ALKALINE-PHOSPHATASE ACTIVITIES AMONG PLANKTONIC COMMUNITIES IN THE NORTHERN RED-SEA

Citation
H. Lil et al., ALKALINE-PHOSPHATASE ACTIVITIES AMONG PLANKTONIC COMMUNITIES IN THE NORTHERN RED-SEA, Marine ecology. Progress series, 173, 1998, pp. 107-115
Citations number
50
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Marine & Freshwater Biology",Ecology
ISSN journal
0171-8630
Volume
173
Year of publication
1998
Pages
107 - 115
Database
ISI
SICI code
0171-8630(1998)173:<107:AAAPCI>2.0.ZU;2-S
Abstract
During a June 1996 cruise in the northern Red Sea, we studied spatial distributions of alkaline phosphatase (AP) activities in different pla nkton size fractions and in the aqueous fraction which passes through 0.2 mu m filters. AP proved to be a highly stable compound in the Red Sea and has potential use as an indicator for inorganic P-availability to planktonic communities. Depth profiles showed that aqueous and par ticulate alkaline phosphatase activities were highest in surface water s. The contribution of the aqueous fraction to total alkaline phosphat ase activity varied between 42 and 74%. The bulk of particulate alkali ne phosphatase activity was associated with picoplankton (50 to 71%) a t all sampling sites. A good correlation was found between depth distr ibutions of alkaline phosphatase activities and Synechococcus, suggest ing that this abundant picoplanktonic cyanobacterium is a significant contributor to the enzyme activity in the northern half of the Gulf of Aqaba. Chlorophyll aspecific alkaline phosphatase activities were hig hest for plankton communities in the surface layers of the northern ha lf of the Gulf. Alkaline phosphatase activities increased in the Gulf of Aqaba in water bodies traveling north, further away from the Strait s of Tiran. At this narrow and shallow entrance to the Gulf, local tur bulent conditions and coral reef flats inject phosphate into the produ ctive layer. Plankton communities immediately north of the Straits sho wed basal levels of alkaline phosphatase activity, and phosphate suppl y presumably satisfied their P-demands. Based on the regulation of alk aline phosphatase synthesis, its secretion and stability, we proposed the use of alkaline phosphatase activities for a (partial) assessment of the P-status of marine planktonic communities. Such an assessment i ndicated that inorganic phosphate availability in the waters of the no rthern Gulf of Aqaba was persistently low during the period prior to s ampling.