Assemblage turnover and taxonomic sufficiency of subtidal macroalgae at multiplespatial scales

Spatial variability in the structure of subtidal macroalgal assemblages in southwest Australia was examined at multiple spatial scales using a three-factor hierarchal design. Spatial extents ranged from metres (between quadrats) to many hundreds of kilometres (between regions), and the study encompassed N2000 km of temperate coastline. In addition, the influence of taxonomic resolution, from species level data to class level, on spatial patterns was investigated to assess the potential evolutionary timescales of the pattern and for developing cost effective regionally applicable surrogates for biodiversity monitoring. Almost 300 species were identified from 14 sites, representing considerable biodiversity and a significant subset of the total benthic macroalgal diversity in the region (∼1000 species). Multivariate variability was significant at all spatial scales examined, but most prominent at smallest spatial scales, regardless of taxonomic resolution. Assemblage and species turnover was pronounced at scales of metres to hundreds of metres. Generally, small scale patchiness was a ubiquitous pattern for all individual taxa examined, regardless of taxonomic resolution, while variability at the scale of 10s of km was less important. Even so, differences in spatial variability between taxa were observed, and ecological and historical reasons for such differences are proposed. Taxonomic aggregation to family level had minimal effect on spatial patterns, but aggregation to order level led to changes in some aspects of patterns of assemblage structure. The unique and speciose macroalgal assemblages on subtidal reefs in southwest Australia are shaped by a complex array of historical and contemporary processes that act at multiple spatial (and temporal) scales. Understanding the relative importance of these processes requires that further manipulative and correlative work is conducted across a range of ecologically-important spatial scales

Seagrass Halophila ovalis is affected by light quality across different life history stages

Seagrass meadows provide crucial ecosystem services to the coastal zone but are threatened globally. Seagrass loss to date has mainly been attributed to anthropogenic activities that reduce light quantity (amount of photosynthetic photon flux density), such as dredging, flooding and eutrophication. However, light quality (wavelengths of light within the visible spectrum) is also altered by these anthropogenic stressors. This study addressed the effect of light quality changes on seagrasses. Aquarium-based experiments were conducted to determine whether the seagrass Halophila ovalis (R.Br.) Hook f. responds to different light quality treatments. Separate experiments were performed in which adults, seeds or seedlings were subjected to monochromatic light treatments in the blue (peak λ %= 451 nm), green (peak λ = 522 nm), yellow (peak λ = 596 nm) and red (peak λ = 673 nm) wavelengths with a control of full-spectrum light (λ = 400 - 700 nm, at 200 µmol photons m-2 s-1). This study is unique in that it measured seagrass responses to light across several plant scales (physiology, productivity, morphology and biomass) as well as across life-history stages (seeds, seedlings, adults and flowering). Adult plants responded differently to seeds and seedlings but were generally consistent with terrestrial angiosperms: blue light decreased below-ground productivity; green light influenced morphology (through increased rhizome internode length); red light enhanced seed germination and survival. The findings indicate that both natural and human-induced changes in light quality could significantly affect seagrass growth and reproduction. As a range of anthropogenic activities are currently contributing to the global losses of seagrasses, this research provides timely information on how light quality influences different seagrass life history stages

A comparative analysis of perceived stigma among HIV-positive Ghanaian and African American males

The purpose of this paper was to address two questions: (i) Do Ghanaian and African American males with HIV/AIDS experience different types and degrees of stigma? and (ii) Is the impact of stigma associated with HIV/AIDS on the self different for Ghanaian and African American males? A quantitative method was used, and the four dimensions of stigma (social rejection, financial insecurity, internalised shame, and social interaction) were identified and measured using combination Likert-type questionnaires. Data regarding positive feelings of selfworth and self-deprecation, stress related to body image, and personal control were also collected in Ghana and the southeastern USA.The sample consisted of 55 men from Ghana and 55 men from the southeastern USA. Results indicate that values for the scales measuring stigma and self-perception were significantly higher for the Ghanaian sample than for the African American sample.Thus we conclude that the Ghanaian sample living with HIV/AIDS experienced a greater amount of negative self-perception and stigma-related strife than the African American sample.Keywords: stigma, HIV/AIDS, social rejection, financial insecurity, internalised shame, cultureRésuméLe but de cette communication est d'aborder deux questions, à savoir: (i) Est-ce que les hommes Ghanéens et Afro-Américains vivant avec le VIH/SIDA éprouvent de types et de degrés différents de stigmatisation? et (ii) Estce que l'impact de stigmatisation liée au VIH/SIDA sur le moi est différent chez les Ghanéens en comparaison aux Afro-Américains? Une méthode quantitative a été employée et les quatre dimensions de stigmatisation (le rejet social, l'insécurité financière, la honte intériorisée et l'interaction sociale) ont été identifiés et mesurés grâce à une combinaison des questionnaires Likert-type. Des données concernant des sentiments positifs de la valeur personnelle et d'auto-dénigrement, le stresse lié à l'image corporel et le contrôle de soi-même ont été recueilles au Ghana et au sud-est des États Unis. L'échantillon consistait de 55 hommes du Ghana et 55 hommes du sud-est des États Unis. Les chiffres des barèmes utilisées pour mesurer la stigmatisation et la perception de soi-même étaient sensiblement élevés pour l'échantillon ghanéen par rapport à l'échantillon afro-américain. L'échantillon ghanéen vivant avec le VIH/SIDA a davantage de perception négative de soi-même ainsi que la lutte liée à la stigmatisation par rapport à l'échantillon afro-américain.Mots clés: stigmatisation,VIH, SIDA, rejet social, insécurité financière, honte intériorisée, culture SAHARA J (Journal of Social Aspects of HIV/AIDS Research Alliance) Vol. 2(3) 2005: 344-35

Patch dynamics driven by wave exposure in subtidal temperate seaweeds are exacerbated by warming oceans

Over the past decades, ocean temperatures have been steadily increasing and are projected to continue to do so, stressing many temperate marine organisms. Changing temperatures do not affect ecosystems in isolation, but interact with many other factors in shaping ecological communities. We investigated the changes over 2 decades in subtidal temperate seaweed communities over a wave exposure gradient in Western Australia, a global warming hotspot. We found higher diversity in the seaweed community and a higher proportion of biomass of species with a warm affinity (expressed as the tropicalization index: TI) over time. There was no decline in biomass of the dominant habitat-forming kelp Ecklonia radiata on low wave exposure reefs, while it was patchier and comprised a lower proportion of the total seaweed biomass on the medium and high wave exposure reefs. Furthermore, the presence of E. radiata was disproportionally associated with low abundances of seaweeds with warm affinity. The increasing patchiness of E. radiata likely provided a competitive release for other seaweeds, and the increase in abundance of Scytothalia dorycarpa likely provided a compensatory effect which resulted in a lower than expected TI. We found no indication of an ameliorating effect by wave exposure, and conclude that the patch dynamics driven by wave exposure are more likely exacerbated by increasing ocean temperatures on subtidal temperate reefs. If this continues, the reduction in E. radiata and increase in warm affiliated seaweeds will result in a more diverse seaweed community, but one with a lower standing biomass

A novel adaptation facilitates seed establishment under marine turbulent flows

Seeds of Australian species of the seagrass genus Posidonia are covered by a membranous wing that we hypothesize plays a fundamental role in seed establishment in sandy, wave swept marine environments. Dimensions of the seed and membrane were quantified under electron microscopy and micro-CT scans, and used to model rotational, drag and lift forces. Seeds maintain contact with the seabed in the presence of strong turbulence: the larger the wing, the more stable the seed. Wing surface area increases from P. sinuosa \u3c P. australis \u3c P.coriacea correlating with their ability to establish in increasingly energetic environments. This unique seed trait in a marine angiosperm corresponds to adaptive pressures imposed on seagrass species along 7,500 km of Australia’s coastline, from open, high energy coasts to calmer environments in bays and estuaries

The risk of multiple anthropogenic and climate change threats must be considered for continental scale conservation and management of seagrass habitat

Globally marine-terrestrial interfaces are highly impacted due to a range of human pressures. Seagrass habitats exist in the shallow marine waters of this interface, have significant values and are impacted by a range of pressures. Cumulative risk analysis is widely used to identify risk from multiple threats and assist in prioritizing management actions. This study conducted a cumulative risk analysis of seagrass habitat associated with the Australian continent to support management actions. We developed a spatially explicit risk model based on a database of threats to coastal aquatic habitat in Australia, spanning 35,000 km of coastline. Risk hotspots were identified using the model and reducing the risk of nutrient and sediment pollution for seagrass habitat was assessed. Incorporating future threats greatly altered the spatial-distribution of risk. High risk from multiple current threats was identified throughout all bioregions, but high risk from climate change alone manifested in only two. Improving management of nutrient and sediment loads, a common approach to conserve seagrass habitat did reduce risk, but only in temperate regions, highlighting the danger of focusing management on a single strategy. Monitoring, management and conservation actions from a national and regional perspective can be guided by these outputs

Ocean connectivity and habitat characteristics predict population genetic structure of seagrass in an extreme tropical setting

Understanding patterns of gene flow and processes driving genetic differentiation is important for a broad range of conservation practices. In marine organisms, genetic differentiation among populations is influenced by a range of spatial, oceanographic, and environmental factors that are attributed to the seascape. The relative influences of these factors may vary in different locations and can be measured using seascape genetic approaches. Here, we applied a seascape genetic approach to populations of the seagrass, Thalassia hemprichii, at a fine spatial scale (~80 km) in the Kimberley coast, western Australia, a complex seascape with strong, multidirectional currents greatly influenced by extreme tidal ranges (up to 11 m, the world\u27s largest tropical tides). We incorporated genetic data from a panel of 16 microsatellite markers, overwater distance, oceanographic data derived from predicted passive dispersal on a 2 km-resolution hydrodynamic model, and habitat characteristics from each meadow sampled. We detected significant spatial genetic structure and asymmetric gene flow, in which meadows 12–14 km apart were less connected than ones 30–50 km apart. This pattern was explained by oceanographic connectivity and differences in habitat characteristics, suggesting a combined scenario of dispersal limitation and facilitation by ocean current with local adaptation. Our findings add to the growing evidence for the key role of seascape attributes in driving spatial patterns of gene flow. Despite the potential for long-distance dispersal, there was significant genetic structuring over small spatial scales implicating dispersal and recruitment bottlenecks and highlighting the importance of implementing local-scale conservation and management measures

Challenges for Restoration of Coastal Marine Ecosystems in the Anthropocene

Coastal marine ecosystems provide critical goods and services to humanity but many are experiencing rapid degradation. The need for effective restoration tools capable of promoting large-scale recovery of coastal ecosystems in the face of intensifying climatic stress has never been greater. We identify four major challenges for more effective implementation of coastal marine ecosystem restoration (MER): (1) development of effective, scalable restoration methods, (2) incorporation of innovative tools that promote climate adaptation, (3) integration of social and ecological restoration priorities, and (4) promotion of the perception and use of coastal MER as a scientifically credible management approach. Tackling these challenges should improve restoration success rates, heighten their recognition, and accelerate investment in and promotion of coastal MER. To reverse the accelerating decline of marine ecosystems, we discuss potential directions for meeting these challenges by applying coastal MER tools that are science-based and actionable. For coastal restoration to have a global impact, it must incorporate social science, technological and conceptual advances, and plan for future climate scenarios

Impact of mooring activities on carbon stocks in seagrass meadows

Boating activities are one of the causes that threaten seagrass meadows and the ecosystem services they provide. Mechanical destruction of seagrass habitats may also trigger the erosion of sedimentary organic carbon (Corg) stocks, which may contribute to increasing atmospheric CO2. This study presents the first estimates of loss of Corg stocks in seagrass meadows due to mooring activities in Rottnest Island, Western Australia. Sediment cores were sampled from seagrass meadows and from bare but previously vegetated sediments underneath moorings. The Corg stores have been compromised by the mooring deployment from 1930s onwards, which involved both the erosion of existing sedimentary Corg stores and the lack of further accumulation of Corg. On average, undisturbed meadows had accumulated ~6.4 Kg Corg m−2 in the upper 50 cm-thick deposits at a rate of 34 g Corg m−2 yr−1. The comparison of Corg stores between meadows and mooring scars allows us to estimate a loss of 4.8 kg Corg m−2 in the 50 cm thick deposits accumulated over ca. 200 yr as a result of mooring deployments. These results provide key data for the implementation of Corg storage credit offset policies to avoid the conversion of seagrass ecosystems and contribute to their preservation

Too Hot to Handle: Unprecedented Seagrass Death Driven by Marine Heatwave in a World Heritage Area

The increased occurrence of extreme climate events, such as marine heatwaves (MHWs), has resulted in substantial ecological impacts worldwide. To date metrics of thermal stress within marine systems have focussed on coral communities, and less is known about measuring stress relevant to other primary producers, such as seagrasses. An extreme MHW occurred across the Western Australian coastline in the austral summer of 2010/2011, exposing marine communities to summer seawater temperatures 2‐5 °C warmer than average. Using a combination of satellite imagery and in situ assessments, we provide detailed maps of seagrass coverage across the entire Shark Bay World Heritage Area (ca. 13,000 km2) before (2002, 2010) and after the MHW (2014, 2016). Our temporal analysis of these maps documents the single largest loss in dense seagrass extent globally (1,310 km2) following an acute disturbance. Total change in seagrass extent was spatially heterogenous, with the most extensive declines occurring in the Western Gulf, Wooramel Bank and Faure Sill. Spatial variation in seagrass loss was best explained by a model that included an interaction between two heat stress metrics, the most substantial loss occurring when degree heat weeks (DHWm) was ≥ 10 and the number of days exposed to extreme sea surface temperature during the MHW (DaysOver) was ≥ 94. Ground‐truthing at 622 points indicated that change in seagrass cover was predominantly due to loss of Amphibolis antarctica rather than Posidonia australis, the other prominent seagrass at Shark Bay. As seawater temperatures continue to rise and the incidence of MHWs increase globally, this work will provide a basis for identifying areas of meadow degradation, or stability and recovery; and potential areas of resilience