Settlement Behavior of Zoospores of Ulva linza During Surface Selection Studied by Digital Holographic Microscopy

Abstract

Settlement of the planktonic dispersal stages of marine organisms is the crucial step for the development of marine biofouling. Four-dimensional holographic tracking reveals the mechanism by which algal spores select surfaces suitable for colonization. Quantitative analysis of the three dimensional swimming trajectories of motile spores of a macroalga (Ulva linza) in the vicinity of surfaces functionalized with different chemistries reveals that their search strategy and swimming behavior is correlated to the number of settled spores found in spore settlement bioassays conducted over 45 min. The spore motility and exploration behavior can be classified into different motion patterns, with their relative occurrence changing with the surface chemistry. Based on the detailed motility analysis we derived a model for the surface selection and settlement process of Ulva zoospores.

Surface Sensing and Settlement Strategies of Marine Biofouling Organisms

“…Interestingly the deceleration shows the same trend as the 45 min settlement assay ( Fig. 5b) [61,62]. However, the surface does not only influence the swimming speed of the spores, but also their behavior.…”

“…Such patterns are also observed by holographic microscopy for the green algae Ulva linza and schematically depicted in Fig. 5c [61]. Within the gyration motion pattern (pattern 1), two extreme cases of motion can be subdivided: hit and run (pattern 2), which describes a single surface contact after which the spores immediately left the surface; and hit and stick (pattern 3), that describes the situation whereby, as soon as spores contacted the surface, they immediately stop swimming and stick to the surface.…”

“…As pointed out by Heydt et al [61], one important prerequisite for settlement is a deceleration of the spores. In Fig.…”

“…From these holograms, three-dimensional information can be retrieved by digital reconstruction algorithms [54,60]. Image analysis of these Recently, an extensive digital in-line holographic microscopy study on Ulva spores by Heydt et al [61] revealed the mechanism by which spores select surfaces suited for settlement. The proposed mechanism is schematically depicted in Fig.…”

“…Such changes are most obvious on very hydrophobic surfaces (i.e. FOTS) as the probability to observe patterns indicative of an attractive surface vanish over time [61]. On such hydrophobic surfaces, conditioning films are formed within hours and Thomé et al [35] revealed that the presence of such overlayers decreases the settlement rates of Ulva zoospores by &50 %.…”