Benthic communities on a sandy Ligurian beach (NW Mediterranean)

Abstract

The different components of the benthic community of a sandy microtidal beach (Arenzano) in Liguria (NW Mediterranean) were investigated during late spring (May) 2002 and. Sampling was carried out in two transects, chosen in order to represent the characteristics of the entire beach and their eventual spatial variations. Each transect included two stations: one placed in the swash zone (SW) and one in the surf zone (SF). Although no significant differences were found in the sediment texture over the 2 years (t-tests p > 0.1 for all the granulometric fractions), notwithstanding an increase in the mean grain size (from 0.8 to 1.1 mm) between the sampling periods, 2002 was characterised by a higher quantity of organic matter (on average 14.4 vs. 3.6 gC m )2 for the sum of proteins, carbohydrates and lipids) and higher bacterial biomass (on average 1.9 vs. 0.9 gC m )2 ). The metazoan assemblages (meiofauna and macrofauna) were also richer (density = 2.9 Â 10 5 vs. 1.0 Â 10 5 ind. m )2 , biomass = 0.09 vs. 0.03 gC m )2 for meiofauna; density = 1988 vs. 739 ind. m )2 , biomass = 0.14 vs. 0.03 gC m )2 for macrofauna) in 2002. A significant quantitative reduction (t-test for proteins, carbohydrates and lipids, at least p = 0.004) in the food supply in 2003 affected the abundance of the metazoans, as confirmed by a multivariate analysis that clearly differentiated the 2 years, and seemed to inhibit their relationships within the benthic food web. The bacterial biomass was always dominant, even under the least favourable trophic conditions, due to the ability of bacteria to adapt to a very harsh environment. Our results suggest that the food supply played an important role in the benthic community structures of the beach during late spring, bacteria being the key organisms within the benthic system. The communities seemed to be bottom-up controlled, while predation seemed to be irrelevant.

Benthic communities along a littoral of the Central Adriatic Sea (Italy)

“…A strong relation between TOM and depth was also reported in a previous study carried out along the nearby coastline of Monte San Bartolo (Covazzi- Harriague and Bittoni 2003). These findings were in accordance with the frequently observed greater retention of sediment-bound organic matter and microorganisms in the finest sediments (Herndl et al 1989;Van Duyl and Kop 1994;Albertelli et al 1999;Covazzi Harriague et al 2006). Both the structure and abundance of meiofaunal and macrofaunal communities resulted as being significantly different between inshore and offshore stations, especially when the interaction of season was considered.…”

“…Predation of the permanent meiofauna over the juvenile macrofauna (the 'meiofaunal bottleneck hypothesis ' Zobrist and Coull 1992) and competition for the food resource (Albertelli et al 1999;Covazzi Harriague et al 2006) are well-known with regard to soft-bottom benthic systems, but no evidence for such interactions was found in this study. The PCA results testing the interaction of the three benthic communities highlighted that most of the stations presented a similar ratio of meiofauna and macrofauna ( Fig.…”

“…It is so evident that the benthic response to changes in environmental conditions (from climate changes to pollution events) can be better understood by taking into account the whole benthic size spectrum (Schwinghamer 1988;Danovaro 2000;Austen and Widdicombe 2006). Nevertheless, to our knowledge, data sets on bacteria, meiofauna and macrofauna have only sporadically been collected in a simultaneous manner in the Mediterranean (Albertelli et al 1999;Covazzi-Harriague et al 2006;Papageorgiou et al 2007) and never in the Adriatic Sea.…”

Ecological studies on the decomposition rate of fish carcasses by benthic organisms in the littoral zone of Lake Constance, Germany

“…Such a negative relationship has been previously found in other studies, where the meiofauna, especially deposit feeders, exerted a grazing pressure on the microbial community, and this pressure was important to the general (global) nutrient cycling (e.g., Montagna and Bauer, 1988;Arndt, 1993;Schmid-Araya and Schmid, 2000). Although other studies argued the opposite, Harriague et al (2006) found that bacteria of the littoral zone in the Mediterranean were not controlled my metazoan predatory pressure.…”

Enzymatic activity and organic substrates on a sandy beach of the Ligurian Sea (NW Mediterranean) influenced by anthropogenic pressure

“…On reflective (sensu Defeo & McLachlan 2005) beaches, especially in areas of intense human activity such as the Ligurian Coast, biological processes are mainly related to microbial activities. It has been observed that bacteria are the key player in the benthic community (Covazzi Harriague et al 2006), though the influence of fungal activity has been observed on the emerged part of the beach . However, in changing environments, where substrate concentrations may vary suddenly, regulatory enzyme expression mechanisms may exhibit a much greater influence on enzymatic activity than bacterial biomass (Rath et al 1993) because enzyme activity response to nutrient variability is more rapid than changes in biomass and species composition (Sala et al 2001).…”