Life-history features of the marine intertidal limpet Notoacmea scutum (Gastropoda) in central California

Growth of individually marked specimens of Notoacmea scutum (Rathke) was followed for 15 months (April, 1978 to June, 1979) at a field site in central California, USA. Growth rates were highly seasonal, being highest from late spring through early summer and lowest during winter. Growth rate also varied significantly with intertidal height: limpets lower in the intertidal zone grew faster. Both relationships may have been related to the relative abundance of food or to the amount of time available for foraging. Recently settled limpets, which were present throughout the year, grew to approximately 17 mm in length by the end of their first year; by then, they had also reached the size at which mature gonads were consistently found (16 mm). Limpets were almost 26 mm long by the end of the second year. Substantial mortality occurred throughout the year, but it was particularly severe during winter, when a large portion of the reproductive population was lost. This pronounced winter mortality was probably not caused by invertebrate predators such as seastars. Most limpets at the study site were less than 2 yr old.     

Settlement of the tube worm Hydroides dianthus (Polychaeta: Serpulidae): cues for gregarious settlement

The larvae of many benthic marine invertebrates settle to form conspecific aggregations and are thought to rely on chemical cues associated with adults as indicators of habitat suitability, although the identification of inductive compounds has proven difficult. Still-water laboratory assays carried out during the summers of 1992 and 1993 with larvae of the serpulid polychaete, Hydroides dianthus (Verrill, 1873), demonstrate that unidentified water-borne compound(s) were responsible for gregarious settlement of competent larvae. Unlike inductive compounds associated with other tube-dwelling polychaetes, the settlement cue was soluble in water and was not associated with the tube, but rather with the body of live adults. In assay chambers divided by a 52-m mesh barrier, a greater percentage of larvae settled on biofilmed substrata when adult worms were present on the other side of the barrier than when adults were absent. Settlement in response to conspecific adults, live worms removed from their tubes, and amputated tentacular crowns of live worms was significantly greater than settlement in response to dead worms, empty tubes, or biofilmed slides. The settlement inducer appears to emanate from the openings of occupied tubes; settlement was greatest along the anterior two-fifths of the tube of living conspecific adults. A single adult was equally capable of eliciting a gregarious response as were five or 25 conspecifics, and newly settled juveniles began to elicit gregarious settlement after approximately 96 h. Extraction of aggregations of adult worms with organic solvents removed the inductive capacity of the tissue, and activity was found in both nonpolar and polar fractions of an extraction series.     

Conspecifics as cues: A mechanism for habitat selection in the Panamanian grass anole (Anolis auratus)

Summary In an experimental choice situation, individuals of both sexes of the lizard Anolis auratus choose to associate with a conspecific individual regardless of its sex. Further, individuals of both sexes associate with an individual of A. tropidogaster, a related species. Given the choice between the two species, they choose their own. Given the choice between a conspecific and a small patch of natural habitat, they do not choose one or the other consistently. These experiments indicate that conspecific association does not function just as a mate selection mechanism as has been previously proposed. The initial association may, in addition, serve a habitat selection function. Conspecifics can thus be seen as cues indicating the presence of suitable habitat as well as being important biological factors in themselves.     

Role of competition and predation in determining habitat occupancy of Cerithiidae (Gastropoda: Prosobranchia) on the rocky,intertidal, Red Sea coasts of Sinai

Six cerithiid snail species occur on rocky intertidal flats along the Sinai coasts of the Red Sea: Clypeomorus moniliferum, Cerithium caeruleum, C. scabridum, C. columna, Clypeomorus tuberculatum and Cerithium echinatum. The present study, conducted at 22 stations covering almost the whole length of Sinai, covered the 4 yr period from October 1972 to August 1976, and describes the habitat occupancy of 5 of these species (C. echinatum is excluded for lack of data). Several of these species (sometimes all) often occur together, and in such cases are distincly segregated by habitat. However all species considerably overlap in their distribution along the axes of four major interrelated abiotic gradients, thus excluding the possibility that habitat segregation is determined by larval settlement preferences. Other distributional patterns observed at some sites, such as lack of overlap or contact between belts of the various species and the relative abundance of food available to all species, make postlarval competitive interactions unlikely. The existence and the degree of proximity of a coral reef with its associated predatory fishes, influence the cerithiids' distributional patterns. Differences between the cerithiid species in their vulnerability to fish predation, associated with differences between sites in the abundance and the accessibility of predatory fishes, and in the availability of refuges for each cerithiid species, can satisfactorily explain the observed distributional patterns including co-occurrence with habitat segregation. It is proposed that habitat segregation is caused by predation on young stages by generalist fishes which may totally eliminate a certain species at a given site; the same site may provide refuges for recruits of another species, allowing these to survive to an advanced age. In general, the flat's structural complexity is associated with its diversity of refuges from predation, and hence with the number of co-existing species. This mechanism for co-existence and habitat segregation in tropical Cerithiidae may also be instrumental in maintaining the high species diversity of other tropical benthic communities.Paper No. 12 in the series Colonization of the Eastern Mediterrancan by Red Sea species immigrating through the Suez Canal     

Foraging and homing behaviour in the high-shore, crevice-dwelling limpet Helcion pectunculus (Prosobranchia: Patellidae)

The foraging activity of the high-shore, crevice-dwelling limpet Helcion pectunculus (Gmelin, 1791) (Prosobranchia: Patellidae) from an exposed shore on the eastern Cape coast of South Africa was monitored. Activity was compared during spring and neap tides and between spring, summer, autumn and winter. Rhythms of activity in this limpet varied depending upon microhabitat; individuals inhabiting both east- and west-facing rock surfaces were active during nocturnal low tides, but limpets on west-facing rock surfaces were also active during daytime low tides, whilst in the shade. Individuals travelled further during foraging excursions in winter (xˉ=85.53 cm) than in either spring (xˉ=55.7 cm) or summer (xˉ=48.8 cm) and also during spring low tides (xˉ=89.8 cm) compared with neaps (xˉ=40.9 cm). H. pectunculus exhibited rigid homing to a fixed scar within a crevice, and feeding excursions were found to consist of three distinct phases: a relatively rapid outward phase, a much slower foraging phase and a rapid homeward phase. Whether or not these limpets graze throughout an excursion is not known. Foraging was always highly directional, with a mean vector which took limpets onto an area of the rock face with the highest microalgal biomass. The fact that H. pectunculus took advantage of optimal feeding areas and memorized their location to enable return visits suggests a learning component in herbivorous gastropod foraging behaviour. Received: 29 December 1997 / Accepted: 8 May 1998     

Environmental chemical cues associated with prey and subsequent prey preference in the wolf spider Hogna carolinensis Hentz (Araneae,Lycosidae)

The purpose of this study was to determine if environmental chemical cues associated with prey can affect subsequent prey choice in wolf spiderlings (Hogna carolinensis). After emergence from the egg sac, three groups of 10 spiderlings were each fed for one-week on one of three naturally-occurring prey species: group 1 fed on nymphs of the field cricket Gryllus pennsylvanicus; group 2 (house cricket, Acheta domesticus); group 3 (mole cricket, Gryllotalpa hexadactyla). They were then tested for subsequent prey preference in choice tests conducted in a plastic arena. Each spiderlings was presented simultaneously with one individual of each prey species in a randomized design. Spiderlings exhibited a significant first preference for the original diet. Thus, experience with certain foods (environmental chemical cues) encountered by newly hatched spiderlings can affect subsequent prey preference in this species.     

Mineralization of major lateral teeth in the radula of a deep-sea hydrothermal vent limpet (Gastropoda:Neolepetopsidae)

Radular teeth of a neolepetopsid patellogastropod limpet, Paralepetopsis ferrugivora, from a deep-sea hydrothermal vent site have similar elemental composition (O, Si, P, S, Cl, K and Fe) to radular teeth of the shallow-waters patellogastropod limpets. However, in contrast to shallow waters limpets, the fully mature teeth of P. ferrugivora do not show any crystalline phases. Amorphous silica was found in the cusp of the teeth and amorphous iron oxide in the junction zone and base of the teeth. Ferritin-rich vesicles were observed in cells adjacent to the junction zone of the early mature teeth, suggesting that these vesicles can mediate the delivery of iron to the tooth matrix. The similarity in the elemental composition between the hydrothermal limpet P. ferrugivora and shallow-waters patellogastropod limpets shows that the extreme hydrothermal environment did not alter the elemental composition of the radular teeth in the deep-sea species.Communicated by P. W. Sammarco, Chauvin     

Recruitment and juvenile survival in the sea hare Aplysia juliana (Gastropoda: Opisthobranchia)

The specificity in settling response of larval Aplysia juliana (Quoy and Gaimard, 1832) on species of its food algae, Ulva spp., provided a rare opportunity for the quantitative study of recruitment and early survival rates in a non-sessile marine invertebrate. Post-metamorphic juveniles spend about 3 weeks feeding and growing on the algae before moving to the rocky habitat of the adults. Recruitment and survival were studied by collecting weekly samples of algae and holding them in the laboratory until the recruits were large enough to be seen and reliably counted. Recruitment occurred throughout the year, although the rates were relatively low in late winter and spring. Recruitment was monitored relative to algal weight and bottom area. Variation in larval abundance and algal standing crop influenced recruitment to the study area. Mortality during the juvenile stage was very high in all cases, although the rates and shapes of the survivorship curves varied between algal species and location.     

Genetic differentiation in the intertidal zone in populations of the alga Enteromorpha linza (Ulvales: Chlorophyta)

Genetic differentiation within the intertidal zone was examined in six populations of the asexually reproducing alga Enteromorpha linza growing in the Long Island Sound, USA. Four of the five populations sampled in 1981 showed significant differentiation between high and low intertidal positions with respect to the GOT-2 locus. The pattern of differentiation was consistent for samples collected at several times during the year with some seasonal modifications. Four additional polymorphic loci, resolved in 1982, identified a total of 13 five-locus genotypes or clones. Four of the six populations sampled in 1982 showed significant differences in clone frequency between high and low intertidal positions. Laboratory experiments revealed differences in response to temperature among the clones. At 24°C a high intertidal associated clone showed an increase in growth, while low intertidal associated clones showed decreased growth compared to growth at 15°C. These results suggest that the microgeographic differentiation observed for E. linza in the intertidal zone may in part be due to the differential adaptation of clones to different intertidal environments. Additional demographic information is needed for individual clones in order to determine the role longevity, reproductive output, recruitment and interclonal competition play in maintaining the observed differentiation.     

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

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

Function of the shell spine in the predaceous rocky intertidal snail Acanthina spirata (Prosobranchia: Muricacea)

Feeding observations revealed that Acanthina spirata (Blainville, 1832) uses the shell spine in a ramming and prying motion, resulting in the fracturing and/or forcing open of opercular plates in the barnacles Balanus glandula (Darwin, 1854) and Chthamalus fissus (Darwin, 1854). Attacking barnacles by using the shell spine may represent a second widespread feeding mechanism (in addition to drilling) in muricacean gastropods. Specialization of the shell spine for attacking barnacles is advantageous over drilling within the context of an optimal foraging theory. Rockey intertidal field and laboratory experiments at Palos Verdes and Los Angeles, California, respectively, in 1981–1982 revealed, that snails with a shell spine have lower handling times and feed at a greater rate than spineless snails which drill their prey. Spine penetration of prey as opposed to drilling takes considerably less time than a tidal cycle. This is expected to increase the success rate for completion of feeding, since during tidal flux snails risk being dislodged. Plasticity in attack mechanisms allows A. spirata with broken spines to penetrate prey by drilling while undergoing spine repair. Differences exist in spine-feeding by A. spirata on B. glandula and C. fissus. The attack process takes more than twice as long when snails attack B. glandula versus C. fissus. However, there is no difference in the mean number of spine thrusts required to penetrate the opercular plates of the two species. When feeding on the larger barnacle B. glandula, A. spirata ingests significantly greater dry weight per unit handling time than with C. fissus.     

Mitochondrial DNA sequence data of the Cape fur seal (Arctocephalus pusillus pusillus) suggest that population numbers may be affected by climatic shifts

The Cape fur seal, Arctocephalus pusillus pusillus is distributed along the southern African coastline from northern Namibia to the south-east coast of South Africa. The species has been impacted by sealing operations since the 1600s, and historical records suggest that the taxon experienced a bottleneck prior to the 20th century. Mitochondrial DNA control region sequences were generated for 106 individuals belonging to six breeding colonies. Haplotype diversity was found to be high (0.975±0.014) whereas levels of nucleotide diversity were much lower compared to other seal species (0.011±0.006). An analysis of molecular variance indicated that the largest percentage of haplotype diversity is distributed within colonies rather than among them. This could be attributed to either extensive gene flow among colonies, a lack of substantial female site philopatry, or incomplete lineage sorting of haplotypes. Mismatch distribution and Fu’s F _S test indicated that the population has experienced a historical population expansion probably between c. 37,000–18,000 YBP and this date coincides very well with the height of the last glacial maximum when food resources were abundant in the South Atlantic. These results also suggest that the recent sealing-induced bottleneck did not have a profound influence on the haplotype diversity and a historical bottleneck prior to a demographic expansion may have been severe enough to reduce nucleotide diversity substantially.     

Asymmetric genetic exchange in the brown seaweed Sargassum fusiforme (Phaeophyceae) driven by oceanic currents

Geological phenomena (e.g. drastic sea level fluctuations during the Quaternary Ice Age in the Northern Hemisphere) have been demonstrated to intensively affect the biogeographic patterns and tempo-spatial compositions of genetic diversity of marine organisms. However, it is poorly understood whether contemporary factors such as oceanic surface currents have also shaped inter-regional population genetics of specific coastal marine flora, with or without limited dispersal capability. In this study, we determined mtDNA Cox1 gene sequences of the brown seaweed Sargassum fusiforme from nine populations along the Chinese coast and one population from the west coast of South Korea, in an effort to understand what factors are contributing to their current genetic structure and geographic distribution patterns. Genetic analyses indicated a deep genetic break between the Yellow-Bohai Sea (YBS) and the other two marginal seas, the East China Sea (ECS) and the South China Sea (SCS). In particular, the amount of genetic exchange from the SCS to each of the ECS and YBS was significantly higher than that from the opposite directions. Our analyses supports the hypothesis that biogeographic patterns of genetic variation in S. fusiforme are probably an interactive consequence of post-glacial colonization from two scattered refugia driven by the offshore Kuroshio Current and asymmetric gene flow among adjacent sea margins.     

Temporal variation of Tubularia indivisa (Cnidaria, Tubulariidae) and associated epizoites on artificial habitat communities in the North Sea

We have analyzed the composition, diversity, density and biomass of a temporal series of samples taken in a Tubularia indivisa community, which dominates a shipwreck in the North Sea waters (N 51°23′,730–E 02°29′,790, 17 nautical miles from the coast, 30 m depth). This shipwreck has structures emerging up to 8 m above the seabed. Water temperature ranged from 4.2°C in March to 20.3°C in August. Salinity showed few variations around 33.9 psu. Bottom tidal currents followed a semi-diurnal cycle and were preferentially NE oriented with 84% of them in the range 0.25–0.75 m s⁻¹. The mean value for total suspended matter was 6.2 mg l⁻¹ with large variations on a monthly scale. The species richness of samples varied from 15 in October to 42 in August with a mean value of 33 species. Diversity indices were higher during autumn and winter because of the strong dominance of a few crustacean species during the warmer months. The total density of individuals ranged from 6,500 ind m⁻² in October to 445,800 ind m⁻² in July, most of these individuals belonging to the amphipod species Jassa herdmani. The biomass of the T. indivisa community varied from 9 g AFDW m⁻² in October to 1,106 g AFDW m⁻² in July, with T. indivisa itself constituting between 59 and 82% of the total biomass. The biomass of T. indivisa was positively correlated with species richness and with the density of 23% of the species identified on this community, suggesting that T. indivisa plays an important structural role in this habitat. This was further confirmed by the number of species associated with T. indivisa which was generally superior to 55% of the sorted species. Multivariate analysis indicated strong differences between spring/summer−autumn/winter assemblages mostly but not solely due to the abundance patterns of species. These findings support the conclusion that shipwrecks in Belgian waters allow the development of assemblages dominated by a high biomass of T. indivisa which in turn provides shelter for high densities and biomass of epizoites. These assemblages will further show large monthly variations in densities and composition due to large variation in T. indivisa biomass under an apparent repetitive annual cycle. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Recruitment and ontogenetic habitat shifts of the yellow snapper (<Emphasis Type="Italic">Lutjanus argentiventris</Emphasis>) in the Gulf of California

We examined recruitment and ontogenetic habitat shifts of the yellow snapper Lutjanus argentiventris in the Gulf of California, by conducting surveys and collections in multiple mangrove sites and major marine coastal habitats from 1998 to 2007. Over 1,167 juvenile individuals were collected and 516 otoliths were aged to describe the temporal pattern of the settlement. L. argentiventris recruits in mangroves, where juveniles remain until they are approximately 100 mm in length or 300-days-old. Back-calculated settlement dates and underwater surveys indicated a major recruitment peak during September and October, around 8 days before and after the full moon. The majority of mangrove sites in the Gulf of California had a similar L. argentiventris average size at the beginning of the settlement season for the cohort of 2003; although there were significant differences in individual sizes at the end of the nursery stage. When sub-adults leave mangroves, they live in shallow rocky reefs and later become abundant in deeper rocky reefs. The density of migratory individuals (10–20 cm SL) decreased exponentially as the distance between a reef and a nearby mangrove site increased. This finding has important implications for local fishery regulations and coastal management plans.     

Brood defence in the great tit (Parus major): the influence of life-history and habitat

Summary We examined the extent to which parental investment, as measured by brood defence, is determined by life-historical selection in a shortlived bird, the great tit (Parus major). Pairs tending first (n=20) and second (n=21) broods in the same Scots pine woods in 1983 were used to test predictions of a cost/benefit model of brood defence based on the species' average demography in coniferous forest. Furthermore, the differences in demography between pine and deciduous forest permitted us to test whether habitat-specific life-history would affect the seasonal pattern of defence. In the model, benefit was defined as the brood's potential contribution to a parent's fitness, and the cost as the potential loss if the defender dies in the act of defence. Univariate and multivariate procedures were applied to six measures of defence response to a live owl (Glaucidium perlatum) plus a taped mobbing chorus. Results proved three of the model's predictions to be false. In coniferous forest, neither the overall strength nor the individual variance of defence behaviour differed among first and second broods, nor was there any consistent difference in defence strength between pairs living in coniferous (n=54) or deciduous (n=84) forest as revealed by comparisons within each brood. These failures could be reconciled with the model by assuming that selection in the past had acted via the average demography of both types of habitat. The model received direct support from defence strength increasing with age of young and, more forcefully, becoming more influenced by brood size in second broods, regardless of habitat.A difference in the strength of defence by the male and female suggests two more functions of behaviour: In first broods, the male risks more than the female as measured by five of six variables. This suggests that defence is facultatively linked to the need for territorial protection from predators all the year round. In the female's presence, the male, taking an additional risk, approaches the owl to half the distance of that of a single, though paired, male, suggesting an additional, social role of defence behaviour.Taken together, anti-predator defence in the great tit serves to protect the brood, the home range and, in the male, the female mate. The magnitude of the benefits envisaged varies among the sexes.     

Influence of habitat on the reproductive biology of the deep-sea hydrothermal vent limpet <Emphasis Type="Italic">Lepetodrilus fucensis</Emphasis> (Vetigastropoda: Mollusca) from the Northeast Pacific

Habitat selection by the hydrothermal vent limpet, Lepetodrilus fucensis, in Northeast Pacific hydrothermal vent ecosystems, may influence its reproductive output, as it occupies habitats with varying physico-chemical conditions that reflect the availability of nutritional resources. Histological techniques were used to determine size at first reproduction, gametogenesis, reproductive output, and fecundity in relation to shell length (SL), through examination of the gonads of male and female L. fucensis, collected from five different hydrothermal vent habitat types with different temperature anomalies and hydrothermal fluid flow vigour: vigorous (VIG), diffuse (DIF), tubeworm bushes (TWB), peripheral (PER), and senescent areas (SEN). Both male and female L. fucensis exhibited early maturity, with the first reproductive event occurring at 3.8 and 3.9 mm shell length, respectively. All stages of gamete development were present in the gonads of males and females, suggesting continuous gametogenesis and asynchronous reproduction in this species. Gametogenic maturity of limpets did not vary among actively venting habitats (VIG, DIF, TWB, and PER), but was significantly lower in males and females from SEN habitats. Mean oocyte diameter was largest in females from VIG habitats, and smallest in females from SEN habitats, than in those from the other habitats (DIF, TWB, and PER). Females from actively venting habitats also had greater actual fecundity than those from senescent habitats. While the gametogenic pattern of L. fucensis appears phylogenetically constrained, selection of actively venting habitats by L. fucensis maximizes its reproductive output. The multiple feeding strategies of L. fucensis may allow for a constant supply of energy to be allocated to reproduction in any habitat except senescent vents. Early maturity, high fecundity, and continuous production of gametes suggest a reproductive strategy characteristic of an opportunistic species, and may be contributing to the extremely abundant populations of L. fucensis observed in the Northeast Pacific vent ecosystem.     

Homing behaviour in the sleepy lizard (Tiliqua rugosa): the role of visual cues and the parietal eye

To investigate how visual cues are integrated into a navigational strategy for homing in the Australian sleepy lizard (Tiliqua rugosa), lizards were displaced beyond their home range, either with full access to visual cues or with no access to visual cues during the displacement. Homeward orientation was significantly worse when lizards were denied visual cues during the displacement than when they were not. However when lizards were displaced with their field of view restricted to the sky, their homeward orientation was equally as good as that of lizards displaced with no visual restriction. These experiments suggest that sleepy lizards use celestial cues to determine the compass bearing of the outward journey, and reverse this bearing to orient in the homeward direction (course reversal). In a subsequent experiment, lizards oriented randomly with respect to home when the parietal eye was entirely covered with a patch during the displacement and return, while control lizards fitted with a sham parietal eye patch were well oriented towards home. In both groups, the lateral eyes were unobstructed and had complete access to visual cues including celestial cues and landmarks. These results suggest that the parietal eye plays a highly significant role in sleepy lizard homing, perhaps mediating a sky polarization compass sense.     

Spawning periodicity and habitat of the palolo worm Eunice viridis (Polychaeta: Eunicidae) in the Samoan Islands

The relationship between the phase of the moon and the emergence of the epitokous segments of the palolo worm Eunice viridis Gray has been known to the natives of the Samoan Islands for centuries. They predict the date and time of day when the emergence occurs so that they can be ready to catch the worms. This phenomenon is one of the best known examples of lunar periodicity. It was first described scientifically at the end of the last century. My own investigations concern the occurrence of the worms in the reef, in which they gnaw long tunnels through the massive blocks of coral limestone at levels characterized by the occurrence of symbiotic algae. Apparently the algae are the main sources of nutrition for the worms. The casting off of the epitokous segments occurs at the third quarter of the moon in October or November. An analysis of known dates on which the swarms of worms have appeared permitted a precise method of prediction to be formulated. The causality of this periodicity is discussed.     

A new fat body associated with the gonad of surgeonfishes (Acanthuridae: Teleostei)

Adults of nine species of surgeonfishes (Acanthuridae) from the Red Sea, Israel and the Eastern Tropical Pacific off Mexico possess previously undescribed fat bodies associated with both male and female gonads. These structures are unique in that they are external to the abdominal cavity, are composed almost entirely of highly-saturated triacylglycerols, and appear to have close circulatory connection with the gonads. In all species except one, the fat bodies rest in triangular pockets between the trunk musculature and skin, which extend posteriorly just above the anal fin base. The composition, arrangement and dynamics of the fat bodies suggest that they support the active gonad during a spawning season that lasts, in one species, from May to September.