Exposure of biofilms to meiofaunal copepods affects the larval settlement of Hydroides elegans (Polychaeta)

Abstract

This study reports significant differences in larval settlement of the polychaete Hydroides elegans (Haswell, 1883) on biofilms treated either by different densities of live harpacticoid copepods or conditioned by particulate organic material (POM) retrieved from harpacticoid copepod cultures. The copepods used in this study were the facultatively predatory Tisbe japonica and the detritivorous Nitocra spinipes. The resulting biofilms covering experimental surfaces exhibited differences in bacterial abundances, bacterial community profiles and bioactivity, as evidenced by differential attractivity provided as percentages of larval settlement. The density of settled larvae decreased on biofilms modified by increasing numbers of copepods. The highest bacterial densities (16 085 ± 915 cells mm -2 ) were found on natural biofilms conditioned with POM from cultures of T. japonica. The lowest bacterial densities (4020 ± 765 cells mm -2 ) were found on biofilms grown in the presence of the highest numbers of live T. japonica. Spearman-rank correlation results revealed a positive trend between increasing bacterial densities and larval settlement. Increasing copepod abundances were correlated with reduced bacterial densities and caused changes in the bacterial community profiles, which were identified by terminal restriction fragment analyses. Changes in microbial biofilms due to the conditioning effects of copepods or their remains/exudates are assumed to be responsible for differential larval settlement. Hence, the present laboratory study demonstrates that effects of predators can be mediated by biofilms and affect larval settlement indirectly.

Copepod feeding study in the upper layer of the tropical South China Sea

“…Copepod feeding processes cannot easily be generalized, as copepods exhibit herbivorous, omnivorous, carnivorous and detritivorous feeding habits (Schultes et al 2006;Dahms and Qian 2005). Copepod feeding also have impacts on microbial assemblages (Schnetzer and Caron 2005), so in their consumption of bacterial production (Bouvy et al 2006).…”

Behavioral responses of invertebrate larvae to water column cues

“…For other larval invertebrates, the presence of predators [36,37] and light [31,32,33,34,35] can also impact larval vertical distributions. None of these factors were present in our experiment, though it would be interesting and potentially ecologically relevant to observe how our results would change with the addition of another factor.…”

“…Some examples of physical cues for the regulation of vertical position include turbulence (Chapters 2, 3, 4, [25,26,27,28,29]), sound [30], and light (Chapter 5, [31,32,33,34,35]). Cues incorporating biological and chemical signals include exudates from predators [36,37], prey or host species [38,39], and conspecific settlement sites (Chapter 6, [40,41]). …”

Effects of food and light on naupliar swimming behavior of Apocyclops royi and Pseudodiaptomus annandalei (Crustacea, Copepoda)

“…are reported to feed primarily on heterotrophic protists, rather than to graze on phytoplankton, and nauplii of various tropical copepod species are shown to feed upon bacterioplankton (Turner et al, 2001a, b), whereas bacterioplankton is generally considered to be too small to be efficiently scavenged by most adult copepods. However, nauplii of various copepod species are shown to feed upon bacteria; besides bacterioplankton in the water column (Turner & Tester, 1992;Roff et al, 1995) also those assembled in biofilms (Dahms & Qian, 2005;Dahms et al, 2006a, b). Naupliar behavior may provide adaptive mechanisms, both, for the escape from predation and for their own foraging (Yen & Fields, 1992;Titelman, 2001;.…”