Complex vertical migration of larvae of the ghost shrimp, Nihonotrypaea harmandi, in inner shelf waters of western Kyushu, Japan

• Published in: Estuarine, coastal and shelf science coastal and shelf science, 2010, Vol.86 (1), p.125-136
• Main Authors: Tamaki, Akio, Mandal, Sumit, Agata, Yoshihiro, Aoki, Ikumi, Suzuki, Toshikazu, Kanehara, Hisao, Aoshima, Takashi, Fukuda, Yasushi, Tsukamoto, Hideshi, Yanagi, Tetsuo
• Format: Article
• Language: English
• Subjects: Adults; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Brackish water ecosystems; Chlorophylls; Coastal; Crustacea; diurnal variations; Fundamental and applied biological sciences. Psychology; Habitats; Invertebrates; Japan; Kyushu; Larvae; Marine; meroplankton; Migration; Photons; selective tidal-stream transport; shelf seas; Synecology; Tachibana Bay; thalassinidean shrimp; Transport; vertical migrations
• ISSN: 0272-7714; 1096-0015
• DOI: 10.1016/j.ecss.2009.11.005

The position of meroplanktonic larvae in the water column with depth-dependent current velocities determines horizontal transport trajectories. For those larvae occurring in inner shelf waters, little is known about how combined diel and tidally-synchronized vertical migration patterns shift ontogenetically. The vertical migration of larvae of Nihonotrypaea harmandi (Decapoda: Thalassinidea: Callianassidae) was investigated in mesotidal, inner shelf waters of western Kyushu, Japan in July–August 2006. The larval sampling at seven depth layers down to 60 m was conducted every 3 h for 36 h in a 68.5-m deep area 10 km off a major coastal adult habitat. Within a 61–65-m deep area 5–7.5 km off the adult habitat, water temperature, salinity, chlorophyll a concentration, and photon flux density were measured, and water currents there were characterized from harmonic analysis of current meter data collected in 2008. The water column was stratified, with pycnocline, chlorophyll a concentration maximum, and 2% of photon flux density at 2 m, recorded at around 22–24 m. The stratified residual currents were detected in their north component, directed offshore and onshore in the upper and lower mixed layers, respectively. More than 87% of larvae occurred between 20 m and 60 m, producing a net onshore transport of approximately 1.3 km d −1. At the sunset flooding tide, all zoeal-stage larvae ascended, which could further promote retention (1.4-km potential onshore transport in 3 h). The actual onshore transport of larvae was detected by observing their occurrence pattern in a shallow embayment area with the adult habitat for 24 h in October 1994. However, ontogenetic differences in the vertical migration pattern in inner shelf waters were also apparent, with the maximum mean positions of zoeae deepening with increasing stages. Zoeae I and II performed a reverse diel migration, with their minimum and maximum depths being reached around noon and midnight, respectively. Zoeae IV and V descended continuously. Zoeae III had behaviors that were intermediate to those of the earlier- and later-stage zoeae. Postlarvae underwent a normal diel migration (nocturnal ascent) regardless of tides, with the deepest position (below 60 m and/or on the bottom) during the day. These findings give a new perspective towards how complex vertical migration patterns in meroplanktonic larvae enable their retention in inner shelf waters before the final entry of postlarvae into their natal populat