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. 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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 Lithophaga 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).