The potential for translocation of marine species via small-scale disruptions to antifouling surfaces

Vessel hull fouling is a major vector for the translocation of nonindigenous species (NIS). Antifouling (AF) paints are the primary method for preventing the establishment and translocation of fouling species. However, factors such as paint age, condition and method of application can all reduce the effectiveness of these coatings. Areas of hull that escape AF treatment (through limited application or damage) constitute key areas that may be expected to receive high levels of fouling. The investigation focused on whether small-scale (mm(2) to cm(2)) areas of unprotected surface or experimental 'scrapes' provided sufficient area for the formation of fouling assemblages within otherwise undamaged AF surfaces. Recruitment of fouling taxa such as algae, spirorbids and hydroids was recorded on scrapes as narrow as 0.5 cm wide. The abundance and species richness of fouling assemblages developing on scrapes > or =1 cm often equalled or surpassed levels observed in reference assemblages totally unprotected by AF coatings. Experiments were conducted at three sites within the highly protected and isolated marine park surrounding Lady Elliott Island at the southernmost tip of the Great Barrier Reef, Australia. Several NIS were recorded on scrapes of AF coated surfaces at this location, with 1-cm scrapes showing the greatest species richness and abundance of NIS relative to all other treatments (including controls) at two of the three sites investigated. Slight disruptions to newly antifouled surfaces may be all that is necessary for the establishment of fouling organisms and the translocation of a wide range of invasive taxa to otherwise highly protected marine areas.     

The potential for translocation of marine species via small-scale disruptions to antifouling surfaces

Vessel hull fouling is a major vector for the translocation of nonindigenous species (NIS). Antifouling (AF) paints are the primary method for preventing the establishment and translocation of fouling species. However, factors such as paint age, condition and method of application can all reduce the effectiveness of these coatings. Areas of hull that escape AF treatment (through limited application or damage) constitute key areas that may be expected to receive high levels of fouling. The investigation focused on whether small-scale (mm² to cm²) areas of unprotected surface or experimental ‘scrapes’ provided sufficient area for the formation of fouling assemblages within otherwise undamaged AF surfaces. Recruitment of fouling taxa such as algae, spirorbids and hydroids was recorded on scrapes as narrow as 0.5 cm wide. The abundance and species richness of fouling assemblages developing on scrapes ≥1 cm often equalled or surpassed levels observed in reference assemblages totally unprotected by AF coatings. Experiments were conducted at three sites within the highly protected and isolated marine park surrounding Lady Elliott Island at the southernmost tip of the Great Barrier Reef, Australia. Several NIS were recorded on scrapes of AF coated surfaces at this location, with 1-cm scrapes showing the greatest species richness and abundance of NIS relative to all other treatments (including controls) at two of the three sites investigated. Slight disruptions to newly antifouled surfaces may be all that is necessary for the establishment of fouling organisms and the translocation of a wide range of invasive taxa to otherwise highly protected marine areas.     

The effects of copper pollution on fouling assemblage diversity: a tropical-temperate comparison

Background

The invasion of habitats by non-indigenous species (NIS) occurs at a global scale and can generate significant ecological, evolutionary, economic and social consequences. Estuarine and coastal ecosystems are particularly vulnerable to pollution from numerous sources due to years of human-induced degradation and shipping. Pollution is considered as a class of disturbance with anthropogenic roots and recent studies have concluded that high frequencies of disturbance may facilitate invasions by increasing the availability of resources.

Methodology/Principal Findings

To examine the effects of heavy metal pollution as disturbance in shaping patterns of exotic versus native diversity in marine fouling communities we exposed fouling communities to different concentrations of copper in one temperate (Virginia) and one tropical (Panama) region. Diversity was categorized as total, native and non-indigenous and we also incorporated taxonomic and functional richness. Our findings indicate that total fouling diversity decreased with increasing copper pollution, whether taxonomic or functional diversity is considered. Both native and non-indigenous richness decreased with increasing copper concentrations at the tropical site whereas at the temperate site, non-indigenous richness was too low to detect any effect.

Conclusions/Significance

Non-indigenous richness decreased with increasing metal concentrations, contradicting previous investigations that evaluate the influence of heavy metal pollution on diversity and invasibility of fouling assemblages. These results provide first insights on how the invasive species pool in a certain region may play a key role in the disturbance vs. non-indigenous diversity relationship.     

Macrophytes as indicators of stream condition in the wet tropics region,Northern Queensland,Australia

This study investigates the use of aquatic macrophytes as indicators of stream condition in catchments with varied land use and levels of riparian disturbance in the Wet Tropics region of North Queensland (Australia), a region of global significance in terms of faunal and floral diversity. In a paired catchment design spatial variations in macrophyte assemblage structure were characterised using multivariate and univariate techniques. Seven metrics were trialled: total macrophyte cover, species richness, % alien taxa, % native taxa, % submerged taxa, % emergent taxa and % Poaceae. Forty-four macrophyte taxa were recorded from the study area. Poaceae, Cyperaceae and mosses were the most frequently recorded taxa. Upper catchment areas in all tributaries surveyed were dominated by mosses and Cladopus queenslandicus (Domin) C.D.K. Cook (Podestemaceae). This assemblage occurred in areas with intact riparian canopy cover and good overall riparian condition. Macrophyte assemblages in lower catchment areas were distributed along gradients of riparian disturbance. Simultaneous autoregression model coefficients indicated that riparian condition had a negative influence on macrophyte cover, species richness and the proportions of alien taxa, emergent taxa and Poaceae present at sites in the Wet Tropics. Macrophyte metrics were not strongly influenced by the types of land use or water quality. These findings suggest that a riparian condition assessment would provide an adequate first assessment of the state of aquatic macrophyte assemblages in Wet Tropics streams.     

Diversity and distribution of hidden cultivable fungi associated with marine animals of Antarctica

In the present study, we surveyed the distribution and diversity of fungal assemblages associated with 10 species of marine animals from Antarctica. The collections yielded 83 taxa from 27 distinct genera, which were identified using molecular biology methods. The most abundant taxa were Cladosporium sp. 1, Debaryomyces hansenii, Glaciozyma martinii, Metschnikowia australis, Pseudogymnoascus destructans, Thelebolus cf. globosus, Pseudogymnoascus pannorum, Tolypocladium tundrense, Metschnikowia australis, and different Penicillium species. The diversity, richness, and dominance of fungal assemblages ranged among the host; however, in general, the fungal community, which was composed of endemic and cold-adapted cosmopolitan taxa distributed across the different sites of Antarctic Peninsula, displayed high diversity, richness, and dominance indices. Our results contribute to knowledge about fungal diversity in the marine environment across the Antarctic Peninsula and their phylogenetic relationships with species that occur in other cold, temperate, and tropical regions of the World. Additionally, despite their extreme habitats, marine Antarctic animals shelter cryptic and complex fungal assemblages represented by endemic and cosmopolitan cold-adapted taxa, which may represent interesting models to study different symbiotic associations between fungi and their animal hosts in the extreme conditions of Antarctica.     

Contribution of non-native species to soft-sediment marine community structure of San Francisco Bay,California

While non-native species (NIS) are important components in many coastal bays and estuaries, quantitative measures that characterize their effects on community structure at bay-wide scales are rare. In this study, we measure species composition and abundance for soft-sediments to assess the contribution of NIS to multiple dimensions of community structure, focusing on one of the most highly invaded bays in the world, San Francisco Bay. Benthic macrofauna was sampled in the high salinity, muddy shallow subtidal (2 m depth) across 10 sites, using replicate 0.1 m² Van Veen grabs. Invertebrates retained on a 1 mm sieve were identified, counted, and used to estimate the overall contribution of NIS to (a) abundance (b) species richness, and (c) community similarity. Soft-sediment communities were dominated numerically by NIS, which accounted for 76 % of all organisms detected and had a mean bay-wide abundance that was three and half-fold higher than native biota. Overall, NIS contributed to 36 % of observed taxa and 24–29 % of total estimated regional diversity. Native species accounted for 21 % of total abundance and 45 % of total species richness. Compared to native species, NIS occurred more frequently among samples and also explained more of the variation in community structure among sites. NIS dominate several key attributes of the soft-sediment infaunal community in San Francisco Bay. Percent contribution of NIS to species richness was at least two-fold higher than reported from two decades ago. Unique to this bay, these measures establish a quantitative baseline on the state of invasions and provide an important model for evaluating the extent of NIS in estuaries. Application of this approach across estuaries, with repeated measures over time, is critically needed to advance scientific understanding of invasions and also evaluation of efficacy and gaps in management to reduce new invasions.     

Distribution of functionally distinct native and non-indigenous species within marine urban habitats

Aim

Trait-based approaches are powerful to examine the processes associated with biological invasions. Functional comparison among native and non-indigenous species (NIS) can notably infer whether novel assemblages result from neutral or niche-based assembly rules. Applying such a framework to biofouling communities, our study aimed to elucidate their distributions within two marine urban habitats (namely floating vs. nonfloating habitats).

Location

Southeast Pacific—Central Chilean coastline.

Methods

Here, we examined the distribution of 12 functional traits in fouling communities established on settlement plates, after 3 and 13 months of deployment in the two habitats and across ports in Central Chile. Based upon previously described differences of assemblages and NIS contribution across habitats, we hypothesized that nonindigenous, cryptogenic and native taxon pools would be functionally distinct (and trait biased), and that functional diversity and structure would vary across habitats and successional stages.

Results

Our results show, as anticipated, that nonindigenous (13 taxa), cryptogenic (12) and native (18) taxon pools are functionally distinct, though overlapping in the trait space. Non-indigenous species are rather related to colonizing traits, while native species are more related to competitive traits. Only one widespread NIS was functionally similar to the late successional and most competitive native species, including taxa elsewhere invasives. Despite differences in taxonomic composition between habitats, we did not observe functional differences between them. In contrast, temporal variations across colonization stages were detected along with an increased contribution in large and long-lived taxa, together with site-specific trajectories.

Main Conclusions

We conclude that the functional distinctness among nonindigenous, cryptogenic and native taxa occupying artificial habitats in ports reflects niche-based processes. Site-specific trajectories indicate that scale-dependent assembly processes, such as dispersal and species interactions, are at play.     

Distribution patterns of benthic foraminifera across the Ypresian–Lutetian Gorrondatxe section,Northern Spain: Response to sedimentary disturbance

We present a study of benthic foraminiferal assemblages from an Ypresian–Lutetian distal submarine fan system in the lower bathyal Gorrondatxe section (Basque-Cantabrian Basin, northern Spain). The objective of our study is to analyze the benthic foraminiferal distribution patterns and their response to sedimentary disturbance and related factors.Assemblages contain a high percentage of allochthonous taxa, such as asterigerinids and other shallow water taxa, which were transported downslope by turbidity currents.Detailed quantitative analyses, supported by R-mode cluster and Detrended Correspondence Analyses (after removing allochthonous taxa from the foraminiferal counts) allowed us to identify 6 assemblages that are divided into two groups related to the turbidite content in the Gorrondatxe section. Assemblages 1, characteristic of the turbidite-poor intervals with low sedimentary disturbance, include assemblage 1a (with highly diverse common middle–lower bathyal calcareous taxa) assemblage 1b (with common agglutinated taxa, mainly trochamminids), and assemblage 1c (characterized by calcareous taxa that are also common in the turbidite-rich interval).Assemblages 2, characterized by a high dominance, prevail in the turbidite-rich interval, and include assemblage 2a (characterized by the dominance of infaunal bolivinids and epifaunal cibicids), assemblage 2b (typified by moderate to low diversity and dominated by deep-infaunal Globobulimina species), and assemblage 2c (typified by very abundant suspension-feeding astrorhizids). The high abundance of bolivinids and Globobulimina species may be related to an enhanced input of low-quality organic matter transported by turbidity currents to the seafloor, representing different stages of recolonisation after disturbance and different energy regimes. High current activity was probably responsible for the abundance of cibicids, while moderate to low diverse and high dominance assemblages characterize the recolonisation of the substrate after disturbance.We conclude that sedimentary disturbance and other related factors such as current activity, resuspension of sediments at the seafloor, and supply of organic matter (and its quality) played an important role in the distribution of benthic foraminifera in the Gorrondatxe section. The identification of allochthonous taxa emerges as an essential aspect of the study of environments with sedimentary disturbance.     

Response of native and non-native ruderals to natural and human disturbance

The ruderal strategy is widely shared among non-native plants, providing a general explanation for the commonly observed positive effects of disturbance on invasions. How native ruderals respond to disturbance and how their abundance compares to that of non-native ruderals remains, however, poorly understood. Similarly, little is known about the role that disturbance type plays in the coexistence between native and non-native ruderals. We proposed that natural disturbance favors native over non-native ruderals, whereas novel anthropogenic disturbance favors non-natives over natives. To assess our general hypothesis, we conducted extensive field samplings in which we measured relative abundance, richness, and diversity of native and non-native ruderals in sites with natural and anthropogenic disturbance in central Argentina, a system where the ruderal strategy is common to a large number of native and non-native species. We found that natives dominated ruderal communities growing in recently burned grasslands, whereas non-natives dominated in roadsides. Additionally, the richness and diversity of native ruderal species were much greater than those of non-natives in sites with fire and in sites with grazing, but species richness and diversity did not differ between groups in roadsides. Because vegetation evolved with fire in our system and, in contrast, the construction and maintenance of roads is recent in it, these results support our hypothesis. Our work indicates that the ruderal strategy does not seem to suffice to explain why disturbance facilitates invasions. According to our data, species origin interacts with disturbance type to determine dominance in communities with coexisting native and non-native ruderals.     

Disturbance: a double-edged sword for restoration in a changing climate

Ecological restoration often relies on disturbance as a tool for establishing target plant communities, but disturbance can be a double-edged sword, at times initiating invasion and unintended outcomes. Here we test how fire disturbance, designed to enhance restoration seeding success, combines with climate and initial vegetation conditions to shift perennial versus annual grass dominance and overall community diversity in Pacific Northwest grasslands. We seeded both native and introduced perennial grasses and native forbs in paired, replicated burned-unburned plots in three sites along a latitudinal climate gradient from southern Oregon to central-western Washington. Past restoration and climate manipulations at each site had increased the variation of starting conditions between plots. Burning promoted the expansion of extant forbs and perennial grasses across all sites. Burning also enhanced the seeding success of native perennial grass and native forbs at the northern and central site, and the success of introduced perennial grasses across all three sites. Annual grass dominance was driven more by latitude than burning, with annuals maintaining their dominance in the south and perennials in the north. At the same time, unrestored grasslands surrounding all sites remained dominated by perennial grasses, suggesting that initial plot clearing may have allowed for annual grass invasion in the southern site. When paired with disturbance, further warming may increase the risk of annual grass dominance, a potentially persistent state.     

Interaction between disturbance and primary productivity in determining stream invertebrate diversity

Invertebrate diversity patterns were examined in 10 streams that differed in substrate disturbance rates, in Taranaki, New Zealand, between April 1999 and January 2000. Two sites on each stream were sampled, one under native forest canopy where light was postulated to limit periphyton growth and a similar site 225–3800 m downstream in open grassland. Periphyton biomass was considerably higher at open stable sites than at closed or unstable sites. Associated with the higher algal biomass, species number and total abundance of animals were higher at open canopy sites. Species number exhibited a negative linear relationship with disturbance but only at open sites. In contrast, rarefied species richness exhibited a negative linear relationship with disturbance at both open and closed sites. This was a result of communities at the more disturbed sites being numerically dominated by only a few taxa compared to the more evenly distributed communities at stable sites. The observed patterns provide little support for contemporary diversity disturbance models but suggest diversity of invertebrates in streams is a function of time since the last disturbance, mediated through recovery of the food base in autotrophic streams.     

Neotropical moth assemblages degrade due to oil palm expansion

Oil palm is one of the most rapidly expanding crops throughout the tropics, yet little is known about its impacts on Neotropical invertebrate biodiversity. Responses of insect assemblages to land conversion may substantially vary among taxa. We assessed geometrid and arctiine moth assemblages in a Costa Rican human dominated landscape, where oil palm plantations are now the second most common land cover. Moths were sampled during 6 months with automatic traps in the interior and margin of old-growth forests, young secondary forests and oil palm plantations in a 30 km² area. Our results show that richness and diversity of both taxa were severely reduced in oil palm compared to all other habitats. Geometrid abundance was highest in forest interiors and lowest in oil palm, while arctiine numbers did not differ between habitats. Dominance was highest in oil palm plantations, where one arctiine species and one geometrid species accounted for over 40% of total abundance in each of their respective taxa. Species composition was distinct in oil palm and forest interior sites, and depicted a gradient of habitat disturbance in ordination space that was strongly related to vegetation diversity and structure. This study demonstrates that oil palm plantations are not a suitable habitat for these moth taxa. Whilst some arctiine species seem adapted to disturbed habitats, geometrids were more dependent on old-growth forests, showing higher bioindicator potential. In the face of accelerated oil palm expansion, conservation strategies should focus on protecting old-growth forest remnants, as well as increasing species diversity and structural complexity of degraded habitats.     

Is vessel hull fouling an invasion threat to the Great Lakes?

Aim  Hull fouling is a leading vector for the introduction of marine, non‐indigenous species (NIS) worldwide, yet its importance to freshwater habitats is poorly understood. We aimed to establish the complement of NIS transported via this vector to the Great Lakes and to determine if they pose an invasion risk. Location  Laurentian Great Lakes. Methods  During 2007 and 2008, we collected scrapings from exterior surfaces as well as underwater video‐transects from 20 vessels shortly after their arrival in Great Lakes’ ports. Invertebrates present were sorted and identified in the laboratory. Results  Total estimated abundance averaged > 170,000 invertebrates per ship belonging to 109 taxa. Most (72%) of these taxa were freshwater species already present in the Great Lakes, whereas 11 and 31% were native to estuarine and marine habitats respectively, and would not be expected to survive in this habitat. Abundance was dominated by barnacles (51%), cladocerans (19%), bivalves (12%) and amphipods (11%). Sea‐chest grating and the rudder were hot‐spots for biofouling. Invertebrate diversity and total abundance were positively associated with total time spent in port during the last year and time in Pacific South American ports and negatively related to time in high latitudes and sailing speed. Although we found some live, established invaders such as Gammarus tigrinus and Dreissena rostriformis bugensis, only one individual of a freshwater NIS (Alexandrovia onegensis, Oligochaeta) not yet reported in the Great Lakes was detected. The animal’s poor condition and seemingly low population abundance indicated the risk of live introduction by this vector was likely quite low. Main conclusion  Our results indicate that hull fouling appears to pose a low risk of introductions of new species capable of surviving in the Great Lakes, unlike foreign‐sourced freshwater ballast water that historically was discharged by these transoceanic vessels.     

Ecosystem functioning impacts of the invasive seaweed Sargassum muticum (Fucales,Phaeophyceae)

Ongoing changes in natural diversity due to anthropogenic activities can alter ecosystem functioning. Particular attention has been given to research on biodiversity loss and how those changes can affect the functioning of ecosystems, and, by extension, human welfare. Few studies, however, have addressed how increased diversity due to establishment of nonindigenous species (NIS) may affect ecosystem function in the recipient communities. Marine algae have a highly important role in sustaining nearshore marine ecosystems and are considered a significant component of marine bioinvasions. Here, we examined the patterns of respiration and light‐use efficiency across macroalgal assemblages with different levels of species richness and evenness. Additionally, we compared our results between native and invaded macroalgal assemblages, using the invasive brown macroalga Sargassum muticum (Yendo) Fensholt as a model species. Results showed that the presence of the invader increased the rates of respiration and production, most likely as a result of the high biomass of the invader. This effect disappeared when S. muticum lost most of its biomass after senescence. Moreover, predictability–diversity relationships of macroalgal assemblages varied between native and invaded assemblages. Hence, the introduction of high‐impact invasive species may trigger major changes in ecosystem functioning. The impact of S. muticum may be related to its greater biomass in the invaded assemblages, although species interactions and seasonality influenced the magnitude of the impact.     

Re‐forestation restores native dominance in an island beetle fauna

Native re‐forestation is a widely used restoration tool, typically undertaken with the expectation that planting native trees will initiate succession processes (including the re‐establishment of native fauna) that will eventually return the ecosystem to a native‐dominated state. Invertebrate groups can be used to assess restoration progress, as their life history traits enable them to respond more rapidly to environmental change than many other organisms. In this study, we assessed beetle responses to re‐forestation. Using two trapping methods (flight intercept traps and pitfall traps), we compared beetle assemblages in exotic pasture (pre‐restoration state), <10‐year‐old planted native forest (restoration intervention) and approximately 40‐year‐old unmanaged regenerating native forest (reference state). Analysis of the flight intercept‐trapped beetles suggests that re‐forestation has initiated a transition from an exotic‐dominated pasture fauna toward a native‐dominated fauna: in planted forests, 75% of all flight‐intercept‐trapped beetles were native (compared with 22% in pasture and 87% in unmanaged forest). Flight intercept‐trapped beetles also had higher native diversity and abundance in both forest types than in pasture. Pitfall‐trapped beetle species were predominantly native in both forest types, but there were few statistically significant differences between the forests and pasture in the pit‐fall trap data set. Both trapping methods detected significant compositional differences between the beetle assemblages in planted forest and unmanaged forest. Replanting native forest has increased native beetle diversity, abundance, and dominance (compared with the pre‐restoration state), but convergence with the unmanaged reference forest has not yet been achieved.     

Links Between Anthropogenic Perturbations and Benthic Macroinvertebrate Assemblages in Afromontane Forest Streams in Uganda

Relationships between environmental variables and benthic macroinvertebrate assemblages were investigated among several sites that varied in disturbance history in Bwindi Impenetrable National Park, an Afromontane site in East Africa. Environmental variables were correlated with the level of past catchment disturbance – logging, agricultural encroachment, and present tourism activity. For example, sites in medium and high disturbance categories had higher values of specific conductance and lower water transparency than low disturbance category sites, these environmental variables may therefore act indicators of ecological quality of rivers. Environmental variables such as conductivity and water transparency were found to be good predictors of benthic macroinvertebrate assemblages, with anthropogenically stressed sites having lower diversity than the reference sites. Impacted sites were dominated by tolerant taxa such as chironomid and leeches, while ‘clean water’ taxa such as Ephemeroptera, Plecoptera and Trichoptera dominated at minimally impacted sites. Comparison of sites with different disturbance histories provided evidence for differences in benthic macroinvertebrate communities that reflect the state of forest restoration and recovery. We recommend quarterly monitoring of water quality to act as an early warning system of deterioration and tracking ecological recovery of previously impacted sites.     

Patterns of benthic mega-invertebrate habitat associations in the Pacific Northwest continental shelf waters

As human impacts and demands for ocean space increase (fisheries, aquaculture, marine reserves, renewable energy), identification of marine habitats hosting sensitive biological assemblages has become a priority. Epifaunal invertebrates, especially the structure-forming species, are an increasing conservation concern as many traditional (bottom-contact fishing) and novel (marine renewable energy) ocean uses have the potential to displace or otherwise impact these slow-growing organisms. The differences in mega-invertebrate species assemblages between high-relief rocks and low-relief sediments are well documented and likely hold for most marine environments. In anticipation of potential development of marine renewable energy faculties off Oregon and Washington (USA), a survey of the benthic invertebrate assemblages and habitats was conducted on the continental shelf of the Pacific Northwest, using video footage collected by ROV, to more finely characterize these assemblage–habitat associations. Four main associations were found: pure mud/sand dominated by sea whips and burrowing brittle stars; mixed mud–rock (which may be further divided based on size of mixed-in rocks) characterized by various taxa at small densities; consolidated rocks characterized by high diversity and density of sessile or motile mega-invertebrates; and rubble rocks showing less diversity and density than the consolidated rocks, possibly due to the disturbance generated by movement of the unconsolidated rocks. The results of this study will help classify and map the seafloor in a way that represents benthic habitats reflective of biological species assemblage distributions, rather than solely geological features, and support conservation and management planning.     

Marine introductions in the Shark Bay World Heritage Property, Western Australia: a preliminary assessment

The presence and impacts of non‐indigenous species (NIS) in marine areas of high conservation or World Heritage significance have rarely been examined. Case studies worldwide suggest that the potential exists for the introduction of NIS to significantly impact conservation values in regions conserved for the uniqueness and diversity of native assemblages. In this study, a preliminary investigation was conducted to provide information essential for managing marine introductions in the Shark Bay World Heritage Property. A focused fouling plate survey sampled a total of 112 encrusting taxa, of which 10 (11.2%) were classified as introduced and 10 others as cryptogenic. Eight introduced bryozoans: Aetea anguina (Linnaeus, 1758), Bugula neritina (Linnaeus, 1758), Bugula stolonifera Ryland, 1960, Conopeum seurati (Canu, 1928), Savignyella lafontii (Audouin, 1826), Schizoporella errata (Waters, 1878), Watersipora subtorquata (d’Orbigny, 1842) and Zoobotryon verticellatum della Chiaje, 1828; one tunicate, Styela plicata Lesueur, 1823; and an introduced hydroid, Obelia dichotoma (Linnaeus, 1758) were frequent, and in some cases dominant, components of encrusting communities. Of the 20 most frequently occurring species detected in the Bay, four were introduced and of the 20 species with highest average percent cover per plate, six were introduced. At one site, space occupation by NIS averaged 71.6% ± 7.4 of plate live cover. Space occupation by an individual NIS was as high as 62.4% of plate area (mean 7.82% ± 1.8). NIS were detected at sites lacking commercial traffic and ballast water discharge and isolated by distance and physical environment, suggesting that hull fouling of recreational craft may be the most important vector in the region. Seventy‐five percent of NIS detected in Shark Bay are established in Australian ports to the south of Shark Bay, while 33% are established to the north, tentatively implicating temperate affinity NIS and the movement of vessels from Australian ports south of Shark Bay as a greater risk to the region.     

Structure of Benthic Diatom Assemblages from a Mangrove Environment in a Mexican Subtropical Lagoon1

The taxonomic list and the structure of benthic diatom assemblages occurring in fine sediments (silt and sand) from the mangrove forest of the Balandra lagoon in Baja California Sur, Mexico was determined based on seasonal samplings for one year. Assemblage structure was analyzed using several ecological indices for estimating diversity (H'), dominance (REDI), equitability, and similarity. A total of 230 diatom taxa were identified and include 109 new records for the Baja California peninsula coast. Taxa representative of highly productive and hypersaline environments were common. Assemblages were characterized by a few abundant species and many uncommon or rare taxa. High diatom diversity estimates at all sampling sites during all seasons suggest that diatom assemblages in sediments of the Balandra lagoon represent a quasi-pristine environment.     

Reduction of pollution impacts through the control of toxicant release rate must be site- and season-specific

The marine environment is commonly used for the deliberate disposal of industrial, mining and metabolic wastes. Managers will benefit from experimental work that identifies ways of reducing environmental impacts by varying the frequency and intensity of toxicant release. Using a field dosing technique we investigated the effects of three frequencies of pulse copper pollution event, and two intensities of copper dose, on developing assemblages of sessile marine invertebrates. The resulting impacts could then be compared in assemblages exposed to the same amount of toxicant via different disturbance regimes. The experiment was replicated simultaneously at three sites within Port Philip Bay, Victoria, Australia. Pulse pollution events altered assemblage composition through a direct negative effect on densities of large solitary ascidians. In response to the removal of the spatially dominant solitary ascidians, there were increases in recruitment of many different phyla, and in the abundance of older individuals of some serpulid and bryozoan taxa. Biodiversity, as measured by total species number and Shannon's H′, did not reflect the dramatic structural changes apparent within assemblages. If pulse pollution events had either a negative or positive effect on a species' density, then that effect was accentuated by increasing the intensity (strength) or the frequency of the pollution disturbance. Within populations, however, adult mortality might benefit new recruits of the same species through the freeing up of settlement space. In this case, the effects of copper pulses were evident as changes in the population size structure rather than the overall density of an organism. There were variable responses to manipulating the output rate of the toxicant between sites that appear to be driven by the rate of recovery of the dominant space occupiers. At one site there was a negligible effect of disturbance intensity and impacts could be minimized through reducing only the frequency of toxicant release. At two other sites both the intensity and frequency of disturbance determined the pollution effect and minimizing impacts was feasible only through an overall reduction in the amount of toxicant released. The management and reduction of pollution impacts through the control of toxicant release will require site- and season-specific modifications.