Population dynamics of calanoid copepods in the subtropical mesohaline Danshuei Estuary (Taiwan) and typhoon effects

Establishing an astaxanthin-rich live feed strain of Pseudodiaptomus annandalei

This study aimed to establish an astaxanthin-rich strain of the calanoid copepod Pseudodiaptomus annandalei, through selective breeding based on RGB (red, green and blue) value, a parameter indicating color intensity. We evaluated the RGB value frequency distributions of the copepod populations, and selected individuals with the highest 10% and the lowest 10% RGB value over six generations. The RGB value, nauplii production, clutch interval and clutch number were assessed, and the genetic gain was calculated across generations (G0-G5). Two strains of copepods were selected and defined as dark body copepod strain (DBS) and light body copepod strain (LBS) at the end of experiment. Results revealed significantly lower RGB values (male: 121.5 ± 14.1; female: 108.8 ± 15) in the G5 DBS population compared to the G0 (male: 163.9 ± 13.1; female: 162.2 ± 14.6), with higher genetic gains of RGB values during G0 to G2. While DBS females exhibited longer clutch intervals in the G3 and G4, there was no significant difference in nauplii production between the two strains across all generations. Significantly higher astaxanthin content was found in the DBS copepods (0.04 μg/ ind.) compared to the LBS copepods (0.01 μg/ ind.) and the non-selective copepods (0.02 μg/ ind.) 20 months post selective breeding, validating the stability of the desired trait in the DBS strain. This study successfully established an astaxanthin-rich strain of P. annandalei, which provides implications for enhancing marine and brackish larviculture production.

Zooplankton Fluctuations in the Surface Waters of the Estuary of a Large Subtropical Urban River

The Danshuei River has a third largest catchment area and third longest in Taiwan. It flows through the capital, Taipei, and more than six million people live within its catchment area. Its estuary is characterized by a highly variable chemical and physical environment that is affected by the interaction of inland freshwater runoff with wastewater, and toward the coast is also influenced by the China Coastal Current and the Kuroshio Current. By collecting zooplankton bimonthly in 2014 from the surface layer (0–2 m depth) at five sites in the estuary, we were able to demonstrate that the composition of the zooplankton, and particularly its copepod fraction, varied significantly among sampling stations and months, thereby revealing seasonal succession. Fourteen higher taxa or other categories of zooplankter were identified, with the following being most common taxa: Decapoda, Copepoda (including Calanoida, Cyclopoida, and Harpacticoida), and “other larvae.” The Copepoda comprised 44 taxa (including eight only identified to genus) belonging to 3 orders, 17 families, and 29 genera, the five most abundant of which were Bestiolina n. sp. (undescribed), Corycaeus spp., Parvocalanus crassirostris, Acartia sp., and Paracalanus parvus. The highest and lowest copepod abundances were recorded in July (2557.88 inds. m–3) and January (1.3 inds. m–3), respectively. Observed changes in abundance of many kinds of copepod appeared to be significantly related to changes in physico-chemical parameters (e.g., salinity, temperature, pH, and dissolved oxygen concentration). Cluster analysis confirmed the existence of distinct copepod communities, each characterized by a preference for a different set of environmental conditions. Our comprehensive literature review of the copepod biodiversity of Taiwan’s major rivers for comparison with similar data compiled for other estuaries in the world, the first time such a review has been compiled, shows that 32 copepod taxa have been recorded from the brackish and freshwater parts of the Danshuei River. They represent 58.2% of the total number of brackish- and freshwater copepod species in Taiwan, and five of them have so far only been recorded in the Danshuei River: the calanoids Acartiella sinensis and Pseudodiaptomus forbesi, the cyclopoids Oithona fragilis and Oithona simplex, and the harpacticoid Tachidius (Tachidius) discipes.

Effects of cyclone Fani on the copepod community of the Ganges River estuary of India

A cyclone temporarily disrupts copepod community structure of an estuary, and during the community rebuilding process, omnivorous copepods dominate. This hypothesis was tested after cyclone Fani affected the Ganges River estuary of India on 5 May 2019. Copepod assemblages and environmental parameters were collected before (25 February 2019), after (24 August 2019) and immediately after (daily between 8 and 14 May 2019) cyclone Fani from three sites of the estuary. Immediately after cyclone Fani, spatial heterogeneity of the estuarine environment was washed away, salinity and temperature levels of the estuary increased, pH level declined, while the total dissolve solids remained constant at high levels of concentration. Copepod diversity and abundance were drastically reduced by cyclone Fani with the exception of the omnivorous Bestiolina similis, which tolerated a wide variability of the environment and dominated the community. Led by small and medium-sized copepods, within days, the community recovered from its initial disruption. Immediately after cyclone Fani, medium-sized omnivorous copepod Acartiella tortaniformis became the second most abundant species replacing the small-sized herbivorous Paracalanus parvus. Changes in species composition and abundance hierarchy observed immediately after cyclone Fani lasted for a few months. The intensity of cyclones is increasing in the Indian Sundarban; therefore, following a cyclone, more severe and prolong disruptions of the copepod community are likely. Institutionalized monitoring of the cyclone-mediated ecological changes of the Ganges River estuary is therefore strongly recommended.

Acute and chronic toxicity of cadmium on the copepod Pseudodiaptomus annandalei: A life history traits approach

We determined the effect of acute and chronic toxicity of cadmium (Cd) on Pseudodiaptomus annandalei, according to their developmental and reproductive stages. Firstly, to estimate the 50% lethal concentration (LC₅₀), acute exposure of nauplii and copepodids to 20, 40, 80, 150, and 300 μg/L of Cd was tested, and the effects of 5 μg/L and 40 μg/L of Cd on copepod developmental rate was done. Female lifespan and number of nauplii produced were compared. Secondly, one generation of copepod was exposed to dissolved (WCd) and dietary (DCd) Cd, and sex-specific Cd uptake and population density were estimated. 96 h LC₅₀ was 40 μg/L Cd for nauplii and 120 μg/L Cd for copepodids. Duration of copepod development was 3.5 days and 5.5 days longer than the control when exposed to 5 μg/L and 40 μg/L of Cd, respectively. Female lifespan in both treatments were 9 and 8 days shorter than in the control, respectively. Total number of nauplii produced per female lifespan was 440 (control), 450 (5 μg/L Cd), and 365 (40 μg/L Cd). Cd uptake in copepods increased from nauplii to adults when exposed to dietary Cd and decreased when exposed to dissolved Cd. Dietary uptake of Cd was significantly higher in males than in females and Cd uptake from water was higher in males than in females, but not statistically significant. The total population of copepods were significantly affected by Cd. The toxic effects of Cd in copepods appear to depend on developmental stage, sex, duration and uptake route.

n-3 PUFA biosynthesis by the copepod Apocyclops royi documented using fatty acid profile analysis and gene expression analysis

The cyclopoid copepod Apocyclops royi (Lindberg 1940) is one of two dominant mesozooplankton species in brackish Taiwanese aquaculture ponds. Periodically low n-3 polyunsaturated fatty acid (PUFA) content in seston could potentially be a limiting factor for zooplankton diversity. Apocyclops royi’s potential ability to biosynthesize n-3 PUFA was investigated through a short-term feeding experiment on four species of microalgae. Furthermore, we analyzed the expression of genes encoding putative fatty acid elongase (ELO) and desaturase (FAD) enzymes in A. royi on long-term diets of the PUFA-poor Dunaliella tertiolecta and the PUFA-rich Isochrysis galbana. The copepods exhibited high contents of docosahexaenoic acid (DHA, C22:6n-3) (>20% of total fatty acid) even when DHA-starved for two generations, and no significant differences were found in absolute DHA content between treatments. Transcripts correlating to the four enzymes Elovl4, Elovl5, Fad Δ5 and Fad Δ6 in the n-3 PUFA biosynthetic pathway were identified. Gene expression analysis revealed a significantly higher expression of two desaturases similar to Fad Δ6 in copepods fed PUFA-lacking algae compared to copepods fed algae with high PUFA content. These findings suggest a highly active n-3 PUFA biosynthesis and capability of DHA production in A. royi when fed low-PUFA diets.

Summary: Here, we demonstrate n-3 PUFA biosynthesis in the copepod Apocyclops royi from Taiwanese aquaculture pond systems using fatty acid profiling and gene expression analysis.

Differences in lethal response between male and female calanoid copepods and life cycle traits to cadmium toxicity

This study determined the effect of cadmium (Cd) toxicity comparatively on two copepods, Eurytemora affinis (Poppe 1880) from a temperate region (Seine Estuary, France) and Pseudodiaptomus annandalei (Sewell 1919) from a subtropical region (Danshuei Estuary, Taiwan), according to their sex and reproductive stages. In addition, the effect of Cd to their life cycle traits was quantified. In the first experiment, both copepod sexes were exposed to 40, 80, 150, 220, and 360 µg/L of Cd and a control cultured in salinity 15, except that the temperature was 18 °C for E. affinis and 26 °C for P. annandalei. This allowed calculating median lethal concentration (LC50) of Cd after 96 h. This was 120.6 µg/L Cd for P. annandalei males which were almost twice as sensitive as P. annandalei females (LC50 = 239.5 µg/L Cd). For E. affinis females, the LC50 was 90.04 µg/L Cd, reflecting a 1.4 times higher sensitivity of females than of males (LC50 = 127.75 µg/L Cd). The males of both species were similarly sensitive; however, the E. affinis females were 2.7 times more sensitive than the P. annandalei females. We also compared the sensitivity of ovigerous females (OVF) and non-ovigerous females (NOF) of both species to Cd. Mortality was higher in NOF than in OVF of both copepod species in both the control and the 40 µg/L Cd treatment. Finally, the total population, fecundity and female morphology of both copepod species were estimated after exposing one generation cycle (nauplius to adult) to 40 μg/L Cd (for E. affinis) and 160 μg/L Cd (for P. annandalei). A significant decrease in cohort production, survival and clutch size but no significant difference in the prosome length of both copepod species exposed to Cd were detected. The ratio of OVF:NOF was high in both copepod species exposed to Cd. Cd toxicity did not significantly affect the M:F sex ratio and % OVF of E. affinis. However, the effect of Cd toxicity in P. annandalei was significant in the M:F sex ratio and was in favor of females and their reproductive activities due to an increase in % OVF. Moreover, there was a significant decrease in total production of P. annandalei due to high mortality in their nauplii and copepodid developmental stages. Toxicity to Cd appears to be affected by multiple factors including sex, reproductive life stage and species. The ecological implication of Cd toxicity on E. affinis and P. annandalei copepod ecology is more related to a skewed sex ratio, low egg production, reduced hatchability and reduced survival that affects the recruitment potential of the copepod nauplii resulting in a decreasing copepod population. Mortality, reproduction and population growth of model species may provide important bio-indicators for environmental risk assessment.