Abstract: In many harpacticoid species, adult males engage in precopulatory mate guarding. We investigated male mate preference in Phyllopodopsyllus sp. by surveying mate guarding in populations from Otsuchi Bay, north-eastern Japan. Adult males were found clasping other individuals throughout the seasons. They generally clasped fifth-and fourth-stage copepodite females. Third-stage copepodites were also occasionally grasped, while coupling with an adult female or a copepodite male was very rare. Statistical analyses suggest that males do not clasp cope podites at all stages randomly, but rather guard juveniles at the third and later stages of development. However, they do not show a clear preference for any one of the three copepodite stages(third-, fourth-, and fifth-stage)that they select. Overall, we documented a very low frequency of pairing, which suggests that males of this species spend much more time feeding or searching for better mates than guarding juveniles until their final molt.
Abstract: A high abundance of Alexandrium spp. resting cysts occur in the fecal pellets of macrobenthic organisms in Hiroshima Bay. However, whether cysts enclosed within fecal pellets of macrobenthic organisms are able to germinate remains unclear. Therefore, cysts enclosed in fecal pellets were incubated for 29 days under two light intensities, sufficient light intensity for germination and near bottom light intensity at 24 m depth in Kure Bay, 50μmol photons/m2/s and 0.28μmol photons/m2/s, respectively. Subsequently, the germination frequency of cysts and the number of remaining cysts in the wells of microplates in each culture condition were compared. It was found that at 0.28μmol photons/m2/s the cysts remaining enclosed in the fecal pellets were mostly unable to germinate. For cysts extracted from the fecal pellets, 27% of the total cysts were not able to germinate at a light intensity of 50μmol photons/m2/s, and 75% at 0.28μmol photons/m2/s. Accordingly, at sites of similar depth to Kure Bay, it is suggested that resting cysts which are ingested and excreted in fecal pellets by macrobenthic organisms largely lose the ability to germinate.
Abstract: A capitelid small polychaete, Capitella sp. I, is a head-side down deposit feeder, which often occurs densely in organically enriched sediment. In this study, we observed burrowing and feeding behaviors of this species, and conducted laboratory experiments, examining the impact of reworking activities of the worms on the physics and chemistry of the organically enriched sediment. The laboratory experiments revealed that the worms fed not only the subsurface sediment but also the surface sediment selectively. The burrowing and feeding activities of the worms in the sediment were activated by the addition of organic matter on the sediment surface. The reworking activities of the worms include burrowing into the sediment, spouting the subsurface layers of the sediment onto the sediment surface, feeding on the sediment and excreting the sediment as fecal pellets on the sediment surface. The amount of spouted sediment on the sediment surface caused by burrowing activities was approximately 2.6 times larger than the amount of sediment reworked by excretion of fecal pellets. We estimated that approximately 162gDW per day of the sediment could be reworked by 30, 000 adult worms with 1 mm of maximum width of thoracic segments. This reworking rate indicated that one square meter of the subsurface sediment with 2 cm in thickness, 75% of water content and 1.7 of specific gravity should be reworked within 52.5 days.
Abstract: We examined the short-term impact of Capitella sp. I on the bacterial abundance and the chemical characteristics in organically-enriched sediment in the laboratory microcosms after three days of incubation. The vertical profiles of the number of aerobic and anaerobic bacteria and ATP content of the sediment in the microcosms indicate that the presence of Capitella sp. I in the sediment markedly enhances the bacterial growth and metabolic activities in the sediment, particularly at relatively shallow subsurface sediment(0.5-2.0cm in depth). The chemical characteristics of the sediment including organic matter content(TOC and TN)and AVS content indicate that the degradation of organic matter and oxidation of the sediment are promoted in the presence of the worms, particularly at relatively deep subsurface sediment(2.5-3.0cm in depth). These differences in vertical profiles of bacterial abundance and organic matter content appear to be ascribable to feeding and defecating activities of the worms. The worms mainly feed the sediment at relatively deep subsurface(2-3cm in depth), decompose the organic matter there and stimulate bacterial growth and activities in relatively shallow subsurface sediment.