Preferential attachment of barnacle larvae to natural multi-species biofilms: Does surface wettability matter?

We tested the hypothesis that surface wettability does not alter the positive effect of natural biofilms on larval attachment in the barnacle Balanus amphitrite. We also answered the question: Does substratum-biofilm interaction affect the larval choice in barnacle? We developed natural multi-species biofilms of different ages on both high (glass) and low (polystyrene) wettability surfaces at mid-intertidal height (native habitat of B. amphitrite). Attachment choice of both young (0-d-old) and old (6-d-old) larvae to biofilms was determined using still water choice bioassay. Irrespective of larval age, cyprid preferred to attach to un-filmed glass than to un-filmed polystyrene. In contrast to aged larvae, young larvae preferred old (6-d-old) biofilms on polystyrene to young (3-d-old) biofilms on glass. In this study, we were also able to examine the interaction between surface wettability, biofilms and larval attachment, by characterizing bacterial community composition in biofilms. Bacterial community composition showed significant differences between biofilms of different ages. Old biofilms positively influenced larval attachment, irrespective of the type of substrata, thereby supporting the hypothesis that surface wettability does not alter the positive effect of natural biofilms on larval attachment.     

The effect of bacterial and diatom biofilms on the settlement of the bryozoan Bugula neritina

Biofilms of marine bacteria and diatoms and their combinations were examined in laboratory choice assays to determine their effects on the attachment and successful metamorphosis of the larvae of the bryozoan Bugula neritina (Linnéus). The larval settlement in response to unfilmed surfaces, a natural biofilm (NBF) and adsorbed cells of three strains of bacteria, five strains of pennate diatoms and combinations of the two at different densities. Bacterial and diatom strains showed different effects on the larval settlement of B. neritina. Bacterial monospecific strains of an unidentified α-Proteobacterium and Vibrio sp. mediated the same percentage of settlement as a filtered seawater control. Biofilms of Pseudoalteromonas sp. caused significantly lower larval settlement. Larval settlement of B. neritina was negatively correlated with increasing densities of Pseudoalteromonas sp. The highest percentages of settlement were mediated by the biofilms of the diatom species Achnanthes sp., Amphora cofeaeformis, Amphora tenerrima, Nitzschia constricta and a 5-day-old natural biofilm, while the lowest settlement was found on a N. frustulum film. A three-way analysis of variance demonstrated that the density of bacteria and the presence of particular species of diatoms and bacteria in combined biofilms, significantly affected the settlement of B. neritina larvae. High settlement of larvae (50-90%) at all treatments indicated that B. neritina larvae are much more indiscriminate settlers than previously expected. Hence, using this species as a monitoring organism to trace ecologically relevant subtle changes of settlement cues in the natural environment should be carefully re-examined.     

Molecular Techniques Revealed Highly Diverse Microbial Communities in Natural Marine Biofilms on Polystyrene Dishes for Invertebrate Larval Settlement

Biofilm microbial communities play an important role in the larval settlement response of marine invertebrates. However, the underlying mechanism has yet to be resolved, mainly because of the uncertainties in characterizing members in the communities using traditional 16S rRNA gene-based molecular methods and in identifying the chemical signals involved. In this study, pyrosequencing was used to characterize the bacterial communities in intertidal and subtidal marine biofilms developed during two seasons. We revealed highly diverse biofilm bacterial communities that varied with season and tidal level. Over 3,000 operational taxonomic units with estimates of up to 8,000 species were recovered in a biofilm sample, which is by far the highest number recorded in subtropical marine biofilms. Nineteen phyla were found, of which Cyanobacteria and Proteobacteria were the most dominant one in the intertidal and subtidal biofilms, respectively. Apart from these, Actinobacteria, Bacteroidetes, and Planctomycetes were the major groups recovered in both intertidal and subtidal biofilms, although their relative abundance varied among samples. Full-length 16S rRNA gene clone libraries were constructed for the four biofilm samples and showed similar bacterial compositions at the phylum level to those revealed by pyrosequencing. Laboratory assays confirmed that cyrids of the barnacle Balanus amphitrite preferred to settle on the intertidal rather than subtidal biofilms. This preference was independent of the biofilm bacterial density or biomass but was probably related to the biofilm community structure, particularly, the Proteobacterial and Cyanobacterial groups.     

Settlement of Pomatoceros lamarkii (Serpulidae) larvae on biofilmed surfaces and the effect of aerial drying

The settlement responses of Pomatoceros lamarkii (Polychaeta: Serpulidae) larvae to biofilms of varying age on slate surfaces and to dried biofilms on slate surfaces were investigated in the laboratory. Settlement experiments were performed as multi-treatment, still water assays. Larvae did not settle on clean, non-biofilmed slates but settled on biofilms up to 28 days old. Settlement intensity was closely related to the bacterial density of a biofilm. Drying a biofilmed surface for 1-2 h at 20 degrees C to simulate a single tidal emersion completely negated the former inductive effect of the biofilm. Drying also negated the larval settlement-inducing effect that normally results from the presence of conspecific adults. The settlement inhibition lasted for approximately 5 days following a single drying event. Larvae settled readily on biofilms exposed to formalin and antibiotics. Treating biofilms with formalin or antibiotics before or after drying had no effect upon larval avoidance of dried biofilms. Freeze-drying a biofilm had the same effect as aerial drying. The biofilm drying effect could not be mimicked by exposing biofilms to hyper-saline seawater. The finding that P. lamarkii larvae do not settle on dried biofilms could have significance in explaining the natural distribution of this species in the intertidal.     

Larval Behaviours and Their Contribution to the Distribution of the Intertidal Coral Reef Sponge Carteriospongia foliascens

Sponges (Phylum Porifera) are an evolutionary and ecologically significant group; however information on processes influencing sponge population distributions is surprisingly limited. Carteriospongia foliascens is a common Indo-Pacific sponge, which has been reported from the intertidal to the mesophotic. Interestingly, the distribution of C. foliascens at inshore reefs of the Great Barrier Reef is restricted to the intertidal with no individuals evident in adjacent subtidal habitats. The abundance of C. foliascens and substrate availability was first quantified to investigate the influence of substrate limitation on adult distribution. Pre-settlement processes of larval spawning, swimming speeds, phototaxis, vertical migration, and settlement to intertidal and subtidal substrate cues were also quantified. Notably, suitable settlement substrate (coral rubble) was not limiting in subtidal habitats. C. foliascens released up to 765 brooded larvae sponge⁻¹ day⁻¹ during the day, with larvae (80%±5.77) being negatively phototactic and migrating to the bottom within 40 minutes from release. Subsequently, larvae (up to 58.67%±2.91) migrated to the surface after the loss of the daylight cue (nightfall), and after 34 h post-release >98.67% (±0.67) of larvae had adopted a benthic habit regardless of light conditions. Intertidal and subtidal biofilms initiated similar settlement responses, inducing faster (as early 6 h post-release) and more successful metamorphosis (>60%) than unconditioned surfaces. C. foliascens has a high larval supply and larval behaviours that support recruitment to the subtidal. The absence of C. foliascens in subtidal habitats at inshore reefs is therefore proposed to be a potential consequence of post-settlement mortalities.     

Differential thermal tolerance and energetic trajectories during ontogeny in porcelain crabs,genus Petrolisthes

Thermal tolerance limits of marine intertidal zone organisms are elevated compared to subtidal species, but are typically just slightly higher than maximal habitat temperatures. The small thermal safety margins maintained by intertidal zone organisms suggest that high thermal tolerance is associated with a physiological cost. If true, we hypothesize that species that transition between intertidal zone and planktonic habitats during ontogeny, will adjust their thermal tolerance accordingly to capitalize upon potential energy savings while in a thermally benign habitat. We tested this hypothesis in porcelain crabs that transition between the thermally stressful, intertidal zone as embryos, to the thermally benign pelagic zone as larvae, and back at settlement. We found the more thermally tolerant, mid-intertidal zone species, Petrolisthes cinctipes, and the less thermally tolerant, subtidal zone species, Petrolisthes manimacilis, exhibited reduced thermal tolerance (LT₅₀) in the transition from embryos to larvae. This was associated with an increased oxygen consumption rate in both species, though P. cinctipes exhibited a significantly greater increase in oxygen consumption. P. cinctipes also showed an increase in thermal tolerance in settled juveniles compared to pelagic zoea I larvae, resulting in an overall V-shaped thermal tolerance relationship during ontogeny, while in P. manimaculis thermal tolerance was significantly lower in juveniles compared to zoea I. In neither species were these changes (zoea I to juvenile) associated with a significant change in metabolism. While embryos and juveniles of P. cinctipes have thermal tolerance limits near intertidal habitat thermal maxima (∼32.5 °C), all three life-history stages in P. manimaculis (especially embryos and larvae) exhibit considerable thermal safety margins. The mechanisms underlying this “excess” thermal tolerance in P. manimacilis embryos are unknown, but suggest that patterns of thermal tolerance in early life history stages are species-specific.     

The role of epibotic bacteria from the surface of the soft coral Dendronephthya sp. in the inhibition of larval settlement

It has been suggested that bacteria associated with soft-bodied organisms are suggested to produce bioactive compounds against the attachment of invertebrate larvae and bacteria onto the surface of these organisms. Our recent study has demonstrated that epibiotic bacteria from the surface of the soft coral Dendronephthya sp. (Coelenterata: Octocoralia, Alcyonacea) inhibit the growth of bacteria commonly found in marine natural biofilms. In the present study, the effect of 11 epibiotic bacteria isolated from the surface of Dendronephthya sp. on larval settlement of the tubeworms Hydroides elegans was examined using laboratory bioassay. Among 11 bacterial isolates, 2 strains (18%) inhibited the larval settlement of H. elegans (Haswell), 4 strains (36%) were “inductive” to larvae and the remaining 5 strains (46%) were “non-inductive”. There was no correlation between the antifouling activities of bacterial isolates and their phylogenetic origin, i.e. closely related bacterial strains showed different effects on larval settlement of H. elegans. When all “inductive”, “non-inductive” and “inhibitive” bacterial isolates were mixed in a 1:1:1 ratio, the effect of the resultant multispecies film on larval settlement became “inhibitive”. Waterborne compounds of Vibrio sp. and an unidentified α-Proteobacterium, which suppressed the settlement of H. elegans and Bugula neritina (L.) larvae, were further investigated using size fractionation and bioassay-guided enzymatic analysis. It was found that antilarval settlement compounds from these bacteria were heat-stable polysaccharides with a molecular weight >100 kDa. The results indicate that the bacteria associated with the soft coral Dendronephthya sp. may contribute to the antifouling mechanisms of the soft-bodied organisms by producing compounds that are against bacterial growth and settlement of macrofoulers on the surface of their host.     

Relative importance of predation and intraspecific competition in regulating growth and survival of juveniles of the soft-shell clam, Mya arenaria L., at several spatial scales

Predation appears to be the single most important biotic factor regulating populations of bivalves in estuarine and coastal soft sediments. However, the relative roles of predation and intraspecific competition are rarely investigated simultaneously over different spatial scales, making generalities about these mechanisms difficult. Using juveniles of the soft-shell clam, Mya arenaria (initial mean shell length [SL] ± 95% CI = 12.4 ± 0.13 mm), I tested the interactive effects of predator deterrence and intraspecific density (660 vs. 1320 individuals m^− 2) on growth and survival responses over a 185-day period from May to November 2003 at spatial scales that spanned four orders of magnitude: embayments, sites within embayments, tidal gradients, and blocks that were 10,000's, 1000's, 100's, and 5 m apart, respectively. Replicate field experiments were conducted from May to November 2003 at the upper and lower tidal heights at each of two intertidal mud flats (sites) within each of two embayments (Passamaquoddy Bay [PB] and Cobscook Bay [CB]) in eastern Maine.Mean survival, relative growth, and the abundance of wild recruits each varied significantly over all spatial scales. Predation was the most important factor affecting clam survival, explaining 45% of the total variability, whereas embayment, sites within embayments, tidal gradient, and intraspecific density collectively accounted for less than 10% of the variation. At all four intertidal sites, clam survival in experimental units designed to deter predators averaged 72%, but the degree of enhancement varied between embayments (PB = 61%; CB = 267%). Average survival rate was higher (by 12-16%), but growth was slower (by ca. 50%) in upper vs. lower intertidal blocks; however, the patterns differed for both variables between sites within each embayment. The effect of increasing intraspecific clam density was to lower survival by ca. 17% (56% [660 m^− 2] vs. 48% [1320 m^− 2]) in both embayments, but growth was unaffected. Overall, clams doubled in SL, although mean relative growth was 15% greater in CB than PB. Tidal gradient, sites within embayments, and blocks were the three most important factors explaining 35%, 19%, and 22% of total variation in relative clam growth, respectively. In Maine and the northeast US, juveniles of Mya reach their highest abundance above mean low tide levels. Experimental evidence presented here suggests that differential predation along the tidal gradient is the dominant factor controlling clam abundance and distribution patterns in the intertidal zone.     

Increase in seagrass distribution at Bourgneuf Bay (France) detected by spatial remote sensing

The changes in spatial distribution of intertidal Zostera noltii seagrass beds were studied with multispectral visible-infrared remote sensing in Bourgneuf Bay (France) over a 14-year period, between 1991 and 2005. Six SPOT satellite images acquired at low tide were calibrated using in situ spectroradiometric data and processed with the Normalized Difference Vegetation Index (NDVI). A steady and linear increase in meadow areas was observed between 1991 and 2005 with total surfaces colonized by Z. noltii increasing from 208 to 586 ha, respectively. A greater increase in the densest part of the meadow (NDVI > 0.4) was also observed: it represented only 15% of total meadow surfaces in 1991 vs. 35% in 2005. The seagrass expansion took place mainly towards the lower part of the intertidal zone, while in the upper intertidal zone the meadow appeared strictly limited by the +4 m (Lowest Astronomical Tide) bathymetric level. The influence of Z. noltii above-ground biomass variations on spectral reflectance was analyzed experimentally by spectrometry. Z. noltii displays a characteristic steep slope from 700 to 900 nm, increasing with increasing biomass. A quantitative relationship obtained experimentally between NDVI and the dry weight of leaves was used to produce a biomass distribution map. The distribution of Bourgneuf Bay intertidal seagrass beds is certainly constrained by the water turbidity and we suggest that tidal flat accretion could be a significant variable explaining the observed expansion downwards. With very limited spatial interactions, oyster aquaculture cannot be considered as a threat, while a recent increase in recreational hand fishing of Manila clams within the beds could become problematic.     

Predation by gulls on crabs in rocky intertidal and shallow subtidal zones of the Gulf of Maine

Most organisms in intertidal areas are marine in origin; many have distributions that extend into the subtidal zone. Terrestrial predators such as mammals and birds may exploit these animals during low tide and can have considerable effects on intertidal food webs. Several studies have shown that avian predators are capable of reducing densities of sessile and slow-moving intertidal invertebrates but very few studies have considered avian predation on mobile invertebrate predators such as crabs. In this study, we investigated predation by Great Black-backed Gulls (Larus marinus Linnaeus) on three species of crabs (Cancer borealis Stimpson, Cancer irroratus Say, and Carcinus maenas Linnaeus). The study was at Appledore Island, ME (a gull breeding island) and 8 other sites throughout the Gulf of Maine, including breeding islands and mainland sites. On Appledore Island, intertidal and subtidal zones provided over one-third of prey remains found at gull nests, and crabs were a substantial proportion (∼ 30% to 40%) of the total remains. Similarly, collections of prey remains from intertidal areas indicated that crabs were by far the most common marine prey. C. borealis was eaten far more often and C. irroratus and C. maenas less often than expected at each site. Comparing numbers of carapaces to densities of crabs in low intertidal and shallow subtidal zones at each site, we estimated that gulls remove between 15% and 64% of C. borealis during diurnal low tides. The proportion of C. borealis eaten by gulls was independent of proximity to a gull colony. Approximately 97% of the outer coast of Maine is within 20 km of a breeding island. Thus, a lot of gull predation on crabs may occur throughout the Gulf of Maine during summer months. Crabs are important predators of other invertebrates; if predation by gulls reduces the number of crabs in intertidal and shallow subtidal areas, gulls may have important indirect effects on intertidal food webs.     

Quantifying horizontal transmission of Nosema lymantriae, a microsporidian pathogen of the gypsy moth, Lymantria dispar (Lep., Lymantriidae) in field cage studies

Nosema lymantriae is a microsporidian pathogen of the gypsy moth, Lymantria dispar that has been documented to be at least partially responsible for the collapse of L. dispar outbreak populations in Europe. To quantify horizontal transmission of this pathogen under field conditions we performed caged-tree experiments that varied (1) the density of the pathogen through the introduction of laboratory-infected larvae, and (2) the total time that susceptible (test) larvae were exposed to these infected larvae. The time frame of the experiments extended from the early phase of colonization of the target tissues by the microsporidium to the onset of pathogen-induced mortality or pupation of test larvae. Upon termination of each experiment, the prevalence of infection in test larvae was evaluated. In the experiments performed over a range of pathogen densities, infection of test larvae increased with increasing density of inoculated larvae, from 14.2 ± 3.5% at density of 10 inoculated per 100 larvae to 36.7 ± 5.7% at 30 inoculated per 100 larvae. At higher densities, percent infection in test larvae appeared to level off (35.7 ± 5.5% at 50 inoculated per 100 larvae). When larval exposure to the pathogen was varied, transmission of N. lymantriae did not occur within the first 15 d post-inoculation (dpi) (11 d post-exposure of test larvae to inoculated larvae). We found the first infected test larvae in samples taken 20 dpi (16 d post-exposure). Transmission increased over time; in the cages sampled 25 dpi (21 d post-exposure), Nosema prevalence in test larvae ranged from 20.6% to 39.2%.     

Body temperature and desiccation constrain the activity of Littoraria irrorata within the Spartina alterniflora canopy

Behavioral patterns of motile ectotherms are often constrained by their microclimate conditions. For intertidal ectotherms, thermal and desiccation stresses are primary limiting factors. In this study, we developed and tested a steady-state heat budget model to calculate the duration of time that the salt marsh snail, Littoraria irrorata (Say), would maintain active behaviors (crawling or attached on stalks of marsh grass Spartina alterniflora) before switching to an inactive state (retracted and glued with a mucus holdfast on the stalks) due to desiccation. The snails' water loss tolerance limit was found to be 43.6±16.0 mg in a laboratory experiment using 5 temperature treatments (25-45 °C in 5 °C increments) with a vapor density (VD) deficit of ∼15 g/m³ (saturated VD-air VD). We found that snails attached to S. alterniflora at lower heights in the canopy had higher body temperatures during daytime hours but lower water loss rates. Furthermore, we found that calculated activity times generally matched daily and seasonal patterns of life history behaviors reported in the literature. If tidal emersion began at night (∼20:00-4:00 h), calculated activity times were much higher than if emersion began in the daytime. The total monthly activity times for 2005-2010 were the highest in May, the lowest in July, and increased from July to September. Therefore, L. irrorata's behaviors appear to be constrained by microclimate conditions within the S. alterniflora canopy as predicted by the heat budget model. The extent to which the snails' life history traits are controlled by environmental conditions will have important implications for their population dynamics as climate change progresses, and heat budget models can help to predict future changes in behavioral responses.     

Characterization of Xenorhabdus isolates from La Rioja (Northern Spain) and virulence with and without their symbiotic entomopathogenic nematodes (Nematoda: Steinernematidae)

Eighteen Xenorhabdus isolates associated with Spanish entomopathogenic nematodes of the genus Steinernema were characterized using a polyphasic approach including phenotypic and molecular methods. Two isolates were classified as Xenorhabdus nematophila and were associated with Steinernema carpocapsae. Sixteen isolates were classified as Xenorhabdus bovienii, of which fifteen were associated with Steinernema feltiae and one with Steinernema kraussei. Two X. bovienii Phase II were also isolated, one instable phase isolated from S. feltiae strain Rioja and one stable phase from S. feltiae strain BZ. Four representative bacterial isolates were chosen to study their pathogenicity against Spodoptera littoralis with and without the presence of their nematode host. The four bacterial isolates were pathogenic for S. littoralis leading to septicemia 24 h post-injection and killing around 90% of the insect larvae 36 h post-injection, except for that isolated from S. kraussei. After 48 h of injection, this latter isolate showed a lower final population in the larval hemolymph (10⁷ instead of 10⁸ CFU per larvae) and a lower larval mortality (70% instead of 95-100%). The virulence of the nematode-bacteria complexes against S. littoralis showed similar traits with a significant insect larvae mortality (80-90%) 5 days post-infection except for S. kraussei, although this strain reached similar of larval mortality at 7 days after infection.     

Why are intertidal snails rare in the subtidal? Predation, growth and the vertical distribution of Littorina littorea (L.) in the Gulf of Maine

The North Atlantic gastropod Littorina littorea exhibits a characteristic “intertidal” distribution: the snail is abundant in the littoral zone but scarce in the shallow subtidal and the relatively few subtidal individuals are larger (in shell size) on average than those in the intertidal zone. For highly mobile species like L. littorea, this vertical distribution is primarily determined by directional movement. Biotic and abiotic factors vary across tidal heights, and natural selection for movement to shore levels where fitness is maximized provides the ultimate (evolutionary) explanation for vertical distribution patterns. In this study, we asked whether variation in growth rate and/or predation pressure among tidal heights provide an ultimate explanation for vertical gradients in L. littorea size and abundance. We used a cage experiment to compare juvenile growth rate among tidal heights and a series of field and laboratory experiments to examine variation in predation pressure among tidal heights and snail size classes. Juvenile growth rates were highest in the low intertidal zone, declining at both higher and lower levels. Predation risk for tethered L. littorea increased with both decreasing tidal height and decreasing body size (shell height). Almost all tethered prey were consumed by shell- breaking predators and a census revealed that the two most abundant such predators were the crabs Carcinus maenas and Cancer borealis. Laboratory feeding experiments were used to compare size-dependent prey vulnerability and prey-size preferences for these two key predators. We found that L. littorea vulnerability decreased with increasing snail size and increased with increasing size of both predator species. However, whereas C. borealis were capable of consuming even the largest L. littorea, most Carcinus were unable to feed on individuals larger than 10 mm in shell height. Additionally, C. borealis preferred larger sizes of L. littorea than did Carcinus. Thus, Carcinus, which co-occurs with L. littorea in the intertidal, is a much less effective predator than C. borealis, which is found primarily in the subtidal. We conclude that predation on L. littorea by C. borealis and other subtidal consumers has resulted in the scarcity of this ecologically important grazer in the subtidal. This effect has been produced both through direct predation and by imposing strong selection for movement of L. littorea to higher tidal zones.     

Endogenous rhythms and entrainment cues of larval activity in the horseshoe crab Limulus polyphemus

The American horseshoe crab, Limulus polyphemus (Linnaeus), typically inhabits estuaries and coastal areas with pronounced semi-diurnal and diurnal tides that are used to synchronize the timing of spawning, larval hatching, and emergence. Horseshoe crabs spawn in the intertidal zone of sandy beaches and larval emergence occurs when the larvae exit the sediments and enter the plankton. However, L. polyphemus populations also occur in areas that lack significant tidal changes and associated synchronization cues. Endogenous activity rhythms that match predictable environmental cycles may enable larval horseshoe crabs to time swimming activity to prevent stranding on the beach. To determine if L. polyphemus larvae possess a circatidal rhythm in vertical swimming, larvae collected from beach nests and the plankton were placed under constant conditions and their activity monitored for 72 h. Time-series analyses of the activity records revealed a circatidal rhythm with a free-running period of ≈ 12.5 h. Maximum swimming activity consistently occurred during the time of expected falling tides, which may serve to reduce the chance of larvae being stranded on the beach and aid in seaward transport by ebb currents (i.e., ebb-tide transport). To determine if agitation serves as the entrainment cue, larvae were shaken on a 12.4 h cycle to simulate conditions during high tide in areas with semi-diurnal tides. When placed under constant conditions, larval swimming increased near the expected times of agitation. Thus, endogenous rhythms of swimming activity of L. polyphemus larvae in both tidal and nontidal systems may help synchronize swimming activity with periods of high water and inundation.     

Subtidal-intertidal trophic links: American lobsters [Homarus americanus (Milne-Edwards)] forage in the intertidal zone on nocturnal high tides

Homarus americanus (Milne-Edwards), the American lobster, is a predator in New England subtidal communities, feeding on ecologically important grazers (sea urchins), mesopredators (crabs), and basal species (mussels). In this study, we provide the first report of adult American lobsters foraging in rocky intertidal habitats during nocturnal high tides. Censuses by SCUBA divers in the low intertidal (Chondrus crispus Stackhouse) zone showed mean densities of 2.2 lobsters/20 m² on nocturnal high tides, with contrasting low densities of 0.18/20 m² during diurnal high tides. Nocturnal high-tide intertidal densities were 62% of those reported in a previous study of lobsters in nearby subtidal rocky areas (Novak, 2004). The average carapace length of lobsters in the intertidal at night was > 50 mm. These lobsters were actively foraging in the intertidal with collected individuals having a mean stomach fullness of 67%. Prey found in the stomach contents primarily consisted of crabs, mussels and snails. Field experiments showed that lobsters rarely fed on medium to large size individuals of the common intertidal snail, Littorina littorea (L.). In contrast, experiments with local crab species demonstrated that lobsters actively and readily prey on Cancer irroratus (Say) and Carcinus maenas (L.), but were significantly less likely to consume Cancer borealis (Stimpson). The abundance of Carcinus maenas and blue mussels (Mytilus edulis L.) in the intertidal zone may explain the upshore movement of lobsters. Since nocturnal migration of Homarus americanus into the intertidal zone has not been documented before, our understanding of the dynamics of New England intertidal communities needs to be expanded to include this predator.     

Using textured PDMS to prevent settlement and enhance release of marine fouling organisms

The antifouling efficacy of a series of 18 textured (0.2–1000 μm) and non-textured (0 μm) polydimethylsiloxane surfaces with the profiles of round- and square-wave linear grating was tested by recording the settlement of fouling organisms in the laboratory and in the field by monitoring the recruitment of a multi-species fouling community. In laboratory assays, the diatoms Nitzschia closterium and Amphora sp. were deterred by all surface topographies regardless of texture type. Settlement of propagules of Ulva sp. was lower on texture sizes less than the propagule size, and settlement of larvae of Saccostrea glomerata and Bugula neritina was lower on texture sizes closest to, but less than, the sizes of larvae. After a six month field trial, all textured surfaces lost their deterrent effect; however, the foul-release capabilities of textures were still present. High initial attachment was correlated with most fouling remaining after removal trials, indicating that fouling organisms recruited in higher numbers to surfaces upon which they attached most strongly.     

In vitro anaerobic biofilms of human colonic microbiota

The human gastrointestinal tract hosts a complex community of microorganisms that grow as biofilms on the intestinal mucosa. These bacterial communities are not well characterized, although they are known to play an important role in human health. This study aimed to develop a model for culturing biofilms (surface-adherent communities) of intestinal microbiota. The model utilizes adherent mucosal bacteria recovered from colonic biopsies to create multi-species biofilms. Culture on selective media and confocal microscopy indicated the biofilms were composed of a diverse community of bacteria. Molecular analyses confirmed that several phyla were represented in the model, and demonstrated stability of the community over 96 h when cultured in the device. This model is novel in its use of a multi-species community of mucosal bacteria grown in a biofilm mode of growth.     

Do effects of ultraviolet radiation on microbial films have indirect effects on larval attachment of the barnacle Balanus amphitrite?

We have examined the indirect effects of UV-A and UV-B on cypris attachment of the barnacle Balanus amphitrite Darwin through their effects on microbial films. Specifically, we tested the hypothesis that both UV-A and UV-B radiation can indirectly affect the larval attachment of barnacles by altering the microbial film bioactivity. Microbial films were developed from mid-intertidal region (∼1 m above Mean Low Water Level) for 6 days and subjected to ambient levels of ultraviolet radiation. Response of cyprids to untreated and UV-treated microbial films was investigated using double-dish still water choice bioassay. Results showed that both UV-A and UV-B caused a decrease in the percentage of respiring bacterial cells in microbial films and this effect increased with UV energy. With the same UV energy, UV-B caused a greater decrease in respiring bacterial cells than UV-A. However, despite strong UV radiation, the bioactivities of microbial films (i.e., stimulation of cypris attachment) remain unchanged. Results of this study suggest that increased UV radiation, which might occur due to ozone depletion, may not significantly affect the barnacle recruitment by means of affecting the inductive larval attachment cues of microbial films.     

Induction of metamorphosis in the Asian shore crab Hemigrapsus sanguineus: Characterization of the cue associated with biofilm from adult habitat

Recruitment of crabs to nursery habitat requires settlement of the megalopal stage on suitable substratum followed by metamorphosis into the first juvenile stage. Reducing the time to metamorphosis may result in higher recruitment and survival. Previous work has shown that metamorphosis of the Asian shore crab is accelerated by cues from three different sources: (a) water-soluble exudate produced by conspecific adult crabs; (b) biofilm covering rocks in natural habitat for this species; and (c) abiotic rock from natural habitat. The objective of the present investigation was to characterize the metamorphic cue associated with biofilm from rocky intertidal habitat and to compare the three metamorphic cues (exudate from conspecific adults, biofilm from rocky intertidal, and texture of substratum) that have been identified for H. sanguineus. Results of our study show that megalopae of the Asian shore crab respond strongly to biofilm associated with rocky intertidal habitat that has developed for at least 8 days. We also found that megalopae respond to textured rock surfaces from natural habitat, even when those surfaces had been rendered abiotic. The cue remains active after the biofilm has been exposed to − 20 ºC for 12 h, but is de-activated by a few minutes exposure to 100 °C. Moreover, the biofilm cue appears to work in synergy with cues from other sources, but requires actual contact with the biofilm. Our findings show that addition of biofilm to an abiotic textured rock surface significantly decreases mean time to metamorphosis, and simultaneous exposure of megalopae to biofilm-covered rock and to exudate from adult H. sanguineus decreases mean time to metamorphosis even further. The response of this species to multiple cues—and particularly to biofilm in the absence of adult conspecifics—provides a clear advantage in the colonization of virgin habitat and helps explain the very rapid spread of this invasive species along the majority of the east coast of the United States in only two decades.