Stocking density and artificial habitat influence stock structure and yield from intensive nursery systems for mud crabs Scylla serrata (Forsskål 1775)

Intensive nursery systems are designed to culture mud crab postlarvae through a critical phase in preparation for stocking into growout systems. This study investigated the influence of stocking density and provision of artificial habitat on the yield of a cage culture system. For each of three batches of postlarvae, survival, growth and claw loss were assessed after each of three nursery phases ending at crab instars C1/C2, C4/C5 and C7/C8. Survival through the first phase was highly variable among batches with a maximum survival of 80% from megalops to a mean crab instar of 1.5. Stocking density between 625 and 2300 m⁻² did not influence survival or growth in this first phase. Stocking densities tested in phases 2 and 3 were 62.5, 125 and 250 m⁻². At the end of phases 2 and 3, there were five instar stages present, representing a more than 20‐fold size disparity within the populations. Survival became increasingly density‐sensitive following the first phase, with higher densities resulting in significantly lower survival (phase 2: 63% vs. 79%; phase 3: 57% vs. 64%). The addition of artificial habitat in the form of pleated netting significantly improved survival at all densities. The mean instar attained by the end of phase 2 was significantly larger at a lower stocking density and without artificial habitat. No significant effect of density or habitat on harvest size was detected in phase 3. The highest incidence of claw loss was 36% but was reduced by lowering stocking densities and addition of habitat. For intensive commercial production, yield can be significantly increased by addition of a simple net structure but rapidly decreases the longer crablets remain in the nursery.     

Assessing common bottlenose dolphin (Tursiops truncatus) population structure in Mississippi Sound and coastal waters of the north central Gulf of Mexico

1. Population structure of highly mobile marine organisms can be complex and difficult to study, but it is important to understand how populations partition themselves within their environment for accurate assessment of both natural and anthropogenic impacts and successful management. The 2010 Deepwater Horizon oil spill negatively impacted common bottlenose dolphins (Tursiops truncatus) within Mississippi Sound and the surrounding north central Gulf of Mexico (GOMx); however, little was known about their underlying population structure in these waters. Thus, it was unclear how many demographically independent populations were affected by the spill.
2. Common bottlenose dolphin samples were collected throughout inshore waters of Mississippi Sound and coastal waters of the north-central GOMx. Mitochondrial DNA control region sequence data and 19 nuclear microsatellite loci were analysed to determine how many populations are present and characterize their range throughout these waters.
3. Bayesian clustering and migration analyses identified two genetically distinct and demographically independent populations: one predominantly inhabiting Mississippi Sound and adjacent coastal waters, and a second population extending generally from offshore of Mobile Bay, Alabama, east along the Florida Panhandle. Neither of these populations align with the currently delineated management stocks previously used to estimate impacts from the oil spill on common bottlenose dolphins in this portion of the GOMx.
4. These results suggest that revisions may be necessary so that management stocks accurately represent the demographically independent populations present in these waters. Furthermore, better comprehension of underlying population structure will enhance impact assessments on common bottlenose dolphins and provide more appropriate baseline data to support future restoration and conservation objectives.

     

Principles and approaches to abate seabird by-catch in longline fisheries

Mortality in longline fisheries is a critical global threat to most albatross and large petrel species. Here we identify key principles and approaches to identify and achieve broad use of effective seabird by‐catch avoidance methods. Despite the availability of highly effective and cost‐saving seabird avoidance methods, few longline fleets employ them. Given the political context and capacity of management authorities of the majority of longline fisheries, it is critical to identify seabird avoidance strategies that are not only highly effective, but are also economically viable and commercially practical. Adoption of an international performance standard for longline baited hook–sink rate, and prescribing minimum gear weighting designs that meet this standard that are achievable by all longline fisheries, would be an important step forward towards resolving low use of seabird avoidance methods by vessels, including those in illegal, unregulated and unreported fisheries. Due to differences between fleets, no single seabird avoidance measure is likely to be effective and practical in all longline fisheries. Therefore, testing of seabird avoidance methods in individual fleets is needed to determine efficacy and economic viability. Longline fishers should directly participate in these trials as they have a large repository of knowledge and skills to effectively develop and improve seabird by‐catch avoidance techniques, and this provides industry with a sense of ownership for uptake of effective by‐catch reduction methods. Establishing protected areas containing seabird colonies and adjacent waters within a nation's EEZ can be an expedient method to address seabird by‐catch. However, establishing high seas marine protected areas to restrict longline fishing in seabird foraging areas, which would require extensive and dynamic boundaries and large buffer zones, may not be a viable short‐term solution because of the extensive time anticipated to resolve legal complications with international treaties, to achieve international consensus and political will, and to acquire requisite extensive resources for surveillance and enforcement. Analysis of results of research on seabird avoidance methods reveals that the most reliable comparisons of the efficacy of alternative strategies are from comparing the effectiveness of methods tested in a single experiment. Benefits from standardizing the reporting of seabird by‐catch rates to account for seabird abundance are described. To provide the most precise inputs for seabird population models, estimates of seabird mortality in longline fisheries should account for seabird falloff from hooks before hauling, delayed mortality of seabirds caught but freed from gear, and mortality caused by hooks discarded in offal.     

Using ecological trajectories to track long-term taxonomic and functional changes in benthic shallow soft-bottom communities (Bay of Saint-Brieuc,English Channel)

1. Taxonomic and functional trajectories of benthic assemblages were studied in shallow soft-bottom sediments in the bay of Saint-Brieuc (Western English Channel). Changes were assessed at different spatial and temporal scales using a macrobenthic dataset based on 38 stations sampled in 1987 and 2019, coupled with data from one station sampled annually between 2005 and 2019 as part of the European Water Framework Directive monitoring programme.
2. Taxonomic trajectories indicated 1) changes in the structure and distribution of benthic assemblages, 2) an homogenization of the assemblages, and 3) significant functional shifts.
3. Fishing activities and nutrient enrichment are probably strong drivers of the observed changes, as suggested by the higher mortality rate of fragile, flexible, tubiculous and burrowing species, and the increase in the abundance of opportunistic species in the assemblages. Certain populations of macroinvertebrates seem jointly controlled by climate change and by the aforementioned local factors of disturbance.
4. The Community Trajectory Analysis framework appears as a new and interesting method to track ecological changes in marine ecosystems by measuring change with respect to a baseline state, to help define ecological recovery (station returning to the initial ecological state) and departure (station presenting increased changes over time), and to analyse trajectory similarity.
5. According to the degradation of habitat over time, we identify the need for the implementation of knowledge-based conservation strategies, especially within Natura 2000 sites.

     

The effect of piscidin antimicrobial peptides on the formation of Gram-negative bacterial biofilms

Fish-derived antimicrobial peptides are an important part of the innate immune system due to their potent antimicrobial properties. Piscidins are a class of antimicrobial peptides first described in hybrid striped bass (Morone chrysops x Morone saxatilis) but have also been identified in many other fish species. Previous work demonstrated the broad antimicrobial activity of piscidins against Gram-negative and Gram-positive bacterial species. This study sought to determine the extent to which class I (striped bass piscidin 1, white bass piscidin 1 and striped bass/white bass piscidin 3) and class II (striped bass piscidin 4 and white bass piscidin 5) piscidins inhibit biofilm formation of different Gram-negative bacteria. In general, the class I and II piscidins demonstrate potent activity against Escherichia coli and Flavobacterium columnare biofilms. The class II piscidins showed more activity against E. coli and F. columnare isolates than did the class I piscidins. The piscidins in general were much less effective against inhibiting Aeromonas hydrophila and A. veronii biofilm growth. Only the class I piscidins showed significant growth inhibition among the Aeromonas spp. examined.     

Inferring biological soil crust successional stage using combined PLFA, DGGE, physical and biophysiological analyses

Arid areas are highly sensitive to climate change and are ideal model systems to study the potential impact of climate change on species' community structure. Biological soil crust (BSC) formation plays an ecological role in a number of key processes in the development of dry ecosystems. It was hypothesized that BSC succession and function are affected by aridity level and limited by rainfall. Furthermore, it is possible to infer the direction of the BSC succession based on aridity level, and the latter can imitate future climate change scenarios. The objectives of this study were to investigate the microbial biomass and diversity of the BSC structure in three sites differing in aridity level (semiarid, arid and hyper-arid), by combining physical and biophysiological measurements with 16S rRNA gene fragment and phospholipid fatty acid (PLFA) analyses. Physical and biophysiological parameters of the BSC were significantly influenced by aridity level. Total protein and polysaccharide contents were strongly correlated with total PLFA-based microbial biomass. Gram-positive biomarkers and microbial biomass were significantly higher in the wettest (semiarid) site than in the driest (hyper-arid) one. Multivariate-analysis based ordination of the PLFA data segregated the cluster of semiarid data from that of the hyper-arid site, while data from the arid site were dispersed between the two. The phylogenetic distribution of prominent 16S rRNA bacterial gene sequences along the aridity levels was in agreement with the PLFA analysis: the hyper-arid site was dominated by the cyanobacterium Microcoleus vaginatus, while diverse populations of cyanobacteria and soil bacteria were found in the other sites. These complementary tools allowed a simple and sensitive measurement of the influence of aridity levels on BSC successional stage. The results demonstrate that different aridity levels correspond to different BSC successional stages and those differences can be used as parameters for global change scenarios.     

Mechanical Evaluation of the Equine Laryngoplasty

Objectives: Mechanical evaluation of the equine laryngoplasty. Study Design: Experimental. Animal Population: Cadaveric cricoid (n=36) and arytenoid (46) cartilages. Methods: Arytenoid and cricoid cartilage specimens were embedded for testing. Suture material (2 Ethilon^®, 5 Ethibond^®, or 5 Fiberwire^®) was inserted simulating laryngoplasty procedures. Constructs were evaluated in single or cyclic loading. Single cycle tests recorded load at failure and stiffness. Cyclical tests recorded displacement after 10,000 cycles. ANOVA and t‐tests were used (significance P<.05). Results: The arytenoid Ethibond^® (241.10±47.67 N) constructs were stronger in single cycle than Ethilon^® (133.85±27.89 N) and Fiberwire^® (142.67±32.40 N). The cricoid Ethibond^® (220.39±49.11 N) constructs were stronger than Ethilon^® (171.93±21.19). The stiffness of Ethilon^® constructs was lower in both the arytenoid and cricoid compared with Ethibond^® and Fiberwire^®. The arytenoids failed at a lower load than the cricoids for Ethilon^® and Fiberwire^® but not Ethibond^® constructs. In cyclic testing complete failure of either cartilage did not occur. Arytenoid Ethibond^® constructs (0.43±0.21 mm) had less distraction than Ethilon^® (0.92±0.41 mm) and a trend for less compared with Fiberwire^® (0.83±0.43 mm; P=.0513). Cricoid Ethibond^® constructs (0.45±0.18 mm) had less distraction compared with Ethilon^® (1.04±0.30 mm) and Fiberwire^® (0.97±0.45 mm). Conclusions: Ethibond^® was superior to Ethilon^® and Fiberwire^® constructs in vitro. Clinical Relevance: Abduction loss after laryngoplasty is a common complication. The results of this study suggest that the use of Ethibond^® should minimize abduction loss after surgery relative to the other materials tested.     

Continuity and discontinuity of the riparian vegetation along a fluvial corridor

The concept of continuity/discontinuity is applied to the riparian vegetation of the corridor of the River Adour (S.W. France), in order to precisely define longitudinal structure, and to test the degree of floristic continuity of the fluvial axis. The measure of floristic connectance along the river course is based on presence/absence data, and is applied to successive stretches of the river, at various resolution levels. This analysis shows that the River Adour corridor cannot be assumed to be floristically continuous. The observed discontinuities may correspond to two types of change in the riparian vegetation: zones of slow change (high level of floristic connectance) or zones of sharp change (low level of floristic connectance).     

Reduced blood flow to peripheral and core body tissues in sheep and cattle induced by endophyte-infected tall fescue

Four wethers and 14 steers (environmentally heat stressed, 32 degrees C, 60% relative humidity) were evaluated for changes in blood flow induced by endophyte-infected tall fescue. Concentration of the ergopeptide ergovaline was used as an indicator of diet toxicity due to the endophytic fungus Acremonium coenophialum. Blood flow to specific tissues was measured using radiolabeled microspheres. Wethers received one of two dietary treatments for 30 d before determination of tissue blood flow: 1) a low-endophyte diet (less than .05 ppm ergovaline) or 2) a high-endophyte (1.18 ppm ergovaline) diet. Blood flows to the adrenal glands and skin covering the inner hind leg were less (P less than .10) in wethers consuming the high-endophyte diet than in those consuming the low-endophyte diet. Tissue blood flows in steers were determined on two occasions: 1) after steers had received a low- (less than .01 ppm ergovaline) or high-endophyte (.52 ppm ergovaline) fescue diet for 14 d and 2) 8 d after steers had been switched to a common, fescue-free diet. Blood flows to skin covering the ribs, cerebellum of the brain, duodenum, and colon were less (P less than .10) in steers consuming the high-endophyte diet. However, 8 d after consuming fescue-free diets, steers that had previously consumed the high-endophyte diet had greater (P = .08) blood flow to the coronary bands of the front hooves than steers that had consumed the low-endophyte diet. Blood flows to all other tissues were similar between treatments. We inferred from these experiments that the toxin(s) associated with endophyte-infected tall fescue caused decreased blood flow to peripheral and core body tissues and that this effect was abated within 8 d of removing the toxin(s).