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Hydrothermal vent ostracoda and faunal association in the deep sea
Deep-SeaResearch,Vol.39, No. 6, pp. 1067-1070, 1992.
0198-0149/92 $5.00+ 0.00 © 1992PergamonPressLtd
Printedin Great Britain.
NOTE
Hydrothermal vent ostracoda and faunal association in the deep sea DICK VAN HARTEN*
(Received 20 February 1991; in revised form 13 September 1991; accepted 24 September 1991) Abstraet--Ostracod faunas from Pacific hydrothermal vents include eucytherurine and pontocypridid Podocopa and are very similar to those previously recorded from experimental wood islands. Both vent and wood-island ostracods may belong to a single deep-sea faunal association that is adapted to a eutrophic regime. This regime, which is quite distinct from normal deep-sea conditions, is probably widespread in the world's ocean, although individual manifestations tend to be localized and ephemeral.
INTRODUCTION
DURING the French cruises HYDRONAUT 1987 and BIOLAU 1989 of R.V. Nadir, macrofauna was collected at two hydrothermal vent fields in the Pacific using the deepdiving research submersible Nautile. In sorting the specimens, several inadvertently captured benthic ostracods were encountered and separately preserved. These assemblages, which originate from vent fields near 13°N at the East Pacific Rise (EPR) and the Lau Basin near Fiji, respectively, are the first ostracods to be recorded from deep-sea vents. For further data on the vent fields, the reader is referred to FUSTECet al. (1987), JOLLIVETet al. (1989) and FOUQUETet al. (1990). RESULTS AND DISCUSSION
The ostracods were found in washings from vestimentiferans (Riftia and Tevnia), polychaetes (Alvinella and other taxa), echiurids, bivalves, gastropods, crustaceans and nematodes. The richest samples come from sites "Parigo" at the EPR (12°48.52'N, 103°56.48'W; depth 2630 m) and "Momoko" in the Lau Basin (22°32'S, 176°43'W; depth 1914 m). At these sites mats of filamentous bacteria were seen from the submersible (SEGONZAC, personal communication, 1990). The material recovered total 95 specimens from the EPR and 20 from the Lau Basin. All specimens contain soft parts and, therefore, are regarded as captured alive. As compared with normal deep-sea ostracods, their calcareous carapaces are excessively thin. Since *Geomarine Centre, Free University, de Boelelaan 1085, 1081 HV Amsterdam, The Netherlands. 1067
1068
D. VAN HARTEN
there are no signs of corrosion, poor calcification is probably a primary feature rather than an artifact of fixation. Unusually thin calcareous shells have also been reported in hydrothermal vent gastropods and tentatively connected with low pH of vent waters (WAR~N and BOUCrtET, 1989). Two new species of the subfamily Eucytherurinae PURI sensu MADOOCKSand STEINECK (1987) (Fam. Cytheruridae) make up about half of the collection: the EPR sites yielded 40 specimens of a species of Xylocythere Maddocks and Steineck, while 16 specimens of a species belonging to an unnamed yet eucytherurine genus were found in the Lau Basin fauna. These two species are represented by both adults and juvenile instars. The remaining half of the collection was not studied in detail due to the fragility of the material. They are smooth-shelled species and, in the case of the EPR, include Propontocypris sp. (Fam. Pontocyprididae). Eucytherurine and pontocypridid ostracods usually are not associated with the deep sea. Species of these taxa are commonly known as shallow-water dwellers in the photic zone, so their present connection with bathyal and abyssal hydrothermal vents may appear quite anomalous. However, MADDOCKS and STEINECK (1987) and STEINECK et al. (1990) described very similar communities, including Xylocythere and Propontocypris, from "experimental wood islands" in the deep sea, that is parcels of wood deployed on the sea bed and later retrieved (TURNER, 1977, 1981). The vent and wood-island ostracod communities are not only similar in a taxonomical sense but also with respect to their population densities which are far higher than is normal for deep-sea soft sediments. The similarity strongly suggests that the ostracods of the two habitats belong to a single deep-sea faunal association. This association apparently is adapted to special environmental conditions and biologically wholly different from that which normally inhabits the deep-sea muds. This implies that the wood-island communities no longer can be considered endemic to deep-sea wood parcels, as was previously believed by MADDOCKSand ST~INECK (1987); likewise, the term "xylophile" that STEINECK et al. (1990) coined to describe their biology now seems somewhat equivocal, other than in a biotopical sense. One ecological factor, which is probably common to wood-island and hydrothermal vent habitats and which is likely to evoke a sharp adaptational response in benthic deepsea fauna, is food abundance. ANGEL (1990) enumerated four main sources of food supply for the deep ocean: (1) finely suspended material; (2) sedimenting particulate matter; (3) large packages; and (4) chemoautotrophy. "Normal" deep-sea conditions are by and large characterized by type (1) and (2) supply. At any given point on the ocean bottom, the arrival of suspended and sedimenting food particles is stochastic and unpredictable (with the possible exception of such instances where there is seasonal enhancement of the flux (e.g. BILLETet al., 1983; LAMPITr, 1985)). Benthic ostracods are motile and, to a degree, able to seek out actively their food, but they still must adjust to overall random supply if they are to survive under "normal" deep-sea conditions. Food restriction over time is likely to be the main cause of the low density of the standing crop of benthic ostracods in ordinary deep-sea muds (see VAN MARTEN, 1990). Large packages and chemoautotrophic sources such as hydrothermal vents represent the opposite case. Once in place, they offer an abundant supply that is highly predictable within the normal life span of individual ostracods or even successive generations, and they allow their utilizers to stand literally in their food. High density populations therefore tend to develop. Hydrothermal vents are now considered widespread features in the oceans, but discrete vent fields appear to be quite restricted in space and time (CoRLISSet al., 1979;
Hydrothermal vent ostracod fauna
1069
GRASSLE, 1986, and references therein). T h e same is true of large f o o d packages which, of course, are also local and ephemeral. T h e very existence of a specifically a d a p t e d association of benthic ostracods, which lack demersal larvae, indicates that individual occurrences o f these e u t r o p h i c habitats must be m o r e c o m m o n than is currently realized. O s t r a c o d s c a n n o t directly utilize the chemical e n e r g y released at vents, n o r is it p r o b a b l e that they can digest w o o d y material (MAoDOCrS and STEINECK, 1987). Surprisingly little is k n o w n a b o u t w h a t ostracods eat u n d e r natural conditions and this is afortiori true o f the deep sea. But w h a t e v e r the nature of the diet, the f o o d in h y d r o t h e r m a l vent and w o o d island habitats is not unlikely to c o m e f r o m a source that is c o m m o n to both. Biomass consisting of w o o d - d e g r a d i n g and c h e m o a u t o t r o p h i c bacteria seems a distinct possibility. Alternatively, the ostracods might primarily be attracted by the a b u n d a n t animal life associated with the food-rich oases and simply act as n e c r o p h a g o u s or c o p r o p h a g o u s scavengers or be e n g a g e d in symbiotic, c o m m e n s a l , or parasitic relationships. T h e E u c y t h e r u r i n a e in part m a y d e p e n d for f o o d on c h e m o a u t o t r o p h i c bacteria as exosymbionts (VAN HARTEN, submitted). T h e u n k n o w n trophic details do not detract from the fact that, so far as the rate of f o o d supply is c o n c e r n e d , conditions at deep-sea vents and near sizable i m p o r t e d parcels are not dissimilar to those in the m o r e productive parts of the photic zone. It m a y be no coincidence, therefore, that the "closest t a x o n o m i c counterparts of w o o d - d w e l l i n g " - - a n d h y d r o t h e r m a l vent ( a u t h o r ) - - " o s t r a c o d s are free-living on algal, sea-grass and organicrich substrates in the photic z o n e " (MADDOCKS and STEINECK, 1987). Acknowledgements--This report benefitted from highly appreciated criticism and comment by R. F. Maddocks, M. Segonzac, R. Whatley, and an anonymous reviewer. The material analysed in this study was collected during the cruises HYDRONAUT 1987 and BIOLAU 1989 aboard N.O.. Nadir organized by IFREMER DERO/EP (chief scientist: A. M. Alayse), and was sorted by the Centre National de Tri d'Oc6anographie Biologique (CENTOB, Brest).
REFERENCES ANGELM. V. (1990) Food in the deep ocean. In: Ostracoda and global events, R. WHATLEYand C. MAYBURY, editors, Chapman and Hall, London, pp. 273-285. BILLETTD. S. M., R. S. LAMPIIq',A. L. RICE and R. F. C. MANTOURA(1983) Seasonal sedimentation of phytoplankton to the deep-sea benthos. Nature, 302,520-522. CORLISSJ. B., J. DYMOND,L. I. GORDON,J. M. EDMOND,R. P. VON HERZEN, R. D. BALLARD,K. GREEN,D. WILLIAMS,A. BAINBRIDGE,K. CRANEand T. H. VANANDEL(1979) Submarine thermal springs on the Galfipagos Rift. Science, 203, 1073-1083. FOUQUETY., J. L. CHARLOU,J. P. DONVAL,J. P. FOUCHER,F. HARMEGNIES,H. PELLE, O. VON STACKELBERG,M. WIEDICKE, J. ERZINGER, P. HERZIG, H. MOHE, S. SOAKAI and H. WHITECHURCH (1990) Hydrothermal
activity in the Lau Basin. First Results from the Nautilau Cruise. Eos, 71,678-679. FtlSTECA., D. DESBRtIYi~RESand S. K. JUNIPER(1987) Deep-sea hydrothermal vent communities at 13°N on the East Pacific Rise: microdistribution and temporal variations. Biological Oceanography, 4, 121-164. GRASSLEJ. F. (1986) The ecology of deep-sea hydrothermal vent communities. Advances in Marine Biology, 23, 301-362. JOLLIVET D., J. HASHIMOTO, J.-M. AUZENDE, E. HONZA, ]~. RUELLAN, S. nuTr, Y. IWABUCHI, P. JARVIS, M. JOSHIMA,T. KAWAI,T. KAWAMOTO,K. KISIMOTO,Y. LAFOY,T. MATSUMOTO,K. M1TSUZAWA,T. NAGANUMA, J. NAKA, K. OTSUKA,A. OTSUKI, B. RAO, M. TANAHASHI,T. TANAKA,J. S. TEMAKON,T. URABE,T. VEIVAU
and T. YOKOKURA(1989) Premi6res observations de communaut6s animales associ6es fi l'hydrothermalisme arri6re-arc du bassin Nord-Fidjien. Comptes Rendus Acaddmie des Sciences, Paris, 309, s~r. III, 301-308. LAMPITrR. S. (1985) Evidence for the seasonal deposition of detritus to the deep-sea floor (Porcupine Bight, N.W. Atlantic) and its subsequent resuspension. Deep-Sea Research, 32, 885-897.
1070
D. VANHARTEN
MADDOCKS R. F. and P. L. STEINECK(1987) Ostracoda from experimental wood-island habitats in the deep sea. Micropaleontology, 33, 318-355. STEINECK P. L., R. F. MADDOCKS,R. D. TURNER, G. COLES and R. WHATLEY(1990) Xylophile Ostracoda in the deep sea. In: Ostracoda and global events, R. WHATLEYand C. MAYBURY, editors, Chapman and Hall, London, pp. 307-319. TURNER R. D. (1977) Wood, mollusks, and deep-sea food chains. Bulletin of the American Malacological Union, 26, 13-19. TURNER R. D. (1981) "Wood islands" and "thermal vents" as centers of diverse communities in the deep sea. The Soviet Journal of Marine Biology, 7, 1-9. VAN HARTEN D. (1990) Modern abyssal ostracod faunas of the eastern Mid-Atlantic Ridge area in the North Atlantic and a comparison with the Mediterranean. In: Ostracoda and global events, R. WHATEEYand C. MAYBURY,editors, Chapman and Hall, London, pp. 321-328. VAN HARTEN D. (submitted) Deep-sea hydrothermal vent eucytherurine Ostracoda: the enigma of the pore clusters and the paradox of the hinge. Proceedings of the llth International Symposium on Ostracoda,
Warrnambool, Australia, 1991. WARI~NA. and P. BOUCHET(1989) New gastropods from East Pacific hydrothermal vents. Zoologica Scripta, 18, 67-102.
0198-0149/92 $5.00+ 0.00 © 1992PergamonPressLtd
Printedin Great Britain.
NOTE
Hydrothermal vent ostracoda and faunal association in the deep sea DICK VAN HARTEN*
(Received 20 February 1991; in revised form 13 September 1991; accepted 24 September 1991) Abstraet--Ostracod faunas from Pacific hydrothermal vents include eucytherurine and pontocypridid Podocopa and are very similar to those previously recorded from experimental wood islands. Both vent and wood-island ostracods may belong to a single deep-sea faunal association that is adapted to a eutrophic regime. This regime, which is quite distinct from normal deep-sea conditions, is probably widespread in the world's ocean, although individual manifestations tend to be localized and ephemeral.
INTRODUCTION
DURING the French cruises HYDRONAUT 1987 and BIOLAU 1989 of R.V. Nadir, macrofauna was collected at two hydrothermal vent fields in the Pacific using the deepdiving research submersible Nautile. In sorting the specimens, several inadvertently captured benthic ostracods were encountered and separately preserved. These assemblages, which originate from vent fields near 13°N at the East Pacific Rise (EPR) and the Lau Basin near Fiji, respectively, are the first ostracods to be recorded from deep-sea vents. For further data on the vent fields, the reader is referred to FUSTECet al. (1987), JOLLIVETet al. (1989) and FOUQUETet al. (1990). RESULTS AND DISCUSSION
The ostracods were found in washings from vestimentiferans (Riftia and Tevnia), polychaetes (Alvinella and other taxa), echiurids, bivalves, gastropods, crustaceans and nematodes. The richest samples come from sites "Parigo" at the EPR (12°48.52'N, 103°56.48'W; depth 2630 m) and "Momoko" in the Lau Basin (22°32'S, 176°43'W; depth 1914 m). At these sites mats of filamentous bacteria were seen from the submersible (SEGONZAC, personal communication, 1990). The material recovered total 95 specimens from the EPR and 20 from the Lau Basin. All specimens contain soft parts and, therefore, are regarded as captured alive. As compared with normal deep-sea ostracods, their calcareous carapaces are excessively thin. Since *Geomarine Centre, Free University, de Boelelaan 1085, 1081 HV Amsterdam, The Netherlands. 1067
1068
D. VAN HARTEN
there are no signs of corrosion, poor calcification is probably a primary feature rather than an artifact of fixation. Unusually thin calcareous shells have also been reported in hydrothermal vent gastropods and tentatively connected with low pH of vent waters (WAR~N and BOUCrtET, 1989). Two new species of the subfamily Eucytherurinae PURI sensu MADOOCKSand STEINECK (1987) (Fam. Cytheruridae) make up about half of the collection: the EPR sites yielded 40 specimens of a species of Xylocythere Maddocks and Steineck, while 16 specimens of a species belonging to an unnamed yet eucytherurine genus were found in the Lau Basin fauna. These two species are represented by both adults and juvenile instars. The remaining half of the collection was not studied in detail due to the fragility of the material. They are smooth-shelled species and, in the case of the EPR, include Propontocypris sp. (Fam. Pontocyprididae). Eucytherurine and pontocypridid ostracods usually are not associated with the deep sea. Species of these taxa are commonly known as shallow-water dwellers in the photic zone, so their present connection with bathyal and abyssal hydrothermal vents may appear quite anomalous. However, MADDOCKS and STEINECK (1987) and STEINECK et al. (1990) described very similar communities, including Xylocythere and Propontocypris, from "experimental wood islands" in the deep sea, that is parcels of wood deployed on the sea bed and later retrieved (TURNER, 1977, 1981). The vent and wood-island ostracod communities are not only similar in a taxonomical sense but also with respect to their population densities which are far higher than is normal for deep-sea soft sediments. The similarity strongly suggests that the ostracods of the two habitats belong to a single deep-sea faunal association. This association apparently is adapted to special environmental conditions and biologically wholly different from that which normally inhabits the deep-sea muds. This implies that the wood-island communities no longer can be considered endemic to deep-sea wood parcels, as was previously believed by MADDOCKSand ST~INECK (1987); likewise, the term "xylophile" that STEINECK et al. (1990) coined to describe their biology now seems somewhat equivocal, other than in a biotopical sense. One ecological factor, which is probably common to wood-island and hydrothermal vent habitats and which is likely to evoke a sharp adaptational response in benthic deepsea fauna, is food abundance. ANGEL (1990) enumerated four main sources of food supply for the deep ocean: (1) finely suspended material; (2) sedimenting particulate matter; (3) large packages; and (4) chemoautotrophy. "Normal" deep-sea conditions are by and large characterized by type (1) and (2) supply. At any given point on the ocean bottom, the arrival of suspended and sedimenting food particles is stochastic and unpredictable (with the possible exception of such instances where there is seasonal enhancement of the flux (e.g. BILLETet al., 1983; LAMPITr, 1985)). Benthic ostracods are motile and, to a degree, able to seek out actively their food, but they still must adjust to overall random supply if they are to survive under "normal" deep-sea conditions. Food restriction over time is likely to be the main cause of the low density of the standing crop of benthic ostracods in ordinary deep-sea muds (see VAN MARTEN, 1990). Large packages and chemoautotrophic sources such as hydrothermal vents represent the opposite case. Once in place, they offer an abundant supply that is highly predictable within the normal life span of individual ostracods or even successive generations, and they allow their utilizers to stand literally in their food. High density populations therefore tend to develop. Hydrothermal vents are now considered widespread features in the oceans, but discrete vent fields appear to be quite restricted in space and time (CoRLISSet al., 1979;
Hydrothermal vent ostracod fauna
1069
GRASSLE, 1986, and references therein). T h e same is true of large f o o d packages which, of course, are also local and ephemeral. T h e very existence of a specifically a d a p t e d association of benthic ostracods, which lack demersal larvae, indicates that individual occurrences o f these e u t r o p h i c habitats must be m o r e c o m m o n than is currently realized. O s t r a c o d s c a n n o t directly utilize the chemical e n e r g y released at vents, n o r is it p r o b a b l e that they can digest w o o d y material (MAoDOCrS and STEINECK, 1987). Surprisingly little is k n o w n a b o u t w h a t ostracods eat u n d e r natural conditions and this is afortiori true o f the deep sea. But w h a t e v e r the nature of the diet, the f o o d in h y d r o t h e r m a l vent and w o o d island habitats is not unlikely to c o m e f r o m a source that is c o m m o n to both. Biomass consisting of w o o d - d e g r a d i n g and c h e m o a u t o t r o p h i c bacteria seems a distinct possibility. Alternatively, the ostracods might primarily be attracted by the a b u n d a n t animal life associated with the food-rich oases and simply act as n e c r o p h a g o u s or c o p r o p h a g o u s scavengers or be e n g a g e d in symbiotic, c o m m e n s a l , or parasitic relationships. T h e E u c y t h e r u r i n a e in part m a y d e p e n d for f o o d on c h e m o a u t o t r o p h i c bacteria as exosymbionts (VAN HARTEN, submitted). T h e u n k n o w n trophic details do not detract from the fact that, so far as the rate of f o o d supply is c o n c e r n e d , conditions at deep-sea vents and near sizable i m p o r t e d parcels are not dissimilar to those in the m o r e productive parts of the photic zone. It m a y be no coincidence, therefore, that the "closest t a x o n o m i c counterparts of w o o d - d w e l l i n g " - - a n d h y d r o t h e r m a l vent ( a u t h o r ) - - " o s t r a c o d s are free-living on algal, sea-grass and organicrich substrates in the photic z o n e " (MADDOCKS and STEINECK, 1987). Acknowledgements--This report benefitted from highly appreciated criticism and comment by R. F. Maddocks, M. Segonzac, R. Whatley, and an anonymous reviewer. The material analysed in this study was collected during the cruises HYDRONAUT 1987 and BIOLAU 1989 aboard N.O.. Nadir organized by IFREMER DERO/EP (chief scientist: A. M. Alayse), and was sorted by the Centre National de Tri d'Oc6anographie Biologique (CENTOB, Brest).
REFERENCES ANGELM. V. (1990) Food in the deep ocean. In: Ostracoda and global events, R. WHATLEYand C. MAYBURY, editors, Chapman and Hall, London, pp. 273-285. BILLETTD. S. M., R. S. LAMPIIq',A. L. RICE and R. F. C. MANTOURA(1983) Seasonal sedimentation of phytoplankton to the deep-sea benthos. Nature, 302,520-522. CORLISSJ. B., J. DYMOND,L. I. GORDON,J. M. EDMOND,R. P. VON HERZEN, R. D. BALLARD,K. GREEN,D. WILLIAMS,A. BAINBRIDGE,K. CRANEand T. H. VANANDEL(1979) Submarine thermal springs on the Galfipagos Rift. Science, 203, 1073-1083. FOUQUETY., J. L. CHARLOU,J. P. DONVAL,J. P. FOUCHER,F. HARMEGNIES,H. PELLE, O. VON STACKELBERG,M. WIEDICKE, J. ERZINGER, P. HERZIG, H. MOHE, S. SOAKAI and H. WHITECHURCH (1990) Hydrothermal
activity in the Lau Basin. First Results from the Nautilau Cruise. Eos, 71,678-679. FtlSTECA., D. DESBRtIYi~RESand S. K. JUNIPER(1987) Deep-sea hydrothermal vent communities at 13°N on the East Pacific Rise: microdistribution and temporal variations. Biological Oceanography, 4, 121-164. GRASSLEJ. F. (1986) The ecology of deep-sea hydrothermal vent communities. Advances in Marine Biology, 23, 301-362. JOLLIVET D., J. HASHIMOTO, J.-M. AUZENDE, E. HONZA, ]~. RUELLAN, S. nuTr, Y. IWABUCHI, P. JARVIS, M. JOSHIMA,T. KAWAI,T. KAWAMOTO,K. KISIMOTO,Y. LAFOY,T. MATSUMOTO,K. M1TSUZAWA,T. NAGANUMA, J. NAKA, K. OTSUKA,A. OTSUKI, B. RAO, M. TANAHASHI,T. TANAKA,J. S. TEMAKON,T. URABE,T. VEIVAU
and T. YOKOKURA(1989) Premi6res observations de communaut6s animales associ6es fi l'hydrothermalisme arri6re-arc du bassin Nord-Fidjien. Comptes Rendus Acaddmie des Sciences, Paris, 309, s~r. III, 301-308. LAMPITrR. S. (1985) Evidence for the seasonal deposition of detritus to the deep-sea floor (Porcupine Bight, N.W. Atlantic) and its subsequent resuspension. Deep-Sea Research, 32, 885-897.
1070
D. VANHARTEN
MADDOCKS R. F. and P. L. STEINECK(1987) Ostracoda from experimental wood-island habitats in the deep sea. Micropaleontology, 33, 318-355. STEINECK P. L., R. F. MADDOCKS,R. D. TURNER, G. COLES and R. WHATLEY(1990) Xylophile Ostracoda in the deep sea. In: Ostracoda and global events, R. WHATLEYand C. MAYBURY, editors, Chapman and Hall, London, pp. 307-319. TURNER R. D. (1977) Wood, mollusks, and deep-sea food chains. Bulletin of the American Malacological Union, 26, 13-19. TURNER R. D. (1981) "Wood islands" and "thermal vents" as centers of diverse communities in the deep sea. The Soviet Journal of Marine Biology, 7, 1-9. VAN HARTEN D. (1990) Modern abyssal ostracod faunas of the eastern Mid-Atlantic Ridge area in the North Atlantic and a comparison with the Mediterranean. In: Ostracoda and global events, R. WHATEEYand C. MAYBURY,editors, Chapman and Hall, London, pp. 321-328. VAN HARTEN D. (submitted) Deep-sea hydrothermal vent eucytherurine Ostracoda: the enigma of the pore clusters and the paradox of the hinge. Proceedings of the llth International Symposium on Ostracoda,
Warrnambool, Australia, 1991. WARI~NA. and P. BOUCHET(1989) New gastropods from East Pacific hydrothermal vents. Zoologica Scripta, 18, 67-102.