THE PRODUCTIVITY OF HAWAIIAN FRINGING-REEF CRUSTOSE CORALLINACEAE AND AN EXPERIMENTAL EVALUATION OF PRODUCTION METHODOLOGY†

Estimates of the mean net total contribution to the Waikiki reef by Porolithon oro rates determined by all three techniques showed the same serial order, by species, from highest to lowest producer. The pH and 0, electrode methods are more useful and reliable than the ‘“C data where high sensitivity is not critical. The Winkler oxygen method has been classically applied to light and dark incubated bottles for studying benthic productivity. Its sensitivity permits significant determinations where OZ evolution is as low as 0.15 mg literl. Where 02 evolution exceeds 0.5 mg liter-l, polarographic OZ analyzers are useful. Variations in COn have also been used to measure photosynthesis, and changes in pH (Beyers et al. 1963) have proven to be reasonably sensitive indices to COa uptake, The 14C technique is the most sensitive, widely accepted, and routinely applied of the methods. Such workers as McAllister et al. ( 1961) and Thomas ( 1964) have compared the 14C method, Winkler 02 (light-dark bottle), and pH measurements for determining the productivity of natural and cultured phytoplankton populations. Miiller and‘ Kniipp ( 1971) evaluated 14C, 02 electrode, and Winkler analyses in a study of primary productivity in flowing waters. In my study, all of the above techniques in addition to others (gas chromatography, Ca electrodes, 45Ca, and atomic absorption spectrophotometry) were used on the same thalli simultaneously, to measure the productivity of reef-building coralline algae. 1 This work was supported by U. S. Atomic Energy Commission Contract AT ( 04-3) 235. Previous workers (e.g. Setchell 1926, 1928; Crossland 1938) have debated the relative importance of calcareous organisms in the reef environment. Biologists have classically stressed the importance of standing stock (usually in subjective terms) and geologists have emphasized sediment mcasurements. Few approaches have considered the functional roles played by reef-building organisms or the correlation between standing stock and the skeletal components that remain after grazing, export, and resolution. As Gorcau ( 1963) pointed out, the missing quantity is a calcification-rate parameter. Among the three studies to date of the functional importance of crustose Corallinaceac, that of Sargent and Austin ( 1954) assumed from the density of crustose coralline algae on the seaward face of the reef at Rongelap Atoll that the area had high photosynthesis. They measured net oxygen production of various reef organisms in jars set in the flowing interisland waters: three measurements of a single Porolithon thallus yielded rates comparable to those of corals (based on sample wet weight). Goreau ( 1963) first measured carbon fixation and calcium carbonate deposition rates for various reef-building algae by radioisotope techniques ( 14C and 4%a simultaneously). He reported the uptake LIMNOLOGY AND OCEANOGRAPHY 946 NOVEMBER 1973, V. 18( 6) UENTHIC ALGAL PRODUCTIVITY 947 rates in terms of milligram moles of C or Ca fixed per milligram N per hour (an index of cell protein), which is difficult to relate either to the standing stock of calcareous organisms or to scdimentological studies, Marsh ( 1970) found the productivity of unidentified crustose Corallinaceac from Eniwetok Atoll and Kaneohe Bay, Hawaii, measured with a specially constructed dissolved-oxygen electrode, to bc within the same order of magnitude but lower than that of other photosynthetic reef organisms. However Smith (1973) compared the productivity at Eniwetok and obtained results that may be contradictory to those of Marsh, Both a transect dominated (visually) by a mixture of corals and corallinc algae and one dominated by a coralline algal turf (Porolithon and Jania) calcified at 4,000 g CaCOn m-2 yr-1, but the coralline algal community showed a higher net production (24-hr day) rate than did the coralalgal community (7.20 vs. 1.56 g C m-3 day-l). It may be that organisms not visually prominent arc rclativcly more important metabolically than the calcifying organisms, since total community metabolism was the parameter measured, I am grateful to M. S. Doty for his advice and encouragement during all phases of this rcscarch and to S. V. Smith for critically reading the manuscript, METHODS AND MATERIALS The productivity of crustose Corallinaceae as measured includes the rate of fixation of particulate and dissolved organic carbon (primary and secondary productivity) as well as the rate of fixation of particulate inorganic carbon (calcification). The experimental chambers used (Fig. 1) are modifications of that of Doty (1967). The metal screws were moved outside the internal cavity to avoid contact with the cuhure medium. Three double-O-ring apertures were constructed in the top to seal three clectrodcs (pH, 02, and Ca) airtight and a tapered stopper was fitted in one corner of the top to facilitate filling and expelling air from the chamber. The chambers hold 600 ml rather than 300 and contain a rack to support the crustose thalli on monofilament Iinc during incubation. The portion of each species incubated consisted of approximateIy equal fragments of the same thallus or similar thallus chipped from the same square meter patch of the Waikiki fringing reef at 0930 hours. Each species was sampled in the area of its peak of abundance (Littler 1973). Three to five small fragments of the freshly collected algae were placed horizontally on a support of monofilament line in each of two duplicate chambers containing MiIlipore-filtered seawater; a third chamber (without electrodes and covered with aluminum foil) was used as a blank to correct for dark uptake by the algae. The lids, with the clectrodcs inserted, were placed on the chambers and secured, and the chambers were completely filled so that no air bubbles remained. The two chambers were placed in a water bath over identical magnetic stirring motors, modified to run cooler, in a photoperiod incubator, at 24.0°C, above the light saturation intensities of the corahine algae (10,800-21, 500 lux). The rate of stirring was adjusted to a standard setting and the chambers were allowed to equilibrate for about 1 hr. During the equilibration period, initial samples were taken. A 300-ml sample of the water used had reagents added for later Winkler analysis. Two ampoules of 10 ml each were labeled and sealed for measurement (by procedures in Strickland and Parsons 1968) of initial dissolved organic carbon and calcium. All seawater was from one 40.0-liter Millipore-filtered (0.45pm pore size) batch that was collected from just inside the algal ridge area of the Waikiki reef, filtered immediately and stored in the dark in a sterilized polyethylene carboy. Data recording began at 1130 each day to minimize any effects of periodicity. Dissolved 02 and pH were monitored for a 1-hr dark period, at the end of which the chambers (including the dark control)