Bolm Inl;1. oceano~., S Paulo, 43(1):27-40, 1C)()S

Studles on chaetognaths off Ubatuba reglon, Brazll. II. 'Feedlng habita

Tsui Hua LIANG & Luz Amelia VEGA-PÉREZ

Instituto Oceanográfico da Universidade de São Paulo (Caixa Postal 66149, 05389-970 São Paulo, SP, Brasil)

• AbstTact: The diet of chaetognath species were studied by examining the gut contents of 9466 specimens coUected off Ubatuba regioo, São Paulo State. The greatest proportion of chaetognaths (7119 individuaIs) showed their gut contents empty. , moUusc eggs, appendicularians, cladocerans and annelidswere the most common food items in tbe gut contents of juvenilesand mature stages. Cannibalism occurred in low frequency. ln Summer the copepods Temonl stylifenl and Paraca/anus spp were more abundant, whereas spp and mollusc eggs were heavi1y preyed in Winter. There was a clear trend of increasing prey size with the developmental stage.

• Resumo: O estudo dos hábitos alimentares das espécies de foi reali7.ado a partir da análise do trato digestivo de 9466 indivíduos dos estágios O - IV. Os quet6gnatos foram coletados ao largo da região de Ubatuba, Estado de São Paulo, com o auxilio da rede Bongo (Malha 0,200 mm e 0,303 mm), nos verões de 1985 - 1987 e invernos de 1986 e 1987. Dos 9466 tratos digestivos analisados, 7119 estavam vazios e 2347 apresentaram de 1 a 3 presas. Grande quantidade de material amorfo e semi-digerido também foram detectados. A dieta esteve constituída basicamente de copépodos ( e Poeci1ostomatoida), clad6ceros, ovos de moluscos, náuplios de crustáceos, apendiculárias e poliquetos, entre outros. O canibalismo foi observado a partir do estágio I, porém com baixa frequência. Os estágios jovens (O-I) mostraram preferência por presas de tamanho pequeno como náuplios e copépodos do gênero Oncaea, enquanto que os estágios maduros por presas maiores como Temora stylifera, Corycaeus sp e Eucalanus pileatus.

• Descriptors: Feeding, Predation, , Chaetognatha, S. enflata, S. friderici, S. hispida, Ubatuba, Brazil, South Atlantic.

• Descritores: Alimentação, Predação, Zooplâncton, Chaetognatha, S. enflata, S. friderici, S. hispida, Ubatuba, Brasi~ Atlântico Sul.

Introduction species bave been neglected. According to Gallager (1988) tbe importance of studyiog predator feeding mecbanisms The interest in the feeding of zooplanktoo has is that we can predict how carnivorous zooplankton will increased considerably during recent years. Behavioral affed community structure and fundion by indirectly responses to food species, concentration and their tropbic measuring feeding behavior, e. g., gut content analyses or interactions bave been studied for many years in an attempt counts of available prey items. to elucidate fundamental patterns structuring Chaetognaths are known as one of the most important communities (Gallager, 1988). and adive predators of zooplankton, preying upon a wide Zooplankton plays a criticai role in the ecology of variety of organisms (Raymont, 1983; Alvariiío, 1985). marine systems by serving as a link between , They may affect the distributioo, density and occurence of and higher trophic leveis in tbe nekton their preys (Cheney, 1985). and benthos. Ao understanding of marine planktonic food ln Brazilian waters, many studies on chaetognaths have webs requires informatioo on the abuodaoce, biomass and examined their systematics, distribution and occurrence rate of ioteractioos betweeo ali trophic leveis (Buskey, (Vannucci & Hosoe, 1952; Almeida-Prado, 1961a, b; 1968; 1993). Ferreira da Costa, 1970; Coelho, 1993). The knowledge of Studies 00 feediog have beeo focuscd maioly 00 the their feeding habits has received little attention, being herbivorous organisms like copepods wbile carnivorous limited to the study of the chaetognath S. friderici off Ubatuba (Vega-Pérez & Liang, 1992).

Contr. no. 775 do Inst. oceanogr. da Usp. 28 Bolm Inst. oceanogr., S Paulo, 43(1), 1995

The aim ofthe present study is to analyse the qualitative Wcll-digested food was called unidentified. Copepods and quantitative food composition of the chaetognath were idcntified hased on Bjõmherg (Boltovskoy, 1981). species collected off Ubatuba region. Percentage numher was used as an index of the importance of eaeh prey item in the dict. Similarities of the diet were calculated using the Schoener index (1968) Material and methods wich measures the overlap hetween two categories of comparison and gives values from O (no overlap) to 1 This study was part of a program of multidisciplinary (complete overlap): study of tropical marine ecosystems: "Brazilian Coastal Ecosystems", off Ubatuba region, São Paulo State, from o 1985 to 1989. D = 1 - 0,5 r~ (Pxi- Pyi)) Zooplankton sam pies studied io this work were i= 1 collected 00 five oceanographic cruises during Oecember were Pxi is the proportioo of food category in lhe diet 1985, 1986, 1987 and July 1986, 1987. A survey grid of 30 of species x. Pyi is lhe proportioo of food category io lhe standard planktoo statioos distributed along six traosects diet of species y, and o is the oumber of food categories. was established in the sea frontal to the Ubatuba regiDo Biologically, overlap is considered signi6cant wheo lhe (24°1O'S-44"30'W and 23"30'S-45"20'W). value exceeds 0,60 (Zaret & Rand, 1971; Wallace, I981). Oblique hauls were made with a Bongo net fitted with a fioer (0,200 mm) and a coaser meshed net (0,303 mm), and provided with flowmeters. Samples were preserved Results in a solution of 10% buffered formalin. ln this study, only samples obtained by regular mesh Si7.e were The analysis of the gut contents of 9466 chaetognaths analysed. 00" Ubatuba region showed a total of 7119 specimens with Temperature and salinity data of the water column empty guts and 2347 containing 1 to 3 preys (Table 1). The were obtained simultaneously with the use of Nansen bulk of chaetognath specimens contained only one prey. bottles. Multiple preys (2 - 3) were found in S. enflata (129), S. lo the laboratory, plankton was subsampled with the hispida (24), S. friderici (16) and S. tenrtis (4). cylindrical Motoda Splitter (Omori & Ikeda, 1984). Ali the Chaetognath species preyed upon a widc variety of chaetognath specimens were removed from the organisms. The food organisms most frequently found in subsamples and identified accordingly to their guts were , mollusc eggs, Almeida-Prado (1961a) and Alvarifio (1969). The appendicularians and polychaetes. ln ali cases, however, maturity stages were determined based on Reeve the most important prey within the global diet were the (1970): (O-II) young stages; (III-IV) adult stages. copepods, specially Calanoida and Poecilostomatoida. Gut content of 9466 specimens were examined by body Cannibalism was observed, but in low frequency mostIy io transparency (Pearre, 1980) and the prey items were S. enflata, S. hispida and S. friderici. This hehavior was identified to species or to the lowest taxonomic levei detected in stage I and tendcd to increase in the later possible using a stereoscopic microscope (Wild M7). stages.

Table 1. Number of chaetognath specles anallsed; P = No. of speclmens with prey items; E = No. of specimnens wlth empty guts

s. enfla/a s.friderici s. hispida s. /enuis s. minima K. pacifica s. serra/adenta s. bipunc/a/a s. hexap/era P. draco CRU/SE E P P P P E P E P P E P E P E P

SUltlER/1985 236 56 242 85 78 14 26 17 14 9 28 4 21 24 47 W/ NTER/l986 1021 470 326 80 96 129 2 20 42 9 154 28 2 SLM4ER/l986 711 135 387 70 278 98 19 45 21 1 8 4 15 19 2 2 1 4 W/ NTER/1987 1845 658 919 123 108 96 16 32 179 8 100 18 9 2 4 SLM4ER/ 1987 84 56 27 26 16 6 14 o 6 3

TOTAL 3897 1375 1901 384 576 343 63 114 270 Z7 295 55 53 44 49 4 1 11 o LIANG & VEGA-PÉREZ: Chaetognaths: Feeding habits 29

Large quantities of well-dige~led food and Food iterns s. enn.ta s. friderici s. hispide considerably high number of unidentified preys were also deteeted in the gut content~ of lhe ehaetognaths. C. giesbrecIJti 27 4 9 The prey diversity generally ehanged wilh the C. typicus 2 1 2 C. africanus 1 1 deveJopmental stage and the ~ea~ons . Older stage~ (II-IV) C. amazonicus 6 5 consumed higher diversity of preys than the younger stages C.flaccus 2 (0-1). Similar results were observed in the Winter surveys C.limbatus 5 1 Farranlllla gracilis 7 2 1 when ehaetognaths showed higher diversity of food than HARPAC'TICOIDA specimens colleeted in the Summer. Microsetella ntNVegica 22 4 3 Only the diet of S. enflata, S. friderici and S. hispida wilt Macrosetella gracilis 9 3 1 ElIterpina acutifrons 5 1 be detaiJed, because the other species were not pre~ent in Unidentified 145 55 36 enough number of individuais. CLADOCERA 12 3 1 Penillia avirostris 15 6 6 Evadne spinifrons 3 E. tergestma 7 3 S. enflata Podonsp 7 8 3 OSTRACODA 1 Copepods dominated the diet of S. enflata. Moltuse AMPHIPODA 1 CIRRIPEDIA 6 eggs, erustaeean nauplii, c1adocerans and DECAPODA 1 1 1 appendicuJarians were also partieulary important in the Lucifer faxoni 2 6 diet of this species (Table 2). nauplii 50 32 26 U nidenlified 15 10 8

Table 2. Number of chaetognath specles anallsed; P = No. of speclmens wlth prey Items; E = No. Mollu~ea (eyp) 396 7 7 of speclmens wlth empty guts; T = total number of . Gastropoda (eggs) 3 1 Pteropoda 1 individuais Food item, S. enflata S. friderici S. hispida SIPHONOPHORA 1

POLYCHAETHA 9 1 3 CRUSTACEA Polyehaeta (Larvae) 6 COPEPODA CALANOIDA 19 3 6 Calanoides carinatus 4 2 UROCHORDATA Nannocalanus minor 2 1 THALIACEA-Salpidae 6 3 Ellcalanus sewelli 1 LARVACEA Oikopleura sp 41 34 28 E. pi/eatus 8 2 Paracalanus sp 12 12 3 CHAETOGNATHA 4 2 2 P. quasimodo 11 4 3 Clausocalanus furcatus 28 3 2 Eggs 40 C. arcuicomis 17 1 3 Sagitta sp 3 4 3 Ctenocalanus sp 1 1 Sarjtta enflata 4 1 Calocalanus styliremis 1 S. Jriderici 5 S. IJispida 1 4 Candacia curta 1 Scolecithricella vitatta 1 1 S. minima 1 Scolecithricella bradyi 2 S. tenuis 1 Calanopia americana 3 1 Temora stylifera 91 27 20 U nidcntified 199 120 105 Centropages veliJicatus 5 1 Euchaeta marina 1 Total prey items 1521 403 363 Pleurommama sp 1 No. indiVIdual wilh preys 1375 384 337 Pontellopsis sp 2 Oithonasp 1 The Shoener index of similarilie~ showed lilltc or no O. plllmifera O. nana overlap in the dict during the Summer surveys with relation POECILOSTOMATOIDA 2 to those in Winter (Table 3). ln the Summer, S. enflata fed Sapltririna angusta 1 1 heavily on Temora stylifera, Clausocalanus sp, Corycaeus sp Oncaea conifera 6 o. venusta 66 7 18 and Oncaea ~p . Crustacean nauplii were lhe main food O. curta 32 2 17 item of juvenile stages (0-1), but in the 1986 Summer the O. subtilis 1 most important prey items of stage I were cladocerans, O. meditemmea 4 mollusc eggs, Oncaea spp. The dict of older slages (II-IV) Oncaea sp 135 21 14 Corycaells sp 3 6 2 was mainly the copepods T. stylifera, C. fllrcahls, Corycaeus 30 Bolm Inst. oceanogr., S Paulo, 43(1),1995

sp and Oncaea. spp. Appeodicularians were aJso very lo the Winter, all developmeotal stages of S. enflata frequeot in the gut cootents. preyed most1y 00 mollusc eggs, the copepods Oncaea spp and appeodicularians. The diet of stages O and I were Tabla 3. Seasonal comparlson of dlet of three aJmost exclusively made up of the crustacean nauplü. chaatognath specias using Index of Schoener Chaetognaths and appendicularians were common from (1968) stage I (F"lgs 1 - 3).

1985 1986 1987 IUllER IIINTER sutlER IIINfER sutIER S. friderici

Copepods comprised the bulk of the diet of S. S. enflata friderici. SUlf4ER/1985 0.5 0.6 0.32 0.44 Appeodicularians, crustacean nauplü and cladocerans III NTER/l986 0.63 0.72 0.41 were also found in the gut contents. SlMIER/l986 0.47 0.49 According to the Schoener index, the diet of different III NTER/1987 0.29 periods showed overlap between Summer and Winter SUlf4ER/1987 (Table 3). S. friderici ln spite of this, in the Summer the most important food SUIIIER/1985 0.6 0.49 0.62 0.41 items were T. stylifera, whereas in the Winter Oncaea IIINTER/l986 0.48 0.58 0.35 spp and appendicularians were the most representative SUlf4ER/l986 0.68 0.56 III NTER/1987 0.45 preys. SUlf4ER/1987 ln the Summer, stages O and I of S. friderici preyed most1y on crustacean nauplli and copepods such as Oncaea S. hispida SUIIIER/1985 0.49 0.58 0.39 0.37 spp, T. stylifera and ParacaJanus sp. At stages II - III lhe III NTER/l986 0.62 0.6 0.12 diet was composed usually of appendicularians and lhe SUlf4ER/l986 0.54 0.29 large sized copepods T. stylifera, EucaJanus pileatus and IIINTER/1987 0.07 Corycaeus sp. During Winter, in all developmentaJ stages SUlf4ER/1987 the principal food was Oncaea spp, crustacean nauplli and

Stage I Stage II A

Nauplii

r.

Stage III Stage IV

OnC888 SPP

Fig. 1. Food items of S. enflata at each maturity stage. A - Summer 1985; B - Winter 1986. LlANG & VEGA-PÉREZ: Chaetognaths: Feeding habits 31

B Stage O Stage I

NavP, i, 11ll1ll1 MOl luSC eggs

Stage "

Chaetognat ha OnC88a SPP Nauplii acutif,ons ;nr "r.RR ,' J.< SPP Par8calanus SPP Cladocera

Stage '" Stage IV

OnC88a SPP

Fig. 1. Cont. appendicularians. However, the older stages (II, III) Corycaeus and Paracalanlls. Older stages (11- IV) preyed showed preference for appendicularians and large sized mainly on T. sty/ifera, Corycaeus spp and copepods like E. pileatus, Scolecithricella bradyi and appendicularians. Cannibalistic bebavior was common in Corycaeus sp (Figs 3-5). these stages. ln the Winter, young stages (0-1) consumed basically crustacean nauplii, Oncaea spp and S: hispida appendicularians, whereas stages II and III preyed heavily on Corycaeus spp and T. stylifera as well as the decapad L. The diet of S. hispida was composed of copepods, faxoni. Cannibalism was observed from stage I to IV (Figs appendicularians, crustacean nauplii and chaetognaths. 6 and 7). The Schoener index of similarities showed overlap in The results obtained in this study showed that the diet from Winter surveys, but no overlap in tbe Summer feeding habits of S. enflata, S. friderici and S. hispida probably due to the few data obtained in this penad. S. were similar. It was also verified that prey size changed hispidá preyed basically on T. sty/ifera in the Summer, with the developmental stages. Younger stages (O -I) whereas the copepods Oncaea spp, Corycaells sp and prefered small sized preys like nauplii and the appendicularians were prefered in the Winter. Oncaea spp, whereas older stages (II-IV) consumed During Summer, the juvenile stages fed on cladocerans, generally larger preys such as T. stylifera, Corycaeus spp. crustacean nauplii and the copepods of the genera Oncaea, and E. pileatus. 32 Bolm lost. oceanogr., S Paulo, 43(1),1995

A Stage I Stage II _.

Stag& III Stage IV

B Stage o Stage I

Stag& II

Oedoc.,. N8IA)Iu Po!yCI'IMt. Cot)'C..w SPO cn.etognetF'le

Stage III Stage IV

Fig. 2. Food items of S. enflata at each maturity stage. A - Summer 1986; B - Winter 1987. LIANG & VEGA-PÉREZ: Chaetognaths: Feeding habits 33

A Stage o Stage I

Stage H

a _

Stage II Stage IV

B Stage O Stage I

Stage II

Stage II StagelV

Fig. 3. Food items at each maturity stage. A-S. enflata in Summer 1987; B - S. friderici in Summer 1985. 34 Bolm lost. oceaoogt'., S Paulo, 43(1), 1995

A

Stage o Stage I

Stage II Stage III

.t.ppen(JICUl8r lll

B Stage o Slage I

Stage II Stage III

$0

Fig. 4. Food items of S. friderici at each maturity stage. A - Winter 1986; B - Summer 1986. LIANG & VEGA-PÉREZ: Chaetognaths: Feeding habits 35

Stage I A Slage o

Slage II Slage III

B stage I Stage II

F.

Stage II StagelV

Fig. 5. Food items of S. friderici at each maturity stage. A - Winter 1987; B - Summer 1987. 36 Bolm Inst. oceanogr., S Paulo, 43(1), 1995

A Stage I

."

Stage III Stage IV

c

• B Stage o Stage I

Stage H Stage III

0>cH0 .p

Fig. 6. Food items of S. h;spida at each maturity stage. A - Summer 1985; B - Winter 1986. LIANG & VEGA-PÉREZ: Chaetognaths: Feeding habits 37

A Slage o Stage I

..~ _- ... Stage •

Slage III StageIV

Slage I Slage II B

, ..

.";' ~.... " '

'o. .~ ,: ., '

• o" • . '

Stage III

Fig, 7, Food items of S. Itispida at each maturity stage. A - Summer 1986; B - Winter 1987, 38 Bolm Inst. oceanogr., S Paulo, 43(1), 1995

Discussion annclids and larvaceans which were not found in lhe gul conteots as suggested by Vega-Pérez & Liang (1992). Chaetognaths feed on a wide variety of food organisms The minimum size of the chaetognath prey is (Alvariõo, 1985), however the gut content is dominated by determined by the ability of the hooks to grasp it and the few zooplankton groups (Sziper, 1978; Alvarez-Cadeoa, maximum by the mouth opening (Pearre, 1980). Thus, a 1993). Off the Ubatuba region, chaetognath species preyed close relationship between the size of the predator and the 00 a wide variety of orgaoisms belooging to six phyla: prey may be expected Our resuks showed that, io S. crustaceaos, molluscs, urochordata, chaetogoaths, enflata, S. friderici and S. hispida, the prey size chaoged aonelids and coidarians. Thus, the gut content analysis with the developmeotal stage. Youog stages fed heavily on reported here, showed that the pattern of feediog habits smaU preys such asnauplii and small copepods Oncaea correspood well with the chaetognath feeding habits spp and Paraca/anus sp, whereas the older stages (II-IV) reported from other regions. preyed on larger copepods Iike T. stylifera, Corycaeus spp Studies 00 chaetognaths indicate that the abundance of and E. pileatus, as weU as appendicularians and other prey types io the diet depends 00 the accessibility or chaetognaths. These data confirm the results of vulnerability of the prey itself, su-e and shape, as weU as Nagasawa & Marumo (1976), Sziper (1978) and Pearre their abuodaoce io the eoviroomeot (Nagasawa & (1981). Marumo, 1972; Cosper & Reeve, 1975; Sullivan, 1980). Cannibalism or inter-intraspecific predation is The importance of copepods as a food source is weU commoo amoog chaetognaths and considered a valuable knowo for chaetognaths. They are the most common food adaptative strategy io a food Iimited environment (Pearre, items fouod in the gut of aU maturity stages of this group 1982). Althougb reducing the number of reproducing (Stooe, 1969; Pearre, 1976; Gibbons, 1992). Dff the individuais io the population, the energetic advantage may Ubatuba region, calanoid and poecilostomatoid copepods a110w an equivalent total reproductive effort (Pearre, were the preys most consumed. This result is not surprisiog, 1982). ln Ubatuba, the cannibalistic behavior increases since copepods were the dominant group in the with the predator size, however it is not frequent, probably zooplanktoo community off Ubatuba, particularly because the population of chaetognaths is composed .Paracalanus quasimodo, Ctenocalanus heronae, C. vanus, basically byyouog stages which tend to Iive more nearshore T. sty/ifera, Oncaea curta, O. venusta and Corycaeus than the older stages. This distribution pattem may reduce giesbrechti (Vega-Pérez, 1993). Thus, the food taken by the frequency of cannibalism (Oresland, 1987; Liang, chaetognaths is closely related to the abundance and 1993). specific composition of the copepods io the planktoo The data presented here suggest that the feeding (Rakusa-Suszczewsk~ 1969, Sullivan, 1980). patterns of chaetognaths are related to the zooplankton The presence of a considerable amount of mollusc eggs community structure. Further studies are necessary to fouod io the gut cootent of S. enflata is probably due to understand the role of this group in the marine accidental ingestion, because chaetognaths generally trophodynamics of the Brazilian tropical waters. locate and attack their preys when the latter are actively swimming and producing vibration (Fdgenbaum & Reeve, 1977). The quantity of food ingested by chaetognaths is Conclusions variable. We observed 1 - 3 prey items io the gut of S. enflata, S. friderici and S. hispida. Similar results were reported by Feigenbaum & Marris (1984) and Stooe 1. ln Ubatuba region, chaetognaths showed a higb (1969). According to these authors the guts contain number of specimens (75,21%) with empty guts. typically just one prey, but multiple preys (2-3) can also be 2. Sagitta enflata, S. friderici and S. hispida are fouod. carnivorous feeders, ingestiog a higb variety of prey items. A higb number of chaetognaths is usually found with 3. Cannibalism was a commom behavior, but io low empty guts (Stone, 1969; Stuart & Verheye, 1991). frequency and it started at stage I. According to Pearre (1973) this is likely due to the hauls 4. ln the chaetognath species studied, the size of the which capture them at depths where they do not necessarily prey changed with the developmental stages. feed. Oresland (1987) suggested that these predators often 5. The most important prey in the diet of S. enflata, S. fail in catching their prey when the latter are in high friderici and S. hispida were calanoid and poecilostomatoid conceotration, because feediog is inhibited in high density copepods. of preys. We also found the presence of a considerable 6. The diversity of preys consumed by the chaetognaths amount of empty guts. It may possibly reflect a great in Winter was higher than io Summer. dependency 00 very digestible soft-bodied preys as LIANG & VEGA-PÉREZ: Chaetognaths: Feediog habits 39

7. The rcsults obtaioed in this study suggcst that lhe FEIGENBAUM, D. L. & REEVE, M. R. 1977. Prcy chaetognath predation 00 copepods can be intensive and detection in the Chaetognatha: response to a it cao even influence the structure of the copepod Vlbratioo probe and experimental determination of community. attack distance in large aquaria. Limool. Oceanogr., 22:1052-1058.

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