Possible mutualism between females of the subsocial membracid Polyglypta dispar (Homoptera)

Summary Female Polyglypta dispar membracids facultatively guard egg masses or oviposit into masses guarded by other females. Defending females repel at least some enemies of both eggs and nymphs. Eggs of guarding females may be partially protected from parasitism by the presence of additional eggs laid by other females. Females sometimes desert egg masses or groups of nymphs, and undefended masses are sometimes adopted by other females. Some individuals remain on or near the plant where they grew up, and littermates sometimes oviposit into the same egg mass. Some copulating pairs are littermates, while others are not. Females with larger numbers of mature and nearly mature eggs in their ovaries are less likely to defend egg masses, and females desert smaller groups of nymphs more often.     

Some distinguishing characteristics of nesting beaches of the green turtle Chelonia mydas on North West Cape Peninsula,Western Australia

On an 85 km stretch of coastline along the western and northwestern edge of North West Cape Peninsula, Western Australia, are numerous beaches used for nesting by the green turtle Chelonia mydas. Many other beaches in the area are not so used. Nesting beaches displayed three characteristics that distinguished them from non-nesting beaches: the salinity of the sand moisture at nesting depth was lower, the salt content of surface sand was lower, and the beaches were sheltered from prevailing winds. Several beaches on which turtles did not nest exhibited these characteristics, but possessed sand platforms of reduced elevation above sea level. These observations are discussed in relation to the question of what cues green turtles use in selecting nesting beaches.     

Offshore spawning by the portunid crabScylla serrata (Crustacea: Decapoda)

The portunid crabScylla serrata (Forskål) is shown to migrate offshore to spawn. Records of 447S. serrata caught as bycatch by trawlers in the tropical waters of northern Australia were analysed with respect to area, depth, distance offshore and month of capture as well as the sex and size of the crabs and whether the females were ovigerous. The crabs were caught mainly in three areas that correspond to the tiger prawn trawl fishery, at between 10 and 60 m depth (mean 28.5 m), 3 to 95 km offshore (mean 17.9 km). Most (87%) of the crabs were captured in October and November, which suggests they move offshore in September and October. No crabs were reported from offshore by February. Over 97% of the crabs caught offshore were female, of these 61.5% were ovigerous. The size range of females (100–109 to 200–209 mm carapace-width size classes) and males (120–129 to 200–209 mm carapace-width size classes) caught was similar. The frequent occurrence in coastal waters of females that are larger than the modal size at spawning, as well as mature females with spent ovaries, suggests that many females return to the coast after spawning. Although some species of portunid crab are euryhaline, mature females of estuarine species migrate to the sea to spawn. The migration byS. serrata described here is far more extensive than would be required to reach sea water salinities; it probably provides a dispersal mechanism for larvae to enable the megalopa stage to recruit to habitats distant from those of the parents.     

Movement within and between different habitats by the portunid crab Scylla serrata

Tagging experiments were carried out on Scylla serrata in three different types of habitat in Moreton Bay, Queensland, Australia, during 1976–1981. A total of 6 233 crabs were tagged and 1 180 recaptured. Two categories of movement were found, a free ranging type and an offshore migration by females. Crabs in a narrow creek with mangrove-covered banks displayed little movement. In areas with large intertidal flats bare of mangroves, crabs underwent more movement and adults (carapace width 150 mm or greater) and subadults (carapace width 100 to 149 mm) moved similar distances (mean 3.9 km). In an area with direct access to the sea, males and females moved equal distances, but in a long channel behind an island, mean female movement (6.6 km) was significantly more than that of males (mean 3.7 km). The distance between tag and recapture site was not greatly affected by the time at liberty over a period of 1 to 36 wk. Tag recaptures showed an exchange between the populations of a mangrove creek and those in the neighbouring bay. There was very limited exchange between the population in an estuary and the adjacent bay and no exchange was found between neighbouring areas separated by a region of habitat unsuitable for S. serrata. None of the more than 3 000 females captured in the study area was carrying eggs, but two tagged ovigerous females were caught at sea after having moved out of the study area. Eight other females were recaptured in other inshore or estuarine areas 20 to 65 km from their release site.     

Analysis of lipid components for determining the condition of anchovy larvae,Engraulis mordax

It has been presumed that intertidal spawning by Limulus polyphemus minimizes the loss of egges to subtidal predators; however, this strategy involves considerable risks. Massive beach strandings of adults accompany seasonal spawning migrations of crabs along Cape May in Delaware Bay, (USA). At least 190000 horseshoe crabs, approximating 10% of the adult population, died from beach stranding along the New Jersey shore of Delaware Bay during the 1986 (May to June) spawning season. Abnormalities of the telson (which is used in righting behavior) were significantly more common among stranded crabs than among individuals actively spawning on the intertidal beach. The number of stranded crabs per day was not correlated with tidal height or environmental variables (wind speed, wave height) which characterized the conditions at spawning. A complex suite of factors, including the size of the available spawning population, tidal and weather conditions, and beach slope, influence the number stranded during the breeding season. Horseshoe crab stranding results in a large loss of gravid females from the population, and may represent a major input of organic matter to intertidal sandy beaches in certain regions of Delaware Bay.     

Satellite tracking experiments on the navigational ability and migratory behaviour of the loggerhead turtle Caretta caretta

Four loggerhead females (Caretta caretta) were caught when emerging at their nesting beach on the Natal coast, prevented from egg laying and displaced along the coast 38 to 70 km from the capture site. They were then released either on the shore or 37 km offshore. The successful journeys back to the capture area and the successive migrations were tracked by satellite. In compensating for the displacement, loggerheads showed a capability of true navigation. The 545 to 1000 km long migratory journeys of three turtles were followed along the Mozambique coast up to the feeding grounds. Migratory speed was similar at night and during the day. During the trip, submergences were shorter and more frequent than during the stay at the feeding grounds. Received: 17 March 1997 / Accepted: 21 April 1997     

Circatidal activity rhythms in ovigerous blue crabs, <Emphasis Type="Italic">Callinectes</Emphasis><Emphasis Type="Italic">sapidus</Emphasis>: implications for ebb-tide transport during the spawning migration

Female blue crabs (Callinectes sapidus Rathbun) with mature embryos have a spawning migration in which they: (1) undergo ebb-tide transport for movement seaward from estuaries, (2) release their larvae, and (3) reverse direction by undergoing flood-tide transport for up-estuary movement. The study determined whether ebb-tide transport during the spawning migration is based upon an endogenous rhythm in vertical migration. Under constant conditions in a rectangular container, which limited horizontal and vertical movements, females with young and mature embryos had circatidal rhythms (periods=12.11-12.95 h) in migratory restlessness (swimming activity) and egg maintenance behavior (abdominal pumping). However, the rhythms were out of phase, as migratory restlessness occurred during the expected time of ebb tide in the field, and egg maintenance behavior, during the time of flood tide. Under constant conditions in vertical columns (1.32 m high), crabs with mature embryos had a circatidal rhythm (periods=12.2-13.7 h) in which they had frequent bouts of swimming to the surface of the column during the expected time of ebb tide in the field and remained on the bottom during the time of flood tide. This rhythm was not present in crabs with young embryos and disappeared after larval release. Thus, an endogenous rhythm in vertical migration does underlie the ebb-tide transport behavior of ovigerous blue crabs with mature embryos during their spawning migration.     

Body shape and burial behavior of the sand crab Emerita analoga (Stimpson 1857) in a reflective to intermediate morphodynamic range of sandy beaches

Sand crabs belonging to the genus Emerita are the dominant species on sandy beaches of the Pacific and Atlantic coasts of America. The success of this genus has been attributed to the great phenotypic plasticity of life history traits that enables them to cope with swash climate variability from beach to beach. The burrowing rate and variation in carapace shape of Emerita analoga from south-central Chile were studied on a series of five sandy beaches with contrasting reflective-intermediate swash conditions (harsher swash to benign swash). Environmental sampling was carried out monthly from September 2009 to November 2010, while biological experiments were conducted in September and October 2010. A combination of field experiments, geometric morphometric tools and multivariate analysis was used to assess the relationship between burrowing behavior and carapace shape with variables of swash climate. Our results showed that (1) body shape of E. analoga is directly affected by the frequency of effluent line crossing, (2) burrowing rate of E. analoga is affected directly by shape variability, (3) burrowing rate is affected directly and indirectly by the swash climate variables: frequency of effluent line crossing and mean grain size of sediment. Thus, the physical conditions in the intertidal zone may be the main environmental constraints determining cephalothorax shape, with a wider cephalothorax on beaches with finer sand and more benign physical dynamics, and a narrower shape on beaches with coarser sand and harsher physical dynamics. The latter phenotype (narrower shape) probably allows compensating the high difficulty of burying in coarser sediments.     

Beach erosion and geochemical factors: Influence on spawning success of horseshoe crabs (Limulus polyphemus) in Delaware Bay

Horseshoe crab spawning activity is spatially patchy within the Delaware Estuary. This study investigated the importance of geochemical and erosional factors to the selection of breeding beaches. Two sandy beaches in Cape May county, New Jersey, USA, were studied; one beach had been subjected to considerable erosion, exposing underlying peat; the second beach, less than 1 km away, had only traces of peat. Reduced sediments with high levels of hydrogen sulfide were correlated with the presence of peat, and significantly fewer crabs utilized sediments in the proximity of peat beds for reproduction. The lower spawning activity on the beach in the vicinity of exposed peat, suggests that crabs may detect, at a distance, the nature of sediments and the quality of beach for spawning activity. Active salt marsh and peat-bank sediments dominate the upper bay shore; these sediments are unsuitable, or at best marginal, for horseshoe crab reproduction. Extensive bulkheading of eroding sandy beach along several New Jersey shore communities has further restricted the availability of suitable spawning habitat, making the remaining stretches of optimal sandy beach critical to the reproductive success of this species.     

Ecology of sandy beaches in Oman

The benthic macrofauna and physical features of 10 sandy beaches along the coast of Oman were surveyed quantitatively. This is a mesotidal regime mostly subject to low to moderate wave energy but more exposed in the south. Five northern beaches are tide-dominated, with low wave energy, and their profiles consist of a berm, a steep, swash-dominated upper shore and a broad tide-dominated terrace from mid-shore downwards. They are composed of moderately sorted fine to medium sands. Southern beaches experience greater wave energy, particularly during the summer southwest monsoon, and exhibit smoother, concave profiles with fine, fairly well sorted carbonate sand. 58 species and species groups were recorded, with crustanceans, polychaetes and molluscs dominant. In general species richness was high, at least 19–25 species per beach, but dry biomass moderate to low at 26–90g/m shoreline, with one high value of 450g/m. Total abundance was moderate at 3–73×10³ organisms/m of beach. Some zonation was evident with ocypodid crabs andTylos in the supralittoral, cirolanid isopods on the upper shore and a variety of species on the lower shore. The coast of Oman appears to constitute a single zoogeographic region, but with some regional differentiation between north and south due to varying physical conditions. Thus, OmanÕs beaches are characterized by tide-dominated morphodynamics and exceptionally high species richness.     

Geographical patterns in reproductive biology of the Pan-American sandy beach isopod<Emphasis Type="Italic"> Excirolana braziliensis</Emphasis>

Eleven populations of the Pan-American sandy beach isopod Excirolana braziliensis, distributed from tropical (9°N) to temperate (39°S) sandy beaches in Atlantic and Pacific Oceans, were analyzed to determine latitudinal variations in: breeding and recruitment patterns, sex ratios, size of ovigerous females and of juveniles and length–fecundity relationships. E. braziliensis exhibited strong latitudinal patterns in all reproductive traits throughout its distribution range. Breeding and recruitment shifted from continuous to seasonal from tropical to temperate beaches, having a predominance of females at higher latitudes. In agreement with the latitudinal gradient hypothesis, ovigerous females inhabiting tropical sandy beaches (low latitudes) were smaller, became sexually mature at smaller sizes and had lower individual fecundity than on temperate beaches. Juveniles were also smallest at low latitudes. Between-ocean comparisons showed very similar reproductive characteristics for roughly the same latitude. These linked reproductive parameters suggest that the intensity of breeding effort is associated with the duration of the breeding season and geographically size-related characteristics of the species. Geographic variations in the breeding and recruitment seasons, as well as in individual fecundity, size structure of mature females and sex ratios, are proposed to have major consequences in explaining local variations in population demography. Our paper also reinforces the notion that sandy beach animals are highly plastic.Communicated by O. Kinne, Oldendorf/Luhe     

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     

Shell choice in<Emphasis Type="Italic"> Pagurus longicarpus</Emphasis> hermit crabs: does predation threat influence shell selection behavior?

Pagurus longicarpus hermit crabs depend on empty gastropod shells for protection against predation. Hermit crabs avoid gastropod shells in which holes have been drilled by naticid gastropods, and hermit crabs forced to occupy drilled shells are more vulnerable to predation by green crabs, Carcinus maenas. In this study, we examined the effect of predator cues on P. longicarpus shell investigation behavior and shell choice. In paired laboratory shell choice trials, we examined hermit crab response to green crab chemical cues. We compared hermit crabs from two sites differing in the percentage of Littorina littorea shells with drill holes. The percentage of time hermit crabs spent occupying intact shells increased significantly in the presence of predator cues. The effect of predator cues on the amount of time hermit crabs spent investigating shells differed between individuals from the two sites. Predator effluent had a marginal effect on the proportion of hermit crabs initially choosing intact shells and within 15 min most hermit crabs in both treatments occupied intact shells due to shell switching. These results indicate that predation cues alter P. longicarpus shell choice behavior favoring intact shells, which provide greater protection. In summary, predation appears to be a key factor influencing hermit crab shell selection behavior.Communicated by T. Czeschlik     

Local mate competition in the solitary parasitoid wasp <Emphasis Type="Italic">Ooencyrtus kuvanae</Emphasis>

Local mate competition (LMC) occurs when brothers compete with each other for mating opportunities, resulting in selection for a female-biased sex ratio within local groups. If multiple females oviposit in the same patch, their sons compete for mating opportunities with non-brothers. Females, in the presence of other females, should thus produce relatively more sons. Sex ratio theory also predicts a more female-biased sex ratio when ovipositing females are genetically related, and sex-ratio responses to foundress size if it differentially affects fitness gains from sons versus daughters. The mating system of the parasitoid wasp Ooencyrtus kuvanae meets assumptions of LMC. Females insert a single egg into each accessible egg of gypsy moth, Lymantria dispar, host egg masses. Wasps complete development inside host eggs and emerge en masse, as sexually mature adults, resulting in intense competition among brothers. We tested the hypothesis that O. kuvanae exhibits LMC by manipulating the number of wasp foundresses on egg masses with identical numbers of eggs. As predicted by LMC theory, with increasing numbers of wasp foundresses on an egg mass, the proportions of emerging sons increased. In contrast, the presence of a sibling compared to a non-sibling female during oviposition, or the size of a female, did not affect the number or sex ratio of offspring produced. The O. kuvanae system differs from others in that larvae do not compete for local resources and thus do not distort the sex ratio in favor of sons. With no resource competition among O. kuvanae larvae, the sex ratio of emergent son and daughter wasps is due entirely to the sex allocation by ovipositing wasp foundresses on host egg masses.     

Tisular and population level responses to habitat harshness in sandy beaches: the reproductive strategy of <Emphasis Type="Italic">Donax hanleyanus</Emphasis>

Microscopic analysis and field sampling procedures were used to compare demographic and reproductive strategies of the intertidal wedge clam Donax hanleyanus (Bivalvia: Donacidae) in two exposed sandy beaches with contrasting morphodynamics (reflective vs. dissipative) during 13 consecutive months. Histological analysis showed that: (1) the reproductive cycle of D. hanleyanus was more extended in the dissipative beach, and this was true for all the three pre-active (beginning of gonadal activity), active (maturation) and spawning stages; and (2) males and females showed significantly smaller sizes at sexual maturity at the reflective beach. Even though successive increments in proportion and mature at size were observed, the sigmoid function was significantly steeper at the reflective Arachania for both sexes, suggesting an abrupt transition to maturity. Field sampling revealed a more extended recruitment period at the dissipative beach, where recruits were also significantly more abundant than at the reflective beach. These results give support for the habitat harshness hypothesis, which predicts that in intertidal species capable of sustaining populations across a wide spectrum of physical conditions, such as D. hanleyanus, abundance, recruitment, size at maturity and extent of reproductive and recruitment seasons increase from reflective to dissipative beaches. However, a recent hypothesis suggests that reflective beaches acting as sink populations were not sustained, because mature and spawning individuals of both sexes were found in the reflective beach throughout the study period. Thus, we suggest that post-settlement processes are critical in modulating population patterns for this bivalve.     

Phenotype-environment matching in the shore crab (Carcinus maenas)

The shore crab (Carcinus maenas) exhibits a range of carapace pattern polymorphisms, but little is known regarding their function or maintenance. If patterns represent some form of crypsis, then associations between carapace colouration and substrate are expected; to determine whether such relationships exist, frequency of crab morphs and quantity of substrate type were measured from fifteen 10×40 m² quadrats at each of three sites along the southern shore of the Firth of Forth, Scotland. Five thousand one hundred and thirty-seven crabs and 3.6 km of line intercept transect data were collected during a 9-week period. Crab abundance, relative frequency of morphs and substrate type varied significantly among the three sites. Plain crabs were strongly associated with macro-algal substrates whereas patterned crabs were associated with mussel beds. This pronounced phenotype-environment matching, as well as various characteristics of the carapace patterns themselves, suggests that patterned crabs are cryptic on polychromatic backgrounds. The frequency of patterned crabs and the percentage of white pigment on the carapace both declined significantly with carapace width. The loss of pattern coincides with an ontogenetic shift in habitat use and we present evidence to suggest that individual crabs lose their pigment, rather than larger patterned crabs being preferentially removed from the population by predators. Throughout their life history, shore crabs encounter high variation in predation, food supply, and physical habitat; to survive they have evolved a strategy that includes elements of pattern polymorphism, crypsis, ontogenetic shifts, and plastic responses.     

Life history of the red mullet Mullus surmuletus from the bottom-trawl fishery off the Island of Majorca (north-west Mediterranean)

The red mullet Mullus surmuletus is one of the main target species of the trawling fishery along the continental shelf off the Island of Majorca. The size distribution of the catches, and the reproduction, age and growth of this species have been studied based on sampling carried out from 1990 to 1992. The length range of the catches was between 10 and 32 cm, with a main distribution between 15 and 20 cm, but this included small specimens (recruits of 10 to 11 cm) from August. In the >19 cm length-class, females clearly dominated. Monthly variations in the gonadosomatic index (GSI) and in the percentage of mature specimens showed that males spawn from December to June, whereas the reproductive activity of the females centres around spring. Fifty percent of males and females mature at 15 and 16.8 cm, respectively, corresponding to 1 yr of age. Otolith age-readings indicate that the population exploited in the trawl fishery consists of six age-groups, including a very high proportion of individuals between 0 and 4 yr old. Population growth curves revealed that females grow comparatively slowly over a longer period of time and attain greater asymptotic sizes than males. The growth parameters for the whole population are: asymptotic length, L =31.28 cm; growth coefficient, K=0.211 yr^-1; theoretical age when length is zero, t ₀=-2.348 yr.     

Population biology of the annual grassTriplasis purpurea in relation to distance from shore on Staten Island, New York

Four populations of the native annual grassTriplasis purpurea were surveyed on coastal beaches along the south shore of Staten Island, NY, to determine the potential of this species to colonize shoreline habitats mostly devoid of other vegetation. If the species can establish and maintain dense populations, it may have conservation value for urban beaches disturbed by human activities. For two populations, survivorship, growth, and reproduction were monitored at different distances from shore to determine the ability of this species to maintain viable populations. At three sites,T. purpurea occurred in >75% of all quadrats and the highest density was 1195 plants/m² at 74 m from shore in one recently disturbed site. Density generally increased with increasing distances from shore at low tide (from ca. 40 – 90 m). Plants showed the greatest growth and reproduction at close distances to shore (30 – 40 m); part of this effect was due to density in one population, but when density effects were removed statistically, there still remained a decline in growth and reproduction with increasing distance from shore. Improved vigor nearest to shore may be due to continual sand deposition. Survivorship showed a Type I pattern, with low mortality throughout the growing season. By colonizing newly-deposited and continually shifting sands,T. purpurea can contribute to the earliest stages of ecological succession along disturbed beaches in eastern North America and may be valuable to the development and management of urban coastal plant communities.     

Population biology of the annual grass Triplasis purpurea in relation to distance from shore on Staten Island, New York

Four populations of the native annual grassTriplasis purpurea were surveyed on coastal beaches along the south shore of Staten Island, NY, to determine the potential of this species to colonize shoreline habitats mostly devoid of other vegetation. If the species can establish and maintain dense populations, it may have conservation value for urban beaches disturbed by human activities. For two populations, survivorship, growth, and reproduction were monitored at different distances from shore to determine the ability of this species to maintain viable populations. At three sites,T. purpurea occurred in >75% of all quadrats and the highest density was 1195 plants/m² at 74 m from shore in one recently disturbed site. Density generally increased with increasing distances from shore at low tide (from ca. 40–90 m). Plants showed the greatest growth and reproduction at close distances to shore (30–40 m); part of this effect was due to density in one population, but when density effects were removed statistically, there still remained a decline in growth and reproduction with increasing distance from shore. Improved vigor nearest to shore may be due to continual sand deposition. Survivorship showed a Type I pattern, with low mortality throughout the growing season. By colonizing newly-deposited and continually shifting sands,T. purpurea can contribute to the earliest stages of ecological succession along disturbed beaches in eastern North America and may be valuable to the development and management of urban coastal plant communities.