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A study has been made of the ecology of the small intertidal lamellibranch Lasaea rubra at various tidal levels at Plymouth and Wembury. In addition, experiments have been carried out to investigate physiological and behavioural differences arising from varying amounts of submersion at different tidal levels, and the following findings have been made.During the first hour after their submersion by sea water, L. rubra from high up the shore filter at a rate approximately twice that of animals which live lower down. After 2 h, however, both sets of animals filter at the same rate.High-level animals respond significantly faster to wetting by splash and can tolerate a considerable range of salinity. They also respire at a rate approximately twice that of low-level animals. Respiration, however, is not detectable when the animal is not immersed in sea water.

A comparison of the effects of ionic stress and an uncoupler on long-term fluorescence transients (the 'Kautsky effect') in the green alga Dunaliella tertiolecta indicated that the large quenching induced by ionic stress was caused by a pH gradient across the thylakoid membrane. This possiblity was given support by the increase in the slow phase of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea-induced fluorescence relaxation in algae subjected to ionic stress. Low-temperature fluorescence emission spectra indicated that salt stress enhanced photosystem-I emission in the dark, and a comparison of simultaneous emissions at 695 and 720 nm at room temperature indicated a further increase in photosystem-I emission during the fluorescence transients. Taken together with the decrease in the fast phase of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea-induced fluorescence relaxation in stressed algae, our results indicate that ionic stress stimulates cyclic electron flow, and that non-cyclic flow is inhibited. The effect of sucrose-induced osmotic stress was similar to, but less marked than, the effects of NaCl and KCl; the effect of decreasing the external salinity was small.

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Spores of fourteen species of red algae were examined in sea water/Indian ink suspensions and the volumes of the spores and their mucilage sheaths measured. The mucilage sheaths occupied 52-8-87-7% of the combined spore + mucilage volumes, depending on the species. Spores of different size of the same species had mucilage sheaths occupying similar proportions of the combined volumes, but spores of similar sizes from different species had mucilage volumes typical of all spores of the same species. Experiments with water jets show that the mucilage sheaths are tenacious, and may play some part in the planktonic phase of the spore's existence. I N T R O D U C T I O NIf newly released spores of red algae are placed in a suspension of Indian ink in sea water, a clear halo of mucilaginous material will be seen. A similar mucilage cover is also a well-known feature with certain phytoplankton organisms, in which cells of spiny appearance (e.g. freshwater desmids) assume a spherical form in Indian ink when the mucilage cover is also observed (Lund, 1959). The attachment of red algal spores is a process in which mucilage clearly plays some part (Suto. There appears to be little information on the sizes of the spore mucilage sheaths, and on their likely significance in the planktonic phase of the spore's existence immediately after release. The present work gives the results of an investigation of the spore mucilage of fourteen species of red algae. MATERIALS AND METHODSThe fourteen species of red algae used in the present work are listed in Table 1, together with the localities in the Plymouth neighbourhood where they were collected in July and August 1972. All material was used directly after return to the laboratory, and spores were obtained by overnight settlements from fruiting plants placed in filtered sea water in Pyrex glass dishes at room temperature. Spore samples were picked out with a pipette using a dissecting microscope and placed in the sea water/Indian ink suspension. Spore measurements were made with preparations in which cover glasses were supported on 'layers' of cover-glass fragments, so as to prevent any spore or mucilage layer distortion. These measurements were checked against those made on spore samples immersed in Indian ink suspension and lacking cover-glasses to ensure that no distortion had taken place. Samples of 100 spores were measured in all cases. 512 A. D. BONEY Species Callithamnion tetricum (Dillw.) S. F. Gray. Ceramiutn ciliatum (Ellis) Ducluz. Ceramium rubrum (Huds.) J. Ag. Ceramium shuttleworthianum (Kiitz.) Silva Chondrus crispus Stackh. Chylodadia venicillata (Lightf.) Bliding Cryptopleura ramosa (Huds.) Kylin ex Newton Lomentaria articulata (Huds.) Lyngb. Nitophyllum punctatum (Stackh.) Grev. Polysiphonia lanosa (L). Tandy Polysiphonia urceolata (Lightf. ex Dillw.) Grev. Polysiphonia brodiaei (Dillw.) Spreng. Rhodymenia pseudopalmata (Lamour.) Silva Stenogramme interrupta (C.Ag.) Mont.

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