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Limpets and barnacles are important components of intertidal assemblages worldwide. This study examines the effects of barnacles on the foraging behaviour of the limpetPatella vulgata, which is the main algal grazer in the North-west Atlantic. The behaviour of limpets on a vertical seawall on the Isle of Man (UK) was investigated using autonomous radio-telemetry, comparing their activity patterns on plots characterized by dense barnacle cover and plots from which the barnacles had been removed. Limpet behaviour was investigated at mid-shore level, but two different elevations were considered. This experiment revealed a significant effect of barnacle cover on the activity ofP. vulgata. Limpets on smooth surfaces spent a greater proportion of total time active than did limpets on barnacles. Movement activity was also greater in areas that were lower down in the tidal range. In general, limpets were either predominantly active during diurnal high or nocturnal low tides and always avoided nocturnal high tides. Individuals on barnacles at the higher elevation concentrated their activity during nocturnal low water. All the other groups of limpets (smooth surfaces on the upper level and all individuals on the lower shore) had more excursions centred around daylight hours with an equal distribution of activity between periods of low and high water. Inter-individual variability was, however, pronounced.

In Brachyura copulation prior to the instar in which females become fully morphologically and functionally mature (i.e., produce fertile eggs) is exceptional. However, in the freshwater crab Candidiopotamon rathbunae (family Potamidae), adult males frequently mate with immature females (precocious mating). The size of female functional maturity is 22-23 mm carapace width. Immature females larger than 15 mm carapace width are observed mating, usually have sperm in their seminal receptacles, and this sperm is retained through subsequent moults. Precocious mating in C. rathbunae could potentially increase the reproductive capacity of females. It could have evolved as an adaptation to a seasonally amphibious life, during which the mating opportunities are reduced compared to a permanently aquatic lifestyle. Data from the few other brachyuran taxa with precocious mating fail to indicate a common rationale.

The growth of the chelae of mature males was examined in three gecarcinid land crabs — Johngarthia lagostoma on Ascension Island, Epigrapsus notatus on Taiwan, and E. politus on Moorea. Chelar dimorphism was found in each species, with a mixture of homochelous and heterochelous males. In J. lagostoma there was progressive polymorphism, with the heterochelous condition appearing only in a proportion of the larger mature males. The situation in Epigrapsus was less clear. The proportion of heterochelous males increased in the larger mature size classes, but progressive polymorphism is yet to be confirmed.

Population structure and moulting of the semi-terrestrial crab Chiromantes haematocheir (De Haan, 1833) were studied in Taiwan. The crab moults nocturnally in small freshwater pools, and newly moulted crabs and cast integuments were used to assess moult increment. Males reached a larger size (max. CW 36 mm, ) than females (max. CW 33 mm, ): from 22 mm CW males increasingly dominated the population. Size at maturity was estimated at 17.5 mm CW. The percentage moult increment averaged 11.5% in males (5.5-19%, ) and 13.9% in females (7-23%, ). Female increment exceeded male increment for all overlapping size classes. The larger size of mature males, despite a smaller percentage increment, is explained by a higher post-puberty moult frequency. Of the moulting crabs, 25% of males and 38% of females had one or more missing or regenerating peraeopods. In both sexes this reduced the percentage increment, more so the larger number of limbs affected. The moulting conditions for C. haematocheir are not ideal, with constraints in relation to calcium supplies, and shelter. So the moult increments are unsurprisingly less than those of shallow water marine crabs moulting in an optimal environment, but larger than those of land crabs moulting without access to standing water.

The land crab, Johngarthia lagostoma, occurs exclusively on Ascension Island and the Brazilian oceanic islands of Trindade, Atol das Rocas, and Fernando de Noronha. Like other gecarcinid crabs, it retains a marine planktotrophic larval phase, and as in some other gecarcinids the Megalops migrate inland into fully terrestrial habitats before moulting to the first crab instar. Due to their limited geographical distribution and their biological characteristics, the populations of J. lagostoma are especially vulnerable to environmental disturbances. The aim of this study was to assess, through analyses of mitochondrial DNA sequences, the genetic structure and diversity of J. lagostoma on the four islands where it occurs. The large differentiation observed indicates that three discrete land crab evolutionary significant units should be considered: Ascension Island, Trindade, and Atol das Rocas/Fernando de Noronha.

The stage at which land crabs of the Gecarcinidae recruit to land is examined, and discussed in relation to recruitment in other terrestrial crabs. New data are presented for species of Johngarthia, and published data on other species are re-examined and evaluated. The gecarcinids Gecarcinus and Johngarthia appear unique in that the megalops migrates inland into fully terrestrial habitats before moulting to the first crab instar. In other land crabs, so far as is known, the moult to the first crab occurs either in the water, or in moist adjacent habitats.

Anchialine systems are unusual among aquatic habitats in that they are subterranean karst systems in which marine and overlying groundwater are separated by distinct haloclines and characterized by high sulphur content, darkness and low nutrient availability. In this study, we examine how the antennulae, antennae, eyes and integument morphology of five anchialine species of decapods (Barbouria yanezi, Agostocaris bozanici, Procaris mexicana, Calliasmata nohochi and Typhlatya pearsei) are adapted for anchialine environments. Our examination of sensorial structures shows that while these species appear to have convergent adaptations for anchialine environments, degrees of specialization in antennular and antennal structures vary, with Barbouria yanezi showing the greatest setation. The eyes of all five species show pores at their tips, but only Calliasmata nohochi also exhibits setae on the eyes. We propose that these additional setae and pores function to enhance the ability of these decapods to sense mechanical and chemical stimuli in the water. In overview, these anchialine crustaceans have evolved anatomical/morphological attributes that appear to function to help detect predators, congeners, food, or refugia.

The effectiveness of Passive Integrated Transponders (PIT tags) was investigated in the robber or coconut crab, Birgus latro. A pilot study was conducted in Chumbe Island, Zanzibar, and a definitive study on Christmas Island, Indian Ocean. No mortality or adverse behaviour was recorded as a result of PIT tagging. On Christmas Island 1150 crabs were tagged in 2009 and 2010. In the period to April 2011, 169 crabs were recaptured, some up to four times. Of these, 67 had moulted before recapture. Approximately equal numbers of each sex were marked, and recaptured. Tag loss was estimated at ~5%. Alternative sampling protocols using grid and transect searches were tested. They produced different results in terms of sampling efficiency and sex ratio: sampling protocol must be considered when interpreting data.PIT tagging in Birgus is a promising method for long term population studies. It promises low tag loss and good recapture rates in comparison with previous studies.

Abbreviated larval development is described and illustrated for Macrobrachium totonacum Mejia, Alvarez & Hartnoll, 2003, a recently described freshwater prawn with three larval stages. The study is based on laboratory-reared material. Females carry 18 eggs on average, with a maximum of 28. The average egg diameter is 2.1 mm. The first larval stage has sessile eyes, and all appendages are developed except the uropods; however, the chelae on pereiopods 1 and 2, and the pleopods, are non-functional. In stage 2 the eyes are articulated, and the chelae and pleopods are functional. In stage 3 the uropods are developed. The larvae are lecithotrophic in the first two stages, and start feeding in stage 3. The larval development of this species is compared with other Mexican and South American species of Macrobrachium with abbreviated development: it has the same number of stages as M. vicconi Roman, Ortega & Mejia, 2000, another Mexican species. El desarrollo larval abreviado es descrito e ilustrado para Macrobrachium totonacum Mejia, Alvarez & Hartnoll, 2003, una especie de langostino recientemente descrita con tres estados larvales. Este estudio esta basado en material obtenido en laboratorio. Las hembras llevan en promedio 18 huevos y un maximo de 28. El diametro promedio del huevo es de 2,1 mm. El primer estadio larval tiene ojos sesiles y todos los apendices estan desarrollados excepto los uropodos; sin embargo, la quela de los pereiopodos 1 y 2 y los pleopodos no son funcionales. En el estado dos, los ojos estan articulados y la quela y pleopodos son funcionales. En el estado tres los uropodos estan desarrollados. Las larvas son lecitotroficas en los primeros dos estadios e inician su alimentacion en el estado tres. El desarrollo larval de esta especie es comparada con otras especies de Macrobrachium de Mexico y Sudamerica con desarrollo abreviado, esta especie tiene el mismo numero de estados que otra especie mexicana: M. vicconi Roman, Ortega & Mejia, 2000.

Reproduction was studied in the land crab Johngarthia lagostoma on Ascension Island in the central South Atlantic from 2005 to 2008. Both sexes are mature by 60-70 mm carapace width (the sample . 4,000 crabs consisted almost entirely of mature specimens). Breeding occurs around the east and south shores of the island, but was studied predominantly at the only easily accessible site at North East Bay. The annual breeding migration extends from January to May, with peak migration in March in most years. The intensity of migration varies between years, and is not obviously related to rainfall. There is lunar entrainment, with increased numbers at the shore in the first quarter, but largest numbers in the last quarter. Both males and females migrate, but with females in greater numbers. At the shore 80% of the crabs are females. A few females mate and lay eggs in the upland residential areas, a greater number do so on the migration route, but the majority only after reaching the shore. Reproductive investment per brood averaged 5% on a dry weight basis, and fecundity averaged 72,000 eggs.

The population structure of the land crab Johngarthia lagostoma was studied on Ascension Island from 2005-2007, predominantly during the period of the seaward breeding migrations; approximately 4000 crabs were examined. Sex ratio varied according to location of sampling. Males predominated in permanent residential areas on high ground. Sexes were equal along migration routes to the sea. Females predominated in the breeding sites on the shore. Very few immature crabs (< 60 mm CW) were found. Males had modal and maximum sizes of 100-109 mm and 120 mm CW, females of 90-99 mm and 110 mm, respectively. An aging population is indicated. Crabs < 40 mm CW were all dark coloured, and colour variation into yellow, purple and intermediate morphs developed between 40-50 mm CW. Overall colour distribution of the population was 85% yellow, 5% intermediate, and 10% purple. Yellow morphs were more abundant in females (89%) than males (81%). The predominance of yellow morphs may be an adaptation to reduce heat st...

The rock crab, Grapsus adscensionis (Osbeck, 1765), was studied on Ascension Island, South Atlantic Ocean. By day crabs were inactive above water level at high tide, but during low tide fed on algal films exposed on the low shore. By night they were inactive at all tidal states. Both sexes reached a maximum carapace width of 74 mm, but were potentially capable of further moulting. Sexual maturity was reached at ∼38 mm carapace width in males, and ∼43 mm carapace width in females. In females one batch of eggs was produced in most intermoults. The ovaries had matured by the time that the eggs had completed incubation. The females moulted shortly after the hatching of the eggs, and re-laid early in the next intermoult. Consequently 78% of mature females were ovigerous. It is estimated that an egg batch is laid every 24 days. Reproductive investment (dry weight) per egg batch averaged 5.5%. Le crabe des rochers Grapsus adscensionis (Osbeck, 1765), a ete etudie sur l'ile d'Ascencion, ocean Atlantique Sud. De jour, les crabes sont inactifs au dessus du niveau de l'eau a maree haute, mais durant la maree basse ils se nourrissent sur le film algal de la cote emergee. La nuit ils sont inactifs quelle que soit la maree. Les deux sexes ont atteint une taille maximum de 74 mm de largeur de carapace, mais sont susceptibles de continuer a muer. La maturite sexuelle est atteinte a ∼38 mm de largeur de carapace pour les mâles, et ∼43 mm pour les femelles. Chez les femelles, une ponte est emise dans la plus part des intermues. Les ovaires sont matures au moment ou les œufs terminent leur incubation. Les femelles muent rapidement apres l'eclosion des œufs et pondent a nouveau au debut de l'intermue suivante. En consequence 78% des femelles mâtures sont ovigeres. Il est estime qu'une ponte est emise tous les 24 jours. L'investissement dans la reproduction (en poids sec) par portee est en moyenne de 5,5%.

Reproductive biology of the black land crab, Gecarcinus ruricola (Linnaeus, 1758), has been studied in the San Andres Archipelago in the Western Caribbean, on the islands of San Andres and Old Providence. Both sexes become mature at about 50 mm maximum carapace width, and very few specimens below this size take part in the annual breeding migration. In females the ovaries mature progressively from January to April, and laying occurs from May to July. There is no evidence that individual females lay more that once in a year. The breeding migrations were monitored in 2003 and 2004 by recording specimens crossing the coast road (running 50-100 m from the upper shore). On both San Andres and Old Providence migration was limited to specific stretches of the western shores. On both islands migration occurred from late April to July, intensity varying with time. Migration peaks were not consistent between islands or years, and could not be clearly linked to environmental factors. Migrating crabs were mo...

Black land crab (Gecarcinus ruricola) populations and their dependent catchery in the San Andres Archipelago, Colombia, are under threat from overexploitation, habitat loss and degradation, and road-kill during annual spawning migrations to the sea. This article discusses the participatory approach used to define management of the species and describes the extensive involvement of local communities, particularly catchers and processors, in research and assessment of management options. Many options were considered. General support exists for continued use of closed areas and seasons in species management, in combination with the introduction of a new minimum size limit of 70 mm carapace width. Licensing receives some support, but the use of total allowable catches or quotas is universally rejected. Establishing a legally defined community-driven body, known as the Black Crab Conservation Unit, is seen as a crucial step in the management of the resource and has widespread support.

Sensory and ambulatory appendages were compared between epigeal and cave species of prawn and crayfish from Mexico. The cave prawn Macrobrachium villalobosi was compared with the epigeal M. totonacum. The cave crayfish Procambarus cavernicola and P. oaxacae reddelli were compared with the epigeal P. olmecorum. In both Macrobrachium and Procambarus the antennules and antennae of the cave species were longer in proportion to carapace length than in epigeal species. In the crayfish the cave species had a longer and narrower first pereiopod, and also showed a greater development of setation on the antennules, antennae, and carapace. These are all considered examples of progressive troglomorphism. They will improve non‐visual sensory capability in the aphotic and resource‐poor cave environment.

It is critical for our knowledge of biodiversity and ecosystem processes to understand how individual species contribute to ecosystem processes and how these contributions vary in space and time. We used a manipulative field experiment in five locations over 17 degrees of latitude [from southern Portugal to the Isle of Man (British Isles)] to determine the relative response of rocky intertidal algal assemblages released from control by the grazing of limpets. Response ratios showed that when limpets were removed there was a trend of effects from north to south. In the north, grazing had a strong effect on algal assemblages, but removing grazers reduced spatial variability in assemblages. In the south, the effect of limpet grazing was far weaker and removal of grazers had a much reduced impact on spatial variability. Here we show a clear trophic control of an ecosystem in that grazing by limpets not only determines macroalgal abundance overall but also modifies ecosystem stability via variability in cover of algae.

A mass return to land of the megalop of the land crab Gecarcinus ruricola is reported. The return occurred in June 2004 on the island of Providencia in the western Caribbean: this is the first detailed report of larval return in this species, and the most detailed report for any gecarcinid. Crabs emerged from the sea as megalops over 2 to 3 days, and moved rapidly landwards. Vast numbers migrated > 50 m across land before moulting to the first crab – the megalop is clearly the invasive stage. The megalop is described for the first time, and criteria are identified to discriminate it from other Caribbean gecarcinids. © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society, 2006, 146, 149–164.

[Cave animals show various adaptations to survival in their unusual environment, involving their physiology, behaviour, life history, and morphology. The morphological adaptations include enlargement of the sensory and ambulatory appendages, reduction or lack of pigment in the integument, and reduction or loss of eyes. In general, the eyes of cave animals show only non-constructive adaptations: however, we have found setae on the corneal surfaces in three different genera of cave decapods (Potamalpheops, Macrobrachium, and Procambarus) where setae are normally never present. We suggest that this constitutes the development of a new function for the obsolescent eyes, either tactile or chemosensory. This obviously underscores the general hypertrophy of non-visual sensory systems in cave organisms. Los animales cavernicolas muestran singulares adaptaciones para sobrevivir en sus ambientes, involucrando principalmente caracteristicas de su fisiologia, comportamiento, historia de vida. Las adaptaciones morfologicas frecuentemente comprenden el alargamiento de los apendices sensoriales y ambulatorios, reduccion o carencia total de pigmentos en el integumento, asi como una disminucion o perdida total de los ojos. En general los ojos de los animales cavernicolas solo tienen adaptaciones no constructivas; sin embargo, nosotros hemos encontrado setas sobre las superficies de la cornea en tres generos diferentes de decapodos cavernicolas (Potamalpheops, Macrobrachium, y Procambarus) donde las setas normalmente nunca estan presentes sobre la cornea. Sugerimos que esto constituye el desarrollo de una nueva funcion para los ojos obsoletos, ya sea tactil o quimioreceptora. Esto obviamente subraya la hipertrofia general de los sistemas sensoriales no visuales en los organismos de cueva., Cave animals show various adaptations to survival in their unusual environment, involving their physiology, behaviour, life history, and morphology. The morphological adaptations include enlargement of the sensory and ambulatory appendages, reduction or lack of pigment in the integument, and reduction or loss of eyes. In general, the eyes of cave animals show only non-constructive adaptations: however, we have found setae on the corneal surfaces in three different genera of cave decapods (Potamalpheops, Macrobrachium, and Procambarus) where setae are normally never present. We suggest that this constitutes the development of a new function for the obsolescent eyes, either tactile or chemosensory. This obviously underscores the general hypertrophy of non-visual sensory systems in cave organisms. Los animales cavernicolas muestran singulares adaptaciones para sobrevivir en sus ambientes, involucrando principalmente caracteristicas de su fisiologia, comportamiento, historia de vida. Las adaptaciones morfologicas frecuentemente comprenden el alargamiento de los apendices sensoriales y ambulatorios, reduccion o carencia total de pigmentos en el integumento, asi como una disminucion o perdida total de los ojos. En general los ojos de los animales cavernicolas solo tienen adaptaciones no constructivas; sin embargo, nosotros hemos encontrado setas sobre las superficies de la cornea en tres generos diferentes de decapodos cavernicolas (Potamalpheops, Macrobrachium, y Procambarus) donde las setas normalmente nunca estan presentes sobre la cornea. Sugerimos que esto constituye el desarrollo de una nueva funcion para los ojos obsoletos, ya sea tactil o quimioreceptora. Esto obviamente subraya la hipertrofia general de los sistemas sensoriales no visuales en los organismos de cueva.]

A study was made of the land crab, Johngarthia lagostoma (H. Milne Edwards, 1837) on Ascension Island in the central South Atlantic: aspects of its distribution, population structure, and reproduction are described. On Ascension it is normally limited to altitudes >200 m, the only parts of the island with substantial vegetation. The population comprised predominantly pale colour morphs, and few immature specimens were sampled. The significance of both factors is examined. The breeding migration to the shore was observed. Migrations occurred in February to April, varied in intensity between years, and were dominated by females. Migrants had to cross the bare arid lowlands, resulting in mortality. There are no recent records of the return of the juvenile crabs after the planktonic larval phase. Une etude a ete menee chez le crabe terrestre Johngarthia lagostoma (H. Milne Edwards, 1837) sur l'ile d'Ascension, dans l'Atlantique sud central : les aspects de sa repartition, la structure de sa population et sa reproduction ont ete decrites. Sur l'ile de l'Ascension, sa presence est limitee normalement aux altitudes >200 m, les seules parties de l'ile avec une vegetation substantielle. La population comprend des formes de couleur pâle et quelques specimens immatures ont ete echantillonnes. La signification de ces deux facteurs a ete examinee. La migration de reproduction vers la mer a ete observee. Les migrations ont lieu de fevrier a avril, varient en intensite suivant les annees, et sont dominees par les femelles. Les migrateurs ont a traverser les parties basses, denudees et arides, qui sont cause de mortalite. Il n'y a pas de donnees recentes sur le retour des crabes juveniles apres la phase larvaire planctonique.

The population biology of the black land crab, Gecarcinus ruricola (Linnaeus, 1758), was studied in the San Andres Archipelago in the western Caribbean. Investigations were conducted on the islands of San Andres (SA), and Old Providence/Santa Catalina (OP). On both islands the mean size differed little between the sexes, but males reached a larger maximum size by ∼5 mm CW. Crabs of both sexes reached greater mean and maximum sizes on OP than on SA (by ∼10 mm CW): this is tentatively attributed to the higher human population and heavier crab exploitation on the latter. The density of crabs was higher on OP than on SA. In natural ‘forest’ habitats it averaged 2174 crabs Ha−1 in the former, and 804 crabs Ha−1 in the latter. On both islands the densities were higher in watersheds adjacent to the coastlines where breeding females migrate to the sea, and to which returning larvae recruit. The total population estimates were about 3 million crabs on OP, and 800,000 on SA. The lower density and populatio...

Carapace setae were examined by SEM in species of spider crabs (Family Majidae). These setae are predominantly hamate (i.e. hooked), to which extraneous materials are attached for the purpose of concealment. They are described for eight species collected around the Isle of Man. In each species setae were sorted to types on the basis of consistent differences in size, shape and fine structure. Diversity ranged from two to six types per species, and this was examined in the context of their masking, or camouflage, habits. Certain setae can be assigned to particular species, so a limited taxonomic usage is indicated: however, further work is required for this to become a comprehensive tool. Distribution of setal types on the carapace is also described, and compared to patterns reported in previous studies.

Biological rhythms with lunar components are common in nature. In the sea, the moon's gravitational pull on earth is the principal cause of the tides, which normally reach maximum amplitudes every new and full moon. Many populations synchronize spawning to this time. Some choose either the new or the full moon, implying that moonlight is important; but one lunar phase usually has higher tides than the other, and many species select the phase with the higher tide to improve the offshore transport of their progeny. However, tidal dominance by one lunar phase is not constant; it switches between new and full moon every seven months. We tested the influence of this 14-month “syzygy inequality cycle” (SIC) on lunar synchrony by sampling 11 populations of intertidal crabs at two locations in East Africa for 21 months. Eight populations synchronized larval release with the SIC. Tidal cues were more important than moonlight in entraining the reproductive rhythm, although two populations synchronized spawning to t...

Eyestalk length, internal eye structure, pigmented eye area, and pigments in eyes and exoskeleton were studied in two stygobiont crayfish, Procambarus cavernicola and Procambarus oaxacae reddelli. Results were compared with the epigeal crayfish Procambarus olmecorum, all three species inhabiting the karstic region of Acatlan, Oaxaca, Mexico. The stygobite species have shorter eyestalks and reduced pigmented areas compared with the epigeal species. For both eye and integument pigments, the stygobite species have a reduction in their total absorbance spectra compared to the epigeal species. Internal eye structure and organisation are reduced in both stygobite species, but to a greater extent in Procambarus cavernicola. These results are discussed in relation to the time of cave colonisation, the degree of adaptation, and the energy economy hypothesis.

Patella vulgata is one of the most common limpet species on rocky shores throughout the north-eastern Atlantic. Foraging activity of this species has been described during various different diel and tidal phases and several factors have been suggested that might influence the timing of its activity. Among these, inclination of rock surfaces seems to have a clear role, with limpets on horizontal rocks being active during daylight at high water, while limpets on vertical rocks were active during night-time low water. However, by comparing the results of previous investigations it is difficult to separate clearly the effect of any single factor from the effects of their interactions. In the present paper we investigated the simultaneous influence of height on the shore, slope of rock surface and date of sampling (August-September and March-April) on the behaviour of a population of P. vulgata on the Isle of Man (UK). The study was carried out using modern telemetric methods, allowing the activity patterns of limpets to be recorded for long periods of time. The results showed that limpets concentrated their activity during two distinct temporal windows-daytime tide-in and night-time tide-out-while no significant activity was observed during daytime tide-out or night-time tide-in. The observed behaviour appeared to be driven by complex interactions among the three factors examined, and the influence of rock slope alone was not so strong as to override the effect of other factors completely. In addition, a key finding of this study was the conspicuous variability in the individual behaviour of P. vulgata. The greatest level of variability was observed in limpets on vertical surfaces on the upper shore, which showed an extreme switch in behavioural patterns, according to date of sampling (daylight/tide-in foraging during the spring and night-time/tide-out foraging during late summer). In addition, individuals apparently sharing the same set of conditions (inclination, height on the shore and sampling date) differed in their behaviour, and a given behavioural pattern was not always shared by all individuals from a given group. Finally, variability was also observed at the 'intra-individual' level since the same individual could be active during different tidal and diel phases. In conclusion, although the existence of endogenous rhythms has previously been demonstrated in this species, our data clearly show that P. vulgata was able to modulate its behavioural patterns in relation to a variety of exogenous determinants.

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.

Discharges of most radionuclides into the Irish Sea from the BNFL site at Sellafield have decreased over the past 20 years or so. For a few radionuclides, however, discharges have peaked more recently. Notably, operation of the Enhanced Actinide Removal Plant (EARP) since 1994 has led to an increase in discharges of (99)Tc, as a result of the treatment of previously stored waste, with consequent increases in (99)Tc activity concentrations in a number of marine species, particularly in crustaceans such as lobsters. Previous research has considered the significance of factors such as sex and body weight on radionuclide concentrations. The current project set out to investigate whether seasonal variations in radionuclide concentrations in crabs and lobsters occur, with particular emphasis on the dynamics of (99)Tc and (137)Cs. Organisms were obtained from a site off the Isle of Man, where radionuclide concentrations were measurable but the site was sufficiently distant from Sellafield that the radionuclides were well mixed in the water column and not likely to be influenced by the pulsed nature of discharges of (99)Tc. Crab and lobster samples were collected monthly, between February 2000 and February 2001. Fifteen or 16 individuals (evenly split as male and female) of each species were collected on each occasion. Seawater samples were also collected over the 12-month period. Activity concentrations of (99)Tc in the edible meat fraction (both brown and white meat) ranged from 0.23 to 2.46 Bq kg(-1) (fresh weight (fw)) in crabs and 124 to 216 Bq kg(-1) (fw) in lobsters, with no observed seasonal variations. Activity concentrations of (137)Cs in both crab and lobster were lower, ranging from0.16 to 0.85 Bq kg(-1) for crab meat (fw) and0.3 to 3.3 Bq kg(-1) for lobster meat (fw). A statistically significant increase in activity concentrations of (137)Cs in the meat was observed in the summer months for both crab and lobster. The cause has not been investigated but may be related to the laying down of energy reserves during the active feeding period over the summer. At all times, uptake of (99)Tc is higher in the brown meat fraction of both crabs and lobsters, whilst (137)Cs is more uniformly distributed. These results are used to discuss the implications for sampling and monitoring programmes.

A new species of the genus Macrobrachium from northern Oaxaca, Mexico, with abbreviated larval development, is described. Macrobrachium totonacum new species, is similar to M. tuxtlaense and M. vicconi in exhibiting abbreviated larval development, but differs from these in the length of the e rst pereiopod and relative proportions of the articles of the second pereiopod. Macrobrachium totonacum occurs in the San Antonio River, which originates in the Cueva del Nacimiento del Ri o San Antonio where the troglobyte M. villalobosi is found. However, both species differ in pigmentation, the number of rostral spines, proportions of the scaphocerite, relative proportions of the carpus and propodus of the e rst pereiopod, and the carpus, merus, and propodus of the second pereiopod.

Seasonal changes in population structure, reproductive activity, and growth of the shrimp Neocaridina denticulata denticulata were examined in a Korean stream between July 1999 and June 2001. Average population density ranged from 34 to 180 indiv.m-2; density declined during the rainy season as the population dispersed into freshly inundated areas. The main breeding season, from June to July, coincided with higher gonadosomatic indices. Within this season ovaries rematured during embryonic development, indicating a potential for multiple ovulations within the reproductive season. Egg batch weight averaged 44% of female weight, indicating a greater investment in egg production than reported in other freshwater and marine shrimps. The carapace length at which 50% of females were mature was estimated as 6.4 mm from the proportion of females with mature ovaries, and as 7.8 mm from the proportion of ovigerous females. Estimates using the modified Von Bertalanffy growth function (VBGF) incorporating seasonal oscillation in growth showed that females (L ∞ = 12.50 mm CL, K = 0.59 year-1, ′ = 1.96) grew faster, and reached a larger size at age, than males (L ∞ = 9.35 mm CL, K = 0.93 year-1, ′ = 1.91). Les variations saisonnieres de la structure de la population, de l'activite reproductrice, et de la croissance chez la crevette Neocaridina denticulata denticulata ont ete examinees dans une riviere coreenne de juillet 1999 a juin 2001. La densite de population moyenne allait de 34 a 180 indiv.m-2; la densite diminuait au cours de la saison humide quand la population etait dispersee dans les eaux fraichement inondees. La principale saison de reproduction, de juin a juillet, coincidait avec des indices gonadosomatiques plus eleves. Au cours de cette saison, les ovaires redevenaient matures au cours du developpement embryonnaire, indiquant un potentiel pour des ovulations multiples durant cette meme saison. Le poids des oeufs representait 44% du poids de la femelle, indiquant un investissement plus grand dans la production des oeufs que chez d'autres crevettes marines et d'eaux douces. La longueur de la carapace a laquelle 50% des femelles sont matures a ete estimee a 6,4 mm en considerant la proportion de femelles a ovaires matures, et a 7,8 mm en considerant la proportion de femelles ovigeres. Les estimations utilisant la formule modifiee de Von Bertalanffy (VBGF) qui incorpore l'oscillation saisonniere dans la croissance ont montre que les femelles (L ∞ = 12,50 mm CL, K = 0,59 an-1, ′ = 1,96) croissaient plus vite, et atteignaient une taille superieure a celle des mâles au meme âge (L ∞ = 9,35 mm CL, K= 0,93 an-1, ′ = 1,91).

Procambarus (Austrocambarus) cavernicola, a new species of stygobitic crayfish known only from Gabriel Cave, Oaxaca, Mexico, is described. The new species is characterised by a body that lacks pigmentation, except for small purple spots on the eyes; with small setae on the tip of the eye; elongated chelipeds, with the surface of chela covered with small tufts of short setae; first pleopod of form I male with mesial process elongated and conical, triangular central projection, reduced cephalic process and cephalic shoulder forming convex border; annulus ventralis with preannular plate covered with short setae, postannuluar plate oval-shaped, with blunt tubercles. The new species is morphologically similar to other stygobite members of the subgenus Austrocambarus from the Oaxaca–Veracruz area, whose relationships are discussed. The distributions and levels of adaptation to the subterranean environment of 16 cave-inhabiting taxa of Procambarus in Mexico are reviewed.

Numerous studies have highlighted the importance of crabs within mangrove ecosystems, but tested methods of enumeration are virtually non-existent. The aim of the present study was to assess the accuracy of quick, non-invasive methods for estimating the population density of three species of mangrove crabs in East Africa: Uca annulipes, Sesarma guttatum and Neosarmatium meinerti. Methods employed depended on the behaviour and habitat of each species. Counts of U. annulipes and N. meinerti individuals that were active on the surface (visual counts) and burrow counts (of U. annulipes) were compared to actual densities. Actual densities were determined by excavation of U. annulipes, and by multiplying counts of N. meinerti burrows by the mean number of crabs per burrow. Visual counts of marked individuals of S. guttatum were compared to known densities of marked crabs. For N. meinerti two visual counting methods were tested: (1) instant counts – crabs were counted every 5 min during 0.5 h and the highest count taken; and (2) continuous counts – all burrows were tagged, and those from which a crab emerged during 0.5 h were totalled. For U. annulipes on Inhaca Island (Mozambique) visual counts underestimated excavated numbers by 27%, whereas burrow counts overestimated numbers by 46%. These values were similar for both sexes, and on both spring and neap tides. Burrow counts and visual counts estimated absolute numbers of U. annulipes with equal consistency. At Mida Creek (Kenya) visual counts underestimated U. annulipes numbers by 37%, again with no differences between spring and neap tides. In Zanzibar 81% of N. meinerti burrows contained a crab. The instant visual count underestimated N. meinerti numbers by 41%, the continuous count, by 12%. Visual counts of S. guttatum in Zanzibar (Tanzania) underestimated crab numbers by 49%.

Sesarmid crabs dominate Indo West-Pacific mangroves, and consume large amounts of mangrove litter. This is surprising, since mangrove leaves have high tannin contents and C/N ratios that far exceed 17, normally taken as the maximum for sustainable animal nutrition. This paradox has led to the hitherto untested hypothesis that crabs let leaves age in burrows before consumption, thereby reducing tannin content and C/N ratio. We excavated burrows of Neosarmatium meinerti within high-shore Avicennia marina mangroves, and investigated whether burrow leaves had C, N or C/N values significantly different from those of senescent leaves. Leaves were found in

The aim of this work was to determine the abundance of crabs inmangrove communities along a latitudinal gradient along the eastern coastof Africa from 4°S to 32°S. Surveys were made atMombasa (Kenya), Zanzibar (Tanzania), Maputo (Mozambique) and in theTranskei (South Africa). Crabs were estimated at three designated levelsin the mangroves by visual census using a common protocol, and numberswere converted to biomass.Even after standardising the selection of sites and methods of censusthere was still extensive variability in the data, emphasising the complexheterogeneity of mangrove ecosystems. Lunar phase (full versus new moonsprings) did not have a consistent effect on results, but shore height hadseveral effects. Total crab biomass was similar in the two lower shore strataexamined, but about twice as high at the top-Avicennia level. Theratio of grapsid biomass:ocypodid biomass also changed with height: fromnear unity in the lower mangrove, to 0.14 in the middle strata, but to 15at the top.There was no consistent latitudinal trend in total crab numbers, but totalcrab biomass increased from north to south. In addition there was aconsistent and marked change in the grapsid biomass:ocypodid biomassratio: this swung from 0.65 at Mombasa to 6.8 in the Transkei. This hasimplications for the transfer of primary production through the food chain. Grapsids are important macrophagous feeders on the leaves and other partsof mangroves, whereas ocypodids are microphagous deposit feeders.

Specimens of the spider crabs Hyas coarctatus and Inachus dorsettensis were reared in the laboratory under ambient temperature conditions. Individuals were retained until they had undergone two moults, or moulted to the terminal instar: they were then replaced by fresh specimens. The percentage increment was recorded for each moult, and the duration for each intermoult period. Both intermoult period and percentage increment either declined with increasing temperature or showed no response. The effect of body size on these variables tended to reflect that expected in species with determinate growth—intermoult period generally increased with size, whereas percentage increment remained unchanged. Percentage increment was compared between juvenile moults and the puberty moult in both this and earlier studies. In males, the puberty moult increment was smaller than juvenile increments, and this is tentatively related to the diversion of resources to the large puberty increase in chelar size. In females, the puberty moult increment was either larger or smaller, dependant on whether the ovaries matured after or before the puberty moult, respectively—again a reflection of resource allocation. Growth curves constructed from the laboratory data were compared with those based on field studies. These analyses emphasised that seasonal constraints in natural populations could compromise predictions from laboratory experiments.

The limpet Patella vulgata L. is an important microphagous grazer on intertidal rocky shores of north-west Europe, occurring across the wave exposure gradient. Groups of P. vulgata were selected at mid-tide level of two exposed shores and two sheltered, fucoid dominated shores on the Isle of Man, British Isles, and manipulated to equivalent densities and population structure. The level of grazing activity and growth rate were determined over a 1-year period. At the same time, the abundance of epilithic microalgae, measured as the concentration of chlorophyll a, was determined as an estimate of food supply. Microagal abundance showed a seasonal pattern in both exposed and sheltered conditions, with higher levels in winter compared to summer. In both seasons, the microalgal resource was more abundant on the sheltered shore studied. The level of grazing activity in P. vulgata showed a seasonal pattern on the exposed but not the sheltered shores. Averaged over the year, grazing activity on the exposed shores was over double that on sheltered shores. Thus, in sheltered conditions, food supply for limpets was high and grazing activity low; in exposed conditions, food supply was low and grazing activity high. The growth rate of P. vulgata, measured as increase in shell length, showed no significant difference between exposed and sheltered shores. Growth rate was also determined in P. vulgata at natural densities. Although the overall density declined with decreasing exposure to wave action, the density per unit area of grazeable substance was higher in shelter. In these populations, the mean growth rate was over twice as high on exposed compared to sheltered shores.

The diet of the common shrimp Crangon crangon (L.) was studied in Port Erin Bay (Isle of Man, Irish Sea) by analysis of stomach contents, with comparison by season and size class of diet composition and prey diversity. Monthly samples were taken from April 1995 to March 1998. Mysids and amphipods together constituted the dominant prey, accounting for >60% of the diet in both per- cent occurrence and percent abundance. Mysids were most important irrespective of season or size class. The small size group ( 10 mm CL) prey on 0-group fish co-occurring in the study area — plaice (Pleuronectes platessa), dab (Limanda limanda) and sandeel (Ammodytes tobiannus). This suggests that predation by adult C. crangon can affect mortality of young fish in Port Erin Bay.

[The common shrimp, Crangon crangon (Linnaeus, 1758) was reared in the laboratory under controlled conditions (15°C; 34; 12/12 LD), using natural food: frozen muscle of Nephrops and prawns. The effects of food supply (fed each day and every fifth day) on growth were investigated for females and males. Each shrimp was maintained individually, the instar size was determined from exuviae, and the intermoult period was recorded. Survival was higher in both sexes when fed daily than when fed less frequently. In both sexes a food reduction both lengthened the duration of the intermoult period and reduced the moult increment. Consequently, this led to a lower growth rate with reduced feeding. The effects were greater on increment in both sexes, and female growth was more affected in both components. The relative importance of extended intermoults and reduced increments in limiting the growth of crustaceans is discussed. La crevette grise, Crangon crangon (Linnaeus, 1758) a ete elevee au laboratoire en conditions controlees (15°C; 34; 12/12 LD), et en utilisant de la nourriture naturelle: du muscle congele de Nephrops et des crevettes. Les effets de la nourriture fournie (chaque jour et tous les cinq jours) sur la croissance ont ete etudies chez les femelles et les males. Chaque crevette etait elevee individuellement, la taille du stade etait determine a partir des exuvies et la periode d'intermue mesuree. La survie etait plus elevee dans les deux sexes lorsqu'ils etaient nourris chaque jour que lorsqu'ils etaient nourris moins frequemment. Dans les deux sexes, une reduction de nourriture allongeait a la fois la duree de l'intermue et reduisait la prise de poids. Par consequent, ceci conduisait a un taux de croissance inferieur avec une alimentation reduite. Les effets etaient plus importants sur la prise de poids dans les deux sexes et la croissance de la femelle etait plus affectee pour les deux facteurs. L'importance relative des intermues prolongees et des prises de poids reduites dans la limitation de la croissance des crustaces est discutee., The common shrimp, Crangon crangon (Linnaeus, 1758) was reared in the laboratory under controlled conditions (15°C; 34; 12/12 LD), using natural food: frozen muscle of Nephrops and prawns. The effects of food supply (fed each day and every fifth day) on growth were investigated for females and males. Each shrimp was maintained individually, the instar size was determined from exuviae, and the intermoult period was recorded. Survival was higher in both sexes when fed daily than when fed less frequently. In both sexes a food reduction both lengthened the duration of the intermoult period and reduced the moult increment. Consequently, this led to a lower growth rate with reduced feeding. The effects were greater on increment in both sexes, and female growth was more affected in both components. The relative importance of extended intermoults and reduced increments in limiting the growth of crustaceans is discussed. La crevette grise, Crangon crangon (Linnaeus, 1758) a ete elevee au laboratoire en conditions controlees (15°C; 34; 12/12 LD), et en utilisant de la nourriture naturelle: du muscle congele de Nephrops et des crevettes. Les effets de la nourriture fournie (chaque jour et tous les cinq jours) sur la croissance ont ete etudies chez les femelles et les males. Chaque crevette etait elevee individuellement, la taille du stade etait determine a partir des exuvies et la periode d'intermue mesuree. La survie etait plus elevee dans les deux sexes lorsqu'ils etaient nourris chaque jour que lorsqu'ils etaient nourris moins frequemment. Dans les deux sexes, une reduction de nourriture allongeait a la fois la duree de l'intermue et reduisait la prise de poids. Par consequent, ceci conduisait a un taux de croissance inferieur avec une alimentation reduite. Les effets etaient plus importants sur la prise de poids dans les deux sexes et la croissance de la femelle etait plus affectee pour les deux facteurs. L'importance relative des intermues prolongees et des prises de poids reduites dans la limitation de la croissance des crustaces est discutee.]

The population structure, growth, mortality, and size at sexual maturity of the common shrimp (Crangon crangon) were examined in Port Erin Bay, Isle of Man, Irish Sea between April 1995 and July 1998. For estimation of parameters of growth and mortality, monthly length-frequency data were analysed by ELEFAN. The population consisted mostly of the first year class, with a similar size composition each year. Regressions of body wet weight on carapace length indicated isometric growth (exponents very close to 3.0). Parameters of growth were estimated, using the modified von Bertalanffy growth function (VBGF) model incorporating seasonal variation in growth. Females grew faster and reached a larger size at age than males (K=1.09 yr −1 and L ∞ =18.5 mm CL for females, and K=0.90 yr −1 and L ∞ =15.1 mm CL for males). The maximum life span is estimated as 3.3 years. The recruitment pattern shows one major recruitment event per year. Total mortality (Z) by length-converted catch curve was estimated at 3.96 yr −1 , fishing mortality (F) 0.36 yr −1 , and natural mortality (M) 3.60 yr −1 . The size at 50% sexual maturity for females ranged from 12.0 to 12.6 mm CL. Fecundity per recruit was 6.2×10 5 . The exploitation rate (E) corresponding to 50% of the unexploited stock was 0.28 at L 25 , 0.32 at L 50 , and 0.35 at L 75 .

Brood loss during incubation was studied in the crangonid shrimp Philocheras trispinosus. Concurrent changes in length, volume, and water content of eggs were followed. During embryonic development, egg length increased by some 40%, egg volume by about 130%, and water content increased from 69-85%. Egg number was an isometric function of body size in all 5 incubation stages. Brood loss did not vary with female size, and averaged 30% in egg number and 33% in brood dry weight. Brood loss occurred mainly during early and late incubation stages, predominantly the latter. Potential causes of early incubation loss are incomplete fertilization and inadequate attachment of eggs to the pleopods. Possible reasons for the large late-incubation loss include abrasion with substrate during burrowing, exacerbated by the increased egg volume. Brood loss during incubation in crustaceans is a common feature which reduces reproductive output and affects reproductive potential. Brood loss has been well documented for a wide range of crustacean taxa, ranging from terrestrial Isopoda, Amphipoda, and Mysidacea to commercially important marine decapods (reviewed by Kuris, 1991). It appears to be an inevitable consequence of brood exposure to a variable environment during incubation, which varies from a few weeks to several months depending on the ambient temperature (Wear, 1974; Talbot, 1991). This loss of eggs can occur due to a variety of factors, such as parasites, mechanical stress, and increase of egg volume during incubation (Balasundaram and Pandian, 1982; Kuris, 1991), and any potential change in the incubation period may alter the risk of egg mortality. Since this will influence subsequent recruitment (Morizur et al., 1981), brood loss must be considered when constructing models of fecundity per recruit, along with information on growth, size at sexual maturity, and mortality (Kuris, 1991; Botsford, 1991). Brood loss has been incorporated into such models either by using fecundity values with allowances for brood loss, or by measuring fecundity only when hatching is imminent (Morizur et al., 1981; Campbell, 1985). Philocheras trispinosus (Hailstone) is a crangonid shrimp which occurs in European coastal waters and together with the brown shrimp Crangon crangon (L.) plays a key role in the ecosystem of shallow soft bottoms (Tiews, 1970; Kuipers and Dapper, 1981; Evans, 1984; Pihl and Rosenberg, 1984; Labat, 1991). The reproductive pattern, size at sexual maturity, and reproductive output of P. trispinosus have been previously described from the Mediterranean by Labat (1984) and from the Irish Sea by Oh and Hartnoll (1999). However, despite this ecological importance, little is known of its brood loss. Brood mortality has been described for the Korean crangonid Crangon affinis de Haan (see Hong and Oh, 1989), but brood loss in other European crangonids, C. crangon and C. allmani Kinahan, has been indicated but not quantified (Boddeke, 1982; Allen, 1960). In general, brood mortality has been estimated by comparison of fecundity between the earliest and latest egg stages (Perkins, 1971; Jones, 1978; Morizur etal., 1981; Jewett et al., 1985; Campbell and Brattey, 1986; Choy, 1988; Hong and Oh, 1989; Kuris, 1991; Reid and Corey, 1991; Ohtomi, 1997). However, this method has limitations, since it does not determine the timing of brood mortality because it compares only the two extremes of incubation. This study investigated the brood loss of P. trispinosus by examining brood mortality in terms of fecundity and brood weight loss at five egg developmental stages. Changes in egg number, length, weight, volume, and water content are considered. MATERIALS AND METHODS Sampling.-Monthly samples of P. trispinosus were taken between April 1995 and August 1997 from Port Erin Bay, Isle of Man (54?05'N, 04?54'W) (Oh and Hartnoll, 1999). Sampling was carried out down to a depth of 5 m below chart datum, using a beam trawl. Ovigerous females

From 1946 to 1951 Dr N. S. Jones sampled the benthos around the south of the Isle of Man from over 200 sites. Multivariate methods have been used here to compare subsets of this historical data with recent data from the same locations: of these locations some have been subject to heavy scallop dredging over the intervening 40 plus years and some to little dredging. Clear changes were apparent regardless of scallop dredging intensity. Some of the changes in the heavily dredged areas were those expected to result from extreme physical disturbance—an increased polychaete mollusc ratio, loss of some fragile species, and an increase in the predominance of scavenger/predator species. However, changes in the lightly dredged areas also included the loss of a number of species including some potentially fragile tube-dwellers. Reasons for these changes were not apparent.

Aspects of the reproductive biology of the crangonid shrimp Philocheras trispinosus were studied. Size of female 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 3.69 ± 0.56-mm carapace length. Brood weight and fecundity were related isometrically with female body size. Based on dry weight, the reproductive output (mass of incubating eggs/mass of female) averaged 0.24. The main spawning season (percentage ovigerous > 50%), from March-August, was reflected by monthly values of the gonad index >9. The ovarian dry weight of females with eggs near to hatching was nearly fivefold higher than for those with newly laid eggs, and the ovarian dry weight was significantly different between each egg stage. This indicates that ovarian maturation occurs during incubation, suggesting that females were potentially consecutive breeders, capable of multiple spawning within a single reproductive season.

In the period 1946–1953 Dr N. S. Jones sampled the benthos around the south of the Isle of Man at over 200 sites. At the time, he analysed the data in the best ways possible with contemporary techniques, and developed the idea that benthic communities were continuously inter-graded and strongly dependent on substrate type. Dr Jones proposed four distinct community types based on a combination of sediment, characterizing species and numbers and size of dominants. Fifty years on, this data set can now be re-analysed using multivariate statistical methods and the huge processing power of modern computers. Here, a re-analysis is presented using hierarchical agglomerative clustering of Bray–Curtis similarity indices, represented by dendrograms and non-metric multidimensional scaling plots, in an attempt to compare Jones’ subjective community groupings with those obtained objectively. Despite problems encountered with the assortment of different gears used, some confirmation of Jones’ divisions was found.

A model was developed for the growth of intertidal algae with photosynthesis simulated both in air and in a tidal water column. Morphological data on dry mass per unit area and length-area relationships were used to separate the growth of different fucoid species. The relative growth rate of fronds at any height on the shore depended on a trade-off between net photosynthetic performance and tolerance to desiccation. 2. The simulated zonation patterns and growth rates were consistent with those observed previously for Fucus spp. and Pelvetia canaliculata. 3. The simulated growth of Ascophyllum nodosum was always slower than for the other species. This species did not form its characteristic distribution zones in simulations without including further processes in the model. However, Ascophyllum collected from the field could be separated into upper and lower shore morphologies which formed separate zones when they were simulated in competition with each other. 4. Several hypotheses were proposed concerning the relative locations and sharpness of interspecies boundaries on the shore. Zonation patterns were relatively insensitive to changes in most model parameters except the desiccation rate.

Female spider crabs can only mate after the terminal moult, which means that they must either mate whilst soft-shelled after moulting, or subsequently when hard-shelled. There is evidence that some, at least, do both, whereas the majority of crabs mate in only one or other of these states. The mating behaviour, and the means of detecting receptive females, have been studied in a spider crab,Inachus dorsettensis. In this species, mating is predominantly hard-shelled, and receptive females are recognized by their emission of chemical pheromones. The implications of the behaviour patterns for male mating efficiency, sperm competition and female reproductive success are discussed. Mate selection and mating behaviour in other spider crabs are compared withI. dorsettensis. Reasons for similarities and differences are reviewed.

[The desiccation tolerance of the barnacle Semibalanus balanoides was investigated in the laboratory. Barnacles were collected from three levels (approximately MLWN, MTL and MHWN) on a shore in the Isle of Man, and the median lethal time under conditions of 20°C and 15% RH determined. For barnacles of the same opercular diameter the median lethal time was significantly longer at higher shore levels. Compared with low-shore barnacles the median lethal time was approximately 40% longer for mid-shore and 70% longer for high-shore barnacles. The relationship between water content and opercular diameter was examined, and barnacles from the three shore levels showed no differences. Therefore it is thought probable that the difference in desiccation tolerance is due either to differences in behaviour affecting rate of water loss, or differences in tolerance of water loss., The desiccation tolerance of the barnacle Semibalanus balanoides was investigated in the laboratory. Barnacles were collected from three levels (approximately MLWN, MTL and MHWN) on a shore in the Isle of Man, and the median lethal time under conditions of 20°C and 15% RH determined. For barnacles of the same opercular diameter the median lethal time was significantly longer at higher shore levels. Compared with low-shore barnacles the median lethal time was approximately 40% longer for mid-shore and 70% longer for high-shore barnacles. The relationship between water content and opercular diameter was examined, and barnacles from the three shore levels showed no differences. Therefore it is thought probable that the difference in desiccation tolerance is due either to differences in behaviour affecting rate of water loss, or differences in tolerance of water loss.]

Reproductive investment was studied in Irish Sea populations of the spider crabs Hyas coarctatus and Inachus dorsettensis. The species are similar in that reproduction is restricted to the terminal instar, but differ in that H. coarctatus produces a single brood per year, whilst I. dorsettensis produces several. In relation to body weight, egg number (and brood weight) was higher in H. coarctatus. In I. dorsettensis, the first brood produced after maturity had a much lower egg number than subsequent broods. Energy content of broods in relation to energy content of females displayed similar trends, with means of 35 and 32% in Hyas and Inachus, respectively. However, the annual investment in reproduction was higher in Inachus. Possible explanations for an apparently suboptimal reproductive strategy in Hyas are discussed.

The reproductive seasonality and the growth rate of Balanus amphitrite were studied in Lake Timsah in the mid-region of the Suez Canal. Some nauplius larvae were recorded in each month, but they were abundant only from April to October. Cyprid larvae were most abundant from July to August, and settlement from June to October. At different stations in the lake, frequency of settlement was related to biotic rather than abiotic factors. Growth rate was faster in summer than winter, and was related to water quality. The seasonal pattern of reproduction in Lake Timsah reflected the marked seasonality in environmental conditions.