Extrait du cours Structure and production of the benthic macroinvertebrate community in a shallow lagoon in the Bay of Cadiz

The benthic macroinvertebrate community and human management of the ecosystem
The human use of the saltmarsh area, where the studied lagoon system is located, has converted this intertidal environment to semi-enclosed lagoon sys-tems and, thus, benthic macrofauna that was found in the studied main water body was typical of coastal la-goons. During most of the year, while reared fish spe- cies were growing, this water body remained continu-ously flooded, but with a low rate of water renewal.
At this time a somewhat horizontal biological zonation of the macrobenthic community was observed. How- ever, when the abundance of larvae of fish species suitable for extensive rearing peaked in the external tidal channels (Drake & Arias 1991), the gates of the main water body were opened (12 February to 15 April) to permit the entrance of fish larvae. This con-verted, temporarily, the -90% of main water body to an intertidal zone. In addition, a substantial propor-tion of pelagic macrofaunal larvae, which probably were present in the water column at this time, could  have been removed from the lagoon. A decrease of the benthic macroinvertebrate number of species and density was observed at the emerged areas (Sites A and C), and the interzone differences, previously ob-served, were not evident. On the other hand, since the temporal timing of a disturbance seems to influ- ence the posterior fauna1 succession (Zajac & Whit-latch 1982b), a change in the timing of the gate open-ing, connected to aquaculture practices, could result in a different benthic community structure to that recorded in this study. Furthermore, the use of a part of the studied system for semi-intensive aquaculture,  and the consequent increase of the rate of water re-newal (by pumping), could have contributed to the appearance in the seabream pond (Site C) of species that were abundant in tidal channel outside the stud-ied area. All these facts suggest that the human use of the ecosystem should be considerated as an important factor affecting the macrobenthic community of the studied lagoon.

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Structure and production of the benthic macroinvertebrate community in a shallow lagoon in the Bay of Cadiz (1,39 MO) (Cours PDF)