Seasonal variability of the red tide-forming heterotrophic dinoflagellate Noctiluca scintillans in the neritic area of Sagami Bay, Japan: its role in the nutrient-environment and aquatic ecosystem

Abstract

Abstract:The role of the heterotrophic dinoflagellate Noctiluca scintillans in affecting the nutrient-environment and aquatic ecosystem was investigated in the neritic area of Sagami Bay, Kanagawa, Japan, from January 2002 to December 2006, based on abundance, intracellular nutrient content, excretion rate and response of phytoplankton (diatoms) to enrichment of nutrients extracted from N. scintillans cells. Seasonal variations in abundance and vertical distribution of N. scintillans were significantly related to the physical structure of the water column, water temperature, chlorophyll a and primary productivity. Intracellular nutrient contents, except for Si(OH) 4 -Si, revealed clear seasonal fluctuations, which were significantly correlated to cell size variations. Thalassiosira rotula increased to higher cell abundances at higher concentrations of nutrients, which were extracted from N. scintillans cells. NH 4 + -N and PO 4 3--P excretion rates were much higher during the first 1-3 h, and decreased rapidly with time. Daily NH 4 + -N and PO 4 3--P supply by N. scintillans excretion was estimated to be on average 34.8% and 55.3%, especially 50.6-85.4% and 80.5-135.8% in April-July (monthly mean), of the daily N and P requirement for primary production, respectively. The large amounts of nutrients regenerated and released by N. scintillans excretion can increase the N and P concentrations in ambient seawater, especially in the upper layer in spring-summer, and consequently affect phytoplankton (diatom) abundance. These may exacerbate eutrophication in these waters by a mutually supportive relationship between phytoplankton and N. scintillans: bottom-up control (phytoplankton-N. scintillans) and nutrient supply by N. scintillans to phytoplankton through excretion.

Influence of Light Availability and Prey Type on the Growth and Photo-Physiological Rates of the Mixotroph Noctiluca scintillans

“…Although it is likely that the endosymbionts benefited from the accumulation of NH 4 + in Noctiluca cells we have to approach this conclusion with caution as we presently do not have the NH 4 + concentrations in the treatment bottles which would have provided us with information as to whether ammonia could have been excreted into the media. Excretion of NH 4 + by blooms of red Noctiluca has been documented (Okaichi and Nishio, 1976;Montani et al, 1998;Ara et al, 2013) which in times of bloom can enhance growth of other phytoplankton (Ara et al, 2013). We have however not observed enhanced nutrients from the large scale blooms of green Noctiluca that we have reported previously in the Arabian Sea (Gomes et al, 2008(Gomes et al, , 2009(Gomes et al, , 2014.…”

Effects of prey of different nutrient quality on elemental nutrient budgets in Noctiluca scintillans

“…Second, Noctiluca , as is the case with many flagellates, is fragile and easily damaged during manipulation. The few attempts to study nutrient excretion rates of Noctiluca have focused on the inorganic nutrients NH 4 + and PO 4 3− , and rates were measured without food 23 , 48 . However, this sort of measurement may only determine the basal metabolic release of a starving grazer.…”

“…It can accumulate and regenerate large amount of dissolved inorganic nutrients (i.e. NH 4 + and PO 4 3− ) 23 – 26 and more complex organic substances 26 , 27 . For example, Ara et al .…”

“…For example, Ara et al . 23 showed that when Noctiluca was abundant during April to July in Sagami Bay, Japan, its intracellular dissolved nutrient contents accounted for an average 49.2–63.7% for NH 4 + and 39.2–63.7% for PO 4 3− of the total nutrient standing stocks respectively in the euphotic zone. Moreover, based on their measurement, daily NH 4 + and PO 4 3− supply by Noctiluca excretion was estimated to account for an average 50.6–85.4% and 80.5–135.8% of the daily N and P requirement for primary production in April–July in Sagami Bay, Japan 23 .…”

“…It has been shown that both the internal dissolved pools of NH 4 + and PO 4 3− , and excretion rates of NH 4 + and PO 4 3− of Noctiluca depend on its nutritional status and growth rate 23 , 28 . Previous studies have verified that consumption of nutrient-limited prey for 3 days, especially P-limited prey, significantly reduced the growth of Noctiluca , even though it was able to feed at a compensatory rate on those nutrient-imbalanced foods (except for P-limited Thalassiosira weissflogii ) 29 .…”