Constantin Koutsikopoulos

Temporal trends and spatial structures of the sea surface temperature in the Bay of Biscay

Abstract A time series spatial grid of sea surface temperature (SST) data provided by the archives of Meteo-France and covering the period 1972–1993 was analysed in order to define both the long-term and periodic (mainly seasonal) components at different locations in the Bay of Biscay. The study confirmed the existence of a long-term increasing trend in the SST, but showed that this trend was not homogeneous over the entire area. It revealed also that the amplitude of the cyclic components (summer-winter differences) is spatially heterogeneous. The south-eastern part of the Bay of Biscay, close to the French—Spanish border, shows the stronger warming trend (a mean increase of 1.4 °C for the period 1972–1993). This trend decreases in the adjacent regions and is not statistically significant in the northern part of the bay and the Celtic Sea. The increasing trend was recorded both in winter and summer periods with the winter slopes being slightly higher. The amplitude of the SST seasonal changes (summer-winter differences) is stronger close to the southern French Atlantic coast in the area off the Gironde estuary. The lowest values were observed in the SW of the bay in the region of intense upwelling processes. Finally, the analysis of the main components of this series provides a simple empirical model describing the time-related changes in the SST. This model could be useful for studies in the field of biological oceanography and in the context of comparative studies. The possible linkage of these observations with changes in the structure of ecosystem in this area is also discussed.

Depth of pupation of the wild olive fruit fly, Bactrocera (Dacus) oleae (Gmel.) (Dipt., Tephritidae), as affected by soil abiotic factors

Abstract:  The influence of four abiotic factors (temperature, soil type, compaction, moisture) on the pupation depth of the wild Bactrocera (Dacus) oleae (Gmel.) larvae was studied using soils sampled in the field. Two temperatures (25 and 12°C), three different soil types (alluvial deposits, soil from decaying of limestone, soil from decaying of flysch), two compaction levels (low and high) and two moisture levels (10 and 50% field capacity) were tested in a factorial experiment with a total of 96 experimental units. Five larvae were placed on the soil surface of each test container and when burrowing was completed pupae were retrieved and pupation depth was recorded. The majority of larvae pupated in the top 3 cm and the mean depth of all units was 1.16 cm. The means differed significantly depending on soil type, moisture, the temperature–soil type interaction and the soil type–moisture interaction. Larvae pupated at a greater depth in limestone than in the other two soils. Depths were greater in soils at 50% field capacity than in those at 10% field capacity. In limestone and flysch the depth was greater at 25°C whereas no differences were found in alluvial soil. Different moisture levels had diverse effects in the three soil types; in alluvial soil and in flysch the increased moisture resulted in greater values but in limestone these were slightly lower. These results can be used in developing non chemical control measures and designing efficient sampling techniques for the insect in the ground.

Otoliths imprinting of sole (Solea solea) from the Bay of Biscay: a tool to discriminate individuals from nursery origins?

Sole nurseries are located in the main bays and estuaries of the Bay of Biscay, where juveniles from the same stock concentrate and constitute temporarily isolated groups. This context being favourable for elemental analyses of juvenile otoliths, this study has been initiated with the aim of obtaining environmental imprints of the main nurseries of origin of juveniles recruiting to the adult stock, and of evaluating the relative contribution of these nurseries to the stock. The objectives were to compare (i) the otolith elemental imprints obtained by sampling juveniles in the Loire and the Gironde nurseries, and (ii) two multi-elemental analysis techniques: laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) and solution-based ICPMS (SB-ICPMS) adapted to small volumes. Depending on the fish origin, differences in Sr and Rb concentrations were shown using LA-ICPMS. Comparisons between the antero-dorsal and postero-ventral sites from where otolith material was ablated also suggested a spatial heterogeneity in otolith composition at least for some metals. From linear discriminant analyses, 73 % and 79 % of individuals (bootstrap estimations) were correctly classified with respect to their origin from the composition of the antero-dorsal and postero-ventral areas, respectively. The SB-ICPMS analysis was more powerful, which resulted in an 89 % rate of correct classification from a 2-variable model (Mg and Cd), whereas a 5-variable model (Li, Mg, Rb, Cd, Th) resulted in a 91 % rate of correct classification (bootstrap estimations). These results confirm that sole juveniles from the main estuaries of the French Atlantic coast could be discriminated by the elemental fingerprints of their otoliths.

The distribution of olive fruit fly captures with McPhail traps within an olive orchard

The spatial distribution of olive fruit flyBactrocera (Dacus) oleae (Gmelin) (Diptera: Tephritidae) field captures with McPhail traps within an experimental orchard was evaluated. Contour maps were constructed to examine the patterns in the 3-year trapping data. Captures varied widely inside the olive orchard, with traps suspended on wild olive trees exhibiting the poorest performance. Favorable microclimate, created by a standing water pool, appeared to be responsible for increased trap captures during the hot summer months. The positive role of the olive tree fruit load is also discussed.

Ovarian atresia in the Mediterranean sardine, Sardina pilchardus sardina

Histological analysis was used to describe and analyse the process of ovarian atresia in sardine ( Sardina pilchardus sardina ) from the central Aegean Sea (eastern Mediterranean). The spawning potential of females in relation to intensity of atresia was evaluated and the rate that the ovary passed from the active to inactive condition was followed in fish collected over an annual cycle. Early postspawning females, defined as those with 100% alpha -atretic oocytes, occurred throughout the spawning period; they had lower gonosomatic and hepatosomatic index, but similar total length compared to reproductively active females.

ELEMENTS OF MATHEMATICAL MODELING OF EVOLUTION IN NUMBER OF A SOLE POPULATION

A spatio-temporal model of the dynamics of a population of soles is presented. The model includes three phases of the life cycle of this species of fishes, starting from the pelagic phase to the adult phase through a recruitment to be in the juvenile phase, depending on the climatic conditions. It also takes into account the migration processes, for larvae towards nurseries, and for adults towards the spawning areas. We used the model to provide an estimate of the probability of arrival of the larvae to the nurseries under the interaction of diffusion and climatic processes.

Summer mesozooplankton distribution in coastal waters of central Greece (eastern Mediterranean). I. Hydrology and group composition

Zooplankton and hydrography of the upper 200 m was studied in coastal and pelagic waters off central Greece eastern Mediterranean) during July 1998. The spatial distribution of the main environmental (temperature, salinity, fluorescence) and zooplankton (abundance, dry-weight, dominant groups) features of the area was delimited over an intense grid of 124 stations. The complex topography of the surveyed area comprised an interesting field for the study of pelagic coastal interaction and its influence on the taxonomic composition of zooplankton. A typical summer thermal stratification was observed over the entire study area. Marked differences were found in surface-salinity between the eastern (Aegean Sea) and the western (Ionian Sea) part of the study area, which was attributed to the presence of less saline waters originating from the Black Sea. A deep fluorescence maximum was present in both coastal and pelagic stations. Zooplankton abundance and biomass showed an inshore-offshore gradient with coastal areas being significantly richer than pelagic areas. The taxonomic composition of zooplankton varied greatly both along the inshore-offshore gradient and among the different semi-enclosed Gulfs. Copepods were the dominant group in the pelagic waters comprising 67 78% in terms of mean relative abundance. In coastal areas, copepods were less important with cladocerans (especially the species Penilia avirostris) being the dominant group (44-51%). Appendicularians and chaetognaths comprised an important component of the zooplankton community over the entire surveyed area with mean relative abundance ranging from 2.5 to 14% and 0.6 to 5.8%, respectively.

Summer mesozooplankton distribution in coastal waters of central Greece (eastern Mediterranean). II. Species assemblages

Mesozooplankton distribution was investigated over an intensive grid of 124 stations in coastal and pelagic waters of central Greece (eastern Mediterranean) during July 1998. The complex topography of the area consisted of various semi-enclosed gulfs as well as open-sea areas and provided excellent fieldwork for determining species assemblages, their relationships to environmental parameters and the distribution and abundance patterns of the copepod species. Three coastal and one pelagic group of stations were revealed by cluster analysis. Inverse analysis of species affinities defined distinct ‘coastal’ and ‘pelagic’ species assemblages. All coastal areas were dominated by a small number of species (e.g. Penilia avirostris , Podon spp., Ctenocalanus vanus , Paracalanus parvus and Centropages typicus ) all belonging to the ‘coastal’ assemblage. Differences among these coastal areas were mainly due to small changes in relative abundance of a common-species list. On the contrary, pelagic stations were characterized by higher species diversity, low dominance and the presence of characteristic epipelagic and mesopelagic species of the Mediterranean Sea (e.g. Calocalanus spp., Haloptilus longicornis , Lucicutia flavicornis , Mecynocera clausi , Farranula rostrata , Mesocalanus tenuicornis and Oncaea mediterranea ). The observed differences in taxonomic composition and abundance of zooplankton were related to the marked differences in salinity values observed between the eastern and western part of the surveyed area. Bathymetry, temperature and fluorescence were also related with the inshore–offshore gradient of the zooplankton community observed in the pelagic areas as well as with the discrimination of the zooplankton communities of the various semi-enclosed gulfs of the region.

A single maturity classification key for five common Mediterranean chaetognath species

A single maturity classification key applied to five common chaetognath species of the eastern Mediterranean is presented. The efficiency of the key was tested using biometrical data: body length (BL), ovary length (OL) and seminal vesicle width (SVW). For each species the key proved easy to use and efficient in the distinction of the maturity stages providing a satisfactory size separation between them.

Spatio-temporal dynamics and management implications of the nightly appearance of Boops boops (Acanthopterygii, Perciformes) juvenile shoals in the anthropogenically modified Mediterranean littoral zone

A remarkable phenomenon of dense Boops boops shoals appearing almost adjacent to the shoreline during nighttime is known to the locals of island communities of the Aegean Sea (eastern Mediterranean). In this work, we investigated this appearance testing the hypotheses that (a) it may occur only in anthropogenically modified locations (as suggested by previous observations), (b) the migration pattern to the littoral is not arbitrary but synchronized to the sunset/sunrise, (c) fish abundance is affected by location, season and/or natural (moon) light fluctuations. Quantitative sampling included visual observations from the coast at five stations in Syros (Cyclades, Greece) from July 2009 to September 2010. Both hypotheses concerning occurrence only in anthropogenically modified locations and timing with sunset/sunrise were confirmed. Fish abundance was modelled using generalized additive models, demonstrating a seasonal pattern and revealing significant differences among sampling stations, but no moon-phase effects. The phenomenon investigated here has implications for fisheries management, as the shoal proximity to the shore renders them prone to illegal harvesting (seasonally at high abundances), aggravating the problem of illegal, unreported and unregulated fishing. Further considerations on the integrated management of the coastal zone arise, especially concerning the effects of habitat structural modification and light pollution.