Features of spatial distribution of benthic infauna in a Mediterranean shallow-water bay

Abstract

Abstract. The unique hydrography of the Western Mediterranean Sea does not favour the formation of typical estuaries, although it does favour that of other land-sea systems. However, in Els Alfacs, a shallow-water bay situated in the Ebre Delta (northeast Spain), where there are considerable continental inputs, the distribution patterns of the macrofauna and the meiofauna reflect a hydrographical regime very similar to that of an estuary. During July 1987, 23 stations were sampled in the Alfacs Bay using plastic cores. The distribution pattern of the meiofauna follows a gradient and presents a less marked zonation than the macrofauna. Nevertheless, in both cases the peak densities of both faunal components are spatially separated from the principal site of freshwater inflow. The average density of the macrofauna (10 430 individuals/m 2) and the meiofauna (704 100 individuals/ m 2) occurs in the bay during the period of maximum flow (spring-summer), and as such this bay is one of the most productive areas of the Western Mediterranean.

Habitat use by a large population of <em>Pinna nobilis</em> in shallow waters

“…Although no depth effect was observed on the size distribution of P. nobilis, a greater proportion of individuals (56.7%) had valves oriented towards the dominant winds (Mistral, N-S, and Garbí, SW-NE), suggesting that this could also be an important factor shaping the structure of the population. At the shallower end of the distribution, the abundance of individuals may also be constrained by strong daily and seasonal variations in temperature (Palacin et al 1991) falling above the thermal tolerance of the species at 38°C (Schlieper et al 1960). At the greater depths, the disappearance of P. nobilis coincided with the depth limit of Cymodocea nodosa at 1.3-1.5 m. Seagrass beds have been considered to be the most suitable substrate for P. nobilis, since their rhizomes allow a complex connection between byssus filaments and the sediments (García-March 2005).…”

Polychaetes associated to a Cymodocea nodosa meadow in the Canary Islands: assemblage structure, temporal variability and vertical distribution compared to other Mediterranean seagrass meadows

“…All them agree in pinpointing high diversity and species richness of these ecosystems (Young and Young 1977;Kikuchi 1980;Howard et al 1989). Among the studies on small-sized seagrass beds (like C. nodosa or Ruppia cirrhosa), those made in the Mediterranean are of special relevance to be compared with the present study (True-Schlenz 1965;Giangrande and Gambi 1986;Palacín et al 1991;Lanera and Gambi 1993;Martin et al 1993;Gambi et al 1995Gambi et al , 1998Martin et al 2000).…”

“…The Bay has a central deeper area and a littoral shelf between 0 and 2 m deep. The Bay is mainly characterized by a marine hydrographical regime, but is also influenced by fresh-water inputs occurring during spring and summer (Palacín et al 1991). In absence of strong winds, there is still an exchange between the…”

Short-term pore water ammonium variability coupled to benthic boundary layer dynamics in Alfacs Bay, Spain (Ebro Delta, NW Mediterranean)

“…bioturbation) remain to be assessed. Macrofauna and meiofauna were found in this sediment at lower densities than in other zones of the Bay and were mainly dis- tributed at the surface (Palacin et al 1991(Palacin et al , 1992, probably because of the high sedimentation and low water current at this site (Camp 1995). Pore water profiles like that of March (Fig.…”