HOUSES FATE

Appendicularian houses fate and role in carbon sedimentation and nutrition of zooplankton

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 Obiettivo del progetto (Objective)

'Little is currently known about the mechanisms by which zooplankton could find and locate sinking particles in the marine pelagic environment. However this process is believe to be an important pathway in reducing the downward carbon flux in the ocean and could also be an important food supply for zooplankton organisms or fishes larvae. In pelagic Ocean, appendicularians are important producers of large sinking particles through the continuous secretion of mucous filtering structures named “the house”. However some indications that houses disappear during the sedimentation, the processes and rates of this degradation are nearly unknown. Here I propose a research program to investigate the rates and mechanisms of the predation and degradation of appendicularian houses linked with copepods, eels larvae or microbial activity alone. Specifically, I will address the following three objectives, 1) to identify and quantify the predator behaviour to track and find discarded houses in the water column (visual, mechanic or chemical trail perception). 2) Quantify the degradation rate of appendicularian houses in regards to the different predator types. 3) Quantify the growth rates of these predators with an appendicularian houses diet. These objectives will gives information on 1) the particles encountering rate in the field, 2) the reduction of the downward flux of matter in the ocean and 3) the importance of particles in the nutrition of predators and would give new perspectives for the culture of eels for commercial uses. The research will employ an integrated approach combining behavioural studies, cultures, and incubations experiments. Research proposed here will be one of the first attempts to identify and quantify these processes. The proposed research will increase the scientific excellence of the European research through development of a novel research theme at the host laboratory (DIFRES, Denmark) and initiation of international collaboration in the research field.'

Introduzione (Teaser)

Appendicularians are transparent, filter feeders that live in the pelagic (open sea) zone. This is any body of water not close to the bottom of a lake or ocean, or near the shore.

Descrizione progetto (Article)

Appendicularians are major producers of sinking particles through a very efficient means of food intake and 'disposal'. They are surrounded by a bubble, known as a 'house' of protein and cellulose; it has numerous filters that concentrate the food before it is consumed. As the species grow, the houses are continuously discarded and replaced. The discarded larvacean houses contribute to a large source of organic material descending to the ocean bed, where the sinking particles are taken up by zooplankton.

Although not much is known about how zooplankton groups locate sinking particles, researchers believe the process plays a critical role in reducing downward carbon flux in the marine environment. It also represents an important source of food for zooplankton organisms and fish larvae.

The 'Appendicularian houses fate and role in carbon sedimentation and nutrition of zooplankton' (Houses fate) project received EU funding to investigate how appendicularian houses are fed on and degraded. Researchers used copepods, eel larvae and microbial activity in their studies to better understand the appendicularian houses and their nutritious importance, as well as their impact on the carbon cycle.

One set of experiments showed that the houses shrink drastically after being discarded: after 1 hour, they lose as much as 60;% of their size. In this first hour, the house releases small, visible particles that can alert potential house consumers to its presence. Following this, all that remains visible is the effect of bacterial degradation.

In terms of house consumption, other Houses fate experiments revealed that appendicularian houses are effectively consumed and that the quality of the resulting faecal pellets depends on house density. This highlighted the importance of discarded houses in providing a major source of nutrition for zooplankton.

Team members also observed the behaviour of copepods as related to sinking appendicularian houses so as to determine and characterise the different detection mechanisms used. Copepods were discovered to use chemical clues that can detect sinking houses more than 4;cm away.

Having accomplished all objectives, the project has contributed to furthering research on the role of zooplankton in degradation processes in the ocean. This has implications for further research on toxicity and nutrition processes in the marine environment.