Notes 377

DINI, M. L. 1989. The adaptive significance of die1 KITCHELL, J. A., AND J. F. KITCHELL. 1980. Size- vertical migration by Daphnia. Ph.D. thesis, Univ. selective predation, light transmission, and oxygen Notre Dame. 108 p. stratification: Evidence from the recent sediments AND S. R. CARPENTER. 1988. Variability in of manipulated lakes. Limnol. Oceanogr. 25: 389- Diphnia behavior following fish community ma- 402. nipulations. J. Plankton Res. 10: 621-635. LAMPERT, W. 1989. The adaptive significance of die1 -, AND OTHERS. 1987. Daphnia size structure, vertical migration of zooplankton. Funct. Ecol. 3: vertical migration and phosphorus redistribution. 21-27. Hydrobiologia 150: 185-19 1. MC-, I. A. 1963. Effects oftemperatnre on growth DODSON, S. I. 1988. The ecological role of chemical of zooplankton, and the adaptive value of vertical stimuli for the zooplankton: Prediction-avoidance migration. J. Fish. Res. Bd. Can. 20: 685-722. behavior in Daphnia. Limnol. Gceanogr. 33: 143 l- -. 1974. Demographic study of vertical migra- 1439. tion by a marine copepod. Am. Nat. 108: 91-102. GABRIEL, W., AND B. THOMAS. 1988. Vertical migra- PLJANOWSKA, J., AND P. DAWIDOWIW. 1987. The lack tion of zooplankton as an evolutionarily stable of vertical migration in Daphnia: The effect of strategy. Am. Nat. 132: 199-216. homogeneously distributed food. Hydrobiologia GELLER, W. 1986. Diurnal vertical migration of zoo- 148: 175-181. plankton in a temperate great lake (L. Constance): PLEW, W. F., AND R. W. PENNAK. 1949. A seasonal A starvation avoidance mechanism? Arch. Hy- investigation of vertical movements of zooplank- drobiol. Suppl. 74, p. l-60. ters in an Indiana lake. Ecology 30: 93-100. GILDERHUS, P. A., V. K. DAWSON, AND J. L. ALLEN. RACH, J. J., T. D. BILLS, AND L. L. MARKING. 1988. 1988. Deposition and persistence of rotenone in Acute and chronic toxicity of rotenone to Daphnia shallow ponds during cold and warm seasons. U.S. magna. U.S. Fish Wildl. Serv. Invest. Fish Control Fish Wildl. Serv. Invest. Fish Control 95. 7 p. 92.~5 p. GLIWICZ. M. Z. 1986. Predation and the evolution of STICH, H.-B., AND W. LAMPERT. 198 1. Predator eva- vertical migration in zooplankton. Nature 320: sion as an explanation of die1 vertical migration 746-748. by zooplankton. Nature 293: 396-398. HODGSON, J. R., AND J. F. KIT~HELL. 1987. Oppor- CARET, T. M., AND J. S. Sumac. 1976. Vertical mi- tunistic foraging by largemouth bass (Micropterus gration in zooplankton as a predator avoidance salmoides). Am. Midl. Nat. 118: 323-335. mechanism. Limnol. Oceanogr. 21: 804-813. HUTCHINSON, G. E. 1967. A treatise on limnology. V. 2. Wiley. JOHNSEN,G. H., AND P. J. JAKOBSEN. 1987. The effect Submitted: 12 February 1990 of food limitation on vertical migration in Daph- Accepted: 23 August 1990 nia longispina. Limnol. Oceanogr. 32: 873-880. Revised: 12 October 1990

Limnol. Oceanogr., 36(2), 1991, 377-383 0 199 I, by the American Society of Limnology and Oceanography, Inc. Bioerosion of coral reefs-A chemical approach

Abstract- We measured total alkalinity changes with it. It is suggested that L. lessepsiana is able as a direct clue to the rate and mechanism (chem- to redissolve chemically up to 40% of the CaCO, ical or mechanical) of boring of the bivalve Li- deposited by S. pistillata. thophaga Zessepsiana in colonies of the coral Sty- lophora pistillata, the most abundant coral-borer association in the reefs of the northern Gulf of Elat (Aqaba), Red Sea. Our experiments included Buildup of the primary framework on comparison between total alkalinity measure- coral reefs is accompanied by continuous ments of seawater surrounding colonies of S. pis- biological, physical, and chemical destruc- tillata free of L. lessepsiana and colonies infected tion. The net rate of CaCO, deposition on the reef is the sum of these processes (MacGeachy and Stearn 1976). Biological Acknowledgments We thank J. Erez for laboratory facilities; Ruth Ben- weathering, or bioerosion (Neumann 1966), Hillel, A. Nehorai, and T. Neuwirth for technical as- destroys and removes the calcareous sub- sistance; N. Chadwick, J. Erez, Y. Shlesinger, and 0. strate by the direct boring or rasping action Mokadi for critical discussions; and M. J. Risk for of organisms. review of the manuscript. This research was supported by grants 86-00 174 and Boring organisms, rather than rasping or- 85-00036 from the United States-Israel Binational Sci- ganisms, have a significant effect on the me- ence Foundation (BSF) Jerusalem, Israel. chanical stability of the reef framework, 378 Notes since they remove material from the inte- corals as direct evidence of a boring mech- rior. The mechanisms by which marine or- anism. A-r change over time, which has been ganisms burrow into hard substrates have widely used to estimate growth rates of coral been the subject of considerable research reefs (e.g. see Smith 1973; Barnes et al. 1976), (Yonge 1955, 1971; Fang and Shen 1988). can potentially quantify the rates of con- Quantitative data on bioerosion rates in reef struction (skeletogenesis) vs. destruction environments are rather scarce (Neumann (bioerosion) of living corals bored by any 1966; MacGeachy and Steam 1976; Kobluk chemical borer. and Risk 1977; Tudhope and Risk 1985; The operational definition of A, is the Hutchings 1986). Most of the research has number of equivalents of strong acid added been aimed at the clionid sponges (Neu- to the sample in order to reach the H&O, mann 1966; MacGeachy 1977; Hutchings endpoint (Stumm and Morgan 198 1). A, in 1986), and little information is available on normal oxygenated seawater is expressed by the role of worms, barnacles, and bivalves. The boring bivalve is an im- AT = mnco,- + 2mco,2- + mB(OH&- portant borer on the reefs of Isla de1 Cafio + man- - mH+ (1) (Costa Rica), Isla Uva (Panama) (Scott and where min- denotes the molal concentration Risk 1988), and on the reefs of the Gulf of of species i having a charge of n-. An im- Elat (Aqaba), Red Sea (Fishelson 1973; Loya portant characteristic of A, is its conser- 1982). In the Gulf of Elat about 15 coral vative behavior, i.e. the ratio A, : salinity is species are infected by this bivalve (Loya constant. Nonconservative A, changes in unpubl. results). Among them, Stylophora normal oxygenated seawater are almost ex- pistillata shows the greatest infestation: typ- clusively due to CaCO, precipitation or dis- ically 300-600 Lithophaga lessepsianabore solution (Stumm and Morgan 198 1). Thus, into a medium-sized (30-cm diam) colony after normalization to salinity, A, increases (Loya 1982). S. pistillata composes -20% by 2 equivalents per mole of CaCO, dis- of the reef framework in the northern part solved. Precipitation decreases A, by the of the gulf (Loya 1972), and an estimate of same amount (Eq. 1). its bioerosional rate and mechanism is ex- A-r is slightly affected by other noncon- tremely relevant. servative processes, i.e. changes of N03- The mode of penetration into calcareous concentration. Aerobic oxidation of average substrates differs among bivalve species. oceanic organic matter by respiration pro- Boring by lithophagid bivalve molluscs is duces nitric acid (e.g. see Redfield et al. believed to occur through chemical disso- 1963): lution of coral substrate (e.g. see Jaccarini et al. 1968; Bolognani Fantin and Bolognani [(CH,O),o,.(NH,),,.H,PO,I + 13Qq, 1979; Morton and Scott 1980) or a com- + 106C0, + 16H+ + 16N03- bination of chemical and mechanical abra- + H,PO, + 122H20. (2) sion (e.g. see Soliman 1969). Fang and Shen (1988) suggested that Lithophaga nigra is a Nitrate regeneration within the skeleton of mechanical and not a chemical borer. They the coral Porites lobata was observed by Risk attributed an observed pH decrease in ar- and Miiller (1983). Nitric acid decreases tificial burrows of L. nigra to excretion of (“titrates”) the alkalinity because hydrogen metabolic CO, rather than to excretion of ions combine with anions of weak acids and a strong acid. The pH decrease that they neutralize them. Thus, respiration lowers observed is capable, however, of reducing A, by the amount of NO,- produced: aragonite saturation state to a level at which A, = &(i, - mN03- = mHC03- + 2’%032- it will dissolve. Thus, pH provides only in- + rnB(OH)d- + moH- - mH+ (3) direct evidence for CaCO, dissolution or precipitation, and a direct estimate is need- where ATcrl denotes the A, before respira- ed to determine the boring mechanism. tion takes place. Consumption of N03- by Here we suggest measurement of total al- primary production (the opposite of Eq. 2) kalinity (AT) in the seawater surrounding will increase A,. The overall change in A, by primary production-respiration, accord- the study. The sample was filtered through ingtoEq.2,is16/106or-15%oftheCOz a 0.45pm Millipore membrane filter. About change due to these processes. 15 g (avg weighing SD was 0.00 1 g) of the The present study applies A, to measure filtrate were weighed directly in the titration chemical boring rates in coralline aragonite. vessel (Radiometer model 956-176) and If L. Iessepsiana is a chemical borer, then placed in a covered, Radiometer model TTA dissolution of coralline aragonite will in- 80 titration assembly. The samples were ti- crease the AT of the surrounding seawater trated with 0.25 N HCl (BDH coned vol- due to addition of Ca(HCO,), to the water. umetric solution). Two types of measuring If the mode of penetration is mechanical, device were used to measure the potential however, then only particulate aragonite will of the pH electrochemical cell (glass elec- be produced and A, will remain constant. trode Radiometer model G2040C and Two colonies of S. pistillata were col- K4040 reference electrode): a very high in- lected in front of the Heinz Steinitz Marine put impedance differential amplifier with an Laboratory (Gulf of Elat). One was heavily A/D converter (AD/7550), and a Radiom- infected (infected colony- IC) with boring eter model PHM 84 pH meter with an an- L. lessepsiana and the other was free of bor- alog output. The digital signal of the pH ers (noninfected colony-NC). Our discus- electrode was fed to an IBM PC-XT sion is based only on the experimental re- equipped with a digital I/O card (PPI 8255) sults from these two colonies. via an interface-controller. The analog out- After an acclimation period of 1 d in a put of the pH meter was fed to the computer tank supplied with running seawater, each via a Data Translation model DT 280 1 sin- colony was transferred to an aquarium con- gle board analog and digital I/O system. The taining 10 liters of freshly collected seawa- acid was delivered by a Radiometer ABU ter. The aquaria were kept open in the lab- 80 autoburette controlled by the PC via the oratory and were illuminated continuously I/O devices. Complete system control for with fluorescent light and aerated with fresh the DT 280 1 was provided by software writ- outdoor air. During each sampling period, ten in ASYST (Macmillan). The PPI 8255 water samples were taken from each aquar- was controlled by software written in TUR- ium with a 60-ml plastic syringe and col- BO PASCAL (Borland). The average SD be- lected in 60-ml glass bottles. Eighty milli- tween duplicate titrations estimated from liters of water were removed during each 200 seawater samples was 0.8 peq kg-‘. sampling period; 20 ml were used to rinse Salinity changes during the experiment the syringe and the sample bottle and the were monitored by Br- concentration. Bro- rest was stored at 4°C until the alkalinity mine was analyzed by ion chromatography titration. with a Dionex 2010 (typical SD of 0.75%). Three days after this experiment, the col- The surface areas of the colonies were de- onies were returned to running seawater and termined by breaking them into subcylin- maintained there for 9 d. Then, the corals drical pieces with a cutter. The length (I) were placed under a strong jet of seawater and two diameters (the largest and the until they were completely cleaned of their smallest), to the nearest 0.1 mm, of each tissue (bleached) as inspected with a bin- piece were taken with a caliper. The radius ocular microscope. During this process the (r) of the cylinder was calculated as half the boring clams in IC closed their valves and average of the two diameters. Two types of appeared unharmed. After an acclimation cuttings were produced: fragments cut on period of 1 d, the clams extended their paired both sides and tips of branches having one siphons out of the burrows and exhibited cut only. The surface area of fragment type normal behavior. The bleached colonies 1 is given by 2arl and the area of type 2 is were placed again in the aquaria, and the estimated by 2m-(l + %r). Replicate surface experiment was repeated. area determinations showed an average SD Computerized alkalinity titration, mod- of 3%. ified and improved from Ben-Yaakov et al. Alkalinities were calculated from the ti- (1982) and Lazar et al. (1983) was used in tration data with a modified Gran method 380 Notes

Table 1. Analytical results from the experiment with Table 2. As Table 1, but with bleached colonies. living colonies. Surface areas are 875 S 26 and 1,330 + 40 cm2 for NC and IC respectively.

NC IC 21 1340 2,445 2,464 75.2 Jun 1988 Time AT kq kg 0 1440 2,437 2,458 - 9 1245 2,452 2,460 75.1 1640 2,428 2,468 - 1435 2,430 2,435 - 1925 2,436 2,510 - 1505 2,424 2,429 - 2150 2,445 2,599 - 1635 2,413 2,404 - 2350 2,457 2,627 - 1835 2,361 2,379 - 22 0830 2,466 2,720 - 2400 2,261 2,314 - 1130 2,514 2,770 - 10 0900 2,177 2,232 - 1340 2,547 2,785 76.0 1945 2,017 2,052 76.3 1740 2,539 2,834 - 11 1050 1,813 1,828 - 2050 2,534 2,838 - 1510 1,776 1,784 - 23 0745 2,571 2,922 - 2100 1,703 1,693 78.9 1130 2,575 2,949 76.9 12 0830 1,599 1,605 79.9

and negative Ar(gain)represents precipitation (Gran 1952). The ratio A, : E,, was used to of CaCO,. correct A, for the degree of evaporation (E,J The integrated rates of CaCO, dissolution of the aquaria seawater, where E,, is defined or precipitation were calculated by dividing by: ATcgain)by the time (t) passed from the be- EDr = Br-/Br-(,,, (4) ginning of the experiment to a particular and Br- and Br(,, denote bromine con- centrations in the sam.ple and “mean” sea- 2500 water (Stumm and Morgan 1981). Br val- ues for samples in which it was not determined (see Tables I, 2) were interpo- 5i lated linearly. s The experiments with living (Table 1 and 2% 2000 Fig. 1A) and bleached corals (Table 2 and Fig. 2A) reflected A, changes due to coral- line aragonite precipitation and dissolution in the aquaria. Comparison between colo- 1500’ I ’ ’ ’ nies was provided via normalized alkalinity 0 20 40 60 data, where ATcgamj(Figs. lB, 2B) is defined Time (h) as: 0

7i i!! -250 i whereAT(galn) is excess alkalinity gained due ” to aragonite dissolution from the beginning of the experiment to any particular sam- pling point per unit of area of coral in peq cmm2, d the density of the aquarium sea- water in kg liter-l, V, the volume of the 0 20 40 60 Time (h) aquarium at this particular point in liters, the initial degree of evaporation Fig. 1. Alkalinity and C&O3 weight as a function of incubation time for the live corals experiment. A- F-?16), ATcrI the initial AT in I.ceqkg-’ and A, curve. B-ATtillj curve, the weight of CaCO, per A COId the surface area of the colony in ‘cm2. unit area of coral is shown on the right. Analytical error Positive ATcgainjmeans dissolution of CaCO, is smaller than the symbol size. Notes 381

10

05 2.5 F . 00 0.0 2 k 0.5 -2.5 0 % IO -5.0 -2 . -=I -0. 15 -7.5 3

.z -0.201 ' I ' ' I ' -10.0 0 20 40 60 Time (h) B I I I k Time (h) =- 2.5 A non infected Fig. 3. Apparent aragonite deposition rate (nega- 100 z tive part) and dissolution rate (positive part) vs. in- cubation time. Live K--O; bleached IC-A; live NC- z 75 8 W; bleached NC-A. To eliminate most of the noise in the derivative calculation, each sampling point was 50 $ divided by the total time passed from the beginning of the experiment, instead of the time interval between 25% two consecutive points. This type of derivative cal- culation introduces some artifacts: the derivative value 0 is not zero when the signal does not change with time, and the derivative of linear trend which does not pass 0 10 20 30 40 50 through the origin is not constant, but decreasesslowly. Time (hl Fig. 2. As Fig. 1, but for the bleached corals ex- periment. much debated, however, in the literature. Numerous papers have demonstrated the sampling point. Plots of this rate vs. time presence of acid glands in Lithophaga are given in Fig. 3. (Yonge 1955; Morton and Scott 1980 and In the live corals experiment, NC and IC references cited there), but none has de- behaved similarly and reflected an A, drop scribed the chemical component that was of -60*/b from the original value (Fig. IA). secreted. Histochemical analyses of the ATLsainjis negative throughout the experi- glands identified few components that can ment with the live corals (Fig. lB), indicat- act as Ca2+ chelators-a neutral mucopro- ing net deposition of skeletal aragonite. Due tein (Jaccarini et al. 1968) and lipoproteic to the continuous illumination, almost no components with acidic groups (Bolognani diurnal growth pattern was observed. NC Fantin and Bolognani 1979). Aragonite dis- deposited - 150 pg cmm2 more aragonite solution caused by the activity ofthese com- than IC at the end of the experiment. Net ponents will result in the observed A, in- deposition rate of skeleton for NC thus is crease. higher than that of IC. Another common acidic component In the bleached corals experiment, A, and probably present in the burrow is metabolic ATcgai,,)curves showed a substantial alkalin- CO,. It was demonstrated experimentally ity increase in the aquarium with IC, in con- that metabolic CO, caused a significant pH trast to a small change for NC (Fig. 2). The decrease in artificial burrows of L. nigra large positive AT(gain)values recorded in the (Fang and Shen 1988). We suggest that this aquarium with IC (Fig. 2B) clearly dem- CO, can dissolve CaCO, via the reaction: onstrate that L. lessepsiana is able to dis- + H,O + CaCO,,,, solve coralline aragonite. The amount of ~%a,, 4 Ca2+ + 2HCO,-. aragonite bioeroded chemically at the end (6) of the experiment is - 100 pg cm-* higher Thus, for every mole of CO, reacted with than that of NC. The exact process of ara- aragonite, the A, of the solution increases gonite dissolution by Lithophaga is still by 2 equivalents. 382 Notes

The drop in AT(win) at the beginning of the Table 3. Calculated potential growth rate (fl of the investigated colonies. The numbers for G and D are experiment with NC (Fig. 2B) is probably averages of the data points that plot on the lines and due to precipitation of aragonite. This in- reflect small changes in rate (Fig. 3). organic deposition may be triggered by in- troduction of the bleached coral to the NC IC aquarium seawater, which is supersaturated rrg (cm’ c~ral-~ h-’ n* with respect to aragonite (Lazar et al. 1983). Net growth rate (G) 6.8-tO.8 4.5kO.3 11 Lazar et al. (1983) demonstrated an A, de- Dissolution rate (0) 0.72kO.47 3.6-tO.S 8 crease upon addition of excess coralline ara- P=G+D 7.5-tl.2 8.1kO.8 gonite powder to Gulf of Elat surface sea- *Number of data pants tien for calculating averages. water. Similarly, the exposed coral surface serves as a CaCO, deposition site, although it is less efficient than the powder, due to a of endolithic algae present in our experi- smaller area : volume ratio. Therefore, one ment will produce a similar photosynthetic would expect ATcgainjto remain somewhat signal (per unit coral area) for both (NC and negative throughout the experiment. The IC) colonies. That area cover of endolithic experiment with NC also exhibited A, in- algae is probably uniform for corals older crease, however (Fig. 2B); this increase than -2 yr is suggested from the experi- probably is due to local dissolution of ara- ments of Tudhope and Risk (1985). There- gonite in places where some remaining or- fore the difference in ATWnj between IC and ganic matter has oxidized microbially. In NC is probably due to dissolution only. The the case of organic matter oxidation in con- A,(,i, of -0 peq cm-* at the beginning of tact with solid carbonate, Eq. 2 will take the the experiment with IC can be explained as form a balance between inorganic aragonite pre- cipitation due to supersaturation and dis- solution of coralline aragonite by the boring + 106CaCO,,, + 1380,,,, clams. - 106Ca2+ + 2 12HCO,- + 16H+ The plots of growth and dissolution rates + 16N03- + H,PO, + 16H,O. (7) (Fig. 3) show that both experiments reached relatively constant rates after - 10 h. This According to Eq. 7, each mole of total steadiness permits calculation of the aver- CO, gained due to “organic matter” oxi- age net growth and dissolution rates (Table dation produces maximally (2 12- 16) : 106 3). It is reassuring that the potential growth = 1.85 equivalents of AT due to aragonite rate (P) calculated for both colonies (Table dissolution. The actual change in A, is most 3) was comparable, averaging 7.8 f 1 .O pg probably smaller than that, because the so- (cm2 coral))’ h-l. This similarity implies that lution is supersaturated with respect to ara- the skeletal density of a heavily infected cor- gonite (Lazar et al. 1983). Therefore, COP al colony should be substantially smaller will locally lower the degree of saturation than that of a noninfected colony of the same before any dissolution takes place. An al- age. The effect of burrows on skeletal den- ternative explanation for the observed A, sity was demonstrated by Scott and Risk increase could be boring by endolithic algae (1988) in their table 1, which reflects a sig- (Kobluk and Risk 1977; Tudhope and Risk nificant negative correlation between the 1985). Their photosynthetic activity could percentage of material removed by Lithoph- cause an increase of A, according to the aga and the skeletal density of P. lobata. inverse of Eq. 2. It was shown by Bellamy and Risk (1982) however, that live S. pis- Boaz Lazar tillata from the Great Barrier Reef is only sparsely infested by boring algae. The same Heinz Steinitz Marine observation was made by Y.L. on S. pistil- Biology Laboratory fata from the Gulf of Elat. Thus, A, increase Hebrew University of Jerusalem due to the activity of boring algae is prob- P.O.B. 469 ably minor. Moreover, the trivial amount Elat 88103, Israel NO1

Yossi Lqya MACGEACHY,J. K. 1977. Factors controlling sponge boring in Barbados reef corals. Proc. 3rd Int. Coral Department of Zoology Reef Symp. 2: 477-483. George S. Wise Faculty of Life Sciences -. AND C. W. STEARN. 1976. Boring by ma- croorganisms in the coral Montastrea a&d&s on Tel-Aviv University Barbados reefs. Int. Rev. Gesamten Hydrobiol. Ramat-Aviv, Tel-Aviv 69978 61: 715-745. Israel MORTON, B., AND P. J. S. SCOTT. 1980. Morpholog- ical and functional specializations of the shell, musculature and pallial glands in the Lithophag- References inae(: ). J. Zool. Lond. 192: 179- BARNES, D. J.. AND OTHERS. 1976. Metabolic pro- 203. cessesof coral reef communities at Lizard Island, NEUMANN, A. C. 1966. Observations on coastal ero- Queensland. Search 7: 436-468. sion in Bermuda and measurements of the boring BELLAMY,N., AND M. J. RISK. 1982. Coral gas: Ox- rate of the sponge Cliona lampa. Limnol. Ocean- ygen production in Millepora on the Grea; Barrier ogr. 11: 92-108. Reef. Science 215: 1618-1619. REDFIELD.A. C.. I3. H. KETCHUM,ANDF. A. RICHARDS. BEN-YAAKOV,S., R. ~VIY, H. GUTERMAN,A. DAYAN, 1963: The’ influence of organisms on the com- AND B. LAZAR. 1982. Application of personal position of seawater, p. 26-77. In M. H. Hill [ed.], microcomputers in the analytical laboratory- 1. The sea. V. 2. Wiley-Interscience. Potentiometric analysis. Talanta 29: 264-267. RISK, M. J., AND H. R. MUELLER. 1983. Porewater in BOL~GNANI Fmm, A. M., AND L. BOLOGNANI. 1979. coral heads: Evidence for nutrient regeneration. The pallial glands of Lithophaga lithophaga (L.): Limnol. Oceanoar. 28: 1004-l 008. A histochemical and biochemical approach of the SCOTT,P. J. B., AND-M. J. RISK. 1988. The effect of rock boring problem. Malacologia 18: 587-589. Lithophaga (Bivalvia: ) boreholes on the FANG, L., AND P. SHEN. 1988. A living mechanical strength of the coral Porites lobata. Coral Reefs 7: file: The burrowing mechanism of the coral-boring 145-151. bivalve Lithophaga nigra. Mar. Biol. 97: 349-354. SMITH,S. V. 1973, Carbon dioxide dynamic: A record FISHELSON,L. 1973. Ecological and biological phe- of organic carbon production, respiration, and cal- nomena influencing coral-species composition on cification in the Eniwetok reef flat community. the reef table at Eilat (Gulf of Aqaba, Red Sea). Limnol. Oceanogr. 18: 106-120. Mar. Biol. 19: 183-196. SOUMAN, G. N. 1969. Ecological aspects of some GRAN. G. 1952. Determination of the eauivalence coral boring gastropods and bivalves of the north- pbint in potetiometric titrations, Part i. Analyst western Red Sea. Am. Zoo]. 9: 887-894. 77: 661-671. STUMM, W., AND J. MORGAN. 1981. Aquatic chem- HUXHINGS, P. A. 1986. Biological destruction ofcor- istry, 2nd ed. Wiley-Interscience. al reefs. Coral Reefs 4: 239-252. TUDHOPE, A. W., AND M. J. RISK. 1985. Rate of JACCARINI,~., W. H. BANNISTER, AND H. MICALLEF. dissolution of carbonate sediments by microbor- 1968. The pallial glands and rock boring in Li- ing organisms, Davis Reef, Australia. J. Sediment thophaga lithuphaga (Lamellibranchia, Mytili- Petrol. 55: 440-447. dae). J. Zool. Lond. 154: 397-401. YONGE, C. M. 1955. Adaptations to rock boring in KOBLUK, D. R., AND M. J. RISK. 1977. Rate and Botula and Lithuphaga (Lamellibranchia. Mytil- nature of infestation of carbonate substratum by idae) with a discussion on the evolution of this boring algae. J. Exp. Mar. Biol. Ecol. 27: 107-l 15. habit. Q. J. Microsc. Sci. 96: 383-410. LAZAR, B., A. STARRYSKY,A. KATZ, E. SASS,AND S. -. 197 1. On functional morphology and adap- BEN-YAAKOV. 1983. The carbonate system in tive radiation in the bivalve superfamily Saxica- hypersaline solutions: Alkalinity and CaCO, sol- vacea (Hiatell = Saxicava), Saxicavella, Panomya, ubility ofevaporated seawater. Limnol. Oceanogr. Panope, Cyrtodaria). Malacologia 11: l-44. 28: 978-986. bYA, L. 1972. Community structure and species diversity of hermatypic corals at Eilat, Red Sea. Mar. Biol. 13: 100-123. -_ 1982. Life history strategies of boring bi- Submitted: 11 September 1989 valves in corals. The reef and man [Abstract.]. Accepted: 27 February 1990 Proc. 4th Int. Coral Reef Symp. 2: 756. Revised: 5 December 1990