Egestion of non-pellet-bound fecal material from the copepod Acartia tonsa: implication for vertical flux and degradation

Abstract

Only a minor fraction of copepod defecation appears to leave the upper water column as fast-sinking fecal pellets in coastal waters. This study suggests that most egested matter from copepods is retained in the water column because (1) > 50% of fecal matter is released as small, slowsinking particles that are not surrounded by a peritrophic membrane and (2) small fecal pellets sink slowly and are degraded rapidly. The production, appearance and fate of fecal material from the calanoid copepod Acartia tonsa (fed on 2 different phytoplankton species, the cryptophyte Rhodomonas salina and the diatom Skeletonema costatum) was followed in association with the grazing activity of the copepod in a laboratory experiment. For both diets, > 50% of the defecation was released as dispersed small (<10 µm) non-pellet-bound particles. The diatom was less suitable as a food item than the flagellate and led to a 3 times higher rate of grazing and egestion. Nevertheless, specific assimilation and egg production per female were 2 times higher for the Rhodomonas diet versus the Skeletonema diet. As a result, the total egestion comprised 18% of the ingestion of Rhodomonas and 27% of the Skeletonema ingestion. In terms of vertical loss, sinking rates for both types of fecal pellets were ca. 5 m d -1 and, in terms of degradation, ca. 0.5 d -1 (18°C) in the absence of copepods. Transferring these findings to similar neritic conditions suggests that 60% of the fecal pellets from copepods will be recycled within a 15 m deep mixed layer and that > 80% of the total fecal matter can be expected to be retained when the unbound fecal material is also included.

Effect of the silica content of diatom prey on the production, decomposition and sinking of fecal pellets of the copepod &lt;i&gt;Calanus sinicus&lt;/i&gt;

“…In addition, the size of fecal pellets increases as the concentration of the food increases, such that they reach a maximum size when the concentration of food is above the saturation level (Dagg and Walser, 1986;Butler and Dam, 1994). Our results confirmed these previous relationship curve generalized by Olesen et al (2005). 587 Figure 5.…”

“…Fecal pellets produced from a diet of the diatom species presented the slowest rate of degradation when compared with those produced from diets of the nanoflagellate or dinoflagellate species. Similarly, Olesen et al (2005) compared the degradation rate of fecal pellets produced on a diet of the diatom, Skeletonema costatum, or the nanoflagellate, Rhodomonas salina, and reported a similar trend but higher degradation rates than Hansen et al (1996). The relationship between the surface : volume ratio and the degradation rate of fecal pellets was used to explain the variation in the degradation rate of pellets produced with different diets.…”

“…HSi and LSi are high-and low-silica-content diatoms, respectively; high and low prey are high and low prey concentrations, respectively; 48 and 24 h are the incubation periods used for the degradation experiments. The error bars show ±1 standard deviation, and the dashed line shows the relationship curve generalized by Olesen et al (2005).…”

Effect of the heterotrophic dinoflagellate Oxyrrhis marina and the copepod Acartia tonsa on vertical carbon flux in and around thin layers of the phytoflagellate Isochrysis galbana

“…It is therefore reasonable to assume that the DOM released into the thin layers in our experiment was not solely due to sloppy feeding but a result of diffusion of DOC through the peritrophic membrane of fecal material (Jumars et al 1989) as well as possible excretion and accumulation of some primary amines (Miller & Glibert 1998). It may also derive from small particulate material that is egested by copepods but not bound by a peritrophic membrane (Olesen et al 2005), and through coprohexy (Lampitt et al 1990). The notion of high fecal pellet production at the site of feeding is supported by experimental studies that show fecal production rate is highly synchronous with grazing activity (measured by gut fluorescence, Bautista et al 1988).…”

Structural and functional patterns of active bacterial communities during aging of harpacticoid copepod fecal pellets

“…Hence a considerable fraction is voided as fecal pellets (fp) and dissolved organic carbon (DOC) (Smetacek 1980, Jumars et al 1989, Turner 2002, Møller et al 2003, Olesen et al 2005. Copepod fp have a high C:N ratio compared to the original food (Morales 1987).…”