Smaragdia Viridis Research Articles

Invertebrate Grazing on Live Turtlegrass (Thalassia testudinum): A Common Interaction That May Facilitate Fungal Growth

In coastal wetlands and tropical reefs, snails can regulate foundation species by feeding on marsh grasses and hard corals. In many cases, their impacts are amplified because they facilitate microbial infection in grazer-induced wounds. Whether snails commonly graze live plants and facilitate microbial growth on plants in tropical seagrass systems is less explored. On a Belizean Caye, we examined patterns in snail-generated grazer scars on the abundant turtlegrass (Thalassia testudinum). Our initial survey showed the occurrence of snail-induced scarring on live turtlegrass blades was common, with 57% of live leaves scarred. Feeding trials demonstrated that two of five common snails (Tegula fasciata–smooth tegula and Smaragdia viridis–emerald nerite) grazed unepiphytized turtlegrass blades and that smooth tegula abundance had a positive relationship with scarring intensity. Subsequent surveys at three Caribbean sites (separated by >150 km) also showed a high occurrence of snail-induced scars on turtlegrass blades. Finally, simulated herbivory experiments and field observations of a turtlegrass bed in Florida, United States suggests that herbivore damage could facilitate fungal growth in live seagrass tissue through mechanical opening of tissue. Combined, these findings reveal that snail grazing on live turtlegrass blades in the Caribbean can be common. Based on these results, we hypothesize that small grazers could be exerting top-down control over turtlegrass growth directly via grazing and/or indirectly by facilitating microbial infection in live seagrass tissue. Further studies are needed to determine the generality and relative importance of direct and indirect effects of gastropod grazing on turtlegrass health.

NERITIDAE (GASTROPODA, NERITIMORPHA) FROM THE MALACOLOGICAL COLLECTION PROF. HENRY RAMOS MATTHEWS OF THE UNIVERSIDADE FEDERAL DO CEARÁ, BRAZIL

The basic information obtained from scientific collections help us to understanding of Earth’s diverse biota and its biological processes. The Malacological Collection Prof. Henry Ramos Matthews (CMPHRM) of the Universidade Federal do Ceará (UFC), Brazil, is a reference about the biodiversity, mainly marine, of northeastern Brazil. In this collection, the gastropod molluscs of the family Neritidae were among the most representative in number of lots. Since an accurate geographical distribution knowledge is one of the fundamental factors to the study of biodiversity, the present study aimed to describe the composition and spatially analyse the neritids deposited in the CMPHRM/UFC. There is a total of 314 lots of the Neritidae deposited at CMPHRM, belonging to eight species (Nerita chamaeleon, Nerita chlorostoma, Nerita fulgurans, Nerita tessellata, Neritina virginea, Neritina meleagris, Neritina zebra, and Smaragdia viridis). The Malacological Collection Prof. Henry Ramos Matthews of the Universidade Federal do Ceará has representatives of all species of Neritidae recorded in the Brazilian Province, which are important for confirming previous records or establishing new occurrence records.
 Keywords: Neritina, Nerita, Smaragdia, Brazilian Province

Reprint of “Associated mollusc communities of a Posidonia oceanica meadow in Cap Zebib (off North East Tunisia)”

Mollusc communities associated with the seagrass Posidonia oceanica were investigated in Cap Zebib (North-Eastern Tunisia). Samples were collected monthly from May 2007 to May 2008, in two stations located at 3 and 12m depths using a corer of 25cm diameter. A total of 753 individuals belonging to 47 species were identified. The species richness (S) and Shannon–Wiener diversity index (H′) showed significant variation in relation with depth and sampling period, with higher values at 3m depth. The community structure at 3m depth varied considerably from one month to another, while 12m depth did not show any significant temporal variability. The results of similarity percentage (SIMPER) and Factorial Correspondence Analysis (FCA) showed that the species Clanculus cruciatus, Cantharus dorbignyi, Columbella rustica and Cardita calyculata contributed most to the distribution pattern of the mollusc community at 3m depth. In contrast, at 12m depth, the highest contributions were given by the species Jujubinus exasperatus, Smaragdia viridis and Tricolia pullus. Taking into consideration a possible relationship between the faunal composition and plant (P. oceanica) features, a negative correlation was found between the number of mollusc species, Shannon–Wiener diversity and water depth. In contrast, a positive correlation was noted between the number of species and meadow shoot density, with high values in shallow area and more dense stands. For the abiotic parameters, a positive correlation was observed between Shannon–Wiener diversity and the dissolved oxygen. The Leaf Area Index was also positively correlated with temperature and dissolved oxygen.

Associated mollusc communities of a Posidonia oceanica meadow in Cap Zebib (off North East Tunisia)

Mollusc communities associated with the seagrass Posidonia oceanica were investigated in Cap Zebib (North-Eastern Tunisia). Samples were collected monthly from May 2007 to May 2008, in two stations located at 3 and 12m depths using a corer of 25cm diameter. A total of 753 individuals belonging to 47 species were identified. The species richness (S) and Shannon–Wiener diversity index (H′) showed significant variation in relation with depth and sampling period, with higher values at 3m depth. The community structure at 3m depth varied considerably from one month to another, while 12m depth did not show any significant temporal variability. The results of similarity percentage (SIMPER) and Factorial Correspondence Analysis (FCA) showed that the species Clanculus cruciatus, Cantharus dorbignyi, Columbella rustica and Cardita calyculata contributed most to the distribution pattern of the mollusc community at 3m depth. In contrast, at 12m depth, the highest contributions were given by the species Jujubinus exasperatus, Smaragdia viridis and Tricolia pullus. Taking into consideration a possible relationship between the faunal composition and plant (P. oceanica) features, a negative correlation was found between the number of mollusc species, Shannon–Wiener diversity and water depth. In contrast, a positive correlation was noted between the number of species and meadow shoot density, with high values in shallow area and more dense stands. For the abiotic parameters, a positive correlation was observed between Shannon–Wiener diversity and the dissolved oxygen. The Leaf Area Index was also positively correlated with temperature and dissolved oxygen.

Contrasting shell morphology, ingestion and grazing preferences in the neritid gastropod Smaragdia viridis (L.) on two seagrass species

The neritid Smaragdia viridis represents the only known native marine mollusc that feeds on seagrass tissues in the European coasts, displaying a strong association with the seagrasses Cymodocea nodosa and Zostera marina in southern Spain. Seasonal dynamics, shell and radular morphology, growth and feeding of this gastropod have been studied in relation to each seagrass species for contrasting trends resulting from a different type of substrate and food source. In both seagrass species, stable populations of this gastropod occur at similar densities and displaying similar growth rates. Nevertheless shells of individuals from C. nodosa are narrower than those from Z. marina and some differences, possibly a consequence of increased wearing on C. nodosa, were noted amongst the radulae. In C. nodosa, a pre-ingestive selection for young epidermal tissues occurs as it was previously observed in Z. marina. The ingestion rate is higher in C. nodosa than in Z. marina but the absorption of ingested tissues is lower in the former. If both seagrasses are present, most individuals ingested preferentially Z. marina rather than C. nodosa, probably due to the lower digestibility of the epidermal tissues in the latter. Seagrass beds, especially those of Z. marina, are suffering a strong regression in southern Spain and the presence of stable populations of this neritid may be restricted to other declining seagrass species in the area.

Caribbean Seagrasses as a Food Source for the Emerald NeritidSmaragdia viridis

Seagrass canopies harbor many different mollusc species, but information about the interaction of these seagrass residents with their host plants remains scarce. Most gastropods inhabiting seagrass meadows are believed to feed on epiphytes rather than directly on living seagrass tissues. In laboratory experiments, we demonstrate that the gastropod Smaragdia viridis (Linnaeus, 1758) feeds preferentially on three seagrass species that are common in the Caribbean and Bermuda, including Thalassia testudinum, Halodule wrightii, and Syringodium filiforme. The percentage of lysed over intact seagrass cells egested was significantly higher in gastropods fed either T. testudinum or H. wrightii (80.3 ± 4.7% and 84.6 ± 11.4%, mean ± SD) but not for S. filiforme (59.7 ± 15.9%). Diet versatility for both pioneer (H. wrightii and S. filiforme) and climax (T. testudinum) Caribbean seagrass species allows S. viridis to adapt to small-scale disturbances that are common in these habitats, but a diet specializing in seagrass may make this animal vulnerable to large-scale seagrass declines occurring worldwide.

A highly diverse molluscan assemblage associated with eelgrass beds (<i>Zostera marina</i> L.) in the Alboran Sea: Micro-habitat preference, feeding guilds and biogeographical distribution

The fauna of molluscs associated with deep subtidal Zostera marina beds (12-16 m) in southern Spain (Alboran Sea) has been characterised in terms of micro-habitat preference, feeding guilds and biogeographical affinity. The species list (162 taxa) is based on sampling completed before the strong eelgrass decline experienced in 2005-2006, using different methods (small Agassiz trawl covering 222 m 2 and quadrates covering 0.06 m 2 ) and different temporal scales (months, day/night). Dominant epifaunal species are Jujubinus striatus, Rissoa spp. and Smaragdia viridis in the leaf stratum and Nassarius pygmaeus, Bittium reticulatum and Calliostoma planatum on the sediment. Nevertheless, the infauna dominated the epifauna in terms of number of individuals, including mainly bivalves ( Tellina distorta, T. fabula, Dosinia lupinus ). The epifauna of both the sediment and leaf strata included high numbers of species, probably due to the soft transition between vegetated and unvegetated areas. The dominant feeding guilds were deposit feeders, filter feeders and peryphiton grazers, but ectoparasites (eulimids), seagrass grazers ( Smaragdia viridis ) and an egg feeder ( Mitrella minor ) also occurred, unlike in other eelgrass beds of Europe. The molluscan fauna of these Z. marina beds is essentially derived from the local fauna, which includes many widely distributed species along European coasts, with a low representation of strictly Mediterranean or strictly Atlantic species. This fauna is richer than that found in other eelgrass beds of Europe, and deserves important attention for conservation.

Herbivory on Zostera marina by the gastropod Smaragdia viridis

The feeding activity of the gastropod Smaragdia viridis on Zostera marina (eelgrass) was studied under laboratory conditions and from shoots collected in a deep eelgrass bed (12–14 m depth) in southern Spain (Alboran Sea). This gastropod preferentially ingested young leaf tissues, such as those located in the central leaf and first pair of adjacent leaves and at close distances from the junction of the leaves with the sheath. The ingestion rate of this gastropod was size dependent, ingesting up to 40.6 mm 2 of epidermal tissues in 24 h (for large individuals), however this value generally represented a very low percentage of the area of a single shoot (0.3–2.1%). The absorption of eelgrass tissues, in relation to digested/non-digested eelgrass cells in faecal pellets, was not size dependent and reached high values (75–90% cells digested). The grazing impact in an eelgrass bed, based on the affected area (length of radular marks by leaf width), also represented a very low value (0.3–1.1%) in relation to the total LAI (Leaf Area Index) available. A seasonal trend of herbivory was registered with maximum values in summer together with maximum densities of S. viridis.

Molluscs associated with a subtidal Zostera marina L. bed in southern Spain: Linking seasonal changes of fauna and environmental variables

The temporal variation of the molluscan fauna associated with a deep Zostera marina bed (12–14 m depth) in Cañuelo Bay (southern Spain) has been studied in relation to water, sediment and eelgrass variables. Samples of molluscs from the sediment and the eelgrass (5 replicates per season) were seasonally collected using a quadrat of 25 × 25 cm. The water column was characterized by the temperature and chlorophyll a concentration. The grain size distribution of the sediment and percentage of organic matter (%OM) were also studied. Estimations of the shoot density, leaf/rhizome biomass and Leaf Area Index (LAI) have been obtained for each sample. Statistical analyses have been performed with SYSTAT and PRIMER software. A total of 2396 individuals and 85 species of molluscs were collected. The most dominant species were infaunal bivalves such as Tellina distorta (28.1%), Dosinia lupinus, Tellina fabula and Chamelea gallina. The gastropods Jujubinus striatus (4.6%), Nassarius pygmaeus and Bittium reticulatum were the dominant epifaunal species. The most frequent species was T. distorta (100%), followed by other infaunal bivalves such as T. fabula, Solemya togata or Lucinella divaricata. The most frequent gastropods were J. striatus (95%), followed by B. reticulatum, N. pygmaeus, Nassarius reticulatus, Mitrella minor and Smaragdia viridis. The abundance of molluscs displayed significant maximum values in summer and autumn (above 2500 indiv. m −2) and minimum values in spring (below 1500 indiv. m −2). The abundance of the epifauna was related with leaf biomass, whereas that of the infauna was positively related with %OM. The species richness also followed a significant seasonal variation with maximum values in summer (64 species in all summer samples) and minimum values in autumn (44 in all autumn samples), and was positively related with LAI. In both qualitative and quantitative cluster/MDS, samples (replicates) mainly grouped according to the season, with significantly different groupings according to ANOSIM analyses. The studied eelgrass bed is less dense, with a lower leaf biomass, than other European eelgrass beds occurring at shallower depths; however the species richness values are the highest along Europe. The latter could be due to its geographical location in the Alboran Sea, where a confluence of Atlantic, Mediterranean and African fauna occurs.

Diel and seasonal variation of a molluscan taxocoenosis associated with a Zostera marina bed in southern Spain (Alboran Sea)

The diel and seasonal variation of molluscs living in a Zostera marina bed (12–14 m depth) from southern Spain have been studied for one year using a small Agassiz trawl for collecting the samples (222 m2). The frequent and dominant species were very similar in both diurnal and nocturnal samples, including mainly gastropods such as Jujubinus striatus, Nassarius pygmaeus, Mitrella minor, Calliostoma planatum, Rissoa membranacea or Smaragdia viridis. Nevertheless, a significant increase of abundance of scavengers (e.g. Nassarius spp.) and carnivores (e.g. cephalopods) was registered in nocturnal samples. The abundance was maximal in spring and summer in diurnal and nocturnal samples and also in autumn for nocturnal ones, displaying significantly higher values in nocturnal samples. The species richness, diversity and evenness displayed a similar seasonal trend for diurnal and nocturnal samples, with maximum values during summer months. Monthly variation of the molluscan composition (species presence-absence data) was more acute than diel variation, according to the Cluster, MDS and ANOSIM results. Nevertheless, both monthly and diel changes in the structure (species abundance data) of the molluscan taxocoenosis were important throughout the year. Diel changes in the structure of the molluscan fauna are related to an increase of abundance of some species at nighttime due to vertical movements from the sediment to the shoots or along them (e.g. J. striatus, Nassarius spp.) or due to horizontal movements from adjacent habitats (e.g. cephalopods). Nevertheless, some species such as Rissoa spp. or Bittium spp. stay on the leaves of Z. marina during day as well as nighttime.

Trophic dependence of the emerald neritid Smaragdia viridis (Linnaeus, 1758) on two seagrasses from European coasts

separately in plastic containers with natural sea water. Using a binocular microscope, shoots of both seagrasses were examined and it was found that 10 – 15% of them displayed characteristic scraping marks along the central part of the leaves. In other shoots, the typical marks of the herbivorous fish Salpa salpa were also seen on the edges of the leaves. Shoots free of any type of marks were selected as food for S. viridis individuals in order to test if it was able to feed on these seagrasses. In each experimental set-up, one shoot of Z. marina or C. nodosa was placed inside a plastic tray (35 24 cm) with natural seawater together with one individual of S. viridis located in the corner of the tray. Only one species of seagrass was given as diet to each individual. Each experiment was replicated 2 – 3 times for each juvenile and adult individual of S. viridis. A total of 41 experiments were carried out, including 22 experiments with C. nodosa and 19 with Z. marina. Each experiment was run for 24 h. At the end of each experiment, faeces egested by S. viridis were collected using a Pasteur pipette and examined for the presence of digested Z. marina or C. nodosa tissues under the microscope. Shoots of both seagrasses were examined for the presence/absence of radular marks of S. viridis under a binocular microscope after the experiment. Some measurements of radular marks on seagrass leaves and in faeces were made using image analysis and the software Visilog 6. In each experiment, all individuals moved fast to the Z. marina or C. nodosa shoot once placed in the trays. After 2 h, individuals of S. viridis moved slowly along the leaves in both seagrasses and started to leave radular marks while eating the epidermal tissues of the plants. In experiments using Z. marina, radular marks of S.

Temporal changes of mollusc populations from a Zostera marina bed in southern Spain (Alboran Sea), with biogeographic considerations

AbstractMolluscs associated with a Zostera marina bed from Cantarriján bay (Southern Spain, Alboran Sea) at 14–16 m depth were sampled monthly from October 1996 to September 1997. A total of 44,819 individuals belonging to 80 species were identified. In spite of the high species richness, only seven species of gastropods showed a dominance value (D) higher than 1%. Jujubinus striatus was the dominant species of the assemblage with 70.8% of the total abundance. The other dominant species were Rissoa membranacea (9.8%), Nassarius pygmaeus (5.8%), Mitrella minor (4%), Smaragdia viridis (1.9%), Rissoa monodonta (1.4%), Bittium reticulatum (1.3%). The dynamic pattern of the mollusc populations showed a temporal trend with monthly values of species richness and abundance ranging between 10 and 25 species and between 178 and 4412 individuals·222 m−2. The species richness and abundance were higher in the spring and summer months than in the autumn and winter ones. The diversity (Shannon–Wiener, H’) follows a similar trend, with increases from April to September and decreases from October to March. H’ values (ranging from 0.45 to 3.10) are more influenced by the evenness (J) than by the species richness. A multivariate analysis (Cluster, Multi‐dimensional Scaling) based on both presence/absence and quantitative data has also pointed out a temporal trend, with spring–summer samples significantly different from autumn–winter samples. The temporal changes in abundance seem related with the species’ biology, such as recruitment events, as well as to the canopy features and shoot density variation in the Zostera meadow. From the biogeographical point of view, most of the molluscs (65%) found in the Cantarriján bed, have a Lusitanian–Mediterranean distribution (sensuEkman 1953). The proximity to Africa is shown by the presence of four species with a mainly West African distribution. Only R. membranacea has a typical Atlantic distribution, driven by that of Z. marina in NW Europe.

LARVAL DISPERSAL AS A MEANS OF GENETIC EXCHANGE BETWEEN GEOGRAPHICALLY SEPARATED POPULATIONS OF SHALLOW-WATER BENTHIC MARINE GASTROPODS

1. Ten species of prosobranch gastropod veligers collected from the open waters of the North Atlantic Ocean have been identified by comparison of their larval shells with the protoconchs of identifiable juvenile or adult museum specimens. The larvae described are those of Cymatium parthenopeum (von Salis), Cymatium nicobaricum (Röding), and Charonia variegata (Lamarck) belonging to the family Cymatiidae; Tonna galea (Linné) and Tonna maculosa (Dillwyn) belonging to the family Tonnidae; Phalium granulatum (Born) belonging to the family Cassidae; Thais haemastoma (Linné), a muricid; Philippia krebsii (Mörch), an architectonicidae; Smaragdia viridis (Linné), a neritid; and Pedicularia sicula Swainson belonging to the family Ovulidae. 2. The geographical distribution of the veligers of these ten gastropod species has been determined in the North and tropical Atlantic from approximately eight hundred and fifty plankton tows. The relationship between the North and Equatorial Atlantic circulation and the dispersal of gastropod veliger larvae can be seen from these data (Figs. 5-12). Charonia variegata, Philippia krebsii, and Pedicularia sicula were found in all three trans-Atlantic currents sampled, namely, the eastwardly moving North Atlantic Drift and the westwardly flowing North and South Equatorial Current. Cymatium parthenopeum and Tonna galea were found throughout the North Atlantic gyre, but only from scattered records in the South Equatorial Current. Phalium granulatum and Thais haemastoma were found in the North Atlantic Drift and South Equatorial Current. These seven species are regularly dispersed in either direction across the North Atlantic barrier. Smaragdia viridis was found in the western half of the North Atlantic Drift and in the eastern half of the South Equatorial Current; it is probably less frequently transported across the Atlantic. Cymatium nicobaricum veligers were found only once in mid-ocean in the North Atlantic Drift; all other records were restricted to the tropical and warm temperate Western Atlantic. Tonna maculosa veligers were found only in the Gulf Stream. The adults of all ten species are amphi-Atlantic in their geographical distribution and occur in the tropical and warm-temperate shelf waters. Adults of Cymatium nicobaricum and Tonna maculosa, however, are known from only a few records in the eastern tropical Atlantic. 3. The duration of pelagic larval development has been estimated for the same ten species of gastropods. Six species, Charonia variegata, Cymatium parthenopeum, Cymatium nicobaricum, Tonna galea, Tonna maculosa, and Phalium granulatum have a period of pelagic development of over three months. Pedicularia sicula and Smaragdia viridis can probably reach the settling state in less than two months. It is possible that the latter four forms have settling responses and can delay metamorphosis. A comparison between the duration of larval development and the velocity of the North and tropical Atlantic surface currents shows that transoceanic dispersal of the first six mentioned species is possible even without a delay in settlement. 4. The frequency of long-distance dispersal across ocean basins is chiefly dependent upon (a) the drift coefficient, that is, the probability that larvae will be carried off-shore into the major ocean surface currents rather than retained in the coastal waters of the parent population, and (b) the size of the parent population from which the larvae originate. There may be considerable variation in the frequency of long-distance dispersal related to larval mortality. 5. The lower limits of sensitivity obtained by using a conventional plankton net are such that it is possible for trans-oceanic dispersal to occur and yet go completely unnoticed. The concentration of only one larva per tow reoccurring at each station along a transect across the Atlantic may represent a significant amount of trans-oceanic dispersal. 6. If pelagic larvae are important in maintaining genetic continuity, then the degree of morphological differentiation between eastern and western Atlantic populations of gastropod species having amphi-Atlantic distributions would be expected to bear an inverse relationship to the frequency with which the veliger larvae of these species were found in the plankton of the open sea. The evidence from the gastropod species considered here seems to support this hypothesis (Table V).