Distribution of Thaliacea in SW Taiwan coastal water in 1997, with special reference to Doliolum denticulatum, Thalia democratica and T. orientalis

Abstract

Diel vertical migration of Thaliacea was monitored during different seasonal cruises in 1997 in the southwestern waters of Taiwan using samples collected by multiple plankton sampling nets and a 1 m plankton net. Overall, Doliolum denticulatum, Thalia democratica and T. orientalis were the 3 most dominant species in all seasons, and contributed ≥ 93% of the numerical total of Thaliacea. These species exhibited about a 2 times higher abundance at night than during the day, if all the data were integrated. In the seasonal multiple net samples, D. denticulatum and T. democratica exhibited an alternation between sexual and asexual reproduction between different sampling seasons, while aggregate zooids of T. orientalis, when compared with solitary zooids, dominated in all seasons and apparently increased from July to December. Different stages of these dominant species had different preferences for water depth in different seasons, suggesting that the vertical distribution of these species might be related to reproduction or food. The abundances of different stages of these thaliaceans were correlated with temperature and salinity. The time-series samples of surface water showed that species richness and abundance of these species varied seasonally, but was always greater at night than during the day. KEY WORDS: Diel vertical migration · DVM · Thaliacea · Season · Taiwan · Western Pacific Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 292: [181][182][183][184][185][186][187][188][189][190][191][192][193] 2005 ported 8 unnamed species from their seasonal samplings in the waters around the Nansha (Spratly) Islands in the South China Sea. He et al. (1988) studied zooplankton in the coastal upwelling area of Zhejiang, China, and found that up to 16% of the total wet weight biomass of tunicates, primarily Thalia democratica, Doliolum denticulatum and Dolioletta gegenbauri, was composed of plankton. They are distributed unevenly, increase clearly in the frontal areas, and are negatively correlated with the abundance of copepods and euphausiids. Tsuda & Nemoto (1992) reported 5 species of pelagic salps; T. democratica, Salpa fusiformis, Traustedtia multitentaculata, Cyclosalpa bakeri and Ritteriella reteacta accounted for 47% of the wet weight of zooplankton in the upper 200 m of a Kuroshio warm-core ring in summer 1987. They found that all salps appeared mainly in the surface mixed layer (0 to 20 m), with the exception of S. fusiformis, which was most abundant from 50 to 75 m. Fu et al. (1995) found only 1 thaliacean species, Cyclosalpa pinnata, with an abundance <1 ind. m -3 in zooplankton samples collected from the Pearl River estuary, southern China between June 1991 and March 1992. Among these studies, 2 were carried out in coastal areas (He et al. 1988, Fu et al. 1995, while others were concerned with salps in the open ocean or over continental slope. Relatively few of these studies discussed the DVM of salps and even fewer studies have dealt with different...

Long-term time-series study of salp population dynamics in the Sargasso Sea

“…This is supported by both 'normal' and reverse T. democratica DVM on different sampling days during individual blooms in both 1996 and 2011. Other studies in the Agulhas Bank (Gibbons 1997), off SW Taiwan (Tew & Lo 2005), and in the Kuroshio Current (Tsuda & Nemoto 1992) found that T. democratica did not exhibit DVM and generally stayed within the upper 200 m. Thus, we conclude that the diel differences we detected in T. democratica were likely due to bloom patchiness and that T. democratica likely does not undergo significant DVM.…”

“…m −3 , which is comparable to a S. fusiformis maximum of 1.6 ind. m −3 in coastal Taiwan (Tew & Lo 2005) and 2 ind. m −3 in the Humboldt Current (González et al 2000).…”

Environmental drivers of salp Thalia democratica population dynamics from in situ observations

“…S1g-j in the Supplement). These findings are in agreement with other studies that found populations mostly dominated by females in autumn and winter samples (Heron & Benham 1985, Tew & Lo 2005. Interestingly Heron & Benham (1985) also observed that blastozooids were not reproducing, although they concluded that, in the typical situation for population latency (what they called 'overwintering'), oozooids arrested their growth while retaining their chains until the onset of favourable conditions.…”

Thaliacean distribution and abundance in the northern part of the Levantine Sea (Crete and Cyprus) during the eastern Mediterranean climatic transient, and a comparison with the western Mediterranean basin

“…Dives, for example, showed a doliolid abundance decreasing by two orders of magnitude over a vertical distance of only 2 m (Paffenhöfer et al 1991). However, time-series suggest that the depth where reproduction takes place and thaliacean stages are distributed seasonally, may be related to environmental variables such as temperature, salinity and food (Licandro et al 2006), depending on species (Paffenhöfer et al 1995;Tew and Lo 2005). But the coupling may be subject to environmental disturbance as examplified by the conspicuous mesopelagic findings of thaliaceans at site C (see above).…”