The Population Biology of the Larvacean Oikopleura dioica in Enclosed Water Columns

Feeding by a natural population of the chaetognath Sagitta enflata in southern Kaneohe Bay, Hawaii, was studied over 1 yr. Detailed examination of gut contents led to refinements of previous estimates of ration and of impact on prey. S. entflata fed at or near its maximum rate of 10 to 12 prey d-' at food concentrations of over 150 prey 1-'. Specific daily ration in terms of nitrogen was 32 %. Chaetognaths apparently select for prey size, with Oikopleura longicauda and adult copepods preferred over smaller prey. Predation on copepod populations removes a substantial fraction of production.but Oikopleura populations can usually grow more rapidly than S. enflata can consume them.Cannibalism provides a minor part of the diet and usually removes only a small fraction of production.

“…Appendicularians are capable of doubling their biomass daily (Fenaux, 1976) but their growth is episodic (King, 1982). Daily consumption of 0 .…”

Section: Discussionmentioning

confidence: 99%

Selective predation and its impact on prey of Sagitta enflata (Chaetognatha)

Kimmerer¹

1984

“…Appendicularian grazing impact on total particulate material was usually higher than on autotrophic prey (Table 5, Fig. 8), probably because our Coulter Counter measurements underestimated the actual food concentration by not taking into account the bacterial size fraction, which also contributes to the appendicularian diet (King 1982). Since bacteria are included in our gut volume but not in our Coulter Counter measurements, which only covered the 2 to 30 µm size fraction, the proportion of total particulate material grazed by appendicularians is overestimated by our method.…”

Section: Impact Of Appendicularians On Phytoplankton and Suspended Pamentioning

confidence: 95%

In situ feeding physiology and grazing impact of the appendicularian community in temperate waters

López‐Urrutia¹,

Irigoien²,

Acuña³

et al. 2003

The physical and biological factors affecting the abundance and ingestion rates of different appendicularian species were investigated from April 1999 to May 2000 at a coastal station in the English Channel and on a transect of 3 stations across the shelf in the central Cantabrian Sea. Individual gut chlorophyll and gut food volume contents were used to determine the ingestion rates on autotrophic prey and on total particulate material. Body size was the variable explaining most of the variability in gut contents. For most species, over 60% of the ingested material came from nonchlorophyll-containing prey. Appendicularian community grazing impact was higher at the oceanic stations during early spring and autumn, with maximum values close to 10% of the total phytoplankton biomass removed daily. Oikopleura longicauda and O. fusiformis were the species with the highest grazing impact. During the study period, appendicularians removed an average of 8% of the primary production (PP) measured at the only station for which we have concurrent measurements. Our results suggest that the bulk of appendicularian populations resides in the surface mixed layer and that their grazing rates increase with increasing PP. However, the percentage of the PP removed by the appendicularian community decreases with increasing productivity, indicating that their grazing impact is relatively more important under oligotrophic conditions. Appendicularians could account for close to 40% of the total mesozooplankton grazing.KEY WORDS: Appendicularian · Gut content · Feeding · Grazing · Tunicate · Oikopleura · Fritillaria Resale or republication not permitted without written consent of the publisher

“…Appendiculanans have the ability to: (1) filter much larger volumes of water than crustaceans do; (2) increase rapidly in response to food increase; and (3) ingest pico-and nano-sized particles and reject larger particles such as large diatoms and dinoflagellates (e.g. Alldredge & Madin 1982, King 1982. Azam et al (1984) studied the incorporation of tritium labeled leucine in a 10 1 microcosm system into bactena and various zooplankton (appendiculannas and the other 5 categones).…”

Section: Relative Contribution Of Two Pathways To Metazooplankton Promentioning

confidence: 99%

Influence of plankton community structure on the contribution of bacterial production to metazooplankton in a coastal mesocosm

Koshikawa¹,

Harada²,

Watanabe³

et al. 1999

To understand energy passing frorn bacterial production to metazooplankton in an aquatic ecosystem, the relative significance of bacterial and photosynthetic production as carbon sources for metazooplankton was determined in a 14 d coastal mesocosm experiment, using frequent in situ batch incubations with dissolved organic and inorganic '-'C tracers. The contnbution ratio (CR) of bacterial to photosynthetic production as rnetazooplankton food resources fluctuated from 6 to 41 O&, according to successional changes in the plankton community structure in the mesocosm. The lowest CR (6%) occurred when nano-sized autotrophs were highly abundant and appendicularians Oikopleura sp., which are capable of ingesting only pico-to nano-sized particles, increased rapidly. After these small autotrophs disappeared, the CR increased to 30-40%, suggesting that the appendicularians were supported largely by bacterial production at that tlme. When the metazooplankton consisted mainly of copepods. the CR reached about 10% despite the relatively low ratio (ca 15%) of net bacterial community production to photosynthesis; also. the copepods would have been able to exploit bactenal production only through intermedianes such as bactenvorous protists. In this penod with copepods dominant, Gymnodinium mikimotoi was the dominant autotroph and might have been a main source of prey for grazers. However, copepods avoid this dinoflagellate, as often reported. Consequently, not much of the autotrophic production of the dinoflagellate might have been ingested by the copepods. We conducted that nano-sized autotrophs and herbivorous protists were likely to be the main suppliers of photosynthetic production for copepods, as nano-sized bactenvores were the suppliers of bactenal production. These findings suggest that bacterial production and the carbon pathway, 1.e. a microbial loop. are not always the terminus of organic carbon flow in food webs, but can be an integral component of the food pool for metazooplankton in the coastal environment.