Dioithona oculata (Farran, 1913)

Received, Tuba Terbiyik Kurtb, Online, Published & Version, Final, 2018, Contribution and acclimatization of the swarming tropical copepod Dioithona oculata (Farran, 1913) in a Mediterranean coastal ecosystem, Turkish Journal of Zoology 42 (5), pp. 567-577 : 569-570

3.3. Distribution of Dioithona oculata

D. oculata was first observed at Station 4 in October 2013 (3.1 ind. m –3). Its abundance and frequency increased in the following years ( Figure 5 ). D. oculata was observed only in October of each year. In 2014 and 2015, the species was found in all sampling stations and reached relatively high abundance levels (40 and 12.4 ind. m –3, respectively). The mean abundance values (367.5 ind. m –3) reached their highest level in 2016 ( Figure 5 ). The lowest abundance value was observed at Station 1 in 2015, while the highest values were observed at Stations 3 and 4 (709 and 834.5 ind. m –3, respectively) in 2016 ( Figure 6 ). Spearman correlation analysis revealed that the abundance of D. oculata had a positive correlation with salinity (P <0.01). No association was found with temperature ( Table 3).

The proportional contribution of D. oculata to the zooplankton and copepod communities was low when we first observed it in 2013. Although they increased in 2014 (2.5% and 5.5%, respectively) and 2015 (0.9% and

Secondary axes Sal n ty 39.5

39

38.5

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37.5

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2.5%, respectively), their proportional contribution was limited during that time. It increased considerably in 2016, contributing to a high proportion of the zooplankton and copepod communities (21% and 29.4%, respectively). D. oculata also predominated among copepods at Stations 3 and 4, which were located near the shore, in October 2016 (51.1% and 65.3%, respectively) ( Figure 7 ).

The dominance of female individuals was observed in the population of D. oculata . The ratio of female to male varied from 1 to 18.7 (mean, 5.67). Moreover, copepodits were observed in populations as well as mature individuals. Most copepodit of D. oculata were at stage 5, however a few of the copepodits were at stage 3. The copepodit ratio was quite low, since the mesh size of zooplankton net was not suitable for the nauplii and the former stages of copepodits ( Figure 8 ).

Figures

Figure 5. Annual mean abundance of D. oculata in autumn.

Figure 6. Abundance distribution of D. oculata in the study area in autumn.

Figure 7. The proportion of D. oculata in Copepoda and zooplankton in autumn.

Figure 8. Interannual variations of proportional ratio in female, male, and copepodits in autumn.