|
VI. BENTHIC INVERTEBRATES
INTRODUCTION Benthic invertebrates are important members of the saltmarsh ecosystem since they are part of detrital food webs linking marsh productivity to resource species (Moy and Levin 1991; Minello and Zimmerman 1992). The effects of oil or its components on invertebrates and their habitats are well documented (Saunders et al. 1980; Suchanek 1993; Burger 1994; Jewett et al. 1999). There is also considerable information available on the benthic invertebrates of created salt marshes compared to those of nearby natural marshes (Moy and Levin 1991; Minello and Zimmerman 1992; Sacco et al. 1994; Levin et al. 1996). Little information is available, however, about the benthic invertebrate assemblages at restored S. alterniflora marshes that were not only destroyed by an oil spill, but also historically affected by petroleum products, trace metals, and other contaminants similar to the sites studied in the Arthur Kill. METHODS AND MATERIALS Sampling methods for benthic invertebrates follow those of Sacco et al. (1994). A 3-cm-diameter (7 cm2) metal coring tube was used to collect 5-cm-deep sediment samples from the marsh surface. During each sampling month and at low tide, two core samples were taken at each of the four stations along the transect at each site, for a total of eight core samples per site per sampling month. Sediments and biota were removed from the core and fixed in 10% buffered Formalin in seawater with rose bengal added to aid in sorting and identification of the invertebrates. Prior to sorting, samples were sieved through a 0.3-mm stainless steel sieve. The retained sediments and invertebrates were transferred to 70% ethanol with 5% glycerin, and were examined using dissecting microscopes. All organisms were removed, identified to the lowest practicable taxonomic level, and counted. Benthic invertebrates are often divided by size and/or taxonomy into: 1) meiofauna (usually defined as organisms passing through a 0.5-mm-mesh sieve, and dominated by nematodes, harpactacoid copepods, oligochaetes, and small polychaetes); or 2) macrofauna (larger polychaetes, crustaceans, mollusks, echinoderms, etc.) that are retained on the 0.5-mm sieve. Since oligochaetes are important members of the saltmarsh ecosystem (Sacco et al. 1994; Levin et al. 1998), a 0.3-mm sieve was used in this study to retain a portion of these smaller invertebrates. Both the meiofauna and macrofauna retained on the 0.3-mm sieve will be referred to as "benthic invertebrates." RESULTS Forty-one taxa were identified in the study collections. Oligochaetes were the most abundant taxon, comprising 60% of all individuals counted. Nematodes were the next most abundant taxon, comprising 20% of all individuals counted, followed by the small tube-building fan worm, Manayunkia aestuarina, comprising 14% of all individuals counted. Together these three taxa made up approximately 94% of all individuals in the samples. Although most of the individuals found are considered meiofauna, juveniles of larger invertebrates, including the ribbed-mussel, were also present. Larger amphipods, isopods, and aquatic insects were found at most sites (Table 14). There were greater mean abundances of benthic invertebrate individuals at all sites in the May samples compared to the September samples. Oligochaetes contributed most to this seasonal increase, except at Con Ed Tower (unplanted) where nematodes contributed the most, and at Saw Mill Creek North (replanted) where M. aesturina contributed the most. In the September survey, M. aesturina was found in greatest abundance at Con Ed Tower, while in the May survey, it was found in greatest abundances at the replanted sites Old Place Creek and Saw Mill Creek North. In September, Old Place Creek had the largest numbers of taxa (19), while both Con Ed Tower and Sawmill Creek South (unplanted) had the lowest numbers of taxa (10); in May, there were 22 taxa at Tufts Point (reference) and only eight taxa at Sawmill Creek North (Table 15). DISCUSSION The invertebrate taxa found at the six marsh sites (Table 15) appear to be typical of invertebrates found in tidal S. alterniflora marshes elsewhere. Most of these invertebrates increase in abundance in late spring to early summer, and decrease in abundance in late summer to early fall (Tables 14 and Table 15). Predation, species-specific reproductive strategies, and the availability of food are important interactive factors controlling fluctuations in densities (Rader 1984; Moy and Levin 1991; Minello and Zimmerman 1992; Sacco et al. 1994; Sarda et al. 1994, 1995, 1998; Levin et al. 1996, 1998; Posey et al. 1997). The variability in the data, which is typical of benthic invertebrate studies, the site-specific differences, and the low number of sites sampled confounded the determination of the effect of replanting of S. alterniflora on benthic invertebrate abundances in the Arthur Kill. Similarities were observed, however, in the abundances of all invertebrates, oligochaetes, and M. aestuarina between the replanted site, Old Place Creek, and at the reference site, Tufts Point, both in September and May (Table 15). Although these preliminary findings suggest, in terms of benthic fauna, structural similarities between the replanted and reference sites in the Arthur Kill, the functional equivalency of these marsh sites could not be determined. REFERENCES CITED Burger, J. 1994. Immediate effects of oil spills on organisms in the Arthur Kill. In: Burger, J., ed. Before & after an oil spill: the Arthur Kill. New Brunswick, NJ: Rutgers Univ. Press; p. 115-129. Jewett, S.C.; Dean, T.A.; Smith, R.O.; Blanchard, A. 1999. `Exxon Valdez' oil spill: impacts and recovery in soft bottom benthic community in and adjacent to eelgrass beds. Mar. Ecol. Prog. Ser. 185:59-83. Levin, L.; Tally, D.; Thayer, G. 1996. Succession of macrobenthos in a created salt marsh. Mar. Ecol. Prog. Ser. 141:67-82. Levin, L.; Tally, T.S.; Hewitt, J. 1998. Macrobenthos of Spartina foliosa (Pacific cordgrass) salt marshes in southern California: community structure and comparison to a Pacific mudflat and a Spartina alterniflora (Atlantic smooth cordgrass) marsh. Estuaries 21:129-144. Minello, T.J.; Zimmerman, R.J. 1992. Utilization of natural and transplanted Texas salt marshes by fish and decapod crustaceans. Mar. Ecol. Prog. Ser. 90:273-285. Moy, L.D.; Levin, L.A. 1991. Are Spartina marshes a replaceable resource? A functional approach to evaluation of marsh creation efforts. Estuaries 14:1-16. Posey, M.H.; Alphin, T.D.; Powell, C.M. 1997. Plant and infaunal communities associated with a created marsh. Estuaries 20:42-47. Rader, D.N. 1984. Salt-marsh benthic invertebrates: small-scale patterns of distribution and abundance. Estuaries 7:413-420. Sacco, J.N.; Seneca, E.D.; Wentworth, T.R. 1994. Infaunal community development of artificially established salt marshes in North Carolina. Estuaries 17:489-500. Sarda, R.; Forman, K.; Valiela, I. 1994. Long-term changes of macroinfaunal assemblages in experimentally enriched salt marsh tidal creeks. Biol. Bull. (Woods Hole) 187:282-283. Sarda, R.; Forman, K.; Valiela, I. 1995. Macroinfauna of a Southern New England salt marsh: seasonal dynamics and production. Mar. Biol. (Berl.) 121:431-445. Sarda, R.; Forman, K.; Werme, C.E.; Valiela, I. 1998. The impact of epifaunal predation on the structure of macrofaunal invertebrate communities of tidal saltmarsh creeks. Estuarine Coastal Shelf Sci. 46:657-669. Saunders, H.L.; Grassle, J.F.; Hampson, G.R.; Morse, L.S.; Garner-Price, S.; Jones, C.C. 1980. Anatomy of an oil spill: long-term effects from the grounding of the barge Florida off West Falmouth, Massachusetts. J. Mar. Res. 38:265-280. Suchanek, T.H. 1993. Oil impacts on marine invertebrate populations and communities. Am. Zool. 33:510-533. |
|
www.nefsc.noaa.gov |
Search |
Link Disclaimer |
webMASTER |
Privacy Policy |
(Modified Jun. 13 2008) |