MARINE ECOLOGY PROGRESS SERIES Vol. 60: 283-290, 1990 Published February 22 Mar. Ecol. Prog. Ser.

Feeding affects phosphate fluxes in the symbiotic Aiptasia pallida*

'chesapeake Biological Laboratory, University of Maryland, Box 38, Solornons, Maryland 20688-0038, USA '~ermudaBiological Station, Ferry Reach GE-01, Bermuda

ABSTRACT: Phosphate uptake by the anemone Aiptasia pallida occurred only when anemones were starved and was due to the presence of endosymblotic zooxanthellae. Anemones fed Artemia nauplii released ~0,~-at 0.26 ~LMPod3-, and showed no evidence of uptake at elevated concentrations (0.66 and 1.26 pM). In contrast, anemones maintained without food for 2 wk to 1 mo took up pod3- at both 0 66 and 1.26 )!M. The uptake of POA3-by anemones freshly collected from the field ([PO,"] = 0.23 btM) was greater than that of anemones fed daily in the laboratory, but less than that of 2-wk to l-mo unfed anemones Replacement of total (host and symbiont) phosphorus (P) solely from uptake of seawater Pod3- at 0 66 ~IMwould require 374 d in fed anemones, indicating that this source is insignificant in coinparison to ingested food Corresponding times for 2-wk and l-mo starved anemones average less than 8 d, whde those for field anemones average 50 d. Field anemones thus appear to be intermediate between fed-daily and starved anemones with respect to phosphate uptake and P turnover. We conclude that the net flux of phosphate between A. pallida and seawater depends not only on the external seawater concentration, but also on the relat~verates of Pod3- regeneration by the host and POa3- uptake by the algae, both of which, In turn, are affected by the supply and assimilation of particulate food by the host anemone.

INTRODUCTION studies and related investigations of nitrogen fluxes (Szmant-Froelich & Pilson 1977, Muscatine & D'Elia The flux of inorganic nutrients between symbiotic 1978, Wilkerson & Muscatine 1984, Wilkerson & Trench associations and seawater has been of interest to marine 1986) have shown that inorganic nutrients required by scientists since the work of Yonge & Nicholls (1931), zooxanthellae are taken up from seawater by and who showed that reef corals containing endosymbiotic other symbiotic cnidarians and are retained. algae (zooxanthellae) retain or take up net amounts of Inorganic nutrients for zooxanthellae may also be pod3- at low environmental concentrations. Later supplied in situ by the feeding activities of the host. studies using more sophisticated analytical procedures This has been shown with laboratory-cultured corals and radioisotopes confirmed these results and provided and anemones maintained under controlled feeding some indication of the lunetics of ~0~~-uptake schedules. Szmant-Froelich & Pilson (1977, 1984) (Yamazato 1970, D'Elia 1977, Propp 1981). Pomeroy & showed that the nitrogen flux of the temperate symbio- Kuenzler (1969) showed that corals with zooxanthellae tic Astrangia danae was greatly affected by the exhibited far greater abilities to retain P than nonsym- feeding history of the host; presumably feeding affects biotic tropical invertebrates. They evaluated P retention the size of nutrient pools available to zooxanthellae. by organisms in terms of turnover time (P/AP). These Subsequent studies have shown that nutrient uptake by zooxanthellae isolated from the anemone Aiptasia -- pallida increases with degree of starvation of the host Contnbution No. 2056, Center for Environmental and (D'Elia & Cook 1988, Muller-Parker et al. 1989). These Estuarine- Studies of the University of Maryland System; observations and those of Johannes et al. (1970) sug- Contribution No. 1231 of the Bermuda Biological Station for gest that zooplankton are an important source of Research nutrients for zooxanthellae, and that the feeding " Present address. Shannon Point Manne Center. Western Washington University, 1900 Shannon Point Rd, Anacortes, activities of the host may affect the directional flux of Washington 98221, USA nutrients in the natural environment. a Inter-Research/Printed in F. R Germany 284 Mar. Ecol. Prog. Ser. 60: 283-290, 1990

We have shown previously that zooxanthellae in cleaned with 10 % HCI followed by 3 rinses with distilled Aiptasiapallida are affected by low nutrients and lack of water. Samples were frozen and subsequently analyzed host feeding (Cook et al. 1988). We now examine the flux for using a modification of the standard procedure of phosphate between A. pallida and seawater We (Technicon Industrial Method. No. 155-710 W/A), in assess the effects of feeding and seawater phosphate which ascorbic acid was omitted from the color-forming levelson P043- fluxes, since uptake from seawater reagent and added independently from the acid-molyb- shoulddepend on both the seawater P043- concentration date stream. Inorganic nutrient concentrations of GF/F- and the availability of Po,~- in host internal pools. filtered Walsingham Pond water and GFSSW (Table 1) Phosphate fluxes and P turnover rates of field popula- were determined using Technicon Industrial Methods tions were compared with those of cultured anemones No. 158-71 W/A for nitrate and nitrite and No. 154-71 W/ maintained under different feeding regimes to estimate B for ammonium. Dissolved organic phosphorus was the P status of zooxanthellae of A. pallida in nature. measured according to D'Elia et al. (1977). Phosphate fluxes in symbiotic and aposymbiotic anemones. Phosphate fluxes of cultured anemones of MATERIALS AND METHODS different feeding histories and of field anemones were measured in Bermuda under standard culture condi- Anemones. Anemones from clonal laboratory tions (60 to 80 pE m-2 S-' irradiance and 25 "C). Indi- cultures were maintained in incubators at 25 "C tvith a vidual anemones in glass vials containing GFSSW were 12:12 L:D photoperiod at irradiance levels of 60 to 80 pre-acclimated to incubation conditions for at least 1 h. biE m-' S-'. Certain anemones were fed daily to reple- At the start of each experiment, the seawater was tion with Artemia nauplii, while others were kept with- replaced with 20.0 m1 of phosphate-enriched (with out food in filtered (> 0.7 kim) low nutrient Sargasso KHpPO,) GFSSW at final concentrations of 0.26, 0.66, seawater (GFSSW) for periods of up to several months and 1.26 pM Either 2.0 or 2.5 m1 samples of the as described by Cook et al. (1988). Aposymbiotic incubation medium were withdrawn at 15 to 20 min (algae-free) anemones were produced by a cold shock intervals for up to 2 h. The seawater removed during treatment (Steen & Muscatine 1987), maintained in sampling was not replaced. The seawater was well darkness, and fed every 2 to 3 d. stirred initially and prior to the removal of each sample, To compare ~0~~-uptake by cultured anemones but remained undisturbed between sampling periods. with that of anemones from the field, Aiptasia pallida The previous incubation procedure was modified in was collected in Bermuda from Walsingham Pond, some experiments to include continuous stirring. In which was formed from a collapsed limestone cave. these experiments, the incubation medium was stirred The pond is ringed by a flourishing com- continuously by a magnetic stirbar placed beneath a munity, and anemones were removed from a single plastic mesh platform supporting each anemone. mangrove root located in an unshaded area at less than Samples for phosphate determinations of the medium 0.5 m depth. The similar patterns on the oral disk and were withdrawn from the incubation vials by a peristal- tentacles of these anemones suggested that they were tic pump which delivered the sample stream directly to from a single clone developed through asexual repro- the autoanalyzer. These anemones were exposed to a duction. PO4" uptake by the field anemones was higher light intensity than in the previous experiments measured within 6 h after collection. (400 uE m-2 S-'). Nutrient analyses. determinations for both We also examined the effect of recent feeding on experimental incubations and seawater samples taken phosphate fluxes in symbiotic and aposymbiotic anemo- from Walsingham Pond and stock GFSSW were per- nes. Pr~orto sampling, uningested Artemia nauplli were formed on either a Scientific Instruments M/CFA 200 removed from the incubation vials, and the seawater continuous flow analyzer or a Technicon AutoAnalyzer (0.06 L~~ PO,~-)replaced at time zero. The seawatertvas 11. All glassware, including incubation vessels, was pre- sampled at periodic intervals for ca 20 h after feeding

Table 1. Nutrient levels (bun01 1. !) in filtered seawater obtained from Walsingham Pond on 29 May 1987 and of Sargasso seawater used for all phosphate uptake experiments. DOP dissolved organic phosphorus, DIN: dissolved inorganic nitrogen; DIP: dissolved inorganic phosphorus

Seawater PO&- DOP NH; NO; NOT DIN/DIP source (atomic)

Walsingham Pond 0.23 <0.01 0.3 0.70 c0.03 4.3 Sargasso (Hydrostation 'S') 0.06 <0.01 < 0.3 0.08 0.03 1.8 Muller-Parker et al.: Phosphate fluxes in an anemone 285

Analysis of phosphate flux data. Phosphate uptake starved for 2 wk. Symbiotic anemones removed ~0~~- rates were calculated from third-order polynomial equa- from solution at an initial of 0.68 ~IM,whereas tions fitted to the raw concentration data. These there was no uptake of Pod3- by unfed algae-free equations were used to calculate fitted concentrations; anemones (Fig. 1). Since the uptake of PO," appeared the first derivative of the fitted curve at each sample to be mediated by zooxanthellae, subsequent compari- point yields instantaneous rates of Pod3- uptake (D'Elia sons of phosphorus uptake between symbiotic anemo- & Cook 1988). This approach minimizes both sampling nes of differing nutritional history were based on data and nutrient analytical errors that increase the variance normalized to zooxanthellar abundance. in the concentration measurements. The fits of these Phosphate uptake by symbiotic anemones suggested curves to the raw data were quite good, with correlation that light might affect uptake. To test this possibility, coefficients generally greater than 0.97. Phosphate PO4"- uptake by 2 wk starved anemones pre-incubated uptake rates of anemones were derived from the fitted in the dark for 12 h was measured at 0.66 and 1.26 ILM curves at equivalent seawater concentrations. and compared to similar experiments with 2-wk The net change in P043- concentration due to anemone starved anemones in the light (Table 2). Phosphate uptake or release at each time point was calculated from uptake rates in the light and dark were not significantly the time zero ~0~~-content of the seawater sampled different (t-test comparisons, p > 0.1). within 30 S of addition to each anemone, the amount of Pod3- removed as samples to that time, and the amount of remaining in the seawater. Net changes in Phosphate release by recently-fed anemones were normalized to biomass expressed as either zooxanthellar abundance (symbiotic anemones) or total The fluxes of symbiotic and aposymbiotic protein (symbiotic vs aposymbiotic comparisons). daily-fed anemones were measured during the first Biomass measurements. Following each experiment, 24 11 after a meal of Artemia nauplii. Although both individual anemones were hon~ogenizedwith a teflon groups of fed anemones released symbiotic tissue grinder and algal numbers and total protein anemones released much less on a protein biomass content of homogenates determined as in Muller- basis than aposymbiotic anemones (Fig. 2). Most of the Parker (1984). Protein was measured by the method of net release of phosphate by symbiotic anemones took Lowry et al. (1951), using bovine serum albumin as a place during the initial 3 h after feeding, with little protein standard. To relate phosphate uptake to P con- further release for the duration of the experiment. In tent of anemones, we measured the amount of P and contrast, aposymbiotic anemones released PO," con- protein in other anemones maintained under similar tinuously during the 24 h period. The amount of phos- conditions (fed daily, 2-wk starved, and l-mo starved), phate released by aposymbiotic anemones over 24 h and used the ratio of P to protein (mg P/mg protein) was about 10 times that released by symbiotic anemo- derived from these anemones to estimate the amount of nes during the same period (Fig. 2). P in the experimental anemones. Measurements of a-* Symbiotic total P (Aspila et al. 1976) and protein of homogenates o --o Aposymbiotic from daily-fed and starved anemones yielded P/protein I ratios ranging from 0.0299 (k 0.0018 SD, n = 3) to 0.0376 (+ 0.0038 SD, n = 3), for fed to l-mo starved anemones respectively. We assumed that the ratio of P/ protein for fed anemones applied to the field anemo- nes. Recent measurements of P and protein of other anemones from Walsingham Pond provide support for this assumption (Muller-Parker et al. unpubl.).

RESULTS -4 I 0 20 40 60 80 Phosphate fluxes in symbiotic and aposymbiotic Time (min) . . anemones Fig. 1. Aiptas~apallida. Uptake of POA3- by 2-wk starved determine if phosphate uptake by anemones aposyrnbiotic (algae-free)and sy~nbiot~canemones at an ini- tial concentration of 0 68 yM. Ordinate values represent On the zooxanthellaelwe presence of meas- the net amount of pod3- accunlulated by anemones, nor- ured ~0,~in continuously stirred seawater incuba- malized to anemone protein biomass. N = 3 anemones; error tions of both symbiotic and aposymbiotic anemones bars are * 2 SEM 286 Mar. Ecol. Prog. Ser. 60: 283-290, 1990

Symbiotic 0~~~~0Aposymbiotic

T T

Hours after feeding

Fig. 2. Aiptasia pallida. release by symbiotic and aposymbiotic anemones after feeding. Anemones were fed Arternid nauplii, then the seawater was replaced and [pod3-] N-T--.--.------T^ ma in- in- 00 vm CM-0CM -- of the seawater measured during the next 20 h. Ordinate 00 00 00 00 00 values are the amount of phosphate released by fed anemo- nes, normalized to anemone protein biomass. N = 3 anemo- nes; error bars are  2 SEM

Effect of starvation on phosphate fluxes in symbiotic anemones

w---- in- inw-- NO-- cow-- 0 r-w LD+ r.r. cot- Changes in PO^^"]at 3 different initial ~0~~-con- 00 ion nio 00 om** NO -0 00-* centrations are shown in Fig. 3 for intermittently stirred (every 10 to 15 min) incubations of cultured anemones mo in0 Of- or*- -in nm O-T ^W in0 ooo 00 n- r-Q' -TO N-T maintained without food for various periods of time. Actual concentrations (not corrected for biomass) are shown for representative anemones from each group. Sequential samples for a given anemone were con- sistent with the initial (30 s) sample, but these initial samples did not always correspond to the ~0~~-con- centrations measured in the incubation media prior to the addition of anemones (Fig. 3). Since there was no mw wm mu no w0 consistent pattern in this difference, either within or 0 -I-. inn -T^ inw 0 ma -TLD nus 00 between experimental groups, we can offer no expla- nation for this discrepancy. All anemones with the exception of the fed group removed ~0~~-from seawater at the 2 higher P043- concentrations (Fig. 3a, b). Fed-daily anemones re- leased phosphate at 0.66 p1M (Fig.3b). At 0.26 pM PO^^, all anemones released POA3for the first hour (Fig,3c). This was followed by a return to near ambient levels for all but the fed anemones, which continued to release phosphate for the remainder of the experiment (Fig.3c). Phosphate concentrations never dropped below 0.20 ~IMin any experiment. Other experiments showed that 2-wk starved anemones were not able to remove POs3" from ambient levels in GFSSW (0.08 pO43-). Both the feeding history of the anemones and the ~0~~-concentration affected the amount of phosphate Muller-Parker et al.. Phosphate fluxes in an anemone 287

U .U

2.week starved 0 l -month starved

Time (min) Time (rnin) Time (rnin)

Fig. 3. Aiptasia pallida. [PO,~-]of seawater containing fed, starved and field anemones. Initial pod3- concentrations were: (a) 1.26 PM, (b) 0.66 PM, (c) 0.26 PM. Seawater [PO,~-]are actual concentrations for individual anemone ~ncubationsrepresentative of each group, and are not corrected for biomass either taken up or released by the anemones (Fig. 4). ate between those of 2-wk starved and fed anemones at The amount of phosphate accumulated by anemones all phosphate concentrations (Fig.4). Field anemones increased with degree of starvation. Anemones starved released phosphate at 0.26 pM, a P043- concentration for 1 mo took up the most phosphate at all 3 concen- similar to that in Walsingham Pond and about 4 times trations, although the amount removed from the sea- that of GFSSW (Table 1). water was similar for anemones placed in 0.66 and 1.26 FM phosphate (Fig. 4a, b). The amount taken up by 2-wk starved anemones in 1.26 yM phosphate sea- Phosphorus uptake and turnover rates of symbiotic water was double that taken up at 0.66 PM, resulting in anemones similar uptake by l-mo and 2-wk starved anemones at 1.26 PM. Daily-fed anemones took up small amounts of Phosphate uptake rates of the anemones were deter- phosphate at 1.26 yM (Fig. 4a), but released phosphate mined at 2 concentrations. 1.06 and 0.56 PM, for exper- at the 2 lower concentrations (Fig. 4b. c). At 0.26 PM. all iments conducted at 1.26 and 0.66 yM, respectively but the l-mo starved anemones released phosphate (Table 2). Uptake rates at these specified concen- (Fig. 4c). trations were close to the maximal uptake rates we Phosphate fluxes of field anemones were intermedi- observed. Uptake rates normalized to either anemone

m-. Doily fed A-A Field e- . -e 2-weekstarved o...O l-month starved 1-

Time (min) Time (min) Time (min) Fig. 4. Aiptasia pallida. Net flux of ~0~~-by fed, starved and field anemones at 3 initial ~0,~-concentrations: (a) 1 26 FM, (b) 0.66 FM, (c) 0.26 pM. Amount of ~0,~-taken up (or released) by anemones was normalized to number of zooxanthellae. N = 3 anemones; error bars are k 2 SEM 288 Mar. Ecol. Prog. Ser.

protein or to number of zooxanthellae were much Feeding history and nutrient fluxes in symbiotic higher for unfed anemones than for anemones fed invertebrates daily, with those of field anemones intermediate between the starved and fed anemones in the labora- The feeding history of the anemones affected the flux tory (Table 2). of PO~~-.Phosphate was released by fed anemones We estimated P turnover rates (T) in Aiptasia pallida (Fig. 2),while phosphate uptake increased with starva- from both P-specific uptake rates (T,,) and phosphate tion (Fig. 4). Phosphate uptake by algae isolated from release rates following feeding (T,). T, is an estimate of fed and starved anemones was also directly related to the time required to completely replace anemone P if the nutritional history of the anemone (Muller-Parker dissolved phosphate was the only source of P, while T, et al. 1989). Szmant-Froelich & Pilson (1984) showed is independent of P uptake and is comparable to turn- that unfed Astrangia danae exhibited slight ammonium over times calculated from excretion rates (Pomeroy & uptake in the light, while excretion of ammonium by Kuenzler 1969). Using our calculated uptake rates at fed corals increased with feeding frequency. Uptake of 1.06 and 0.56 yM and extrapolating these to a 24 h the ammonium analogue '4C-methylamine by both basis (Table 2),T, ranged from hundreds of days for fed intact Aiptasia pallida and isolated symbionts anemones to under 10 d for 2-wk and l-mo starved increased with the degree of starvation of the host anemones (Table 2). Field anemones had intermediate (D'Elia & Cook 1988). It thus appears that inorganic turnover times averaging ca 50 d. P turnover rates (T,) nutrient fluxes are influenced by the nutritional history calculated from phosphate release rates (see Fig. 2) of cnidarian hosts. exceeded 29 d for symbiotic anemones, and were D'Elia (1977) previously measured dissolved P fluxes under 10 d for aposymbiotic anemones. in several species of Pacific corals. He found that sym- biotic corals in the light could reduce POA3- concen- trations in seawater to as low as 0.03 PM. In our experi- DISCUSSION ments, unfed anemones released Pod3- at concen- trations between 0.2 and 0.3 yM (Fig. 3c). The 'deple- Role of zooxanthellae in ~0~~-uptake by symbiotic tion-diffusion' hypothesis of dissolved nutrient uptake invertebrates by symbiotic associations (D'EIia et al. 1983, D'Elia & Cook 1988) implies that external concentratlons at Uptake of phosphate by the symbiotic anemone Aip- which the net flux of ~0,~-is zero are indicative of tas~apallida required the presence of zooxanthellae, concentrations in host tissue. If this hypothesis is cor- since unfed aposyrnbiotic anemones did not remove rect, these data suggest that even starvlng anemones P043- from seawater (Fig. 1). P uptake has been previ- have higher tissue levels of than do reef corals. ously attributed to zooxanthellae in both anemones This is supported by other measurements of the phos- (Smith 1939, Cates & McLaughlin 1979) and corals phorus and protein content of tissue from 2 corals (Yonge & Nicholls 1931, Yamazato 1970, D'Elia 1977). (Montastrea annularis and Madracis mirabilis), where Zooxanthellae are also responsible for the uptake and the P/protein ratio was 0.016 (Muller-Parker et al. retention of dissolved inorganic nitrogen in symbiotic unpubl.), about half that of Aiptasia pallida (see associations (Cates & McLaughlin 1976. Szmant- 'Materials and methods'). Froelich & Pilson 1977, Muscatine et al. 1979,Muscatine Uptake of ~0,~-was related to substrate concen- & D'Elia 1978, Muscatine 1980, Wilkerson & Muscatine tration and feeding history (Table 2). We did not obtain 1984, Zamer & Shick 1987). Active uptake by zooxan- Michaelis-Menten kinetics in any experiment, as has thellae is implied by our results, but the potential con- been typical of other studies of nutrient uptake by tribution of active transport mechanisms in host tissue, symbiotic associations (e. g. Wilkerson & Muscatine particularly in the epithelia, was not determined Light 1984, Wilkerson & Trench 1986). While this may be due was not a s~gnificantfactor in PO," uptake by 2-wk to the narrow range of substrate concentrations (0.06 to starved A. pallida, suggesting that phosphate uptake is 1.28 uM) used in our experiments, the applicability of not enhanced by algal . Michaelis-Menten kinetics to nutrient uptake relies on The lower biomass-specific release of ~0,~-(Fig. 2) the measurement of inltial uptake rates without the and the longer P turnover times (T,) of symbiotic effect of accumulated product on uptake. This condi- anemones relative to those of aposymbiotic anemones tion is rarely realized in these studies. Accordingly, we suggest that zooxanthellae promote the retention of compared instantaneous uptake rates at 0.56 and phosphate by Aptasia pallida. Algae may possibly 1.06 LLMP043 for experiments with initial levels of stimulate the host to store inorganic phosphorus, or PO4" of 0.68 and 1.28 pM P, respectively (Table 2). may be directly responsible for the uptake of phos- Uptake rates at these specified concentrations were phate in host tissue. close to the maximal uptake rates we observed. Muller-Parker et al.: Phos jphate fluxes in an anemone 289

Nutrient uptake kinetics for intact associations are 44 to 51 d (Table 2), very close to the algal mean further complicated by the passage of nutrients through turnover time of 68 d in field populations of the related host tissue (Muscatine & D'Elia 1978) and bidirectional anemone Aiptasia pulchella (Muller-Parker 1987). fluxes (D'Elia 1977). Other experimental variables can Phosphate uptake may thus potentially supply a sig- affect the apparent measured uptake of nutrients, such nificant fraction of the P required by zooxanthellae in as the time interval between samples, the volume of anemones under natural conditions. A similar analysis incubation medium relative to that of the experimental showed that the uptake of inorganic N alone could organism, or the degree of expansion of the organism. support a coral doubling time of 100 d (D'Elia & Webb Uptake may be influenced by the biomass and algal 1977),although the relative importance of uptake could density of individual anemones, parameters which are not be determined since the growth rates of the coral also affected by food supply (Clayton & Lasker 1984, and zooxanthellae were unknown. Muller-Parker 1985, Cook et al. 1988). This study has shown that the uptake of ~0~~-by Aiptasia pallida is directly related to its nutritional history. Both the magnitude and direction of pod3- flux Particulate feeding and supply of phosphorus to further depend on the supply of P043- in the host symbiotic zooxanthellae versus that available in the surrounding seawater. Cou- pled with a similar dependency for ammonium fluxes It is generally agreed that invertebrate hosts provide (Szmant-Froelich & Pilson 1984, D'ELia & Cook 1988), inorganic nutrients for symbiotic zooxanthellae (Mus- these conclusions support the general view that the catine & Porter 1977), and that zooplankton feeding is uptake of inorganic nutrients in symbiotic associations an important source of nutrients (Johannes et al. 1970). depends on zooxanthellae, but the direction and mag- Our experiments with field and laboratory-cultured nitude of the net flux is regulated by the relative supply Aiptasia pallida have shown that phosphate availabil- of available nutrients in host tissue and the surround- ity to zooxanthellae in field anemones is intermediate ing water. Yet to be determined are the specific between that of daily-fed and starved laboratory popu- mechanisms responsible for nutrient uptake. How are lation~.pod3- uptake rates and P turnover times of field different nutrients, of differing charges (e.g. NHdf, anemones were less than those of anemones starved in NO3-), transported to zooxanthellae? What is the role the laboratory, but exceeded those obtained from fed (if any) of the membrane in nutrient uptake? cultures (Table 2). The relative importance of dissolved How does the availability of a given nutrient affect the and particulate sources of P for zooxanthellae in field uptake of another nutrient? Our work suggests that anemones could not be directly measured, but dissol- feeding on zooplankton affects the size of nutrient ved nutrient concentrations at the field site (Walsing- pools in the host, but this has not been directly meas- ham Pond) were much higher than those present in the ured. The Aiptasia-zooxanthellae symbiotic associa- stock Sargasso seawater used for starving anemones tion, easily cultured in the laboratory, should prove to (Table l), and exceeded values typically reported for be a useful experimental organism in which to examine other inshore waters in Bermuda (Morris et al. 1977, these processes in more detail. von Bodungen et al. 1982). We have not made similar measurements on anemone populations from habitats Acknowledgements. We thank J. A. Love, D. P. Ferrier, S. with more typical ambient low nutrient concentrations. Refetoff and A. Pate1 for assistance, and K. Webb for helpful Elevated concentrations could provide symbiotic algae comments on the manuscript. This research was supported by grants from the National Science Foundation: OCE-8719701 with nutrients both through dissolved uptake, and by (GMP), OCE-8602190 and OCE-8718257 (CBC); and OCE- supporting a higher zooplankton density. Although the 8515699 (CFD). field anemones did not take up phosphate at levels typical of Walsingham Pond (Fig. 4c), concentrations of phosphate may vary over very small spatial and tem- LITERATURE CITED poral scales. We can infer the importance of particulate food as a Aspila, I., Agemian, H., Chau, A. S. (1976). A semi-automated source of P for zooxanthellae in symbiotic anemones method for the determination of inorganic, organic and total phosphate in sediments. Analyst 101: 187-197 from the relative times required for uptake-supported P Cates, N., McLaughlin, J. J. A. (1976). Differences of ammonia turnover (T,) and algal cell turnover. In daily-fed metabolism in symbiotic and aposymbiotic Condylactus anemones, T, ranged from 355 to 596 d (Table 2), 20 to and Cassiopea spp. J. exp. mar. Biol. Ecol. 21: 1-5 40 times that of the 16 d turnover time of zooxanthellae Cates, N., McLaughlin, J. J. A. (1979). Nutrient availability for zooxanthellae derived from physiological activities of Con- in fed anemones calculated from Cook et al. (1988); dylactus spp. J. exp. mar. Biol. Ecol. 37: 31-41 these zooxanthellae clearly depend on food-derived P. Clayton. W. S. Jr, Lasker, H. R. (1984). Host feedng regime In contrast, the T, of field anemones ranged from only and zooxanthellal photosynthesis in the anemone, Aiptasia 290 Mar. Ecol. Prog Ser. 60. 283-290, 1990

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This article was presented by Professor K. R. Tenore, hfanusci?pt first received: February 16, 1989 Solomons, Maryland, USA Rev~sedverslon accepted: November 8, 1989