Dynamics of ciliate abundance, biomass and community composition in an oligotrophic coastal environment (NW Mediterranean)

In temperate coastal zones, episodic meteorological forcing can have a strong impact on the classical seasonal phytoplankton succession. Episodes of continental runoff and wind storms involve nutrient enrichment and turbulence, 2 factors that can promote primary production and alter the planktonic community species composition and size structure. We determined the joint influence of these 2 variables on the osmotrophic plankton of an oligotrophic NW Mediterranean open bay. We used an 8 yr long time series of monthly physical, chemical and biological water-column parameters, and we looked for correlations between these and several meteorological and physical highfrequency time series through cross-correlation analyses. Influence of river runoff in this particular location was found to be very important for phytoplankton dynamics, whereas no immediate response of bacterioplankton was detected. Resuspension events caused by waves had a secondary importance. Cross correlations allowed defining a sequence of responses to these types of forcing, from changes in water turbidity and salinity, to increases in phytoplankton and bacteria abundances through nutrient enrichments. The maximum response of the ecosystem in terms of chlorophyll a concentration lagged nutrient enrichment events by about 1 wk. A more detailed analysis was performed between June 2003 and June 2004, a period characterised by an intense drought in summer and by 6 strong meteorological events afterwards. The increase in the frequency of meteorological events during this period drove the system from heterotrophy to autotrophy. Our data stress the importance of episodic meteorological events in coastal planktonic communities. KEY WORDS: Episodic meteorological forcing · Coastal osmotrophic plankton · Waves · Terrestrial runoff · Sediment resuspension · Nutrients · Time series · NW Mediterranean Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 381: [139][140][141][142][143][144][145][146][147][148][149][150][151][152][153][154][155] 2009 3 different environments, and thus are subjected to the variability in continental, atmospheric and oceanic forcing. In particular, Mediterranean littoral systems offer a good template to study how such episodic types of forcing may alter the dynamics of the osmotrophic plankton away from the typical seasonal pattern, for 2 reasons. First, because the Mediterranean Sea is generally oligotrophic, and thus signals of allochthonous inputs may be more easily detected. Second, because one of the main characteristics of the Mediterranean climate is the irregularity of its temporal pattern of precipitation and storms (e.g. Cebrián et al. 1996).Episodes of rainfall and wind storms are both likely to cause an input of allochthonous material into the Mediterranean coastal zone. On the one hand, sporadic heavy rainfall events often result in catastrophic terrestrial runoff, a general characteristic of the Mediterranean climate (e.g. Cebrián et al. 1996). Such cases of runo...

Section: Methodsmentioning

confidence: 99%

Section: Sequence Of Responsesmentioning

confidence: 99%

Episodic meteorological and nutrient-load events as drivers of coastal planktonic ecosystem dynamics: a time-series analysis

Guadayol¹,

Peters²,

Marrasé³

et al. 2009

“…Thus, Dinophysis acuminata seems, in most cases, to be growth limited by prey concentration and, thus, appears to receive a large fraction of its carbon uptake from photosynthesis; that is unless D. acuminata has alternative food sources. Even if D. acuminata feeds on other ciliates, this would not change the conclusion, because ciliates are typically found at concentrations of 1 to 10 cells ml -1 (Lynn & Montagnes 1991, Nielsen & Kiørboe 1994, Vaqué et al 1997). If, however, D. acuminata feeds on other algae, this may indeed change the conclusion.…”

Section: Ecological Implicationsmentioning

confidence: 99%

Role of food uptake for photosynthesis, growth and survival of the mixotrophic dinoflagellate Dinophysis acuminata

Riisgaard¹,

Hansen²

2009

Dinophysis acuminata is a mixotrophic dinoflagellate frequently causing diarrhetic shellfish poisoning. D. acuminata was isolated from Danish coastal waters and cultivated using the mixotrophic ciliate Mesodinium rubrum as prey. The roles of food uptake and photosynthesis for the growth and survival of D. acuminata were studied. The observed maximum growth rate was ca. 0.45 d -1 at an irradiance of 100 µmol photons m -2 s -1 when supplied with well-fed M. rubrum at concentrations >1000 M. rubrum ml . Apart from the importance of prey concentration, data revealed that ingestion and growth of D. acuminata are, to a certain degree, dependent on the growth rate of its ciliate prey. Photosynthesis was studied in a culture of D. acuminata, initially grown at prey saturation (>1000 M. rubrum cells ml -1) and subsequently allowed to deplete the prey. When the ciliate prey was added, the photosynthetic rate of D. acuminata increased from about 7 to 38 pg C cell -1 h -1 within the first 2 d. When subsequently subjected to starvation, the photosynthetic activity rapidly decreased to a pre-feeding level, and, without a minimum food uptake, D. acuminata was not able to maintain photosynthetic growth. At high prey concentrations, 70 to 90% of the gross C uptake can be explained by food uptake. However, at low prey concentrations, only 0 to 55% of the gross C uptake is likely to be derived from food uptake. The data indicate that in natural environments, D. acuminata may often be food limited, and, in this situation, photosynthesis may not only be a supplement to the basic nutrition, but rather the primary C source.KEY WORDS: Dinophysis acuminata · Dinoflagellate · Mixotrophy · Photosynthesis · Growth · Survival · Mesodinium rubrumResale or republication not permitted without written consent of the publisher

“…In the Western Basin (the less oligotrophic part of the Mediterranean) considerably more effort has been devoted to the study of pelagic ciliates, regarding distribution (Rassoulzadegan 1977, 1979, Bernard & Rassoulzadegan 1994, Dolan & Marrase 1995, Vaque et al 1997 or biological processes (Rassoulzadegan 1982, Sherr et al 1989, Ferrier & Rassoulzadegan 1991, PCrez et al 1997. However, in the Eastern Basin, information is restricted to the coastal waters (Pitta & Giannakourou 1995, Pitta et al 1999 or mainly refers to the distribution of tintinnids only (IQmor & Wood 1975, Dowidar et al 1983, Abboud-Abi Saab 1989.…”

Section: Inter-research 2000mentioning

confidence: 99%

Planktonic ciliates in the oligotrophic Eastern Mediterranean:vertical, spatial distribution and mixotrophy

Pitta¹,

Giannakourou²

2000

Abundance, biomass, vertical distribution, species composition and rnivotrophy of planktonic ciliates were investigated during March 1997 in the oligotrophic Eastern Mediterranean. Six depth layers were sampled in the euphotic zone (0 to 100 m) at 7 stations in the North and 4 in the South Aegean Sea, resulting in a total of 66 samples and 82 ciliate species. Abundance was in general very low (0 to 780 cells I-') except from specific stations in the North Aegean stations (20 to 2040 cells I-'), influenced by the Black Sea Water. Aloricate species dominated the depth-integrated abundance and biomass in both the North and the South. South Aegean stations presented more diverse cihate fauna, uniform distribution down to 100 m and higher values of integrated abundance and biomass than the North Aegean stations. Among North stations, those subjected to the influence of the Black Sea presented very pronounced stratification, with mixotrophs and heterotrophs decreasing sharply below 20 m; at these stations, mixotrophic species of 18 to 30 pm dominated the ciliate community at the surface whereas at the South as well as at the rest of the North stations, nanociliates were the major mivotrophic size class Mixotrophs (20% of abundance in the South, 38% in the North) and nanoc~li-ates (28% of abundance in the South, 44% in the North) were found to be very important components of the community, which indicates that these organisms play also an important role in oligotrophic systems.