Right place, right height: Habitat connectivity and condition underpin fish community structure across coastal seascapes

Community ecology seeks to understand the variety of factors that influence biodiversity. Early work has recognised that local habitat quality is important (e.g., niche theory), but so is spatial context (e.g., Island Biogeography Theory). In my PhD, I build upon these concepts in marine biomes by combining underwater surveys with Geographic Information Systems to explore how habitat quality and spatial context shapes fish community structure and function in a variety of soft-structure coastal habitats. Local-scale aspects of habitat quality, like three-dimensional hard complexity, are recognised as key predictors of fish diversity. However, relatively little is known about the effects of soft-structure habitat complexity on fish diversity. Using a best-subsets modelling approach and data from three temperate mesohabitats, I assessed what aspects of soft structure best predicted differences in reef fish community composition. I found that high levels of canopy cover and height were key predictors in supporting a diverse fish community across mesohabitats. Thus, it is important that habitat quality in soft-structure environments account for variation across three dimensions. In addition to local habitat quality, the spatial context of an area within the wider seascape mosaic can influence patterns of diversity. Using a patch network of tropical macroalgal meadows that varied in size and distance to a coral reef, I assessed the relative importance of local patch quality and spatial context for predicting the diversity and structure of the local fish community. Multivariate analysis showed the relative importance of these variables differed depending on a taxonomic or functional focus of fish diversity. Most importantly, when species identity was explicitly examined, the placement of macroalgal patches within 500m of a coral reef was among the key predictors, along with hard complexity and soft canopy height. Many accounts of local habitat quality as a predictor of diversity are based on observational studies, such as the results I report on above. Therefore, I used an experimental unseasonal reduction of tropical macroalgal canopy height to explore the consequences of unseasonal canopy loss on resident fishes over short-to-long time-scales. Despite these meadows undergoing a similar, seasonal change in canopy structure, experimental sites, relative to nearby reference sites, had significant decreases in fish species richness and density within five days of canopy height reduction which was coupled with a short-term increase in the density of higher-order carnivores. Some of these effects were still evident two years later, despite an overall recovery in canopy structure. Habitat variation across multiple-scales has often shown to influence patterns of diversity, but their effects on ecological processes are less well known. Predators, through regulation of prey populations, may structure ecological communities via top-down effects. Therefore, I explored the behavioural ecology of a common mesopredatory fish (Thalassoma lunare) to understand how local habitat quality and spatial context may influence predation patterns. While T. lunare showed indications of habitat preference in early life history stages, adult fish were habitat generalists who varied their foraging behaviour according to spatial context. Specifically, individuals in isolated patches would forage across significantly smaller distances than those in well-connected patches, and may therefore contribute to differing local predation pressures in different spatial contexts. My work shows that a holistic, multi-scale approach is needed to understand ecological patterns and processes in marine biomes. I discuss how these insights add to our understanding of marine ecology, and can inform management and design of marine reserves by identifying well connected and structurally complex areas of the seascape to facilitate movement between these high quality areas

Seascape Configuration and Fine-Scale Habitat Complexity Shape Parrotfish Distribution and Function across a Coral Reef Lagoon

Structural complexity spanning fine to broad spatial scales can influence the distribution and activity of key organisms within marine ecosystems. However, the relative importance of hard (e.g., corals) and/or soft (e.g., macroalgae) structural complexity for marine organisms is often unclear. This study shows how both broad-scale (seascape configuration of coral structure) and fine-scale habitat complexity (structure height, number of holes, and presence of macroalgae) can influence the abundance and spatial ecology of reef fish. Underwater visual census of fish, surveys of habitats, remote underwater videos, and behavioral observations by following individual fish were used to quantify fine-scale habitat characteristics (e.g., complexity, coral structure height, macroalgae presence) and the abundance, size structure, and behavior (rates of herbivory, tortuosity ratios and total distance travelled) of abundant parrotfish. Both seascape configuration and macroalgae influenced the patterns of fish abundance and rates of herbivory. However, these relationships varied with trophic groups and ontogenetic stages. Abundance of adult and intermediate-phase parrotfishes was positively influenced by densely aggregated coral structures, whereas juvenile abundance was positively influenced by the presence of macroalgae. Foraging path and bite rates of an abundant parrotfish, Chlorurus spilurus, were not influenced by coral structure configuration or height, but the presence of macroalgae increased the bite rates of all juvenile parrotfish. Our results suggest that a combination of seascape configuration, fine-scale habitat complexity, and microhabitat selectivity influence reef fish community structure and foraging behavior, thus altering herbivory. However, these relationships can differ among functional groups of fish and life-history stages. Information on these fish-habitat interactions is critical for identifying habitats that facilitate ecological functions and ensures the successful management and conservation of essential habitats

Seascape Configuration and Fine-Scale Habitat Complexity Shape Parrotfish Distribution and Function across a Coral Reef Lagoon

Structural complexity spanning fine to broad spatial scales can influence the distribution and activity of key organisms within marine ecosystems. However, the relative importance of hard (e.g., corals) and/or soft (e.g., macroalgae) structural complexity for marine organisms is often unclear. This study shows how both broad-scale (seascape configuration of coral structure) and fine-scale habitat complexity (structure height, number of holes, and presence of macroalgae) can influence the abundance and spatial ecology of reef fish. Underwater visual census of fish, surveys of habitats, remote underwater videos, and behavioral observations by following individual fish were used to quantify fine-scale habitat characteristics (e.g., complexity, coral structure height, macroalgae presence) and the abundance, size structure, and behavior (rates of herbivory, tortuosity ratios and total distance travelled) of abundant parrotfish. Both seascape configuration and macroalgae influenced the patterns of fish abundance and rates of herbivory. However, these relationships varied with trophic groups and ontogenetic stages. Abundance of adult and intermediate-phase parrotfishes was positively influenced by densely aggregated coral structures, whereas juvenile abundance was positively influenced by the presence of macroalgae. Foraging path and bite rates of an abundant parrotfish, Chlorurus spilurus, were not influenced by coral structure configuration or height, but the presence of macroalgae increased the bite rates of all juvenile parrotfish. Our results suggest that a combination of seascape configuration, fine-scale habitat complexity, and microhabitat selectivity influence reef fish community structure and foraging behavior, thus altering herbivory. However, these relationships can differ among functional groups of fish and life-history stages. Information on these fish–habitat interactions is critical for identifying habitats that facilitate ecological functions and ensures the successful management and conservation of essential habitats.This research was funded by the Swedish Research Council (Grant numbers 2015-05848, 2015-01257, E0344801)

The contribution of macroalgae-associated fishes to small-scale tropical reef fisheries

Macroalgae-dominated reefs are a prominent habitat in tropical seascapes that support a diversity of fishes, including fishery target species. To what extent, then, do macroalgal habitats contribute to small-scale tropical reef fisheries? To address this question we: (1) Quantified the macroalgae-associated fish component in catches from 133 small-scale fisheries, (2) Compared life-history traits relevant to fishing (e.g. growth, longevity) in macroalgal and coral-associated fishes, (3) Examined how macroalgae-associated species can influence catch diversity, trophic level and vulnerability and (4) Explored how tropical fisheries change with the expansion of macroalgal habitats using a case study of fishery-independent data for Seychelles. Fish that utilised macroalgal habitats comprise 24% of the catch, but very few fished species relied entirely on macroalgal or coral habitats post-settlement. Macroalgal and coral-associated fishes had similar life-history traits, although vulnerability to fishing declined with increasing contribution of macroalgae association to the catch, whilst mean trophic level and diversity peaked when macroalgal-associated fish accounted for 20%-30% of catches. The Seychelles case study revealed similar total fish biomass on macroalgal and coral reefs, although the biomass of primary target species increased as macroalgae cover expanded. Our findings reinforce that multiple habitat types are needed to support tropical fishery stability and sustainability. Whilst coral habitats have been the focus of tropical fisheries management, we show the potential for macroalgae-associated fish to support catch size and diversity in ways that reduce vulnerability to overfishing. This is pertinent to seascapes where repeated disturbances are facilitating the replacement of coral reef with macroalgal habitats

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Microhabitat selectivity shapes the seascapeecology of a carnivorous macroalgae-associatedtropical fish

Habitat quantity and quality can be key drivers for the distribution and abundance of animals in heterogeneous landscapes. Macroalgal meadows are often a prominent component of tropical marine ecosystems, yet we have little understanding of how dynamic shifts in this habitat type may affect patterns of fish biodiversity. We examined whether a tropical carnivorous wrasse, Xenojulis margaritaceus, was a macroalgal specialist that responded to changes in canopy habitat structure across space and time. Field surveys revealed X. margaritaceus exclusively occupied macroalgal meadows, where it foraged for invertebrate epifauna on a range of macroalgal genera such as Sargassum and Lobophora. During summer, X. margaritaceus preferentially occupied the canopy-forming macroalgae Sargassum. Sargassum canopy height, percent cover of understorey algae and the abundance of strong competitors and roving predators provided the best predictors for the abundance of X. margaritaceus abundance across the seascape. Despite seasonal shifts in habitat use to include more understory algae during winter, X. margaritaceus displayed significant declines in abundance from summer to winter according to the extent of seasonal canopy habitat loss within each meadow. We conclude that carnivorous fishes can be dependent on tropical macroalgal meadows, where they may be vulnerable to a loss of canopy habitat quality arising from local factors and climatic forcing.L.N.W. was supported by an Honours Scholarship from the Australian National University (ANU). Funding was provided by the Australian Academy of Science (Thomas Davies Research Award to C.J.F.), the Research School of Biology at ANU and a Julian E. Tenison Woods Award to L.N.W. from the Linnean Society of NSW

Importance of soft canopy structure for labrid fish communities in estuarine mesohabitats

Hard structural complexity is widely recognised as important for assessing fish habitat quality, but our understanding of the importance of soft habitat microstructure for temperate marine fishes is less developed. We used best-subsets modelling of underwater surveys in sponge, soft coral, and macroalgae mesohabitats within a temperate estuary to assess what measures of soft habitat structure best predicted differences in wrasse (family: Labridae) fish community composition. We found that significant differences in the labrid fish community among and within mesohabitat types were best explained by a combination of percent canopy cover and soft canopy height, with increased canopy height being correlated with increased fish abundance and species richness. Sponge and macroalgae mesohabitats emerged as particularly important, but vulnerable habitats for a diversity of fishes unique to these mesohabitat types. Ultimately, mesohabitats with high percent canopy cover and height appear to be particularly valuable for supporting estuarine fish communities. Due to this importance, and the potential for decadal-scale recovery times within sponge canopies, we suggest patches with high-quality canopy structure warrant special protection from local threats, such as anchor and fishing damage

Habitat connectivity and complexity underpin fish community structure across a seascape of tropical macroalgae meadows

In heterogeneous landscapes, local patterns of community structure are a product of the habitat size and condition within a patch interacting with adjacent habitat patches of varying composition and quantity. While evidence for local versus landscape factors have been found in terrestrial biomes, support for such multi-scale effects shaping marine ecological communities is equivocal. We investigated whether within-patch habitat condition can override seascape context to explain the community structure of macroalgae-associated reef fishes across a tropical seascape. We mapped the distribution and abundance of a diverse family of reef fishes (Labridae) occupying macroalgae meadows within a tropical reef ecosystem, and using best-subsets model selection, investigated the potential for habitat structural connectivity and/or local habitat quality for predicting variations in fish community structure across the seascape. Local habitat quality (canopy structure, hard habitat complexity) and area of coral-dominated habitat within 500 m of a macroalgal meadow provided the best predictors of fish community structure. However, the specific importance of a given predictor varied with fish life history stage and functional trophic group. Interestingly, macroalgae meadow area was among the least important predictors. Given the complex interplay between local habitat quality and spatial context effects on fish biodiversity, our study reveals the multi-scale predictors that should be used in spatial conservation and management approaches for tropical fish diversity. Moreover, our findings question the ubiquity of habitat area effects in patchy landscapes, and cautions against a sole reliance on habitat quantity in spatial management.This research is supported by an Australian Government Research Training Program (RTP) Scholarship, as well as with funding provided by the Linnean Society of New South Wales

Macroalgal meadow habitats support fish and fisheries in diverse tropical seascapes

Canopy‐forming macroalgae can construct extensive meadow habitats in tropical seascapes occupied by fishes that span a diversity of taxa, life‐history stages and ecological roles. Our synthesis assessed whether these tropical macroalgal habitats have unique fish assemblages, provide fish nurseries and support local fisheries. We also applied a meta‐analysis of independent surveys across 23 tropical reef locations in 11 countries to examine how macroalgal canopy condition is related to the abundance of macroalgal‐associated fishes. Over 627 fish species were documented in tropical macroalgal meadows, with 218 of these taxa exhibiting higher local abundance within this habitat (cf. nearby coral reef) during at least one life‐history stage. Major overlap (40%-43%) in local fish species richness among macroalgal and seagrass or coral reef habitats suggest macroalgal meadows may provide an important habitat refuge. Moreover, the prominence of juvenile fishes suggests macroalgal meadows facilitate the triphasic life cycle of many fishes occupying diverse tropical seascapes. Correlations between macroalgal canopy structure and juvenile abundance suggests macroalgal habitat condition can influence levels of replenishment in tropical fish populations, including the majority of macroalgal‐associated fishes that are targeted by commercial, subsistence or recreational fisheries. While many macroalgal‐associated fishery species are of minor commercial value, their local importance for food and livelihood security can be substantial (e.g. up to 60% of landings in Kenyan reef fisheries). Given that macroalgal canopy condition can vary substantially with sea temperature, there is a high likelihood that climate change will impact macroalgal‐associated fish and fisheries.Support was provided by The Australian National University (National Institutes Grant—Research School of Biology), WA Department of Biodiversity, Conservation & Attractions, Australian Institute of Marine Science, the Environment Conservation Fund of the Government of Hong Kong SAR (ECF15/2015 to PTYL and PKSL), the Philippine Department of Science and Technology Grants-in-Aid Program (to RAA and AAB), the Australian Research Council (DE130100688 to ASH), the Royal Society (UF140691 fellowship to NAJG), and the Swedish Research Council (2015-01257, E0344801). We thank Sofia Wikström and three anonymous peer reviewers for constructive comments on earlier drafts

Macroalgal meadow habitats support fish and fisheries in diverse tropical seascapes

Canopy-forming macroalgae can construct extensive meadow habitats in tropical seascapes occupied by fishes that span a diversity of taxa, life-history stages and ecological roles. Our synthesis assessed whether these tropical macroalgal habitats have unique fish assemblages, provide fish nurseries and support local fisheries. We also applied a meta-analysis of independent surveys across 23 tropical reef locations in 11 countries to examine how macroalgal canopy condition is related to the abundance of macroalgal-associated fishes. Over 627 fish species were documented in tropical macroalgal meadows, with 218 of these taxa exhibiting higher local abundance within this habitat (cf. nearby coral reef) during at least one life-history stage. Major overlap (40%-43%) in local fish species richness among macroalgal and seagrass or coral reef habitats suggest macroalgal meadows may provide an important habitat refuge. Moreover, the prominence of juvenile fishes suggests macroalgal meadows facilitate the triphasic life cycle of many fishes occupying diverse tropical seascapes. Correlations between macroalgal canopy structure and juvenile abundance suggests macroalgal habitat condition can influence levels of replenishment in tropical fish populations, including the majority of macroalgal-associated fishes that are targeted by commercial, subsistence or recreational fisheries. While many macroalgal-associated fishery species are of minor commercial value, their local importance for food and livelihood security can be substantial (e.g. up to 60% of landings in Kenyan reef fisheries). Given that macroalgal canopy condition can vary substantially with sea temperature, there is a high likelihood that climate change will impact macroalgal-associated fish and fisheries