Notes on the Nerita (Archaeogastropoda) populations of Aldabra Atoll,Indian Ocean

Nerita undata, N. plicata, N. polita, N. albicilla and N. textilis are common intertidal gastropods on Aldabra Atoll. Each species prefers a different level on the shore and/or different degrees of exposure to wave action. Patterns of zonation, population size-frequency structure and biomass are given. N. undata exhibits 2 distinct ecophenotypes. Normal types occur on expsed to moderately sheltered shores but are replaced by type B in extremely sheltered conditions. Differences in shell morphology and population structure are also noted. Foraging by all species was confined to hours of darkness, generally at low tide. Activity of N. polita was induced slightly on overcast days. N. undata and N. textilis are cryptically coloured and often visible during the day. N. plicata is conspicuous, but is protected by a strong shell. N. polita and N. albicilla are often brightly and variably coloured, but both are concealed during daylight. No Nerita were found infected with trematodes, suggesting that the degree of infection was extremely low. Habitats of the Aldabran Nerita are compared with 3 species on Barbados, West Indies.     

Some notes on Tubiluchus corallicola (Priapulida) from Barbados,West Indies

The occurrence of Tubiluchus corallicola (van der Land) in a lagoon on the East coast of Barbados, West Indies, is reported. 23 adult and 2 larval specimens were found in a sample taken from a subtidal stromatolite on which the animals presumably inhabited the algal surface layer. A comparison with data from earlier findings shows that the species is not confined to a particular type of substratum, yet morphologically it seems to be well adapted for a life in the interstitial sand habita. For the first time, living animals were observed and photographed. Their behavior and movements are briefly described and an account of morphological and histological details, as seen in squeezing preparations and photomicrographs, is presented.Supported in part by NSF Grant GB-7952     

Host specificity in sponge-encrusting zoanthidea (Anthozoa: Zoantharia) of Barbados,West Indies

Six species of common Caribbean Zoanthidea, Parazoanthus swiftii, P. parasiticus, P. catenularis, P. puertoricense, Epizoanthus cutressi, and Epizoanthus sp., are virtually restricted to living on surfaces of reef-dwelling sponges. Quantitative surveys on Barbados reefs indicate that substrate specificity is relatively high among these zoanthids with three restricted to a single primary host sponge species and three restricted to three closely related sponges. One species, P. swiftii, exhibits a broad range of acceptable secondary substrates, due to its unique ability to execute migrational spread in the adult polyp stage. Variations in substrate specificity have been noted between island populations within the extensive Caribbean range and appear to be due to different species compositions of local sponge communities and slight differences in zoanthid larval settling specificities.     

Dynamic zonation of Nerita plicata,N. undata and N. textilis (Prosobranchia: Neritacea) populations on a rocky shore in Kenya

Vertical zonation of Nerita plicata Linnaeus, N. undata Linnaeus, and N. textilis Dillwyn, inhabiting the rocky cliffs of Nyali, Kenya, was studied through several spring-neap tidal cycles from November to December (northeastern monsoon) 1981 and May to July (southeastern monsoon) 1982. For the first time, a monsoon-related cycle of migration in Nerita plicata and N. undata, superimposed on the shorter term spring-neap cycle is demonstrated. Both species rest predominantly in the upper eulittoral zone and the littoral fringe. N. plicata and N. undata rest at significantly higher levels during the southeastern monsoon (SEM) than during the northeastern monsoon (NEM) (P<0.001). On and around neap-tide days N. plicata, N. undata, and N. textilis occupy significantly distinct mean resting positions (P<0.001) in both seasons; N. undata being the highest in the SEM, followed by N. plicata, with N. textilis always in the lowest level. In the NEM, N. plicata and N. undata sometimes change order. On and around springtide days in both seasons, the upper two species, N. plicata and N. undata, rest close together with no significant difference in their mean resting positions, but with both significantly higher than N. textilis (P<0.001). Both the spring-neap and the monsoon migrations of N. plicata and N. undata are interpreted as either direct or indirect responses to wave action.     

Solar orientation in the snail Nerita plicata (Prosobranchia: Neritacea) on a beach near Watamu,Kenya

Investigations carried out under natural conditions suggest that Nerita plicata Linné is capable of orientating to the sun. Behaviour is predominatly photonegative during the morning, and photopositive during the afternoon. Accuracy of orientation improves as the brightness of the sun increases. At Watamu (Kenya), snails tended to orientate away from the sea at all times of the day. Orientatory performance is not affected by the temporal proximity of high or low water, and locomotory speeds seem to be unaffected by the strength of the sun, the time of day, or the state of the tide.     

Nocturnal feeding migrations of Nerita plicata,N. undata and N. textilis (Prosobranchia: Neritacea) on the rocky shores at Mkomani,Mombasa, Kenya

The vertical zonation of the three common rocky shore neritids at Mkomani, Mombasa, Kenya, Nerita plicata Linnaeus, N. undata Linnaeus, and N. textilis Dillwyn, as a function of feeding migrations and of size, was studied from 28 February to 24 March 1983. These snails perform feeding migrations at night starting at around mid-ebb tide and return to their resting positions with the flood tide. They remain in their resting positions throughout the day until the next nocturnal ebb tide. The direction of migration is sizerelated, with the larger snails of each species moving in the opposite vertical direction to the smaller ones, so that the populations as a whole exhibit no statistically significant net vertical displacement. The larger individuals of two of the species, N. plicata and N. undata, invariably move downwards to their feeding levels, while the smaller individuals move upwards; the larger individuals of N. textilis display a different pattern of migration, moving downwards on and around spring-tide days and upwards on and around neap tide days, while the smaller individuals move in the opposite directions. N. textilis rest above their feeding level around spring tides, and below that level around neap tides. It is demonstrated how these nocturnal migratory feeding rhythms are integrated into the spring-neap and seasonal cycles of the snails' daytime resting positions. The adaptive significance of these migrations is also discussed.     

Significance of ammonia in determining the N:P ratio of the sea water off Barbados,West Indies

N:P atomic ratios calculated on NO₃-N alone for the upper waters of the tropical Atlantic Ocean off Barbados are very low, being only 9.8:1. Absolute values are also low, the integrated values between O and 100 m for NO₃-N and PO₄-P being 0.59 and 0.06 g-at l^-1, respectively. However, when ammonia is included as a nitrogen source the ratio becomes 28.8:1. This is the average value obtained from 42 samples taken over a 21-month period, and suggests that phosphorus, and not nitrogen, is the more critical nutrient in phytoplankton growth off Barbados.     

Origins of green turtle (<Emphasis Type="Italic">Chelonia mydas</Emphasis>) feeding aggregations around Barbados,West Indies

Although green turtles (Chelonia mydas Linnaeus) do not nest in Barbados, the easternmost island in the Caribbean archipelago, juveniles are regularly seen foraging in nearshore waters. To examine the stock composition of this foraging population, mitochondrial (mt) DNA control region sequences were analysed from 60 juvenile (31–70 cm curved carapace length) green turtles and compared with data published for key nesting populations in the Atlantic, as well as other feeding grounds (FGs) in the Caribbean. Eight distinct haplotypes were recognised among the 60 individual green turtles sampled around Barbados. Three of the haplotypes found have only previously been reported from western Caribbean nesting beaches, and two only from South Atlantic beaches. The nesting beach origin of one of the Barbados FG haplotypes is as yet unidentified. Stock mixture analysis based on Bayesian methods showed that the Barbados FG population is a genetically mixed stock consisting of approximately equal contributions from nesting beaches in Ascension Island (25.0%), Aves Island/Surinam (23.0%), Costa Rica (19.0%), and Florida (18.5%), with a lesser but significant contribution from Mexico (10.3%). Linear regression analysis indicated no significant effects of rookery population size or distance of the rookery from the FG on estimated contributions from the source rookeries to the Barbados FG. Our data suggest that the similar-sized green turtles sampled on the Barbados FG are a mixed stock of more diverse origins than any previously sampled feeding aggregations in the Caribbean region. The relatively large contribution from the Ascension Island rookery to the Barbados FG indicates that hatchlings from distant rookeries outside the Caribbean basin enter the North Atlantic gyre and become a significant part of the pool from which eastern Caribbean foraging populations are derived. These data support a life cycle model that incorporates a tendency of immatures to migrate from their initial foraging grounds at settlement towards suitable foraging grounds closer to their natal rookeries as they mature.Communicated by P.W. Sammarco, Chauvin     

Identification of Amazon River water at Barbados,W. Indies,by salinity and silicate measurements

Salinity and silicate concentrations were studied at about fortnightly intervals for 21 months at a station near Barbados, W. Indies; latitude 13°15 N, longitude 59°42 W. A sensitive inverse correlation was found to exist at 5 and 25 m, but not at greater depths. Salinity near the surface varied between 33.5 and 36.0, and silicate between a little less than 1 and 4 g at/l. Low salinity water, rich in silicate, was found from February to July; salinity increased and silicate decreased from September to December. It is argued that the low salinity water at Barbados can be identified with the areas of reduced salinity found by Ryther et al. (1967) about latitude 8° to 10° N, longitude 50° to 55° W, and that this water originates from the Amazon River. Local precipitation does not seem to be a significant factor.     

Genetic divergence among three sympatric species of Mediterranean Patella (Archaeogastropoda)

Patella caerulea L., P. aspera Lam. (=P. ulyssiponensis Gmelin). P. rustica L. (=P. lusitanica Gmelin) are coexisting Mediterranean species of the genus Patella. P. caerulea and P. rustica have a haploid complement of n=9 with seven metacentric and two telocentric chromosomes, while P. aspera has a haploid complement of n=8 without telocentric chromosomes. To better define the phylogenetic relationships among these three species, an electrophoretic analysis of 12 enzyme coding loci was performed on samples of the three species collected from Laigueglia (Liguria, Italy) in 1989. On the whole, genotypic frequencies were in agreement with Hardy-Weinberg expectations and no significant differences were observed among the populations of the three species as far as their genetic structure is concerned. Nearly 50% of the sampled loci were diagnostic. Nei's genetic distance was 0.82 between P. caerulea and P. aspera, 0.97 between P. aspera and P. rustica and 0.94 between P. caerulea and P. rustica. By greatly separating P. rustica from the other two species, results of the electrophoretic analysis are consistent with the traditional view, which regards P. aspera and P. caerulea as more closely related than P. rustica on the basis of radular teeth morphology. Using genetic distances and the assumptions of the molecular clock, lineages leading to P. aspera and to P. caerulea may have diverged from the stem common to P. rustica ca. 18 million years ago.     

Field observations on the rhythmic behaviour of Nerita textilis (Gastropoda: Prosobranchia)

Field observations on Nerita textilis Dillwyn inhabiting rocky cliffs at Sar Uanle (Southern Somalia) revealed that during the resting phase some of the snails are scattered on the upper cliff and some are clustered at lower levels. During feeding they all migrate downward, but to different extents. Maximum activity of both groups occurs during low water (LW) between midday and midnight. During spring tides (ST), the scattered snails reside higher up and make smaller feeding excursions than during neap tides (NT). During ST, some clustered snails join the belt of scattered individuals, while the trend reverses during NT. A diurnal and a tidal component appear in their periodicity.Publication of the Centro di Studio per la Faunistica ed Ecologia Tropicali del C.N.R. Researches on the coast of Somalia. The shore and the dune of Sar Uanle, No. 14.     

Physiological energetics of cultivated mussel (Mytilus edulis) populations in two Scottish west coast sea lochs

Physiological responses of suspended cultured mussels, Mytilus edulis L., in two Scottish sea lochs (Lochs Etive and Leven) were investigated in their native and transplanted environments, after 15 d, 4.5 mo and 1 yr acclimatization, during the main growing season of May to September 1992. These measurements were integrated by means of the balanced energy equation, and scope for growth was calculated to assess the performance of each stock. Transplanted mussels showed clear signs of stress during the first 15 d after transfer, with low clearance rates and energy retention and high rates of respiration and nitrogen excretion. There were significant differences in some of the physiological responses (clearance, respiration and excretion rates), scope for growth and growth efficiency between the native populations, with the responses of mussels in Loch Etive being more favourable than those in Loch Leven. With newly transplanted mussels after 15 d acclimatization, almost all these measurements also differed significantly from native mussels in their host site and the original stocks but, with the exception of ammonia excretion rates, all the variables of cross-transplanted mussels after 4.5 mo acclimatization were the same as those of the native stock at the host site. Good agreement between observed long-term growth rates and estimated scope for growth suggests that, like growth rate, differences in physiological responses are mainly controlled by environmental factors; i.e., stock or origin had no significant influence on variations in physiological response (except ammonia excretion). The results further indicate that scope for growth estimated during the main growing season can be used to assess the actual growth rate and to compare sites for on-growing.     

Spermatozoon structure of some North American prosobranchs from the families Lottiidae (Patellogastropoda) and Fissurellidae (Archaeogastropoda)

The spermatozoa of four species of the patellogastropod family Lottiidae (Lottia pelta, L. digitalis, L. strigatella, Tectura scutum) and one species of the archaeogastropod family Fissurellidae (Diodora aspera) were examined in 1990 using transmission electron microscopy. All have primitive or ect-aquasperm, typical of invertebrates using external fertilization. Sperm of the lottiid limpets are characterized by a 5 to 9 m-long head composed of a conical acrosome which constitutes >50% of the head length, and a cylindrical nucleus. The acrosome of all species of lottiids is differentiated internally, and has a posterior invagination 0.9 to 1 m in depth, into which an elongate acrosomal lobe protrudes. Between the posterior acrosomal lobe and the nucleus, the subacrosomal material is aggregated as a fibrous column. The midpiece of the sperm has a ring of 4 to 5 spherical mitochondria of 0.6 m diam, posterior to which is a collar of cytoplasm 1 m long, which sheaths the anterior portion of the axoneme. The size and morphology of the acrosome and large cytoplasmic collar clearly distinguish the spermatozoa of the Lottiidae from other families of Patellogastropoda. The sperm of D. aspera (Fissurellidae) is typical of the family of archaeogastropod; the head has a length to breadth ratio of 4:1, and the cylindrical nucleus is capped by a small acrosome, <25% of the total head length, which is deeply invaginated.     

Light absorption and utilization among hermatypic corals: a study in Jamaica,West Indies

The chlorophyll specific absorption coefficient ( _c) was measured for zooxanthellae from six hermatypic coral species obtained, where possible, from four depths (1, 10, 30, 50 m) on reef sites near Discovery Bay, Jamaica in February and March 1983. Measurements of photosynthetic rates versus irradiance, as well as cellular and areal chlorophyll a, were also performed on these colonies or sister colonies. Together the data were used to compare minimum quantum requirements (1/Φ m) among species and depths and to assess the importance of light utilization to the growth and depth distribution of these corals. Our data suggest that, although _c was found to decrease with depth, interspecific differences in _c do not occur for zooxanthellae from the corals investigated. Minimum quantum requirements (1/Φ m) decreased significantly with depth, thereby reflecting an increase in photosynthetic light utilization efficiency with decreasing irradiance. Interspecific differences in 1/Φ m determinations were suggested but not statistically conclusive. We conclude that interspecific differences in gross photosynthesis, and perhaps growth and depth distribution, are primarily attributable to differences in the light utilization capacity of the whole coral, as reflected by the product of _c ^′ and chlorophyll per unit surface area, and in-situ quantum efficiencies. This research was performed under the auspices of the US Department of Energy under Contract No. DE-AC02-76CH00016     

The song of the humpback whale Megaptera novaeangliae in the West Indies

Songs of the humpback whale Megaptera novaeangliae were recorded and analyzed from Grand Turks in the Bahamas to Venezuela. The design features of the song are as follows. The basic song evolves through a series of different sounds in a fixed order. The song is produced only in the winter tropical calving grounds, just before the whales arrive on the banks. Redundancy is high in that syllables, motifs, phrases and the entire song are repeated. Low, intermediate, and high-frequency sounds are scattered throughout the song. One sound is associated with blowing. The song appears to be partially different each year and there are some differences within a year between banks which may indicate that dialects are present. It is suggested that songs from other populations are quite different. The apparent yearly changes do not occur at one point in time. Only single individuals produce the song and they are hypothesized to be young, sexually mature males. The implications of these various design features are discussed.     

Migrational orientation in two species of littoral gastropods (Littorina angulifera and Nerita senegalensis)

Littorina angulifera (Lamark) and Nerita senegalensis Gmelin, both intertidal gastropods, appear to have a preference for specific levels of the shore. In some experiments conducted both in the laboratory and in the field, displaced snails exhibited a general homing behaviour when displaced upshore or downshore. Cues involved in this migrational behaviour have not clearly been identified.     

Model of Japanese serow (Capricornis crispus) energetics predicts distribution on Honshu, Japan.

Understanding what determines a species' range is a central objective in ecology and evolutionary biology. It has important applications for predicting species distributions and how they might respond to environmental perturbations. This paper describes a mechanistic approach to predict past and present distribution of the Japanese serow (Capricornis crispus) on Honshu, Japan. We applied state-of-the-art microclimate and animal biophysical/behavioral models coupled with climate and vegetation data to estimate the distribution of potential range expansion under protection. We tested the model results against detailed empirical distribution data from the Ministry of the Environment for a five-prefecture area in central Honshu. We also applied the models to time-series land use/cover maps to investigate the historical transitions in habitat suitability during 1947-1999 in the Arai-Keinan region. This is the first time to our knowledge that mechanistic models have successfully predicted the landscape scale distribution of a mammal species in the absence of other animal species interactions, such as predators. In this case, animal energetics/behavior-plant interactions seem to be critical. Forest cover appears to be important in summer and winter for suitable serow habitats. The energetics model results indicate that the serow can overheat in some open environments in midday hours in summer. In winter, simulation results suggested that forest cover provides effective refuge to avoid increased metabolic demands of cold temperatures and strong winds. The model simulations suggested that land use/cover changes documented during 1947-1999 resulted in increased suitable serow habitat due to expanding forest cover from agricultural marginalization and ecological succession. The models provide a unique tool for estimating species' range expansion under protection or for selecting suitable reintroduction sites.     

Differences in the structures of fish assemblages inThalassia testudinum beds in Guadeloupe,French West Indies,and their ecological significance

The structures of fish assemblages in twoThalassia testudinum beds in Guadeloupe, French West Indies, one adjacent to mangroves and the other adjacent to coral reefs, were compared between January 1983 and May 1984. The aim of the study was to compare the influences of mangroves and coral reefs on the utilization of seagrass beds by fishes through examination of species composition, catch rate, size of fishes and temporal changes. The two fish assemblages were similar in terms of the number of species they had in common (nearly 44% of the total number of species collected) and the great abundance of juveniles. They both comprised species that usually inhabit other habitats, i.e., estuaries, open waters or coral reefs. Estuary-associated species (e.g. Gerreidae) were the most abundant species in the seagrass bed near the mangroves, while small pelagic species (e.g. Clupeidae) were the most abundant species in the seagrass bed near the coral reefs. The seagrass bed near the mangroves was preferentially utilized as a nursery area by small juveniles of various species (e.g. Clupeidae, Sparidae, Gerreidae, and at least one coral reef species,Ocyurus chrysurus). The abundance of these species varied frequently, suggesting successive arrivals and departures of juveniles over time. The seagrass bed near the coral reefs was characteristically utilized by fishes that are more able to avoid predation, i.e., fishes that forage over seagrass beds at night and shelter in or near the coral reefs during the day (large juveniles of coral reef species and adults of schooling pelagic species, respectively). The constant migrations of these fishes between the coral reefs and seagrass beds explained the relative stability of the structure of the fish assemblage in the seagrass bed over time. Thus, the two seagrass beds were not equivalent habitats for fishes. The distinct ecological influences of the mangroves (as a nursery for small juveniles) and coral reefs (as a shelter for larger fishes) on the nearby seagrass beds was clearly reflected by the distinct utilizations of these seagrass beds by fishes.