Adaptive advantages of patterns of growth and asexual reproduction of the sea anemone Metridium senile (L.) in intertidal and submerged populations

Individual size, rate of growth, and mode and frequency of asexual reproduction are life-history traits of primary importance for sea anemones. These traits determine sexual reproductive output, affect an individual's probability of survival, and are crucial in adapting an individual to its environmental surroundings. The sea anemone Metridium senile (L.) is highly variable in ecological distribution and life history, including rate of growth, individual size, and rate of asexual reproduction. Gonad size (measured as cross-sectional area of gonadal tissue) increases with body weight, so individuals should grow as large and as rapidly as possible to maximize individual sexual reproductive output. Cessation of growth and small body size in intertidal populations suggest that growth is constrained by genetic or environmental conditions. The growth of intertidal individuals transplanted to harbor-float panels demonstrated that growth limits are imposed by environmental factors, most probably limited food and feeding time and damage from wave exposure (which stimulates fragmentation). Individuals in harbor-float populations, which are continuously immersed, grow much larger, and large individuals comprise a greater proportion of the population than in the intertidal zone. The highest rate of fragmentation observed was on harbor-float panels. Patterns of growth and asexual reproduction provide adaptive advantages for M. senile. For harborfloat individuals, large individual size increases gamete production and may increase feeding efficiency. For intertidal individuals, asexual reproduction allows growth despite individual size constraints and rapid population growth, with specific advantages resulting from clone formation.     

Shell colour variation in Bullia digitalis, a sand-dwelling, intertidal whelk (Gastropoda: Prosobranchia)

Bullia digitalis is an intertidal whelk that lives on sandy beaches in South Africa. It is highly variable in shell colour, with individuals varying from white to dark brown. This paper describes shell colour variation of B. digitalis at seven sites, along a 230 km coastline east of the Cape Peninsula. Seven colour forms were found: striped, violet, banded violet, banded brown, orange, pale yellow and white. These forms are probably genetically determined morphs. The striped form is the most common at all sites, constituting 53–62% of each sample. The violet is the second most common morph. Its frequencies are remarkably stable at 15–17%. The striped form blends well into the sandy environment and may therefore be of considerable cryptic value in concealing B. digitalis from predators. The violet form is highly conspicuous. Its stable frequency throughout the study area may represent a genetic balance that is not relevant to any visual advantages of the violet colour.     

Amphibious behaviour and feeding ecology of the four-eyed blenny (Dialommus fuscus, Labrisomidae) in the intertidal zone of the island of Santa Cruz (Galapagos, Ecuador)

The labrisomid Dialommus fuscus , endemic to the Galapagos archipelago, is a predator of crustaceans, which moves up and down the intertidal zone with the tides. Its divided eye and elongated body permit it to forage in the wet sections of the intertidal habitat during low tide, both on the rocks and below the water line and in tide pools. Compared with other intertidal fishes (e.g. Bathygobius sp.), it was present on the rock flat in significantly smaller tide pools nearer to the water line during low tide.     

The spatial and vertical distribution of living (stained) benthic foraminifera from a tropical,intertidal environment,north Queensland,Australia

We investigated the distribution of living (stained) benthic foraminifera across a tropical, intertidal shoreline adjacent to Cocoa Creek, Queensland, Australia for the purpose of better understanding the nature of test production and ultimately fossil assemblage development within such environments. Short cores (up to 1 m) were collected during the wet and dry season, along an elevational gradient comprising non-vegetated intertidal mudflat and higher-intertidal mangrove forest environments. The distribution of stained specimens can be broadly delineated into assemblages characterising ‘upper mangrove’ (2.64–2.91 m above Lowest Astronomical Tide (LAT)) and ‘low mangrove-mudflat’ (1.62–2.18 m above LAT) environments. Agglutinated species were generally limited to upper mangrove stations. Calcareous species occurred within all of the intertidal environments examined but differ in their composition between upper and lower intertidal settings. Upper mangrove faunas were characterised by the agglutinated species Arenoparrella mexicana, Haplophragmoides wilberti, Miliammina fusca, Miliammina obliqua and Trochammina inflata and the calcareous species Helenina anderseni. Live (stained) assemblages at lower intertidal elevations were dominated by the calcareous species Ammonia aoteana, as well as Rosalina spp., Elphidium oceanicum, Triloculina oblonga, Ammonia pustulosa and Shackoinella globosa.     

Characterization of extracellular polymers synthesized by tropical intertidal biofilm bacteria

AIM: This study was performed to determine the potential of tropical intertidal biofilm bacteria as a source of novel exopolymers (EPS). METHODS AND RESULTS: A screening procedure was implemented to detect EPS-producing biofilm bacteria. Isolates MC3B-10 and MC6B-22, identified respectively as a Microbacterium species and Bacillus species by 16S rDNA and cellular fatty acids analyses, produced different EPS, as evidenced by colorimetric and gas chromatographic analyses. The polymer produced by isolate MC3B-10 displays significant surfactant activity, and may chelate calcium as evidenced by spectroscopic analysis. CONCLUSIONS: Polymer MC3B-10 appears to be a glycoprotein, while EPS MC6B-22 seems to be a true polysaccharide dominated by neutral sugars but with significant concentrations of uronic acids and hexosamines. EPS MC3B-10 possesses a higher surfactant activity than that of commercial surfactants, and given its anionic nature, may chelate cations thus proving useful in bioremediation. The chemical composition of polymer MC6B-22 suggests its potential biomedical application in tissue regeneration. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report of a Microbacterium species producing EPS with surfactant properties, which expands our knowledge of the micro-organisms capable of producing these biomolecules. Furthermore, this work shows that tropical intertidal environments are a nonpreviously recognized habitat for bioprospecting EPS-producing bacteria, and that these molecules might be involved in ecological roles protecting the cells against dessication.     

Polychaete assemblages inhabiting intertidal soft bottoms associated with mangrove systems in Coiba National Park (East Pacific,Panama)

The Coiba National Park is located off the Pacific coast of Panama andincludes several small islands and a larger one which gives its name to the park. Anumber of rivers in Coiba Island have well developed mangrove systems attheir mouths and two of these were selected for the present study: SantaCruz and El Gambute. The first one comprises an assemblage of Rhizopora mangle, Laguncularia racemosa and Pellicierarhizoporae, and shows no evidence of recent human activity. The secondone is a smaller forest, solely composed of short Rhizoporamangle trees, and is recovering from the impact of human activities.During 1997, the tidal flats associated with each system were studied. Toasses the polychaete distribution within each tidal flat, three transects werearranged from the low to the upper intertidal level. Every transect hadthree sampling sites: the first one was adjacent to the low water level, thesecond one at an intermediate point, and the third one close to the highwater level and the mangrove line. At each site, three randomly chosensamples of sediment were taken for faunal study and a further one wascollected for sedimentology study.The polychaetes were identifiedto species or genus level. For each flat, a matrix summarizing the actualnumber of individuals of each species in every sample was created, andpopulation density, species richness and diversity were computed for eachsite. After matrix data had been transformed, a similarity analysis of thesamples was carried out.     

The energetics of asexual reproduction: Pedal laceration in the symbiotic sea anemone Aiptasia pulchella (Carlgren, 1943)

Asexual reproduction of the symbiotic sea anemone Aiptasia pulchella (Carlgren, 1943) was studied in the context of energy budgets determined under a variety of light and feeding conditions. Continuous darkness significantly increased rates of pedal laceration (the method of asexual reproduction), while different feeding rates had no significant effect. Digestive assimilation efficiency averaged 63% for whole brine shrimp, and conversion efficiencies (assimilated energy into biomass) averaged 31%. There were no significant differences between the conversion efficiencies of energy obtained from light or food. The index of reproductive effort (RE) for pedal laceration was very low, ranging from 0.004 to 0.044. This low RE associated with a substantial rate of asexual reproduction may, in part, explain the widespread success of certain sea anemones.     

Cnidae in the sea anemone Sagartiogeton viduatus (Muller, 1776) (Cnidaria,Anthozoa); A comparison to cnidae in the sea anemone Metridium senile (Linnaeus, 1761) (Cnidaria,Anthozoa)

The cnidom of the sea anemone Sagartiogeton viduatus (Muller, 1776) is described from interference‐contrast light micrographs (LMs) and scanning electron micrographs (SEMs). Special attention is given to nematocyst maturation, including the differentiation of the shaft into proximal and main regions as helical folding of the shaft wall proceeds. Comparisons are made with Metridium senile (Linnaeus, 1761), whose cnidom, with a few exceptions, is closely similar to that of S. viduatus. The two anemones possess b‐ and p‐mastigophores, p‐amastigophores, isorhizas and spirocysts. Although the majority of cnidae in S. viduatus is smaller than corresponding ones in M. senile, they are grouped into the same size classes as those of M. senile, namely small, medium and large. The main differences from M. senile cnidae are the followings: (1) Large acontia p‐amastigophores are the largest nematocysts in S. viduatus. (2) They are noticeably larger than the large acontia b‐mastigophores, and (3) they are separated from the p‐amastigophores of M. senile by the sinusoid pattern of their U‐shaped capsular matrix. (4) The large acontia b‐mastigophores are microbasic and not mesobasic as in M. Senile, and (5) they do not produce darts. (6) Another difference from M. senile is the absence of catch‐tentacle isorhizas.     

Aspects of the biology of Pantinonemertes californiensis,a high intertidal nemertean

I studied the distribution, feeding biology, and reproductive biology of Pantinonemertes californiensis, described as a semi-terrestrial nemertean, along the central California coast. At the sites used in this study, maximal tidal height is about 2 m, and P. californiensis typically occurred under boulders between 1.3 and 1.7 m tidal height. Worms fed primarily on the semi-terrestrial amphipod Traskorchestia traskiana. Distribution of nemerteans was similar to that of the prey, although prey extended higher on the beach than did the worms. Nemerteans were largest and most abundant at the site with highest abundance of T. traskiana and smallest and least abundant at the lowest prey abundance site. In laboratory feeding trials, nemerteans from the site with lowest prey abundance fed most readily. Non-reproductive nemerteans lived for at least a week when submerged in sea water; some prey died within a week of being submerged. Nemerteans only lived minutes when submerged in fresh water; 50% of prey lived 4.5 h. Eggs are approximately 90–100 μm in diameter and hundreds to thousands are shed per female. Larvae are planktonic and apparently planktotrophic, and are morphologically similar to other marine hoplonemertean larvae. At the sites studied life history characteristics of P. californiensis provided little evidence of adaptations to terrestrial life in these worms and were not helpful in elucidating the role of semi-terrestrial nemerteans in the evolution of terrestrial nemerteans.     

Laboratory observations on the feeding behaviour, reproduction and morphology of Galeodea echinophora (Gastropoda: Gassidae)

Galeodea echinophora fed on Echinocardium cordatum in an aquarium. Every few days, each G. echinophora emerged from the sand and foraged for 1–3 h. On detecting an Echinocardium , the Galeodea stopped locomotion and attacked the buried prey from the surface of the sand. The proboscis was extended down to the prey and a small area of test was cleared of spines. A disc was cut out of the softened test, leaving a hole of about 2 mm in diameter. All flesh except the gut was removed from the prey, the entire procedure taking 50–180 min.
One Galeodea echinophora laid 120 egg capsules on the side of the aquarium. These were kept at 13^oC and hatched after 112–159 days. Within the capsule, veligers fed on the yolk cells of abortive embryos. Juveniles hatched at the crawling stage, and at first secreted strings of mucus acting as drogues, but after 1 day the juveniles crawled over the substratum. They readily attached themselves to adult Echinocardium cordatum , apparently feeding on the epithelium between the spines or tube feet. Dissection revealed entry of the acinar glands into the proboscis gland ducts, a widening of these ducts as they empty into the buccal cavity and a dorsal fold in the anterior oesophagus. Radular teeth and jaws of Galeodea differ little among species; a taxonomic review of the genus is needed.     

Food quality, feeding preferences, survival and growth of shredders from temperate and tropical streams

1. The importance of leaf quality to the nutritional ecology of lotic shredders is well established for temperate species but virtually unknown for tropical taxa. In the present study, we compared the feeding behaviour and performance of two tropical and two temperate shredders in a series of pair‐wise experiments. 2. Specifically, we tested whether leaf conditioning status (stream‐conditioned versus unconditioned leaves) and geographical origin (temperate Alnus glutinosa versus tropical Hura crepitans leaves) affect the food preference, survivorship, and growth of selected shredders from low and high latitudes in a consistent manner. The animals used in experiments were the caddis‐flies Nectopsyche argentata and Phylloicus priapulus from Venezuela, Sericostoma vittatum from Central Portugal, and the amphipod Gammarus pulex from Northern Germany. 3. In general, all shredders exhibited the same high preference for conditioned over unconditioned leaves, irrespective of the geographical origin of the leaf or shredder species. 4. A corresponding tendency for higher growth was found for sets of animals offered conditioned leaves, with the differences in growth being clearer in the two tropical shredders. Survivorship of the two temperate species was consistently high (> 83%) regardless of the diet offered, whereas the tropical shredders survived better on conditioned (77–90%) as compared with unconditioned (54–87%) leaves, although not significantly so. 5. With the exception of the temperate S. vittatum, shredders did not select or perform better on leaves to which they had previously been exposed, indicating a potential adaptation to native leaf species is over‐ridden by intrinsic leaf properties. 6. Taken together, the results of this study suggest that tropical shredders may exhibit the same basic patterns of food exploitation as their temperate counterparts. Consequently, current concepts relating to the role of shredders in stream detritus dynamics may well be applicable to tropical streams, although essentially derived from temperate systems.     

High diversity of tropical intertidal zone sponges in temperature, salinity and current extremes

The wide intertidal zone of the Quirimba Archipelago (Mozambique, East Africa) encompasses many different habitats, which all experience wide environmental variation. Large daily fluctuations in temperature occur when standing water is heated up at low tide to >10°C above ambient. Salinity may be high in the dry season and periodically almost fresh in the wet season. Very high current velocities (≈3 ms⁻¹) may occur and the direction of water flow is often complex. Sponges were a major component of the fauna (and dominate the sessile forms) in most of the eight habitats studied: exposed reef, sheltered reef, sand-rock, cave, reef boulders, boulders on sand, mangrove swamp and seagrass meadows. The highest number of sponge species occurred in the two reef habitats: from mean values of between ≈2.5 and ≈0.5 species/m² (upper and lower shore, respectively). The diversity of species present yielded a high Shannon index value of H=2.95 for the total of 33 species. A rank-abundance plot of the data showed a high level of equitability (J=0.84). Community similarity measurement using Bray–Curtis index showed two clusters; the exposed habitats of the reefs and sand-rock and the refugia of cave, reef and sand boulders.     

The importance of crevices to the intertidal snail Littoraria articulata (Philippi) in a tropical mangrove forest

The intertidal gastropod, Littoraria articulata (Philippi), is common on the trunks of mangroves at Coorooman Creek, Central Queensland. Individuals of shell length less than 3 mm were only found in empty tests of the barnacle Hexaminius popeiana (Foster). Larger snails were exposed on the trunk or occasionally in crevices such as knot holes. The relationship between shell length and shell strength differed between barnacle dwelling and larger L. articulata: in both cases it was linear, but the rate of increase of strength with increasing length was significantly greater for barnacle dwelling snails than for exposed ones. In contrast, there was an exponential relationship between shell strength and length for the weaker shelled Littoraria filosa (Sowerby), which occurs higher on the tree and does not inhabit barnacles. The survival of L. articulata was affected by the presence of crevices: significantly fewer disappeared from posts with artificial crivices than from those which lacked them, and some snails testhered to posts appeared to have been eaten by fish. The importance of crevices is discussed in relation to predation pressure, growth and habitat selection by larval L. articulata. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reproduction and morphology of Central American and Tres Marias spinner dolphins in the eastern tropical Pacific

Four geographic forms of spinner dolphin (Stenella longirostris) occur in the eastern tropical Pacific. Two of the forms are pelagic: the eastern and whitebelly, and two are coastal: the Central American and Tres Marias spinner dolphins. Of these, only the Tres Marias form lacks recognition appropriate for developing management and conservation plans. Vertical aerial photographs of 57 spinner dolphin schools taken between 1988 and 2006 were used to examine the range of coastal forms and to characterize their calving seasons. On the basis of adult body length, spinner dolphins photographed off Guerrero, Mexico, were identified as those of the Central American form, which is north of their known range, and those photographed farther north, approximately 112 km off Nayarit, Mexico, were identified as the Tres Marias form. Calving peaked from October through March, and there was evidence that calving seasons differed among geographic forms with coastal forms calving later than pelagic forms. We present the first life history parameter estimates for the coastal forms of spinner dolphins, provide additional support for recognition of the Tres Marias form, and the first evidence of the Central American form occurring north of the Gulf of Tehuantepec, Mexico.     

Comparative ultrastructure of catch tentacles and feeding tentacles in the sea anemone Haliplanella

TEM observations of catch tentacles revealed that the tentacle tip epidermis is filled with two size classes of mature holotrich nematocysts and a gland cell filled with electron-dense vesicles. Vesicle production is restricted to upper-middle and tentacle tip regions, whereas holotrich development occurs in the lower-middle and tentacle base regions. Thus, catch tentacles have a maturity gradient along their length, with mature tissues concentrated at the tentacle tip. Occasional feeding tentacle cnidae (microbasic p-mastigophores and basitrichs) and mucus gland cells occur in proximal portions of catch tentacles, but are phagocytized by amoeboid granulocytes and transported to the gastrodermis for further degradation. No feeding tentacle cnidae or mucus cells occur distally in catch tentacles. Unlike catch tentacles, feeding tentacles are homogeneous in structure along their length with enidocytes containing mature spirocysts, microbasic p-mastigophore or basitrich nematocysts distributed along the epithelial surface. Cnidoblasts are recessed beneath cnidocytes, occurring along the nerve plexus. Mucus gland cells and gland cells filled with electron-dense vesicles are present in feeding tentacles, distributed at the epithelial surface. Granular phagocytes are rare in the feeding tentacle tip, but common in the tentacle base.     

Observations on feeding in a South African suctorial hoplonemertean, Nipponnemertes sp. (Family Cratenemertidae)

Marine hoplonemerteans were collected intertidally inAlgoa Bay, Port Elizabeth, South Africa in 1983.Algoa Living worms appear to belong to the genus Nipponnemertes, perhaps N. africanus (Wheeler, 1940). The external morphology and thestylet apparatus are described and illustrated. Laboratory observations showed that this speciesattacked and consumed two species of sympatricamphipods, Elasmopus pectenicrus and Hyalegrandicornis (the only two species tested). Thefeeding behavior was similar to that documented forother suctorial nemerteans that feed on amphipods. Onecomplete feeding sequence, from the initial strike tocompletion of feeding on H. grandicornis,took approximately 12 min: the proboscis struck theventral side of the amphipod, which was immobilized in<1 min; the head eventually wedged between thesternal plates, and the internal organs were evacuatedby suctorial action. The addition of E. pectenicrus andH. grandicornis as potentialprey for suctorial hoplonemerteans brings the totalknown number of amphipod species to 25, involving atleast ten families. A summary of all species ofAmphipoda known to be potential prey for suctorialhoplonemerteans is presented.     

Community structure of an assemblage of tidepool fishes on a tropical eastern Pacific rocky shore, Colombia

The composition, abundance, species richness and diversity of a rocky intertidal fish assemblage in the central zone of the Pacific coast of Colombia were determined. From July to December 2002, 10 tidepools with volumes ranging from 0·087 to 1·350 m³ were surveyed. A total of 893 fishes belonging to 14 species and 12 families were found. The most abundant species were Bathygobius ramosus and Abudefduf concolor , representing 71% of all fishes collected. Bathy gobius ramosus , Malacoctenus zonifer and Gobiesox adustus were residents, Abudefduf concolor , Abudefduf troschelii , Microsphatodon bairdii , Chaenomugil proboscideus , Halichoeres aestuaricola and Echidna nocturna were transients, and Apogon dovii , Sargocentron suborbitalis , Cerdale sp, Rypticus nigripinnis and Ctenochaetus marginatus were considered as accidental visitors. The temporal and spatial variation of assemblage structure was tested. The fish assemblage structure did not differ between months and there was not a clear relationship between tidepool surface area and depth, and community variables. Diversity and species richness were negatively correlated with tidepool height. It is suggested that the tidepool assemblage was stable and resilient in time on short (annual) scales. The constancy in time and space could have been a consequence of eurytopic features of the organisms and the lack of drastic seasonal changes in the tropics.     

The intertidal soft-bottom infaunal macrobenthos in three Basque estuaries (Gulf of Biscay): a feeding guild approach

Feeding types of the infaunal macrobenthos of the intertidal soft-bottom communities from the estuaries of La Arena, Plentzia and Gernika, along the Basque coast (Gulf of Biscay) were studied in relation to habitat conditions, characteristics of each estuary and seasonal variation. General feeding structure observed in La Arena estuary was different from the other estuaries: omnivores were dominant, both in number of species and individuals, while surface deposit-feeders were the main feeding group in Plentzia and Gernika both in the finest sediment communities and in the sandy ones. Subsurface deposit-feeders were abundant in Plentzia and Gernika but scarce in La Arena estuary. Feeding types were related to the environmental variables. Sandy sediment communities presented a more balanced proportion among different feeding types and showed higher values of feeding diversity; suspension-feeders and predators were abundant only in that communities. By estuaries, feeding diversity was higher in Gernika and lower in La Arena. Seasonal variation in feeding diversity was observed, explained by changes in density of certain feeding groups; a common pattern of variation was found in Gernika communities, with an increase in June and a decrease in September. Oscillation of this index in Plentzia and La Arena depended on the estuary and the different communities; nevertheless a decrease of feeding diversity in September was commonly observed. Finally, feeding structure observed in our estuaries was compared to those described in coastal areas with organic enriched sediments, in order to assess the degree of perturbation of the environment based on the relative dominance of a certain feeding type in the macrobenthos.