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     

Population dynamics of the commensal spider crab Inachus phalangium (Decapoda: Maiidae)

The ecology of the spider crab Inachus phalangium (Fabricius, 1775) (Decapoda: Maiidae) was studied in the field. I. phalangium inhabits the sublittoral on the sea anemone Anemonia sulcata Pennant. From July 1981 to April 1984 in the Mediterranean (Banyuls sur Mer, southern France) more than 3000 anemones were examined and ca 1800 I. phalangium were found on them. The population dynamics' generation cycles, reproductive activities and the dynamics of the sex ratio were investigated. The density of juveniles (crabs before the pubertal moult) on anemones changed in a yearly cycle from low in the first six months to very high in the second six months. The first occasional young crabs of a generation appeared in March/April (3rd and 4th decapodite stages) on the anemones. Their density increased enormously in the following months. The generation grew gradually on the anemones and moulted into puberty in September-January. Density of adults (crabs after the pubertal moult) on anemones changed in a yearly cycle from low to high from the summer to winter months. A new adult generation was recruited every autumn through the pubertal moult and disappeared in the following summer. Female reproductive activity continued throughout the year. Females carried several broods in succession, but the frequency of breeding females fluctuated on a yearly cycle. The highest percentage of egg-carrying females, i.e. the peak of the reproductive season, lay in the first half of the year. The maximal life span of a generation, from the hatching of the first larvae to the disappearance of the last adults, lasted 1.5 to 2 years. Males moulted into puberty ca one month later than females. The moulting distribution of adult males had roughly the same course as in females. An adult male generation diet out about one to two months before the female generation. Life expectancy was therefore 14 to 17 months for females and 12 to 15 months for males. The sex ratio of juveniles shortly before the pubertal moult was balanced. The sex ratio of adults shifted from 1:1 at the beginning of the reproductive period to ca 1:9 in favour of females at its end.     

A genetic analysis of the pea crabs (Decapoda: Pinnotheridae) of New Zealand

Seven populations of the pea crabPinnotheres atrinicola Page were sampled from around the North Island of New Zealand from February to October 1987, and individuals were scored at 23 presumptive enzymatic loci. For a brachyuran crab,P. atrinicola revealed high levels of polymorphism and heterozygosity. Of the loci scored, phosphoglucose isomerase (Gpi) and phosphoglucomutase (Pgm) were distinguished by high variability ( =0.602 and 0.526, respectively). A clinal variation in electromorph frequency was evident at several loci, and atGpi in particular. Statistical analyses revealed that, despite relatively small genetic distance separation, a high degree of structuring was present between the geographic populations. The degree of population subdivision observed in this study is atypical of brachyuran crabs. It is suggested that the genetic differentiation observed between pea crab populations is maintained by life-history attributes and current movements which restrict gene flow between populations and, to some extent, by random genetic drift.Publication No. 41 from the Evolutionary Genetics Laboratory, University of Auckland     

Population dynamics and reproductive biology of the commensal isopod Colidotea rostrata (Crustacea: Isopoda: Idoteidae)

Colidotea rostrata (Benedict, 1898) is the only known commensal idoteid isopod, living on and mimicking the color of two northeastern Pacific sea urchins of the genus Strongylocentrotus. The population dynamics and reproductive biology of C. rostrata on its host urchins were studied at a low rocky intertidal area in southern California (33°40N; 118°30W) from December 1984 to December 1986. Isopod populations remained relatively stable throughout the 2 yr study, with isopods inhabiting an average of 56.1% of the urchins at 6.1±0.6 (x±2 SE) isopods per urchin. Female isopods reach sexual maturity at a length of 6.8 mm. Fecundity in C. rostrata averaged 11.8±0.9 (x±2 SE) embryos per brood, and increased with female body size. Breeding occurs all year long in C. rostrata, with a main reproductive period between the warmer spring and summer months. Newly released mancas and juvenile isopods were present during all months of the study. C. rostrata differs from the free-living Idoteidae in its smaller maximum size, reduced fecundity, 1:1 sex ratio, and low juvenile mortality. These features may represent adaptations to a commensal life style that reflect a reduced mortality pressure on these isopods.     

Latitudinal variation in the Dungeness crab,Cancer magister: zoeal morphology explained by incubation temperature

The difference in morphology between zoeae of Cancer magister Dana from Alaskan and Californian waters was documented to determine if the morphological variation is attributable to environmental influences. First-stage zoeae from Alaska have significantly longer carapace spines than zoeae from central California. The dorsal, rostral and lateral carapace spines were 14, 14 and 29% longer, respectively, in the Alaskan zoeae. The effect of temperature was tested on zoeal morphology as it is an obvious environmental difference between Alaskan and Californian waters. Ovigerous female crabs collected in southeastern Alaska in 1984 were held at 1°, 5°, 10° and 15° C until hatching occurred. Eggs were sampled seven times during the incubation period, and relative mortality, egg diameter and development stage were measured. All of the crabs and eggs at 1° C died before hatching occurred. Egg mortality averaged less than 2% in the other temperature treatments. Egg diameter increased significantly over the incubation period for all temperatures. Developmental rate of the embryos was inversely related to temperature. Hatching first occurred in 42 d at 15° C, 60 at 10° C and 160 d at 5° C. Newly hatched zoeae were collected and body length, dorsal, rostral and lateral carapace spines were measured. Significant differences existed between all temperatures for all spine lengths, with longer spines occurring at lower temperatures. Zoeal body lengths were also significantly different between the three temperatures. The results of this study question the use of spine lengths to distinguish similar larval species.     

Rhythms in larval release of the sublittoral crab Neopanope sayi and the supralittoral crab Sesarma cinereum (Decapoda: Brachyura)

Ovigerous females of the subtidal xanthid crab Neopanope sayi (Smith) and the high intertidal grapsid crab Sesarma cinereum (Bosc) were collected during the summers of 1986 and 1987 in the Beaufort, North Carolina (USA), area and brought into the laboratory, where rhythms in larval release were monitored. When crabs with late-stage embryos were put under a 14 h light:10 h dark cycle in an otherwise constant-environment room, an apparent tidal rhythm in release of larvae was observed for both species, with N. sayi releasing near the time of day and night high tides, and S. cinereum releasing around the time of night high tides. The time of sunset relative to high tide was a complicating factor, since larval release for both species was often concentrated around sunset when evening high tides fell several hours before sunset. When a group of N. sayi and S. cinereum were brought into the laboratory and placed under constant lowlevel light for 5 d, the release rhythm of the population persisted, thus implying that the rhythm is endogenous. Larval release near the time of high tide and often at night is common among brachyurans living in tidal areas, regardless of specific adult habitat, suggesting a common functional advantage. Possibilities include transport of larvae from areas where predation and the likelihood of stranding and exposure to low-salinity waters are high, as well as a reduced probability of predation on adult females. Results of the present study suggest that the importance of release after darkness may increase with increasing tidal height of the adult.     

Vertical migrations in the tree crab Sesarma leptosoma (Decapoda,Grapsidae)

Sesarma leptosoma, somewhat similar to the Atlantic related species, Aratus pisonii, is an East-African mangrove crab which spends its entire life on the roots and branches of mangrove trees (mostly Rhizophora mucronata, Bruguiera gymnorhiza and Ceriops tagal). S. leptosoma never enters the water, nor does it ever venture onto the free mud surface at low tide. Part of the day and night it remains on the lower parts of the mangrove aerial roots, which are often encrusted with a wet algal mat of Bostrichia spp., searching for food and water. Twice a day, from ca. 06:00 to 08:00 hrs in the morning and 16:00 to 18:00 hrs in the afternoon, many of the crabs migrate as far as the leaves at the top of the tree on which they feed. However, they only spend a brief period among the leaves, from ca. 07:00 to 10:00 and 17:00 to 19:00 hrs, after which time they make their way back towards the roots again in two downward migrations. In the morning, the downward migration brings all the crabs back to the roots, but in the evening not all the crabs take part in the downwards migration and some of them pass the whole night in the tree tops. A comparison of the migration time patterns for two different periods of the year (June–July and November) shows that the number of crabs migrating along the tree trunk is modulated by the spring-neap tidal cycle, while the onset of daily migration seems to be controlled mostly by the light level and/or other climatological cues. The adaptive significance of this migratory behaviour is discussed. Observations reported in our study were made in Mida Creek, Dabaso, Kenya in 1991 and 1992.     

Demography and reproductive biology ofMelinna palmata (Ampharetidae: Polychaeta) in Inner Galway Bay on the west coast of Ireland

A high-density population of the polychaeteMelinna palmata Grube was the focus of a two-year study at a shallow-water location in Inner Galway Bay on the west coast of Ireland. Mean densities were highest in the second year of the study following successful recruitment. Size-frequency analysis of population structure (April 1983 to March 1985) revealed the presence of four cohorts, with the 1983 settlement becoming the dominant modal class. Size comparison of this cohort with the 1982 settlement showed that growth rates were lower and mortality higher in the 1983 settlement, which may be related to density dependent intra-specific competition.M. palmata at this location live for 2 to 2.5 yr with a small number surviving to 3 yr of age.M. palmata in Galway Bay is dioecious and has an even sex ratio. Reproductively mature worms were approximately 2 yr old when they first spawned. Spawning took place between May and July, when mature oocytes had a modal size of ca. 290µm. Proliferation of previtellogenic oocytes (ca. 10µm) from the gonads occurred following spawning. Growth over the winter was slow and was followed by a period of rapid growth between March and May, coincident with rising water temperatures. The presence of mature unspawned oocytes, which were resorbed after commencement of new proliferation, was taken as evidence of the species propensity for polytely. However, post-spawning mortality appeared to be high, so that only a small number of individuals survived to spawn the following year. The highest abundance of mature males was encountered between May and August, but lower levels of mature stages were present throughout the year.     

Larval settlement and metamorphosis in the sand crab Emerita talpoida (Crustacea: Decapoda: Anomura)

The effects of various potential cues on the survival and time to metamorphosis of larvae of the sand crab Emerita talpoida (Say) were examined. Zoeal duration, which ranged from 25 to 43 d, was not correlated with subsequent megalopal survival but had a weak, negative correlation with the duration of the megalopal stage. Neither food, sand nor water from containers with adults directly affected megalopal survival or duration. In a second experiment, the presence of sand both increased the probability of survival and shortened the duration of late zoeal stages. This is the first experimental evidence for delayed zoeal metamorphosis in a decapod. Settlement of E. talpoida appears to occur primarily during the zoeal phase, not at the megalopal stage.     

Latitudinal variation in aspects of the biology of Cyclothone braueri and C. microdon (Pisces: Gonostomatidae) in the eastern North Atlantic Ocean

Samples from a series of RMT-8 tows along 20°W in spring and autumn of various years were used to study the variability in aspects of the breeding biology of two species of Cyclothone: C. braueri and C. microdon in the eastern North Atlantic Ocean. Variables compared within each species included length-frequency distribution, maximum size, size at maturity, sex ratio, egg size and fecundity. Populations of both species at lower latitudes were generally smaller, reached maturity at a smaller size, and probably spawned earlier in the year and over a longer period than populations at higher latitudes. In both species, fecundity was highest at 40°N in the spring. The results suggested that C. microdon may not spawn at the northern extent of its range.     

The annual reproductive cycles of Uca annulipes,Portunus pelagicus and Metapenaeus affinis (Decapoda: Crustacea) from the South-west coast of India

Employing the gonad index method, the reproductive cycles of three decapod crustaceans, Uca annulipes (Latreille), Portunus pelagicus (Linnaeus) and Metapenaeus affinis (Milne-Edwards) have been studied. In these crustaceans breeding is not continuous all the year round, but extends over several months of the year with distinct peak periods of gonadal activity. The male and female reproductive cycles are not concurrent. The peak of the reproductive cycle of males occurs slightly earlier in the breeding season than that of females. These studies indicate the possibility of production of successive broods of eggs during the same breeding season. In these species, the low saline conditions of the monsoon period are unfavourable for breeding. The medium and high saline conditions during the post-monsoon and pre-monsoon months, respectively, with plenty of planktonic food for the larvae, seem to be the favourable periods for breeding activity.     

Larval development of the red crab Pleuroncodes monodon (Decapoda Anomura: Galatheidae) under laboratory conditions

Larvae of Pleuroncodes monodon (Milne-Edwards, 1837), a red crab of commercial importance in South America, were reared in the laboratory at 2 different temperatures (15° and 20°C), from hatching up to the last larval stage. The 5 typical stages, with their corresponding functional appendages, are described and figured. The main characteristics useful in differentiating larvae of P. monodon from those of the other Chilean species of Galatheidae and its northern congener P. planipes are discussed. Data on duration of each larval stage, length of moulting intervals and mortality at the 2 test temperatures are also given.This study was financially supported by the Chilean Ministry of Agriculture and by the National Commission for Scientific and Technological Research (CONICYT).     

Sand disposal of the painted ghost crab Ocypode gaudichaudii (Decapoda: Ocypodidae): A possible role in courtship

In 1991/1992, we studied the sand disposal behavior of the painted ghost crabs Ocypode gaudichaudii on the Pacific coast of Panamá. O. gaudichaudii either kick, dump or tamp sand they excavate from their burrows. Here we relate these three kinds of sand disposal to burrow structure and distribution, as well as to crab size and sex. Our objective was to determine whether tamping may be a male courtship signal. Burrows whose owners tamped sand were on average longer, deeper, and higher on the beach than were burrows whose owners kicked or dumped sand. Five burrow shapes were distinguished, with half-spiral and spiral shapes being most common among tamped burrows. All crabs excavated from tamped burrows were males. Tamped burrows peaked in abundance around full and new moons. These observations, together with what is known about mating and breeding behavior of other ghost crabs, suggest that tamping may be involved in O. gaudichaudii courtship.     

Population dynamics and growth of juveniles of the velvet swimming crab Necora puber (Decapoda: Portunidae)

Recruitment variability plays a critical role in determining local population densities of benthic organisms, but extreme vulnerability at the onset of juvenile life is a trait that is largely responsible for population survivorship trends. The aim of the present study was to determine the role of juvenile recruitment in the population structure of Necora puber. Juveniles of N. puber were collected from the lower intertidal of rocky shores of Plymouth Sound (southwest coast of the UK) and monthly size–frequency distribution were used to determine the dynamics and the growth of the population. The parameters of the von Bertalanffy growth function were estimated (K=0.281 year⁻¹; t ₀=0.043; C=0.103; and t _s=0.268) assuming a L _∞=105 mm. Growth was markedly seasonal and present results indicated a slower juvenile growth rate than described previously for N. puber. The recruitment period was extensive and was two times higher in 2001 than in 2000 at the start of the 1+ year, but levelled off at the end of the 1+ year class on three of the four shores studied. Instantaneous mortality as high as 5.1 year⁻¹(99.4% year⁻¹) was observed during the higher recruitment year. Early juvenile mortality appears to be density dependent and a demographic bottleneck appears to limit the number of juveniles on some shores.     

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     

Latitudinal patterns of shell thickness and metabolism in the eastern oyster Crassostrea virginica along the east coast of North America

The goal of this study was to quantify growth and metabolic responses of oysters to increased temperatures like those that will occur due to global warming. Impact of temperature on eastern oyster (Crassostrea virginica) shell growth and metabolism was investigated by sampling 24 sites along the eastern North American seaboard ranging from New Brunswick, Canada, to Florida, USA, in March and August 2013. There was a positive correlation between oyster shell thickness and site temperature. At southern sites, shells were up to 65 % thicker than at the northernmost site, likely due to higher precipitation of CaCO₃ in warmer water. This was supported by laboratory experiments showing that thicker shells were produced in response to temperatures 2, 4, and 6 °C above ambient seawater temperatures (8–14 °C) in Connecticut, USA. Field experiments with oyster respiration were conducted during winter and summer at 13 sites to compare responses to thermal stress with latitude. Respiration rates were much higher during summer than winter, but the combination of summer and winter data fell along the same exponential curve with respect to temperature. At all sites, temperature-specific metabolic rates at elevated temperatures were lower than predicted, indicating significant seasonal acclimatization by C. virginica.     

Ultrastructural changes in the gill epithelium of the crab Chasmagnathus granulatus (Decapoda: Grapsidae) in diluted and concentrated seawater

Chasmagnathus granulatus Dana, 1851 is an intertidal estuarine crab that experiences acute salinity changes ranging from <1‰ to full-strength seawater and even hypersaline waters in tide pools concentrated by evaporation. Ultrastructural changes induced by salinity in the posterior gills were examined in crabs collected from the Rio de la Plata estuary Argentina during March 1999. The posterior gills of C. granulatus are involved both in ion uptake and ion secretion depending on the acclimation medium. These organs are mostly lined with a thick tissue, which presents the characteristics of a typical salt-transporting epithelium. Electron microscopy analysis of gill tissue from crabs acclimated to dilute, full, and concentrated seawater (12‰, 34‰, and 45‰ salinity) showed significant development of basolateral membrane interdigitations, with numerous mitochondria and conspicuous apical membrane infoldings. Morphometrical analysis indicated that the subcuticular space delimited by the infolding of the apical membrane was significantly increased in the gills of high-salinity acclimated crabs. Septate junctions, which are thought to define the paracellular permeability, were significantly shorter in high-salinity acclimated crabs, suggesting a possible role of the paracellular pathway in salt secretion.     

Soleidae macroparasites along the Portuguese coast: latitudinal variation and host–parasite associations

Parasite assemblages are increasingly being used as indicators of their hosts’ biology and ecology, especially for economically important marine species such as the Soleidae. In this study, seven species inhabiting Portuguese coastal waters were examined for external and internal macroparasite infections using standard procedures: Dicologlossa cuneata, Microchirus azevia, Microchirus variegatus, Solea lascaris, Solea senegalensis, Solea solea and Synaptura lusitanica. Despite being closely related, these species present different life history patterns and ecological preferences which were expected to be mirrored by their macroparasite assemblages. The aim of the study was, therefore, to study the variation of these assemblages, within and between host species, along the Portuguese coast in order to evaluate the importance of the hosts’ features and environmental factors in the assemblage compositions. Flatfish were obtained seasonally from commercial fishing vessels operating in three areas (northern, central and southern) along the Portuguese coast. Prevalence and mean abundance were calculated and tested for differences between host sex, areas and seasons. The host specificity index and the importance of the host–parasite relationship were computed based on mean abundance. The total number of parasite individuals, species richness, total prevalence, total mean abundance, diversity and evenness were also calculated. A canonical correspondence analysis (CCA) was performed using prevalence and mean abundance data. A total of 44 macroparasite species were found. No significant differences were observed in prevalence and mean abundance between sexes and sampling seasons but, for three of the parasite species, significant differences were found between areas. The highest values of the parasitological and ecological indices were generally registered in the hosts S. lascaris and S. senegalensis and in the southern area. The CCA using the prevalence data revealed the differentiation of S. lascaris samples, which was mainly related to the total prevalence and to the number of important species of macroparasites. When using mean abundance data, the CCA revealed the differentiation of D. cuneata from the south, S. lascaris from the three areas and S. senegalensis from the south, mainly related to total prevalence and richness. The differences found between infection levels and assemblages’ composition were mainly due to differences in hosts’ diet, namely prey type consumption, given that most macroparasites found were transmitted through the food web. However, environmental factors were also important given that they regulate the distribution of ectoparasites and the availability of prey, and therefore the infections’ pattern. These findings were in agreement with the ones from similar studies performed in other species, revealing the importance of parasites as indicators of their hosts’ ecology.     

On the introduction of the Kamchatka King crab Paralithodes camtschatica (Decapoda: Anomura: Lithodidae) into the Barents Sea

About 2,500 specimens of the Kamchatka king crab Paralithodes camtschatica (Tilesius), ca. 5 to 15 years old, and about 10,000 juveniles, ca. 1 to 3 years old, were released into the Barents Sea from 1961 to 1969. One large berried female was caught in 1974, and the number of records increased in 1976 (at least 100 records, including 6 reliable ones). The crab therefore seems to have become a permanent inhabitant of the Barents Sea. It will be important in future to continually record new occurrences of the crabs, especially of juveniles, in order to document the extent of their distributional range and to obtain evidence of successful reproduction of the species.