Temporal Variability in Abundance and Biomass of Ciliates and Copepods in the Eutrophicated Part of Kasˇtela Bay (Middle Adriatic Sea)

Helgol Mar Res (2005) 59: 107–120 DOI 10.1007/s10152-004-0199-x ORIGINAL ARTICLE Natalia Bojanic´Æ Mladen Sˇolic´Æ Nada Krstulovic´ Stefanija Sˇestanovic´Æ Ivona Marasovic´Æ Zˇivana Nincˇevic´ Temporal variability in abundance and biomass of ciliates and copepods in the eutrophicated part of Kasˇtela Bay (Middle Adriatic Sea) Received: 23 February 2004 / Revised: 25 October 2004 / Accepted: 2 November 2004 / Published online: 11 December 2004 Ó Springer-Verlag and AWI 2004 Abstract Seasonal variations in abundance and carbon invertebrates, and fish larvae (Bernard and Rass- biomass of ciliated protozoa and micrometazoa were oulzadegan 1993; James and Hall 1995; Gonza` lez 1999). studied from May 1998 to November 1999 in the eu- Some studies show that ciliates, dinoflagellates and mi- trophicated area of Kasˇ tela Bay (Middle Adriatic Sea). croflagellates larger then 50 lm3 can consume up to Ciliates showed peaks in spring and autumn, primarily 100% of the daily primary production (Beers and due to changes in the abundance and biomass of tin- Stewart 1971; Verity et al. 1993), and also an important tinnines, which participated in total ciliate abundance part of the bacterial production. For example, ciliated and biomass with 40.48 and 60.02%, respectively. The protozoans alone can graze about 20% of the bacterial highest tintinnine density was 4,278 ind. lÀ1, while their production (Sanders et al. 1989;Sˇ olicánd Krstulovic´ average biomass varied from 0.611 to 26.557 lgC lÀ1. 1995). In recent decades, the classic food chain concept Maximal average density and biomass of non-loricates has been replaced by the concept of a complex food web, were 1,430 ind. lÀ1 and 3.925 lgC lÀ1, respectively. The and it has been shown that the relationship between micrometazoa community was dominated by copepod primary producers and primary consumers is not simply nauplii, especially during the summer and autumn. The one way (Azam et al. 1983; Stone and Berman 1993; copepod biomass ranged between 3.47 and 26.75 lgC Legendre and Rassoulzadegan 1995). Metabolic prod- lÀ1 . High abundance and biomass values of the inves- ucts, released during remineralisation processes, increase tigated zooplankton groups point to an important role the primary production (Revelante and Gilmartin 1983), of these organisms in the secondary production in the and zooplankton excretion products and detritus are Bay, indicating that they may be (1) a crucial factor in suitable media for bacterial growth. In addition, the controlling the populations of nano-/pico-phytoplank- short generation time of small zooplankton allows these ton and heterotrophic nanoflagellates, and (2) a signifi- organisms to adapt rapidly to ecosystem changes, sta- cant prey for larger micrometazoans. bilising their communities and preventing energy losses (Heinbokel 1978; Capriulo and Carpenter 1980). In such Keywords Abundance Æ Adriatic Sea Æ Biomass Æ circumstances, ciliates and micrometazoans may act as Ciliated protozoa Æ Micrometazoa important links between the microbial food web and the classic food chain. There are still very few studies in the Adriatic Sea on Introduction temporal changes in abundance and biomass of ciliated protozoans and micrometazoa. Previous studies con- Protozoans and micrometazoans play an important role ducted in Kasˇ tela Bay (Krsˇ inic´1980a, 1982; Bojanic´ in transferring organic matter from bacteria and phy- 2001; Bojanicét al. 2001) have indicated that this area is toplankton to large-dimensional zooplankton, benthic ideal for analysing the impact of eutrophication on the abundance and community structure of ciliated protozoa and micrometazoa. The aim of the present study was Communicated by H.-D. Franke to investigate the composition of the ciliates and mi- N. Bojanic´(&) Æ M. Sˇ olic´Æ N. Krstulovic´Æ S. Sˇ estanovic´ crometazoa assemblages in the eutrophicated part of I. Marasovic´Æ Zˇ . Nincˇ evic´ Kasˇ tela Bay, to estimate ciliate and copepod biomass, Institute of Oceanography and Fisheries, and to evaluate their role in marine food web dynamics. sˇ etalisˇ te Ivana Mesˇ trovicá 63, 21000 Split, Croatia E-mail: [email protected] In addition, relationships between zooplankton com- Tel.: +385-358688 ponents and both abiotic and biotic factors were anal- Fax: +385-358650 ysed. 108 cylinder and sedimented for the following 48 h. The Methods excess volume was reduced to 200 ml. Decanting was carried out using a vacuum pump and curved glass Study area pipette that removed water from the surface (Krsˇ inic´ 1980b). After 24 h, the volume was reduced down to Samples were collected at the station Vranjic in the 20 ml for microscopical studies. Counting and identifi- eastern part of Kasˇ tela Bay (43°31.9¢N, 16°27.2¢E) cation of the species were performed in a glass chamber (Fig. 1). Kasˇ tela Bay is a semi-enclosed shallow system (76·47·6 mm) with ‘Olympus’ inverted microscopes (average depth 23 m) located in the eastern part of the IMTÀ2 and CK40 at 100· and 400· magnification. Middle Adriatic Sea. The most important influx of fresh For a quantitative analysis of non-loricate ciliates, we water is the river Jadro, which discharges into the Bay also used a 100-ml aliquot volume, and counting was near the sampling station. Several submarine springs made at 200· magnification. The organisms were fixed and the brook Pantan, located along the southeastern with formaldehyde in the same way as tintinnines and and northwestern part of the Bay, are of lower signifi- micrometazoans. Formaldehyde was chosen instead of cance. The investigated area of the Bay also receives acid Lugol because it does not stain detritus that can be large quantities of untreated municipal and industrial abundant in the eastern part of Kasˇ tela Bay. Since effluents. An agricultural area extends along the north- formaldehyde causes cell loss of the naked ciliates ern coast, so precipitation waters also carry considerable (Leakey et al. 1994), our data for ciliates may be quantities of nutrients. Geographical characteristics of somewhat underestimated. the Bay, vicinity of land and anthropogenic impact re- The biovolume of non-loricates was calculated from sult in marked oscillations of hydrographic parameters. the aliquot volume of 100 ml by comparing the shape of Water circulation in the Bay is generated mostly by the plasmatic body of each individual organism to one or local wind. Hydrographic properties indicate strong more geometrical bodies (Edler 1979). After measure- continental influences on the eastern part of the bay ment of dimension, cells were divided into four size which shows considerably lower water exchange than categories: (1) biovolume <103 lm3; (2) biovolume 103 – the western one (Zore-Armanda 1980). 104 lm3; (3) biovolume 104–105 lm3; and (4) biovolume >105 lm3 . The biovolume of tintinnines was estimated separately for each species, by measuring linear dimen- Sampling methods and measurement techniques sions of the lorica. The geometrical method was also applied to deter- Microzooplankton samples were collected on a monthly mine the biovolume of copepod nauplii and postnaup- basis from May 1998 to November 1999, at 5-m depth liar copepods. The biovolume of copepod nauplii was intervals, between surface and bottom (17 m), using 5 l calculated according to the modified formula for the Niskin bottles. Organisms were preserved in buffered biovolume of rotifers (Ruttner-Kolisko 1977). The body formaldehyde (final concentration 2.5%). Samples were of almost all copepods may be equated to two geomet- sedimented in the laboratory for 2 days in plastic con- rical forms: cephalothorax to the ellipsoid, and abdomen tainers and were decanted down to a volume of to the cylinder (Shmeleva 1965). For the determination approximately 2 l. The remainder was poured into a of length and diameter, 20–150 organisms were measured microscopically at 200· and 400· magnification with a calibrated ocular micrometer. Unlike the biovo- lumes of ciliates that were calculated from all collected samples, the biovolume of copepods was evaluated by measuring the dimensions of organisms in one sample every month. Conversion factors used to transform these biovo- lumes into carbon biomass values were: for non-loricate ciliates 0.14 pgC lmÀ3 (Putt and Stoecker 1989), for nauplii and postnaupliar copepods 0.08 pgC lmÀ3 (Beers and Stewart 1970; Monti and Fonda Umani 1999), and the formula of 444.5 pgC + (lorica volume in lmÀ3·0.053 pgC) per cell for tintinnines (Verity and Langdon 1984). Samples for bacterial and heterotrophic nanoflagellates (HNF) counts and for chlorophyll a measurements were collected in parallel with microzooplankton sampling. Samples were poured into sterile acid washed glass bottles, fixed with formaldehyde (final concentration 2%). Chlorophyll a content was measured on a Turner Fig. 1 Study area (Kasˇ tela Bay) with the sampling station 112 fluorometer after aceton extraction (Strikland and 109 Parsons 1972). Samples were filtered through a plankton eastern part of Kasˇ tela Bay the water column average net (net mesh diameter 10 lm) and separated in two size temperature values ranged from 10.60°C (February categories: microphytoplankton (>10 lm,) and nano-/ 1999) to 24.00°C (July 1998). The maximal temperature pico-fraction (<10 lm). Enumeration of bacteria and of 27.16°C and the highest vertical gradient of 10.69°C HNF were made by epifluorescence microscopy using occurred in August 1998. the standard acridine orange direct counting technique Throughout the year, salinity ranged from 33.81 to (Hobbie et al. 1977) for bacteria, and proflavine staining 38.18 PSU (Fig. 2b). Both values were observed in technique for HNF (Haas 1982). For biovolume esti- summer 1998, in the surface layer in July and in the mates, length and width of bacterial and HNF cells were bottom layer in August, respectively. Salinity increased measured with an eyepiece graticule (New Portion G12, with depth, while its seasonal changes decreased with Graticules, UK).

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