Peak Recruitment Research Articles

Within-host adaptive speciation of commensal yoyo clams leads to ecological exclusion, not co-existence.

Symbionts dominate planetary diversity and three primary symbiont diversification processes have been proposed: co-speciation with hosts, speciation by host-switching, and within-host speciation. The last mechanism is prevalent among members of an extraordinary marine symbiosis in the Indian River Lagoon, Florida, composed of a host mantis shrimp, Lysiosquilla scabricauda, and seven host-specific commensal vasconielline "yoyo" clams (Galeommatoidea) that collectively occupy two distinct niches: burrow-wall-attached, and host-attached/ectocommensal. This within-host symbiont radiation provides a natural experiment to test how symbiont coexistence patterns are regulated in a common ancestral habitat. The competitive exclusion principle predicts that sister taxa produced by adaptive speciation (with distinct morphologies and within-burrow niches) are most likely to coexist whereas the neutral theory predicts no difference among adaptive and non-adaptive sister taxa co-occurrence. To test these predictions, we engaged in (1) field-censusing commensal species assemblages; (2) trophic niche analyses; (3) laboratory behavioral observations. Although predicted by both models, the field census found no mixed-niche commensal assemblages: multi-species burrows were exclusively composed of burrow-wall commensals. Their co-occurrence matched random assembly process expectations, but presence of the single ectocommensal species had a highly significant negative effect on recruitment of all burrow-wall commensal species (P<0.001), including on its burrow-wall commensal sister species (P < 0.001). Our stable isotope data indicated that commensals are suspension feeders and that co-occurring burrow-wall commensals may exhibit trophic niche differentiation. The artificial burrow behavioral experiment yielded no evidence of spatial segregation among burrow-wall commensals, and it was terminated by a sudden breakdown of the host-commensal relationship resulting in a mass mortality of all commensals unattached to the host. This study system appears to contain two distinct, superimposed patterns of commensal distribution: (1) all burrow-wall commensal species; (2) the ectocommensal species. Burrow-wall commensals (the plesiomorphic condition) broadly adhere to neutral theory expectations of species assembly but the adaptive evolution of ectocommensalism has apparently led to ecological exclusion rather than coexistence, an inverse outcome of theoretical expectations. The ecological factors regulating the observed burrow-wall/ectocommensal exclusion are currently obscure but potentially include differential recruitment to host burrows and/or differential survival in "mixed" burrow assemblages, the latter potentially due to changes in host predatory behavior. Resampling host burrows during commensal recruitment peak periods and tracking burrow-wall commensal survival in host burrows with and without added ectocommensals could resolve this outstanding issue.

Size distribution and growth parameters of blue swimming crab (Portunus pelagicus, Linnaeus 1758) in Awur Bay, Jepara

Blue swimming crab (Portunus pelagicus) is a fishery commodity that has important economic value. One of the catch landings in Teluk Awur, Jepara is blue swimming crab. Intensive crab catching carried out with small sizes has an effect on decreasing crab stocks in the waters. This study aims to determine the size distribution, the relationship between carapace width and weight, growth parameters and recruitment patterns. The research was conducted in May, June, July and August 2022 in the waters of Teluk Awur, Jepara. Sampling using systematic sampling method. The data collected is carapace width (mm) and crab weight (grams). Data analysis was performed using FiSAT II software. The results of the analysis of the relationship between carapace width and weight showed that the growth of the male crab was positive allometric and the growth of the female crab was isometric, with the equation of the male crab W = 0.0000214cW3.251 and the female crab W = 0.0000232cW3.220. The growth parameters obtained by the equation of the male and female crabs were cWt = 158,55(1- e(-1,2(t+0,083))], and cWt = 158.55(1 – e(-0.67(t+0.152) ))). The peak of male crab recruitment was in October at 22,71%, while the female crab was in May at 13,52%, indicating that in that month new crab individuals were added. Based on these results, the stock of crab resources in Jepara's Awur Bay must always be considered and always support the recruitment process of crab. Beside that, the goverment can enforce management of crab fishing.Keywords: Allometric; Carapace Width; Crab; Recruitment

Macrophage transcriptome changes in response to cardiac injuries are determined by the type of lesion rather than their ontogenetic nature

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): CRC1425 - DFG Introduction Resident macrophages account for 5% of the cells in the healthy heart. In response to cardiac injury, monocytes infiltrate and differentiate into recruited macrophages complementing the original resident macrophage population, and together orchestrate cardiac remodeling. We aim to identify the extent to which macrophage origin, tissue location and type of cardiac injury determine macrophage phenotypes in ischemic and non-ischemic cardiac injuries over time. Results and methods We use a reporter mouse line CX3CR1Yfp CreER/+:R26tdT/+ to visualize and quantify fluxes of resident and recruited macrophages and their respective localizations within the heart following ischemia and reperfusion (I/R) injury and pressure overload after transversal aortic constriction (TAC), respectively. Interestingly, macrophage numbers peaked during the first week post-surgery in both the local/acute and the global/continuous injury models. Initially, recruited macrophages outnumbered the resident macrophage pool within the infarct area but ultimately reached a near 1:1 equilibrium at 4 weeks post I/R injury. In the remote myocardium the 1:1 equilibrium established already during the first week. In TAC-injured hearts, the 1:1 ratio of recruited and resident hearts also established within the first week post-surgery and persisted up to 8 weeks of follow-up even as cardiac function deteriorated. In the infarct, recruited macrophages showed increased cytokine synthesis, defensive response, and cell adhesion pathways during the first week after injury. Many inflammatory pathways remained activated up to day 28 post MI despite simultaneous activation of the anti-inflammatory response. Formerly resident macrophages and their progeny also mounted an immune response throughout the healing process. Unexpectedly, by day 28 post MI when a stable scar had formed, resident and recruited macrophage population transcriptomes converted onto a common, pro-inflammatory steady state phenotype, that differed from their originally divergent gene expression profiles in the healthy heart by over one thousand genes. In the remote zone, however, resident macrophages maintained cellular homeostasis function, unlike recruited macrophages that retained an inflammatory program. Following TAC surgery, transcriptional profiles remained differentially regulated at all time points tested, where recruited subset induced immune response and resident macrophages upregulated tissue remodeling genes. Conclusion Ischemic and non-ischemic cardiac injuries induce a transient peak of monocyte recruitment and macrophage differentiation in and around cardiac lesions which lead to a permanent integration of recruited monocyte-derived macrophages into the pool of tissue resident macrophages – albeit at different paces. The type of injury and macrophage localization within the changing tissue microenvironment determine partial or complete override of ontogenic cell programs.

Spatiotemporal variation in clam recruitment among beaches in Washington State (USA)

AbstractAbundant clam populations provide ecosystem services and commercial and recreational shellfish harvests worldwide. Two non‐native clams (Manila clams, Ruditapes philippinarum; eastern soft‐shell clams, Mya arenaria) commonly populate mid‐intertidal zones of coarse‐sediment beaches in Washington State, USA. To better understand factors influencing their abundance, we used passive mid‐intertidal spat collectors to determine the density and distribution of clam recruits (150–500 μm shell length) at eight beaches spanning over 500 km and over two reproductive seasons (2016 and 2017). Cumulative seasonal recruitment (clams &lt;500 μm) in 2016 and 2017 at +1.0 m MLLW ranged from 800 to 125,000 m−2 for Ruditapes philippinarum and 50–85,000 m−2 for M. arenaria, and did not differ by substrate type at small scales (gravel vs. crushed shell). At larger scales, different interannual recruitment patterns across sites did not dramatically shift the ranked order of highest and lowest recruitment sites. Cumulative recruitment tended to be lower at warmer sites, while timing of peak recruitment was not consistently related to temperature. Sites also differed in the relative recruitment of the two clam species, but most beaches had greater densities of R. philippinarum than M. arenaria at both recruitment and juvenile stages. Although recruitment densities differed by two orders of magnitude across sites, post‐settlement factors eliminated initial spatial variation within a year, dampening recruitment variability among these beaches that all contribute to commercial and recreational clam production.

Anomalous sea temperatures can impair coral reef fish recruitment

Understanding how temperature affects coral reef fish recruitment success is crucial for assessing impacts of ocean warming on coral reef resilience. We utilized a long-term fish survey dataset along the west coast of Hawai‘i Island to investigate the role of sea surface temperature (SST) in influencing recruitment timing and density. The dataset consisted of 17 years of surveys, with 25 sites annually surveyed in the months of May, July, September and November. We found that peak recruitment, i.e. the maximum number of recruits recorded across all surveys per year, usually occurred during July surveys. For sites where peak recruitment for that year occurred outside July, there were significantly fewer fish recruits than for sites whose peak recruitment occurred in July. In addition, the timing of peak recruitment is influenced by anomalously warm or cool years prior to spawning. The decrease in recruit density outside these times is likely influenced by recruits being exposed to temperatures warmer and cooler than their optimum. Our results show that climate variability is having an impact on the timing of peak recruitment, creating a mismatch between the thermal optimum of developing recruits and the thermal environment they develop in, negatively affecting recruit density in critical coral reef habitats. Altered and reduced recruitment has the potential to disrupt reef community structure and long-term fisheries sustainability in Hawai‘i, with important management implications for coral reefs in the future.

Chen Lifu and Characteristics of Wartime Higher Education in China (1937-1944)

The development and change of wartime higher education significantly impacted China's modern history, and its evolution was closely related to the advocacies and ideas of Chen Lifu, who served as the Minister of Education from 1938 to 1944. This paper first analyzes the merger and relocation of universities with examples such as the Southwest United Nations University and the National Central University, arguing that relocations ensured the continuity and development of higher education in China and nurtured many professional talents. The paper also focuses on the loan and publicly-funded student system, which Chen Lifu adopted mainly to compete for the youth with the Communist Party and the Japanese forces. The system helped a large number of economically disadvantaged students to complete their studies, enhanced young students' sense of responsibility towards the country, stabilized society, and increased the public's trust in the government. Besides, the paper analyzes the military recruitment of young people, briefly describes the recruitment of medical, engineering, and translation students, the peak of military recruitment, and the participation of young expeditionary force in the war, as well as the critical role of these recruitments in the victory of the war.

The influence of freshwater inflow and seascape context on occurrence of juvenile spotted seatrout Cynoscion nebulosus across a temperate estuary.

Spotted seatrout, a popular recreational sport fish in the southeastern United States, are affected by freshwater flow conditions and the availability of estuarine habitat. However, the relative influence of these factors, particularly on early life stages of seatrout, remains uncertain. We used generalized linear models to quantify relationships between the probability of encountering juvenile spotted seatrout during seine surveys and various factors, including freshwater inflow conditions, the availability and richness of estuarine habitats (seagrass, salt marsh, oyster beds) around (400-m radius) fish collection sites (seascape-scale context), as well as distance to the nearest inlet to the Gulf of Mexico (estuary-scale context) across shallow waters (< 1.5 m depth) of Apalachicola Bay, Florida. Modelling results showed a consistent positive correlation between seagrass area and the probability of encountering juvenile seatrout (all four size classes from 15mm-200mm Standard Length (SL)). The probability of encountering the two smallest juvenile seatrout size classes (15-50mm and 51-100mm SL) was also related to freshwater inflow conditions, particularly within a 3-month period prior to and including peak recruitment. Freshwater inflow may affect early life stages by influencing passive transport of eggs and larvae, planktonic food availability, and predation pressure through increases in turbidity. In contrast, encounter probabilities of the two larger size classes (101-150mm and 151-200mm) were unrelated to freshwater inflow. Inflow-related processes may be less important to the larger juveniles as they have typically settled out of the plankton into benthic habitats which provide refuge from predation and abundant benthic food sources which are not as closely tied to freshwater inflow effects. In addition, models revealed that occurrence of the larger juveniles was related to the availability of nearby habitat types such as oyster beds and salt marshes, suggesting that increased mobility as seatrout grow may allow them to use nearby habitat types as additional sources of food and refuge. These results add to a growing body of literature aimed at understanding the influence of freshwater inflow as well as seascape context on vulnerable juvenile life stages of fishery species to provide more informed strategies for freshwater inflow management and habitat conservation.

Recruited macrophages incorporate into the resident cardiac macrophage pool and converge into a common phenotype in the healing infarct, but not in the failing heart exposed to pressure overload

Abstract Introduction Resident macrophages account for 5% of the cells in the healthy heart. In response to cardiac injury, monocytes infiltrate and differentiate into recruited macrophages which function distinctly from the resident subset of primarily embryonic origin. In this work, we aim to identify the extent to which macrophage origin, tissue location and type of cardiac injury determine macrophage phenotypes in ischemic and non-ischemic cardiac injuries over time. Results and methods We use a tamoxifen inducible CX3CR1 Yfp CreER/+ :R26tdT/+ mouse line to visualize and quantify fluxes of resident and recruited macrophages, and their respective localizations within the heart following ischemia and reperfusion (I/R) injury and pressure overload after transversal aortic constriction (TAC), respectively. Interestingly, macrophage numbers peaked during the first week post-surgery in both the local/acute and the global/continuous injury models. Initially, recruited macrophages outnumbered the resident macrophage pool within the infarct area but ultimately reached a 1:1 equilibrium at 4 weeks post I/R injury and at 8 weeks post TAC. In I/R injury, the 1:1 equilibrium established already during the first week in the remote myocardium. Gene expression profiles changed alongside shifts in macrophage ratios. For instance, in the infarct, recruited macrophages showed upregulation of cytokine production and cell chemotaxis pathways at early stage. By 4 weeks post MI their gene expression profiles have converged with those of resident macrophages. Likewise, in the remote myocardium, recruited and resident macrophages assimilated post MI, overexpressing genes associated adaptative immune response activation and cellular homeostasis. Similar to the I/R injury setting, a 1:1 equilibrium of resident and recruited macrophages established in the hypertrophied and dilated hearts within 4 to 8 weeks post TAC surgery. However, transcriptional profiles remained differentially regulated between recruited and resident cardiac macrophages at all time points tested, and distinct from those observed post I/R injury: recruited macrophages behavior changed from a profibrotic into a proliferative phenotype, meanwhile resident macrophages featured prominently in tissue homeostasis. Conclusion Ischemic and non-ischemic, focal and global, acute and chronic cardiac injuries induce a transient peak of monocyte recruitment and macrophage differentiation in and around cardiac lesions which lead to a permanent integration of recruited monocyte-derived macrophages into the pool of tissue resident macrophages – albeit at different paces. The type of injury and macrophage localization within the remodeling tissue determine partial or complete override of ontogenic cell programs.

Timing of deployment does not affect the biodiversity outcomes of ecological enhancement of coastal flood defences in northern Europe

Timing of installation is an important factor when planning the deployment of ecological enhancements to intertidal coastal and marine infrastructure. Such nature-based solutions (NbS) are increasingly used worldwide, so understanding whether the timing of deployment affects colonisation success is crucial to enhance their success and identify any ecological sensitivities that must be taken into consideration during construction. To date, none of the previous marine eco-engineering studies globally have looked specifically at timing. An unexpected COVID19 interruption in retrofitting Ecotiles designed to improve urban marine biodiversity provided a unique window of opportunity to address this research gap. We examined if time of deployment affects the early colonisation (within 18 months) success of eco-engineering enhancements. Thirty concrete tiles (Ecotiles) cast with a novel multi-scale, multi-species textured formliner were deployed on rock armour in three sites along the coast in Edinburgh, Scotland, at two different time periods (early March and late May 2020). After two settlement seasons, the colonisation success of 85% of the studied species did not vary between the times of deployment. Early colonisation success of intertidal species equalised within two settlement seasons of deployment, along with an overall increase in species richness. Crucially, these results also show that summer construction periods designed to reduce impacts on overwintering birds, do not adversely impact intertidal species during their peak (spring-summer) recruitment period in northern Europe. This novel result provides further support for widespread use of eco-engineering to enhance large coastal infrastructure projects and achieve ecological goals in northern Europe. More widely, this work contributes to the understanding of the impact of deployment timing on the success of similar NbS worldwide.

Pelagic connectivity of European sea bass between spawning and nursery grounds

The sea bass stock around the UK (northern stock) has declined rapidly over the past decade, likely due to a combination of both overfishing and low recruitment. Understanding mechanisms that drive the number of young reaching nursery grounds is important for explaining observed recruitment variability and therefore developing effective management strategies. An individual-based model (IBM) has been developed here to investigate factors affecting sea bass settlement on nursery grounds for the northern stock. Simulations considered seven years with varying environmental conditions and year class strength, and outputs were compared to empirical data from monitoring of nursery areas in the UK and Ireland. The IBM includes hydrodynamics to simulate the drift of eggs and larvae, temperature-dependent growth and mortality, and behavior affecting position in the water column. Comparison between the model and ICES assessment abundance of age class zero fish showed similar temporal variability, but with higher recruitment predicted for 2018, and a lower peak recruitment in 1997. The model reproduced general patterns of interannual variability for the Thames estuary, but performed less well for some other regions. Further investigation is needed to understand differences between modelled supply and observations, as these could be due to uncertainties in reproducing the physical environment (e.g., currents, temperature) or biology (e.g., spawning, behavior, mortality), as well as uncertainty in recruitment derived from stock assessments or data collected from nursery grounds. Nevertheless, the model provides a useful demonstration of connectivity between spawning and nursery grounds, showing spawning regions that are likely to have greatest influence on recruitment in different estuaries, and how these may vary interannually. For example, sources from western Channel and Celtic Sea can supply larvae to many areas, leading to connectivity across the Channel and Celtic Sea, and into the Irish Sea. However, other regions may depend on more local areas. For example, with the Solent estuary dependent on sources within the Channel each year. With the temperature-dependence on growth, and therefore duration of the pelagic stage, results show the potential influence of spawning timing, in relation to ocean temperatures, for connectivity between spawning and nursery grounds.

Demographic characteristics and exploitation rate of Dormitator lebretonis (Pisces: Eleotridae: Steindachner, 1870) from four coastal lagoons of Southern Benin, West Africa

Dormitator lebretonis (Pisces: Eleotridae) is the dominant eleotrid in the Benin coastal waters, where this species constitutes an important fisheries component. The current fisheries survey investigates demographic parameters and the exploitation of D. lebretonis from the Benin coastal waters to contribute to species conservation and sustainable use. Individuals of D. lebretonis have been sampled monthly for 18 months at four locations in the Benin coastal waters. Overall, D. lebretonis showed moderate asymptotic length (L∞) ranging between 11.55-12.08 cm. The growth rate (K) ranged between 0.74yr-1 and 3.1yr-1. The species exhibited moderate longevity ranging between 0.968 and 4.054 years. The growth performance index (φ’) varied between 1.994-2.617, indicating that D. lebretonis is a relatively slow-growing eleotrid. Annual mortalities dominate population growth (Z/K&gt;1), and lengths at first capture (3.80≤L50≤5.05cm) indicated that D. lebretonis was exploited at immature stages. Nevertheless, the exploitation rate (E) was under 0.5, showing the stock was underexploited. The species showed two peaks of recruitment, except in Lake Ahémé. Sustainable exploitation of D. lebretonis in the coastal waters requires a holistic management scheme that should include fisheries regulation enforcement, spawning ground protection, ecosystem restoration, and follow-up.

The best of both worlds: mastering nerve regeneration combining biological and nanotechnological tools.

The best of both worlds: mastering nerve regeneration combining biological and nanotechnological tools.

Reproductive cycle and size at maturity of wild mud crab, Scylla tranquebarica(Fabricus, 1798) in Marudu Bay, Sabah

This study was conducted to investigate the reproductive cycle and size at maturity of wild mud crab, Scylla tranquebarica, in the mangrove forest of Marudu Bay. The sampling was conducted for 12-month consecutively with the assistance of local fishermen. Each sampling was carried out for 2 days, and baited crab traps were deployed in the river. During the sampling period, a total of 1459 crab specimens were caught. The different maturation stages of crab can be found throughout the year. The percentage of mature female crabs (Stage III to V) was relatively higher in February (38.5%) and May (50.5%), and lower in March (17.6%) and June (17.4%). A similar trend was observed in the male crab. Recruitment of crabs into the mangrove forest was observed after the breeding season. It was observed through histological observations that when 50% of the crabs were sexually mature, the size at maturity was in the range of 94.0 to 96.1 mm and 97.0 to 99.5 mm carapace width for female and male, respectively. This study suggests that S. tranquebarica breeds throughout the year and shows two peak breeding seasons and recruitment in Marudu Bay. This information can be used as baseline for mud crab fisheries management in Sabah.

Life‐stage‐dependent effects of multiple flood‐associated stressors on a coastal foundational species

AbstractGlobal changes in precipitation patterns have increased the frequency and duration of flooding events. Freshwater inflows into estuaries reduce salinity levels and increase nutrient inputs, which can lead to eutrophication and impaired water quality. Oysters are important ecosystem engineers in coastal environments that are vulnerable to co‐occurring environmental stressors associated with freshwater flooding events. Successful recruitment is necessary to maintain adult oyster populations, but early life stage responses to multiple stressors are not well understood. Flood‐associated stressor conditions were observed near oyster habitats at multiple locations across the northern Gulf of Mexico during peak recruitment months in the spring and summer of 2021. In the laboratory, we examined the interactive effects of acidification, hypoxia, and low salinity on larval and juvenile life stages of the eastern oyster (Crassostrea virginica) to better understand the impact of flooding events on oyster development and survival. Salinity stress in isolation reduced larval growth and settlement, and decreased survival and growth at the juvenile stage. Hypoxia was more stressful to oyster larvae than to juveniles, whereas low pH had negative effects on juvenile growth. There were no synergistic effects of multiple flood‐associated stressors on early oyster life stages and effects were either additive or predicted by the salinity stress response. The negative impacts of flooding disturbances on recruitment processes in benthic populations need to be considered in restoration planning and flood control mitigation strategies as the frequency and intensity of extreme freshwater events continue to rise worldwide.

The recruitment pattern of Macrobrachium species from Igbedi Creek, Bayelsa State, Niger Delta, Nigeria

The recruitment pattern of Macrobrachium species at Igbedi Creek, Bayelsa State, Nigeria, were investigated to show if it can support optimum shrimp catch in the year 2020. The riparian settlements of Ogoubiri, Toruibeni, Amassoma and Otuan were chosen for this research. The result showed that there are three species in the Creek which were Macrobrachium macrobrachion, Macrobrachium vollenhovenii and Macrobrachium felicinum. Juveniles and ovigerous females were observed for all three species. The recruitment model in FiSAT II was utilized and the result showed that the percentage recruitment peak for Macrobrachium macrobrachion was 23.78% in the month of June while Macrobrachium vollenhovenii was 17.40% in the month of July. Recruitment peaks were recorded for both sexes in the months of March to September in all four locations and there was year-round recruitment for the both species. The species Macrobrachium felicinum was captured in the month of November with few catches. Male domination of females for Macrobrachium vollenhovenii and Macrobrachium felicinum were recorded. Therefore, this study recommend that optimum catch can be attained through closed season policies and further research on Macrobrachium species at Igbedi Creek.

Population dynamics and fecundity estimates of Long-spined Black Sea Urchin Diadema savignyi (Audouin, 1890) from the Red Sea, Saudi Arabia

Sea Urchin is not only the crucial keystone species for the coral reef restoration but also it has antimicrobial and anti-cancer activities. This study undertaken to focus on length weight relationship, size fecundity distribution and the estimation of fecundity from the long-spined Sea Urchin, Diadema savignyi at the coastal water of the middle Red Sea, Saudi Arabia. A total of 633 specimen of D. savignyi has been collected from the coastal water of Obhur Creak during the sampling time. In each species, total length (TL) measured as a TW = 11.908 × 0.9995 (R2 = 0.8975) through the linear regression graph and digital slide callipers and, individual body weight estimated by the digital balance. The natural and fishing mortality 2.02/yr and 0.19/yr respectively has documented from study area. The Asymptotic length value (L∞) (cm) were estimated 7.35 where the growth coefficient (K) was 0.67 from the monthly length-frequency numeric data by using FAO FISAT II software for generating and estimating the population parameters and age. However, the recruitment pattern was observed to be increased gradually with the maximum recruitment peak between the months of September and October 2021. Therefore, the estimation of fecundity varied from 49,226 ova (total length 3.1 cm) to 466,133 ova (total length 6.8). As a result, analysis of the relationship between the absolute fecundity (F) and total length (TL), and between the fecundity and drained body weight (DW), revealed a linear regression model with a positive and significant relationship at p < 0.05. This is the first approach to study the detailed population dynamic of the ecologically and economically important tropical long spine sea urchin (D. savignyi) endemic to the region. However, the result so far obtained from this research would greatly be useful towards the understanding of the detailed population structure and growth patterns that will undoubtedly help us to develop captive breeding, seed production, culture protocols, conservation strategies and isolation bioactive compounds of this high-valued species incommensurate with national and international perspectives.

Oyster and Barnacle Recruitment Dynamics on and Near a Natural Reef in China: Implications for Oyster Reef Restoration

Oysters and barnacles are dominant inhabitants of natural and restored oyster reefs around the world, and high areal coverage of barnacles at natural or restored reefs commonly decreases substrate accessibility for oyster settlement. The overall understanding of oyster and barnacle recruitment dynamics provides invaluable information on site selection and strategies employed for oyster reef restoration. This study documented the temporal and spatial patterns of oyster and barnacle recruitment on and near the largest natural intertidal oyster reef (Liyashan) in China during 2019–2020. The oyster Crassostrea sikamea recruitment appeared as a continuous process from June through late November or early December, with the peak in August. Greater recruits of oyster spat occurred on the sheltered inshore at the upstream of the natural oyster reef than on the reef and the nearby open coast (p &amp;lt; 0.05). The barnacle recruitment extended from spring to early winter, with mid-spring and mid-summer peaks. Conversely, higher barnacle recruitment appeared on the natural oyster reef and the nearby open coast than on the sheltered inshore. Across all the monitoring sites, the cumulative recruits of oysters in each of 2019 and 2020 was negatively correlated with those of barnacles (p &amp;lt; 0.05). The inshore sites (SH1 and SH2) with high oyster recruitment and low barnacle recruitment should be recognized as the natural spatfall sites for the natural oyster reef restoration. The separation in the recruitment peak between the oyster and the barnacle indicated that August was the most favorable window for capturing oyster spat through substratum addition to the water around the natural reef.

Contrasting Life Traits of Sympatric Calanus glacialis and C. finmarchicus in a Warming Arctic Revealed by a Year-Round Study in Isfjorden, Svalbard

The calanoid copepod Calanus glacialis dominates the mesozooplankton biomass in the Arctic shelf seas, but its smaller North Atlantic sibling Calanus finmarchicus is expanding northwards and may potentially replace it if the climate continues to warm. Here we studied the population structure, overwintering strategies, gonad maturation and egg production of C. glacialis and C. finmarchicus over a period of 15 consecutive months in a high-Arctic fjord with sub-Arctic ocean climate and no sea ice formation in winter. The relative proportions of C. glacialis and C. finmarchicus varied throughout the study period, but with an overall dominance of C. glacialis. The overwintering population of C. glacialis was dominated by copepodite stage CIV (74%) while C. finmarchicus overwintered mainly as CV (65%), reflecting a primarily two- and one-year life cycle, respectively. Adult males and females of C. glacialis appeared as early as October with a peak during December-January, two months earlier than in C. finmarchicus, with a corresponding one-month earlier peak in recruitment for C. glacialis. While C. glacialis reproduced prior to the bloom with egg production peaking during the bloom, C. finmarchicus started egg laying during the bloom and continued to reproduce throughout the summer. Seasonal changes in the population structure suggest that C. finmarchicus born early in spring are able to develop to CV during summer and overwinter successfully, while offspring born later in the season do most likely not reach the CV overwintering stage. The ability to reproduce early and the flexibility to alter between 1- and 2-year life cycles give C. glacialis an advantage over C. finmarchicus in high-Arctic unpredictable environments with short-pulsed primary production regimes. Our data indicate that C. glacialis and C. finmarchicus occupy similar environmental niches, but different timing in reproduction reduces the competition. If sea temperatures remain within their temperature-tolerance ranges, both C. glacialis and C. finmarchicus seem to benefit from warming due to accelerating growth and higher survival of the recruits as long as C. glacialis has access to a colder refuge by descending to deeper depths.

Recruitment variability and sampling design interact to influence the detectability of protected area effects.

Correctly identifying the effects of a human impact on a system is a persistent challenge in ecology, driven partly by the variable nature of natural systems. This is particularly true in many marine fishery species, which frequently experience large temporal fluctuations in recruitment that produce interannual variations in populations. This variability complicates efforts to maintain stocks at management targets or detect the effects of rebuilding efforts. We address this challenge in the context of no-take marine reserves by exploring how variable larval recruitment could interact with the timing of reserve establishment and choice of sampling design to affect population dynamics and the detectability of reserve effects. To predict population changes in the years following a no-take reserve implementation, we first tested for periodicity in larval recruitment in an important U.S. Pacific coast recreational fishery species (kelp bass, Paralabrax clathratus) and then included that pattern in a population model. We also used this model to determine the detectability of population increases under alternative sampling approaches and minimum age sampled. Kelp bass larval recruitment in the Channel Islands, California, peaked every about six (major) and about two (minor) years. Our model showed that establishing a reserve during a peak or trough enhanced or delayed, respectively, the post-reserve population increases. However, establishing a reserve during a recruitment peak could obscure a failing reserve, that is, a reserve that is unable to secure longer-term metapopulation persistence. Recruitment peaks and troughs also interacted with sampling design to affect the detectability of reserve effects. Designs that compared inside-outside were the most robust to variable recruitment, but failed to capture whether the reserve has improved metapopulation growth. Designs that included a time element (e.g., before-after) are more suited to assessing reserve effectiveness, but were sensitive to recruitment variation and detectability can change year-to-year. Notably, detectability did not always increase monotonically with reserve age; the optimal time for detectability depended on the minimum age of organisms sampled and was greatest when the cohort of a major recruitment peak first appeared in the sampling. We encourage managers to account for variable recruitment when planning monitoring and assessment programs.

Distribution, drivers and population structure of the invasive alien snail Tarebia granifera in the Luvuvhu system, South Africa

AbstractInvasive alien species continue to spread and proliferate in waterways worldwide, but environmental drivers of invasion dynamics lack assessment. Knowledge gaps are pervasive in the Global South, where the frequent heavy human‐modification of rivers provides high opportunity for invasion. In southern Africa, the spatio‐temporal ecology of a widespread and high‐impact invasive alien snail, Tarebia granifera, and its management status is understudied. Here, an ecological assessment was conducted at seven sites around Nandoni Reservoir on the Luvuvhu River in South Africa. The distribution and densities of T. granifera were mapped and the potential drivers of population structure were explored. T. granifera was widespread at sites impacted to varying extents due to anthropogenic activity, with densities exceeding 500 individuals per square meter at the most impacted areas. T. granifera predominantly preferred shallow and sandy environments, being significantly associated with sediment (i.e., chlorophyll‐a, Mn, SOC, SOM) and water (i.e., pH, conductivity, TDS) variables. T. granifera seemed to exhibit two recruitment peaks in November and March, identified via size‐based stock assessment. Sediment parameters (i.e., sediment organic matter, sediment organic carbon, manganese) and water chemistry (i.e., pH, total dissolved solids, conductivity) were found to be important in structuring T. granifera populations, with overall snail densities highest during the summer season. We provide important autecological information and insights on the distribution and extent of the spread of T. granifera. This may help in the development of invasive alien snail management action plans within the region, as well as modelling efforts to predict invasion patterns elsewhere based on environmental characteristics.