Roskilde University, Department of Environmental, Social and Spatial Change, DK-4000 Roskilde, Denmark.
J Exp Biol. 2010 Sep 15;213(Pt 18):3237-46. doi: 10.1242/jeb.038810.
The behavior of the ubiquitous estuarine planktotrophic spionid polychaete larvae Polydora ciliata was studied. We describe ontogenetic changes in morphology, swimming speed and feeding rates and have developed a simple swimming model using low Reynolds number hydrodynamics. In the model we assumed that the ciliary swimming apparatus is primarily composed of the prototroch and secondarily by the telotroch. The model predicted swimming speeds and feeding rates that corresponded well with the measured speeds and rates. Applying empirical data to the model, we were able to explain the profound decrease in specific feeding rates and the observed increase in the difference between upward and downward swimming speeds with larval size. We estimated a critical larval length above which the buoyancy-corrected weight of the larva exceeds the propulsion force generated by the ciliary swimming apparatus and thus forces the larva to the bottom. This modeled critical larval length corresponded to approximately 1 mm, at which, according to the literature, competence for metamorphosis and no more length increase is observed. These findings may have general implications for all planktivorous polychaete larvae that feed without trailing threads. We observed bell shaped particle retention spectra with a minimum prey size of approximately 4 microm equivalent spherical diameter, and we found that an ontogenetic increase in maximum prey size add to a reduction in intra-specific food competition in the various larval stages. In a grazing experiment using natural seawater, ciliates were cleared approximately 50% more efficiently than similar sized dinoflagellates. The prey sizes retainable for P. ciliata larvae covers the microplankton fraction and includes non-motile as well as motile prey items, which is why the larvae are trophically positioned among the copepods and dinoflagellates. Not only do larval morphology and behavior govern larval feeding, prey behavior also influences the feeding efficiency of Polydora ciliata.
普遍存在于河口区的浮游型担轮幼虫多毛类 Polydora ciliata 的行为研究。我们描述了形态、游泳速度和摄食率的个体发育变化，并使用低雷诺数流体动力学开发了一个简单的游泳模型。在该模型中，我们假设纤毛游泳器官主要由原担轮组成，其次由后担轮组成。模型预测的游泳速度和摄食率与测量的速度和速率非常吻合。将经验数据应用于模型，我们能够解释特定摄食率的显著下降，以及观察到的与幼虫大小相关的向上和向下游泳速度之间的差异增加。我们估计了一个临界幼虫长度，超过该长度，幼虫的浮力修正重量超过纤毛游泳器官产生的推进力，从而迫使幼虫下沉。该模型预测的临界幼虫长度约为 1 毫米，根据文献，在此长度，幼虫就具有变态能力，且不再生长。这些发现可能对所有不拖着丝状体摄食的浮游多毛类幼虫具有普遍意义。我们观察到的颗粒保留谱呈钟形，最小猎物尺寸约为 4 微米等效球形直径，我们发现最大猎物尺寸的个体发育增加有助于减少各个幼虫阶段的种内食物竞争。在使用天然海水进行的放牧实验中，纤毛虫被清除的效率比类似大小的鞭毛藻类高约 50%。P. ciliata 幼虫可保留的猎物大小涵盖了微微型浮游生物部分，包括非运动和运动猎物，这就是为什么幼虫在营养位置上介于桡足类和鞭毛藻类之间。不仅幼虫的形态和行为控制着幼虫的摄食，猎物的行为也会影响 Polydora ciliata 的摄食效率。
