Population Size Structure and Feeding Biology of Bathynerita Naticoidea Clarke 1989 (Gastropoda: Neritacea) from Gulf of Mexico Hydrocarbon Seeps Jill M
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Gulf of Mexico Science Volume 19 Article 4 Number 2 Number 2 2001 Population Size Structure and Feeding Biology of Bathynerita naticoidea Clarke 1989 (Gastropoda: Neritacea) from Gulf of Mexico Hydrocarbon Seeps Jill M. Zande Marine Advanced Technology Education Center Robert S. Carney Louisiana State University DOI: 10.18785/goms.1902.04 Follow this and additional works at: https://aquila.usm.edu/goms Recommended Citation Zande, J. M. and R. S. Carney. 2001. Population Size Structure and Feeding Biology of Bathynerita naticoidea Clarke 1989 (Gastropoda: Neritacea) from Gulf of Mexico Hydrocarbon Seeps. Gulf of Mexico Science 19 (2). Retrieved from https://aquila.usm.edu/goms/vol19/iss2/4 This Article is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Gulf of Mexico Science by an authorized editor of The Aquila Digital Community. For more information, please contact [email protected]. Zande and Carney: Population Size Structure and Feeding Biology of Bathynerita nati Gulf (!/'1\l('Xiro ScintCI', 2001 (2), pp. 107-118 Population Size Structure and Feeding Biology of Bathynerita naticoidea Clarke 1989 (Gastropoda: Neritacea) from Gulf of Mexico Hydrocarbon Seeps JILL M. ZANDE AND ROBERTS. CARNEY Bathynerita naticoidea is a numerically dominant gastropod in upper continental slope chemosynthetic communities of the northern Gulf of Mexico. A comparison of population size structure at four sites off Louisiana revealed site-specific dif ferences in mean shell size consistent with different recruitment histories and growth rates. ~ere individuals grow to the largest size, population numbers are low and recruitment seems to be limited. Where individuals grow to the smallest size, populations are high and recruitment seems to be high. These patterns ap pear to parallel the population size pattern of the beds of Bathymodiolus childressi Gustafson et. al. 1998 inhabited by the snail, which suggests a link between the control of the two. Analysis of gut contents and fecal matter of B. naticoidea and the organic film on the shell surface of B. childressi confirmed initial assumptions that the snail feeds by radular browsing. Free-living bacteria are abundant on mussel surfaces and are ingested by the snail. The presence of bacteria in the gut and feces was, however, lower, possibly because of dilution by mucus and diges tion. It is proposed that B. childressi provides more than a passive surface for organic film development. The mussel may control the organic film development, thus controlling availability of food to the snail. athynerita naticoidea Clarke 1989 (Fig. 1) is ied. It is here that B. naticoidea is abundant on B a numerically dominant gastropod in up the surface of mussel shells, predominantly per continental slope chemosynthetic com Bathymodilous childressi (Gustafson eta!., 1998). munities in the Gulf of Mexico (Clarke, 1989; The logistical complexity of research below Waren and Bouchet, 1993; Carney, 1994) and 1000 m has limited the extent of seep explo sitnilar depths on the Barbados Excretionary ration, but studies of other Gulf of Mexico Prism (Olu eta!., 1996). Related, if not iden seep sites, such as Alatninos Canyon at 2200 m tical, species have been associated with che and the west Florida escarptnent at 3300 m, mosynthetic systems since the :tviiocene; Nerita indicate geographic or bathymetric restriction. ( Thalassonerita) megastoma Moroni in Italian de B. naticoidea appears to be absent from these posits (Taviani, 1994) and Thalassonerita? eocen systems, and there is a shift in the dominant ia Squires and Goedert in the Humptulips For n:russel from B. childressi to B. broohsi and B. mation of the Olympic Peninsula, ~Washington hecheri (Gustafson eta!., 1998). State (Squires and Goedert, 1996). The habi The work reported herein was intended to tats of contemporary B. naticoidea in the north answer two questions that grew out of initial west Gulf of Mexico are sites of hydrocarbon field observations of B. na1icoidea. The first seepage in a region where geological processes concerned population differences over a geo of sediment movement on the continental graphic region. The species composition of the slope interact with tnigrating salt layers within seep community above 1000 m has proved to the slope. The result is an unusually complex be remarkably uniform for both the large sub seafloor topography with numerous geochem strate-forming organisms and the smaller as ically unique local environments characterized sociated fauna (Carney, 1994). It is well estab by combinations of methane, hydrogen sulfide, lished, however, that the population structure liquid petroleum, and brine seepage (Roberts and growth of the clominan t chemosynthetic and Carney, 1997). These environments are mussel, B. childressi, show site-to-site variation colonized by symbiont-hosting metazoans only linked to local geochemical processes (Nix et below a depth of ~400 m. Below that bathy a!., 1995). It was, therefore, questioned wheth metric threshold, dense aggregations of mus er the population of a dominant heterotrophic sels and vestimentiferan tubeworms are pre associate would show similar variation. This sent. Between 400 and 1,000 m, the depth limit question was addressed by intersite sampling of the Johnson Sea-Link submersible, selected and determination of size-frequency relation examples of this habitat have been well stud- ships. The second question concerned feeding. © 2001 by the J..Iarine Environmental Sciences Consortium of Alabama Published by The Aquila Digital Community, 2001 1 Gulf of Mexico Science, Vol. 19 [2001], No. 2, Art. 4 108 GULF OF MEXICO SCIENCE, 2001, VOL. 19(2) METHODS AND MATERIALS The four sites sampled (Fig. 2, Table 1) were chosen to meet multiple objectives of the Che mosynthetic Ecosystems Study (MacDonald et al., 1995), which is primarily concerned with making initial comparisons and contrasts of the ecology, geochemistry, and geology of hy drocarbon seep communities at nmltiple loca tions. Prelinrinary surveys had established that the sites had seep communities, offered a range of bottmn topography, and were logisti cally convenient. It was anticipated that all four Fig. 1. Lateral, dorsal, and ventt·al views of a typ would have sufficient community development ical Bathynerita naticoidea specimen collected at GC- to allow for replicated long-term sampling. 184. The color is white, and the shell lacks markings The sites, designated by the seafloor lease and sculpture except of growth lines. Usually, the apical region has undergone some dissolution. The blocks in which they lay, were within the Green specimen is 12 mrn in length. Canyon (GC) region, specifically in blocks 185, 234, 233, and 272. The specific bottom feature sanrpled in block GC-185 was a large carbon ate-topped diapir called "Bush Hill" because vVhat is it within the seep community that sup of the abundance of chemosynthetic tube ports such an abundant population of consurn worm clumps on its sumnrit (MacDonald et al., ers? This work is a portion of a larger study of 1989). GC-234 and GC-272 both contained car the organism-level biology and ecology of B. bonate outcrops with hydrocarbon seepage naticoidea (Zande, 1994). and chemosynthetic communities. Once exten An. initial supposition that B. naticoidea is a sive sampling began, however, only one small grazer of surface films is supported by mor mussel bed was located and santpled at GC- phology. Shallow-water Neritacea are known to 272, whereas extensive scattered beds were graze algal fihns (Hughes, 1986). Although B. found at GC-234. The conununity at GC-233 naticoidea has a radula with distinct modifica was unique in being a brine pool (MacDonald tions (\-\Taren and Bouchet, 1993), it shares et al., 1990a), a 22 X 11 m elliptical crater with all species in the Neritaceam superfamily filled with a heavier-than-seawater brine and surrounded by a ring of mussels. a rhipidoglossan radula associated with grazing The platfonn for sampling was the ] ohnson (Fretter and Graham, 1962). A trophic link to Sea-Link subnrersible operated by the Harbor chernosynthesis has been dernonstrated from Branch Oceanographic Institution of Fort 13C and 15N stable isotope analysis; the tissues Pierce, Florida. Operating at depths down to of B. naticoidea resemble that of the chemosyn 1000 m, beds of the chemosynthetic mussel B. thetic mussels of the cornmunity (:tvlacAvoy et childressi ranging in size from ~2 to > 100 m. 2 al., in press; Kennicutt, pers. comm.). The pos were located and sampled with a hydraulic sibility that these isotopic values reflected sym grab integral to the manipulator of the sub biosis within B. naticoidea can be rejected. Al mersible. The cylindrical grab was designed to though there are three confirmed and two sus take a uniform sanrple area of 341 cm2, which pected symbiont-hosting gastropods found in allowed the samples to be considered quanti hydrotherrrml systems (de Burgh and Singla, tative. Caution in treating the samples as quan 1984; Stein et al., 1988; Waren and Bouchet, titative is necessitated by the difficulty in equat 1993), B. naticoidea shows no evidence of such ing grab volume to the mussel shell surface a relationship. Its gills are typical fm the su area actually sampled. The grab sar:nplecl the perfamily, not hypertrophied, lack internal entire thickness of the mat, scraping the nms symbionts, and have shown no enzyme activity sels fi-onr the underlying substrate. for chemosynthesis. Assays for ribulose-1,5-bis Each of the four samples consisted of the phosphate carboxylase-oxygenase, adenosine within-site pooled specimens from multiple triphosphate sulfurylase, and methanol dehy grabs (Table 1). Within site pooling was con drogenase were negative (C. Fisher, pers. sidered a priori the appropriate design for two comm.). A fungal associate on the gill has been reasons. First, B. naticoidert has been observed reported (Zande, 1999), but there are no spe to be highly mobile and forming temporary ag cific indications of a chemosynthetic symbiosis.