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
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).
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
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
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 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
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.
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
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.
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.
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
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.
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.
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.
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
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).
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
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
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.
Levin LA and TS Bridges. 1994. Control and consequences of alternative
developmental modes in a poecilogonous polychaete. American Zoologist
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.
Levin LA, Zhu J, and E Creed. 1991. The genetic basis of life-history
characters in a polychaete exhibiting planktotrophy and lecithotrophy.
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
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
Whitlach RB. 1980. Patterns of resource utilization and coexistence in
marine intertidal deposit-feeding communities. Journal of Marine Research
J. Masterson, Smithsonian Marine Station
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Page last updated: October 1, 2008