Vol. 1 Contributions to the Study of East Pacific 2002

Carbon sources and trophic position of two abyssal species of , Munidopsis alvisca (Galatheidae) and diomedeae (Lithodidae)

Elva Escobar-Briones1, Pedro Morales 2, Edith Cienfuegos2 and Manuel González3 1Instituto de Ciencias del Mar y Limnología, UNAM, A.P. 70-305 (corresponding author), 04510 México, D.F.; 2Instituto de Geología, UNAM, Laboratorio de Espectrometría de Masas de Isótopos Estables, Circuito de la Investigación s/n, Ciudad Universitaria, 04510 México, D.F. e-mail: [email protected]; 3Facultad de Ciencias, UNAM

ABSTRACT.- The carbon sources and trophic position of the abyssal species Munidopsis alvisca and Neolithodes diomedeae are described on the basis of stable carbon and nitrogen isotopes. These two species occur in large abundance at the hydrothermal vents in the central . As domi- nant components in the assemblage they define the use of resources and export of vent mate- rials to the abyssal ecosystem. The δ13C and δ15N values of the squat lobster Munidopsis alvisca sug- gest a mixed diet based on sediment surfur bacteria and metazoans associated with bacterial mats. The anomuran crab Neolithodes diomedeae is a scavenger feeding on infauna of the where photoautotrophic sources play the major role in the diet. The influence of the vents on the organic mat- ter composition of sediments is limited to the immediate venting area and is not recorded in sediments at distance from the active vent structures.

Key words: deep-sea, megafauna, stable isotopes, trophic structure. Palabras clave: mar profundo, megafauna, isótopos estables, estructura trófica.

Introduction trophic level and their potential prey items allows us to track the transfer of organic carbon and

nitrogen in the food web. It offers a powerful tool to Exogenous carbon sources affect the distribu- delineate the utilization of carbon compounds, the tion and composition of benthic fauna (Grassle source of nitrogen, and food web interactions 1986). The presence of hydrothermal vents has a (Harrigan et al. 1989). These interactions are large influence on patterns of the deep sea fauna, understood by assessing the isotope enrichment providing food sources and spatial complexity during trophic transfer in which 3‰ enrichment in (by the gradient in water temperature and water 15N occurs with each trophic level transfer (Voss chemistry) to the abyssal plain (Johnson et al. 1991). Carbon isotopes exhibit an increase of 1986). A clear zonation closely related to the approximately 1‰ per trophic level (Macko 1992). microhabitats is determined by these gradients A dual tracer approach with elemental carbon (Hessler & Smithey 1983). and nitrogen and δ13C and δ15N stable isotopes Substantial information regarding the source and was analyzed in the abyssal species Munidopsis transfer of both carbon and nitrogen to and within alvisca and Neolithodes diomedea and in the deep sea lies in the isotopic composition of sediment from the abyssal plain obtained in the organic matter (Macko 1992). The signature of the central Gulf of California. These two species stable isotopic composition of the tissues of higher have been reported dominant components in the

37 Escobar-Briones, E., P. Morales, E. Cienfuegos & M. González crustacean assemblage both in the abyssal plain dried onboard at 60º. Due to the reduced size of and the ecosystem. By their the squat lobsters, analysis were carried out in a dominant condition these species determine the mixture that included both muscle and gills. In biological control of resources originated in the the laboratory both the tissues and sediment were vent. These two species were chosen to define the finely ground and acidified with 0.1N HCl, to use of resources originated in the vents and remove carbonates. Later the materials were evaluate the potential export of vent material to washed with de-ionized water, oven dried at 60ºC the abyssal ecosystem in the central Gulf of and finely ground. The dried material was California. weighted on a Mettler ME22 microbalance. Three milligram tissue and 500 mg sediment were used for multiple stable isotope analysis, and 2-3 mg Materials and Methods tissue and 10-15 mg sediment were used for carbon and nitrogen elemental analysis. Analysis Specimens of the two species and sediments of the proportions of carbon and nitrogen were were collected in dives on the DSV NAUTILE run in triplicate on a Carlo Erba Elemental from two venting sites in the central Gulf of Analyzer Model 1106. California (27°00.94'N, 111°24.66W, 2022 m) Stable isotope samples were placed in pre- during the French Mexican expedition GUAY- combusted quartz tubes containing purified NAUT. cupric oxide beads and high purity granular The area of study is a hydrothermally active, copper. The tubes were evacuated and sealed. sediment covered sea-floor spreading segment The combustion processed followed included (Lonsdale et al. 1980), 20 km in length and 5 km heating for an hour at 900C, and then cooled to 700ºC at a rate of 4ºC min-1, and finally from 700 in width (Peter & Scott 1991). It is characterized -1 by a high sedimentation rate (1-2 m /1000 yrs; to 500ºC at a rate of 0.6ºC min to ensure that Peter et al. 1991) of hemipelagic muds and any oxides of nitrogen were converted to N2. The turbidites (Tunnicliffe 1991). The adjacent CO2 and N2 gases were isolated cryogenically abyssal sediment is pelagic in origin (Baba et al. from other combustion products and analyzed 1991), composed primarily of diatoms that separately on a Finnigan 251 CNOS and a contribute 3 to 4% of the total organic carbon in Nuclide 3-60 isotope ratio mass spectrometers, the sediments (Calvert 1966). Chimneys are respectively, and expressed as ‰ differences from a standard. The standard reference used for characteristic of the morphology of the deposits; 15 sediments are generally saturated with high N was atmospheric nitrogen and the standard molecular weight hydrocarbons that appear to be reference for carbon was the PeeDee belemenite derived from hydrothermal alteration of recent limestone with an assigned value of 0.0‰. On the organic material (Peter et al. 1991). basis of replicate analysis of samples, the reproductibility in combustion and measurement Sediment was obtained from cores 10 cm in was within ±0.2‰. Data were presented as: diameter off the venting structures along a 50 m 3 transect, starting at the base of an active vent, and δX=[(Rsample/Rstandard)-1]x 10 (‰) (1) at distances of 5, 20, and 50 m. Sediment samples with: X= stable isotope elements 13C or 15N were frozen upon collection. Onboard samples R= ratios 13C/12C or 15N/14N were thawed and oven dried at 60ºC to later determine both the C and N elemental and stable isotope composition. The resulting isotopic ratios were compared NAUTILE's mechanical arm and tweezers with those of several hydrothermal vent sites in were employed to capture living organisms the Eastern Pacific. within the 50 m radius of active vent structures. All specimens in both species were dissected, and Results and Discussion the muscle tissue was extracted. The gills of the lithodid crab N. diomedeae were analyzed separately, rinsed with distilled water, and oven Sediments.- The sediment organic carbon and

38 Carbon sources and trophic position of Anomura nitrogen values ranged from 2.7 to 16.2% and 0.1 18.1±0.5‰). to 3.3%, respectively of the dry weight. Sediment The nitrogen isotopic composition values in obtained at the base of vents had the highest sediment ranged from δ15N +3.4 to +11.1‰. The content of both carbon (mean 15.1%) and stable isotope composition of sediments nitrogen (mean 3.1%). Organic carbon and progressively increased away from the active nitrogen values at 50 m from the vents had hydrothermal sites. The lowest sediment value impoverished (1-2%) deep-sea values (Fig. 1). (+3.4‰) was recorded at the base of the vent. The lowest sediment C/N ratio was recorded at This sediment consisted mostly of tubeworm the base of the vent, among large amounts of debris and was covered by a thin bacterial mat. tubeworm debris (4.9), indicating the presence of From the d15N perspective, the values resemble large bacterial activity. The C/N ratios increased 4 those recorded for the tubeworm collagen to 6 times in the most distant samples from the vent analysed. The elemental carbon content in (13.1 to 20.6) and characterize the abyssal sediment. sediment changes at the same rate as does the The carbon stable isotope values recorded in the δ13C with distance from the vent site (r2= 0.95). sediment, along the vent to abyss transect ranged 13 The influence of endogenous organic carbon was from -32.2 to -18.0‰. A δ C significant enrich- restricted to the vent site. Sediment collected in ment of the sediment organic matter was recorded the proximity of the vent was 13C depleted, with distance from the active vent. The carbon suggesting the presence of sulfur bacteria in the value recorded at the vent base (-32.2‰) was sediment (Rau 1981). The 13C enrichment impoverished by -14.0‰. In contrast, the sediment insediment observed with increasing distance collected at distances 5, 10 and 50 m showed values from the vent reflects the change in the source of that were enriched. These results suggest sulfur- the organic matter; the endogenous organic based sediment at the base of the active vent site 13 carbon is being replaced by particulate organic (δ C-32.2‰) and the input of organic matter of carbon (POC) of pelagic origin (Peters et al. pelagic photoautotrophic origin for samples from 1978). The carbon value at greatest distance from 13 distances 5, 20, and 50 m (mean of δ C - the vent approaches values for POC recorded in

pphotoautotrophichotoautotrophic source 1 18 NN.. diomedeae 4 15 non - vent faunafauna 16 δ N 14 12 50 mm 10 20 mm 5 m MM.. alvisca 8 2 S- based energy energy source source 6 tube debrisdebris 4 0 m 4 vent faunafauna bacterial mat mat 3 2 hydrothermal petroleumpetroleum 5 0 -60 -50 -40 -30 -20 -10-10 0

13 δ C Fig. 1. Stable isotope composition of sediment samples and the abyssal species Munidopsis alvisca and Neolithodes diomedeae (large black boxes). White boxes depict the resulting δ13C 1‰ and δ15N 3.4‰ decrease to define potential food sources (arrow in direction of potential food source). Boxes of energy sources delimited according to (1) Brooks et al. (1987), Kennicutt et al. (1992); (2) MacDonald et al. (1990); (3) Rau (1981), van Dover & Fry (1994), (4) Fisher et al. (1994); (5) Schoell et al. (1990).

39 Escobar-Briones, E., P. Morales, E. Cienfuegos & M. González the northeastern Pacific Rise (-21‰) and considered a non-vent scavenger (Fig.1). resembles other sediment values in the area Differences larger than 3‰ in isotopic δ13C (Peters et al. 1978). composition in N. diomedeae were observed at The 15N enrichment recorded with distance different sites, indicating a variation in carbon from the hydrothermal flow suggests a rather composition among sites, which might be related pelagic-sedimentary origin, related to signatures to the variability in vent input into the abyssal 15 of particulate organic nitrogen (PON) exported to sediment. The δ N values in N. diomedeae were the deep-sea (Saino & Hattori 1987) that will higher (muscle δ15N +15.4±0.5‰; gills δ15N determine the 15N enriched diets of abyssal +15.3±1‰) than the values recorded for M. species (van Dover & Fry 1989). Similar enriched alvisca. The lithodid crab N. diomedeae can be nitrogen values (9.2 ‰) are suggested to derive considered a typical non-vent scavenger whose from phytoplankton export in the region (e.g., diet is based on deep-sea debris resulting in the diatoms, Peters et al. 1978). enriched d15N values recorded (Fig. 1). Fauna.- The crustacean elemental values Carbon and nitrogen stable isotope composi- ranged from 33.1 to 43%C and 8 to 12.1%N of tion in the study site were in general more 13C the dry weight. The C/N ratio ranged from 3.6 to depleted and less 15N enriched than values 4.1. The elemental values of both carbon and recorded at other hydrothermal vent sites in the nitrogen were lower in M. alvisca (muscle: Pacific (Table 1). In spite of the similarities 33.7±0.4%C, 8.2±0.1%N) than in N. diomedeae shared among vent sites, the nature (quality and (muscle 41.1±0.3%C, 11.7±0.2%N, gills quantity) of outflows from the vent sulfide 9.8±0.04%C, 38.0±0.1%N). Both species have a concentration in the water flow (Johnson et al. C/N ratio close to 4 (range 3.6 to 4.1), which is 1986), the bacteria, and other nutritious particles similar to values identified for grazers, omni- (Hessler et al. 1988) help to create a variety of vores, and scavengers in which enrichment in microhabitats (Fisher et al. 1988). both %C and %N correlates with higher trophic The main carbon sources identified include a position, structural complexity of tissues, and sulfurbased source produced by seeping through increasing size of the organisms. Few studies the soft sediments that is utilized by infauna and have described the ecology of the abyssal fauna M. alvisca and a photoautotrophic source that in the Gulf of California (Grassle 1986). The supports the abyssal, non-vent crab N. diomedeae organic carbon and nitrogen values appear to be (van Dover & Fry, 1989). Its aggregated more enriched than values previously recorded in distribution pattern in the areas affected by the similar fauna by Fisher et al. (1988) in the hydrothermal venting shows that the lithodid crab Galapagos. These are as well attributed to the is an opportunstic species. Pogonophoran tubes sedimentary condition of the basin. and bacterial mats contribute to the organic The δ13C values ranged from -26.4 to 13.8‰. matter and are potential substrates for bacteria The δ13C values of species M. alvisca (-26.4‰) and smaller invertebrates of the smaller benthic suggest a mixed diet based on sulfurbased energy fauna that provide food to the abyssal Crustacea. sources, probably bacteria that obtain their energy sources from sulfur-based activity in the sediment Acknowledgments and photoautotrophic organic debris exported (Rau 1981) (Fig.1). The δ15N value recorded in M. alvisca was significantly lower (5.5‰). M. Funding was provided by CONACYT- alvisca uses more than one energy source, G35442-T, DGAPA-IN-208089 and IN211200 feeding on deep-sea materials, vent debris and UNAM research grants. The carbon/nitrogen free-living sulfurbased bacteria, suggesting the elemental analyses were made by A. Szmant, U. farming of microbes to supplement the nutrition. of North Carolina at Wilmington. Stable isotopes The δ13C values of N. diomedeae (muscle were analyzed at the Department of Oceanogra- -13.8±3.1‰; gills -18.2±1.2‰) indicated that the phy, TAMU, under the supervision of L.A. diet of the crab consists mainly of deep-sea Cifuentes. organic matter of pelagic origin, the crab can be

40 Carbon sources and trophic position of Anomura

41 Escobar-Briones, E., P. Morales, E. Cienfuegos & M. González

M.C. Kennicutt, R.A. Lutz, S.A. Macko, A. Resumen Newton, M.A. Powell, G.N. Somero, & T. Soto. 1988. Variation in the hydrothermal vent clam, Calyptogena magnifica, at the Las fuentes de carbono y la posición trófica Rose Garden vent on the Galapagos spread- de las especies abisales Munidopsis alvisca y ing center.– Deep-Sea Research 35: 1811- Neolithodes diomedeae se describen con base 1831. en isótopos estables de carbono y nitrógeno. Estas dos especies son abundantes en las –––––, –––––, S.A. Macko, & J.M. Brooks. ventilas hidrotermales del golfo de California 1994. Nutritional interactions in Galapagos central. Al ser componentes dominantes de las Rift hydrothermal vent communities: infer- comunidades de crustáceos, éstas definen el uso ences from stable carbon and nitrogen iso- de los recursos y de la exportación de materia- tope analyses.– Marine Ecology Progress les procedentes de las ventilas al ecosistema Series 103: 45-55. 13 15 abisal. Los valores de δ C y δ N del galateido Grassle, J.F. 1986. The ecology of deep-sea Munidopsis alvisca sugieren una dieta mixta hydrothermal vent communities.– Advances basada en bacterias sulforreductoras del in Marine Biology: 301-362. sedimento y metazoas asociados con los tapetes Harrigan, P., J.C. Zieman, & S.A. Macko. 1989. bacterianos. El cangrejo anomuro Neolithodes The base of nutritional suppport for the gray diomedeae es un carroñero que se alimenta de snapper (Lutjanus griseus): an evaluation macrofauna de la planicie abisal donde el based on a combined stomach content and detrito de origen fotoautotrófico ocupa la dieta stable isotope analysis.– Bulletin of Marine principal. La influencia de las ventilas sobre la Science 44: 65-77. composición de la materia orgánica de los sedimentos se limita al área inmediata a las Hessler, R.R., & W.M. Smithey. 1983. The ventilas y no ha sido observada en sedimentos distribution and community structure of que se encuentran a cierta distancia de las meiofauna at the Galapagos Rift hydrother- estructuras hidrotermales activas. mal vents. Pp. 735-770 in: P.A. Rona, K. Bostrom, L. Laubier & K.L. Smith, eds.,

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