Biondo, R.

Bouquegneau, J.-M.

Cardigos, F.

Gobert, S.

Lepoint, G.

Santos, R.S.

Sirjacobs, D.

Tempera, F.

Open Marine Archive

  - 56 - 
STUDY OF THE STRUCTURE, DISTRIBUTION AND DYNAMICS OF CODIUM 
ELISABETHAE POPULATIONS IN THE REEF ECOSYSTEM OF FAIAL ISLAND 
(AZORES), USE OF SUBMARINE IMAGE ANALYSIS 
Sirjacobs D.1,2, F. Tempera2, F. Cardigos2, S. Gobert1, G. Lepoint1, R. Biondo 1, 
R.S. Santos2 and J.-M. Bouquegneau1 
1 Laboratory of Oceanology, Liege University 
B6c,Sart-Tilman 4000 Liege, Belgium 
E-mail: D.Sirjacobs@ulg.ac.be 
2 Department of Oceanography and Fisheries, University of the Azores 
PT- 9901-862 Horta, Azores, Portugal  
 
In the context of the Network Natura 2000, several Sites of Community Interest (SCI) 
were established within the Azores archipelago. In the SCI of Monte-da-Guia (Faial), 
two sites were delimited in order to investigate particularly the links between habitat 
characteristics, population structure, distribution and dynamics of the green alga 
Codium elisabethae. The first site is a large protected rocky seafloor of an ancient 
volcano crater (20m deep) and classified as no-go reserve. It shows very high density 
stands of Codium elisabethae (up to 105ind.m-2), representing the main vegetal 
biomass. At similar depth but distant of about two kilometers, the second site is in a 
more exposed area, where a sparse population (about 13ind.m-2) occupies rocky tables 
and boulders emerging from shallow sandy deposits. These contrasting densities reflect 
different population dynamic equilibrium resulting from the particular environmental 
pressures of each site. A two-year population survey started in August 2003, aiming 
principally at building submarine image mosaics of each site on a seasonal basis. 
Further, a computer assisted detection is run on the images to derive valuable 
information about the Codium elisabethae present. This technique allows to study a 
comparatively large zone regarding to the diving time invested and to focus on the 
particular evolution of well-localized individuals. Thus, seasonal fluctuations of growth 
rate (from 0.5 to 3cm.month-1) and primary production (from 1 to 15kg.m-².month-1) 
could already be described. Further processing will allow to relate these parameters to 
individual size. Various sensors where deployed during a complete year for the 
characterization of the natural physical constraints experimented by the benthos 
(temperature, currents, turbidity, photosynthetic active radiation). Nutrients 
concentrations where quantified both in the water close to sea-bed and in the internal 
volume of sea water isolated by the spherical thallus of Codium elisabethae. This 
confirmed that the lumen of this alga trap and concentrate nutrients, as compared to 
the outer environment. These characteristics are particularly interesting as they show 
how important can be the links between the spatial variations of benthic habitat 
characteristics, the structure and dynamic of the Codium elisabethae populations and 
the role they may play on the local capture and release of nutrients at the scale of this 
oligotrophic reef ecosystem. 
 


Study of the structure, distribution and dynamics of <i>Codium elisabethae</i> populations in the reef ecosystem of Faial Island (Azores), use of submarine image analysis

Study of the structure, distribution and dynamics of <i>Codium elisabethae</i> populations in the reef ecosystem of Faial Island (Azores), use of submarine image analysis

Abstract

Similar works

Full text

Available Versions

Open Marine Archive