The effect of macrofaunal disturbance on Cerastoderma edule post-larvae

Populations of the Common European cockle (Cerastoderma edule) often have highly patchy distributions and variable recruitment success. One of the proposed reasons is that high densities of filter feeders and/or bioturbators are thought to reduce the success of larval settlement and post-settlement survival, but the direct causal processes driving these observations are not clearly identified and validated. Through combined field and laboratory experiments, we test the hypothesis that macrofauna cause decreases in post-larval density through feeding and movement activities. The effect of excluding the bioturbating lugworm Arenicola marina and filter-feeding adult cockles on post-larval cockle densities was estimated in separate field experiments at two locations from the time of initial larval settlement in May 2012 to late summer August 2012. Lugworm exclusion led to a significant increase in cockle post-larval densities whereas the opposite was true for adult cockles, where exclusion led to a reduction in C. edule post-larval density. Although clear effects were observed in the field, experiments conducted in the laboratory failed to detect changes in mortality or byssus drifting of post-larvae as a consequence of macrofaunal activity. This study demonstrates that the presence of macrofauna can have both positive and negative effects on post-settlement density of C. edule post-larvae. Thus the density, distribution and identity of macrofauna have significant effects on the density and spatial distribution of C. edule post-larvae during the post-settlement period. These observations have implications for conservation and fishery management of this species

Whole-genome sequencing reveals host factors underlying critical COVID-19

Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease

Processes controlling spatial and temporal variations in cockle Cerastoderma edule (L.) abundance and distribution

The common cockle Cerastoderma edule (L.) is an ecologically and commercially important species in Wales, and other North West European tidal flats and estuaries. Cockle populations often exhibit high inter-annual variability in recruitment strength but also spatially within population distributions. The post-larval stage is a critical period for determining recruitment strength in cockle populations, and likely to be a key period for creating spatial structure. This thesis aimed to record and quantify the spatio-temporal changes in post-larval cockle (newly settled 0-group individuals) density over large and small spatial scales, and investigate what processes may create or maintain these patterns. I found that over large scales (100s of metres) the initial settlement can be restricted to certain areas of the shore with high densities, but as time progresses, post-settlement redistributions move post-larvae across the shore. These redistributions recorded over two years extended post-larvae from initial low shore settlements into the mid and high shore, and resulted in a distribution similar to that of the adult population. Over small spatial scales (10s of metres) highly patchy and intense initial settlement of C. edule was also observed. Over time the spatial distribution of post-larvae became more dispersed resulting in significant positive correlation with the adult population post-settlement. To understand what is driving changes in density, experiments were conducted in the field and laboratory. Lugworms and adult cockles can be very abundant and disturb surface sediment during feeding and movements, which may kill or negatively affect C. edule post-larvae. Lugworms and adult cockles were excluded from areas of sediment in the field and the effect on post-larval densities over time investigated. Removing lugworms increased the densities of post-larvae but removing adult cockles decreased the post-larval density. Laboratory experiments looking at the possible role of lugworms and adults cockles causing direct mortality or increasing benthic and pelagic migrations showed no evidence that these were producing the results seen from the field experiment. I also tested if patchiness of post-larval cockles, compared to a uniform distribution, was beneficial for survival under predation from juvenile shore crabs Carcinus maenas, which experience a negative effect of interference competition on their foraging efficiency. Due to the behaviour of ‘take away foraging’ in the juvenile shore crabs, C. edule post-larvae still had higher mortality when aggregated. It is concluded in this thesis that spatial distribution and structure of post-larval C. edule change significantly during the post-settlement period, over large and small scales, and that macrofaunal interactions and predation may be a significant factor in producing these observations

Processes controlling spatial and temporal variations in cockle Cerastoderma edule (L.) abundance and distribution

The common cockle Cerastoderma edule (L.) is an ecologically and commercially important species in Wales, and other North West European tidal flats and estuaries. Cockle populations often exhibit high inter-annual variability in recruitment strength but also spatially within population distributions. The post-larval stage is a critical period for determining recruitment strength in cockle populations, and likely to be a key period for creating spatial structure. This thesis aimed to record and quantify the spatio-temporal changes in post-larval cockle (newly settled 0-group individuals) density over large and small spatial scales, and investigate what processes may create or maintain these patterns. I found that over large scales (100s of metres) the initial settlement can be restricted to certain areas of the shore with high densities, but as time progresses, post-settlement redistributions move post-larvae across the shore. These redistributions recorded over two years extended post-larvae from initial low shore settlements into the mid and high shore, and resulted in a distribution similar to that of the adult population. Over small spatial scales (10s of metres) highly patchy and intense initial settlement of C. edule was also observed. Over time the spatial distribution of post-larvae became more dispersed resulting in significant positive correlation with the adult population post-settlement. To understand what is driving changes in density, experiments were conducted in the field and laboratory. Lugworms and adult cockles can be very abundant and disturb surface sediment during feeding and movements, which may kill or negatively affect C. edule post-larvae. Lugworms and adult cockles were excluded from areas of sediment in the field and the effect on post-larval densities over time investigated. Removing lugworms increased the densities of post-larvae but removing adult cockles decreased the post-larval density. Laboratory experiments looking at the possible role of lugworms and adults cockles causing direct mortality or increasing benthic and pelagic migrations showed no evidence that these were producing the results seen from the field experiment. I also tested if patchiness of post-larval cockles, compared to a uniform distribution, was beneficial for survival under predation from juvenile shore crabs Carcinus maenas, which experience a negative effect of interference competition on their foraging efficiency. Due to the behaviour of ‘take away foraging’ in the juvenile shore crabs, C. edule post-larvae still had higher mortality when aggregated. It is concluded in this thesis that spatial distribution and structure of post-larval C. edule change significantly during the post-settlement period, over large and small scales, and that macrofaunal interactions and predation may be a significant factor in producing these observations

Changes in small scale spatial structure of cockle Cerastoderma edule (L.) post-larvae

Understanding the spatial structure of populations at different scales can help reveal the processes controlling abundance and distribution. For species with a pelagic larval stage and highly mobile post-larval stage, such as the common cockle Cerastoderma edule, changes in spatial distribution from settlement through to juvenile stages are likely to occur at various spatial scales influencing the population dynamics observed. To record such changes a small-scale high-resolution field survey of C. edule post-larvae over an area of 60 � 80 m of tidal mudflat was conducted using a spatially-explicit staggered-nested design in the Dee estuary, UK. The survey was repeated three times from initial settlement in June 2011 to March 2012. Changes in spatial structure were described using Moran's I correlograms and prediction mapping, with analysis of correlations between cockle cohorts and sediment composition. At the first sampling event in June 2011, when initial settlement was occurring, post-larvae were highly aggregated in patches of 10�14 m in size and 16�20 m apart. By October 2011 the post-larvae had become more evenly dispersed with some small scale (< 4 m) random patchiness and a gradient in post-larval density. This spatial structure was maintained into March 2012 but with increased patchiness. At settlement post-larval density showed no correlation with adult abundance or sediment mud content, but by October 2011 and March 2012 there was a strong positive correlation with adult abundance. Such changes in spatial structure, abundance and adult association after settlement show the likely importance of small scale (metres to tens of metres) processes on post-larval survival from predation and adult interactions, thereby potentially shaping adult distributions. Small scale patchiness in post-larvae can be created at settlement; however the distribution and association with adults change over time