Development in an estuarine fouling community: The influence of early colonists on later arrivals

Summary Experiments were performed to determine if earlier colonists inhibited, enhanced, or were necessary for establishment of later colonists during development of an estuarine fouling community at Lewes, Delaware. We determined the significance of earlier stages on the successional process by functionally removing early colonizing species. Since settlement of sessile invertebrates onto our experimental test plates was seasonal, we were able to accomplish functional removal of early colonists by putting out clean test panels after these species had ceased settling. Comparisons between panels initially submerged at three different times in 1974 and 1975, and between panels put out at one-month intervals throughout the study (to describe seasonal settlement patterns) allowed us to determine interactions between adult populations of earlier colonists and colonizing individuals of later arriving species.The dominant sessile species in our system and their times of settlement were: a barnacle (Balanus improvisus) — April through June, a polychaete (Hydroides dianthus) — July and August, a tunicate (Molgula manhatensis) — June through October, a hydroid (Tubularia crocea) — July through October, and a mussel (Mytilus edulis) — November through April. All successional series eventually came to be dominated by M. edulis, and it persisted as the dominant for over a year.A variety of species interactions were observed. M. edulis inhibited colonization by all other dominants and B. improvisus partially inhibited settlement of M. manhattensis. The presence of adult M. manhattensis had no influence on summer settlement of T. crocea, but the hydroids enhanced settlement of tunicates in the fall. During both years of our study, larger settlements of mussels were noted on panels harboring tunicates and hydroids than on bare surfaces. H. dianthus, on the other hand, became established only on bare substrates, and colonization was almost totally inhibited by other dominants.Development in our fouling community did not conform to any single model of community development presented to date. Instead, components of several models were observed within our relatively simple (in terms of number of species) system. For example, facilitation (enhancement of later colonists by earlier ones) and inhibition (resistance of earlier colonists to invasion by later colonists) were both observed. However, we found no evidence earlier colonists were essential for establishment of the next developmental stage. In fact, inhibitory interactions appeared to be much more prevalent than facilitative interactions. The former may also have more profound effects on community development since they more often determine eventual species compositions.     

Photosynthesis and dark respiration in Antarctic mosses—an initial comparative study

Rates of dark respiration (DR), gross photosynthesis (GPS) and net photosynthesis (NPS) were investigated for 14 species of moss from a maritime Antarctic locality. The rates found were similar to those reported in studies of temperate, alpine and Arctic species, indicating no physiological specialisation to the Antarctic environment. There was no relationship between the habitat occupied by a species (hydric, mesic, xeric) and physiological measures. There was, however, a loose correlation between NPS and a species' ecology or reproductive behaviour in the maritime Antarctic — species with high NPS being either colonists or those that show high and regular investment in sporophyte production.     

Species colonisation,not competitive exclusion,drives community overdispersion over long‐term succession

Ecological communities often transition from phylogenetic and functional clustering to overdispersion over succession as judged by space‐for‐time substitution studies. Such a pattern has been generally attributed to the increase in competitive exclusion of closely related species with similar traits through time, although colonisation and extinction have rarely been examined. Using 44 years of uninterrupted old‐field succession in New Jersey, USA, we confirmed that phylogenetic and functional clustering decreased as succession unfolded, but the transition was largely driven by colonisation. Early colonists were closely related and functionally similar to residents, while later colonists became less similar to the species present. Extirpated species were generally more distantly related to residents than by chance, or exhibited random phylogenetic/functional patterns, and their relatedness to residents was not associated with time. These results provide direct evidence that the colonisation of distant relatives, rather than extinction of close relatives, drives phylogenetic and functional overdispersion over succession.     

A tri-oceanic perspective: DNA barcoding reveals geographic structure and cryptic diversity in Canadian polychaetes

Background

Although polychaetes are one of the dominant taxa in marine communities, their distributions and taxonomic diversity are poorly understood. Recent studies have shown that many species thought to have broad distributions are actually a complex of allied species. In Canada, 12% of polychaete species are thought to occur in Atlantic, Arctic, and Pacific Oceans, but the extent of gene flow among their populations has not been tested.

Methodology/Principal Findings

Sequence variation in a segment of the mitochondrial cytochrome c oxidase I (COI) gene was employed to compare morphological versus molecular diversity estimates, to examine gene flow among populations of widespread species, and to explore connectivity patterns among Canada''s three oceans. Analysis of 1876 specimens, representing 333 provisional species, revealed 40 times more sequence divergence between than within species (16.5% versus 0.38%). Genetic data suggest that one quarter of previously recognized species actually include two or more divergent lineages, indicating that richness in this region is currently underestimated. Few species with a tri-oceanic distribution showed genetic cohesion. Instead, large genetic breaks occur between Pacific and Atlantic-Arctic lineages, suggesting their long-term separation. High connectivity among Arctic and Atlantic regions and low connectivity with the Pacific further supports the conclusion that Canadian polychaetes are partitioned into two distinct faunas.

Conclusions/Significance

Results of this study confirm that COI sequences are an effective tool for species identification in polychaetes, and suggest that DNA barcoding will aid the recognition of species overlooked by the current taxonomic system. The consistent geographic structuring within presumed widespread species suggests that historical range fragmentation during the Pleistocene ultimately increased Canadian polychaete diversity and that the coastal British Columbia fauna played a minor role in Arctic recolonization following deglaciation. This study highlights the value of DNA barcoding for providing rapid insights into species distributions and biogeographic patterns in understudied groups.     

Woody species colonisation in relation to habitat productivity

A study was conducted to analyse the effect of habitat productivity on woody species colonisation. Three soil types were distinguished: a relatively poor sandy soil type (1), a somewhat richer sandy type (2) and a relatively rich sandy loamy type (3). Chronosequences were established on these three soil types of 38 (type 1), 20 (type 2) and 54 years (type 3) after abandonment. In total 117 vegetation relevées were used to analyse life form change and species responses during old field succession via regression models. On the rich soil type the colonisation rate of woody species was slower than on the poor soil type. This can be explained by higher abundances of perennial species during the first 20 years after abandonment on the rich soil type in contrast to the poor soil type. Perennial species may delay the woody species colonisation. First they close the bare ground which inhibits germination and next they compete with woody seedlings for light, water and nutrients. The effect of habitat productivity on woody species colonisation can only be determined appropriately by taking life history traits into account. Early successional 'pioneer' woody species dispersed by wind have less difficulties colonising old fields than late successional 'forest' species; they colonise old fields prior to the development of a dense perennial sward. Forest species depend on animals to be dispersed which are attracted by vegetation structure. In ± 30 years on the poor soil type and in ± 45 years on the rich soil type woody species become dominant relative to other life forms. Forest species like Quercus robur L. invaded relatively early (<5 years) in contrast to other studies which probably coincides with the distance to seed sources (forest edges).     

The effects of potential larval supply, settlement and post-settlement processes on the distribution of two species of filter-feeding caddisflies

1. Hydropsychid caddisfly larvae are often abundant in fast flow habitats and on highly textured substrata. Such patterns are usually inferred to result from habitat preference, but the roles of larval supply to the benthos and post‐settlement events are rarely examined for stream populations. We describe a manipulative field experiment that examined larval supply, habitat preference and post‐settlement events simultaneously for two co‐occurring species of hydropsychids. 2. Ten artificial channels were constructed in a natural riffle to create fast and slow flow habitats and within each channel we placed six artificial substrata whose surfaces had been modified to create three different texture treatments. We measured discharge through channels and monitored hydropsychid colonisation of substrata every 3–4 days. Half of the substrata had all hydropsychids and nets removed every 3–4 days (short‐term colonisation) whereas the remaining half were counted but nets and hydropsychids left attached (long‐term colonisation). Short‐term counts of nets and individuals were summed to allow comparison with long‐term colonisation substrata. 3. Smicrophylax sp. AV2 larvae were more abundant in fast flow channels than slow flow channels, but these differences were proportional to discharge through each of the channels, suggesting that supply of settlers can explain this pattern. Smicrophylax larvae were least abundant on smooth substrata, which suggests that this species selects habitats based on surface texture. Alternatively, Asmicridea sp. AV1 larvae were only found in fast flow channels and this most likely reflects an active habitat choice by this species, but there was no significant difference between different texture treatments. 4. There were no differences between summed, short‐ and long‐term counts of recruits for either species, but there were more nets than larvae, especially in slow flow channels, by the end of the experiment, suggesting that larval mortality or re‐dispersal after settlement could be considerable. 5. Our results indicate that supply, habitat selection at settlement and post‐settlement processes all contributed variously to the distribution of hydropsychid caddisfly larvae, but that each species was affected differentially by these factors. Larval supply and post‐settlement processes are rarely examined by stream researchers and our results demonstrate these factors deserve much more consideration. Calculating accurate larval supply rates to sites is challenging, but we suggest that such detailed information is necessary if we are to sort out what sets limits to distributions and the underlying population structure of stream invertebrate populations.     

Surface water connectivity drives richness and composition of Arctic lake fish assemblages

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The shell of <Emphasis Type="Italic">Hexaplex (Trunculariopsis) trunculus</Emphasis> (Gastropoda: Muricidae) as a mobile hard substratum for epibiotic polychaetes (Annelida: Polychaeta) in the Ria Formosa (Algarve coast—southern Portugal)

This work reports and illustrates secondary colonisation of Hexaplex (Trunculariopsis) trunculus shells by polychaetes in the Ria Formosa lagoon (Algarve coast—southern Portugal). Information is presented in terms of qualitative and quantitative data on epibiotic polychaetes, fouling frequency, degree of epibiosis, preferential areas for colonisation and incidence of shell damages. A total of 2,880 polychaetes belonging to 10 families were identified. Besides Spirorbidae (not quantified), the most abundant families were Serpulidae (67.5%), Sabellidae (10.2%), Sabellariidae (9.6%) and Cirratulidae (8.5%). From a total of 2,264 T. trunculus individuals analysed for epibiosis, 28.4% were non-fouled, 66.8% were intermediately fouled and 4.8% were heavily fouled. The fouling frequency, degree of epibiosis and incidence of damages in the shell spire increased markedly with T. trunculus shell length. Some epibiotic polychaetes were located preferentially on/or nearby particular features of T. trunculus shells, which probably facilitate settlement and tube construction, in addition to provide some protection against tube damage. The main consequences of epibiosis (benefits and disadvantages) for the gastropod basibiont (T. trunculus) are discussed. The present study apparently indicates that besides burrowing into soft bottom substrates, sporadic inter-tidal exposure and mutual predation on epibiosis, T. trunculus lacks other typical antifouling defence adaptations. Handling editor: K. Martens     

Diversity and species distribution of polychaetes,isopods and bivalves in the Atlantic sector of the deep Southern Ocean

We examined deep-sea benthic data on polychaetes, isopods and bivalves from the Atlantic sector of the Southern Ocean. Samples were taken during the expeditions EASIZ II (1998), ANDEEP I and II (2002) (depth: 742–6,348 m). The range between sites varies from 3 to 1,900 km. Polychaetes (175 species in total) and isopods (383 species) had a high proportion of species restricted to one or two sites (72 and 70%, respectively). Bivalves (46 species) had a higher proportion of species represented at more sites. Beta diversity (Whittaker and Jaccard) was higher for polychaetes and isopods than for bivalves. The impact of depth on species richness was not consistent among groups; polychaetes showed a negative relationship to depth, isopods displayed highest richness in the middle depth range (2,000–4,000 m), whereas bivalves showed no clear relationship to depth. Species richness was not related to latitude (58–74°S) or longitude (22–60°W) for any group.     

Growth and viability of mycorrhizal extraradical mycelia associated with three temperate orchid species

Growth and enzymatic activities of extraradical mycelia (ERM) of native mycorrhizal symbionts associated with three orchid species, Dactylorhiza fuchsii, D. majalis and Platanthera bifolia, were studied. ERM extracted from the mycorrhizosphere of these species showed features typical for fungi that form orchid mycorrhiza. In the first pot experiment, three different treatments were applied on tubers of D. fuchsii transplanted from a natural site: control (no specific treatment), reinoculated (surface-sterilized tubers reinoculated with mycorrhizal fungi-colonised roots), and benomyl (nonsterilized tubers treated with fungicide). However, no significant differences in ERM growth and intensity of root mycorrhizal colonisation at harvest were observed among these treatments. ERM associated with reinoculated D. fuchsii plants showed significantly higher alkaline phosphatase (ALP) enzymatic activity at week 36 than at week 24, but no differences were observed for NADH diaphorase activity. Benomyl application significantly reduced ALP activity in comparison with reinoculated plants at week 36. In the second experiment, plants of all three species were either untreated (control), or repeatedly treated with benomyl. Similarly to the results of the first experiment, benomyl application did not reduce the ERM growth of mycorrhizal symbionts associated with D. majalis and D. fuchsii. The low ERM growth associated with benomyl-treated P. bifolia was probably caused by poor root system development in this treatment. Significantly higher mycorrhizal colonisation was found for D. fuchsii compared to P. bifolia in control treatments at the end of cultivation. The ERM of native symbionts of the three orchid species studied seemed to have a different growth pattern over time and responded differently to fungicide application.     

Convergent Antifouling Activities of Structurally Distinct Bioactive Compounds Synthesized Within Two Sympatric Haliclona Demosponges

A wide range of sessile and sedentary marine invertebrates synthesize secondary metabolites that have potential as industrial antifoulants. These antifoulants tend to differ in structure, even between closely related species. Here, we determine if structurally divergent secondary metabolites produced within two sympatric haliclonid demosponges have similar effects on the larvae of a wide range of benthic competitors and potential fouling metazoans (ascidians, molluscs, bryozoans, polychaetes, and sponges). The sponges Haliclona sp. 628 and sp. 1031 synthesize the tetracyclic alkaloid, haliclonacyclamine A (HA), and the long chain alkyl amino alcohol, halaminol A (LA), respectively. Despite structural differences, HA and LA have identical effects on phylogenetically disparate ascidian larvae, inducing rapid larval settlement but preventing subsequent metamorphosis at precisely the same stage. HA and LA also have similar effects on sponge, polychaete, gastropod and bryozoan larvae, inhibiting both settlement and metamorphosis. Despite having identical roles in preventing fouling and colonisation, HA and LA differentially affect the physiology of cultured HeLa human cells, indicating they have different molecular targets. From these data, we infer that the secondary metabolites within marine sponges may emerge by varying evolutionary and biosynthetic trajectories that converge on specific ecological roles.     

Diet of black guillemots and northern fulmars breeding beside a High Arctic polynya

In the Arctic, the availability of early-season open water (shore leads, polynyas) is a key factor influencing annual reproduction by marine birds, as these relatively productive locations provide the only sites where migrating and breeding birds can feed. We examined the diet of two marine birds, black guillemots (Cepphus grylle) and northern fulmars (Fulmarus glacialis), feeding in the Hell Gate–Cardigan Strait Polynya in the Canadian High Arctic during the breeding seasons of 1980–1984. There was little overlap in prey items consumed between these two species, except that both relied on similar sympagic amphipods. Guillemots fed principally on benthic prey, and compared to earlier High Arctic studies, they consumed proportionally more benthic fish, mysids and decapods. Fulmars appeared to feed on swarms of pelagic or surface prey, and in this polynya they consumed proportionally fewer fish and more polychaetes than has been reported for fulmars at other High Arctic locations. Given that climate change may alter marine food webs by changing the types and availability of prey, our results set a baseline of dietary information for these predators against which future conditions can be compared.     

Mycorrhizas and dark septate root endophytes in polar regions

We review the distributions and functions of mycorrhizas and dark septate root endophytes in polar regions. Arbuscular mycorrhizas (AM) are present in the Arctic and Antarctic to 82 °N and 63 °S, respectively, with fine endophyte being the dominant form of AM in roots at higher latitudes. Ecto- (ECM) and ericoid (ERM) mycorrhizas both occur in the Arctic to 79 °N, owing to the presence of species of Salix, Dryas, Vaccinium and Cassiope to this latitude. ECM and ERM are not present in Antarctic ecosystems, owing to an absence of suitable hosts. Arbutoid and orchid mycorrhizas are infrequent in the Arctic, whilst the latter are present at one location in the sub-Antarctic. Data from studies of AM, ECM and ERM colonisation along a latitudinal transect through the Arctic indicate that the frequency of plant species not colonised by mycorrhizas increases at higher latitudes, largely owing to an increase in non-mycorrhizal and a decrease in obligately mycorrhizal plant families at more northerly locations. A separate group of root- and rhizoid-associated fungi, the dark septate root endophytes (DSE), are widespread to 82 °N and 77 °S, and are apparently more frequent than mycorrhizal fungi in polar regions. The functions of DSE are largely unclear, but studies suggest beneficial effects on plant growth under defined conditions. We advocate further research into the effects of DSE on their host plants in polar regions.     

The effects of Relic fauna on initial patch colonisation in a British saltmarsh

When a disturbance impacts an area it rarely leads to a complete defaunation, some individuals survive forming a relic fauna. Relic fauna in azoic patches in an intertidal soft-bottom habitat were simulated by the separate introduction of individuals ofNereis diversicolor, Hydrobia ulvae andLittorina littorea into defaunated cores. These were exposed in the field for 24 hours and the effects of relics on colonisation were assessed separately for colonisation via the sediment surface and colonisation via the surface and laterally through the sediment. After 24 hours all the species in the ambient community were recorded from at least some experimental cores. Densities of the most abundant infaunal taxa,Corophium volutator, Enchytraeus buchholzi, Manayunkia aestuarina, Tubificoides benedeni and nematodes, varied between 1% and 279% of ambient. MDS ordinations showed significant differences in the fauna of experimental cores, a result of the lack of full colonisation by some species and the presence of other species at densities in excess of ambient. Comparisons (ANOSIM and ANOVA) of the fauna of the relic addition cores vs. no-addition cores showed an influence ofN. diversicolor on colonisation. However, this relic effect appeared to be masked by the high degree of variation in colonisation. Densities ofL. littorina andH. ulvae were not maintained in all of the experimental cores and there was no significant difference in the fauna of cores in which the treatments were maintained. It therefore seems that initial colonisation of patches in the emergent saltmarsh is controlled by the (i) supply of colonists and (ii) attraction to under-exploited organic matter and that any relic fauna exerts little influence on the early stages of the colonisation process.     

Community diversity outweighs effect of warming on plant colonization

Abiotic environmental change, local species extinctions and colonization of new species often co‐occur. Whether species colonization is driven by changes in abiotic conditions or reduced biotic resistance will affect community functional composition and ecosystem management. We use a grassland experiment to disentangle effects of climate warming and community diversity on plant species colonization. Community diversity had dramatic impacts on the biomass, richness and traits of plant colonists. Three times as many species colonized the monocultures than the high diversity 17 species communities (~30 vs. 10 species), and colonists collectively produced 10 times as much biomass in the monocultures than the high diversity communities (~30 vs. 3 g/m²). Colonists with resource‐acquisitive strategies (high specific leaf area, light seeds, short heights) accrued more biomass in low diversity communities, whereas species with conservative strategies accrued most biomass in high diversity communities. Communities with higher biomass of resident C4 grasses were more resistant to colonization by legume, nonlegume forb and C3 grass colonists, but not by C4 grass colonists. Compared with effects of diversity, 6 years of 3°C‐above‐ambient temperatures had little impact on plant colonization. Warmed subplots had ~3 fewer colonist species than ambient subplots and selected for heavier seeded colonists. They also showed diversity‐dependent changes in biomass of C3 grass colonists, which decreased under low diversity and increased under high diversity. Our findings suggest that species colonization is more strongly affected by biotic resistance from residents than 3°C of climate warming. If these results were extended to invasive species management, preserving community diversity should help limit plant invasion, even under climate warming.     

Relatedness affects the density,distribution and phenotype of colonisers in four sessile marine invertebrates

Genetic diversity has emerged as an important source of variation in the ecological properties of populations, but there are few studies of genetic diversity effects on colonisation processes. This relative scarcity of studies is surprising given the influence of colonisation on species coexistence, invasion, and population persistence. Here, we manipulated relatedness in experimental populations of colonising larvae in four sessile marine invertebrates. We then examined the influence of coloniser relatedness on the number, spatial arrangement and phenotype of colonisers following permanent settlement. Overall, relatedness influenced colonisation in all four species, but the effects of relatedness on colonisation differed among species. The variable responses of species to manipulations of relatedness likely reflect differences in intensity of inter‐ and intra‐specific competition among adults, as well as the differential consequences of larval behaviours for each species. Relatedness appears to play an underappreciated role in the colonisation process, and we recommend that future studies of genetic diversity effects consider not only adult stages – the focus of most work to date – but also the importance of genetic diversity in early life history stages.     

Sediment-associated cues for larval settlement of the infaunal spionid polychaetes Polydora cornuta and Streblospio benedicti

Do patchy distribution patterns of infaunal polychaetes result from active site selection of larvae influenced by sediment-associated microbial cues? This hypothesis was tested with still-water laboratory settlement assays revealing the acceptance or rejection of polychaete larvae to qualitatively different sediments. Laboratory brood cultures of the spionid polychaetes Polydora cornuta and Streblospio benedicti yielded a sufficient number of larvae with planktotrophic development for bioassays. High settlement rates (75-95%) of test larvae were observed in response to natural sediment. Sterilization of natural sediment significantly decreased settlement of P. cornuta (25-55%) while combustion of sediment significantly decreased the settlement rate in both species (5-50%). Differences in settlement responses to sediments treated by sterilization or combustion most likely resulted from a variety of factors such as modified sediment fabric, grain size distribution and quantity of adsorbed organic matter. To experimentally address the potential role of microorganisms and microbial metabolites as mediators of larval settlement, ashed sediment was inoculated with viable microorganisms obtained from natural sediment. In both polychaete species, this treatment significantly increased larval settlement in comparison to the control of ashed sediment indicating that larval settlement was at least partially mediated by the presence of microorganisms associated with sediment.     

Dispersal and colonisation of plants in lowland streams: success rates and bottlenecks

Plant dispersal and colonisation, including rates of dispersal, retention, colonisation and survival of dispersed propagules (shoots and seeds), were studied in a 300-m stream reach in a macrophyte-rich lowland stream during one growing season. Relationships between colonisation processes and simple flow parameters were tested. Each fortnight during a growing season, the number of dispersed plant propagules and the number of new and lost plant colonisations since the last sampling day were recorded. The retention of dispersing shoots was tested on two occasions during the growing season by releasing plant shoots and subsequently re-collecting the retained shoots in the study reach. The main bottleneck for plant colonisation in macrophyte-rich lowland streams is the primary colonisation (development of attached roots in the sediment from vegetative propagules or seedlings) of retained shoots and seeds, due in part to low retention success (1% of the dispersed shoots per 100-m reach) and to unsuccessful colonisation of retained shoots (3.4% of retained shoots colonised). The number of drifting shoots and seeds per day during the growing season were 650–6,950 and 2,970–62,780, respectively, and caused no constraint to colonisation. The survival rate of primary colonists was high with 80% surviving during the first growing season and about 50% surviving the first winter. There was no relationship between number of drifting shoots and flow, but the number of drifting seeds increased with flow. The number of colonisations between two consecutive sampling days correlated to the extent of low flow in the period. The loss rate of colonisations correlated to high flow events, but was low overall. My study strongly indicates that the number of propagules is not a constraint to colonisation in macrophyte-rich lowland streams. Rather, I conclude that primary colonisation is the main constraint to regaining vegetation in lowland streams in general and in vegetation-free rehabilitated streams in particular. Therefore, if plant colonisation is a target for stream rehabilitation, it is important to enhance retention and colonisation of propagules by creating areas of low flow and by providing physical obstacles to work as retention agents in the stream. Handling editor: L. M. Bini     

Body condition of shorebirds upon arrival at their Siberian breeding grounds

Arctic breeding shorebirds carry substantial body stores on their long-distance migrations from their non-breeding grounds. Upon arrival at the breeding area the remains of these stores can be used for egg formation, insurance against poor feeding conditions or rebuilding organs. We quantified body condition (body mass, total body water, lean body mass and fat mass estimated using the deuterium dilution method) in seven shorebird species caught upon arrival in the Siberian Arctic. Arrival condition was compared with incubation condition in a subset of species. After correction for structural size, body mass was significantly lower at arrival than during incubation in most of the species (but 3–18% above lean mass). Fat index (fat mass/lean mass) varied between 5.1 and 13.2%. Fat stores were estimated to enable survival for 0.6 days for the smallest and 2.5 days for the largest species. We discuss possible functions of arrival stores: insurance, egg-formation or rebuilding organs. G. H. Visser: Deceased.