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Species Name:    Streblospio benedicti
Common Name:                       None

 

I. TAXONOMY

Kingdom Phylum/Division: Class: Order: Family: Genus:
Animalia Annelida Polychaeta Canalipalpata Spionidae Streblospio



The polychaete Streblospio benedicti. Photo David Samuel Johnson.


Streblospio benedicti, closeup of head region. Photo David Samuel Johnson.

Species Name: 
Streblospio benedicti Webster, 1879

Common Name:
None

Species Description:
Streblospio benedicti is a small, segmented, tube-dwelling infaunal polychaete belonging to the family Spionidae (Levin 1984a, Bridges and Heppel 1996). The head is conspicuous, conical in shape, with four eyes, two banded gills and a pair of coiling, tentacle-like feeding palps. Each body segment is equipped with paired, paddle-like setose parapodia that are less robust than in many polychaetes. Individuals are typically reddish-brown and slightly transluscent, with dark green-brown gill bands (Weiss 1995).

The mucoid sediment tubes occupied by S. benedicti are soft and gray and occur at and just below the sediment-water interface (Weiss 1995).


Potentially Misidentified Species:
Streblospio benedicti is morphologically similar to a number of spionid polychaetes, and positive identification to species level is generally beyond the scope of amateur naturalists.

The species has undergone recent revision that separated Gulf of Mexico populations into a morphologically distinct species, Streblospio gynobranchiata (see below). Detailed morphological examination reveals S. gynobranchiata to be a branchiate-brooding form while S. benedicti possesses specialized brood pouches.


II. HABITAT AND DISTRIBUTION 

Regional Occurrence:
Streblospio benedicti occurs along the Atlantic US coast from Maine south to Florida. The species also occurs on the Pacific US coast. Previous studies describing Gulf of Mexico S. benedicti populations are presumably erroneous. Recent taxonomic revision, based on genetic and morphological evidence, now recognizes Gulf of Mexico populations as belonging to a separate, closely related species, S. gynobranchiata (Schulze et al. 2000).

IRL Distribution:
Streblospio benedicti occurs in suitable soft sediment habitats throughout the IRL.


III. LIFE HISTORY AND POPULATION BIOLOGY

Age, Size, Lifespan:
Streblospio benedicti is a small polychaete, less than 20 mm in length, and often only growing to around 6 mm (Gosner 1978, Bridges and Heppel 1996).

Individuals have the potential to be relatively long-lived. Levin and Huggett (1990) report that fall cohort females live for 5-6 months and over-winter to produce the following year's spring cohort. Levin and Bridges (1994) report that individuals exhibit lifespans typically ranging from 30 to 75 weeks, with the oldest individuals tending to exhibit a lecithotrophic reproductive mode rather than a planktotrophic mode (see below).

Abundance:
Larsen and Dogget (1991) report that Streblospio benedicti is among the most abundant and characteristic taxa occurring in Gulf of Maine mud flats. Sears and Mueller (1989) note that S. benedicti was one of three numerical dominant polychaete species on Galveston, TX, intertidal mud flats. These authors report peak densities of more than 5,000 individuals per square meter. Cammen (1979) reports that S. benedicti was among the four taxa dominating the North Carolina saltmarsh macrofauna he studied.

Reproduction:
Reproduction in Streblospio benedicti is sexual and the sexes are separate (Levin et al. 1987). Embryos are brooded by the female in a series of dorsal brood pouches during early development (Levin et al. 1987, Levin and Bridges 1994).

The species is poecilogonous, i.e., it exhibits two distinct, genetically determined developmental strategies (Levin and Bridges 1994, Levin et al. 1991). Some females exhibit planktotrophic brood development in which a relatively large number of small eggs develop into small planktotrophic larvae. In contrast, other females exhibit lecithotrophic brood development, in which fewer, larger offspring spend only a short time in the water column and subsist on yolk reserves rather than feeding in the plankton prior to settlement to the benthic environment.

Both reproductive forms occur along the US Atlantic coast, and sometimes (but apparently not always) within the same population. (Levin and Bridges 1994). Levin (1984) first reported the occurrence of both reproductive strategies from a single North Carolina. The occurrence of both reproductive forms in the same population has subsequently also been reported from Maine, Massachusetts, New York, and Virginia (Levin et al. 1991). Florida populations appear thus far to be exclusively planktotrophic.

Egg diameters in planktotrophic forms range around 60-70 µm, while those from Lecithotrophic forms measure 100-200 µm. Brood sizes from planktotrophic females range from 15 to 70 individuals, whereas those from lecithotrophic females range from around 70 to more than 460 individuals (Levin and Bridges 1994).

Levin and Huggett (1990) observed the production of four annual cohorts in a North Carolina S. benedicti population.

Embryology:
Bridges (1993) estimates an average 800% increase per offspring investment in lecithotrophic-brooding females compared to planktotrophic brooders.

Planktotrophic larvae (i.e., those typical of Florida populations) bear long swimming setae typical of many spionid polychaete larvae. They are released from brood pouches at around 250-300 µm and live and feed in the plankton for up to 7 weeks. In contrast, non-feeding lecithotrophic larvae are considerably larger (550-650 µm) at the time of release, and lack swimming setae. They are metamorphically competent (capable of immediate settlement), but typically remain in the water column for a period of time ranging from a few hours to just over one week (Levin 1984a, Levin et al. 1991, Levin and Bridges 1994).

In regard to animals exhibiting the lecithotrophic brood development strategy, Bridges and Heppel (1996) experimentally determined that female age and size had a significant and opposite effect on brood size (brood size decreased with female age/size). However, female age had a significant, positive effect on offspring survival and on fitness, measured as per offspring carbon and nitrogen investment. The authors suggest it mat be adaptive for long lived fall cohort females to sacrifice reduced fecundity for increased per offspring investment in later broods.

Experiments performed by Smith and Brumsickle (1989) indicate that post-settlement migration by early benthic juvenile S. benedicti is probably a more important dispersal mechanism than adult dispersal.


IV. PHYSICAL TOLERANCES

Temperature:
Although distribution of the species along the entire US Atlantic coast indicates broad overall temperature tolerance, temperature may be limiting to some populations. Keith and Hulings (1965), for example, speculate that cold water temperature may limit the winter and spring occurrence of S. benedicti in some Gulf of Mexico subtidal habitats.

Salinity:
Streblospio benedicti is moderately euryhaline. Ristich et al. (1977) note the species occurs in polyhaline (18-30 ppt) and mesohaline (5-18) portions of the Hudson River estuary, NY. These authors note, however, a decrease in abundance as salinity decreases within the estuary.

Pollution:
Streblospio benedicti is relatively tolerant to elevated levels of sediment organics (Reish 1979), a trait that contributes to its success as a pioneering, opportunistic species.


V. COMMUNITY ECOLOGY

Trophic Mode:
Streblospio benedicti is a surface-deposit feeding polychaete (Levin and Bridges 1994). It typically captures fine mud particles and detritus by sweeping its feeding palps across the sediment surface. However, Streblospio benedicti can also function as a facultative suspension feeder by extending the tentacles up into the water column to capture particles (Gosner 1978).

Virnstein (1977) suggests that ingestion of fine sediments and their subsequent consolidation and deposition by S. benedicti and other surface-feeding worms may in some cases lead to an increase in the percentage of fine sediments in the upper benthos.

Competitors:
Results from predator inclusion/exclusion field experiments by Virnstein (1977) suggest predation is more important than competition in shaping Streblospio benedicti populations. Whitlach (1980) indicates that S. benedicti is a resource specialist and a habitat generalist, and a capable competitor if resources are limiting.

Predators:
Streblospio benedicti is consumed by a variety of epibenthic predators, such as grass shrimp (Palaemonetes pugio), blue crabs (Callinectes spp.), and juvenile fish like spot (Leiostomus xanthurus), flounder, (Virnstein 1977, Kneib and Stiven 1982, Posey and Hines 1991). The proximity of this small surface-feeding polychaete to the sediment surface leaves it vulnerable to such predators.

Habitats:
Streblospio benedicti is common in muddy/soft-sediment estuarine habitats including mud flats, seagrass beds, and marshes (Cammen 1979, Virnstein 1977, Larsen and Dogget 1991, Levin and Bridges 1994). It is an opportunistic, pioneering species exhibiting high growth rates and high rates of reproduction, as well as high mortality (McCall 1977, Sears and Mueller 1989). Populations typically thrive in areas where there is reduced competition resulting from stochastic disturbance or environmental stress. Small-scale postlarval dispersal abilities are among the factors allowing rapid colonization of disturbed habitat patches like stingray feeding pits (Thistle 1981, Levin 1984b). Grassle and Grassle (1974) refer to S. benedicti and also to the polychaete Capitella capitata as dramatic exploiters of newly disturbed areas.


VI. SPECIAL STATUS

Special Status:
None.

Economic/Ecological Importance:
Streblospio benedicti is important as a food resource to a number of estuarine consumer species. It has also been used as a marine nutrient pollution indicator organism (Grassle 1974).


VII. REFERENCES

Bridges TS. 1993. Reproductive investment in four developmental morphs of Streblospio (Polychaeta: Spionidae) and its implications for life-history evolution. Biological Bulletin 184:144-152.

Bridges TS and S Heppell. 1996. Fitness consequences of maternal effects in Streblospio benedicti (Annelida: Polychaeta). American Zoologist 36:132-146.

Gosner KL. 1978. A Field Guide to the Atlantic Seashore. Houghton Mifflin Company, Boston, MA. 329 p.

Grassle IF and JP Grassle. 1974. Opportunistic life histories and genetic systems in marine benthic polychaetes. Journal of Marine Research 32:253-284.

Kneib RT and AE Stiven. 1982. Benthic invertebrate responses to size and density manipulations of the common mummichog, Fundulus heteroclitus, in an intertidal salt marsh. Ecology 63:1518-1532.

Larsen PF and LF Doggett. 1991. The macroinvertebrate fauna associated with the mud flats of the Gulf of Maine. Journal of Coastal Research 7:365-375.

Levin LA. 1984. Multiple patterns of development in Streblospio benedicti Webster (Spionidae) from three coasts of North America. Biological Bulletin 166:494-508.

Levin LA. 1984. Life history and dispersal patterns in a dense infaunal polychaete assemblage: Community structure and response to disturbance. Ecology 65:1185-1200.

Levin LA and TS Bridges. 1994. Control and consequences of alternative developmental modes in a poecilogonous polychaete. American Zoologist 34:323-332.

Levi LA, Caswell H, DePatra KD, and EL Creed. 1987. Demographic consequences of larval development mode: Planktotrophy vs. lecithotrophy in Streblospio benedicti. Ecology 68:1877-1886.

Levin LA. and DV Huggett. 1990. Implications of alternative life histories for the seasonal dynamics and demography of an estuarine polychaete. Ecology 71:2191-2208.

Levin LA, Zhu J, and E Creed. 1991. The genetic basis of life-history characters in a polychaete exhibiting planktotrophy and lecithotrophy. Evolution 45:380-397.

McCall PL. 1977. Community patterns and adaptive strategies of the infaunal benthos of Long Island Sound. Marine Research 35:221-266.

Posey MH and AH Hines. 1991. Complex predator-prey interactions within an estuarine benthic community. Ecology 72:2155-2169.

Reish DJ. 1979. Bristle worms (Annelida: Polychaeta). Pp 77-125 in: Hart CW and Fuller SLH (eds). Pollution Ecology of Estuarine Invertebrates. Academic Press, New York.

Ristich SS, Crandall M, and J Fortier. 1977. Benthic and epibenthic macroinvertebrates of the Hudson River. I. Distribution, natural history and community structure. Estuarine and Coastal Science 5:255-266.

Schulze SR, Rice SA, Simon JL, and SA Karl. 2000. Evolution of poecilogony and the biogeography of North American populations of the polychaete Streblospio. Evolution:1247-1259.

Sears NE and AJ Mueller. A survey of the polychaetes of Bolivar Flats and Big Reef, Galveston, Texas. The Southwestern Naturalist 34:150-154.

Smith CR and SJ Brumsickle. 1989. The effects of patch size and substrate isolation on colonization modes and rates in an intertidal sediment. Limnology and Oceanography 34:1263-1277.

Thistle D. 1981. Natural physical disturbances and communities of marine soft bottoms. Marine Ecology Progress Series 6:223-228.

Virnstein RW. 1977. The importance of predation by crabs and fishes on benthic infauna in Chesapeake Bay. Ecology 58:1200-1217.

Weiss HM. 1995. Marine animals of southern New England and New York. Bulletin 115 of the State Geological and Natural History Survey of Connecticut. Hartford, Connecticut: Connecticut Department of Environmental Protection.

Whitlach RB. 1980. Patterns of resource utilization and coexistence in marine intertidal deposit-feeding communities. Journal of Marine Research 38:743-765.

Report by: J. Masterson, Smithsonian Marine Station
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Page last updated: October 1, 2008