Volume 17, Number 4 December 29, 1983 BIOGENIC SHELL DAMAGE in the SMALL GASTROPOD ODOSTOMIA IMPRESSA
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TULANE STUDIES IN GEOLOGY AND PALEONTOLOGY Volume 17, Number 4 December 29, 1983 BIOGENIC SHELL DAMAGE IN THE SMALL GASTROPOD ODOSTOMIA IMPRESSA (SAY) WILLIAM MILLER, III TULANE UNIVERSITY CONTENTS Page I. ABSTRACT ............ ............... ..... 105 II. INTRODUCTION ...................... 106 III. METHODS ............................... .. 107 IV. VARIETIES OF BIOGENIC DAMAGE .... 108 V. DISCUSSION AND CONCLUSIONS ........... .. .. .. ........ .... 112 VI. ACKNOWLEDGMENTS. ................... .... 115 VII. LITERATURE CITED .. 115 ILLUSTRATIONS FIGURE I . • . ... 106 FIGURE2 ····························· · · · · .............. 1~ FIGURE3 ... 109 FIGURE4 .. ...... .. .. 110 FIGURES .... Ill FIGURE6 .... 114 PLATE! ...................... 113 I. ABSTRACT also appear to be the result of attack by crabs, rather than physical breakage by Nearly every shell and fragment of the waves or compaction. Most of the speci small pyramidellid snail Odostomia im mens are infested by an algal microborer, pressa,* occurring in very large numbers in which gives shells a challky, excoriated and around modern intertidal oyster banks appearance. Gastropod borings in the in coastal Georgia, shows evidence of bio Georgia odostomes were very rare. In a genic shell damage. Almost all of the shells comparison with 0. impressa shells from have repaired or unrepaired fractures subtidal oyster banks in Virginia, it was caused by crabs; most of the shell fragments fo und that crab damage in the Georgia sam- sake of simplicity, as the present study is not a *The generic label Odostomia will be used in this taxonomic treatment; 2) because the revision paper, although it should be pointed out that begun by Robertson, although it represents a Robertson (1978) has recently proposed that step in the direction of a more realistic supra Ame rican odostomes be separated into two gen specific grouping of the odostomes. is prelimi era: Boonea Robertson, 1978 (which includes nary and not exhaustive; and 3) because paleon Odostomia impressa). and Fargoa Bartsch. t955. tologists like myself cannot employ the sexual For the present, I prefer to retain the traditional anatomical criteria used to allocate species to name Odostomia for three reasons: 1) for the Boonea or Fargoa. EDITORIAL COMMITTEE FOR THIS PAPER: ROBERT ROBERTSON, Academy of Natural Sciences, Philadelphia, Pennsylvania GEERAT J. VERMEIJ, University of Maryland, College Park, Maryland 105 106 Tulane Studies in Geology and Paleontology Vol. 17 attacks (e.g., snail borings in bivalve shells, crab damage inflicted upon snail shells), by endolithic organisms exploiting mollusk shells as habitats (e.g., boring algae and fungi in various types of mollusk shells, polydorid worm borings in bivalve shells), and by shell-growth adjustments to infesta tion by parasites (e.g., pyramidellid infesta tion of oysters). Skeletal overgrowths by epilithic organisms represent a special cate gory of biogenic shell damage affecting both living and abandoned mollusk shells. (Good summaries of the literature dealing with the interpretation of shell damage are found in the following sources: Reyment, 1971 ; Bishop, 1975; Golubic et al., 1975; Vermeij, 1978; Boucot, 1981; Dodd and Stanton, 1981.) Nearly all of the studies of she ll damage inflicted by the activities of predatory or ganisms on mollusks focus on large prey species. With the exception of a study of the frequency of crab predation on minute Figure 1. Map showing general location of cerithiacean gastropods by Dudley (1980), I the study area (inset) and the lower know of no studies that make use of small Wilmington River-Wassaw Sound estuary. mollusks. The purpose of the present study Locality 1, just upstream from Sister Island; is to describe the varieties and significance samples H-1 through H-4. Locality 2, near of shell damage in a diminutive pyramidel mouth of Blue Bank Creek; samples W-1 lid snail, Odostomia impressa (Say, 1821), through W-5 (see Table 2). (Based on from intertidal oyster banks in the Wassaw N.O.A.A. Savannah River and Wassaw Sound area of coastal Georgia. Odostomia Sound Map, 1980.) i1npressa was used because of its abun dance in modern shell deposits along the ples was much more extensive, but that margin of the sound, and because nearly many of the Virginia shells had been bored every specimen examined showed some by the bryozoan Electra. form of biogenic shell damage. A conservative estimate of the average During a survey of the environmental dis frequency of fatal attacks on Georgia odes tribution of pyramidellid snails from Was tomes from intertidal oyster banks is about saw Sound (Miller, in press), it was dis 25 percent, using samples from time covered that the most common and easily averaged shelly deposits. The predator on detected form of damage evidenced by 0. 0. impressa in this setting is probably the impressa had been inflicted by predatory xanthid crab Panopeus herbstii, which is in crabs; many of the shells had been infested turn preyed upon by raccoons, birds, and by algal microborers, and a few had been fish. The algal microborer responsible for attacked by boring gastropods. Because all microscopic holes and striations in ados of these forms of shell damage caused by tome shells appears to be a cyanophyte typi predators (or potential predators) and cal of lower intertidal zones. endolithic associates leave a more or less indelible trace in the carbonate substrate of 0 . impressa shells, all are potentially pre II. INTRODUCTION servable as trace fossils. Moreover, the Over the past two decades a large litera traces of predation on 0. impressa give an ture has accumulated on the varieties and indica tion of the position of this abundant ecologic significance of biogenic shell dam and widely distributed gastropod in the age in fossil mollusks. This type of she ll trophic structure of intertidal oyster bank damage is caused largely by predatory communities. No.4 Biogenic Shell Damage 107 TABLE 1. Sample station data. The location of the two oyster banks sampled is shown in F1g. 1. SAMPLE ENVIRONMENTAL SAMPLE NUMBER SETTING VOLUME WASSAW SOUND W -1 high intertidal rubble flat behind oyster bank 1.00 liter W -2 low intertidal slope in front of oyster bank 1.00 W -3 shallow tidal slough near oyster bank 1.00 W -4 high intertidal sediment pond within oyster bank 1.00 W -5 high intertidal sediment pond within oyster bank 0.75 WILMINGTON RIVER H-1 shelly bar in tidal creek near oyster bank 1.00 H-2 middle inte rtidal oyster bank (dead) 0.75 H-3 low intertidal rubble slope in front of oyster bank 0.75 H-4 high intertidal shell-arruored levee 1.00 III. METHODS were examined using a scanning electron Nine bulk samples of shelly sediments microscope. An inventory of the condition were collected from two oyster banks lo of shells is shown in Table 2. cated along the edge of the lower Wilming In addition, two samples collected from ton River and Wassaw Sound (Fig. 1). A subtidal "oyster rocks" in the lower James variety of intertidal to very shallow subtidal River, Virginia, by Mr. James P. Whit environments was sampled representing a comb, were used in comparisons with the cross-section of estuarine margin settings intertidal material from Georgia. These (Table 1). Samples were wet-sieved on a samples were collected from Brown Shoal screen having 1 mm openings, dried, and (V-1) and Wreck Shoal Rock (V-2) by dredg picked for specimens of Odostomia im ing 30 and 22 liters, respectively, of oyster pressa. All shells and fragments were care shells and sediments. The 1 to 5 mm sedi fully examined using a dissecting micro ment fraction was dried and picked for 0. scope for signs of predation and endolithic impressa; all specimens were examined for infestation, and selected typical specimens shell damage using a dissecting microscope. TABLE 2. Condition of Odostomia impressa shells from Wilmington River and Wassaw Sound oyster banks. Sample numbers are keyed to Table 1; percentages are given in parentheses. An asterisk indicates a percentage used in a statistical test for significant difference between W-1 and H-3, the largest samples from Georgia (see text). SAMPLE Whole Apical Decollate Apertural Whorl TOTAL NUMBER Shells Fragments Shells Fragments Shards SPECIMENS W-1 234 (32.4) 171 (23. 7)* 74 (10.2) 172 (23.8) 71 ( 9.8) 722 W-2 0 0 0 1 (50.0) 1 (50.0) 2 W-3 5 (83.3) 0 I (16. 7) 0 0 6 W-4 37 (46.3) 15 (18.8) 0 24 (30.0) 4 ( 5.0) 80 W-5 166 (30.0) 129 (23.3) 35( 6.3) 124 (22.4) 99 (17.9) 553 H-1 6(27.3) 7 (31.8) 2 ( 9.1) 7 (31.8) 0 22 H-2 9 (69.2) 4(30.8) 0 0 0 13 H-3 73 (33.6) 59 (27.2)* 18 ( 8.3) 60 (27.6) 7 ( 3.2) 217 H-4 53 (57.6) 24 (26.1) 5 ( 5.4) 9( 9.8) 1 ( 1.1) 92 108 Tulane Studies in Geology and Paleontology Vol. 17 IV. VARIETIES OF BIOGENIC DAMAGE ments of the outer lip with the other (Bishop, 1975, Fig. 12.2), the by-products of Crab-Inflicted Damage. - Shells damaged which are the numerous whorl shards by crab predation occur in three forms: I) found in some samples (Pl. 1, fig. 2; Table 2). whole shells with minor apertural damage, Chipped apertures represent unsuccessful caused by an unsuccessful attack (Pl. I , fig. predation attempts that have been repaired I ); 2) various kinds of shell fragments, sug in some specimens by new shell growth (Pl. gesting in some cases the death of the prey 1, fig. 6). Repaired peeling is distinguished (Pl. 1, figs. 2, 3, 4, and 5); and 3) shell dam from other cracks and shell blemishes by age that was repaired by the would-be vic the following charactertistics: 1) newly tim (Pl.