Small-scale temporal variation in propagule supply of an intertidal red alga

Abstract

A. Bellgrove and M.N. Aoki. 2006. Small-scale temporal variation in propagule supply of an intertidal red alga.Phycologia 45: 458–464. DOI: 10.2216/05-53.1

Information on the variability in supply of algal propagules is scarce, hindered by the difficulty in identifying propagules, but this variability may affect the distribution and abundance of algal assemblages. This study examined the small-scale (½ hourly to hourly) temporal variation in propagule supply of Chondrus verrucosus (Gigartinaceae, Rhodophyta) over a dense, isolated bed in south-eastern Japan in summer and winter of 1999. Either 0.5 litre scoop samples or 5 litre pump samples were collected ½ hourly to hourly over 13, 22.5, and 30 h on three occasions in summer (June & July) and 32 h on one occasion in winter (December). Sampling was conducted around either the new moon (two occasions in summer) or full moon (one occasion in both summer and winter) and incorporated full tidal sequences including daytime (summer) and nighttime (winter) low-low (LL) tides. Chondrus verrucosus was the only red alga with spores within the size range of 15–20 μm that was fertile in the study area and surrounds at the time of sampling facilitating identification of spores. Spores in scoop samples were settled onto Petri dishes and identified on the basis of cell shape, colour and size. Pump samples were filtered onto transparent membrane filters and identified using epifluorescence microscopy: C. verrucosus spores fluoresced bright yellow and were easily distinguished from other micro-organisms of similar size, which fluoresced red or green. Results showed that while propagules could be found in the water column at most times, propagule supply of C. verrucosus was greatest during the 1–2 h period following LL tides. Variability in propagule supply was less than in previous studies examining surface or offshore waters. Spore release is thought to be stimulated by either desiccation or salinity changes associated with periods of emersion at low tide followed by re-immersion on incoming tides.

Key Words::

• Chondrus verrucosus
• Propagule supply
• Spore release
• Supply-side ecology
• Temporal variation
• Tidal rhythm

ACKNOWLEDGMENTS

Prof. T. Kuramoto is thanked for his guidance and administrative assistance. Assoc. Prof. Y. Saito is thanked for loaning laboratory equipment and providing technical assistance. This project would not have been possible without the tireless field assistance of H. Ueda, T. Sato and H. Shinagawa. H. Ueda and T. Sato also provided much technical assistance for which they are also thanked. Dr K. Tanaka and S. Watanabe in particular are thanked for their language and practical assistance to A. Bellgrove that ensured that the project ran smoothly. The manuscript was improved by critical reviews from Prof. J. Tanaka, A. Harrington and two anonymous referees. Additionally, discussions with Prof. G. Quinn and Dr B. Robson improved the presentation of results. This research was supported by a Japan Society for the Promotion of Science Postdoctoral Fellowship and a Ministry of Education (Monbusho) grant (Tokubetsu Kenkyuin Shoreihi) to A. Bellgrove (grant number 11–99704). This is publication 718 of the Shimoda Marine Research Centre.