Comparative study on the reproductive biology of the intertidal barnacles, Tetraclita kuroshioensis and Tetraclita japonica formosana (Cirripedia: Thoracica) in the Kuroshio and the East China Sea systems in Taiwan

Taiwan is a large island located in the subtropical to tropical region of West Pacific Ocean and the hydrography is influenced by different ocean systems. The Kuroshio Current flows along the east side of Taiwan and continues northward, which brings warm water to the East coast throughout the whole year. The Northeast coast adjacent to the East China Sea also experiences the warm water from Kuroshio Current during the summer season, whereas at the winter season, the strong northeasterly monsoon weakens the effect of the Kuroshio current at the Northeast coast by bringing cold water southward and lowering the water temperature. In the intertidal, most of the species are invertebrates and the reproductive cycle is very sensitive to the temperature change. The water temperature difference with the seasonal variation in Taiwan can be suitable to examine the influence of temperature changes to coastal organisms. Under such circumstances, it is hypothesized that the reproductive cycles of intertidal species at the Northeast coast and at the East coast of Taiwan can be different.
In this study, we examined the reproductive status and the gonad development of two common barnacles, Tetraclita japonica formosana and Tetraclita kuroshioensis, in the Northeast coast (He-Ping-Dao and Badouzi) and the East coast (Shi-Ti-Ping and Chenggong) in Taiwan from April 2006 to December 2010. The experiment was conducted by macroscopic and histological approaches. The morphological developments of ovaries, testes, seminal vesicles and eggs were first examined and then histologically sectioned to investigate the development of male and female germ cells. The levels of development were classified into ranked categories.
The result showed that during 2006 to 2009, the development of male and female gonads was strongly correlated to water temperature. The testes were mature from April to September at the Northeast coast and from February to November at the East coast. The seminal vesicles were all filled with spermatozoa all year round in all sites. At the Northeast coast, the breeding period was shorter, range from May to September and one to two broods produced per year; whereas at the East coast, the breeding period was longer, range from February to October and two to three broods produced per year. The ovaries were almost mature (with mature oocytes) all year round in both Northeast and East coasts, yet revealed better development in T. kuroshioensis at the East coast than the Northeast coast. It is concluded that in T. kuroshioensis and T. j. formosana, the durations of testes maturation and breeding period were longer at the East coast than the Northeast coast as a result of the influence of temperature.