Zoë Hilton

Energetics of Byssus Attachment and Feeding in the Green-Lipped Mussel Perna canaliculus

In most animals, significant increases in metabolic rate are due to activity and to feeding (known as apparent specific dynamic action). We determined the energetic costs of activity and feeding in adult green-lipped mussels (Perna canaliculus). Maximal metabolic rate was determined, using closed-chamber respirometry, during byssus re-attachment, during specific dynamic action after 16 h of feeding with Isochrysis galbana, and for the two activities combined, in 23 mussels. Metabolic rate was significantly elevated above rest by about 1.9-fold during byssus attachment (17.1 ± 1.53 μg O2 h–1 g–1 whole mussel wet weight at rest, increased to 27.9 ± 0.91 μg O2 h−1 g−1), and by 2.2-fold after feeding (31.4 ± 1.20 μg O2 h−1 g−1). Combined feeding and byssus attachment led to a still higher metabolic rate (34.0 ± 1.23 μg O2 h−1 g−1). Behavior was also significantly altered, with mussels being almost continuously open during attachment and after feeding (90%–99% of the time); however, the time spent open during the day decreased, reaching a minimum of 52% ± 9% 3 days after feeding, and remained low (67%–82%) for the following 45-day starvation period. Significant diurnal differences were observed, with mussels continuously (92%–100%) open at night. The key findings from this study are that green-lipped musssels (1) have an aerobic scope of approximately 2-fold; (2) reach a higher metabolic rate during feeding than during activity, and the two combined can raise the metabolic rate higher still; (3) display a marked diurnal behavior.

Practical Fertilization Procedure and Embryonic Development of the New Zealand Geoduck Clam (Panopea Zelandica)

Cultivation of the geoduck Panopea zelandica (Quoy & Gaimard, 1835) requires knowledge on embryonic development to produce spat in hatcheries. This study investigated the development of P. zelandica embryos at 15°C and 35 ppt and the optimal sperm:egg ratios for fertilization under hatchery conditions. Panopea zelandica broodstock were induced to spawn by serotonin injection. Sperm and eggs were collected and fertilization was conducted at sperm:egg ratios of: 50:1, 100:1, 500:1, 1000:1 and 10,000:1 over 40 min. The optimal sperm:egg ratio was Panopea zelandica eggs (~80 μm diameter) developed the first and second polar bodies within 15–20 and 50–55 min post-fertilization, respectively. The blastula appeared at ~8 hpf, including the X R and X L cells and the presumptive shell field depression. Gastrulation occurred at 12–18 hpf with organic material apparent at the shell field depression. The mid-stage trochophore, which appeared at around 35 hpf had an apical plate with an apical tuft. The shell field spread to form the periostracum, which expanded and folded into right and left segments covering the late trochophore. The early D-stage veliger appeared at 45 hpf with the soft body being enclosed by two valves and the appearance of the velum. These observations will serve as the basis for future analyses of P. zelandica embryogenesis and for optimization of commercial production of D-veliger larvae.