Benthic invertebrate communities are generally separated into two major size classes. The meiofauna are organisms (metazoans plus foraminiferans) that typically range from 63 to 500 mm in size, and the macrofauna are all of the larger organisms greater than 500 mm in size. Both groups include species that are considered to be either epifauna because they reside primarily on the surface of the sediments and other substrata, or infauna because they burrow or live beneath the surface of the sediment-water interface. A brief description of both the meiofaunal and macrofaunal assemblages from estuarine and freshwater areas of the ACE Basin or other similar habitats is provided in the following sections.
Meiofaunal assemblages are generally most abundant in the upper few centimeters of fine muddy sediments. In some cases, more than 90% of the organisms can be found in the top centimeter of these sediments (Kennish 1986). In subtidal habitats of South Carolina, Coull and Bell (1979) found that 70% of all of the estuarine meiofauna they studied were present in the upper two centimeters and 95% were found in the top seven centimeters of the sediments. Although some meiofaunal organisms can be found in deeper sediments, they are primarily limited to the burrows created by larger macrofaunal species.
Studies of meiofaunal communities and their distribution patterns in both the estuarine and freshwater portions of the ACE Basin drainage system are lacking, but a substantial amount of research has been conducted on this faunal group in North Inlet, a small high salinity estuary located in the northern portion of South Carolina. The dominant meiofaunal taxa found in shallow creek and vegetated marsh habitats of that inlet were nematodes and copepods (Coull et al. 1977, Bell et al. 1978). Other taxa commonly found at lower densities include some species of polychaetes, ostracods, oligochaetes, turbellarians, bivalves and other miscellaneous taxa (Bell 1982, Bell and Woodin 1984, Kennish 1986). Several of these species may include life stages that are meiofaunal in size only as juveniles, whereas other species remain as meiofauna throughout their entire life cycle.
In shallow water salt marsh and tidal creek habitats of the North Inlet estuary, Coull et al. (1979) documented clear distribution patterns among the meiobenthic copepod species sampled. Species that were primarily restricted to subtidal habitats included Halectinosoma winonae and Pseudobradya pulchella, both of which are considered to be epibenthic species. Nannopus palustris occurred only on the mudflats and low marsh and is well adapted to low dissolved oxygen environments. Species found in the intertidal zone of the salt marsh flats included Diarthrodes aegideus, which was abundant only during the winter and spring months, Pseudostenhelia wellsi and Robertsonia propinqua, which were limited to the lower marsh zone, and Nitocra lacustris and Schizopera knabeni, which were limited to the high marsh flats. Species found across the entire subtidal-intertidal gradient included Microarthridium littorale, Halicyclops coulli, and Enhydrosoma propinquum (Coull et al. 1979).
Long-term studies of shallow water meiofaunal assemblages at North Inlet have documented substantial seasonal and annual variability in the abundance, and to a lesser extent, the composition of the meiofauna (Coull and Bell 1979, Coull and Dudley 1985). Meiofaunal assemblages at a subtidal muddy station were dominated by nematodes throughout most of a 63-month study period, with greatest densities observed during the spring and summer months (Coull and Bell 1979). Copepod assemblages at North Inlet also showed distinct seasonal changes at a muddy site, but seasonal effects were less pronounced at a sandy station.
Data on deeper-water meiofaunal assemblages in southeastern estuaries are lacking, but those assemblages are likely to include many of the same subtidal and widely distributed species noted above. Data are also lacking on freshwater meiofaunal assemblages in South Carolina. In other freshwater systems, the smaller taxa that are typically considered to be meiofaunal in size include nematodes, rotifers, gastrotrichs and tardigrades (Hynes 1970).
Meiofaunal organisms play an important role in the estuarine food web complex since they consume bacteria, other microfauna and flora, and detritus, and they are, in turn, consumed by many larger macrofaunal invertebrates and juvenile finfish (Stickney et al. 1975, Bell and Coull 1978, Alheit and Scheibel 1982, Kennish 1986, Smith and Coull 1987, Coull 1990). Their densities can be quite high (2.6 x 107 individuals/m2) and standing crop dry weight biomass can average about 1-2 g/m2 (Coull and Bell 1979). This, combined with their short life cycle and high turnover rates in the sediments, make the meiofauna an extremely important contributor to the total carbon production of estuarine bottom habitats.
A diverse array of epifaunal species was found at most of the estuarine stations sampled in the ACE. Species present at more than 70% of the stations sampled by Calder and Boothe (1977a) and Van Dolah et al. (1979) included the arthropods Callinectes sapidus, Balanus improvisus, Penaeus setiferus; the chordate Mogula manhattensis; several cnidarians (Ectopleura dumortieri, Obelia bidentata, Clytia kincaidi), several bryozoans ( Aeverrillia setigera, Anguinell palmata, Membranipora tenuis, Amathia distans, Bowerbankia gracilis, and Electra monostachys) and the polychaete Sabellaria vulgaris, which was attached to shell fragments and other hard surfaces in the samples. Of the 23 stations sampled, 15 had more than 30 species present in the oyster dredge sample and only 3 stations had fewer than 5 species. Review the table of epifauna . Stations in the North Edisto River, and at Rock Creek had the greatest diversity of species. The North Edisto River had high and relatively stable salinities throughout the areas studied by Calder and Boothe (1977a) and Van Dolah et al. (1979), and several of the sites had shell or hard bottom substrata. These environmental characteristics are conducive to the growth of sessile epifauna which, in turn, provide attractive habitat for many motile species.
Stations in the South Edisto River showed a much greater variation in salinity than the North Edisto (Calder and Boothe 1977b, Calder et al. 1977). They found the highest diversity of epifaunal organisms in the polyhaline and euhaline sections of the river and lowest species diversity at the oligohaline sites. Review the Venice System of salinity classification for information on salinity ranges. The reduced presence of many of the cnidarians, bryozoans and other invertebrate taxa that can not osmoregulate would be expected in low salinity environments.
Subtidal infaunal communities were also quite diverse at the stations sampled by Calder and Boothe (1977b), Calder et al. (1977), Van Dolah et al. (1984, 1991), and Hyland et al. (1996, 1998), with only six of the 26 sites having fewer than 10 species per grab, and only seven of the sites having fewer than 500 animals/m2. Review the table of infauna . An average of 20 species were found at the sites sampled by these investigators, with the average infaunal density equal to 2,430 individuals/m2.
Species diversity of the benthic infaunal assemblages collected from the 26 stations, as measured by the H' index developed by Shannon and Weaver (1949), ranged from 0.8 to 4.4, with the average value of all the stations equal to 2.8. This average is close to the mean H' values observed for infaunal assemblages at undegraded sites (2.8-3.0) that were sampled throughout the southeastern region by EMAP during 1994 and 1995 (Hyland et al. 1996, 1998). Seven of the stations had H' values that were near or below average H' values noted for degraded stations (1.7-1.8) in the EMAP program. Sediment contaminants were measured at three of those sites (CP94076, CP94077 and CP95156, but only one of the sites (CP95156) had elevated levels of total DDT, DDD, arsenic, chromium and nickel that could account for the low diversity values observed. This station also had a very low benthic index score (1.0), which is indicative of a severely degraded benthos (Hyland et al. 1998, Van Dolah et al. 1999). The other two sites had no elevated contaminant levels and they were located in relatively pristine areas in St. Pierre Creek and the North Edisto River. Thus, the low diversity values observed at those sites must be attributable to other unknown factors. The remaining four stations with low average diversity values were all located in areas that were disturbed by either dredging or disposal operations during the study conducted by (Van Dolah et al. 1984).
Although a large number of species was collected at the 26 stations sampled for the infauna, only 10 species were found at more than five of these stations. They included the polychaetes Paraprionospio pinnata, Sabellaria vulgaris, Streblospio benedicti, Nereis succinea, and Heteromastus filiformis; the amphipods Ampelisca vadorum, Batea catharinensis, Melita nitida, and Paracaprella tenuis; and the bivalve Mulinia lateralis. A few species were found at only one or a few sites, but were very abundant (> 1000 individuals/m2). These included the polychaetes Sphaerosyllis perkinsi, Tharyx killariensis, Pista palmata and Parapionosyllis longicirrata. Other taxa that were commonly found at many of the sites, often a high abundances, that were not identified to the genus or species level included oligochaetes, nemerteans, and actinarians. Both sediment characteristics and salinity conditions appear to be the primary environmental factors influencing the distribution of the infaunal species, as well as some of the epifaunal taxa that were collected by grab. Stations with sandy sediments generally had a relatively high abundance of amphipods, as well as syllid polychaetes, particularly in the more saline environments. Some of the dominant amphipods collected (e.g., M. nitida, P. tenuis, B. catharinensi, and Ericthonius brasiliensis) and many of the syllid polychaetes are commonly associated with the sediment surface and tend to have life habits that are more epifaunal than infaunal. At sites with predominantly muddy sediments and at many of the sites with mixtures of sand and mud, polychaetes tended to be the predominant taxa along with oligochaetes and the bivalve Mulinia lateralis. Some stations with mixtures of mud and sand also had high abundances of other bivalves, such as Nucula proxima and Tellina texana.
Stations with relatively low salinities frequently had a lower mean number of species per grab and lower faunal densities than many of the more saline sites sampled. This pattern was not consistent, however, since some of the stations in polyhaline and euhaline locations also had relatively low numbers of species and faunal abundance. Data on salinity patterns were lacking for many of the benthic infaunal stations sampled. Thus, the effects of salinity on the distribution of these species is not well documented by the studies conducted in the ACE Basin area. Other studies have documented clear effects of salinity on infaunal distribution patterns in southeastern estuaries and other regions (e.g. Boesch 1977, Van Dolah et al. 1990, Hyland et al. 1998).
In a study of a tidal creek near Cat Island, South Carolina (Georgetown County), Wenner and Beatty (1988) also found that oligochaetes and polychaetes were the most abundant taxa, although they also observed relatively high densities of mollusks, amphipods and decapods in their samples. Species collected from their study site included the mollusks Macoma balthica, Tellina sp., Mulinia lateralis; the polychaetes Scolecolepides viridis, Laeonereis culveri, Polydora sp. Heteromastus filiformis, Glycera americana, and Sabellaria vulgaris; the decapods Palaemonetes vulgaris, P. pugio, Rhithropanopeus harissii, and the amphipods Melita nitida and Corophium lacustre. Oligochaetes and nemerteans were not identified to lower taxonomic levels.
The study of invertebrate macrofaunal assemblages by Knott et al. (1997) in marsh flats of the Charleston Harbor estuary focused on species that were retained in pit traps or could be counted in quadrats, rather than on many of the smaller epibenthic and infaunal species, such as the amphipods and polychaetes. Major taxa collected from their pit traps included the fiddler crab Uca pugnax, the snails Hydrobiidae (undet.) and Ilyanassa obsoleta, as well as oligochaetes, ostracods and the tanaid Hargeria rapax. Although not collected in their pit traps, the snail Littorina irrorata, the mussel Gukensia demissa, and other Uca spp. were also common on the vegetated flats. All of the taxa collected in the studies by Wenner and Beatty (1988) and Knott et al. (1997) are common to marshes throughout South Carolina, and should be representative of the species that would be found in the ACE Basin system.
Dominant infaunal species collected from the lower intertidal zone (mean sea level [MSL]to mean low water[MLW]) were similar among the three studies cited above, although there were seasonal and spatial differences in the abundance of each species. Species that were most abundant at MSL in one or more of the three studies included bivalve Donax variabilis, the haustoriid amphipods Neohaustorius schmitzi, Parahaustorius longimerus, Protohaustorius deichmannae, Haustoirius canadensis, and Acanthohaustorius millsi, and the polychaete Scolelepis squamata. Most of these species were also the dominant taxa at MLW, where the bivalve Mulinia lateralis and the polychaete Paraonis fulgens were also found in relatively high abundances. Fauna dominant in the surf zone (within 15 m of MLW) included P. deichmannae, A. millsi, D. variabilis, M. lateralis, S. squamata, S. texana, and P. fulgens. Total faunal densities species number per core sample were lowest at MSL, greater at MLW and greatest in the subtidal surf zone area. Although densities of each species varied seasonally, most were present throughout all of the seasons sampled in these studies. Larger macrofauna, such as the ghost crab, Ocypode quadrata, the mole crab Emerita talpoida, and the burrowing ghost shrimp Callianassa spp., were not sampled well in these studies due to the small core size used, but they are known to be abundant on South Carolina beaches (Ruppert and Fox 1988). Many of the smaller invertebrate species found in the beach sands are an important food source for a variety of birds. In the lower intertidal zone, these invertebrates are also fed on by many fish species which are present during high tide.
Only one station in the ACE Basin system was located in the tidal freshwater portion of the study area, and this station had oligohaline salinities on several sampling dates. The dominant taxa found at that site (upper S. Edisto River station) included the amphipods Lepidactylus dytiscus, Gammarus fasciatus, Parapleustes aestuarius, and other Gammaridae (undet.); the polychaete Scolecolepides viridis, the isopod Chiridotea sp, and insects (Ceratopogonidae undet.).
In freshwater areas with harder substrates, other taxa can often be found, including sessile sponges, hydrozoans, bryozoans, flatworms, other amphipod and isopod species, and many species of insect larvae (Hynes 1970). One relatively large invertebrate that is commonly found in many of the freshwater rivers and streams of South Carolina is the crayfish. Wishart and Loyacano (1974) documented 24 species of crayfish in South Carolina. Crayfish found in the ACE Basin were not present in densities considered high enough to support a commercial fishery. Most of the freshwater taxa are stenohaline and their distributions do not extend very far into estuarine habitats.
In general, there are many factors that play an important role in regulating the distribution and abundance of the meiofaunal and macrofaunal communities described above. Since these biota represent an important food source for many other larger taxa, predation effects are often a major regulating factor. Competition, both among individuals within a species as well as among species, can also play a major role in limiting faunal abundances and distribution. These factors, when combined with the effects of various physicochemical factors such as salinity, temperature, dissolved oxygen, sediment grain size, depth of the redox (reducing) layer within the sediments, and distribution along the intertidal-subtidal depth gradient in estuarine environments, result in very complex spatial and temporal patterns in the structure of these assemblages. Readers interested in learning more about the effects of various biotic and physicochemical factors on both meiofauna and macrofaunal assemblages should review general texts on freshwater and estuarine ecology, such as those published by Hynes (1970), Kennish (1986), Mann and Lazier (1991), Ruttner (1971), Valiela (1995), and Levinton (1995). Those interested in learning more about the life habits and distribution of the dominant macrofauna in South Carolina estuaries should review general guides to marine and estuarine life, such as the text by Ruppert and Fox (1988).
R. Van Dolah, SCDNR Marine Resources Research Institute
Alheit, J. and W. Scheibel. 1982. Benthic harpacticoids as a food source for fish. Marine Biology 70:141-147.
Bell, S. S. 1982. Notes and discussion on the population biology and meiofaunal characteristics of Manayunkia aestuarina (Polychaeta: Sabellidae: Fabrincinae) from a South Carolina salt marsh. Estuarine, Coastal and Shelf Sciences 14:215-221.
Bell, S. S. and B. C. Coull. 1978. Field evidence that shrimp predation regulates meiofauna. Oecologia 35:141-148.
Bell, S. S. and S. A. Woodin. 1984. Community unity: Experimental evidence for meiofauna and macrofauna. Journal of Marine Research 42:605-632.
Bell, S. S., M. C. Watzin, and B. C. Coull. 1978. Biogenic structure and its effect on the spatial heterogeneity of meiofauna in a salt marsh. 1978. Journal of Experimental Marine Biology and Ecology 35:99-107.
Boesch, D. F. 1977. A new look at the zonation of benthos along the estuarine gradient. p. 245-266. In: B. C. Coull (ed.). Ecology of Marine Benthos. University of South Carolina Press, Columbia, SC.
Calder, D. R. and B. B. Boothe, Jr. 1977a. Some subtidal epifaunal assemblages in South Carolina estuaries. South Carolina Marine Resources Center Data Report No. 4. South Carolina Wildlife and Marine Resources Department, Charleston, SC.
Calder, D. R. and B. B. Boothe, Jr. 1977b. Data from some subtidal quantitative benthic samples taken in estuaries of South Carolina. South Carolina Marine Resources Center Data Report No. 3. South Carolina Wildlife and Marine Resources Department, Charleston, SC.
Calder, D. R., B. B. Boothe, Jr., and M. S. Maclin. 1977. A preliminary report on estuarine macrobenthos of the Edisto and Santee River Systems, South Carolina. South Carolina Marine Resources Center Technical Report No. 22. South Carolina Wildlife and Marine Resources Department, Charleston, SC.
Coull, B. C. 1990. Are members of the meiofauna food for higher trophic levels? Transactions of the American Microscopical Society 109(3):233-246.
Coull, B. C. and B. W. Dudley. 1985. Dynamics of meiobenthic copepod populations: a long-term study (1973-1983). Marine Ecology Progress Series 23 (3):219-229.
Coull, B. C. and S. S. Bell. 1979. Perspectives of marine meiofaunal ecology. In: R. J. Livingston (ed.). Ecological processes in coastal marine systems. Plenum Press, New York, NY.
Coull, B. C., S. S. Bell, A. M. Savory, and B. W. Dudley. 1979. Zonation of meiobenthic copepods in a southeastern United States marsh. Estuarine and Coastal Marine Science 9:181-188.
Hyland, J. L., L. Balthis, C. T. Hackney, G. McRae, A. H. Ringwood, T. R. Snoots, R. F. Van Dolah, and T. L. Wade. 1998. Environmental quality of estuaries of the Carolinian Province: 1995. Annual statistical summary for the 1995 EMAP-Estuaries Demonstration Project in the Carolinian Province. NOAA Technical Memorandum NOS ORCA 123. NOAA/NOS, Office of Ocean Resources Conservation and Assessment, Silver Spring, MD.
Hyland, J. L., T. J. Herrlinger, T. R. Snoots, A. H. Ringwood, R. F. Van Dolah, C. T. Hackney, G. A. Nelson, J. S. Rosen, and S. A. Kokkinakis. 1996. Environmental quality of estuaries of the Carolinian Province: 1994. Annual statistical summary for the 1994 EMAP-Estuaries Demonstration Project in the Carolinian Province. NOAA Technical Memorandum NOS ORCA 97. NOAA/NOS, Office of Ocean Resources Conservation and Assessment, Silver Spring, MD.
Hynes, H. B. N. 1970. The ecology of running waters. University of Toronto Press, Toronto, ON, Canada.
Kennish, M. 1986. Ecology of estuaries. Volume II. Biological aspects. CRC Press, Boca Raton, FL.
Knott, D. M., E. L. Wenner, and P. H. Wendt. 1997. Effects of pipeline construction on the vegetation and macrofauna of two South Carolina, USA salt marshes. Wetlands 17:65-81.
Lerberg, S. B. 1997. Effects of watershed development on macrobenthic communities in tidal creeks of the Charleston Harbor area. M.S. Thesis. University of Charleston, Charleston, SC.
Levinton, J. S. 1995. Marine biology: Function, biodiversity, ecology. Oxford University Press, New York, New York.
Levisen, M. V. and R. F. Van Dolah. 1996. Environmental evaluation of the Kiawah Island beach scraping project. Final Report to the Town of Kiawah Island, Kiawah Island, SC. South Carolina Department of Natural Resources, Charleston, SC.
Mann, K. H. and J. R. N. Lazier. 1991. Dynamics of marine ecosystems. Blackwell Scientific Publications, Boston, MA and Oxford University Press, New York, NY.
Ruppert, E. E. and R. S. Fox. 1988. Seashore animals of the southeast. University of South Carolina Press, Columbia, SC.
Ruttner, F. 1971. Fundamentals of limnology. University of Toronto Press, Toronto, ON, Canada.
Sandifer P. A., J. V. Miglarese, D. R. Calder, J. J. Manzi, and L. A. Barclay. 1980. Ecological characterization of the sea island coastal region of South Carolina and Georgia. Vol. III: Biological features of the characterization area. U.S. Fish and Wildlife Service, Office of Biological Services, Washington, DC. FWS/OBS-79/42.
Shannon, C. E. and W. Weaver. 1949. The mathematical theory of communication. University of Illinois Press, Urbana, IL.
Smith, D. L. and B. C. Coull. 1987. Juvenile spot (Pices) and grass shrimp predation on meiobenthos in muddy and sandy substrata. Journal of Experimental Marine Biology and Ecology 105:123-136.
Stickney, R. R., G. L. Taylor, and D. B. White. 1975. Food habits of five species of young southeastern United States estuarine Sciaenidae. Chesapeake Science 16:104-114.
Valiela, I. 1995. Marine ecological processes. 2nd Edition. Springer-Verlag, New York, NY.
Van Dolah, R. F., D. R. Calder, and D. M. Knott. 1984. Effects of dredging and open water disposal on benthic macroinvertebrates in a South Carolina estuary. Estuaries 7:28-37.
Van Dolah, R. F., D. R. Calder, F. W. Stapor, Jr., R. H. Dunlap, and C. R. Richter. 1979. Atlantic Intracoastal Waterway environmental studies at Sewee Bay and North Edisto River. South Carolina Marine Resources Center Technical Report No. 39. South Carolina Wildlife and Marine Resources Department, Charleston, SC.
Van Dolah, R. F., P. H. Wendt, E. L. Wenner (eds.). 1990. A physical and ecological characterization of the Charleston Harbor estuarine system. Final Report submitted to the South Carolina Coastal Council. South Carolina Wildlife and Marine Resources Department, Charleston, SC.
Van Dolah, R. F., P. H. Wendt, and M. V. Levisen. 1991. A study of the effects of shrimp trawling on benthic communities in two South Carolina sounds. Fisheries Research 12:139-156.
Van Dolah, R. F., P. H. Wendt, R. M. Martore, M. V. Levisen, and W. Roumillat. 1992. A physical and biological monitoring study of the Hilton Head beach nourishment project. Final Report submitted to the town of Hilton Head Island and the South Carolina Coastal Council. South Carolina Wildlife and Marine Resources Department, Charleston, SC.
Van Dolah, R. F., R. M. Martore, A. E. Lynch, M. V. Levisen, P. H. Wendt, D. J. Whitaker, and W. D. Anderson. 1994. Environmental evaluation of the Folly Beach nourishment project. Final Report. U.S. Army Corps of Engineers, Charleston District and Marine Resources Division, South Carolina Department of Natural Resources, Charleston, SC.
Van Dolah, R. F., J. L. Hyland, A. F. Holland, J. S. Rosen, and T. R. Snoots. 1999. A benthic index of biological integrity for assessing habitat quality in estuaries of the Southeastern United States. Marine Environmental Research 48: 269-83.
Wenner, E. L. and H. R. Beatty. 1988. Macrobenthic communities from wetland impoundments and adjacent open marsh habitats in South Carolina. Estuaries 11: 29-44.
Wishart, M. A. and H. A. Loyacano. 1974. A survey of edible crawfish for the coastal plain of South Carolina. Completion Report for the Coastal Plains Regional Commission. Department of Entomology and Economic Zoology. Clemson University, Clemson, SC.