Enviror~mental Biology of Fishes 33: 275-286, 1992. 0 1992 Kiuwer Academic Publishers. Printed in the Netherlands. Are crustaceans linked to the ciguatera food chain? Anita M. Kelly’, Christopher C. Kohler’ & Donald R. Tindall’ ‘Fisheries Research Laboratory and Department of Zoology, Southern Illinois University. Carbondale, IL 62901, U.S.A. ‘Department qf Plant Biology, Southern Illinois University, Carbondale, IL 62901, U.S.A. Received 0.6.1990 Accepted 4.11.1990 Key words: Dinoflagellate toxins, Artemia, Bioassay, Cichlid fish Synopsis Adult brine shrimp, Artemia spp., were used as an experimental organism to elucidate the role that crustacea may play in the transference of ciguatera toxins. Some ciguatera-implicated dinoflagellates were highly toxic to brine shrimp that had consumed them. Four clones of Gambierdiscus toxicus were fed in four trials at rates ranging from 2 to 480 cells per adult brine shrimp; the 24 h LD,,, for the four clones were 2.8,33.4,41.1, and 104.5 cells per brine shrimp. Dinoflagellates Prorocentrum concavum and P. lima were also fed to adult brine shrimp, but minimal mortalities occurred at cell concentrations ranging up to 1000 cells per test animal. Tilapine cichlid (Oreochromis niloticus x 0. mossambicus) young fed brine shrimp containing G. toxicus cells displayed behavioral abnormalities ranging from spiral swimming to loss of equilibrium. The present data suggest that toxins accumulated by dinoflagellate-consuming crustaceans could produce toxicity in zooplanktivorous fish species, or to detritivores in cases where dinoflagellate consumption resulted in crustacean mortalities. Field studies of the ciguatera food chain should be expanded to include examination of crustacean diets to more fully define their role in toxin transfer. Introduction Ciguatera is a biotoxication which can cause human illness and, in rare instances, death, from the in- gestion of certain tropical and subtropical marine fishes. Ciguatera investigators have been in general agreement that the toxin(s) originates somewhere in the environment of the fish since Randall (1958) developed the food chain hypothesis, which was an expanded elaboration of a previous algal food chain theory credited to Chisolm (1808). Randall’s hypothesis stated that the toxin was produced by a benthic alga, then transferred to herbivorous fish- es, and in turn, to carnivorous fishes. The hypothe- sis was not substantiated until nearly 20 years later when Yasumoto et al. (1971) concluded that the dinoflagellate Gambierdiscus toxicus (Adachi & Fukuyo 1979), found in the gut contents of the surgeonfishes, Acanthurus lineatus and Ctenochae- tus striatus, and in detritus samples collected from the Gambier Islands, was the principal ciguatera- toxin producing organism in the Pacific. Since Ya- sumoto’s original findings, several species of di- noflagellates have been implicated in ciguatera poi- sonings circumtropically (Yasumoto et al. 1980, Nakajima et al. 1981, Murakami et al. 1982, Tindall et al. 1984, Carlson & Tindall 1985, Tindall et al. 1984). The association of these ciguatera-implicat- ed dinoflagellates with macro-algae adds further credence to the food chain hypothesis in that her- bivorous fishes are believed to be the first link in the food chain (Yasumoto et al. 1979).
Transcript
Enviror~mental Biology of Fishes 33: 275-286, 1992. 0 1992 Kiuwer Academic Publishers. Printed in the Netherlands.
Are crustaceans linked to the ciguatera food chain?
Anita M. Kelly’, Christopher C. Kohler’ & Donald R. Tindall’ ‘Fisheries Research Laboratory and Department of Zoology, Southern Illinois University. Carbondale, IL 62901, U.S.A. ‘Department qf Plant Biology, Southern Illinois University, Carbondale, IL 62901, U.S.A.
Received 0.6.1990 Accepted 4.11.1990
Key words: Dinoflagellate toxins, Artemia, Bioassay, Cichlid fish
Synopsis
Adult brine shrimp, Artemia spp., were used as an experimental organism to elucidate the role that crustacea may play in the transference of ciguatera toxins. Some ciguatera-implicated dinoflagellates were highly toxic to brine shrimp that had consumed them. Four clones of Gambierdiscus toxicus were fed in four trials at rates ranging from 2 to 480 cells per adult brine shrimp; the 24 h LD,,, for the four clones were 2.8,33.4,41.1, and 104.5 cells per brine shrimp. Dinoflagellates Prorocentrum concavum and P. lima were also fed to adult brine shrimp, but minimal mortalities occurred at cell concentrations ranging up to 1000 cells per test animal. Tilapine cichlid (Oreochromis niloticus x 0. mossambicus) young fed brine shrimp containing G. toxicus cells displayed behavioral abnormalities ranging from spiral swimming to loss of equilibrium. The present data suggest that toxins accumulated by dinoflagellate-consuming crustaceans could produce toxicity in zooplanktivorous fish species, or to detritivores in cases where dinoflagellate consumption resulted in crustacean mortalities. Field studies of the ciguatera food chain should be expanded to include examination of crustacean diets to more fully define their role in toxin transfer.
Introduction
Ciguatera is a biotoxication which can cause human illness and, in rare instances, death, from the in- gestion of certain tropical and subtropical marine fishes. Ciguatera investigators have been in general agreement that the toxin(s) originates somewhere in the environment of the fish since Randall (1958) developed the food chain hypothesis, which was an expanded elaboration of a previous algal food chain theory credited to Chisolm (1808). Randall’s hypothesis stated that the toxin was produced by a benthic alga, then transferred to herbivorous fish- es, and in turn, to carnivorous fishes. The hypothe- sis was not substantiated until nearly 20 years later when Yasumoto et al. (1971) concluded that the
dinoflagellate Gambierdiscus toxicus (Adachi & Fukuyo 1979), found in the gut contents of the surgeonfishes, Acanthurus lineatus and Ctenochae- tus striatus, and in detritus samples collected from the Gambier Islands, was the principal ciguatera- toxin producing organism in the Pacific. Since Ya- sumoto’s original findings, several species of di- noflagellates have been implicated in ciguatera poi- sonings circumtropically (Yasumoto et al. 1980, Nakajima et al. 1981, Murakami et al. 1982, Tindall et al. 1984, Carlson & Tindall 1985, Tindall et al. 1984). The association of these ciguatera-implicat- ed dinoflagellates with macro-algae adds further credence to the food chain hypothesis in that her- bivorous fishes are believed to be the first link in the food chain (Yasumoto et al. 1979).
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Extensive research has been conducted with re- spect to determining causal agents and their rela- tionship to ciguatera (Tindall et al. 1984, Carlson & Tindall1985, Yasumoto et al. 1987), dinoflagellate ecology (Carlson & Tindall1985, Taylor 1985, Gil- lespie et al. 1985), pharmacology (Li 1965, Tachi- bana 1987, Legrand & Bagnis 1984, Yasumoto 1985, Ohizumi et al. 1985, Miller & Tindall 1985, Ohizumi 1987), and chemistry (Scheuer et al. 1967, Yasumoto & Scheuer 1969, Chungue et al. 1977, Miller et al. 1984, Dickey et al. 1984, Bomber et al. 1990, Legrand et al. 1990, Yasumoto 1990). How- ever, much less research has been done on aspects dealing with the food chain dynamics (Helfrich & Banner 1963, Davin et al. 1986,1988, Kohler et al. 1988)) and apparently no research has been done to examine the role crustacea may play in the transfer- ence of ciguatera toxins. In addition to herbivorous fish, zooplanktivorous fishes and life stages may obtain ciguatera toxins by consuming herbivorous crustacea. For example, White (1981) showed that fish kills of Atlantic herring, Clupea harengus, were linked to their consumption of zooplankton that had previously consumed Gonyaulax excava- tu, a dinoflagellate whose toxins are responsible for paralytic shellfish poisoning.
Marine crustaceans exist in enormous numbers and are found in nearly every niche of the coral reef system (Barnes 1987). Randall (1967) found that crustaceans were the most important food of 5526 specimens of 212 species of reef and inshore fishes, which included both plankton feeders, herbivores, and bottom feeders. The crustaceans found in the gut contents of these fish included copepods, sto- matopods, crabs, shrimps, scyllarid lobsters, spiny lobsters, amphipods, isopods, and tanaids.
Crustaceans display a variety of feeding habits from particulate-feeding to filter-feeding. Some copepods feed preferentially on dinoflagellates rather than diatoms or detritus (Uchima & Hirano 1986). A number of fish species and/or life stages feed directly on this abundant crustacean food source (Randall 1967). Several coral reef species of fish are particulate-feeding carnivores during some or all their life, but may still obtain dinoflagellate cells and/or toxins in their diet via herbivorous crustaceans. Direct consumption of G. toxicus cells
has been shown to have severe adverse effects on several species of fish (Davin et al. 1986, 1988, Kohler et al. 1989). Accordingly, the objectives of this study were to determine if dinoflagellate toxins are transferred and accumulated in crustacea, and to determine the relative effects these toxins may have on crustacea, and, in turn, crustacean con- sumers.
Materials and methods
The brine shrimp, Artemiu spp., served as the ex- perimental organism for this study. Adult brine shrimp were chosen because they are reasonably homogeneous genetically, economical, readily available, and easy to maintain. Live adult brine shrimp were obtained from a commercial source in Florida. The brine shrimp, which arrived in healthy condition, were placed in two 110 liter aquaria containing dechlorinated water mixed with Instant OceanR at 32 ppt. The artifical seawater was gently aerated to keep the shrimp in suspension. The brine shrimp were stored in a cold room at 13°C the optimum temperature for maintenance as rec- ommended by the supplier. The brine shrimp were not fed for 16-24 h prior to experimental treat- ment .
Cultured cells of four clones of Gumbierdiscus toxicus and one clone each of Prorocentrum conca- vum and P. lima were used to determine the median lethal dose (LD,,), reported as cells con- sumed per individual organism assayed. The G. toxicus clones included live and freeze-dried cells of SIU-175 from Martinique, French Antilles; SIU-350 Virgin Gorda, British Virgin Islands; SIU-172 Great Isaacs Light, Bahamas; and freeze dried cells only of SIU-157 collected off drift algae from the Straits of Florida. Prorocentrum conca- vum SIU-364 was isolated from Salt Island, and P. lima SIU-700 from South Sound, Virgin Gorda, both of which are in the British Virgin Islands. In determining the LDS, values of the specified di- noflagellates to the brine shrimp the following pro- tocol was used. Four replicates of 10 brine shrimp were utilized for each experimental concentration. Dinoflagellate cells were enumerated, from 2 to
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1000 cells per test animal, and placed in individual wells of a white spot plate. The wells of the spot plate were filled with artificial seawater, mixed as previously specified, and one adult brine shrimp was placed in each well. The spot plates were placed in a refrigerator at 13” C for 24 h, after which time the number of dead shrimp were recorded. The controls were fed a nontoxic commercial algal food (Ocean GreenR). For the LDso determina- tions, at least four dinoflagellate concentrations and a control were used for each clone of G. fox- icus. Death was indicated by complete cessation of movement of Artemia. The LDSo, 95% confidence limits, and the slope function were calculated using probit analysis on SAS (Finney 1971). Mean values of replicates were compared using the Student’s t-test.
The second aspect of this study involved deter- mining the LD,, values for the specified dinoflagel- lates in tilapia (Oreochromis niloticus x 0. moss- ambicus) juveniles. Embryos were taken from a brooding female one week after spawning and placed in a 39 liter aquarium in a recycle system at room temperature. The embryos were observed until they accepted food, at which time they were considered to be early juveniles. After 24 h of fast- ing, one early juvenile was placed in a 150 ml con- tainer with 50 ml of water from the recycle system in which they were previously held. Each was fed between 5 and 96 cells of a given clone of G. tox- icus, following the probit method. The experiment utilized four replicates of five early juveniles per cell concentration, and five control juveniles which were fed an equal amount of a commercial fish food (TetraminR). Each experiment lasted 24 h and the number of dead fish observed at the end of that period was recorded.
The final phase of this study was to determine if crustacea could transfer ciguatera toxins through the food chain. Brine shrimp were placed in indi- vidual wells of spot plates and given between 10 and 100 cells per test animal of a given clone of G. toxicus. The dinoflagellate cells were purged from the digestive tract of the brine shrimp either by natural excretion or, in cases where the shrimp died, by cutting open the digestive tract and wash- ing out the remaining cells. The purged brine
shrimp were placed in aluminum foil and frozen at - 20” C. Brine shrimp that had consumed a known amount of dinoflagellate cells, and still contained all those cells in their digestive tract, were placed in aluminum foil and frozen at - 20°C.
The early juvenile tilapine cichlids were placed in 150ml containers with 50ml of water from the recycle system in which they were held. Three rep- licates of five fish were then fed 1 or 2 of the previously described frozen brine shrimp. After 24 h the fish were observed for either mortality or abnormal behavior.
Comparisons of dosage (grams), for each clone of G. toxicus per surface area (cm’) for mouse, fish and brine shrimp were conducted utilizing the stan- dard weight and surface area measurements of sev- eral different species as provided by Casarett & Doull (1986). A linear relationship was achieved when surface area was plotted against (body weight)“‘. Using the wet weight of the fish and brine shrimp the surface areas of these respective organisms were extrapolated.
Results
Ciguatera-implicated dinoflagellages proved toxic to the brine shrimp. LD,,, values of 2.8, 33.4, 41.1, and 104.5 cells were obtained for freeze-dried sam- ples of SIU-175, SIU-350, SW172, and SW-157, respectively (Fig. 1). For living cells, LDS,, values of 2.9,35.5, and 42.6 cells were obtained for samples of SIU-175, SIU-350, and SIU-172, respectively (Fig. 2). No live cells were available for SIU-157. No difference (p > 0.05) existed between the LD,,, values obtained for freeze-dried or live cells of the respective clones. The order of toxicity based on dried cell data was SIU-175 > SIU-350 > SIU-172 > SW-157.
Minimal toxicity was observed in the brine shrimp which had been fed either Prorocentrum species. Only five shrimp died throughout any of the assays. Therefore, the Prorocenfrum spp. were not utilized in the remaining phases of this study.
Two clones of G. toxicus, SW-175 and SIU-350, were toxic when fed to the tilapine juveniles (Fig.
278
-6.0 4.5 L$l 7.1 10.5 .
-11.3 8.8 Lgy 60.0 76.0 .
CWIS cells
SIU-172 SIU-157
1.0 r
P 0.6 1 0.5 ----------
0.4
t I'
;
0 : 0.3
8 : 1
0.70 18.8 g;O 63.3 81.4
dells
0.9
0.8
0.7
0.01 , -126.0 -22.5 PM? 231.6 336.0
C&S Fig. 1. Dose response curves, with 95% confidence intervals, representing percent mortality of Artemiu fed dried cells of four clones of Gambierdixus toxicus. LD%‘s were determined using probit analysis.
3). The LDsO values were 15.8 and 28.9 cells for SIU-175 and SIU-350, respectively.
Minimal toxicity was observed in early tilapine
juveniles fed SIU-172 and SIU-157. Approximately 24 h after ingestion tilapine juveniles displayed ab- normal swimming behavior which included an in-
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SNJ-175 SW-350
l.Or
0.9 -
0.5 - ---- - ----
-2.8 -0.2 LD60 8.0 8.5 2.9
cells
1.0 r
0.9 -
0.8 -
0.7 -
-18.1 14.4 LDSO 76.7 106.5 35.5
Cells
SIU-172
1.0
0.9
0.8
0.7 /
3.9 21.3 LDSO 64.0 81.4 42.6
Cells
Fig. I. Dose response curves, with 95% confidence intervals, representing percent mortality of Artemia fed live cells of four clones of Gamhierdiscus toxicus. LD,,,‘s were determined using probit analysis.
ability to feed normally, quiescence, and loss of dinoflagellates. Control fish remained asympto- equilibrium. All of these signs disappeared approx- matic during the course of the 24 h assay. imately 21 d after the initial ingestion of the toxic No mortality was observed in fish ingesting brine
Fig. 3. Dose response curves, with 95% confidence intervals, representing percent mortality of post-yolksac juvenile tilapia Gambierdiscus toxicus clones SIU-175 and SIU-350. LD,,‘s were determined using probit analysis.
shrimp containing a known amount of toxic di- noflagellates in their digestive tracts. Fish dis- played abnormal behavior 24 h after ingestion of brine shrimp containing 8 cells of SIU-175,16 cells of SIU-350, 16 cells of SIU-172, and 32 cells of SIU-157 (Table 1). The abnormal behavior includ- ed corkscrew swimming, floating nose up, swim- ming upside down, swimming at approximately a 45” angle, floating on the surface, lying on their sides on the bottom, and an inability to hit food that was presented to them. No abnormal behavior was observed among any of the fish fed brine shrimp which had been purged of any of the four G. toxicus clones. Likewise, control fish did not display any abnormal behavior during the course of the 24 h assays.
Regression lines of the mouse (Tindall unpub- lished data), shrimp and fish bioassays of SIU-175 and SIU-350 are nearly parallel, with no difference (p > 0.05) between slopes. Regression lines of the mouse (Bomber et al. 1989) and brine shrimp bioassays of SIU-172 and SIU-157 were also nearly parallel, with no difference (p> 0.05) between
fed
slopes (Fig. 4). Dosage per surface area compari- sons indicated that each clone of G. toxicus had the same magnitude of toxicity to the various test orga- nisms exposed to them (Table 2).
Table 1. Median lethal dose in cells for four clones of Gambier- discus toxicus to the mouse, brine shrimp and young tilapine chilids.
i Tindall unpublished data. 2 Bomber et al. 1989. 3 Abnormal swimming behavior detected after indicated cell consumption.
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9 9 7 6 5 4
3 2 1 0
10 -
9- 6- 7-
SW-1 72 A C
I I 0 : I I I I I
0 1.0 2.0 3.0 4.0 5.0
Log cells
10
9 6 7
g 6 % 5 p’ 4
0 1.0 2.0 3.0 4.0 5.0
Log cm3
SIU-157
Fig. 4. Comparison of the probit regression lines for (a) Artemia, (b) young tilapine chichlid. and (c) mouse in response to the four clones of Gamhierdiscus toxicus.
Discussion Table 2. Dosage per surface area comparision of the mouse, brine shrimp and young tilapine cichlids for four clones of Gam- bierdiscus toxicus.
G. toxicus clone
SII-J-175 SW-350 SIU-172 SW-157
Mouse ‘2.9 x lo-’ ‘0.006 20.004 20.006 Fish 7.35 x 10-7 0.002 - - A rtemia 2.15x 10-T 0.004 0.005 0.009
‘. Tindall unpublished data. ?. Bomber et al. 1989.
All four clones of G. toxicus tested were highly toxic to Artemia, though differences in LDSo levels existed. Bomber et al. (1989) showed that the tox- icity of crude extracts of G. toxicus injected in- traperitoneally into mice (ICR, 20g) decreased with increasing geographic latitude of the cell strain tested; the closer to the equator the clone of G. mkus is found, the more toxic it is. Based on this premise the order of toxicity was SIU-175 > SIU-350 and SIU-172 > SIU-157; the same order of toxicity
282
found in this study in which G. toxicus cells were directly fed to brine shrimp.
The minimal toxicity observed in brine shrimp exposed to the Prorocentrum concavum or P. lima is consistent with results obtained from fish fed these Prorocentrum spp. (Kohler et al. 1989). No reaction was observed when ocean surgeon, Acan- thuris bahianus, were fed various quantities of these species of dinoflagellates. The brine shrimp deaths observed were at cell concentrations of 1000 cells per test animal. Brine shrimp deaths were perhaps caused by mechanical hindrance possibly leading to suffocation. Inspection of the digestive tracts of the shrimp revealed that low numbers of cells were consumed. Bioassay results of the same number of cells consumed at lower cell densities in the spot plate yielded no mortalities.
This study did not demonstrate that crustaceans accumulate ciguatera toxins. Roberts et al. (1979) found that crustaceans did not accumulate paralyt- ic shellfish toxins from the dinoflagellate Gymnodi- nium breve ( = Ptychodiscus brevis). Conversely, White (1977,198O) and Hayashi et al. (1982) found that zooplanktonic crustaceans accumulate toxins from Gonyaulax excavata, a dinoflagellate associ- ated with paralytic shellfish poisoning in the Bay of Fundy. The inability to demonstrate accumulation in this study could be a result of the size of the crustacean and fish that were utilized. Brine shrimp were unable to ingest enough toxic dinoflagellate cells prior to their death to accumulate sufficient amounts of toxins to elicit a response in juvenile fish consumers. Similarly, the juvenile fish were not large enough to consume more than 2 brine shrimp in a 24 h period, thus limiting the amount of toxins they could acquire from the potentially toxic crustaceans.
Observation of brine shrimp showed that cells remained in the digestive tract of the shrimp for several hours. In nature, during the digestive peri- od, the shrimp would be susceptible to predation and have the potential to pass the toxic dinoflagel- lates to secondary consumers which may not other- wise consume these cells directly. Shrimp which die with cells in their digestive tracts may also be con- sumed by detritivores, opening another food chain pathway.
Previous bioassay studies utilizing brine shrimp (Trieff 1973, Granade et al. 1976, Davinet al. 1978) were limited to nauplii exposed to various dosages of extracted toxins. The advantage to using adult brine shrimp is that unlike nauplii they can con- sume whole dinoflagellate cells. Thus, the toxins need not be extracted, which is a timely and costly procedure.
All clones of G. toxicus produced abnormal be- havior in the juvenile fish which had consumed them directly or indirectly via consumption of brine shrimp. The abnormal behavior displayed by the juvenile fish was similar to those reported by White (1981, 1984) and Baden (1983), who fed various species of fish extracts of the red tide dinoflagel- lates Gonyaulax excavata and Ptychodiscus brevis, by Davin et al. (1986, 1988) who fed various fish species ciguatoxic fish flesh and G. toxicus cells, and by White et al. (1989), who fed various fish species toxic G. excavata cells directly or toxin- containing zooplankton. Dinoflagellate-induced behavioral abnormalities among juvenile fish could have important implications with respect to preda- tor: prey relationships. Larkin (1978) suggested that predators have a predilection for prey which are conspicuously different from conspecifics. Fish displaying abnormal swimming behavior are ‘dif- ferent’ and generally subject to higher rates of pre- dation (Parker et al. 1963). Davin et al. (1986) demonstrated a negative correlation between mean capture time of blueheads, Thafassoma bi- fasciaturn, and dose of ciguatera toxins suggesting that ciguatera intoxicated fish may be more suscep- tible to predation than they would be otherwise.
LD,, values were obtained only for young fish less than five days after yolksac absorbtion, in- dicating a sensitivity period of early juvenile tila- pine cichlids to the dinoflagellate toxins. This sensi- tive period could have an affect on the recruitment of young fishes exposed to ciguatera-implicated dinoflagellates. Kohler et al. (1987) found highest toxic dinoflagellate densities occurred at sites in close proximity to mangrove stands in Lameshur Bays, St. John, USVI. Mangroves serve as nursery grounds for many species of fish, shrimps, lobsters, crabs, mussels and oysters (Rutzler & Feller 1988). Juvenile fish, as well as the crustaceans previously
Fig. 5. The expanded ciguatera food chain. The top portion represents the pelagic route, the middle portion the classic route. and the bottom portion the benthic route.
mentioned, have access to toxic dinoflagellates and, as the present study has demonstrated, rela- tively small numbers of toxic dinoflagellates are needed to elicit a response in young fish.
Since 1977, when Yasumoto first discovered a causal agent for ciguatera poisoning, the general pathway envisioned by most researchers has been: dinoflagellates associated with macroalgae are con- sumed by herbivorous fish, the herbivorous fish are than eaten by carnivorous fish, and humans sub- sequently become intoxicated by ingesting either the toxic herbivore or carnivore. This study sug- gests that several other pathways may exist in the ciguatera food chain.
In examining the food chain it is important to note that ciguatera-implicated dinoflagellates were, in general, considered epiphytic on benthic macroalgae. Recently, Bomber et al. (1988) found G. toxicus cells in 30 of 198 drift algae samples and 9 of 16 benthic stations collected in the Straits of
Florida and the Bahamian waters. These floating dinoflagellates represent a pelagic mode in the food chain which could explain how pelagic fish and zooplanktivorous fish and life stages may ac- quire these toxins. Zooplanktivorous fishes such as the herring and anchovies, may indirectly acquire the toxins by consuming zooplankton that have previously ingested dinoflagellate cells or directly acquire cells by consuming the planktonic dinofla- gellates. Reef-dwelling crustacean-eating fish such as squirrelfishes, porgies, jacks and groupers may ingest lobsters, crabs or shrimp which had con- sumed toxic dinoflagellates from detritus or algae upon which they feed. Detritivores such as floun- ders, could indirectly consume toxic dinoflagellates by ingesting dead crustaceans or fish with dinofla- gellates in their guts or by directly consuming the dinoflagellates in the detritus. All of the previously mentioned predators could in turn be consumed by carnivorous fish and/or humans. These pathways.
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in addition to the traditional herbivore pathway, constitute an expanded ciguatera food chain (Fig. 5).
Sensitivity of the experimental organism to the ciguatera-implicated dinoflagellates has broad con- sequences. Although there have been no reports of human ciguatera poisonings from the ingestion of crustaceans, the possibility of their being an impor- tant link in the food chain exists. Though the find- ings of this study have shed new light on the trans- fer of ciguatera toxins, there is a need to further elucidate the myriad of factors involved in the transference of ciguatera toxins through the food chain.
Acknowledgements
This article is based, in part, upon research con- ducted by the senior author for the Masters of Science degree in the Department of Zoology, Southern Illinois University, Carbondale, Illinois. We thank Mike McKee and Joe Beattie for provid- ing review comments.
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