Towards reproducible metabarcoding data: Lessons from an international cross-laboratory experiment.

Advances in high-throughput sequencing (HTS) are revolutionizing monitoring in marine environments by enabling rapid, accurate and holistic detection of species within complex biological samples. Research institutions worldwide increasingly employ HTS methods for biodiversity assessments. However, variance in laboratory procedures, analytical workflows and bioinformatic pipelines impede the transferability and comparability of results across research groups. An international experiment was conducted to assess the consistency of metabarcoding results derived from identical samples and primer sets using varying laboratory procedures. Homogenized biofouling samples collected from four coastal locations (Australia, Canada, New Zealand and the USA) were distributed to 12 independent laboratories. Participants were asked to follow one of two HTS library preparation workflows. While DNA extraction, primers and bioinformatic analyses were purposefully standardized to allow comparison, many other technical variables were allowed to vary among laboratories (amplification protocols, type of instrument used, etc.). Despite substantial variation observed in raw results, the primary signal in the data was consistent, with the samples grouping strongly by geographical origin for all data sets. Simple post hoc data clean-up by removing low-quality samples gave the best improvement in sample classification for nuclear 18S rRNA gene data, with an overall 92.81% correct group attribution. For mitochondrial COI gene data, the best classification result (95.58%) was achieved after correction for contamination errors. The identified critical methodological factors that introduced the greatest variability (preservation buffer, sample defrosting, template concentration, DNA polymerase, PCR enhancer) should be of great assistance in standardizing future biodiversity studies using metabarcoding.

An evaluation of strategies for restoring a degraded New Zealand scallop fishery using stochastic dynamic simulation modelling.

A decision-theoretical approach was used to evaluate strategies to rebuild a severely depleted scallop (Pecten novaezelandiae) populations in the Tasman Bay and Golden Bay of New Zealand. These strategies were: no intervention, cessation of seabed bottom contact fishing, and reduction of sediment and nutrient runoff from surrounding land through on-farm practices. Our approach combined outputs of estimated effects of on-farm practices on erosion and nutrient reduction with a stochastic dynamic model of the scallop populations. The most effective individual intervention is eliminating bottom contact fishing through dredging and trawling which increased scallop biomass on average by 73% compared to the no intervention scenario. Although on-farm practices have reduced sedimentation and nutrient runoff significantly (28-36% and 2%, respectively), they have no effect on scallop biomass if implemented individually and led to only marginal improvements in scallop biomass if implemented alongside cessation of bottom contact fishing (2-4%). Although our results showed, on average, substantial recovery in the scallop population when reducing seabed bottom contact and water pollution, the large uncertainty boundaries makes it unclear whether these improvements would be realized. The long-term success of such strategies will depend on the available habitat being able to sustain high densities of healthy scallop adults and recruits, a situation that has been posited in our analysis. Where scallop juvenile survival is compromised by sedimentation, nutrient pollution, or other exogenous influences, proposed interventions may be insufficient to aid recovery.

The risks of using molecular biodiversity data for incidental detection of species of concern.

Incidental detection of species of concern (e.g., invasive species, pathogens, threatened and endangered species) during biodiversity assessments based on high-throughput DNA sequencing holds significant risks in the absence of rigorous, fit-for-purpose data quality and reporting standards. Molecular biodiversity data are predominantly collected for ecological studies and thus are generated to common quality assurance standards. However, the detection of certain species of concern in these data would likely elicit interest from end users working in biosecurity or other surveillance contexts (e.g., pathogen detection in health-related fields), for which more stringent quality control standards are essential to ensure that data are suitable for informing decision-making and can withstand legal or political challenges. We suggest here that data quality and reporting criteria are urgently needed to enable clear identification of those studies that may be appropriately applied to surveillance contexts. In the interim, more pointed disclaimers on uncertainties associated with the detection and identification of species of concern may be warranted in published studies. This is not only to ensure the utility of molecular biodiversity data for consumers, but also to protect data generators from uncritical and potentially ill-advised application of their science in decision-making.

Trends in the detection of aquatic non-indigenous species across global marine, estuarine and freshwater ecosystems: A 50-year perspective.

Aim: The introduction of aquatic non-indigenous species (ANS) has become a major driver for global changes in species biogeography. We examined spatial patterns and temporal trends of ANS detections since 1965 to inform conservation policy and management. Location: Global. Methods: We assembled an extensive dataset of first records of detection of ANS (1965-2015) across 49 aquatic ecosystems, including the (a) year of first collection, (b) population status and (c) potential pathway(s) of introduction. Data were analysed at global and regional levels to assess patterns of detection rate, richness and transport pathways. Results: An annual mean of 43 (±16 SD) primary detections of ANS occurred-one new detection every 8.4 days for 50 years. The global rate of detections was relatively stable during 1965-1995, but increased rapidly after this time, peaking at roughly 66 primary detections per year during 2005-2010 and then declining marginally. Detection rates were variable within and across regions through time. Arthropods, molluscs and fishes were the most frequently reported ANS. Most ANS were likely introduced as stowaways in ships' ballast water or biofouling, although direct evidence is typically absent. Main conclusions: This synthesis highlights the magnitude of recent ANS detections, yet almost certainly represents an underestimate as many ANS go unreported due to limited search effort and diminishing taxonomic expertise. Temporal rates of detection are also confounded by reporting lags, likely contributing to the lower detection rate observed in recent years. There is a critical need to implement standardized, repeated methods across regions and taxa to improve the quality of global-scale comparisons and sustain core measures over longer time-scales. It will be fundamental to fill in knowledge gaps given that invasion data representing broad regions of the world's oceans are not yet readily available and to maintain knowledge pipelines for adaptive management.

Considerations for incorporating real-time PCR assays into routine marine biosecurity surveillance programmes: a case study targeting the Mediterranean fanworm (Sabella spallanzanii) and club tunicate (Styela clava) 1.

Molecular techniques may provide effective tools to enhance marine biosecurity surveillance. Prior to routine implementation, evidence-based consideration of their benefits and limitations is needed. In this study, we assessed the efficiency and practicality of visual diver surveys and real-time PCR assays (targeting DNA and RNA) for detecting two marine invasive species whose infestation levels varied between species and location: Sabella spallanzanii and Styela clava. Filtered water samples (n = 171) were collected in parallel with dive surveys at two locations as part of the New Zealand Marine High Risk Site Surveillance programme: Nelson Harbour (27 sites) and Waitemata Harbour (30 sites). Diver surveys resulted in a greater number of detections compared to real-time PCR: S. clava - 21 versus 5 sites in Nelson, 6 versus 1 in Auckland; S. spallanzanii - 18 versus 10 in Auckland, no detections in Nelson. Occupancy modelling derived detection probabilities for the real-time PCR for S. clava were low (14%), compared to S. spallanzanii (66%). This could be related to abundances, or species-specific differences in DNA shedding. Only one RNA sample was positive, suggesting that most detections were from extracellular DNA or non-viable fragments. While molecular methods cannot yet replace visual observations, this study shows they provide useful complementary information.

Combining morpho-taxonomy and metabarcoding enhances the detection of non-indigenous marine pests in biofouling communities.

Marine infrastructure can favor the spread of non-indigenous marine biofouling species by providing a suitable habitat for them to proliferate. Cryptic organisms or those in early life stages can be difficult to distinguish by conventional morphological taxonomy. Molecular tools, such as metabarcoding, may improve their detection. In this study, the ability of morpho-taxonomy and metabarcoding (18S rRNA and COI) using three reference databases (PR2, BOLD and NCBI) to characterize biodiversity and detect non-indigenous species (NIS) in biofouling was compared on 60 passive samplers deployed over summer and winter in a New Zealand marina. Highest resolution of metazoan taxa was identified using 18S rRNA assigned to PR2. There were higher assignment rates to NCBI reference sequences, but poorer taxonomic identification. Using all methods, 48 potential NIS were identified. Metabarcoding detected the largest proportion of those NIS: 77% via 18S rRNA/PR2 and NCBI and 35% via COI/BOLD and NCBI. Morpho-taxonomy detected an additional 14% of all identified NIS comprising mainly of bryozoan taxa. The data highlight several on-going challenges, including: differential marker resolution, primer biases, incomplete sequence reference databases, and variations in bioinformatic pipelines. Combining morpho-taxonomy and molecular analysis methods will likely enhance the detection of NIS from complex biofouling.

Enhancing passive sampling tools for detecting marine bioinvasions.

Early detection is important for successful management of invasive species, but optimising monitoring systems to detect multiple species from different taxonomic groups remains a major challenge. Settlement plates are often used to monitor non-indigenous marine species (NIMS) associated with vessel biofouling, but there have been few assessments of their fitness-for-purpose. We deployed arrays of settlement plates ("settlement arrays") containing combinations of treatments that reflected conditions associated with the vessel transport pathway (i.e., copper based antifouling coatings, shaded habitat) to determine the treatment combinations that maximised NIMS diversity. Horizontal (shaded) treatments preferentially sampled higher NIS diversity than vertical plates. Although plates with copper-based biocides had larger proportions of NIS to indigenous species, they sampled only a subset of NIS diversity. Overall diversity was greatly enhanced through use of multiple treatments, demonstrating benefits of multi-faceted sampling arrays for maximising the potential taxonomic and species richness.

The impact of artificial surfaces on marine bacterial and eukaryotic biofouling assemblages: A high-throughput sequencing analysis.

Vessel hulls and underwater infrastructure can be severely impacted by marine biofouling. Knowledge on which abiotic conditions of artificial structures influence bacterial and eukaryotic community composition is limited. In this study, settlement plates with differing surface texture, orientation and copper-based anti-fouling coatings were deployed in a marina. After three months, biofouling samples were collected and bacterial and eukaryotic communities characterised using DNA metabarcoding. The copper anti-fouling coating treatments incurred the most significant compositional changes (p ≤ 0.001) within both domains. Bacterial diversity decreased, with Gammaproteobacteria becoming the dominant phylum. In contrast, protist diversity increased as well as opportunist nematodes and bryozoans; urochordates and molluscs became less abundant. Network analyses displayed complex relationships on untreated plates, while revealing a simpler, but disturbed and unstable community composition on the anti-fouling coated plates. These networks of copper treatments displayed opportunist taxa that appeared as key organisms in structuring the bacterial and eukaryotic communities.

Development of a real-time polymerase chain reaction assay for the detection of the invasive Mediterranean fanworm, Sabella spallanzanii, in environmental samples.

The Mediterranean fanworm, Sabella spallanzanii Gmelin 1791, was first detected in the Southern Hemisphere in the 1990s and is now abundant in many parts of southern Australia and in several locations around northern New Zealand. Once established, it can proliferate rapidly, reaching high densities with potential ecological and economic impacts. Early detection of new S. spallanzanii incursions is important to prevent its spread, guide eradication or control efforts and to increase knowledge on the species' dispersal pathways. In this study, we developed a TaqMan probe real-time polymerase chain reaction assay targeting a region of the mitochondrial cytochrome oxidase I gene. The assay was validated in silico and in vitro using DNA from New Zealand and Australian Sabellidae with no cross-reactivity detected. The assay has a linear range of detection over seven orders of magnitude with a limit of detection reached at 12.4 × 10-4 ng/µL of DNA. We analysed 145 environmental (water, sediment and biofouling) samples and obtained positive detections only from spiked samples and those collected at a port where S. spallanzanii is known to be established. This assay has the potential to enhance current morphological and molecular-based methods, through its ability to rapidly and accurately identify S. spallanzanii in environmental samples.

Invasion Expansion: Time since introduction best predicts global ranges of marine invaders.

Strategies for managing biological invasions are often based on the premise that characteristics of invading species and the invaded environment are key predictors of the invader's distribution. Yet, for either biological traits or environmental characteristics to explain distribution, adequate time must have elapsed for species to spread to all potential habitats. We compiled and analyzed a database of natural history and ecological traits of 138 coastal marine invertebrate species, the environmental conditions at sites to which they have been introduced, and their date of first introduction. We found that time since introduction explained the largest fraction (20%) of the variability in non-native range size, while traits of the species and environmental variables had significant, but minimal, influence on non-native range size. The positive relationship between time since introduction and range size indicates that non-native marine invertebrate species are not at equilibrium and are still spreading, posing a major challenge for management of coastal ecosystems.

Using temporal sampling to improve attribution of source populations for invasive species.

Numerous studies have applied genetic tools to the identification of source populations and transport pathways for invasive species. However, there are many gaps in the knowledge obtained from such studies because comprehensive and meaningful spatial sampling to meet these goals is difficult to achieve. Sampling populations as they arrive at the border should fill the gaps in source population identification, but such an advance has not yet been achieved with genetic data. Here we use previously acquired genetic data to assign new incursions as they invade populations within New Zealand ports and marinas. We also investigated allelelic frequency change in these recently established populations over a two-year period, and assessed the effect of temporal genetic sampling on our ability to assign new incursions to their population of source. We observed shifts in the allele frequencies among populations, as well as the complete loss of some alleles and the addition of alleles novel to New Zealand, within these recently established populations. There was no significant level of genetic differentiation observed in our samples between years, and the use of these temporal data did alter the assignment probability of new incursions. Our study further suggests that new incursions can add genetic variation to the population in a single introduction event as the founders themselves are often more genetically diverse than theory initially predicted.

Using habitat suitability index and particle dispersion models for early detection of marine invaders.

Eradication and control of invasive species are often possible only if populations are detected when they are small and localized. To be efficient, detection surveys should be targeted at locations where there is the greatest risk of incursions. We examine the utility of habitat suitability index (HSI) and particle dispersion models for targeting sampling for marine pests. Habitat suitability index models are a simple way to identify suitable habitat when species distribution data are lacking. We compared the performance of HSI models with statistical models derived from independent data from New Zealand on the distribution of two nonindigenous bivalves: Theora lubrica and Musculista senhousia. Logistic regression models developed using the HSI scores as predictors of the presence/absence of Theora and Musculista explained 26.7% and 6.2% of the deviance in the data, respectively. Odds ratios for the HSI scores were greater than unity, indicating that they were genuine predictors of the presence/ absence of each species. The fit and predictive accuracy of each logistic model were improved when simulated patterns of dispersion from the nearest port were added as a predictor variable. Nevertheless, the combined model explained, at best, 46.5% of the deviance in the distribution of Theora and correctly predicted 56% of true presences and 50% of all cases. Omission errors were between 6% and 16%. Although statistical distribution models built directly from environmental predictors always outperformed the equivalent HSI models, the gain in model fit and accuracy was modest. High residual deviance in both types of model suggests that the distributions realized by Theora and Musculista in the field data were influenced by factors not explicitly modeled as explanatory variables and by error in the environmental data used to project suitable habitat for the species. Our results highlight the difficulty of accurately predicting the distribution of invasive marine species that exhibit low habitat occupancy and patchy distributions in time and space. Although the HSI and statistical models had utility as predictors of the likely distribution of nonindigenous marine species, the level of spatial accuracy achieved with them may be well below expectations for sensitive surveillance programs.

Changes in the management of ductal carcinoma in situ before the release of clinical practice recommendations in Australia: the case in Victoria.

BACKGROUND: This study examines changes in the management of ductal carcinoma in situ between 1995 and 1999 in the Australian State of Victoria. This period was before the release of Australian treatment recommendations. METHODS: All new cases of ductal carcinoma in situ diagnosed between 1 April and 30 September in 1995 and 1999 were identified from the population cancer registry. Treating surgeons completed a questionnaire on the presentation and management of each case. In 1995, 64 out of 70 surgeons returned questionnaires for 137 cases (case response, 94%). In 1999, 68 surgeons treated 159 registered cases and 141 completed surveys were returned (case response, 89%). RESULTS: More cases underwent an image-guided biopsy in 1999 (54%) than in 1995 (34%). Breast-conserving surgery (BCS) was used to treat 69% of cases in 1999 and 63% in 1995. The use of axillary procedures (clearance or sampling) for women treated by mastectomy decreased from 61% in 1995 to 30% in 1999. More patients treated with BCS had margins simply described as "clear" in 1995 (49%) than in 1999 (21%). In 1995, only 7% of cases treated with BCS had radiotherapy, and this was 25% in 1999. CONCLUSION: In both 1999 and 1995, the majority of patients were treated by BCS, but only a minority received radiotherapy.

Sensitivity and cost considerations for the detection and eradication of marine pests in ports.

Port surveys are being conducted in Australia, New Zealand and around the world to confirm the presence or absence of particular marine pests. The most critical aspect of these surveys is their sensitivity-the probability that they will correctly identify a species as present if indeed it is present. This is not, however, adequately addressed in the relevant national and international standards. Simple calculations show that the sensitivity of port survey methods is closely related to their encounter rate-the average number of target individuals expected to be detected by the method. The encounter rate (which reflects any difference in relative pest density), divided by the cost of the method, provides one way to compare the cost-effectiveness of different survey methods. The most cost-effective survey method is site- and species-specific but, in general, will involve sampling from the habitat with the highest expected population of target individuals. A case study of Perna viridis in Trinity Inlet, Cairns, demonstrates that plankton trawls processed with gene probes provide the same level of sensitivity for a fraction of the cost associated with the next best available method-snorkel transects in bad visibility (secchi depth=0.72 m). Visibility and the adult/larvae ratio, however, are critical to these arguments. If visibility were good (secchi depth=10 m), the two approaches would be comparable. Diver deployed quadrats were at least three orders of magnitude less cost-effective in this case study. It is very important that environmental managers and scientists perform sensitivity calculations before embarking on port surveys to ensure the highest level of sensitivity is achieved for any given budget.

Secondhand smoke exposure and respiratory symptoms among casino, club, and office workers in Victoria, Australia.

OBJECTIVE: To examine the association between smoke-free policies, exposure to secondhand smoke (SHS) at work, and self-reported respiratory and sensory symptoms of workers. METHOD: Ninety-one nonsmoking workers recruited from three workplaces with varying smoking policies completed a telephone-administered questionnaire and provided saliva samples (before and after usual work shift) for cotinine analysis. RESULTS: Mean before-after shift saliva cotinine per hour worked was significantly higher among club (0.42 ng/mL/hr worked) than casino workers (0.18 ng/mL/hr worked) (P < 0.001), club than office workers (0.03 ng/mL/hr worked) (P < 0.001), and casino than office workers (P < 0.001). Casino and club workers reported similar levels of respiratory morbidity and were more likely to have sore eyes (odds ratio [OR] = 5.5, P < 0.01) and a sore throat (OR = 4.3, P < 0.05) compared with office employees. CONCLUSION: Air-conditioning interventions reduce, but fail to eliminate, exposure of hospitality workers to SHS. Such exposure is associated with measurable increases in the risk of respiratory symptoms.

A risk-based predictive tool to prevent accidental introductions of nonindigenous marine species.

Preventing the introduction of nonindigenous species (NIS) is the most efficient way to avoid the costs and impacts of biological invasions. The transport of fouling species on ship hulls is an important vector for the introduction of marine NIS. We use quantitative risk screening techniques to develop a predictive tool of the abundance and variety of organisms being transported by ocean-going yachts. We developed and calibrated an ordinal rank scale of the abundance of fouling assemblages on the hulls of international yacht hulls arriving in New Zealand. Fouling ranks were allocated to 783 international yachts that arrived in New Zealand between 2002 and 2004. Classification tree analysis was used to identify relationships between the fouling ranks and predictor variables that described the maintenance and travel history of the yachts. The fouling ranks provided reliable indications of the actual abundance and variety of fouling assemblages on the yachts and identified most (60%) yachts that had fouling on their hulls. However, classification tree models explained comparatively little of the variation in the distribution of fouling ranks (22.1%), had high misclassification rates (approximately 43%), and low predictive power. In agreement with other studies, the best model selected the age of the toxic antifouling paint on yacht hulls as the principal risk factor for hull fouling. Our study shows that the transport probability of fouling organisms is the result of a complex suite of interacting factors and that large sample sizes will be needed for calibration of robust risk models.

The management of early breast carcinoma before and after the introduction of clinical practice guidelines.

BACKGROUND: Clinical practice guidelines for the management of breast carcinoma were introduced in Australia in October, 1995. This article describes the management of early-stage breast carcinoma both before and after the introduction of these guidelines. METHODS: All cases of early breast carcinoma that were diagnosed over the same 6-month period in 1995 and 1999 and registered with a state-based cancer registry were identified. Treating surgeons completed a survey assessing tumor characteristics and primary treatment. In 1995, 95% of 188 surgeons who were approached participated and 96% of the surveys were returned. In 1999, 92% of 159 surgeons who were approached participated and 91% of the surveys were returned. Analyses are based on 1066 cases from 1995 and 1001 cases from 1999. RESULTS: The pathologic disease stage of the patients was similar in both study years. The proportion of patients who underwent breast-conserving therapy (BCT) increased from 54% in 1995 to 69% in 1999. This increase was noted across most levels of disease characteristics but was not evident among those patients treated by the least active surgeons. The proportion of patients treated with BCT who received radiotherapy increased from 59% in 1995 to 80% in 1999. This trend was observed across most levels of tumor characteristics and surgeon caseload. The proportion of women with receptor-positive tumors who were treated with endocrine therapy increased, whereas the proportion of patients with receptor-negative tumors who received this therapy decreased from 39% in 1995 to 17% in 1999. CONCLUSIONS: The management of early breast carcinoma in the state of Victoria appeared to change between 1995 and 1999 in the direction expected if the national guidelines had been incorporated into the practice patterns of surgeons treating breast carcinoma patients.

Exposure to secondhand smoke at work: a survey of members of the Australian Liquor, Hospitality and Miscellaneous Workers Union.

OBJECTIVE: To measure workers' attitudes towards and experiences of exposure to secondhand smoke (SHS) in the workplace. METHOD: A stratified random sample of members from the Victorian Branch of the Australian Liquor, Hospitality and Miscellaneous Workers Union (LHMU) was interviewed by telephone in September 2001. Of the 1,078 respondents surveyed (77% response rate), hospitality workers comprised 49% of the sample, while the remainder comprised community services, property services and manufacturing workers. RESULTS: Overall, 54% of union members were employed in workplaces that did not completely ban smoking and 34% reported being exposed to SHS during their typical working day. Workplaces with total smoking bans had a high level of compliance with these restrictions, with no workers in these settings indicating exposure to SHS at work. Compared with other workers, hospitality workers reported working in environments that had more permissive smoking policies. Consistent with this, 56% of hospitality workers said they were exposed to SHS during a typical day at work compared with 11% of other workers. Overall, 79% of workers expressed concern about exposure to SHS, including 66% of smokers. Compared with other workers, hospitality workers reported a higher level of concern about exposure to SHS at work. CONCLUSION: These findings provide evidence that many workers, and especially those employed in the hospitality sector, are exposed to SHS during their working day and are concerned about the effects of such exposure on their health. IMPLICATIONS: These findings indicate that workplace smoke-free policies are effective in reducing worker exposure to SHS and demonstrate support for the extension of smoke-free policies to hospitality workplaces.

Association between exposure to workplace secondhand smoke and reported respiratory and sensory symptoms: cross-sectional study.

The purpose of this work was to assess the relation between exposure to secondhand smoke (SHS) at work and reported respiratory and sensory symptoms. A cross-sectional telephone survey of 382 nonsmoking indoor workers in Victoria, Australia was used. After controlling for potential confounders, exposure to SHS at work for part of the day was significantly associated with an increased risk of wheeze (OR = 4.26), frequent cough (OR = 2.26), sore eyes (OR = 3.77), and sore throat (OR = 2.70). Among workers who had not experienced a cold in the past 4 weeks, we found strong dose-response relationships between increasing levels of exposure to SHS at work and morning cough, frequent cough, sore eyes and sore throat, and a positive relationship for wheeze. These findings provide compelling evidence that nonsmoking indoor workers are adversely affected by exposure to SHS at work and underline the importance of workplace smoke-free policies in protecting the health of workers.

Effects of Self-Guided Snorkeling Trails on Corals in a Tropical Marine Park.

Underwater trails are intended as interpretative tools in marine parks, but concentrating divers and snorkelers in defined areas may negatively affect the surrounding environment. We examined spatial and temporal patterns in the effects of use of underwater trails on coral reef flats in the Great Barrier Reef Marine Park, Australia. Changes in benthic assemblages were assessed on two new trails used by snorkelers, two unused (control) trails, and two undisturbed areas. Total percent coral cover, numbers of broken colonies, and living coral fragments were counted 6 months before and 6 months after the new trails began to be used. Spatial patterns of effects around concentrated nodes of use were determined by stratified sampling around and away from the interpretative signs within each trail. Despite comparatively low levels of use (approximately 15 snorkelers per trail per week), snorkelers caused significant damage to corals along the trails. Branching corals (non-Acropora branching corals and Millepora spp.) were most affected. More damage occurred near the interpretative signs than elsewhere on the trails. The numbers of broken branches and damaged coral colonies in the snorkeling trails increased rapidly but stabilized within 2 months of the commencement of use. There was no significant change in overall benthic assemblages within the trails after 6 months of use by snorkelers. Although concentrating snorkelers within confined trails caused increased damage to corals, the effects can be mitigated by appropriate design and placement of the trails and by managing the behavior of snorkelers. Interpretative information should warn users about the damage they may cause when swimming along the trails. Managing the behavior of snorkelers in the water is likely to be more effective in reducing damage than simply applying fixed limits to the amount of use the trails receive.

RESUMEN: Los senderos submarinos tienen la intención de servir como herramientas interpretativas en los parques marinos, pero la concentración de buzos y buceadores libres en áreas definidas puede tener un efecto negativo en el ambiente de los alrededores. Examinamos los patrones temporales y espaciales de los efectos del uso de senderos submarinos en relieves de arrecifes de coral en el arrecife del Parque Marino de la Gran Barrera de Arrecifes en Australia. Los cambios en los ensamblajes bénticos fueron evaluados en dos senderos nuevos usados por buceadores libres, dos senderos sin usar (controles) y dos áreas sin perturbar. Evaluamos el porcentaje de cobertura de coral, el número de colonias rotas, y fragmentos de coral vivo 6 meses antes y seis meses después de que se iniciara el uso de los senderos nuevos. Los patrones espaciales de los efectos alrededor de nódulos concentrados de uso fueron determinados por un muestreo estratificado alrededor y en sitios lejanos de las señales interpretativas de cada sendero. A pesar de los niveles significativamente bajos de uso (∼15 buceadores libres/sendero/semana), los buceadores libres causaron un daño significativo a los corales a lo largo de los senderos. Los corales ramificados (spp. de corales que no pertenecen a Acropora o Millepora) fueron los más afectados. Se observó más daño cerca de las señales interpretativas que en cualquier otra parte del sendero. Los números de ramas rotas y de colonias de coral dañadas en los senderos se incrementaron rápidamente, pero se estabilizaron a los dos meses de haber iniciado el uso de los senderos. No hubo un cambio significativo dentro de los senderos después de seis meses de uso. A pesar de que la concentración de buceadores libres dentro de senderos confinados incrementó el daño a los corales, los efectos pueden ser mitigados mediante el diseño y la ubicación apropiada de los senderos y mediante el manejo de la conducta de los buceadores libres. La información interpretativa debería prevenir a los usuarios sobre el daño que ellos mismos pueden ocasionar cuando nadan en estos senderos. El manejo de la conducta de los buceadores libres en el agua probablemente sea más efectivo en la reducción del daño que la simple aplicación de límites fijos a la cantidad de uso que un sendero puede recibir.