Infauna

An analysis of the organisms present in the interstices of the sandy sea beds (infauna) is a reliable tool for establishing the environmental quality of an area. A total of 32 sediment samples were collected to study the macro-fauna community of the soft sea beds in the test bed area.

A total of 3,201 species from 13 taxonomic groups were counted, corresponding to 237 species. 119 of these 237 species had not been reported in the Canary Islands according to the Canary Island list of Marine Species (algae, fungi, plants and animals) edited by the Ministry of Regional Policy and Environment of the Canary Island Government. The most abundant taxon was the worm Eunice vittata with 348 specimens (11% of total abundance). Other species with significant densities were the worms Aponuphis bilineata (268 specimens, 8%) and Amphicteis gunneri (259 specimens, 8%). 70 species, on the other hand, were only represented by a single specimen.

The most abundant taxonomic group were the worms, accounting for 65.8% of total density. Another important group in terms of abundance were the amphipods with 21.6% of total density. The most poorly-represented taxonomic group on the other hand, were the stomatopoda, with a single specimen.

Furthermore, the AMBI index AMBI (Azti Marine Biotic Index) (Borja et al. 2000) was used to classify the soft sea beds in accordance with the degree of disturbance or pollution, based on the infauna community found in them, thus giving an idea of the health status of the ecosystem.

The AMBI index is based on the proportions of five ecological groups:

  • Group I (GI): Species highly sensitive to organic enriching and only present in conditions without any kind of disturbance (initial state). It includes specialist carnivores and some tubular depositivores.
  • Group II (GII): Species always present in low densities, constant throughout the year. This is the initial, undisturbed state of the ecosystem and they are mainly represented by suspensivores and to a lesser extent by selective carnivores and scavengers.
  • Group III (GIII): Species that tolerate an increase in organic matter in the sediment, present in normal conditions but their populations are favoured by organic enrichment. Represented mainly by surface depositivores.
  • Group IV (GIV): They make up the “second order” of opportunist species, present in unbalanced ecosystems. The group is made up of non-surface depositivores.
  • Group V (GV): These make up the “first order” of opportunist species, typical of highly disturbed ecosystems. They are characterised by depositivore species, which proliferate in sediments with low oxygen concentrations.

The AMBI index is calculated at each of the sediment sampling points by considering the relative abundance of each ecological group and by applying the following formula:

AMBI = {(0 x % GI) + (1,5 x % GII) + (3 x % GIII) + (4,5 x % GIV) + (6 + % GV)}/100

The value of the AMBI index enables us to determine the dominant ecological group, the general status of the community, whether or not there is environmental disturbance and the ecological status of the ecosystem (Borja et al., 2005).

The figure below shows the proportions of each of the groups obtained at each sampling point of the test bed and the corresponding value of the AMBI index. This assessment leads to the conclusion that the test bed environment, with a mean AMBI score of 1.391, is in a good ecological state.

References

  • Borja, Á., J. Franco & V. Pérez. 2000. A marine biotic index to establish the ecological quality of soft-bottom benthos within European estuarine and coastal environments. Marine Pollution Bulletin, 40 (2): 1100-1114.
  • Muxika, I., A. Borja, W. Bonne, 2005. The suitability of the marine biotic index (AMBI) to new impact sources along European coasts. Ecological Indicators, 5: 19-31.