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Abstract
Marine substrata possess cues that influence the behavior of fouling organisms. Initial adhesion of fouling algal zoospores to surfaces is also theorized to depend primarily upon interactions between substrata and spore cell bodies and flagellar membranes. In an effort to identify cues and surface characteristics that influence spore settlement and early development, the effects of bioactive echinoderm extracts, surface charge, and surface hydrophobicity were examined individually and in tandem on zoospore settlement and germination in Hincksia irregularis. Experiments utilizing 96-well plastic culture plates confirmed that spore settlement and germination were significantly affected by surface charge and hydrophobicity as well as by echinoderm metabolites, both individually and in tandem. Spore settlement rates in the dark over 30 min were > 400% higher on hydrophobic surfaces than on positively and negatively charged surfaces. Spore germling numbers were > 300% higher on hydrophobic surfaces than on positively and negatively charged surfaces when spores were allowed to settle in the light for 30 min and the settled spores allowed to subsequently germinate for 24 h. Spore germling numbers were consistently > 25% higher on hydrophobic surfaces than on positively and negatively charged surfaces when equal numbers of spores were allowed to completely settle in the light and subsequently germinate for 24 h. H. irregularis germ tube lengths were also significantly longer on positively charged plates than on negatively charged plates. All echinoderm extracts tested had significant effects on germination and settlement at levels below those of estimated ecological concentrations. Short-term (30 min) exposure and subsequent germination experiments indicated that higher concentrations of extracts had rapid toxic effects on algal spores. Synchronous effects of echinoderm extracts and plate charge upon spore settlement varied considerably and did not show a strong dose response relationship. Long-term (24 h) exposure of spores to echinoderm extracts had dosage dependent effects on germination and spore survival. The results of this study indicate that H. irregularis spores possess the capacity for complex responses to their environment, utilizing combined cues of surface charge, surface energy and biochemistry to determine where to settle and germinate. These responses may aid spores in the detection of suitable substrata and conditions for settlement in the marine environment.
Acknowledgements
We thank Dr Robert Angus and Dr Scott Brande for their help and insight regarding statistical methods and Dr David Krauss for the use of his inverted microscope. This work is a result of research sponsored in part by the National Science Foundation's GK-12 Fellowship Program Grant (L Krannich, PI), the National Oceanic and Atmospheric Administration, the US Department of Commerce under grant No R/MT 40 to CDA and JBM, the Mississippi Alabama Sea Grant Consortium, and the University of Alabama at Birmingham. The US Government is authorized to produce and distribute reprints notwithstanding any copyright notation that may appear hereon. The views expressed herein are those of the authors and do not necessarily reflect the views of NOAA or its subagencies.
