Degradation of discarded appendicularian houses by oncaeid copepods

Abstract

We examined the degradation of discarded appendicularian houses due to feeding by oncaeid copepods in surface waters of the Kuroshio region. Vertical distributions of oncaeid copepods and discarded houses were investigated by optical sampling using a video plankton recorder (VPR). In situ VPR observations revealed that oncaeid copepods were commonly associated with discarded houses: the proportion of individuals attached to discarded houses reached saturated values of 25-39% at house concentrations above 2000 houses m 23 , suggesting that feeding by oncaeids was not limited by encounters at house concentrations typically observed in the upper 50 m. Laboratory observations confirmed that oncaeid copepods attached to the surface of discarded houses and ingested both house membranes and adhering particles. Individual feeding rates of the dominant Oncaea species, O. venusta and O. media, determined by measuring fecal pellet production and assimilation efficiency, varied from 0.13 lg C ind. 21 d 21 to 1.3 lg C ind. 21 d 21 (10-37% body C d 21 ).Our results indicate that the oncaeid copepod community consumed up to 10% of house biomass each day in the upper 100 m of the water column, and show that through their close trophic coupling with discarded appendicularian houses, the oncaeids contribute significantly to house degradation in surface waters.

Do functional groups of planktonic copepods differ in their ecological niches?

“…Carnivorous FGs contribute to the top‐down control of other FGs. The detritivores graze upon particulate organic matter, therefore affecting its re‐mineralization and attenuation at depth (Nishibe et al., ).…”

“…They actively transport particles to the deeper ocean through vertical migration (Jónasdóttir, Visser, Richardson, & Heath, ) and produce rapidly sinking faecal pellets after grazing on primary producers in the euphotic layer (Turner, ). They participate in the remineralization of organic matter by feeding on particle aggregates (Alldredge, ; Nishibe et al., ) and are, thus, involved in nutrient cycling and in the biological carbon pump (Turner, ). Additionally, they represent a pivotal link between the basis of the food web and the upper trophic levels (Beaugrand, Brander, Lindley, Souissi, & Reid, ; Beaugrand & Kirby, ).…”

Phytoplankton as Key Mediators of the Biological Carbon Pump: Their Responses to a Changing Climate

“…Discarded appendicularian houses are highly abundant (thousands per m 3 in surface waters) and are microbial hotspots with high concentrations of bacteria, ciliates, flagellates and phytoplankton. These discarded houses are therefore among the most important sources of aggregates directly produced by zooplankton in terms of carbon cycling potential [33].…”

Mesozooplankton structure and functioning in the western tropical South Pacific along the 20° parallel south during the OUTPACE survey (February–April 2015)

“…A relationship between Oncaea and Trichodesmium was previously suggested by Dupuis et al (2016) in the Indian Ocean around Madagascar, based on stable isotope data. They interpreted this association as direct consumption of filaments, but also possibly indirect as Oncaea species have been shown to have a predominantly omnivorous/detritivorous diet (Atkinson, 1998) being able to use their 30 sharp maxillipeds to catch large prey, such as chaetognaths (Go et al, 1998) and appendicularian houses (Nishibe et al, 2015). Thus, the detritus and aggregates associated with Trichodesmium, and even the large trichomes, may benefit this copepod.…”