Plankton Distribution Patterns in a Mediterranean Dilution Basin: Amvrakikos Gulf (Ionian Sea, Greece)

Abstract. The present work describes Amvrakikos Gulf (Ionian Sea, Greece) as a dilution basin and provides information concerning the relationships between the hydrology and plankton composition and distribution.
Amvrakikos Gulf is characterized by a differentiated planktonic system which is apparently directly influenced by the input of the rivers located at the northern part of the gulf.     

Influence of sample size on ecological status assessment using marine benthic invertebrate‐based indices

Routine monitoring of the quality status of water bodies demands the best cost‐benefit relation and sample‐size reduction is therefore welcomed. However, great caution is needed because such reduction affects the accuracy and variation of the results. In the present study we tested the influence of sample size (number of replicate samples) on reference condition values and within‐sample ecological quality ratio (EQR) variability of six commonly used ecological indices (taxa richness, Shannon–Wiener diversity, AMBI, Medocc index, Bentix and M‐AMBI). Analysis of soft‐bottom benthic invertebrate data from Slovenian coastal waters showed that sample size influenced the reference condition values of richness/diversity indices (taxa richness and Shannon–Wiener diversity) but not of the sensitivity/tolerance indices (AMBI, Medocc index, Bentix). Increased sample size decreased the within‐sample EQR variability and, concomitantly, increased the accuracy of site ecological status classification for all indices. The size of EQR variability differed depending on the index used. EQR variability of M‐AMBI, an index composed of metrics with different within‐sample EQR variability, was statistically the same as that of the metric with the lowest within‐sample EQR variability. Whether this is a common principle for multimetric indices remains to be confirmed. Based on these results, the use of at least three replicates is suggested to obtain reliable measures of reference condition and EQR for the assessment of ecological status. This level of replication is particularly necessary in areas with high diversity and environmental patchiness, and when richness/diversity measures and indices that include these measures are used.     

Polychaete Communities of Greece: An Ecological Overview

Abstract. Benthic samples were collected from 188 stations distributed over the Aegean and Ionian Seas (Greece, Eastern Mediterranean). Sampled substrata represented a variety of biotopes in soft bottoms with depths ranging from 3 to 380 m. The samples yielded a total of 398 species of polychaetes. Detrended Correspondence Analysis was applied to the whole set of data as well as to three bathymetric groups into which the data was divided. The results showed that in each bathymetric group, different factors determine the spatial distribution of species. Over the whole data set the type of substrata proved to be the major factor, whereas depth is the second most important. Other controlling factors were the substratum type and exposure to hydrodynamism in the shallow group, depth and substratum in the intermediate, and sediment granulometry and depth in the deep one. Diversity, species number and density tended to decrease with depth, while diversity and species number are favoured by coarse material in the sediment.     

A Baseline Study on Benthic Species Distribution in Two Neighbouring Gulfs, With and Without Access to Bottom Trawling

Abstract. An extensive survey of the benthic fauna was carried out at two neighbouring regions of the Aegean Sea, one normally trawled and the other closed to trawlers. Benthic samples were collected from seven areas located away from land-based sources. The faunistic analysis showed that species diversity and abundance was higher in the trawled area compared with the untrawled area, a fact which was attributed to the difference in sediment characteristics between the two areas. A degree of disturbance detected in the trawled area was evidenced by an increase in the number of polychaetes at the expense of other benthic groups and an abundance of some opportunistic species. This could possibly be related to trawling activities. as no other causes of disturbance were found in either area.     

Benthic Communities of the lnfralittoral in the N. Sporades (Aegean Sea): a Variety of Biotopes Encountered and Analysed

Abstract. The infralittoral benthos was studied on three islands of the Northern Sporades in the Aegean Sea. Thirteen stations were sampled on both hard and soft substrata and 408 taxa were identified, some of zoogeographical interest. Multivariate statistical methods such as classification, ordination and Similarilies Terms Analysis were combined with existing ecological information to delineate the various communities present and to point to the indicator species characterising them. The communities were then defined using the indicator species and their affinities to typical biocoenoses. The main factor responsible for the observed distribution proved to be the type of substratum (algal cover or sediment type), which reflects the light and hydrodynamic conditions. The observed bathynietric zonation was similar lo that of the Balearic Islands in the western Mediterranean.