A deep dive into the ecology of Gamay (Botany Bay, Australia): current knowledge and future priorities for this highly modified coastal waterway

Context: Gamay is a coastal waterway of immense social, cultural and ecological value. Since European settlement, it has become a hub for industrialisation and human modification. There is growing desire for ecosystem-level management of urban waterways, but such efforts are often challenged by a lack of integrated knowledge. Aim and methods: We systematically reviewed published literature and traditional ecological knowledge (TEK), and consulted scientists to produce a review of Gamay that synthesises published knowledge of Gamay’s aquatic ecosystem to identify knowledge gaps and future research opportunities. Key results: We found 577 published resources on Gamay, of which over 70% focused on ecology. Intertidal rocky shores were the most studied habitat, focusing on invertebrate communities. Few studies considered multiple habitats or taxa. Studies investigating cumulative human impacts, long-term trends and habitat connectivity are lacking, and the broader ecological role of artificial substrate as habitat in Gamay is poorly understood. TEK of Gamay remains a significant knowledge gap. Habitat restoration has shown promising results and could provide opportunities to improve affected habitats in the future. Conclusion and implications: This review highlights the extensive amount of knowledge that exists for Gamay, but also identifies key gaps that need to be filled for effective management

Using trait-based approaches to understand morphological variation in macroalgae and its influence on associated communities

Subtidal temperate reefs are often dominated by habitat-modifying macroalgae which form highly productive and structurally complex environments. The physical structure of macroalgae often correlates with associated community structure, however, identifying which elements of their structure drive these relationships remains challenging. Traditional assessments of macroalgae – associated community relationships use broad-scale classifications to group macroalgae according to identity or gross morphology. Trait-based approaches instead measure the unique traits of individuals and in doing so allow for predictions that are not constrained to taxonomic groups. By measuring at the level of the individual, trait-based approaches have the potential to capture not only interspecific variability, but also the intraspecific variation that is often overlooked by traditional approaches. Macroalgal morphology can vary substantially through ontogeny, and commonly varies with local environmental conditions (e.g. temperature, nutrients, exposure). Thus, intraspecific variability will likely play a significant role in determining associated community structure. My research used a trait-based approach to understand the relationship between macroalgae and their associated communities in south-eastern Australia, a region of rapidly changing ocean conditions. I focused particularly on the influence of intraspecific variation in these ecosystems. Furthermore, whilst large-scale patterns in the biomass and morphology of habitat-formers are well known for terrestrial plants, how marine habitat-formers vary across large-scales is poorly understood. I documented extensive inter-and intraspecific morphological variability across six species of macroalgae, and when morphological traits were ranked against identity, traits better predictors of invertebrate density than identity. A manipulative experiment showed that variation in the density of epifauna amongst alga of different morphologies was the result of habitat structure mediated predation pressure, and not habitat selection. A large-scale survey found the biomass and morphology of macroalgae varied with ocean climate. Interestingly, the epifaunal communities associated with macroalgae were found to be discontinuous. This is the first time discontinuities have been explicitly detected in epifaunal communities, and showed that these communities comprised two distinct body size aggregations that responded to different aspects of the environment. Across large-scales the strong influence of habitat structure on epifauna weakened and instead abiotic variables were more important in driving variability in the body size distributions of epifaunal communities. The results of this thesis show that both the structure of macroalgal habitat and the epifaunal communities associated with macroalgae are strongly influenced by local environmental conditions. Climate change predicts significant changes to the ocean climate are likely in the future, which these results suggest will have strong implications for the structure and functioning of temperate reef habitats. Trait-based approaches offer a useful method which we can not only develop our understanding of the relationships between habitat-formers and their associated communities, but also to assist in the transformation of ecology into a predictive science

Responses of ghost crabs and other scavengers to habitat modification of urban sandy beaches

Populations in coastal areas are growing at a rate far exceeding that of other areas, resulting in escalating pressures on coastal areas around the world. Sandy beaches make up over 70% of the world coastlines, comprising some of the most highly sought after areas for human activities. Consequently, sandy beaches are some of the most vulnerable habitats to the effects of urbanisation, with beaches now threatened by a wide range of anthropogenic practices. Ghost crabs are widely used as ecological indicators of ecosystem health on sandy beaches, but have rarely been studied on beaches within large urban centres. In this thesis, ghost crab burrow densities were used to assess human impacts on beaches in the highly urbanised estuary, Sydney Harbour. Across 38 beaches in the harbour, mechanical beach cleaning frequency was found to be the most influential predictor of ghost crab distributions in the area, with burrow counts reduced on the most frequently cleaned beaches and highest burrow counts found on beaches that were cleaned no more than three times per week. Mechanical cleaning was associated with the volume of wrack accumulated onshore, with frequently cleaned beaches supporting significantly lower volumes of wrack then beaches that were cleaned less frequently. To examine how organic subsidies on sandy beaches affect crab behaviour, I experimentally manipulated the availability of organic marine matter (wrack and carrion). Ghost crabs demonstrated no short term response to either subsidy (measured by the initiation of new burrows near food source), while vertebrate scavengers demonstrated a rapid response to carrion subsidies only. The presence of vertebrate scavengers in treatment plots reduced the fossorial behaviour of ghost crabs, suggesting biological interactions among invertebrates and vertebrates. The arrival of marine subsidies to sandy beaches facilitates the exchange of resources between the marine and terrestrial zone. Given that these systems can rely heavily on this resource exchange any alteration in the natural supply of organic marine matter, e.g. more frequent beach cleaning in response to urbanisation, could have far reaching implications for both zones

Habitat traits and predation interact to drive abundance and body size patterns in macroalgae associated fauna

Habitat-forming organisms provide three-dimensional structure that supports abundant and diverse communities. Variation in the morphological traits of habitat-formers will therefore likely influence how they facilitate associated communities, either via food and habitat provisioning, or by altering predator-prey interactions. These mechanisms, however, are typically studied in isolation and thus we know little of how they interact to affect associated communities. In response to this, we used naturally occurring morphological variability in the alga Sargassum vestitum to create habitat units of distinct morphotypes to test whether variation in the morphological traits (frond size and thallus size) of S. vestitum, or the interaction between these traits, affect their value as habitat for associated communities in the presence and absence of predation. We found morphological traits did not interact, instead having independent effects on epifauna that were negligible in the absence of predation. However, when predators were present, habitat units with large fronds were found to host significantly lower epifaunal abundances than other morphotypes, suggesting large frond alga provided low-value refuge from predators. The presence of predators also influenced the size structure of epifaunal communities from habitat units of differing frond size suggesting the refuge value of S. vestitum was also related to epifauna body size. This suggests that habitat-formers may chiefly structure associated communities by mediating size-selective predation, and not through habitat-provisioning. Furthermore, these results also highlight that habitat traits cannot be considered in isolation, for their interaction with biotic processes can have significant implications for associated communities.To test whether habitat unit size (i.e., algal biomass/thallus size) interacted with frond size diversity (small, large and mixed mean frond size) to affect the abundance and size structure of associated communities, we created and deployed five types of habitat units: a single branch with small fronds, a single branch with large fronds, two branches with small fronds, two branches with large fronds and a unit with one branch with small fronds and one branch with large fronds (hereafter 'mixed frond' in text and 'mix' in plots). To test how variation in algal morphology and predation risk structure epifaunal communities, we used an orthogonal design with predation risk (three levels) and habitat unit morphology (three levels, as only double-branched habitat units were used); with 6 replicates for each combination level. After five days, all algae were retrieved by snorkelling. Each branch was collected separately by removing cage (if present), then the cable tie at the attachment point and quickly placing each branch of the habitat unit in a jar underwater (i.e., for double-branched habitat units branches were placed in separate jars). Back in the laboratory, all jars were stored in the refrigerator (~2 °C) until processing (maximum three days). Digital zooplankton scanner technology was then used to count and measure (total body length: µm) all epifauna

Habitat traits and predation interact to drive abundance and body size patterns in associated fauna

Abstract Habitat‐forming organisms provide three‐dimensional structure that supports abundant and diverse communities. Variation in the morphological traits of habitat formers will therefore likely influence how they facilitate associated communities, either via food and habitat provisioning, or by altering predator–prey interactions. These mechanisms, however, are typically studied in isolation, and thus, we know little of how they interact to affect associated communities. In response to this, we used naturally occurring morphological variability in the alga Sargassum vestitum to create habitat units of distinct morphotypes to test whether variation in the morphological traits (frond size and thallus size) of S. vestitum or the interaction between these traits affects their value as habitat for associated communities in the presence and absence of predation. We found morphological traits did not interact, instead having independent effects on epifauna that were negligible in the absence of predation. However, when predators were present, habitat units with large fronds were found to host significantly lower epifaunal abundances than other morphotypes, suggesting that large frond alga provided low‐value refuge from predators. The presence of predators also influenced the size structure of epifaunal communities from habitat units of differing frond size, suggesting that the refuge value of S. vestitum was also related to epifauna body size. This suggests that habitat formers may chiefly structure associated communities by mediating size‐selective predation, and not through habitat provisioning. Furthermore, these results also highlight that habitat traits cannot be considered in isolation, for their interaction with biotic processes can have significant implications for associated communities