Fire reduces eucalypt forest flowering phenology at the landscape-scale.

Plant phenology describes the timing of reproductive events including flowering and fruiting, which for many species are affected by fire disturbance. Understanding phenological responses to fire provides insights into how forest demographics and resources may shift alongside increasing fire frequency and intensity driven by climate change. However, isolating the direct effects of fire on a species' phenology and excluding potential confounders (e.g. climate, soil) has been difficult due to the logistical challenges of monitoring species-specific phenological events across myriad fire and environmental conditions. Here, we use CubeSat-derived crown-scale flowering data to estimate the effects of fire history (time since fire and fire severity over a 15-year time span) on flowering of the eucalypt Corymbia calophylla across a Mediterranean-climate forest (814km2) in southwest Australia. We found that fire reduced the proportion of flowering trees at the landscape-scale, and flowering recovered at a rate of 0.15 % (±0.11% SE) per year. Further, this negative effect was significant due to high crown scorch fires (>20% canopy scorch), yet there was no significant effect from understory burns. Estimates were obtained using a quasi-experimental design which identifies the effect of time since fire and severity on flowering by comparing proportional flowering within target fire perimeters (treatment) and adjacent past fire perimeters (control). Given the majority of fires studied were managed fuel reduction burns, we applied the estimates to hypothetical fire regimes to compare flowering outcomes under more or less frequent prescribed burning. This research demonstrates the landscape-scale effects of burning on a tree species' reproduction, which could broadly impact forest resiliency and biodiversity.

ENSO feedback drives variations in dieback at a marginal mangrove site.

Ocean-atmosphere climatic interactions, such as those resulting from El Niño Southern Oscillation (ENSO) are known to influence sea level, sea surface temperature, air temperature, and rainfall in the western Pacific region, through to the north-west Australian Ningaloo coast. Mangroves are ecologically important refuges for biodiversity and a rich store of blue carbon. Locations such as the study site (Mangrove Bay, a World Heritage Site within Ningaloo Marine Park and Cape Range National Park) are at the aridity range-limit which means trees are small in stature, forests small in area, and are potentially susceptible to climate variability such as ENSO that brings lower sea level and higher temperature. Here we explore the relationship between mangrove dieback, and canopy condition with climatic variables and the Southern Oscillation Index (SOI)-a measure of ENSO intensity, through remote sensing classification of Landsat satellite missions across a 29 year period at a north-west Australian site. We find that the SOI, and seasonal mean minimum temperature are strongly correlated to mangrove green canopy (as indicator of live canopy) area. This understanding of climate variations and mangrove temporal heterogeneity (patterns of abundance and condition) highlights the sensitivity and dynamics of this mangrove forest and recommends further research in other arid and semi-arid tropical regions at mangrove range-limits to ascertain the extent of this relationship.

Assessing the Capability and Potential of LiDAR for Weed Detection.

Conventional methods of uniformly spraying fields to combat weeds, requires large herbicide inputs at significant cost with impacts on the environment. More focused weed control methods such as site-specific weed management (SSWM) have become popular but require methods to identify weed locations. Advances in technology allows the potential for automated methods such as drone, but also ground-based sensors for detecting and mapping weeds. In this study, the capability of Light Detection and Ranging (LiDAR) sensors were assessed to detect and locate weeds. For this purpose, two trials were performed using artificial targets (representing weeds) at different heights and diameter to understand the detection limits of a LiDAR. The results showed the detectability of the target at different scanning distances from the LiDAR was directly influenced by the size of the target and its orientation toward the LiDAR. A third trial was performed in a wheat plot where the LiDAR was used to scan different weed species at various heights above the crop canopy, to verify the capacity of the stationary LiDAR to detect weeds in a field situation. The results showed that 100% of weeds in the wheat plot were detected by the LiDAR, based on their height differences with the crop canopy.

Resistance of Amphiphilic Polysaccharides against Marine Fouling Organisms.

Amphiphilic coatings are promising candidates for fouling-release applications. As hydrophilic components, polysaccharides are interesting and environmentally benign building blocks. We used covalently coupled alginic acid (AA) and hyaluronic acid (HA) and postmodified them with a hydrophobic fluorinated amine. The surfaces showed good stability under marine conditions and fluorination led to a decreased uptake of Ca(2+) ions after modification. In single species settlement assays (bacteria, diatoms, barnacle cypris larvae), the modification decreased the settlement density and/or the adhesion strength of many of the tested species. Field studies supported findings of the laboratory experiments, as hydrophobic modification of AA and HA decreased diatom colonization.

Conditioning of self-assembled monolayers at two static immersion test sites along the east coast of Florida and its effect on early fouling development.

Among the first events after immersion of surfaces in the ocean is surface 'conditioning'. Here, the accumulation and composition of the conditioning films formed after immersion in the ocean are analyzed. In order to account for different surface chemistries, five self-assembled monolayers that differ in resistance to microfouling and wettability were used. Water samples from two static immersion test sites along the east coast of Florida were collected at two different times of the year and used for experiments. Spectral ellipsometry revealed that conditioning films were formed within the first 24 h and contact angle goniometry showed that these films changed the wettability and rendered hydrophobic surfaces more hydrophilic and vice versa. Infrared reflection adsorption spectroscopy showed that the composition of the conditioning film depended on both the wettability and immersion site. Laboratory and field assays showed that the presence of a conditioning film did not markedly influence settlement of microorganisms.

A comparison between different fouling-release elastomer coatings containing surface-active polymers.

Surface-active polymers derived from styrene monomers containing siloxane (S), fluoroalkyl (F) and/or ethoxylated (E) side chains were blended with an elastomer matrix, either poly(dimethyl siloxane) (PDMS) or poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS), and spray-coated on top of PDMS or SEBS preformed films. By contact angle and X-ray photoelectron spectroscopy measurements, it was found that the surface-active polymer preferentially populated the outermost layers of the coating, despite its low content in the blend. However, the self-segregation process and the response to the external environment strongly depended on both the chemistry of the polymer and the type of matrix used for the blend. Additionally, mechanical testing showed that the elastic modulus of SEBS-based coatings was one order of magnitude higher than that of the corresponding PDMS-based coatings. The coatings were subjected to laboratory bioassays with the marine alga Ulva linza. PDMS-based coatings had superior fouling-release properties compared to the SEBS-based coatings.

Attribution of sources to metal accumulation in an alpine tarn, the Snowy Mountains, Australia.

This study analyses 1800 years of heavy metal accumulation in a remote alpine lake experiencing long-range atmospheric contamination and additional inputs of Ag from cloud seeding. In comparison to previous work undertaken on peats, lake sediments show limited post-industrial metal enrichment with enrichment factors of Ag: 1.3, Pb: 1.3, Zn: 1.1, Cu: 1.2 compared to Ag: 2.2, Pb: 3.3, Zn: 2.1, Cu: 4.1 for peat. We show this to be the result of substantial fluvial lithogenic flux of metals (92-97% of total metal flux) to the lake. Total annual metal flux to the lake ranges from: Ag: 4-12 ng/cm(2)/yr to Zn: 3 383-11 313 ng/cm(2)/yr. As a result, any contribution of cloud seeding to additional enrichment of Ag in lake sediments is considered negligible. Results show that metal enrichment is not necessarily ubiquitous through a landscape. This has implications for predicting the impacts of atmospheric metal pollution to complex environmental systems.

Settlement behavior of zoospores of Ulva linza during surface selection studied by digital holographic microscopy.

Settlement of the planktonic dispersal stages of marine organisms is the crucial step for the development of marine biofouling. Four-dimensional holographic tracking reveals the mechanism by which algal spores select surfaces suitable for colonization. Quantitative analysis of the three dimensional swimming trajectories of motile spores of a macroalga (Ulva linza) in the vicinity of surfaces functionalized with different chemistries reveals that their search strategy and swimming behavior is correlated to the number of settled spores found in spore settlement bioassays conducted over 45 min. The spore motility and exploration behavior can be classified into different motion patterns, with their relative occurrence changing with the surface chemistry. Based on the detailed motility analysis we derived a model for the surface selection and settlement process of Ulva zoospores.

Controlling the adhesion of the diatom Navicula perminuta using poly(N-isopropylacrylamide-co-N-(1-phenylethyl) acrylamide) films.

Poly(N-isopropylacrylamide)-co-N-(1-phenylethyl) acrylamide [P(NIPAAm-co-PEAAm)] thermo-responsive thin films with a lower critical solution temperature (LCST) adjusted to fit marine applications were used to investigate the effect of changes in the wetting properties of a surface on the adhesion of the diatom Navicula perminuta, an organism which forms slime films on surfaces immersed in an aquatic environment. Although the strength of attachment of cells was affected by whether the film was collapsed or expanded, no significant decrease in adhesion strength occurred upon temperature decrease. The effects were attributed to possible strong interactions between the hydrophobic segments of the responsive film when collapsed with components in the adhesive complex.

Interactions of zoospores of Ulva linza with arginine-rich oligopeptide monolayers.

We recently reported on the strong interactions of zoospores of the green alga, Ulva linza with an arginine-rich oligopeptide self-assembled monolayer (SAM) [Biofouling 2008, 24, 303-312], where the arginine-rich peptide induced not only high spore settlement, but also a form of abnormal settlement, or "pseudo-settlement", whereby a proportion of spores do not go through the normal process of surface exploration, adhesive exocytosis, and loss of flagella. Further, it was demonstrated that both the total number of settled spores and the fraction of pseudosettled spores were related to the surface density of the arginine-rich peptide. Here we present a further investigation of the interactions of zoospores of Ulva with a set of oligomeric, de novo designed, arginine-rich peptides, specifically aimed to test the effect of peptide primary structure on the interaction. Via variations in the peptide length and by permutations in the amino acid sequences, we gain further insight into the spore-surface interactions. The interpretation of the biological assays is supported by physicochemical characterization of the SAMs using infrared spectroscopy, ellipsometry, and contact angle measurements. Results confirm the importance of arginine residues for the anomalous pseudosettlement, and we found that settlement is modulated by variations in both the total length and peptide primary structure. To elucidate the causes of the anomalous settlement and the possible relation to peptide-membrane interactions, we also compared the settlement of the "naked" zoospores of Ulva (which present a lipoprotein membrane to the exterior without a discrete polysaccharide cell wall), with the settlement of diatoms (unicellular algae that are surrounded by a silica cell wall), onto the peptide SAMs. Cationic SAMs do not notably affect settlement (attachment), adhesion strength, or viability of diatom cells, suggesting that the effect of the peptides on zoospores of Ulva is mediated via specific peptide-membrane interactions.

Anomalous settlement behavior of Ulva linza zoospores on cationic oligopeptide surfaces.

Identification of settlement cues for marine fouling organisms opens up new strategies and methods for biofouling prevention, and enables the development of more effective antifouling materials. To this end, the settlement behaviour of zoospores of the green alga Ulva linza onto cationic oligopeptide self-assembled monolayers (SAMs) has been investigated. The spores interact strongly with lysine- and arginine-rich SAMs, and their settlement appears to be stimulated by these surfaces. Of particular interest is an arginine-rich oligopeptide, which is effective in attracting spores to the surface, but in a way which leaves a large fraction of the settled spores attached to the surface in an anomalous fashion. These 'pseudo-settled' spores are relatively easily detached from the surface and do not undergo the full range of cellular responses associated with normal commitment to settlement. This is a hitherto undocumented mode of settlement, and surface dilution of the arginine-rich peptide with a neutral triglycine peptide demonstrates that both normal and anomalous settlement is proportional to the surface density of the arginine-rich peptide. The settlement experiments are complemented with physical studies of the oligopeptide SAMs, before and after extended immersion in artificial seawater, using infrared spectroscopy, null ellipsometry and contact angle measurements.

Membrane recycling and calcium dynamics during settlement and adhesion of zoospores of the green alga Ulva linza.

Recruitment of individuals of the marine alga Ulva linza on to a suitable habitat involves the settlement of motile zoospores on to a substratum during which a preformed adhesive is secreted by vesicular exocytosis. The fluorescent styryl dye FM 1-43 and fluorescent Ca(2+) indicators were used to follow membrane cycling and changes in cytosolic Ca(2+) ([Ca(2+)](cyt)) associated with settlement. When swimming zoospores were exposed continuously to FM 1-43, the plasma membrane was preferentially labelled. During settlement, FM 1-43-labelled plasma membrane was rapidly internalized reflecting high membrane turnover. The internalized membrane was focused into a discrete region indicating targeting of membrane to an endosome-like compartment. Acetoxymethyl (AM)-ester derivatives were found to be unsuitable for monitoring [Ca(2+)](cyt) because the dyes were rapidly sequestered from the cytoplasm into sub-cellular compartments. [Ca(2+)](cyt) was, however, reliably measured using dextran-conjugated calcium indicators delivered into cells using a biolistic technique. Cells loaded with Oregon Green BAPTA-1 dextran (Invitrogen, Paisley, UK) showed diffuse cytosolic loading and reliably responded to imposed changes in [Ca(2+)](cyt). During settlement, zoospores exhibited both localized and diffuse increases in [Ca(2+)](cyt) implying a role for [Ca(2+)](cyt) in exocytosis of the adhesive.

The influence of surface lubricity on the adhesion of Navicula perminuta and Ulva linza to alkanethiol self-assembled monolayers.

The settlement and adhesion of Navicula perminuta and Ulva linza to methyl-terminated alkanethiol self-assembled monolayers (SAMs) of increasing chain length has been investigated. Organisms were allowed to settle onto the monolayers and were subsequently exposed to hydrodynamic shear stress in order to determine their adhesion strength. Results show that as the SAM structure changes from amorphous to crystalline (C14), there is a marked change in the adhesion of N. perminuta and U. linza. Given that the SAMs in the series all exhibit similar contact angle behaviour and surface energy, it is hypothesized that the lubricity of the surface plays a role in determining the surface adhesion.

Mussel (Mytilus edulis) byssus deposition in response to variations in surface wettability.

Mussels (Mytilus edulis) are economically important in their role as an aquaculture species and also with regard to marine biofouling. They attach tenaciously to a wide variety of submerged surfaces by virtue of collagenous attachment threads termed 'byssi'. The aim of this study was to characterize the spreading of the byssal attachment plaque, which mediates attachment to the surface, on a range of surfaces in response to changes in wettability. To achieve this, well characterized self-assembled monolayers of omega-terminated alkanethiolates on gold were used, allowing correlation of byssal plaque spreading with a single surface characteristic--wettability. The present results were inconsistent with those from previous studies, in that there was a positive correlation between plaque size and surface wettability; a trend which is not explained by conventional wetting theory for a three-phase system. A recent extension to wetting theory with regard to hydrophilic proteins is discussed and the results of settlement assays are used to attempt reconciliation of these results with those of similar previous studies and, also, with recent data presented for the spreading of Ulva linza spore adhesive.

Biofilms.

Biofilms of bacteria, frequently in association with algae, protozoa and fungi, are found on all submerged structures in the marine environment. Although it is likely that for the majority of organisms a biofilmed surface is not a pre-requisite for settlement, in practice, colonization by spores and larvae of fouling organisms almost always takes place via a biofilmed surface. Therefore, the properties of the latter may be expected to influence colonization, positively or negatively. Biofilms are responsible for a range of surface-associated and diffusible signals, which may moderate the settling behaviour of cells, spores and larvae. However, there is no consensus view regarding either cause and effect or the mechanism(s) by which biofilms moderate settlement. Studies with mixed biofilms, especially field experiments, are difficult to interpret because of the conflicting signals produced by different members of the biofilm community as well as their spatial organisation. Molecular techniques highlight the deficiencies of culture methods in identifying biofilm bacteria; hence, the strains with the most impact on settlement of spores and larvae may not yet have been isolated and cultured. Furthermore, secondary products isolated from cultured organisms may not reflect the situation that pertains in nature. The evidence that bacterial quorum sensing signal molecules stimulate settlement of spores of the green macroalga, Ulva, is discussed in some detail. New molecular and analytical tools should provide the opportunity to improve our fundamental understanding of the interactions between fouling organisms and biofilms, which in turn may inform novel strategies to control biofouling.

Settlement behavior of swimming algal spores on gradient surfaces.

When surfaces possessing gradients of surface energy are incubated with motile spores from the green seaweed Ulva, the spores attach on the hydrophilic part of the gradient in larger numbers than they do on the hydrophobic part. This result is opposite to the behavior of the spores observed on the homogeneous hydrophobic and hydrophic surfaces. The data suggest that the gradients have a direct and active influence on the spores, which may be due to the biased migration of the spores during the initial stages of surface sensing.

The influence of surface energy on the wetting behaviour of the spore adhesive of the marine alga Ulva linza (synonym Enteromorpha linza).

The environmental scanning electron microscope has been used to image the adhesive pads secreted by zoospores of the marine alga Ulva linza as they settle on a range of self-assembled and grafted monolayers of different wettability, under natural, hydrated conditions. Results reveal that the diameter of the adhesive pad is strongly influenced by surface wettability, the adhesive spreading more (i.e. wetting the surface better) on the more hydrophilic surfaces. This is in direct contrast to previous observations on the spreading of marine bioadhesives and is in apparent contradiction to the predictions of the Young-Dupre equation for three-phase systems. In this paper, we attempt an explanation based upon thermodynamic analysis of the wetting properties of hydrophilic proteins.

Roughness-dependent removal of settled spores of the green alga Ulva (syn. Enteromorpha) exposed to hydrodynamic forces from a water jet.

Topographic features change the hydrodynamic regime over surfaces subjected to flow. Hydrodynamic microenvironments around topographic structures may have consequences for recruitment and removal of propagules of marine benthic organisms. The settlement and adhesion of zoospores from the green alga Ulva linza (syn. Enteromorpha linza) to defined topographies was investigated. A range of topographic size scales (Rz: 25-100 microm) was manufactured from plankton nets, creating patterns with ridges and depressions. The topographic scales span a roughness similar to that of natural substrata and antifouling coatings. Spores were removed from the surfaces by a calibrated water jet. Fewer spores were removed from the smallest topographic structure tested (Rz: 25 microm) compared to both the smooth (Rz: 1) and the roughest (Rz: 100 microm) structures. Zoospores that settled in depressions were less likely to be removed compared to spores on the ridges. The results in terms of the interaction between surface topography and hydrodynamic forces have implications for both natural substrata exposed to wave action and antifouling surfaces on ships' hulls. The possible effects of topography on increasing zoospore adhesion and offering a refuge from hydrodynamic forces are discussed.

Activity of commercial enzymes on settlement and adhesion of cypris larvae of the barnacle Balanus amphitrite, spores of the green alga Ulva linza, and the diatom Navicula perminuta.

Fouling species produce adhesive polymers during the settlement, adhesion and colonization of new surfaces in the marine environment. The present paper tests the hypothesis that enzymes of the appropriate specificity may prevent biofouling by hydrolysing these adhesive polymers. Seventeen commercially available enzyme preparations designed originally for bulk use in a range of end-use applications were tested for their effects on the settlement and/or adhesion of three major fouling species, viz. the green alga Ulva linza, the diatom Navicula perminuta and the barnacle Balanus amphitrite. The serine-proteases were found to have the broadest antifouling potential reducing the adhesion strength of spores and sporelings of U. linza, cells of N. perminuta and inhibiting settlement of cypris larvae of B. amphitrite. Mode-of-action studies on the serine-protease, Alcalase, indicated that this enzyme reduced adhesion of U. linza in a concentration-dependent manner, that spores of the species could recover their adhesive strength if the enzyme was removed and that the adhesive of U. linza and juvenile cement of B. amphitrite became progressively less sensitive to hydrolysis as they cured.

Adhesion and motility of fouling diatoms on a silicone elastomer.

Recent demands for non-toxic antifouling technologies have led to increased interest in coatings based on silicone elastomers that 'release' macrofouling organisms when hydrodynamic conditions are sufficiently robust. However, these types of coatings accumulate diatom slimes, which are not released even from vessels operating at high speeds (>30 knots). In this study, adhesion strength and motility of three common fouling diatoms (Amphora coffeaeformis var. perpusilla (Grunow) Cleve, Craspedostauros australis Cox and Navicula perminuta Grunow) were measured on a poly-dimethylsiloxane elastomer (PDMSE) and acid-washed glass. Adhesion of the three species was stronger to PDMSE than to glass but the adhesion strengths varied. The wall shear stress required to remove 50% of cells from PDMSE was 17 Pa for Craspedostauros, 24 Pa for Amphora and >>53 Pa for Navicula; the corresponding values for glass were 3, 10 and 25 Pa. In contrast, the motility of the three species showed little or no correlation between the two surfaces. Craspedostauros moved equally well on glass and PDMSE, Amphora moved more on glass initially before movement ceased and Navicula moved more on PDMSE before movement ceased. The results show that fouling diatoms adhere more strongly to a hydrophobic PDMSE surface, and this feature may contribute to their successful colonization of low surface energy, foul-release coatings. The results also indicate that diatom motility is not related to adhesion strength, and motility does not appear to be a useful indicator of surface preference by diatoms.