Biology subjects

Dinh, K. V.

Publications and source records attributed to Dinh, K. V..

6 recordsLinked to original sources

bioRxiv2026

Biochemical Indicators of Atlantification and Diapause Strategy in Arctic Copepods Point to a Decrease in Copepod-mediated Carbon Sequestration

Arctic ecosystems are critically endangered by rising temperatures and changing hydrography, especially the intrusion of increasingly warm water from the Atlantic Ocean known as Atlantification. In addition to housing fragile biodiversity, Arctic copepods and their lipids play a crucial role in cycling carbon by transporting carbon into the deep ocean through their diapausing behaviors. Here, we explored the lipidomes of the Arctic copepod Calanus glacialis, collected from three fjords around Svalbard during November 2022 when C. glacialis are known to be in diapause. These three field sites provide a natural laboratory experiment, as they are influenced by different water masses with varying degrees of Atlantic water, and experience vast differences in sea ice coverage over the year. These environmental differences were clearly reflected in the lipidomic analysis, with stations influenced most by Atlantic Warm Water having the lowest total lipid concentrations and the lowest accumulation of storage lipids necessary for entering diapause. Membrane lipids were a significant proportion of the Svalbard copepod lipidomes, with the highest ratios observed at the Atlantified site. The high membrane lipid and high triacylglycerol concentrations were interpreted as signs of active feeding. This was further corroborated by fatty acid composition analysis, which revealed dietary biomarkers of carnivory at Atlantified sites. The copepods from the site most insulated from Atlantic influence had more than double the amount of storage lipids per individual and fatty acids associated with diatom biomass, indicating assimilation in the spring. Ultimately, the decrease in lipid content observed in association with Atlantification around Svalbard will impact diapause patterns, as Calanus species need 20-30% more WE to successfully complete diapause. In turn, this will impact the magnitude of carbon sequestration through the seasonal lipid pump, not to mention having radiating effects through the Arctic food web where Calanus glacialis plays an important role. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=131 SRC="FIGDIR/small/738257v1_ufig1.gif" ALT="Figure 1"> View larger version (49K): org.highwire.dtl.DTLVardef@131e2org.highwire.dtl.DTLVardef@72071aorg.highwire.dtl.DTLVardef@3059f0org.highwire.dtl.DTLVardef@60a5ea_HPS_FORMAT_FIGEXP M_FIG C_FIG

ecology↗

bioRxiv2026

Feeding and reproduction of a tropical coastal copepod across warming and copper gradients

Tropical coastal ecosystems in Southeast Asia are facing rapid warming and increasing pollution. Shallow coastal waters now frequently exceed 34 {degrees}C, potentially pushing tropical ectotherms beyond their thermal optimum while they are simultaneously exposed to copper (Cu) contamination, especially from aquaculture and shipping activities. However, how warming alters Cu toxicity in dominant tropical zooplankton remains poorly understood. We examined the effects of Cu (0, 10, 20, 30 and 40 {micro}g L-1) and temperature (26, 29, 32 and 35 {degrees}C) across realistic gradients on the calanoid copepod Pseudodiaptomus annandalei, a dominant grazer of coastal plankton communities. Adult survival, cumulative faecal pellet production (as a proxy for energy intake), and cumulative nauplii production were quantified over seven days. No significant effects of temperature or Cu on adult survival were detected, likely reflecting variability among wild-collected individuals. In contrast, temperature was the main driver of feeding and reproductive performance, which peaked at 32 {degrees}C and declined at 35 {degrees}C. Cu exposure alone had no significant effects at 26 - 35 {degrees}C due to high variability in responses. At 32 {degrees}C, cumulative feeding and reproductive responses did not statistically differ among copper concentrations, whereas variability increased at both lower and higher temperatures. At 35 {degrees}C, Cu effects were non-linear, with nauplii production reduced at 30 {micro}g Cu L-1 but highest at 20 {micro}g Cu L-1, while faecal pellet production showed treatment-specific reductions, particularly in non-exposed individuals at 26 {degrees}C and in high Cu treatments at 29 and 35 {degrees}C. These findings indicate that warming can modify contaminant effects in tropical zooplankton and highlight the importance of incorporating realistic thermal regimes and natural population variability into ecological risk assessments under climate change.

ecology↗

bioRxiv2025

Stressed Overwintering Bottleneck Hypothesis: Ocean warming and acidification synergistically disrupt Arctic zooplankton overwintering

Ocean warming (OW), driven by the influx of warm Atlantic water masses, and acidification (OA) are threatening Arctic marine ecosystems. However, their potential synergistic effects are poorly understood, especially during the Polar Night when marine species are particularly vulnerable to stressors. Here, we tested our novel Stressed Overwintering Bottleneck Hypothesis (SOBH): warming will disrupt the overwintering of the keystone pan-Arctic copepod Calanus glacialis, a pivotal secondary producer, by impairing fitness-related traits underpinning survival and reproduction. We exposed C. glacialis to current and projected future OW levels (0 {degrees}C and 4 {degrees}C) and OA levels (pH 8.0 and 7.4-7.3) for 53 days during the mid-Arctic Polar Night. We assessed survival, development, and physiological and molecular mechanisms (oxygen consumption, lipid depletion, the expression of nine targeted genes related to oxidative stress and damage repair, and DNA damage). OW alone did not affect C. glacialis mortality; however, OA increased copepod survival at 0 {degrees}C. Notably, their combined effects (OWA) synergistically doubled mortality, as predicted by SOBH. Warming also accelerated moulting from copepodite stage V to adulthood in December, and increased respiration, exhausted lipid reserves entirely by early March, approximately one to four months before the spring algal bloom, further supporting SOBH. DNA damage and gene expression patterns indicated low investment in maintenance and damage repair. Collectively, these findings reveal hidden mechanisms by which OW and OA synergistically threaten overwintering Calanus copepods by drastically increasing mortality, accelerating moulting, raising metabolic rates, and causing early lipid depletion. These effects generate cross-seasonal phenological mismatches among overwintering survival, energy reserves, reproduction, and primary production. Such stressed overwintering bottlenecks in foundational secondary producers like Calanus copepods provide novel explanations for how OW and OA can constrict Arctic marine food webs. At a broader perspective, SOBH highlights how multiple stressors induced overwintering disruption could reshape pan-Arctic and global biodiversity.

ecology↗

bioRxiv2025

Sea surface freshening can suppress the thermal tipping point of marine copepods

Tipping points govern species distributions, which could be impacted by ocean warming (OW) and sea surface freshening (SSF). Interactions between these stressors may affect tipping points. Also, the accumulation of stress over time (degree day) could condition the reaching of tipping points. Yet, these aspects have never been studied. Here, we hypothesise that SSF reduces the thermal tipping point of Calanus spp., key copepods that play a structuring role in marine food webs. Calanus spp. from the Oslofjord were exposed to a temperature gradient from 8 to 20 {degrees}C and a salinity range from 35 to 10 PSU. We found that the survival of Calanus spp. tipped and decreased above temperatures of 14 - 18 {degrees}C, which are already reached in the surface waters of the Oslofjord during summer months. At 29 PSU, this corresponded to a tipping point of heat accumulation of 28 {degrees}C.d above which survival decreased. Reduced salinity below 29 PSU, prevalent year-round in surface waters, suppressed this tipping point, inducing linear decreases in survival when temperature rises above 8 {degrees}C. Thus, the thermal niche of Calanus spp. will decrease with SSF, impacting whole ecosystems. We provide the first statistical determination of heat accumulation tipping points. We also demonstrate that exposure to a secondary stressor can suppress tipping points to a primary stressor, thereby removing the ability of phenotypic plasticity to buffer negative impacts on fitness. This advances our knowledge of physiological tipping points, which are essential in a world where they are increasingly reached by environmental changes.

ecology↗

bioRxiv2023

Density effects on a tropical copepod Acartia sp.: implications as live feed in aquaculture

Calanoid copepod Acartia species are major live feeds for the early stages of economically important marine fish in hatcheries in Southeast Asian countries. However, rearing Acartia copepods at high densities to increase productivity remains a major challenge. To address the issue, we conducted two experiments on 1) Acartia sp. nauplii (1000, 3000, 6000, 9000, 12000, and 15000 individuals L-1) and 2) adults (1000, 1500, 2000, and 2500 individuals L-1). We assessed key parameters for biomass production: development, survival, and egg production. In general, increased density resulted in longer development time, and lowered survival and egg production, but did not affect the size of adult males and females. Despite survival to adulthood decreasing at higher stocking nauplii densities, the number of surviving adults was highest at a stocking density of 12000 ind L-1. Egg production was very low which may be the result of high egg predation. The total eggs harvested were highest at the lowest adult density. These results are essential for the biomass production of Acartia sp. in central Vietnam.

zoology↗

bioRxiv2022

Direct and delayed synergistic effects of marine heatwaves, metals and food limitation on tropical reef-associated fish larvae

Tropical fish are fast-growing and high energetic-demand organisms, which can be highly vulnerable to long-lasting effects of heat stress and pollution, particularly under food shortages. We tested this by assessing highly complex direct and delayed interactive effects of an extreme temperature (32{degrees}C) from a simulated marine heatwave (MHW), copper (Cu, 0, 100, 150 and 175 {micro}g L-1) and food availability (limited and saturated food) on larvae of a tropical, reef-associated seaperch (Psammoperca waigiensis). Cu, MHW, and food limitation independently reduced survival and growth, partly explained by reduced feeding. The negative effect of Cu on fish survival was more substantial under MHW, particularly under limited food. Delayed interactive effects of Cu, MHW, and food limitation were still lethal to fish larvae during the post-exposure period. These results indicate that reef-associated fish larvae are highly vulnerable to these dominant stressors, impairing their ecological function as predators in the coral reefs. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=101 SRC="FIGDIR/small/481600v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@1bc37aborg.highwire.dtl.DTLVardef@1eaedaeorg.highwire.dtl.DTLVardef@9a409eorg.highwire.dtl.DTLVardef@1087cc6_HPS_FORMAT_FIGEXP M_FIG C_FIG

ecology↗