Biology of Acartia tonsa Dana 1849

Acartia tonsa (Figure 1) are pelagic calanoid copepods (Crustacea/Copepoda/ Calanoida/Acartiidae). A. tonsa are distributed worldwide, occurring in the Atlantic, Indian, and Pacific oceans, and the Azov, Baltic, Black, Caspian (a recent invader), and Mediterranean seas. They are euryhaline and eurythermal; and tolerate salinities ranging from 1 ppt to 38 ppt, and temperatures ranging from 0°C to 30°C (Mauchline, 1998). They are neritic, being most commonly found near-shore in 0 to 20 m depths, but have been reported from depths to 600 m. It is the dominant estuarine calanoid copepod in our region of the Gulf of Mexico, being present year-round, but exhibiting seasonal population density fluctuations. A. tonsa reproduces throughout the year in North Florida.

Adults are approximately 1.5 mm in length, and their N1 nauplii are approximately 70 µm in length. Acartia eggs are 70-80 µm in diameter, spherical, covered with short spines, and are slightly heavier than seawater. At 25°C, most eggs hatch to nauplii within 48 h. Nauplii progress through six stages (N1 through N6) to become copepodites, which then progress through six stages (C1 through C6) to become sexually mature adults (C6).

Figure 1. Acartia tonsa

Adult males and females are visually distinguished by conformation of their antennae, urosome, and swimmerets (Figures 2, 3, Sabatini 1990). Males use their antennae to clasp a female to allow them to deposit a spermatophore on the female urosome (Figure 3) for fertilization. Males live shorter lives than the females (Parrish and Wilson 1978, Sazhina 1987) which has an impact on egg viability in maturing batch cultures. Females release an average of 18-50 eggs per brood (Mauchline, 1998) every 5-6 days (Sazhina 1971), and can produce up to 718 eggs in their lifetime (Parrish and Wilson 1978). A. tonsa are broadcast spawners, and do not carry their eggs as some copepods do. This allows for easier egg collection and storage.

Acartia primarily feed on phytoplankton, but also consume ciliates, rotifers, and their own eggs and nauplii (Mauchline, 1998). Consumable prey size ranges from 5 µm to 100 µm (Petipa, 1959). Acartia are typically fed phytoplankton, because of the ease of culturing this food source. Our laboratory uses two species of cryptomonads (Rhodomonas spp.) and some dinoflagellates (Akashiwo, Oxhyrris, and Prorocentrum), and this has worked well. Acartia have been reported to survive on microalgal cultures of Chaetoceros, Isochrysis, and Tetraselmis (Apeitos et al 2004).

Copepod populations were selected from plankton collections done in Apalachee Bay, Florida (29 052’N, 84 026’W). A. tonsa can be collected here by plankton tow any time of the year, but are most common during the warmer months. Adult Acartia were manually selected from plankton concentrate with the aid of a dissecting microscope.

Figure 2. Male and female morphological features.

 

 

 

 

Figure 3. Female (left) and male (right) urosomes.