Seasonal dynamic and in situ division rates of the dominant Dinophysis species in Punic harbors of Carthage (Gulf of Tunis, South Mediterranean)

Abstract

This study investigates spatio-temporal variations of in situ division rate (μ) of two species of the genus Dinophysis. Based on a postmitotic index approach, estimates of μ from net-haul samples were compared during five daily cell cycles studies in three stations of the Punic harbors of Carthage (Gulf of Tunis). To study the annual cycle of Dinophysis spp., weekly sampling were carried out from March 2008 to June 2010. In addition, sampling over 24 h was conducted on three-cycle studies in late spring and two-cycle studies in autumn, seasons characterized by Dinophysis proliferations. We recorded important abundances of Dinophysis sacculus stein (2.25 × 10(4) cells/l, June 2008) and Dinophysis cf. acuminata (3 × 10(4) cells/l, June 2009). Cellular division was phased in D. sacculus stein and D. cf. acuminata, but the division time, required for the population cohorts to pass from one phase to another, and values of estimated division rates varied between seasons and stations for the same species. D. cf. acuminata exhibit moderate (0.22 day(-1)) to high (0.68 day(-1)) value of μ. In contrast, D. sacculus shows very low μ values (0.02-0.17 day(-1)) in autumn season to moderate values (0.21-0.35 day(-1)) in late spring. The results presented here confirm that the postmitotic index approach allowed estimated of μ at low field depths and concentrations (10(2)-10(3) cells/l).

Field observation of Ornithocercus spp. (Dinophysiales, Dinophyta): reproductive stages and phased cell division (South Atlantic Ocean, Brazil)

“…Previous studies have identified the megacytic zone and the dorsal megacytic bridge as reproductive stages of Dinophysis (REGUERA; GONZALEZ-GIL, 2001;REGUERA et al, 2003;GONZALEZ-GIL, 2007;AISSAOUI et al, 2013). Likewise, based on our findings from the South Atlantic Ocean, these stages are also present in the genus Ornithocercus, whose dorsal megacytic bridge showed a heavily striated pattern.…”

“…at different depths of the water column) changes and vary considerably among dinoflagellate species. Aissaoui et al (2013) observed higher rates in different species of Dinophysis during the fall and summer months, with proliferation occurring between 13°C and 30°C and within a salinity range of 33 to 40, which is suggestive of the broad adaptation of these species to environmental changes throughout the year. Given that our study involved only one season (the dry season), additional research is necessary to determine the potential effects of environmental changes on the reproductive cycle of Ornithocercus spp.…”

“…This is also the case for the genus Ornithocercus, based on our findings in the presence of dividing cells throughout the day (before, during, or after dawn or sunset) in the four species. In a study of Dinophysis acuminata Claparède & Lachmann in the Mediterranean Sea, Aissaoui et al (2013) showed that cell division reached a maximum soon before or after sunrise, which indicates that the first rays of sunlight activated cell division. On the other hand, these same authors observed that for other species of this genus, cell division reached its maximum at several hours after dawn, suggesting that these organisms require higher intensity sunlight.…”

“…Remnants of this bridge can still be found in recently divided cells of Ornithocercus spp., even after dissolution of the megacytic zone and the separation of cells (TAYLOR, 1973). However, this structure can be easily destroyed by sample manipulation, especially during dragging of the net or because of formalin fixation (AISSAOUI et al, 2013). Thus, given that our results are based on field observations, laboratory experiments should be performed to confirm these results and generate further detailed information that is specifically aimed at assessing the time required for the formation of the dorsal megacytic bridge and how long the bridge structure lasts in Ornithocercus spp.…”

Diel Variations in Cell Abundance and Trophic Transfer of Diarrheic Toxins during a Massive Dinophysis Bloom in Southern Brazil

“…Blooms of Dinophysis spp. are usually associated with marked thermohaline stratification of the water column [ 10 , 38 , 39 , 40 ]. The ciliate prey of Dinophysis spp., frequently reported as Mesodinium rubrum , usually benefits from vertical water stratification as well [ 41 , 42 ], although blooms of the ciliate may also occur along horizontal thermohaline gradients in shallow estuaries [ 43 ].…”