, u,__ -- - . -~ PART V: RESPIRATION OF ZOOPLANKTON AND BENTHOS Introduction 245. Respiration is the sum of all physical and chemical pro­ cesses by which organisms oxidize organic matter to produce energy. During aerobic respiration. oxygen and organic matter are consumed and carbon dioxide and water produced (Pennak 1964). Components of respira­ tion include specific-dynamic action (SDA). basal-respiratory rate (BRR). standard-respiratory rate (SRR), and a respiratory component for activ~ ity. Specific-dynamic action refers to the energetics of digestion and is the s~allest component of respiration--e.g., 15.4 percent of the total in the plecopteran Acroneuria californica (Heiman and Knight 1975). Basal-respiratory rate is the minimum energy expenditure required to sustain life. Standard-respiratory rate (SRR) is equal to the sum SDA + BRR. The activity component is highly variable and accounts for most of the variation in total respiration (Calow 1975). 246 . Respiration is a very important parameter in energy budgets. Maintenance energy constitutes a major portion of energy expenditures by populations of aquatic invertebrates (80 to 90 percent) and therefore can be used as a first approximation of total assimilation (Moshiri et a l. 1969). Respiration was 92.7 percent of assimilation in the cladoceran Leptodora kindtii (Moshiri et al . 1969) and 81.8 percent in the isopod Asellus aquaticus (Klekowski 1970). Since maintenance costs must be met for survival, respiration may exceed assimilation under unfavorable environmental conditions. Under such conditions, biomass may be catabolized to meet the increased demand for energy . Methodology 247. Respiration rates of aquatic invertebrates usually are estimated directly by monitoring oxygen consumption, since the estima­ tion of heat loss from ectotherms is impractical by direct calorimetry (Hughes 19 70 ) . By multiplying 02 consumed by an oxycaloric coefficient. 127 e .g . , 4 .83 c a l/ml 0 2 (Wi nberg et a l . ) 9 34 ), respiratory r a t e c a n be est i ma t e d . Some de g ree o f e r r or i s inherent t o the a p pl i cat ion o f an oxy c a loric coeffic i e nt because the c oe f f i c i e n t v ari es wi th t he type o f body c ompo n e n t ox i d i z e d . Winbe r g e t al . ( 1934 ) found diffe rent o xyca lor ic coe f f icien t s f or oxidat i o n o f c a r b oh y d r a t e (4. 68 6 ca l / ml 0 2 ) ' pro t e i n ( 4 .72 1 c al/ ml 02)' a n d f a t ( 5 .04 3 c a l/ml 02) . With out measu r ing n i t rogen e x c r e tion and CO p roducti o n du r i n g experimen t s , on e h a s no way o f d e ­ 2 ter mi ning what type o f materi al is bein g o x idize d and t h e refore i s u nabl e t o app r opri ately a dj us t t he oxyc a loric c oe f f icie n t. As a resul t , t h e oxy c a lor i c c oe f f icie n t s fo r the thr e e body c ompo nents usually are a ver­ a ged ( i .e., i t is a ssumed that s peci me ns b u r n pro tein, f at , and c a r bo­ hydra t e s e qua l l y) . Hug h e s ( 1970) s t a ted t hat the e r ror i nvolved in a pp l y i n g a mean coe f f icien t wa s s ma l l - - cer t a i nly s ma lle r t han the e rro r i nh e r e nt to an ext rap o lati o n o f lab r e s u l t s t o a field s i t u a t ion . 248 . Manome tric methods ( e .g . , t h e use of Warburg , Gi lson , and Cart esian d iver respirometers) r e quire a manometer t o me a sur e d e c r e a s e s i n gas p ressu re wi t hin a c los e d c ha mbe r . In the r e spiratory c h a mbe r , s pe c i me ns consume 02 a nd produc e CO . Be c aus e t he experimental medium 2 i s a l kali ne and a bs o r bs CO , the ga s pre s sure i n the c h ambe r d e c r e a s e s 2 i n proportion to the r ate of 0 2 c o ns ump t i o n (Urnbreit e t a l . 196 4 ) . There a r e two disadvanta ge s t o manome tric t e chni que s : ( a ) alka l ine sol u t i o ns ma y affe c t r e s p i r ati on i n some s pe c i e s ( Sus h ch e ny a 19 6 9 ) and (b) s ha k i n g (often e mpl oyed t o ensur e abs o rpti o n o f CO ) may excite s pecimens a nd 2 eluci d a te a r tif i c ia l ly h i gh rate s o f r e spirat i o n ( Rueger et a l . 1969 ) . I n contras t t o Wa rbur g a n d Gilson r espiromete r s. Ca r t esian d ivers have e xtreme ly s ma l l c h a mbe rs f or s peci me ns a nd , cons e q u e n tly, a r e t he o n ly resp i r ometers s u i t ed t o meas u r e r e s p iratio n rates o f ind i v idual zoopl ank ­ t ers . Diffe renc e s i n t he r e spiratory r a t e s o f i nd i v i duals o f the s ame s pecies o f ten be c ome apparent in Cartesian d i vers ( I v a n ova a nd K1e kows k i 19 72 ) . Suc h d i f f erenc e s are u sually mas ke d i n o t h e r me tho d s where ma ny s pe cime ns are e ncl o s e d c o ncomi t ant l y i n o ne c h amber . 249 . Chemi c a l methods . u sual l y Wi n k l e r t i t r a t i o n ( Am e r i can Pu b lic He a l t h As s o c iat i o n 19 71 ) , Modi f i e d-Win k l e r t i t r a t i o n , o r Micro-Wi n k ler titra t i o n, me a s u r e 02 con c e n t ra t ions i n a c los e d s ys t e m befo re a n d a f ter 12 8 a suitabl e experi mental pe riod . Th e pe r i od must be l ong enough for a detectable differen ce i n 0 2 c o n c e ntr atio n to develop but short enough to prec lude s i gn i f i c a n t development o f b a c t eri a l populations or starvation of experimental s peci me ns (Marshal l 19 73 ) . The dif f e r e n c e between the initial a nd final 02 concentration i s taken to r epr e s e n t oxygen c ons ump ­ t ion by t he encl o s e d s peci me ns. Th e combined use o f a c l o s e d bottle and Wi nkler titration has been the most pop u l ar means of d etermini ng r e s p i­ r ati on i n a qu a tic i nvertebrates (Appendix D, Pa r t s I and I I). Part of t he popularity is due to t h e fact that t h e s ystem is s i mpl e and c a n be u s e d i n the f ield o r laboratory . 250. Polarographi c me thod s require the me a s u r e ment o f c u r r e n t f l owing i n the externa l c ircu i t of a polarographic c e l l (Lingane 1961). These methods are advantageous in that t hey p rovi d e c o n t i n u o us mo n i t o r­ ing of 02 t ensions ( Rue ger e t a l .