Structural, morphological and genetic variability in Halophila stipulacea (Hydrocharitaceae) populations in the western Mediterranean

Halophila stipulacea (Forssk.) Ascher. is a dioecious seagrass that colonized the Mediterranean basin probably following the opening of the Suez Canal (1869). Natural meadows have been reported since the end of the last century on the eastern side of the basin and only recently along the northern coast of Sicily. In the present study we examined the morphological and genetic variability of two natural meadows located along the Sicilian coast (Vulcano Island and Oliveri-Tindari coastal lakes). In order to determine morphological and genetic polymorphism, samples were collected at different depths (5, 15 and 25 m depth at the Vulcano site) and positions (edge vs mid-bed) within the meadows. Statistically significant differences in phenotypic features were found between the factors “depth” and “position” within the same meadow and between the two localities. Genetic diversity was assessed using randomly amplified polymorphic DNA and found to be high. Deep and shallow stands of the Vulcano Island meadow clustered in different positions in the UPGMA tree. The shallow Vulcano stand was found to be closer to the shallow Oliveri-Tindari meadow than to the deeper stand from Vulcano. Mantel's test did not allow rejection of the null hypothesis of independence of morphological and molecular distance matrices. We conclude that (i) H. stipulacea shows high morphological and genetic polymorphism, (ii) environmental and/or ecological barriers exist between different depths, and (iii) trends of morphological and genetic variability may be influenced by different environmental and/or ecological factors. Received: 15 November 1998 / Accepted: 21 May 1999     

Accumulation, contamination, and seasonal variability of trace metals in the coastal zone – patterns in a seagrass meadow from the Mediterranean

Amongst a plethora of threats to seagrass ecosystems, contamination with heavy metals may well be one of the most significant. We therefore set out to track contamination levels with Cu, Zn, Pb and Cd in the principal autotrophic compartments and sediments of a meadow of Posidonia oceanica in the Gulf of Naples, Mediterranean Sea. With respect to metal levels, leaves and their associated epibiota are certainly not a homogenous compartment, as might perhaps be inferred from the common use of the term “leaf–epiphyte complex” in the literature. Save for Cu, all metal species analysed showed appreciable differences in concentration between seagrass leaves and epibiota. These results give strength to our argument that in ecotoxicological work leaves and epibiota should not be treated as a single unit. Although absolute differences in trace-metal levels among sampling periods varied somewhat with the specific component analysed (i.e. macrophyte organs, epibiota, sediment), an overall trend of markedly higher heavy-metal levels during the winter season is a striking one. Whilst annual cycles in growth dynamics of the seagrasses explain a significant fraction of the temporal variance, seasonality in productivity is a doubtful explanation for similar patterns in non-living sedimentary components; consideration of additional variables therefore seems sensible. As variables with consistent explanatory powers we suggest: (1) seasonal cycles in storm frequency and amplitude which remobilise metals bound in the sediments of the sea floor, and (2) increased precipitation during the cold season which may significantly increase marine metal levels through elevated weathering of rocks and elevated fluvial inputs of anthropogenic contaminant loads. Whereas Cd and Pb concentrations in seagrass leaves from the Gulf of Naples fall within the range for coastal areas subjected to low levels of heavy-metal pollution, Cu and Zn reach levels typical of highly contaminated regions, such as the waters bordering major coastal cities. Any direct comparisons of the pollution status of seagrass beds between different geographic areas are, however, likely to be confounded by the indiscriminate application of the “leaf–epiphyte complex”: the magnitude of the confounding effect depends on the ratio of epibiota/leave biomass, time of sampling, and metal species analysed. Received: 15 May 1997 / Accepted: 2 February 1998     

Predator stimuli and calling behavior of Carolina chickadees (Poecile carolinensis), tufted titmice (Baeolophus bicolor), and white-breasted nuthatches (Sitta carolinensis)

Evidence from different chickadee species (Poecile genus) indicates that birds can modify the note composition of their “chick-a-dee” calls in the presence of predator stimuli. Here, we tested the effects of predator models and the distance of those models on calls of three species foraging together at feeding stations: Carolina chickadees (Poecile carolinensis) and tufted titmice (Baeolophus bicolor), both members of the Paridae family, and white-breasted nuthatches (Sitta carolinensis), a member of the Sittidae family. Model and distance affected seed-taking rates in all three species. “Chick-a-dee” calling rates were higher in the predator context for both chickadees and titmice, but we detected no predator context effects on “quank” call rates for nuthatches. Predator and distance contexts affected acoustic parameters of notes of the “chick-a-dee” calls of chickadees and titmice; no such effects were detected for nuthatch “quank” calls. These results suggest species differences in encoding of information in the primary social calls of these three species that commonly occur in multi-species flocks. Chickadees and titmice are “nuclear” species and nuthatches are “satellite” species, and these different roles might be related to the differences in vocal signaling that we detected.     

Evolutionary relationships of deep-sea hydrothermal vent and cold-water seep clams (Bivalvia: Vesicomyidae): results from the mitochondrial cytochrome oxidase subunit I

Phylogenetic relationships among vesicomyid clams (Bivalvia: Vesicomyidae) and their placement within the order Heterodonta were examined using mitochondrial encoded cytochrome oxidase subunit I (COI) DNA sequences. The presently analyzed vesicomyids represent a recent monophyletic radiation that probably occurred within the Cenozoic. Nucleotide phylogenetic analyses resolved discrete clades that were consistent with currently recognized species: Calyptogena magnifica, C. ponderosa, Ectenagena extenta, C. phaseoliformis, Vesicomya cordata, Calyptogena n. sp. (Gulf of Mexico), C. kaikoi, C. nautilei, C. solidissima and C. soyoae (Type-A). However, specimens variously identified as: V. gigas, C. kilmeri, C. pacifica, and V. lepta comprised two “species complexes”, each composed of multiple evolutionary lineages. Most taxa are limited to hydrothermal-vent or cold-seep habitats, but the “vent” versus “seep” clams do not constitute separate monophyletic groups. Current applications of the generic names Calyptogena, Ectenagena, and Vesicomya are not consistent with phylogenetic inferences. Received: 24 July 1997 / Accepted: 22 August 1997     

Migratory activity by hatchling loggerhead sea turtles (Caretta caretta L.): evidence for divergence between nesting groups

The South Florida subpopulation of loggerhead sea turtles (Caretta caretta L.) nests with great fidelity on either the southeast or the southwest coast of Florida, USA. The hatchlings that emerge from those nests must swim in opposite directions and search for different surface currents to migrate away from continental shelf waters. In this laboratory study, we compared the pattern of swimming activity shown by the hatchlings from each coast over the first 6 days of migration. Turtles from both coasts were equally active during their “frenzy” period (the first 24 h of swimming) and during the daylight hours of the 5 days that followed (the “postfrenzy” period). However, the west coast turtles were significantly more active than the east coast turtles during the nocturnal portion of the postfrenzy period. This difference may be related to the greater distance southwest coast turtles must negotiate to locate surface currents for transport out of the Gulf of Mexico and into the Atlantic Ocean basin. These differing behavioral strategies may be genetically determined, as similar correspondence between activity and distance is well known among migratory populations of birds and fish and is often based upon inherited programs of endogenously driven activity. Alternatively, behavioral differences between the two nesting groups could be a manifestation of phenotypic plasticity that arises as the hatchlings respond to unique environmental cues on each coast.     

DNA sequence analysis identifies genetically distinguishable populations of harp seals (Pagophilus groenlandicus) in the Northwest and Northeast Atlantic

Harp seals (Pagophilus groenlandicus Erxleben, 1777) comprise three populations based upon whelping areas in the Greenland Sea, White Sea, and Northwest Atlantic. The last comprises two subpopulations, one whelping in the Gulf of St. Lawrence (“Gulf ”) and one on the pack ice of the southern Labrador/northern Newfoundland coastal shelf (“Front”). A total of 40 female seals from the four whelping areas were collected during the 1990 and 1992 whelping seasons. DNA sequence variation was examined in a 307 bp region of the mitochondrial cytochrome b gene. Eleven variable nucleotide positions defined 13 genotypes: a significant fraction of the genotypic variance (F _ST=0.12, or 0.09 as measured by Weir's coancestry coefficient θ) is attributable to differentiation between Northwest and Northeast Atlantic populations. There was no significant differentiation between the two whelping areas in the Northwest Atlantic, or between the Greenland Sea and White Sea. These findings suggest significant reproductive isolation exists between trans-Atlantic breeding populations. Received: 18 January 1999 / Accepted: 22 February 2000     

Fine structure of the “button setae” in the deep-sea pelagic copepods of the genus Euaugaptilus (Calanoida: Augaptilidae)

 Many species of the carnivorous copepod family Augaptilidae, a primarily meso- and bathypelagic group, possess specialized “buttons” on the setae of their maxilla and maxilliped, which have been thought to be a simple cuticular outgrowth. The fine structure of the button setae in three species of Euaugaptilus was examined by light- and electron microscopy from samples collected in the eastern Indian Ocean and the subtropical western North Pacific. The buttons are arranged in two rows along the inner surface of the setae. There are differences in the shape, size, and arrangement of buttons among the three species, Euaugaptiluslaticeps, E.longimanus, and E.magnus. The button setae have an elaborate internal structure consisting of “setal shaft”, “stalk”, “disc”, and “outer membrane”, with microtubule bundles in the setal lumen, but have no muscular tissues. The disc has only pin-point contact to the core of the stalk, but has connection over a wider area with the fibrous tissue surrounding the core, and the contact area between the stalk and the setal shaft is also small. These structures suggest that the disc will move freely on the apex of the core of the stalk and the stalk may be movable at its connection to the setal shaft. All these components of the button setae may function in concert to fit the surface of the discs firmly to the surface of a prey, and to absorb the energy generated by the struggling prey. Received: 30 November 1999 / Accepted: 19 May 2000     

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     

The effects of air exposure on the desiccation rate and photosynthetic activity of Thalassia hemprichii and Enhalus acoroides

The effects of air exposure on the desiccation rate and photosynthetic activity of Thalassia hemprichii and Enhalus acoroides were studied using chlorophyll fluorescence. The desiccation rate of T. hemprichii was higher than that of E. acoroides, while the critical threshold of relative water content (RWC_critical) showed opposite trend. Neither the desiccation rate nor RWC_critical of T. hemprichii was significantly affected by temperature, while the desiccation rate of E. acoroides was affected significantly. For both species, the effective photochemical efficiency of PSII decreased gradually above the RWC_critical, while declined rapidly below the RWC_critical. After initial air exposure, the relative maximum electron transport rate of both seagrasses increased gradually to a maximum and then decreased to initial value near the RWC_critical. Therefore, short-term air exposure above the RWC_critical is beneficial for both seagrasses, and the RWC_critical should be considered when examining the response of seagrass photosynthesis to air exposure and selecting transplantation sites.     

Inhibition and facilitation of bryozoan and ascidian settlement by natural multi-species biofilms: effects of film age and the roles of active and passive larval attachment

Sessile marine invertebrate larvae can recognize suitable settlement substrata by using various environmental cues, including organic/microbial biofilms. In laboratory choice assays, the effect of biofilms of varying ages on the settlement behaviour of two fouling organisms was assessed. The species included the arborescent cheilostome bryozoan Bugula flabellata (Thompson) and the solitary ascidian Ciona intestinalis (L.), both of which are characteristic of temperate sublittoral hard substratum assemblages in northwest Europe. Experiments were carried out using polystyrene petri dish substrata preconditioned with multispecies biofilms from natural laboratory-aquarium seawater for 1, 3, 6 or 12 d. Unfilmed (new, initially sterile) dishes were used as control substrata. Whereas the coronate larvae of B. flabellata generally were inhibited by biofilming, irrespective of film age, the settlement of tadpole larvae of C. intestinalis was facilitated on biofilmed substrata, and numbers of settled larvae generally increased with biofilm age: the highest mean numbers were counted on 12 d-old biofilms. In C. intestinalis, settlement and metamorphosis are processes which can be temporally separate and are possibly induced by different environmental cues. This study therefore distinguished between C. intestinalis larvae which were attached to the biofilm surface by the anterior, and those larvae entrapped by the biofilm but not settled in the conventional meaning of the term. As reported in previous studies, we did observe that such entrapped larvae could subsequently attach and develop successfully into sessile juveniles. Both the numbers of “attached” and “trapped” tadpoles increased with biofilm age. Assuming that “settlement” is essentially a process involving the active behavioural response of larvae to environmental cues, it seems that the facilitated attachment of C. intestinalis onto biofilmed substrata is due to the combined effect of active habitat selection and passive deposition/“entrapment” of larvae onto the “sticky” substratum. Received: 21 August 1996 / Accepted: 21 November 1996     

Environmental determinants of distribution and foraging behaviour of cormorants (Phalacrocorax spp.) in temperate estuarine habitats

The distribution and behaviour of cormorants in estuarine environments was examined on the central coast of New South Wales, Australia, with respect to habitat associations at different spatial scales. No consistent variation in abundance was found for four species of cormorants (great Phalacrocorax carbo, pied P. varius, little black P. sulcirostris, and little pied P. melanoleucos) with state of tide (high and low) and time of day (early, middle, and late) at five estuarine locations. Differences in abundance were found among locations that were not confounded by short-term temporal variation (i.e. time of day and tide). Differences in abundance were detected among habitats (e.g. bays, creeks, and headlands) separated by hundreds of metres to kilometres in different estuaries. Cormorants of all species were rare on the open coast and near the entrance of estuaries. Abundances of cormorants varied greatly within and among creeks, bays, and river channels. Presence of seagrass beds explained much of this variation and most of the cormorants swimming and feeding were found near seagrass. Mapping of seagrass beds and the positions of cormorants at scales of metres to hundreds of metres showed a close relationship between the presence of swimming and roosting beds and the presence of seagrass beds for P. melanoleucos and for P. carbo. We argue that cormorants make decisions to visit particular estuarine habitats, especially those with seagrass, where many types of prey (e.g. fish and crustaceans) are probably most abundant. These choices must be interpreted in the context of decisions that cormorants make on scales of hundreds to thousands of kilometres during periodic excursions to the interior of Australia. Further, environmental threats to seagrass beds could impinge on these mobile visitors to the same extent as on more permanent residents. Received: 14 February 2000 / Accepted: 17 July 2000     

Population and reproductive biology of two sibling amphipod species from ascidians and sponges

 The population dynamics and reproductive biology of an ascidian- and a sponge-dwelling amphipod were examined. The two undescribed amphipod species, Leucothoe“ascidicola” and L.“spongicola”, are closely related to each other, and occur in ascidians and sponges, respectively, along the Florida Atlantic coast. L. “ascidicola” was abundant in solitary ascidians during fall 1997, disappeared during spring/early summer, and became abundant again in September 1998. During the time when L. “ascidicola” were absent from their hosts, a copepod became a frequent inhabitant of the ascidians but disappeared again when L.“ascidicola” returned to the ascidians in September 1998. The numbers of L.“spongicola” in sponges increased substantially during spring, when high reproductive activity was observed. Following this reproductive peak, both adult and juvenile amphipods apparently left the sponges, and during the summer amphipod numbers in the sponges were very low. Another small amphipod species, which often co-occurred with L.“spongicola”, showed less seasonal variation and was found in sponges throughout the whole study period. The percentage of ovigerous females per host unit was usually lower in the ascidian-dwelling than in the sponge-dwelling amphipods. In solitary ascidians, L.“ascidicola” amphipods usually occurred in groups of several adults, yet there never was more than one ovigerous female per ascidian. In contrast, several ovigerous L.“spongicola” females were found to cohabit in the same spongocoel. This suggests that intrasexual aggression may be stronger among reproductive amphipod females in the ascidians than in sponges. The size distributions of juvenile cohorts indicate that juvenile L.“ascidicola” remain for relatively long time periods in the parental ascidian, where they may reach sexual maturity. In contrast, in L.“spongicola”, only cohorts of very small juveniles could be identified, indicating that juveniles disperse shortly after emerging from the female's brood pouch. It is concluded that extended parental care is of very short duration or does not occur in the sponge-dwelling amphipod L. “spongicola”, possibly because fast-growing sponges with a highly branched spongocoel system do not allow long-lasting coexistence of parent-offspring groups. In contrast, the discrete character of the solitary ascidians may enhance the potential for exclusion of other species, resource monopolization by reproductive females, and furthermore for long-lasting extended parental care in the ascidian-dwelling amphipod. Groups of single parents together with cohorts of large juveniles are reported in the literature for amphipods and isopods from brachiopods, bivalves and ascidians, suggesting that these discrete biotic microhabitats may favor the evolution of extended parental care in peracarid crustaceans. Received: 30 July 1999 / Accepted: 8 May 2000     

Flux by fin: fish-mediated carbon and nutrient flux in the northeastern Gulf of Mexico

Seagrass meadows are among the most productive ecosystems in the marine environment. It has been speculated that much of this production is exported to adjacent ecosystems via the movements of organisms. Our study utilized stable isotopes to track seagrass-derived production into offshore food webs in the northeastern Gulf of Mexico. We found that gag grouper (Myctereoperca microlepis) on reefs as far as 90 km from the seagrass beds incorporate a significant portion of seagrass-derived biomass. The muscle tissue of gag grouper, a major fisheries species, was composed on average of 18.5–25% seagrass habitat-derived biomass. The timing of this annual seagrass subsidy appears to be important in fueling gag grouper egg production. The δ³⁴S values of gag grouper gonad tissues varied seasonally and were δ³⁴S depleted during the spawning season indicating that gag utilize the seagrass-derived biomass to support reproduction. If such large scale trophic subsidies are typical of temperate seagrass systems, then loss of seagrass production or habitat would result in a direct loss of offshore fisheries productivity.     

Relative impact of a seagrass bed and its adjacent epilithic algal community in consumer diets

The aim of this work was to identify and compare, using nitrogen and carbon stable isotope data, the food sources supporting consumer communities in a Mediterranean seagrass bed (Gulf of Calvi, Corsica) with those in an adjacent epilithic alga-dominated community. Isotopic data for consumers are not significantly different in the two communities. Particulate matter and algal material (seagrass epiflora and dominant epilithic macroalgae) appear to be the main food sources in both communities. Generally, the δ¹³C of animals suggests that the seagrass Posidoniaoceanica (L.) Delile represents only a minor component of their diet or of the diet of their prey, but the occurrence of a mixed diet is not excluded. P. oceanica dominates the diet of only of few species, among which holothurians appear as key components in the cycling of seagrass material. Received: 30 July 1999 / Accepted: 17 January 2000     

Thermal reaction norms for growth vary among cohorts of Pacific cod (Gadus macrocephalus)

While much effort has been directed at determining the spatial scales of adaptation in thermal reaction norms for growth, it is widely assumed that these reaction norms have high temporal stability. Water temperatures in the Gulf of Alaska in 2007 were the coldest on record since the mid-1970s and we present evidence that the thermal reaction norm for growth of age-0 Pacific cod (Gadus macrocephalus) in this cohort differed significantly from two adjacent cohorts. In addition to exhibiting higher growth potential at low temperatures, the 2007 cohort had a higher mean vertebral count, consistent with the widespread thermal effect known as “Jordan’s Rule.” Variation among cohorts in these physiological and morphological traits suggests a persistent response to environmental history (epigenetic effect). Temperature-induced phenotypic plasticity in the reaction norm for growth has significant implications for using growth rates to evaluate habitat quality and illustrates the complex responses of fishes to climate variability.     

Concentration of Aluminium in Halophila stipulacea (Forsk.) archers. and the substrate of the Antikyra Gulf,Greece

The concentrations of Aluminium in the marine phanerogam Halophila stipulacea and in the sediment, sampled at eight stations in the Gulf of Antikyra (Greece) were presented. The seasonal variation in concentrations of Al in the seagrass and in the substrate in all these stations were studied. The quantitative differences in Al between the different parts of the phanerogam, between H. stipulacea‐sediment and among the different sample stations have also been examined.     

Phylogeography of the diamond turbot (Hypsopsetta guttulata) across the Baja California Peninsula

We compared morphology and sequenced nuclear and mitochondrial genes from 11 populations of a previously genetically unstudied “Baja California disjunct” species, the diamond turbot (Hypsopsetta guttulata). This species exhibits very limited adult movement and restriction to soft-bottom habitats but has a moderately long pelagic larval duration. Therefore, if pelagic larval duration is correlated with gene flow between Gulf of California and Pacific populations, we expect a reduced level of genetic and morphological differentiation. However, if adult habitat and ecology have more effect on gene flow, we expect the populations in the two bodies of water to be more highly differentiated. We used logistic regression to compare morphological features and phylogenetic and population genetic analyses to compare nucleotide sequence data. Gulf of California H. guttulata are different from Pacific populations in morphology and both mitochondrial and nuclear gene sequences. MtDNA shows reciprocal monophyly, and nuclear sequences from the Gulf of California formed a monophyletic group. Population genetic analyses also suggest further population subdivision within the Pacific and within the Gulf of California. We argue that adult ecology has a significant effect on migration rates among populations in the Pacific Ocean and the Gulf of California.     

Photosynthetic utilisation of inorganic carbon by seagrasses from Zanzibar, East Africa

Photosynthetic rates of eight seagrass species from Zanzibar were limited by the inorganic carbon composition of natural seawater (2.1 mM, mostly in the form of HCO₃ ⁻), and they exhibited more than three time higher rates at inorganic carbon saturation (>6 mM). The intertidal species that grew most shallowly, Halophila ovalis, Halodule wrightii and Cymodocea rotundata, showed the highest affinity for inorganic carbon (K _1/2 = ca. 2.5 mM), followed by the subtidal species (K _1/2 > 5 mM). Photosynthesis of H. wrightii, C. rotundata, Cymodocea serrulata and Enhalus acoroides was >50% inhibited by acetazolamide, a membrane-impermeable inhibitor of carbonic anhydrase, indicating that extracellular HCO₃ ⁻ dehydration is an important part of their inorganic carbon uptake. Photosynthetic rates of H. wrightii, Thalassia hemprichii, Thalassodendron ciliatum, C. serrulata and E. acoroides were strongly reduced by changing the seawater pH from 8.2 to 8.6 in a closed system. In H. ovalis, C. rotundata and Syringodiumisoetifolium, photosynthesis at pH 8.6 was maintained at a higher level than could be caused by the ca. 30% CO₂ concentration which remained in the closed experimental systems at that pH, pointing toward HCO₃ ⁻ uptake in those species. It is suggested that the ability of H. ovalis and C. rotundata to grow in the high, frequently air-exposed, intertidal zone may be related to a capability to take up HCO₃ ⁻ directly, since this is a more efficient way of HCO₃ ⁻ utilisation than extracellular HCO₃ ⁻ dehydration under such conditions. The inability of all species to attain maximal photosynthetic rates under natural conditions of inorganic carbon supports the notion that seagrasses may respond favourably to any future increases in marine CO₂ levels. Received: 19 March 1997 / Accepted: 31 March 1997     

Primary co-culture as a complementary approach to explore the diversity of bacterial associations in marine invertebrates: the example of <Emphasis Type="Italic">Nautilus macromphalus</Emphasis> (Cephalopoda: Nautiloidea)

The recent application of molecular tools to address associations between bacteria and marine invertebrates has provided access to an immense diversity of unidentified microbes resistant to cultivation. However, the role of bacteria as partners in animal physiology remains unclear and in most cases difficult to investigate in the absence of adequate condition of cell growth and proliferation. In this work, we studied the reservoir of microbes associated with the excretory organs of Nautilus macromphalus as a model. Using the bacterial 16S RNA gene as a marker, we compared three complementary approaches for bacterial detection: bacterial DNA extraction from N. macromphalus tissues (“molecular approach”), strain isolation to provide a bacterial culture collection (“microbiological approach”) and finally, maintenance of N. macromphalus excretory organ cells with associated bacteria (“cellular approach”). Our results stress the potential of the “cellular approach” as a promising new tool as it promotes the detection of as yet uncultured β-proteobacteria and spirochaetes associated with N. macromphalus, and serves as a foundation for future studies describing potential roles that these bacteria may play in Nautilus.     

Ontogenetic habitat shift,population growth,and burrowing behavior of the Indo-Pacific beach star, <Emphasis Type="Italic">Archaster typicus</Emphasis> (Echinodermata; Asteroidea)

Archaster typicus, a common sea star in Indo-Pacific regions, has been a target for the ornamental trade, even though little is known about its population biology. Spatial and temporal patterns of abundance and size structure of A. typicus were studied in the Davao Gulf, the Philippines (125°42.7′E, 7°0.6′N), from February 2008 to December 2009. Specimens of A. typicus were associated with intertidal mangrove prop roots, seagrass meadows, sandy beaches, and shoals. Among prop roots, specimens were significantly smaller and had highest densities (131 ind. m⁻²) between November and March. High organic matter in sediment and a relatively low predation rate seemed to support juvenile life among mangroves. Size and density analyses provided evidence that individuals gradually move to seagrass, sandy habitats, and shoals as they age. Specimens were significantly larger at a shoal (maximum radius R = 81 mm). New recruits were found between August and November in both 2008 and 2009. Timing of recruitment and population size frequencies confirmed a seasonal reproductive cycle. Juveniles had relatively high growth rates (2–7 mm month⁻¹) and may reach an R of 20–25 mm after 1 year. Growth rates of larger specimens (R > 30 mm) were generally <2 mm month⁻¹. The activity pattern of A. typicus was related to the tidal phase and not to time of day: Specimens moved over the sediment surface during low tides and were burrowed during high tides possibly avoiding predation. This is one of the first studies to document an ontogenetic habitat shift for sea stars and provides new biological information as a basis for management of harvested A. typicus populations.