Seasonal changes in ambient phosphate and phosphatase activities of the cyanobacterium Rivularia atra in intertidal pools at Tyne Sands, Scotland

Abstract

• (i) A study was made of Rivularia atra at a sheltered bay in S-E. Scotland, where it is frequent in summer in pools of the upper eulittoral. Monthly measurements of water chemistry and phosphate activities were made at the same stage in the tidal cycle during April 1992–October 1993, together with other short intensive studies.

• (ii) Drift seaweed deposited at high tide levels (>4.9 m) released high concentrations of inorganic nutrients to adjacent pools, where the water sometimes exceeded 6000 µg l⁻¹ PO₄−P. Combined inorganic N was, however, always low and the N:P ratio fell to 0.001–0.003:1 (by weight) in August, when the temperature was relatively high: much N was lost to the atmosphere as ammonia.

• (iii) Total P concentrations in the Rivularia pools (mostly covered by 4.5–4.8 m tides) were much lower than in the drift seaweed pools, but similar to the sea, though with higher % organic P in the former (means of 50% v. 28%): total N concentrations were much lower in the Rivularia pools than in seawater, leading to a very low N:P for most of the time. Aqueous organic P tended to increase (in summer) during the period between tidal cover, even in pools lacking input drainage, suggesting that much of the organic P may be autochthonous.

• (iv) All 9 Rivularia pools showed high concentrations of P in June in one or both years. At the same time the Rivularia colonies formed abundant hormogonia, followed 4–8 weeks later by a marked increase in macroscopically obvious colonies.

• (v) Assays of ‘surface’ phosphomonoesterase activity by Rivularia colonies showed different results according to whether p-nitrophenyl phosphate (pNPP) or 4-methylumbelliferyl phosphate (4-MUP) was used as substrate. Both substrates indicated obvious activity at intervals during the year. Using pNPP, activity was very low in June, usually followed by a very high value in July or August; use of 4-MUP showed a different response, with a high value one or two months later than with pNPP.