Effects of food concentration and temperature on development, growth, reproduction and survival of the copepod Pseudodiaptomus euryhalinus

Harmful blooms of nanophytoplankton (2–20 μm) are increasingly common and sometimes severe, but requirements and controls of such blooms (e.g., water quality constraints, requirements for nutrients, and the presence of different guilds of grazers) are poorly understood. Laboratory grazing experiments were conducted to evaluate the potential for top-down control by the copepod Parvocalanus crassirostris on a small harmful algal species (an unidentified chlorophyte Picochlorum, 1–4 μm) and to test the effects of cell sizes on grazing rates. The Picochlorum sp. is a strain isolated from a long-lasting harmful algal bloom in the Indian River Lagoon that reached high densities (>1 × 106 cells ml–1). Experiments contrasted grazing on Picochlorum sp. with grazing on the palatable prymnesiophyte Isochrysis galbana (4–6 μm) in monocultures and mixed cultures. When presented in monocultures, grazing rates on Picochlorum sp. were lower than grazing rates on the palatable alternative. When Picochlorum sp. were presented alongside I. galbana, copepods essentially ceased feeding on the former. In additional experiments, P. crassirostris were fed plastic beads with diameters of 2.0–17.9 μm to control for differences in taste, toxicity, production of mucilage and shape of potential food. Paracalanus crassirostris fed most efficiently on beads with diameters of 7.0–7.9 μm. Results revealed that P. crassirostris can consume Picochlorum sp., but small size and the presence of palatable cells reduces the likelihood of top-down control of blooms of Picochlorum sp.

Section: Discussionmentioning

confidence: 99%

Grazing by the Copepod Parvocalanus crassirostris on Picochlorum sp. at Harmful Bloom Densities and the Role of Particle Size

Jacoby

Johnson

2021

“…In an environment where food is not a limiting factor, the temperature is the main environmental factor regulating the development time of copepods (Ban, 1994;Anzueto-Sánchez et al, 2014), and temperature changes could increase or decrease the hatching time of eggs (Castro-Longoria, 1998;Chinnery & Williams, 2004). Previous investigations indicated that the development time of copepod decreased with increasing temperature (Ozaki & Ikeda, 1997;Chinnery & Williams, 2004), as does the hatching time of B. amoyensis eggs, which shortened progressively as temperature increased at a range of 22°C-30°C.…”

Section: Discussionmentioning

confidence: 99%

Embryo Development and Effects of Temperature, Salinity, and Light Intensity on Egg Hatching of Calanoid Copepod Bestiolina amoyensis (Calanoida: Paracalanidae)

Wang

Wang²,

Wang³

et al. 2022

Bestiolina amoyensis distributes in subtropical inshore waters across the Pacific Ocean, with a relatively long reproductive lifespan and high intrinsic population increase rate compared with other small paracalanid species, which makes it a good candidate to develop culture techniques for hatchery larval rearing. However, the reproductive biology of this subtropical broadcast spawning species is still largely unknown. The present investigation provides the first published data on the embryo development and effects of different light intensities (0, 500, and 1,000 lx), temperatures (16°C, 18°C, 20°C, 22°C, 24°C, 26°C, 28°C, 30°C, 32°C, and 34°C), and salinities (22, 24, 26, 28, 30, 32, and 34 psu) on hatching success rates of B. amoyensis. The same batch of eggs were collected from gravid females to observe their embryonic development and incubated under designed light intensities, temperatures, and salinities. Results showed that the whole embryonic development of B. amoyensis lasted, on average, 6 h and 40 min at 26°C, and egg hatching time of B. amoyensis shortened exponentially with the increasing temperature. The highest egg hatching rate (100%) was recorded from the 0-lx treatment, indicating that the dark condition was favorable for the egg incubation of B. amoyensis. The optimum temperature and salinity range for the hatching success of B. amoyensis was 22°C–30°C (above 94%) and 22–34 psu salinity (above 88%), respectively, indicating that B. amoyensis had wide adaptability to temperature and salinity. Light and too low or high temperature leads to abnormal embryonic development and malformed nauplii. The relatively wide adaptability to temperature and salinity and fast embryo development also suggests that B. amoyensis was a good candidate as live feed for hatchery larval rearing.

“…Mean grazing rates on I. galbana in monocultures ranged from 1.1 × 10 3 to 1.8 × 10 4 cells copepod −1 h −1 , and are similar to rates reported for P. crassirostris feeding on other nanoplankton (Calbet et al, 2000), Tisbe furcata feeding on a flagellated haptophyte and a flagellated cryptophyte of similar size (Abu-Rezq et al, 1997), and Pseudodiaptomus euryhalinus feeding on an Isochrysis sp. (Anzueto-Sánchez et al, 2014). P. crassirostris has been documented to be a suspension feeder, with no evidence of raptorial behavior (McKinnon and Klumpp, 1998).…”

Section: Discussionmentioning

confidence: 99%

High Densities of a Prochlorophyte (Unresolved Species) Inhibit Grazing by the Herbivorous Copepod Parvocalanus crassirostris

Jacoby

Johnson

2021

Harmful algal blooms (HABs) are increasing in frequency and severity, underscoring the importance of understanding potential top-down controls of blooms. In the Indian River Lagoon (IRL), a shallow subtropical estuary, one harmful bloom was co-dominated by an unresolved prochlorophyte in the Family Prochlorothricaceae, which reached densities of > 106 cells ml–1 engendering the term “Superbloom.” Experiments were conducted to evaluate grazing rates and the potential for top-down control by an abundant herbivorous copepod, Parvocalanus crassirostris, on the prochlorophyte. Those grazing rates were lower than the rates on a palatable alternative algal food, Isochrysis galbana, when both algal species were presented in monocultures with identical densities. Grazing on the prochlorophyte decreased or ceased at densities over 4.8 × 105 cells ml–1. When the prochlorophyte and the palatable alternative each comprised half of the total density, both species were consumed, but grazing on I. galbana was reduced compared to the grazing rates in a monoculture of this species, especially at higher cell densities. Copepod mortality was observed in treatments with high concentrations of the prochlorophyte, and these treatments contained mucilage. Experiments simulating viscosities produced by prochlorophyte mucilage yielded results consistent with the original grazing experiments (i.e., copepods showed lower grazing rates and higher mortality rates in higher viscosity treatments). Results reveal potential limitations of top-down controls by this grazer on prochlorophyte blooms and HABs that produce mucilage.