Regional extinction of a conspicuous dorid nudibranch (Mollusca: Gastropoda) in California

Felimare californiensis (=Hypselodoris californiensis) was once common throughout the Southern California Bight (SCB) and California Channel Islands. This well-known shallow-water nudibranch, which specializes on dysideid sponges, has persisted for decades in Mexico, but in California disappeared from its entire range by 1984. Since reappearing in 2003, it has been found only at Santa Catalina Island, plus sightings of single individuals in 2011 at Santa Cruz Island and San Diego. The decline of F. californiensis in California was documented using published historical records, museum collections, unpublished field accounts, and images posted online. The loss of this emblematic species is unique among Californian nudibranchs, including (1) its congener Felimare porterae (=Mexichromis porterae), with which it appears to overlap in diet, and (2) opisthobranch species with similar historical geographic ranges and mode of development. The decline in F. californiensis is not predicted by warming trends and climate variation over the past 40 years, including the strong El Niño events of 1983 and 1998. Coastal pollution from the large human population in southern California may have impacted Dysidea amblia, the primary reported prey of F. californiensis. Historical overcollecting of the nudibranch and habitat loss through the development of major ports likely also contributed to its decline. Sightings since 2003 are consistent with a nascent recovery, as elements of water quality have improved in the SCB in recent decades.     

Biodiversity in Littorina species (Mollusca: Gastropoda): a physiological approach using heat-coma

 The upper critical thermal limits were measured as heat-coma temperatures in Littorina species as a tool for examining physiological diversity. Thermal tolerance was found to be stable within a population, but extensive variation occurred between populations and species. All species examined displayed heat-coma values of ∼30 °C and did not show a positive correlation with shore height. Eulittoral-fringe species tended to have higher coma temperatures than eulittoral species. Coma temperatures varied both seasonally and geographically. Lethal thermal limits were also investigated; these were ∼10 C° higher than coma temperatures. Received: 16 August 1999 / Accepted: 13 June 2000     

A molecular phylogeny of the Patellogastropoda (Mollusca: Gastropoda)

Phylogenetic analyses of partial 18S rDNA sequences from species representing all living families of the order Patellogastropoda, most other major gastropod groups (Cocculiniformia, Neritopsina, Vetigastropoda, Caenogastropoda, Heterobranchia, but not Neomphalina), and two additional classes of the phylum Mollusca (Cephalopoda, Polyplacophora) confirm that Patellogastropoda comprises a robust clade with high statistical support. The sequences are characterized by the presence of several insertions and deletions that are unique to, and ubiquitous among, patellogastropods. However, this portion of the 18S gene is insufficiently informative to provide robust support for the monophyly of Gastropoda, or to address the division of the Gastropoda into the subclasses Eogastropoda (= Patellogastropoda + hypothetical coiled ancestors) and Orthogastropoda. These sequence data invariably group Patellogastropoda in a weakly supported clade with cocculiniform limpets, despite greater sequence divergences between Patellogastropoda and “Cocculiniformia” than between the Patellogastropoda and Orthogastropoda. Partial 18S sequences support the inclusion of the family Neolepetopsidae within the superfamily Acmaeoidea, and refute its previously hypothesized position as sister group to the remaining living Patellogastropoda. This region of the 18S rDNA gene diverges at widely differing rates, spanning an order of magnitude among patellogastropod lineages, and therefore does not provide meaningful resolution of the relationships among higher taxa of patellogastropods. Data from one or more genes that evolve more uniformly and more rapidly than the 18S rDNA gene (possibly one or more of the mitochondrial genes) seem more likely to be informative about relationships within Patellogastropoda. Received: 5 February 1999 / Accepted: 16 May 2000     

Chemical defense and evolution in the Sacoglossa (Mollusca: Gastropoda: Opisthobranchia)

Summary. Recent advances in both the systematics and the natural products chemistry of the order Sacoglossa (=Ascoglossa) in the gastropod subclass Opisthobranchia suggest a revised and improved historical account of the evolution of the group. Although the algal genus Caulerpa makes a suitable model for the ancestral food of the order, other siphonaceous algae are consistent with both morphological and chemical data. At an early evolutionary stage terpenoids are sequestered from the food, and used defensively, often with modification. With an evolutionary switch to different kinds of algal food, there is often a shift to other, related defensive chemicals. A switch to new food source sometimes leads to the abandonment of chemical defense, but in other cases there is de-novo synthesis of defensive metabolites. The synthesis of polypropionates, which are used defensively, occurs in some other gastropods, but otherwise is known only in fungi. The systematic distribution of the defensive polypropionates suggests that their defensive use has evolved several times among gastropods. Failure to detect them may mean that synthetic capacity has evolved more than once, or it may mean that they exist at low levels, perhaps having a non-defensive function. Received 9 February 1998; accepted 20 March 1998.     

The nature of heat coma in Littorina littorea (Mollusca: Gastropoda)

 The nature of heat coma was examined in the edible periwinkle Littorina littorea (L.). Duration of acclimation did not influence heat-coma temperature at 12 °C, although other acclimation temperatures were important in influencing thermal tolerance, with positive shifts in coma temperature observed in response to elevated temperatures. Previous thermal history also influenced heat-coma temperatures. Individuals subjected to repeat heat-coma events on a daily basis showed significant declines (P < 0.05) in coma-temperature; in contrast individuals exposed to repeat heat-coma events on a weekly basis showed no decline in thermal tolerance. Size-effects occurred at selected sites, where decreased heat-coma temperatures were recorded in large individuals. Received: 16 August 1999 / Accepted: 13 June 2000     

Intertidal distribution and long-term movements of Littorina irrorata (Mollusca: Gastropoda)

The distribution of Littorina irrorata Say on a low-energy barrier beach on the northern Gulf of Mexico is described, and correlated with the presence of Spartina alterniflora and other plants in the upper intertidal zone. The movements of 66 individually tagged snails were followed in the S. alterniflora zone for an average of 226 days, during which time an average of 10.6 positions were recorded per snail. The snails travelled an average total path distance of at least 995 cm, but due to contorted paths, ended up an average resultant distance of only 399 cm away from their original positions. They moved an estimated resultant distance of approximately 20 to 25 cm per activity period. Despite a slight offshore movement during the fall and winter, the snails moved more parallel to the shoreline than perpendicular to it.     

Density-dependent mortality of recruits of the abaloneHaliotis rubra (Mollusca: Gastropoda)

In three wild populations ofHaliotis rubra surveyed off southeastern Australia during the three years 1987–1989, 0 to 10% post-settlementH. rubra survived for 5 mo. Sequential censuses (February, May and December in each year) provided evidence that mortality of post-settlementH. rubra increased with the density of settlement. The occupation of cryptic habitat byH. rubra soon after settlement may well be an adaptation for avoiding predators or grazers and dislodgement by violent water movement.     

Spawning behaviour and egg capsules of Concholepas concholepas (Mollusca: Gastropoda: Muricidae)

Observations on the spawning behaviour of the commercially important muricid snail Concholepas concholepas are reported. The sequence of events relating to external transportation, molding and hardening, and attachment of the egg capsules to a substratum were timed and divided into 6 major events. The snails studied in the laboratory spawned between April and Septemer. These results and data from the literature reveal an all-year-round spawning activity for the species. The frequency, size and time of spawning were studied over 1 year. Spawning activity always began at night, suggesting that the species retains its spawning rhythm in the laboratory. These was a direct relationship between length of the snail and size of the capsules spawned. No nutritive eggs were found; the number per capsule varied between 668 and 14,250 according to capsule size. Hatching time varied between 69 and 128 days at 13.5° to 14.5°C.     

<Emphasis Type="Italic">Terebralia palustris</Emphasis> (Gastropoda; Potamididae) in a Kenyan mangal: size structure,distribution and impact on the consumption of leaf litter

Although the role of macroinvertebrates in the nutrient cycling of the Indo-Pacific mangrove ecosystems is now a paradigm of ecological research, most of the research and scientific assumptions deal with decapod crustaceans alone. However, decapods are not the only representatives of mangrove macrobenthos and in certain mangals they are surely outnumbered by gastropods, especially by potamidids of the genus Terebralia. This paper aims at bridging the gap in the knowledge of the ecological role of the largest and most abundant potamidid species of the Indo-Pacific mangals, the semiterrestrial T. palustris. In particular we studied size structure and distribution in relation to micro-environmental factors and feeding ecology, both in terms of diet composition and grazing rate, of two populations of this gastropod colonising a Kenyan mangrove creek. In contrast to what has been described by various authors concerning other mangals, in our study site juveniles and adults of T. palustris were present throughout the whole forest, from the landward belt to the seaward fringe, locally reaching very high densities at various levels. Both life stages showed a preference for patches characterised by soil with high organic content; thus the habitat of juveniles largely overlapped with that of the adults, although they are known to occupy different ecological niches. Indeed, gut-content analysis confirmed that juveniles are detritivorous and adults are mainly leaf-litter consumers. In situ experiments on the grazing activity of the adult snails showed that, in contrast to the litter-consuming crabs, they feed in every light and tidal condition, for an hourly consumption rate of ~0.65 g per snail. Considering an average density of about 10.5 adults m^–2, it is estimated that a total of 10.5 leaves m^–2 are removed by adult snails in each tidal cycle (i.e. about every 6 h). T. palustris is the only leaf consumer capable of searching for food under water during high tide and is responsible for the removal of a great quantity of mangrove litter. The results of the present study strongly suggest that T. palustris plays a major role in the food web, mangrove litter degradation and nutrient cycling of the Kenyan mangal.Communicated by R. Cattaneo-Vietti, Genova     

Chemical defense and evolutionary trends in biosynthetic capacity among dorid nudibranchs (Mollusca: Gastropoda: Opisthobranchia)

Summary. An evolutionary scenario incorporating recent advances in phylogenetic research begins with an opisthobranch-pulmonate common ancestor that was herbivorous and had some diet-derived chemical defense. The Nudibranchia and their closest relatives, the Notaspidea, form a lineage the ancestors of which had switched to feeding upon sponges and deriving protection from metabolites contained in them. Subsequently there have been repeated shifts in food and defensive metabolites, and trends are evident in the ability to detoxify, sequester and utilize metabolites from food, as well as to synthesize defensive compounds de novo. The Notaspidea display a minor adaptive radiation that foreshadows a more extensive one in the various lineages of nudibranchs. This review emphasizes changes that have occurred within the Holohepatica, or dorid nudibranchs (order Doridacea). Their sister-group, the Cladohepatica, consists of three other orders, Dendronotacea, Arminacea, and Aeolidiacea, in which there has been a shift from sponges to Cnidaria as food. The Dendronotacea often feed upon Octocorallia, which combine spicules, chemical defense, and stinging capsules and thereby suggest a transition from feeding on sponges. A previous diet of Octocorallia is suggested by the defensive use of prostaglandins in the dendronotacean Tethys fimbria, which eats crustaceans. A shift to bryozoans in some Arminacea is accompanied by use of different metabolites. Dorid nudibranchs evidently began as sponge-feeders, but some lineages have shifted to a variety of other food organisms, and others have specialized in the kind of sponges they feed on and how they do it. There have been shifts to bryozoans (Ectoprocta) and ascidians (Chordata: Urochordata) that track metabolites rather than the taxonomy of the food. There is a crude correlation between the genealogy and the defensive metabolites of the sponge-feeding dorids. De novo synthesis is well documented in this order and the metabolites are appropriately positioned so as to have an adaptive effect. The hypothesis that the capacity for de novo synthesis was acquired by gene transfer across lineages is rejected, partly on the basis of different chirality of metabolites in the nudibranchs and their food organisms. Instead it is proposed that there has been a preadaptive phase followed by evolution in a retrosynthetic mode, with selection favoring enzymes that enhance the yield of end products that are already present in the food. Received 5 February 1999; accepted 26 July 1999     

Evolution and systematics in Haliotidae (Mollusca: Gastropoda): inferences from DNA sequences of sperm lysin

Abalone taxonomy and systematics have remained unresolved: neither stable species-level nomenclature nor a cladistic hypothesis of relationships among species have been established. To infer the phylogeny of the genus Haliotis and to identify species using molecular data, we compared complementary DNA (cDNA) sequences of sperm lysin from 27 species-group taxa from California, Japan, Australia, New Zealand, Taiwan, Borneo, Madagascar, South Africa, Greece, France, Italy and the Azores. The lysin cDNA sequences reveal that 22 of the 27 taxa are clearly distinguishable by >20 nucleotide differences. Of the remaining 5, H. coccinea from the Azores may be a subspecies of H. tuberculata, if not a sibling species (10 nucleotide differences). The other four taxa are most probably the same species as one of the 22 taxa: the lysin sequences are almost identical between H. madaka and H. discus hannai, H. conicopora and H. rubra, H. diversicolor supertexta and H. diversicolor aquatilis, and H. tuberculata lamellosa and H. tuberculata tuberculata. The phylogeny of lysin cDNA suggests that there are three groups among the 27 species-group taxa: (1) all California species and 3 Japanese species (H. gigantea, H. discus hannai, and H. madaka): (2) 1 New Zealand species (H. iris); (3) 1 Japanese species (H. diversicolor aquatilis), Indo-West Pacific species and European species. These groups can be assigned to three previously recognized subgenera (Nordotis, Paua and Padollus) in the genus Haliotis. Two historical hypotheses are proposed to explain the biogeography and evolution within these abalone: (1) Tethyan distribution of the ancestral abalone, during the Cretaceous, followed by extinction in most of the habitat, but radiation in California and Southeast Asia which later spread to the other areas; (2) North Pacific rim distribution of the ancestral abalone, followed by dispersal to the other areas during the Paleogene.     

Use of time, space and food resources in the mangrove climbing crab Selatium elongatum (Grapsidae: Sesarminae)

The activity patterns and use of space of the mangrove dweller Selatium elongatum were studied in the field, in combination with gut content analyses for evaluation of the crab's natural diet. This sesarmine crab proves to be one of the most adapted to climbing and living on mangroves. Moreover, S. elongatum showed a strong preference for being active at high tide, both during the day and night, always along the trunks a few centimetres above the water level, feeding on floating algae and mangrove leaves. Larger males were always recorded within activity areas into which they allow females and smaller males but exclude males of the same size, which probably compete for females. These results confirm that, in spite of the homogeneous herbivorous diet, little niche overlap exists among the several sesarmine crabs inhabiting the East African mangroves, all being leaf consumers segregated on the basis of their horizontal and vertical zonation, and/or of their activity rhythm. Received: 28 September 1998 / Accepted: 14 June 1999     

Effect of microclimatic factors and tide on vertical migrations of the mangrove crab Sesarma leptosoma (Decapoda: Grapsidae)

The tree crab Sesarma leptosoma Hilgendorf migrates up the mangrove trunks twice a day, both in the morning and in the evening, leaving its refuge near the tree base to feed on fresh leaves. In spite of the 150 cm of tide excursion at the base of the trees, the timing of the migrations seems largely controlled by nontidal factors. The timing of the morning upward migration is controlled by the light level alone. The morning downward migration takes place as soon as the temperature rises and relative humidity falls, with no relationship to tidal cycle or light level. Only the evening upward flow seems primarily controlled by the tide, while the evening downward flow, which ends at twilight, seems to be related to the timing of the evening upward migration, to the tide and again to light levels. During the day, crabs abandon the canopy to avoid low relative humidity, usually coupled with the higher wind speeds, which would quickly dehydrate them. At night, crabs stop migrating, probably because their movements and orientation capability along the trunk and in the canopy are largely vision dependent. Nontidal factors have never previously been shown to influence the migratory behaviour of an intertidal crustacean species so extensively. Received: 14 June 1997 / Accepted: 17 July 1997     

Seasonal changes in the biochemical composition of the chiton Chiton iatricus (Polyplacophora: Mollusca) and the marine pulmonate Onchidium verruculatum (Gastropoda: Mollusca) in relation to their reproductive cycles

Seasonal changes in the biochemical composition of two molluses, gonochoric Chiton iatricus and a marine pulmonate, Ochnidium verruculatum inhabiting the same tropical area, but having different modes of reproduction, were studied. Protein is the major biochemical component stored in C. iatricus, whereas lipid is predominantly stored in O. verruculatum. The correlation between these quantifications and the annual reproductive cycles of the two species investigated suggest that nutrients stored in the somatic body parts are channeled towards the gonad during the gametogenesis. In C. iatricus sexual differences efrist in the biochemical needs of the ovary and the testis. The ovary always has a higher protein content than the testis. In the hermaphrodite pulmonate O. verruculatum, biochemical expenditure on gamete production is relatively low because this species has to spend energy on the reproductive propagation viz. copulation and egg-laying. On the contrary, in C. iatricus the biochemical energy is mainly utilized for the production of gametes which have to be produced in great numbers in order to counter-balance the loss of gametes caused by external fertilization. The collected data are discussed in the light of comparative physiology of reproduction.     

Competition for the home and aggressive behaviour in the chiton Acanthopleura gemmata (Blainville) (Mollusca: Polyplacophora)

Summary Computerized screening of all the positions recorded during a synodic month on 120 individually marked chitons (Acanthopleura gemmata) pinpointed their preferential resting points. Unlike the majority of intertidal chitons so far studied, A. gemmata rests in well-defined homes actively dug in the rock. Homes proved to be not strictly individual and periodically interchangeable. A complex aggressive behaviour was recorded in the field when two animals came in contact at home. When competing for ownership of a resting site rival chitons may suppress their nocturnal feeding activity. Despite its strong home-related territoriality A. gemmata showed no mutual exclusion on the feeding area. The highly specialized resting habits clearly protects A. gemmata from its most important predator, the toad fish Arothron immaculatus. The behaviour of A. gemmata is compared to that of other chitons and gastropods, and the current hypotheses concerning the adaptive value of the homing behaviour in littoral molluscs are discussed.     

Factors affecting variability of foraging excursions in a population of the limpet Patella vulgata (Mollusca,Gastropoda)

Paths moved by the limpet Patella vulgata L. were monitored on a sheltered vertical rocky shore in North Wales using time-lapse photography throughout nocturnal low tides in April and November 1992, roughly corresponding to periods of minimum and maximum gonad ripeness, respectively. Various motion parameters, including total duration, total length, and maximum distance reached from home were computed from 124 complete foraging routes obtained from 18 higher-zoned and 18 lower-zoned limpets. P. vulgata typically performed a single loop per night (average total length, ca. 70 cm), moving from the individual home scar to graze the surrounding algal grounds (average maximum distance, ca. 25 cm), then following its own trail back home. On the average, limpets moved from the home scar during three of four available nocturnal low tides and exploited about half the emersion time. Evidence for size-related variability in behaviour was found, as a positive correlation was assessed between both total duration and legth of the excursions, and shell length. In addition, zonation was proved to affect the limpets' foraging behaviour, since low-shore limpets moved faster and covered greater distances than high-shore ones. Moreover, consistent seasonal variation in foraging behaviour emerged, since in April the excursions were longer and longer-lasting than in November, but limpets exploited a larger fraction of potential activity phases in November than in April. The within-population variability in the temporal and spatial characteristics of the foraging excursions is discussed in relation to the available data on zonal and seasonal variation of food resources and in relation to physiological changes due to reproductive cycle.     

Factors affecting fertilization success in two species of patellid limpet (Mollusca: Gastropoda) and development of fertilization kinetics models

Laboratory experiments were undertaken to examine fertilization success in the intertidal prosobranch limpets Patella ulyssiponensis and Patella vulgata. Alkalization of eggs (10 min in pH 9.0 sea water) prior to fertilization trials improved fertilization rates greatly. Fertilization success was found to be a function of sperm concentration, gamete age and contact time. Sperm concentration needed for optimum fertilization success in vivo ranged between 10⁵ and 10⁷ sperm ml⁻¹ for both species although at higher concentrations the number of normally developing trochophore larvae decreased. For P. vulgata, sperm longevity (at a concentration of 10⁶ sperm ml⁻¹) did not exceed 6 h, whereas eggs of both species were fertilizable for up to 12 h. Maximum fertilization success occurred after 15–30 min gamete contact time. The Vogel et al. (Math Biosci 58:189–216, 1982) fertilization kinetics model is developed to allow for non-complete fertilizations under optimal sperm concentrations, and a new parameter fitting technique is developed to improve estimates of fertilization success for short gamete contact times.     

Spread ofCyclope neritea (Mollusca: Gastropoda) along the north-eastern Atlantic coasts in relation to oyster culture and to climatic fluctuations

The geographic distribution ofCyclope neritea (Linné) (Mollusca: Gastropoda) along the Atlantic coasts of Portugal, Spain and France is reported. Analysis of information published over the last 90 yr indicates that, since 1983,C. neritea has extended its range northwards from Arcachon Bay along the coast of the Bay of Biscay. The spread of this small gastropod is directly related to the commercial transport of the Pacific cup oyster (Crassostrea gigas Thunberg) to the Atlantic from Mediterranean oyster-culture sites, and to its encountering climatic conditions suitable for its settlement and reproduction in its new habitat. Its transport by human intervention explains the rapid spread ofCyclope neritea during 1983 and 1984, despite its lack of a planktonic stage or of effective natural migration by adults. Climatic conditions in the southern parts of the Bay of Biscay are similar to those of the French Mediterranean lagoons, explaining the easy acclimatization of this eurythermic gastropod. Also, coastal air and sea-surface temperature records over the last two decades (1971–1988) have revealed a slight warming of the southern parts of the Bay of Biscay. This has resulted in a more strongly marked latitudinal thermal gradient along the Bay of Biscay and has furthered survival and reproduction ofCyclope neritea emigrants. A detailed analysis of commercial supplies of cup oysters to the Bay of Biscay from the Mediterranean coast indicates that theC. neritea emigrants undoubtedly originated from the salt-water lagoons of Salse-Leucate and Thau (French Mediterranean coast).     

Heavy metal contamination and physiological variability in the Brazilian mangrove crabs Ucides cordatus and Callinectes danae (Crustacea: Decapoda)

 Physiological studies were made on the crabs Ucides cordatus (L.) and Callinectes danae sampled from populations living in “polluted” mangroves on the southeast littoral of Brazil. Analysis of Cu, Cd, Zn, and Fe of sediments and crab tissues showed interspecific differences in tissue concentrations, and significantly higher levels of Cu, Cd, and Zn in “polluted” populations compared to “unpolluted” crabs living in uncontaminated mangrove in the same geographical area. Individuals of both species from the polluted site showed significantly greater capacities for regulating blood osmotic concentrations at low salinity (9‰). However, U. cordatus showed a reduced hypo-regulatory ability in 34‰S. Differences in ionoregulation were also seen. “Polluted”C. danae showed significantly higher Na/ K-ATPase levels in posterior gills compared to “unpolluted” crabs. Oxygen consumption rates (M˙ _O2) were elevated in U. cordatus, but depressed in C. danae from the “polluted” population. Individuals of both species from this site showed significantly lower O:N ratios, mainly because of an increased net efflux of ammonia. Adenylate energy charge (AEC) values of muscle and hepatopancreas in “unpolluted” and “polluted” populations of both species were not significantly different. These physiological differences are discussed in relation to the known acute physiological and metabolic effects of heavy metals in crustaceans, and interpretated in the light of possible adaptive changes following long-term exposure to contamination. Received: 6 August 1999 / Accepted: 22 June 2000