Physiological versus viscosity-induced effects of water temperature on the swimming and sinking velocity of larvae of the serpulid polychaete Galeolaria caespitosa

Abstract

Water viscosity is inversely related to water temperature. Because marine invertebrate larvae generally operate in a hydrodynamic environment dominated by viscous forces (i.e. Reynolds numbers < l ) , temperature-induced changes in water viscosity may exert profound influence on the swimming and sinking velocity of larvae. Wh~lst the physiological effects of water temperature on larval locomotion have received considerable experimental investigation, the influence of temperatureinduced changes in water viscosity has received little attention. We investigated the relative physiological and viscosity-induced effects of water temperature at 25 and 15°C on the swimming and sinking velocity of larvae of the serpulid polychaete Galeolaria caespitosa (L.). Larvae of this species undergo considerable growth and development during their planktonic period such that the Reynolds number of the larval body (trochosphere) increases from 0.19 at hatching to 1.11 at 120 h post-hatching. Consequently we suggest that inertial forces may exert an influence on swimming at the later stages of larval development and therefore the influence of viscosity may change over the course of larval development. We also suggest that a temperature-induced increase in water viscosity will reduce the sinking velocity of larvae and may reduce the energy expenditure required to maintain location in the water column. Our results indicate that both physiological and viscosity components of water temperature influence the swimming velocity of G. caespitosa larvae. However, the influence of water viscosity did not change significantly over the course of larval development. The sinking velocity of G. caespitosa larvae was reduced with a temperature-induced increase in water viscosity. The reduction in sinking velocity of the larvae was proportional to the increase in water viscosity. We estimated and compared the metabolic costs of swimming to counteract sinking at 25 and 15°C by estimating Qlo values from the metabolic effects of temperature on swimming velocity. We suggest that the metabolic costs of stvimming to counteract sinking in G. caespitosa larvae are similar at 25 and 15"C, but that the metabolic costs of swimming are slightly higher at 15°C.

Effect of temperature and viscosity on swimming velocity of the copepod Acartia tonsa, brine shrimp Artemia salina and rotifer Brachionus plicatilis

“…This statement is in agreement with Podolsky & Emlet (1993) who found that the swimming velocity of larvae of the sand dollar Dendraster excentricus was reduced by about 40% when the temperature was reduced from 22 to 12°C, and about 40% of this decrease could be ascribed to the increase in viscosity. Similar results were obtained by Bolton & Havenhand (1997) who studied the viscosity-induced effects of water temperature on the swimming velocity of larvae of the polychaete Galeolaria caespitosa. On average, about half the decline in swimming velocity was found to be caused by mechanical effects of increased viscosity while the remainder was presumed to be due to physiological effects.…”

“…Bolton & Havenhand (1997, their Table 2), for example, found a 31% reduction in swimming velocity of small (posthatched) larvae of the serpulid polychaete Galeolaria caespitosa in response to a 20.6% increase in viscosity by inert polymer (Ficoll) addition at 25°C. However, the decrease in swimming velocity was 60.4% in response to a lowering of the temperature of seawater from 25 to 15°C, which gave the same 20.6% increase in viscosity.…”

Influences of biofilm-associated ciliates on the settlement of marine invertebrate larvae

“…Polychaete larvae are less likely to be disrupted because of their faster swimming speeds, e.g. 4 mm s −1 in metatrochophores of G. caespitosa (Bolton & Havenhand 1997). Once larvae are crawling on the substratum, they could be more easily affected by ciliate movements and currents.…”

Effect of temperature on Temora longicornis swimming behaviour: illustration of seasonal effects in a temperate ecosystem

“…It is therefore difficult to differentiate between the direct effect of temperature and the indirect effect of viscosity on the swimming activity of Temora longicornis. However, previous results have indicated environmental changes in viscosity associated with temperature can influence the small-scale processes of marine zooplanktonic organisms (Po dolsky & Emlet 1993, Bolton & Havenhand 1997, even in free-swimming copepods (Larsen et al 2008). Thus, the observed de crease in swimming velocity could have been the result of an adaptation to increased viscosity, which would have involved an increase in the energy required to move the swimming appendages or a mechanical hindrance of the appendages.…”