominantly during Moult Stage D₂. There was no evidence of intermoult growth by intersegmental dilation.     

Contribution of moulting and eggs to secondary production in Nyctiphanes australis (Crustacea: Euphausiacea)

This study was designed to assess the contribution of moulting and eggs to production of the euphausiid Nyctiphanes australis G. O. Sars. For this purpose, live specimens were collected from Storm Bay, south-eastern Tasmania, between August and December 1981, while preserved samples, collected between February 1980 and February 1981, were also examined. The intermoult period of N. australis increased exponentially with increase in body length and weight. Larvae moulted approximately every 2.5 to 3 d and adults every 4 to 5 d at 15°C. A decrease in temperature from 15° to 10°C resulted in the intermoult period almost doubling. The mean weight of exuviae produced represented nearly 6% of the body dry weight of the individual. Continuous maturation of ova was observed, with an individual female capable of releasing a total of 1 100 eggs in a lifetime. These are deposited as a series of batches into a pair of external ovisacs every 30 d. The size of the batch of eggs was dependent on the size of the female. Moulting of euphausiids forms a significant contribution of organic matter to detrital food webs. A value of 42.01 mg m^-3 yr^-1 was obtained for the production of exuviae. Egg production was calculated to be between 1.41 and 4.22 mg m^-3 yr^-1. Production and mean annual biomass of N. australis was previously calculated as 78.29 mg m^-3 yr^-1 and 5.39 mg m^-3, respectively. Thus, the total production integrated for the whole of Storm Bay was 125 mg m^-3 yr^-1 or 2 309 tonnes dry wt yr^-1, representing an overall P:B ratio of 23.1.     

Long-Term observations on the moulting frequency of the shrimp Lysmata seticaudata

The effects of body-size and temperature on moulting frequency of the shrimp Lysmata seticaudata Risso were examined under controlled laboratory conditions. Shrimp ranging in weight from approximately 0.4 to 1.14 g and maintained at 17°C exhibited intermoult periods of similar duration (20 d). On the other hand, small individuals (0.23 g) held at the same temperature moulted on the average every 14.5 d. Over a temperature range from 8° to 20°C mean intermoult periods were inversely and linearly related to temperature; an increase of 1 C⁰ resulted in a decrease in the intermoult period of approximately 1.5 d. Although temperature acted to regulate the intermoult period of each shrimp in increments of whole days, it had little effect on the time of moulting within any 24 h period, since moulting occurred more than 93% of the time between 18.00 and 08.00 hrs. The night-time moulting pattern also tended to be most pronounced at lower temperatures (8° and 13°C) and in larger individuals. Possible factors controlling this phenomenon and its occurrence in other crustacean species are discussed.     

Effects of seasonality and population density on the reproduction of the Indo-Pacific echinoid<Emphasis Type="Italic"> Echinometra mathaei</Emphasis> in Kenyan coral reef lagoons

Reproduction in the widely distributed tropical sea urchin Echinometra mathaei (de Blainville) was examined in three Kenyan reef lagoons that differed in substrate cover and E. mathaei population density. Histological examination of the gonads and gonad index measurements for 3 years showed a seasonal reproductive cycle with gametogenesis commencing in July, when temperature and light are at their lowest, and spawning commencing in December and peaking in February to May, when temperature and light reach their annual maxima. Monthly gonad indices correlated significantly with seawater temperature and light intensity. Male urchins had mature gametes for a longer period (8 months) than females (6 months), possibly an adaptive strategy that increases the probability of fertilization. Lunar periodicity was not observed, as male and female gonads were full of gametes on all days of the lunar cycle during the period of spawning. The peak in spawning activity coincides with the peak in phytoplankton abundance, which could ensure high food availability for the planktonic larvae. Gonad weights were significantly higher relative to urchin weight at the reef having the largest mean sizes and lowest population of urchins, indicating availability of food resources for growth and reproduction. E. mathaei at the reef with the highest density had the smallest urchins and high relative gonad sizes, indicative of a tradeoff between growth and reproduction when food is limited.Communicated by O. Kinne, Oldendorf/Luhe     

Reproductive trade-off in male Antarctic krill,Euphausia superba

Freshly caught male and female Euphausia superba from the same swarm exhibited different rates of mortality subsequent to capture. Mortality was significantly higher for reproductive males (100%, n=68) than for females (3%, n=186) within the first 3 d of capture. Total lipid and triacylglycerol levels in male, female and juvenile Euphausia superba were analysed and compared. All reproductive male krill analysed from this swarm had low lipid levels (1 to 3% dry weight) with negligible triacylglycerol stores (0 to 2% of total lipid). Somatic lipid stores in female and juvenile krill ranged from 8 to 30% of which up to 40% was triacylglycerol. The levels of algal sterols in the digestive gland of males, females and juveniles indicate that all krill had been feeding recently. An analysis of the sex ratio of krill catches derived from data collected over seven summers from the Prydz Bay region showed a decrease in the proportion of males with increasing size. There was a sharp decline in numbers of male krill once they attained a length of 51 to 55 mm. Low lipid levels in redroductive male krill may be due to reproductive costs. The resulting low storage-lipid levels are accompanied by high mortality in male krill.     

The reproductive biology of a new species of sea cucumber, Holothuria (Mertensiothuria) arenacava in a Kenyan marine protected area: the possible role of light and temperature on gametogenesis and spawning

The sea cucumber Holothuria arenacava was discovered in the Mombasa marine reserve in 1997 and described by Samyn et al. (2001). The reproductive biology of this holothurian was investigated in order to (1) characterize the reproductive pattern, (2) examine the relationship among environmental parameters including temperature, light and lunar period, and (3) examine the relationship between the reproductive pattern and feeding of this new species. The gonad index method and microscopic examination of gonads was used to analyze samples collected for a period of 13 months. H. arenacava displayed an annual reproductive cycle with gametogenesis commencing in July during the south-east monsoons, when temperature and light intensity are lowest along the Kenyan coast. Gonad growth peaked in February–March at the end of the north-east monsoons when temperatures and light reach their annual maxima along the Kenyan coast. The higher correlation between light intensity and gonad growth (r=93) than temperature (r=0.71), coupled with the fact that temperatures continued to drop for a month after gametogenesis had already commenced, suggests that light intensity and not temperature is the cue for the onset of gametogenesis in this species. Spawning was synchronized between females and males and occurred during a short period between March and May (inter-monsoonal period) when both temperature and light intensity decrease along the Kenyan coast. Male and female gonad indices showed significant variation with lunar day and no lunar periodicity was observed in this sea cucumber. The sex ratio of the population of H. arenacava was skewed towards significantly more females than males, and females were significantly larger and had larger gonads and gonad indices than males. These life history strategies including spawning during a short discrete period, more and larger females that have larger gonads (i.e., typically more fecund), and spawning just prior to the peak in phytoplankton concentrations, a time that is probably more favorable for larval development, may serve to increase the reproductive success of this sea cucumber.     

Reproduction and condition of female Octopus mimus (Mollusca: Cephalopoda)

The relationship between reproduction and condition was studied in a 15 mo sample of 919 maturing, mature and post-spawning female Octopus mimus (388 to 3714 g) caught in Iquique (North Chile). O. mimus is a semelparous species, with reproduction taking place all year round. Investment in reproductive tissues was, on average, 9.9% of mature female body weight, independent of season. However, somatic growth during maturation was dependent on season and varied between 26 and 63% of the whole-body growth in weight. The condition of females did not vary markedly until spawning, although seasonal variations were apparent, winter being the most unfavourable. Condition deteriorated dramatically after spawning, during parental care of the eggs. During this period, somatic-tissue depletion, mainly from the muscles, was >25% of the total body weight of mature females. The fecundity of O. mimus was probably limited by the costs associated with parental care of the eggs.     

Mating behaviour of Macrophthalmus hirtipes (Brachyura: Ocypodidae)

 We examined the mating behaviour of the New Zealand ocypodid crab Macrophthalmus hirtipes in the laboratory between February and June 1998. This species has a discrete breeding season. Mating and moulting were not linked and only intermoult females with mobile gonopore opercula were attractive to males. Allometry and compatibility of gonopods and gonopores of different-sized crabs was investigated. Under laboratory conditions, the opercula of intermoult females remained mobile on average for 11.4 d, but the duration of receptivity did not appear to be under female control. The operational sex ratio in the laboratory fluctuated greatly, but was always male-dominated. During the period of opercular mobility, females mated many times with several different males. Matings in the absence of burrows were relatively short (mean duration = 23 min, max. = 122 min) and the mating behaviour of M. hirtipes lacked courtship and mate-guarding. Males used a search-intercept method to acquire mates, with very low levels of intrasexual competition. There was no evidence of mate preference in M. hirtipes, and males spent just as long mating with ovigerous females as with non-ovigerous ones. Although M. hirtipes has ventral-type spermathecae, as do several other ocypodid crabs, it is unclear whether this promotes last-male sperm precedence. The role of burrows in modifying the mating behaviour of M. hirtipes in the field remains to be established. Received: 7 January 2000 / Accepted: 5 June 2000     

Patterns of the electric organ discharge during courtship and spawning in the mormyrid fish,Pollimyrus isidori

Summary Pollimyrus isidori's electric organ discharge (EOD) is of the pulse type. Patterns of EOD intervals were investigated prior to, during and following spawning behaviors as related with overt behaviors, and with the sound production by the nestbuilding male. Prior to the time of reproduction, isolated and socially interacting fish (n=15) showed characteristic discharge interval patterns for resting, swimming, probing, hovering and hiding activities. Males (n=8) and females (n=6) did not differ in their mean EOD repetition rates during resting (11.6±2.5 Hz), nor Short Bursts/min (less than 20 intervals of 8–13 ms). In interacting fish Long Bursts (greater than 20 intervals of 8–13 ms, lasting for more than 300 ms) were observed only during the attack and bite sequence. A pursuing fish displayed a rapid alternation of Long Bursts with Discharge Breaks (300–1000 ms silence) during the chase behavior. Avoidance behavior which followed from several attacks was correlated with a Medium Uniform Rate (8–12 Hz) normally lasting for 20 to 60 s, or a Discharge Arrest (silence greater than 1 s) in the submissive fish. The nocturnal courtship behavior began soon after dark (1900 h). Spawning typically started 2 to 5 h after dark, continuing for 2 to 6 h until about 0200 h. During courtship and spawning the female's brief visits (15–25 s) to the male's territory recurred every 30–60 s. At all other times the female was aggressively excluded from the nest region. Courtship and spawning behaviors are described along with the electrical displays identified from 19 spawnings in three fish pairs (from a total of 37 spawnings in 4 males and 4 females). Just prior to the onset of courtship behavior, with male territorial aggression beginning to decline, females switched from a Medium Sporadic Rate pattern (resting and hiding patterns; 13 Hz) to a Medium Uniform Rate pattern (6–8 Hz) while still in their hiding area. Females continued to display this uniform rate throughout the courship and spawning period, including the courtship and spawning bouts when Discharge Breaks or Arrests also occurred. This persistance distinguishes the courtship pattern from the similar avoidance pattern (see above). The male courtship and spawning EOD pattern was similar to the female's and unique for a territorial male. He switched from a High Sporadic Rate (swimming EOD pattern; about 18 Hz) to a regularized Medium Uniform Rate (about 9 to 11 Hz) only during courtship and spawning bouts, including 1–3 EOD Breaks during Vent-to-Vent coupling (average interval: 272±71 ms, n=37). No sooner had the female left the spawning site than he resumed displaying a High Sporadic Rate. This temporal correlation of reproductive behaviors with electrical displays suggests their instrumental role in mutual acceptance of mates. Males showed their sex-specific type of EOD phase-locking, the Preferred Latency Response, only during the first few hours of entry of a fish in their tank. Two females with EOD waveform features more typical of males also spawned repeatedly; waveform does not appear to be critical. Males stopped their nocturnal sound production for the later part of courtship and the whole spawning period. Except for infrequent attacks on the female between spawning bouts, the male did not resume singing until the end of spawning when all eggs were shed (around 0200 h); from this time on the male sang until dawn. The sequencing of the three acoustic elements (moans, grunts, growls) are described. A catalogue of discharge patterns correlated with overt behaviors (Tables 1, 2), and an integrated summary time table of P. isidori's complex reproductive behavior are presented.     

Seasonal cycle of gonadal development and serum levels of vitellogenin of the red porgy, Pagrus pagrus (Teleostei: Sparidae)

Histological examination of gonads of female and male red porgy, Pagrus pagrus, reared in captivity, was carried out in order to describe the main gonadal changes related to gametogenesis and the seasonal changes of environmental factors. The gonadosomatic index (GSI) and the concentration of serum vitellogenin (VTG) were also determined. The frequency distribution of gonad development stages and the GSI and vitellogenin concentration during the annual cycle indicated the separation of the female and male reproductive cycles into three main periods. The autumn period when gametogenesis begins (October-November), the period of exogenous vitellogenesis (December-March) or spermiation (December-March), and the spawning season (March-May). The spawning period coincided with an increase in temperature (15-19°C) and daylength. Serum levels of vitellogenin rose significantly in January, reached a peak at the beginning of the spawning period (March, 405.5 µg ml^-1) and remained high until the end of the spawning period (May).     

Does the spawning of Calanus finmarchicus in high latitudes follow a reproducible pattern?

In the spring of 1989, an experimental study of the spawning behaviour of Calanus finmarchicus was carried out in Malangen, northern Norway. Here, a single cohort of females reproduce from mid-March to May, approximately coinciding with the wax and wane of the spring phytoplankton bloom. An evaluation of population characteristics such as the proportion of adults, sex ratio, as well as gonad maturation and daily productivity of the females clearly reveals three phases within the population's reproductive period. In between incline and decline, the highest spawning rates (on average >20 eggs female^-1 d^-1, equivalent to 5.7% body C d^-1) occur after the males have disappeared from the population and almost all females have mature gonads. During this period, the ratio of adults to copepodid Stage Vs changes from dominance of adults to that of CVs. Although first egg production was observed prior to the phytoplankton increase, it is suggested that the onset of the phytoplankton spring bloom in the first few days of April enhances the final maturation of ovaries in the females and therefore triggers the onset of the main spawning period. The clutch sizes (max. 95 eggs clutch^-1) vary with the age of the females, while the spawning frequencies depend on the available food quantities. The overlap of an estimated minimal 4 wk spawning period for the individuals leads to a main reproductive phase for the population of ca. 3 wk, during which time mean clutch sizes and spawning frequencies are maximal (highest average clutch size: 70 eggs female^-1 clutch^-1, 100 to 60% of the females spawning). This period ends before the end of the phytoplankton bloom. Calculated by stepwise interpolation and summation of the mean daily egg production in the population, an average female produced ca. 600 eggs during the spring bloom in Malangen 1989. We suggest that reproduction and population development of C. finmarchicus in spring follows a reproducible pattern for a given temperature regime and non-limiting food conditions. In the case of clearly identifiable cohorts, it seems possible to trace the state of reproduction by evaluating population parameters.     

Seasonal variations in biochemical constituents during the reproductive cycle of the female dog cockle Glycymeris glycymeris

In an attempt to describe the biochemical events associated with the main stages of the annual and reproductive cycles of the female dog cockle Glycymeris glycymeris L., we studied seasonal variations in the various stages of oocyte development of the ovaries, and the glycogen, total protein and total lipid content of five body tissues – adductor muscle, foot, tunic coat, visceral mass and mantle. From November 1991 to November 1994, microscopic examination of the ovaries and measurement of the tissue concentrations of glycogen, total proteins and total lipids in these five body tissues were made monthly on ten female dog cockles originating from the sea area around Douarnenez (south Brittany, France). Morphological studies revealed that in the population investigated the annual cycle is characterised by three major periods: a first period of vitellogenesis extending from February/March to April/May and preceding a spawning in spring; a second period of vitellogenesis extending from May/June to September/October and leading to either no spawning, a single autumnal spawning event, or to two spawning events in summer and autumn; and a third period extending from October/November to February/March and characterised by a high level of oocyte lysis. In the muscular body tissues of the dog cockle, i.e. the adductor muscles, the foot and the tunic coat (the muscular envelope containing the visceral mass), the concentrations of glycogen, total proteins and total lipids underwent very similar variations during the annual cycle. During each stage of vitellogenesis, a typical glycogen–protein–lipid sequence was observed in the muscular tissues that was characterised firstly by a peak of glycogen concentration 2 to 3 mo before spawning, followed by a peak in total proteins 1 mo before spawning, and finally by a peak in lipid content just before spawning. A similar glycogen–protein–lipid sequence was also recorded in the first half of the winter period. However, these events were followed by general atresia affecting all oocytes in the gonad. Maximum energetic value of biochemical constituents in females coincided with peaks in lipid content in the visceral mass and mantle. These biochemical events occurred principally immediately before and at the end of oocyte lysis (December/January). A drop in the total energetic value, affecting mainly the visceral mass and the mantle, was recorded each year during the period January to March, coinciding with the period of shell growth in this species. Our data clearly indicate that in female G. glycymeris all muscular tissues contribute to the storage of glycogen and proteins, and suggest that glycogen may be the source of energy triggering vitellogenesis. Biochemical and microscopic observations revealed that oocyte development takes place during the first half of winter, but that these oocytes undergo atresia in December/January. The metabolites produced from oocyte lysis could contribute to somatic growth, which occurs in late winter. Received: 3 March 1997 / Accepted: 23 July 1997     

Nucleic acids and growth of larval and early juvenile spider crab,Hyas araneus

The spider crabHyas araneus (L.) was collected from the North Sea in winter 1986–1987 and reared in the laboratory from hatching of the Zoea I (ZI) through the first juvenile instar (CI). Within a given moult cycle, individuals of the same age were sampled in intervals of 2 (ZI, ZII, CI) or 3 d (megalopa) for analysis of dry weight (W), carbon (C), nitrogen (N), hydrogen (H), protein, DNA, and RNA. Lipid was calculated from C. Biomass, growth rate and nucleic acid contents showed high variability during each moult cycle and between instars. Instantaneous growth rates of C were high in postmoult and intermoult, and low in the premoult period of each moult cycle. A shift was observed from high rates of lipid accumulation in the postmoult and intermoult stages to proportionally increasing protein accumulation during late premoult (ZI), or throughout a major part of the remaining moult cycle (in all other instars). DNA was accumulated throughout the ZI and ZII instars, but decreased in late premoult megalopa. It increased again from late intermoult through intermediate premoult in juveniles. RNA increased continuously during ZI and ZII, and decreased in the megalopa, almost to levels that had been found immediately after hatching. In juveniles, variation in RNA followed closely those in DNA. Cell multiplication (expressed by DNA increase) dominated over increase in cell size (defined by the C/DNA ratio) during the zoeal instars and in postmoult through early intermoult in the megalopa and CI. When specific (C-related) RNA values and RNA/DNA ratios were compared with instantaneous growth rates in C and N, no general correspondence was detected. The only significant relationship between specific RNA values and instantaneous C or N growth rates was found in the megalopa. The same held for the relationship between the RNA/DNA ratio and growth. Here, in addition to the megalopa, a correspondence with C growth was also found in the CI instar. Our results suggest that variation in nucleic acids may provide useful insights into mechanisms of growth on the cellular level (cell multiplication vs cell enlargement). However, lack of general correlation with variation in growth rates ofH. araneus larvae shows that the use of nucleic acids as a measure of growth is probably based upon too simplistic assumptions; it may not yield reliable predictions, when growth is associated with developmental events.     

Reproductive biology of the antipatharian black coral Antipathes fiordensis in Doubtful Sound, Fiordland, New Zealand

The reproductive biology of Antipathes fiordensis Grange, a species endemic to south-western New Zealand, was followed from April 1994 to May 1995. Ten colonies were individually tagged in Doubtful Sound and sampled on a monthly basis in order to determine their reproductive activity. The fecundity of each of the five tagged female colonies was determined by estimating the total number of polyps per colony from photographs of each colony and by planimetry, the proportion of gravid polyps per colony, and the mean number of oocytes per gravid polyp. In addition, 56 colonies were sampled in March 1995 to estimate the sex ratio, height at sexual maturity, and mean sizes of females and males. A. fiordensis was found to be a dioecious species which, in the absence of gonads in the polyps, has no obvious external morphological differences between the sexes. Broadcast spawning of gametes is the likely mode of reproduction. Gametogenesis began in November 1994 and was highly synchronous within and between colonies, with spawning occurring in March 1995. The sex ratio in adults was 1:1. Colonies reached sexual maturity between the heights of 70 and 105 cm which, based on existing estimates of growth rate, corresponds to a minimum age for sexual maturity of about 31 yr. The largest oocytes measured ranged from 100 to 140 μm in size. Female colonies produced between 1.3 and 16.9 million oocytes, with the larger colonies dominating the reproductive output of the population. Received: 23 June 1997 / Accepted: 1 August 1997     

Reproductive cycle and gametogenesis in the black abalone Haliotis cracheroidii (Gastropoda: Prosobranchiata)

Seasonal changes in gonald size and stages of gametogenesis in the black abalone Haliotis cracheroidii were related to changes in environmental parameters. H. cracheroidii showed an annual reproductive cycle terminating in a synchronized spawning in late summer. Gametogenesis was initiated immediately after spawning. Gametes were present in the gonad through the winter months. Gametogenesis was initiated a second time in the spring months. Maximal gonad growth (to a gonad index of 20%) occurred during summer months prior to spawning. Changes in gonad size andperiods of initiation of gametogenesis revealed no apparent correlation with changes in seasonal water temperature. Changes in gonad size showed no apparent relation to change in day length. Total polysaccharide levels in foot tissue changed seasonally, indicating that food availability is probably not a factor in directly regulating gonad growth. Gonad index data for the chiton Katharina tunicata (collected over a 10 year period) showed no apparent correlation to seasonal change in water temperature.     

Metabolic activity and elemental composition of krill and other zooplankton from Prydz Bay,Antarctica, during early summer (November–December)

Oxygen uptake and ammonia excretion rates, and body carbon and nitrogen contents were measured in krill (Euphausia superba) and eight other zooplankton species collected during November–December 1982 in the Prydz Bay, Antarctica. From these data, metabolic O:N ratios (by atoms), body C:N ratios (by weight) and daily metabolic losses of body carbon and nitrogen were calculated as a basis from which to evaluate seasonal differences in metabolism and nutritional condition. Comparison of the present data with mid-summer (January) data revealed that early-summer E. superba were characterized by higher metabolic O:N ratios (58.7 to 103, compared with 15.9 to 17.5 for mid-summer individuals). Higher O:N ratios of early-summer E. superba resulted largely from reduced ammonia excretion rates and, to a lesser degree, from slightly increased oxygen uptake rates. Body C:N ratios of E. superba were low in early-summer (3.8 to 4.2) compared with mid-summer krill (4.1 to 4.7) due to lowered body-carbon contents in the former (42.6 to 43.6% compared with 43.2 to 47.5% dry weight of midsummer individuals); gravid females formed an exception, since no seasonal differences in body elemental composition were detected for these. No significant changes in water content (75.3 to 81.4% wet wt) and nitrogen content (9.9 to 11.1% dry wt) in E. superba were evident between the two seasons. Seasonal differences in metabolic rates and elemental composition were less pronounced in a salp (Salpa thompsoni), but a higher metabolic O:N ratio occurred in early-summer individuals. Interspecific comparison of the seven remaining zooplankton species studied with twelve species from mid-summer zooplankton investigated in an earlier study indicated that higher metabolic O:N ratios in early-summer are characteristic not only of herbivore/filter-feeders, but also of some carnivores/omnivores. No relationship between metabolic O:N ratios and body C:N ratios was apparent either intraspecifically or interspecifically, within or between early-summer and mid-summer seasons.     

In situ variation in heart rate of the shore crab Carcinus maenas in relation to environmental factors and physiological condition

Heart rate of Carcinus maenas was recorded continuously for two days in situ, together with water temperature, salinity, depth and light intensity. Of each sex, 25 crabs were used and assigned to groups on the basis of size and colour (the carapace changes colour with prolongation of the intermoult phase). Wet weight:dry weight ratios of midgut gland, muscle, gonads and whole body were examined together with midgut gland lipid content and haemolymph protein concentration. Heart rates and wet wt:dry wt ratios for all the tissues examined were higher in early intermoult than in late intermoult stages of the adult C. maenas (P<0.05). Heart rate, lipid content and haemolymph protein concentrations were higher and wet wt:dry wt ratios of midgut gland, gonads and whole body were lower in juvenile crabs than in adults (P<0.05). The relationship between heart rate and wet wt:dry wt of whole body differed among C. maenas in early and late intermoutl. Heart rate was positively correlated with midgut gland lipid content (a Darwinian fitness parameter) in crabs that were in late intermoult. Physico-chemical environmental parameters, sex and colour accounted for 12% of the variation in heart rate of C. maenas recorded in situ. Temperature and prolonged intermoult were the most important factors influencing heart rate. The findings are discussed in relation to laboratory studies of cardiac activity and observed behaviour of C. maenas in the field.