Comparing the Invasibility of Experimental “Reefs” with Field Observations of Natural Reefs and Artificial Structures

Natural systems are increasingly being modified by the addition of artificial habitats which may facilitate invasion. Where invaders are able to disperse from artificial habitats, their impact may spread to surrounding natural communities and therefore it is important to investigate potential factors that reduce or enhance invasibility. We surveyed the distribution of non-indigenous and native invertebrates and algae between artificial habitats and natural reefs in a marine subtidal system. We also deployed sandstone plates as experimental ‘reefs’ and manipulated the orientation, starting assemblage and degree of shading. Invertebrates (non-indigenous and native) appeared to be responding to similar environmental factors (e.g. orientation) and occupied most space on artificial structures and to a lesser extent reef walls. Non-indigenous invertebrates are less successful than native invertebrates on horizontal reefs despite functional similarities. Manipulative experiments revealed that even when non-indigenous invertebrates invade vertical “reefs”, they are unlikely to gain a foothold and never exceed covers of native invertebrates (regardless of space availability). Community ecology suggests that invertebrates will dominate reef walls and algae horizontal reefs due to functional differences, however our surveys revealed that native algae dominate both vertical and horizontal reefs in shallow estuarine systems. Few non-indigenous algae were sampled in the study, however where invasive algal species are present in a system, they may present a threat to reef communities. Our findings suggest that non-indigenous species are less successful at occupying space on reef compared to artificial structures, and manipulations of biotic and abiotic conditions (primarily orientation and to a lesser extent biotic resistance) on experimental “reefs” explained a large portion of this variation, however they could not fully explain the magnitude of differences

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

Improved fish and crustacean passage in tidal creeks following floodgate remediation

1. Estuarine wetlands are important nurseries for fish and decapod crustaceans. Flood mitigation structures (such as levees, culverts and floodgates) that fragment wetland habitat can reduce fish and crustacean passage and subsequently impact biodiversity. 2. Remediating structures to enhance connectivity, tidal flushing and fish and crustacean passage are assumed to be important ways to rehabilitate estuarine wetlands, but they are rarely evaluated with a robust sampling protocol. Furthermore, studies are inconsistently applied across different barrier types, and success is variable. Consequently, those rehabilitating wetlands are left with an incomplete understanding of what trajectories of change (if any) may be expected from barrier remediation. 3. In collaboration with landholders and managers, 'floodgate remediation' (structural and operational changes to increase tidal flushing and connectivity) was undertaken in three tidal creeks in two coastal river systems in northern New South Wales, Australia. Changes in fish and crustacean passage were measured for two different techniques (flap gates built into larger gates and the intermittent opening of gates with manual winching) using a BACI design over 2 years. Temporal changes in assemblages and species richness in managed creeks were compared to those in reference creeks (i.e. without floodgates) and control creeks (with closed floodgates). 4. Both types of floodgate remediation enhanced the passage of fish and crustaceans and had significant impacts on assemblages in managed creeks when compared to control and reference creeks. This shift was sustained for the duration of our study in two of the three creeks and was driven primarily by an increase in the number of estuarine-marine-dependent species. 5. Synthesis and applications. Our study demonstrates that floodgate remediation can facilitate fish and crustacean passage and rehabilitate aquatic assemblages in defaunated, tidally restricted wetlands. Given that the vast majority of floodgates throughout south-eastern Australia can be altered to promote connectivity, such remediation may play an important part in guarding against future declines in estuarine connectivity arising from climate change

Impacts of detritus from the invasive alga Caulerpa taxifolia on a soft sediment community

Invasive primary producers can dramatically reorganize food webs through detrital subsidies. This study assessed (1) contributions of the invasive alga Caulerpa taxifolia to detrital resources of temperate Australian estuaries, and (2) effects of these contributions on sediment-dwelling invertebrates. In an invaded estuary, sampling of an intertidal shore indicated C. taxifolia fragments were consistently present in organic matter deposits and were particularly abundant following storms. Sampling of the alga across 6 invaded estuaries showed that the ratio of organic carbon to nitrogen (C:N) in fresh tissue varied between 7 and 16. To determine how C. taxifolia detritus influences benthic macrofaunal assemblages and whether this influence depends on the quantity and C:N ratio of C. taxifolia detritus, a manipulative field experiment was performed. On a sheltered intertidal mudflat, 0.25 m2 plots of sediment were experimentally enriched with either a high (90 g DW) or low (30 g) loading of high C:N (14) or low C:N (7) C. taxifoliadetritus. Experimental enrichment negatively affected the total abundance and species richness of macroinvertebrates relative to controls, and these effects increased with detrital loading. For some macrofauna, reducing the C:N ratio tended to exacerbate negative effects on abundances, whereas it moderated these effects for other species. Given that organic matter derived from invasive species can be transported beyond the distribution of live invaders, greater consideration should be given to the potential broad-scale effects of invasive primary producers on detrital pathways

Positive versus negative effects of an invasive ecosystem engineer on different components of a marine ecosystem

Habitat-forming invasive species have complex impacts on native communities. Positive above ground and negative below ground impacts are reported, suggesting that habitat-forming invasive species may affect community components differently. Furthermore, such effects may vary depending on the density of the invader. We determined the responses of community components to different densities of the invasive green alga Caulerpa taxifolia in southeastern Australia. Initially we investigated differences in soft-sediment faunal communities (above and below ground) across a biomass gradient at two invaded sites. Caulerpa taxifolia biomass was positively associated with the composition and abundance of the epifaunal community, but negatively correlated with the abundance of infauna. To examine the response of common community members in more detail, we caged two species of mollusk (the infaunal bivalve, Anadara trapezia and the epifaunal gastropod, Batillaria australis) across the same biomass gradient to determine lethal and sublethal effects of C. taxifolia biomass on individuals. Survivorship of A. trapezia was low when C. taxifolia was above 300 g m−2. Negative sublethal effects were also density-dependent with A. trapezia tissue weight being lowest above this same C. taxifolia biomass. The proportion of B. australis surviving was unaffected by C. taxifolia biomass. However, the total number of live B. australis recovered in cages increased as C. taxifolia biomass increased, providing further evidence of positive density dependent effects (in line with the survey data) of C. taxifolia on epifauna. Finally, we removed C. taxifolia from plots of differing C. taxifolia biomass and followed community change for 5 months. Community change following C. taxifolia removal was also density dependent as recovery 5 months post-removal depended on the initial biomass of C. taxifolia, suggesting a lag in the recovery of communities due to residual environmental effects post-removal (i.e. hysteresis). We have shown that the effects of a habitat-forming invasive species are biomass dependent and also affect community components differently, suggesting that, globally, the impact of these types of invaders may be context dependent

Sediment and light intensity collected during deployment of experimental “reef”.

<p>(a) Sediment (g/dry weight) was collected from individual plates prior to final collection of plates and (b) light (lux) was sampled above the plates with loggers for 28 days during the experiment. The averages are presented for each measure and bars are separated by (a) orientation (horizontal or vertical) and assemblage (new or established) and (a/b) coded for shading treatment (unshaded, shade control or shaded).</p

Differences in benthic metabolism, nutrient fluxes, and denitrification in Caulerpa taxifolia communities compared to uninvaded bare sediment and seagrass (Zostera capricorni) habitats

Benthic metabolism, nutrient fluxes, and denitrification were measured in Caulerpa taxifolia communities that had recently invaded (between 2003 and 2008) bare sediments following the loss of Zostera capricorni (prior to 2003), and in adjacent Z. capricorni communities and bare sediments, to determine the likely changes in ecosystem function following C. taxifolia colonization. Areas colonized by C. taxifolia had higher gross primary production (GPP), net primary production (NPP), and dark benthic N2 effluxes than adjacent bare sediments, but lower dark benthic NH+4 effluxes. C. taxifolia invasion of bare sediments had a beneficial role in removing excess nitrogen from the system through enhanced denitrification. In contrast, areas occupied by C. taxifolia had similar GPP and NPP relative to Z. capricorni beds and similar benthic N2 and NH+4 effluxes. Thus, C. taxifolia appears to play a comparable role to Z. capricorni in terms of some ecosystem functions, although the degree of similarity is likely to be affected by the relative densities of the two macrophytes. However, replacement of Z. capricorni communities by C. taxifolia appears to significantly alter the quantity and quality (higher ratio) of benthic dissolved organic carbon and dissolved organic nitrogen fluxes

Pairwise comparisons of the non-indigenous and native algal species percent cover and richness sampled from artificial and natural habitats.

<p>Non-indigenous algal e) percent cover and f) species richness, native algal g) percent cover and h) species richness compared between the vertical surfaces of artificial and natural structures. Habitat was the factor of interest in the comparisons and the direction of difference indicated in the left column. The sites and years at which these patterns occurred are indicated in the right column. Habitat  =  Pi (piling), Po (pontoon), Re (reef).Sites  =  BA (Balmain), CL (Clontarf), GB (Gore Bay) and FT (Fig Tree). Years  = 06 (2006) and 07 (2007).</p

PERMANOVA results comparing non-indigenous and native invertebrate species percent cover and richness sampled from artificial and natural habitats.

<p>Non-indigenous invertebrate a) percent cover and b) species richness, native invertebrate c) percent cover and d) species richness compared between vertical surfaces of artificial (pilings and pontoons) and natural (reef) habitats. Habitats were sampled at twice at 4 sites. Significant results (p<0.05) are indicated in bold.</p