Ioannis Tzovenis

Optimisation of T-ISO biomass production rich in essential fatty acids: I. Effect of different light regimes on growth and biomass production

T-ISO is a microalgal strain widely used in aquaculture for its favourable lipid composition. In this study, we report on the results of an optimisation scheme for maximal biomass production under three different photoperiods (24:0, 16:08 and 12:12-h L/D) combined with three photon flux densities (PFD, 120, 220 and 460 μmol photons m−2 s−1) at 25 °C. Sampling for growth took place in both the exponential and post-exponential (light-limited only) phase. Results showed that specific growth rate of T-ISO maximised with an increase of the total PFD supplied per day. Under continuous light, cell size of T-ISO (both cell dry weight (CDW) and cell volume) correlated positively to PFD with a further increase when the cells were transiently light-limited in the post-exponential phase. In contrast, cell dry weight under discontinuous light increased only at subsaturating PFD with a significant decrease in the post-exponential phase. Cell size, as volume, did not correlate to CDW under discontinuous light, revealing an intracellular density change particularly for the 16:08-h L/D regimes. As a result, biomass yield and productivity had different patterns for continuous and discontinuous light whereas cell yield and productivity were simply a function of total PFD per day. Biomass productivity under continuous light was inferior than under discontinuous light, although the final yield was maximal compared to those under discontinuous light.

Effect of different light regimes on the docosahexaenoic acid (DHA) content of Isochrysis aff. galbana (clone T-ISO)

The culture of Isochrysis aff. galbana Green (T-ISO) in hatcheries is promoted for its high docosahexaenoic acid (DHA) content which favours the successful rearing of aquatic larvae. In this paper we identified the need for well-defined culture conditions of microalgae if sufficient DHA content is the final goal. Using photoperiods of 24:0 h, 12:12 h, and 16:8 h L/D combined with photon flux densities (PFDs) of 110, 220, and 460μE m-2 s-1, batch cultures of T-ISO were sampled for DHA content in the exponential as well as the post-exponential (light limited) growth phase. The various light regimes resulted in differences of DHA content of T-ISO revealing influences and strong interactions among the three variables studied. For fast and economic production of T-ISO cells rich in DHA it is recommended to harvest batch cultures at the end of the exponential phase using high photon flux densities (PFDs) under 12:12 h L/D cycles. The same regime or lower PFD under 24:0 h L/D seem to be sufficient for a continuous culture optimization scheme. In any case a strict following of culture protocols is very important since there is evidence for coexistence of different clones within the parental cultures leading to different results depending on which one prevails.

Production and Marketing Trends of the Cultured Mediterranean Mussel Mytilus galloprovincialis Lamarck 1819, in Greece

ABSTRACT Bivalve production in Greece pertains to a vast extent of mussel farming and a few other species of fishery products. Mussel farming in Greece covers 375.5 ha primarily located in the northern part of the country. About 523 farms have been licensed since 1976, of which 218 are using the single long-line floating technique for a nominal production capacity of about 100 t/ha and a farming area of 1–2 ha on average. The total annual production (gross pergolari weight) increased to 36,000 t in 2008. Currently, there is a trend for further expansion by licensing new farming sites. Eighty percent of the farmed mussels are exported fresh and intact, primarily to Italy. One major problem seems to be the increasing number of harmful algal bloom incidents during the past decade. The future of the industry depends on the industrialization of production methods and the development of scale to suppress the production cost. Support of product branding and development of a quality scheme would further strengthen the sector.

Optimisation of T-ISO biomass production rich in essential fatty acids: II. Effect of different light regimes on the production of fatty acids

Abstract It is well documented that culture conditions affect the fatty acid content of microalgae. We report in this study the fatty acid profiles and n −3 HUFA productivity of T-ISO, a popular haptophyte in the aquaculture industry, cultured under three photoperiods (24:0, 16:08 and 12:12 h L:D) combined with three photon flux densities (PFD: 120, 220 and 460 μmol photon m −2 s −1 ), at 25 °C. Sampling took place in both the exponential and post-exponential (light-limited) phase. In general, fatty acid proportions were effected by a strong interaction of L:D×PFD resulting in metabolic changes difficult to be modelled. At the 12:12 and 24:0 h L:D the fatty acid pattern can be summarised as PUFA>SAFA>MUFA, while at 16:08 h L:D as SAFA>PUFA>MUFA reflecting a differential acclimation of the strain under light–dark cycles. At the 12:12 h L:D the PUFA content of biomass was significantly higher than at the other photocycles. PUFA content differences were located in the n −3 fraction with the n −6 content being rather constant. The n −3/ n −6 and DHA/EPA ratios under 24:0 h or 12:12 h L:D were optimal according to the literature for fish and shellfish nutrition requirements. In contrast, the 16:08 h L:D regimes, especially at low PFD, produced inadequate ratios. The production of n −3 HUFA in T-ISO is essentially influenced by the total photon flux available per day in a similar manner with growth. The capacity of the strain for storing lipid is limited under the conditions tested; consequently, the fatty acid content follows the biomass yield and productivity pattern. Hence, in the context of aquaculture a light regime of 12:12 h L:D and a PFD within the photolimitation–photoinhibition range offers advantages for the culture of T-ISO. If the high investment could be substantiated, continuous cultures under 24:0 h L:D at the same PFD range could serve as an optimisation basis using advanced photobioreactors.

The Recruitment of the Endangered Fan Mussel Pinna nobilis (Linnaeus, 1758) on the Ropes of a Mediterranean Mussel Long Line Farm

ABSTRACT The fan mussel Pinna nobilis (Linnaeus, 1758) is an endangered bivalve species and is endemic to the Mediterranean Sea. Juvenile animals have been found growing on mussels Mytilus galloprovincialis (Lamarck, 1819) long line aquaculture bounces and ropes within the Maliakos Gulf (Aegean Sea). Animals were sampled from the harvested mussel lines. The results show twelve juvenile P. nobilis per ton of harvested M. galloprovincialis.

Risk Factors Affecting the Profitability of the Mediterranean Mussel (Mytilus galloprovincialis Lamarck 1819) Farming in Greece

ABSTRACT Public support of mussel farming in Greece is an important factor because of its financial viability. The profitability of the activity is seriously reduced in small farms (1–3 ha) as a result of their high production costs; however, small farms represent a major part of the industry. Mussel farming is an extensive activity, with space availability regulated by public administrators via licensing of marine cultivation area property rights. The available space, though, is limited and, consequently, impedes any future expansion, restricting the production capacity of small farms. Nevertheless, the cost of new establishments and the modernization of existing ones (suitable boats, grading equipment, and so on) is affordable only by the larger companies. For small farms, it seems harder to recruit the large labor teams needed to work on a seasonal basis because this is the optimum to effect least operational costs, as shown by sensitivity analyses. In conclusion, for financial sustainability this sector needs to be restructured and organized into larger schemes, such as with producer organizations or cooperatives, to achieve economies of scale.

Spat Settlement of the Smooth Scallop Flexopecten glaber (Linnaeus, 1758) and Variegated Scallop Chlamys varia (Linnaeus, 1758) in Amvrakikos Gulf, Ionian Sea (Northwestern Greece)

ABSTRACT The seasonal variation and spat recruitment pattern of the scallops Flexopecten glaber and Chlamys varia in the protected aquatic ecosystem of the northwestern Amvrakikos Gulf (Natura, 2000) were examined by using a combination of plankton sampling and spat collection techniques during the spring and summer of 2007. The presence of the larvae was reported in all samples from the beginning of May to the end of August. Peak numbers were obtained at the beginning of June and in mid-July. The highest settlement density was recorded at a depth of 8 m below the surface, indicating the most suitable placement for the spat collectors despite the hypoxic bottom layer underneath.