Hemolymph ferritin and radula structure in the limpets Patelloida alticostata and Patella peronii (Mollusca: Gastropoda)

• 1.1. The mean concentration of total hemolymph iron was 3060μg/100 ml in Patella peronii and 2950μg/100 ml in Patelloida alticostata.
• 2.2. Ferritin was found to act as a major iron-binding protein in the hemolymph of both P. peronii and P. alticostata.
• 3.3. P. alticostata ferritin has a molecular weight of approximately 505,000, while that of P. peronii has a mol wt. of approximately 520,000.
• 4.4. The lateral radula teeth of both species are mineralized by deposits of silica (SiO₂) and iron in the form of goethite (α-FeOOH).
• 5.5. Hemolymph ferritin is suggested to act as a high capacity transport system to supply iron to the mineralizing front of the radula.

     

Reproductive effort in two subtidal populations of the limpet,Patelloida mufria

Summary The reproductive cycle and reproductive effort (RE) of 2 populations of the acmaeid limpet Patelloida mufria were investigated in a subtidal region of N.S.W., Australia. These two populations had vastly different densities, rates of growth and mortality. Nonetheless, their patterns of spawning were remarkably similar with 5 spawning periods during the year of monitoring, and their values for RE were very similar; individuals from each population spawned about 35% of their somatic weight each 6 months. This does not, therefore, conform with theories that the RE of populations should be correlated with their rates of mortality. The results for P. mufria were compared with those of 4 populations of Cellana tramoserica and 2 of P. alticostata which had been studied previously at this location. There was still no general correlation between RE and mortality, but by only using certain combinations of these 8 populations (i.e. only one from each species at a time), positive or negative correlations could be obtained. This illustrated the need to ensure that intraspecific variability is accounted for in any analysis of life-history strategies. Finally, it was concluded that instead of the absolute vale of RE being important, the amount of flexibility in this and other traits may represent the real difference in strategies amongst species.     

Intraspecific interactions between adults and juveniles of the subtidal limpet,Patelloida mufria

Summary Regular monitoring of populations of the subtidal limpet Patelloida mufria (Hedley), which were at naturally large densities (>1000/m²), showed that at the times when there were peaks in juvenile recruitment, the mortality of adults increased greatly. This produced a cyclical pattern in the density of adults, suggesting the juveniles play a partial regulatory role. Experimental manipulations were done to test the influence of overall density and the density of juveniles on the growth and survival of adults. These indicated that an increase in overall density reduced the rate of growth of individuals and increased the rate of adult mortality during the peaks in juvenile recruitment. Similarly, removing these juveniles as they recruited averted this decline in adult abundance. The proposed mechanism to explain these results is that the juveniles have a competitive advantage over adults as they are much smaller and therefore require less energy to survive. It is hypothesisied, therefore, that there will be a threshold of adult size below which the recruits will lose their competitive advantage. Furthermore, if their density became too great, the cover of crustose algae (which is the main food of this species) would be removed resulting in a rapid decline in the numbers of P. mufria. Such an occurrence could be the ultimate regulatory agent for this species.     

A test of Brown's principle in the intertidal limpet Collisella scabra (Gould, 1846)

Aim Brown's principle predicts that a species will peak in density near its range centre, and decline gradually towards the margins of its geographical distribution. The decline is assumed to reflect a decrease in individual performance near range margins. I test this abundance–performance hypothesis by comparing patterns in density and size across the northern half of the geographical distribution of the marine patellogastropod Collisella scabra (Gould, 1846). Location Collisella scabra is a high intertidal patellogastropod species distributed along the Pacific coast of North America from Cape Mendocino (CA, USA) to southern Baja California (Mexico). I surveyed 11 research sites spanning c. 36–44° N. Methods In each of the 11 research sites I surveyed four distinct microhabitats, and compared spatial patterns in density and in the size of solitary limpets. Results Both density and size were highly variable across the species range. Density peaked near the northern range margin, and showed greater variance at small spatial scales (< 10 km) than at large scales (> 100 km). In contrast, large size occurred uniformly across the survey area, and size was strongly associated with microhabitat. Main conclusion Collisella scabra does not show spatial patterns of density or performance that are consistent with Brown's principle. The underlying assumptions of Brown's principle may conflict with specific characteristics of C. scabra's life history and/or patterns of environmental variation across its range. Because such conflicts may be common in a large number of marine and terrestrial species, the generality of Brown's principle is questioned.     

Distribution and abundance of the acmaeid limpet,Patelloida latistrigata,and its interaction with barnacles

Summary At Cape Banks, New South Wales, adults of the small intertidal limpet, Patelloida latistrigata occur exclusively in the barnacle zone, and are primarily associated with the barnacle, Tesseropora rosea. Limpet density increases with barnacle density. Juvenile limpets can be found throughout the barnacle zone, and on patches of bare rock that may be temporarily available at lower levels on the shore. The failure of juveniles to survive and grow in places other than among Tesseropora is due to a combination of factors. These include desication at high levels on the shore, smothering by rapidly growing algae low on the shore, and the grazing activities of the larger limpet, Cellana tramoserica. These latter two factors also reduce the survival of experimentally transplanted adult Patelloida: algae by covering the substratum and smothering the limpets, and Cellana by outcompeting them for food. The density of Cellana is greater on patches of bare rock than among barnacles, and these large limpets may be unable to move and feed effectively over the irregular surface created by Tesseropora. Patelloida, however, is small enough to feed over and among these barnacles, and hence has a refuge from competition with Cellana. Barnacles may also provide shelter from the effects of desiccation and strong wave action, and thus increase the survival of juvenile Patelloida. By being associated with barnacles, however, Patelloida becomes vulnerable to intermittent predation by the whelk, Morula marginalba. This effect may be serious enough to eliminate small local populations of limpets, either by direct predation or by removing the refuge-providing barnacles. The association with barnacles may also limit the maximum size to which Patelloida can grow. Patelloida is not always found with Tesseropora, and adults in different localities can be found in association with other sessile organisms. It may be argued that small species of limpets require a spatial refuge from physical and/or biological pressures. To examine this hypothesis, the relationship between Patelloida and Tesseropora is compared to other published accounts of limpets with specialised modes of life.     

Population regulation in lake whitefish, Coregonus clupeaformis (Mitchill)

Mechanisms that might compensate for changes in mortality are well known but documentation of their operation and determination of their relative capacities is difficult. In this study the potential of lake whitefish to compensate for fishing mortality is quantified using a conventional fishery stock assessment model. The mechanisms examined are proportion of females, fecundity, survival of eggs and larvae, decrease in age at maturity and growth. The change in each of these parameters necessary to maintain constant recruitment with increasing fishing pressure is determined. Decrease in age of maturity and increased survival of larvae and eggs have the greatest potential for compensation. The total capacity for compensation appears large even when the mechanisms are considered alone. A review of several lake whitefish population studies indicates a large variation in the vital statistics. There is a close relation between total mortality and growth. There is also a close relation between growth and age at maturity. The analyses indicate that increased fishing results in increased growth which then results in a lower age at maturity. This feedback mechanism enables lake whitefish to respond to changes in environmental conditions and on average to maintain a birth rate in balance with mortality.     

Simultaneous polyphenism and cryptic species in an intertidal limpet from New Zealand

The small intertidal limpets known under the name Notoacmea helmsi occupy a wide variety of habitats in New Zealand and exhibit a variety of shell forms. Phylogenetic analyses of DNA sequences from two genes, mitochondrial COI and nuclear ITS1, reveal that this taxon comprises at least five morphologically cryptic species, with at least one of these species, N. scapha, consisting of individuals with two obviously different shell types. One of these forms is an ecophenotypic response to living on eelgrass (Zostera) fronds. Unlike its extinct relative, Lottia alveus, N. scapha is not restricted to this substrate, but individuals living elsewhere are larger and have a different shell shape. Although there is significant overlap in shell form among the different cryptic species, there is some habitat differentiation, with two species predominantly found on exposed shores and three confined to mudflats. One species exhibits distinctive light-avoiding behaviour, the first known case in which behaviour can be used to separate cryptic species in molluscs.     

Population genetics of the endangered limpet Patella ferruginea (Gastropoda: Patellidae): taxonomic, conservation and evolutionary considerations

The limpet Patella ferruginea is the most endangered marine invertebrate in the western Mediterranean rocky shores, whereas Patella caerulea is the most common Mediterranean limpet. From Pleistocene to historic age, P. ferruginea was distributed around the whole Mediterranean basin, since the shells of this species are a characteristic feature of Palaeolithic and Neolithic deposits in this area. However, its Mediterranean range has progressively contracted to a few restricted areas. The ancient origin of the species (18 Ma) and the present geographical isolation among relic populations could have led to a great genetic difference among populations, taking into account the supposedly low dispersal ability of the species. However, we have observed a few genetic differences among populations and a 'star phylogeny' of COI haplotypes from the 41 individuals of P. ferruginea analysed; a similar pattern has also been observed for the seven individuals of P. caerulea studied. Genetic evidences show a possible bottleneck event on late Pleistocene that affected the two species. The results have an important implication on the future management of this endangered species. Additionally, two different morphological types of P. ferruginea have been described by Payraudeau in 1826 : lamarcki and rouxi forms. Clear morphological differences occur between these two types and some authors pointed out the hypothesis about the existence of two different species. The results of the present study conclude that the two different forms of P. ferruginea are ecotypes, rather than different species or subspecies, and intermediate steps are an ecological range instead of hybridization events among different species.     

Development of the musculature in the limpet Patella (Mollusca, Patellogastropoda)

 Whole-mount technique using fluorescent-labelled phalloidin for actin staining and confocal laser scanning microscopy as well as semi-thin serial sectioning, scanning and transmission electron microscopy were applied to investigate the ontogeny of the various muscular systems during larval development in the limpets Patella vulgata L. and P. caerulea L. In contrast to earlier studies, which described a single or two larval shell muscles, the pretorsional trochophore-like larva shows no less than four different muscle systems, namely the asymmetrical main head/foot larval retractor muscle, an accessory larval retractor with distinct insertion area, a circular prototroch/velar system, and a plexus-like pedal muscle system. In both Patella species only posttorsional larvae are able to retract into the shell and to close the aperture by means of the operculum. Shortly after torsion the two adult shell muscles originate independently in lateral positions, starting with two fine muscle fibres which insert at the operculum and laterally at the shell. During late larval development the main larval retractor and the accessory larval retractor become reduced and the velar muscle system is shed. In contrast, the paired adult shell muscles and the pedal muscle plexus increase in volume, and a new mantle musculature, the tentacular muscle system, and the buccal musculature arise. Because the adult shell muscles are entirely independent from the various larval muscular systems, several current hypotheses on the ontogeny and phylogeny of the early gastropod muscle system have to be reconsidered. Received: 23 June 1998 / Accepted: 25 November 1998     

Range limits and geographic patterns of abundance of the rocky intertidal owl limpet,Lottia gigantea

Aim We evaluate the stability of the range limits of the rocky intertidal limpet, Lottia gigantea, over the last c. 140 years, test the validity of the abundant centre hypothesis, and test indirectly the roles played by recruitment limitation and habitat availability in controlling the range limits. Because this species is size‐selectively harvested, our results also allow us to assess conservation implications. Location The Pacific coast of North America, from northern California to southern Baja California (41.74° N–23.37° N), encompassing the entire range of L. gigantea. Methods The historical and modern distributions of L. gigantea were established using museum data and field observations. Overall and juvenile abundances of local populations were estimated at 25 field sites. The spatial distribution of abundance was evaluated statistically against the predictions of five hypothetical models. The availability of habitat was estimated by measuring the percentage of unavailable sandy beach within cumulative bins of coast across the range of L. gigantea. Results The northern limit of L. gigantea has contracted by c. 2.4° of latitude over recent decades (after 1963), while the southern limit has remained stable. The highest abundances of L. gigantea occur in the centre of its geographic range. Habitat availability is ample in the centre and northern portions of its range, but is generally lacking in the southern range. The northern range is only sparsely populated by adults, with sharp declines occurring north of Monterey Bay (36.80° N). In the southern range, abundance drops precipitously south of Punta Eugenia (27.82° N), coinciding with the region where suitable habitat becomes sparse. Main conclusions Support for the abundant centre hypothesis was found for L. gigantea. Northern populations are characterized as being recruitment‐limited, demographically unstable and prone to local extinctions, while southern populations are suggested to be habitat‐limited. The abundant centre is suggested to result partly from a combination of the indirect effects of human harvesting, generating denser populations of smaller individuals, and larval recruitment from well‐protected offshore rocky islands primarily found in the range centre.     

Genetic and morpho-physiological differentiation in a limpet population across an intertidal gradient

Marine organism adaptive capacity to different environmental conditions is a research priority to understand what conditions are important in structuring the spatial distribution of natural populations. In this context, this study evaluates whether potential differences in Siphonaria lessonii morphology (size and shell shape) and physiology (water loss regulation) at different shore heights are linked to genetically distinguishable individuals. To achieve this goal, we compared size-frequency distribution, morphometric, and genetic data (ISSR-PCR technique) of S. lessonii from the upper, middle and lower shore. We complemented these field samplings with laboratory experiments on water loss and mortality. Genetic analysis showed different genetic composition for individuals from the upper and lower shore. This pattern was accompanied by morpho-physiological variations: the upper shore had fewer small limpets, lower shell shape dispersion (with a morphotype characterized by a higher shell), and less water loss and mortality related to air exposure than the lower shore. The results reported herein support the idea that the extreme and unpredictable conditions of the upper shore may impose strong selection pressure on its inhabitants, leading to considerable morpho-physiological differentiation consistent with different genetic composition. This probably plays an important role in structuring the spatial distribution of natural S. lessonii populations with a possible effect on size-structure distribution.     

Mutualism between the territorial intertidal limpet Patella longicosta and the crustose alga Ralfsia verrucosa

Mutualistic relations between plants and animals are well documented on land but have received less attention in marine systems. This study examined the relationship between the territorial intertidal limpet Patella longicosta and the crustose brown alga Ralfsia verrucosa. Adult Patella are found exclusively in association with Ralfsia, on which they feed, while Ralfsia occurs primarily, but not exclusively, in Patella territories. Ralfsia benefits directly from both the presence and the territorial behaviour of Patella. Algal productivity was assessed by measuring oxygen evolution and utilization in situ and deriving photosynthesis/irradiance curves. Productivity was increased by about 30% by the presence of Patella in both summer (P _max of grazed algae 0.0098; ungrazed algae 0.0063 mg C · cm^-2 · h^-1) and winter (P _max grazed algae 0.0081; ungrazed algae 0.0053 mg^-2 · C · h^-1). Algal growth rates were not significantly increased by the application of limpet mucus in the laboratory. We did not examine nutrient regeneration by the limpet, but the increase in photosynthetic rate may depend on the limpet's grazing pattern which creates secondary sites for growth. Ralfsia also benefited from the territorial behaviour of Patella. The effects of different grazing regimes were investigated in different seasons by removing territorial limpets and either excluding all limpets using copper-based antifouling paint, or allowing access to non-territorial limpets (mostly P. oculus) using partial paint barriers. Exclusion of all limpets resulted in rapid overgrowth of Ralfsia plants by the foliose green alga Ulva sp.. Where non-territorial limpets had access to the plants overgrowth was reduced but Ralfsia plants were entirely removed by destructive grazing. Non-territorial grazers removed 90% of Ralfsia plants within 4 weeks in summer and 60% in winter. In control treatments P. longicosta prevented overgrowth by Ulva and actively excluded vagrant grazers, preventing overgrazing. Based on these findings, the association between the limpet and alga can be regarded as a nonobligate mutualism.     

Population regulation in parasitic nematodes (Thelastomatidae) of cockroaches

Abstract

Populations of four species of thelastomatid nematode in six species of cockroach were regulated by a density- and sex-dependent mechanism. Regulation resulted in an underdispersed (regular) or random distribution of parasites. No cockroach contained more than one adult or juvenile male and rarely more than two adult females, and monogamy was common. Juvenile males were rare whereas juvenile females were relatively common, suggesting that males developed rapidly and were eliminated rapidly from hosts (leaving one). Prevalence of infection varied markedly between cockroach species.     

Brain Structure in Calamoichthys calabaricus Smith 1865 (Polypteridae,Brachiopterygii)

The brain of Calamoichthys calabaricus is reconstructed including the arrangement of the parts of the brain and the cranial nerves and their nuclei. Histologically, the analysis includes structure of the rhombencephalon with its cranial and tegmental nuclei, and the cerebellum.     

Community stability: effects of limpet removal and reintroduction in a rocky intertidal community

Summary The stability of a high rocky intertidal community was assessed in a controlled field experiment in which the most common consumers, limpets, were temporarily removed. Compared to the unmanipulated plots, the exclusion plots developed greater algal abundance and altered species composition of both algae and barnacles. The community was not perturbed beyond its capacity to recover, since the community structure of the limpet-removal plots converged on the structure of the unmanipulated plots following limpet reintroduction. Different components of the community recovered at different rates, depending on whether or not the species had a size-related escape from the limpets. Algae had no size-related escape from limpets. The difference in algal abundance between manipulated and unmanipulated plots lasted less than six months after limpet reintroduction. Barnacles, however, had a size-related escape from limpets and therefore recovered more slowly. The difference in barnacle species composition between the perturbed and unperturbed plots lasted for 17 months after limpet reintroduction. The length of the limpet removal period (16 or 28 months) did not appear to affect the rate of community recovery.     

Studies on the oxygen consumption of a tropical intertidal limpet Cellana radiata (Born): Effect of body size and tidal rhythm

Some observations on the effect of body size on the respiratory metabolism of the tropical limpet Cellana radiata (Born) were made. In addition the tidal rhythm in the oxygen consumption of the animals was also studied.     

Predation by small mobile aquatic predators regulates populations of the intertidal limpet Patella vulgata (L.)

Highly mobile aquatic predators are known to forage in the intertidal during periods of immersion. There is limited quantitative information, however, on the extent to which these predators influence the abundance of grazing molluscs which are known to have a key role in structuring intertidal assemblages. Our preliminary video observations revealed that crabs and small fish were abundant on shores in southwest England during high-tide. We then used manipulative experiments to quantify the effect of small mobile aquatic predators on the abundance of limpets (Patella vulgata L.). On the lower shore at two moderately sheltered rocky shores three treatments were established: complete cage, partial cage (cage control) and uncaged (natural condition). The complete cages excluded all predators. The partial cage treatment allowed full access to small predators and the uncaged treatment allowed access to all predators. After two months, limpet abundance in uncaged and partial cage treatments had declined by around 50% compared to the complete cage treatment. Population structure also changed with survival of larger individuals being greater than smaller individuals in the open and partial cage treatments compared to the complete cage treatment. The effects of excluding predators were consistent at small (meters) and large spatial scales (kilometres) and hence, it would appear that the outcomes of our research are generally applicable to similar shores in the region.To explore the mechanism behind the differential effects of predators according to prey size, we compared the detachment force required to remove limpets of differing sizes from the shore. This was around four times greater for larger individuals than for smaller ones indicating that smaller limpets were more vulnerable to predation. These effects were also consistent between locations. Subsequent laboratory observations showed that the crabs Carcinus maenas (L.), Necora puber (L.) and Cancer pagurus (L.) which are locally abundant predators of limpets, had differing handling behaviour but were all highly efficient at removing limpets from substratum. Hence, shell width and attachment force appeared to be critical factors influencing the vulnerability of limpets to predation by these crabs. Limpets are known to control the abundance of macroalgae on shores in the North-east Atlantic and so our conclusions about the role of mobile predators in regulating the abundance of these grazers are important to our broader understanding of the ecology of these shores.     

Short- and long-term movements of the patellid limpet Patella flexuosa within gaps in intertidal mussel beds

Short-term and long-term movements of the patellid limpet Patellaflexuosa Quoy & Gaimard were studied on an intertidal rockyshore where a mytilid, Hormomya mutabilis (Gould), formed anextensive mussel zone. At low tide, all the limpets were found restingwithin gaps in the mussel zone, which were formed after massdislodgement of the mussels by waves. The foraging areas ofall the marked limpets were restricted to within the gaps duringfour 24h diving observations. All of these limpets displayedhoming behaviour after short excursions with a maximum averagedistance of 6.7 cm from their homes. During short-term observationperiods of about 4–5 days, no marked limpets moved fromone gap to another gap across the mussel bed of H. mutabilis.During long-term observation periods of one month, however,10–30% of marked limpets shifted their homes to differentgaps that had a lower limpet density. The shell length of theseemigrants was, in general, significantly smaller than that ofnon-emigrants. The percentage of emigrants tended to be higherin summer and autumn than in winter and spring. The movementof P. flexuosa within patchy habitats is discussed with a focuson the difference in site fidelity between small and large limpets. (Received 14 April 1998; accepted 7 September 1998)     

Germinoma in razor clam Ensis arcuatus (Jeffreys, 1865) in Galicia (NW Spain)

Germinoma is a gonadal neoplasm originating from progenitor cells in germinal epithelium. Over the last four decades it has been diagnosed in several species of marine bivalve molluscs but most consistently in some populations of Mercenaria mercenaria and Mya arenaria in North America. Tissue sections of gonads from Ensis arcuatus (family Pharidae--superfamily Solenacea), collected in Ría de Vigo (Galicia-NW Spain), revealed germinoma in both males and females. Proliferating, undifferentiated, germ cells, with no evidence of maturation, had formed discrete masses in the walls and lumens of gonadal follicles. This is the first report of germinoma in superfamily Solenacea.