(DRAFT) - Taxonomy
Species shrimp, grass
Species Id M070010
Date 26 AUG 96
TAXONOMY
NAME - shrimp, grass
OTHER COMMON NAMES - grass shrimp, jumpers, glass shrimp, popcorn shrimp, glass pawns and hardbacks
ELEMENT CODE -
CATEGORY - Aquatic Crustaceans
PHYLUM AND SUBPHYLUM - , Crustacea
CLASS AND SUBCLASS - Malacostraca,
ORDER AND SUBORDER - Decapoda,
FAMILY AND SUBFAMILY - Palaemonidae,
GENUS AND SUBGENUS - Palaemonetes,
SPECIES AND SSP - vulgaris;pugio;intermedius;, Species cont.:paludosus;kadiakensis
SCIENTIFIC NAME - Palaemonetes vulgaris;pugio;intermedius; Species cont.:paludosus;kadiakensis
AUTHORITY -
TAXONOMY REFERENCES - 73
COMMENTS ON TAXONOMY -
The grass shrimp in the Gulf of Mexico area consist of five species, all
relatively similar in morphological characteristics and most with
over-lapping distribution. Because of their similarities, these species are
often misidentified or lumped as P. vulgaris.*73*
Taxonomy - 1 (DRAFT) - Status
Species shrimp, grass
Species Id M070010
Date 26 AUG 96
STATUS
Coded Status
Biological Indicator
See Comments
REFERENCES FOR STATUS - 73
COMMENTS ON STATUS -
Brackish water Palaemonetes are among the most widely distributed, abundant,
and conspicuous of the shallow water benthic macroinvertebrates in the
estuaries of the Atlantic and Gulf Coasts. Although grass shrimp have only
limited value as fish bait or food for cultured fish or humans, their
ecological importance is unquestioned. Grass shrimp have been extensively
documented as prey of fishes and other carnivores and they are instrumental
also in transporting energy and nutrients between various estuarine trophic
levels: primary producers, decomposers, carnivores, and detritivores.*73*
Since grass shrimp have been recommended for use as bioassay test organisms
(American Public Health Association 1975), much information has been
published about mortality and sublethal effects of various toxicants on
grass shrimp.*73*
Status - 1 (DRAFT) - Distribution
Species shrimp, grass
Species Id M070010
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Estuarine
REFERENCES FOR NWI - 73
Habitat Associations - 1 (DRAFT) - Food Habits
Species shrimp, grass
Species Id M070010
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
OMNIVORE
REFERENCES FOR TROPHIC LEVEL - 73
LIFESTAGE FOOD FOOD PART
General Microorganisms Not Applicable
General Detritus - Organic Not Applicable
General Polychaetes Not Specified
General Oligochaetes Not Specified
Larva Zooplankton Not Applicable
General Crustaceans Not Specified
REFERENCES FOR GENERAL FOOD - 73
REFERENCES FOR LARVAE FOOD - 73
COMMENTS ON FOOD -
Grass shrimp eat a wide variety of aquatic foods. Depending on the
availability of a particular food they may be detritivores, primary
consumers, or secondary consumers.
As detritivores, grass shrimp aid in the mechanical breakdown of refractory
organic material such as fibrous plant materials, as well as assimilate the
associated microflora, microfauna, and fungi. The assimilation of dissolved
organic matter sorbed to finely divided particulate matter such as clay
particles is important in grass shrimp nutrituion. Although grass shrimp
often live among aquatic macrophytes, there is little evidence that the
macrophyte structure is actually consumed. More likely, grass shrimp eat
and assimilate the epiphytic microalgae that coat the plant structure.
Grass shrimp also are predators of meiofauna and small infaunal polychaetes,
oligochaetes, nematodes,and even motile prey such as mysids. As epibenthic
predators and sediment disturbers, grass shrimp alter infaunal community
structure. For example, in North Carolina a sharp decline in the abundance
of P. pugio due to predation by mummichogs (Fundulus heteroclitus) brought
about significant changes in infaunal composition.*73*
COMMENTS ON LARVAE FOOD -
Larvae are planktonic and feed upon zooplankton, algae, and detritus.*73*
Food Habits - 1 (DRAFT) - Environment Associations
Species shrimp, grass
Species Id M070010
Date 26 AUG 96
ENVIRONMENTAL ASSOCIATIONS
G = General A = Adult
LIM = Limiting RA = Resting Adult
J = Juvenile FA = Feeding Adult
RJ = Resting Juvenile BA = Breeding Adult
FJ = Feeding Juvenile P = Pupae
L = Larvae E = Egg
RL = Resting Larvae
FL = Feeding Larvae
LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
G Water Temperature: Specified in Comments
G
G Dissolved Oxygen: Specified in Comments
G Turbidity: Specified in Comments
G Water Depth Preference: Specified in Comments
G Density of Aquatic Vegetation: Specified in comments
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 73
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Aquatic Vegetation:
Grass shrimp, macrophytes, and algae live in the same communities and are
subject to many of the same environmental factors. Studies in Florida
showed the P. pugio was most abundant in habitats characterized by aquatic
macrophytes, relatively high turbidities, and low salinities.
Because grass shrimp depend on aquatic vegetation in many coastal waters,
alterations of estuaries that destroy vegetation could seriously reduce
their abundance. In one instance, weirs built in marshes to benefit
wildlife produced dense masses of aquatic vegetation that supported an
abundance of grass shrimp far higher than that in nearby less densely
vegetated waters. In another study in West Bay, Texas, dredging,
bulkheading, and filling of marshes caused a permanent loss of intertidal
vegetation. The reduction of detrital input into the adjoining aquatic
systems caused a noticeable decrease in abundance of grass shrimp.*73*
Salinity:
The abundance of freshwater and brackish-water grass shrimp in estuaries is
clear evidence of their survival in a wide range of salinities.
Brackish-water shrimp:
Field and laboratory studies indicate that P. pugio adults tolerate
salinities from 0 to 55 ppt but are most common in salinities of 2 ppt to
36 ppt. The 96 h LD 50 values for adults are 0.5 and 44 ppt.
Attempts to assess salinity tolerances of larvae on a broad scale have
yielded mixed results. When larvae were exposed to a wide range of
arbitrarily selected salinities, the low and high salinities required to
kill 50% of the larvae during a 96-h exposure (LD50) were 16 ppt and 46
ppt, respectively. Optimum salinity for complete larval development is 20
to 25 ppt. Possible reasons for the conflicting findings are differences
in populations in different geographic locations, and differences in
laboratory procedures.
Environment Associations - 1 (DRAFT) - Environment Associations
Species shrimp, grass
Species Id M070010
Date 26 AUG 96
P. vulgaris is more tolerant of high salinity water and less tolerant of
low salinity water than is P. pugio. Although salinities as low as 3 ppt
have been lethal to adult P. vulgaris, they have been collected in
freshwater. 96-h LD50 values of 0.8 and 51 ppt have been reported for
adults. Larvae of P. vulgaris are less tolerant of low salinity than are
adults. Larvae thrive at salinities between 10 ppt and 30 ppt; the
optimun is 20 ppt. Larvae do not survive at salinity extremes of 5 and 35
ppt. Larvae of both P. pugio and P. vulgaris survive best, mature early,
and often pass through fewer larval stages when salinities are near
optimum. Interspecific differences in salinity tolerance in estuaries are
likely to segregate P. pugio and P. vulgaris, although biotic interactions
such as competition for food and space are probably more important for
segregation and coexistence.
Although P. intermedius is euryhaline, it has been collected from waters
with salinities of 5 to 39 ppt.
The larvae thrive at salinities of 20 ppt but survival is low at
salinities less than 10 ppt. The larvae have been reared at salinities
near 30 ppt.
Freshwater shrimp:
The two freshwater species, P. paludosus and P. kadiakensis, often live in
brackish waters. P. paludosus was reported in salinities of 0 ppt to 10
ppt, and one specimen was captured in a salinity of 25 ppt. In a laboratory
experiment, P. paludosus survivied for 7 days at a salinity of 30 ppt but
died when the salinity was raised to 37 ppt. In another experiment, adult
P. kadiakensis survived at salinities up to 20 ppt but died at 25 ppt.
Larvae are relatively intolerant of salinities higher than 5 ppt but are
more tolerant of higher salinities after they reach stage IV.*73*
Water Temperature:
Grass shrimp are eurythermal. In coastal waters, P. pugio thrives at
temperatures of 5 to 38 degrees C, but survival is greater at 18 to 25
degrees C. Growth is most rapid in waters at temperatures above 30 degrees
C but drops rapidly at water temperature below 14 degrees C. This species
breed at temperatures of 22 to 27 degrees in Rhode Island and from 17 to 38
degrees C in Texas. Preferred water temperatures range from 5 to 35
degrees C for P. vulgaris and P. paludosus and from 10 to 35 degrees C. for
P. paludosus. Tolerance for warmer waters is greater for P. pugio than P.
vulgaris, but both species are relatively tolerant of the heat stress of
effluents from a power plant. The breeding temperatures for P. paludosus
range from 18 to 33 degrees C.
Physiological responses of grass shrimp to temperature indicated that P.
vulgaris adults and P. pugio larvae are metabolically active over a broad
range of water temperatures, exhibiting physiological compensation to
seasonal temperature changes.*73*
Dissolved Oxygen:
Dissolved oxygen is another factor that helps regulate the distribution and
abundance of grass shrimp. In Louisiana waters, P. vulgaris and P. pugio
are common in dissolved oxygen (DO) concentrations of 6 to 11 ppm. In
Rhode Island, the mortality of P. vulgaris was higher than that of P.
pugio, when both species were caged together in a hypoxic microhabitat (DO
= 0.3 ppm) during a tidal cycle. In the laboratory, at oxygen
concentrations lower than 1 ppm, survival was higher in P. pugio than in P.
vulgaris at all test temperatures (10 to 30 degrees C). In nature, grass
shrimp sometimes climb out of the water during periods of oxygen
Environment Associations - 2 (DRAFT) - Environment Associations
Species shrimp, grass
Species Id M070010
Date 26 AUG 96
deficiency, especially during warm summer nights, but such attempts to
avoid hypoxia can be effective only for a few hours. Respiratory studies
indicated that P. pugio is an oxyconformer; its oxygen uptake decreases as
oxygen tension declines from 8 to 2 ppm.*73*
Physical Factors: Depth:
Grass shrimp usually inhabit the shallows near the water's edge but have
been reported at depths as great as 8 fathoms. In winter, during
temperature lows and in summer, when water temperatures approach seasonal
highs, P. pugio moves from shallow to relatively deep water. The extent of
the movement of grass shrimp among various depths often coincides with the
distribution of oyster shell substrates, which in some waters, are
preferred by P. pugio and P. vulgaris. Oyster beds provide food and
protection.
Turbidity:
Grass shrimp are abundant where turbidity is relatively high. This is
particularly true in habitats where water currents tend to keep sediments
suspended, such as in shallow tidal creeks or near river mouths. Turbidity
may provide some degree of protection from predators in habitats with
little vegetation. In less turbid habitats, macrophytes afford protection
from predators. Although grass shrimp abundance has been found to be
positively correlated with turbidity, turbidity may not be an environmental
requirement. In some habitats, grass shrimp have been observed in clear
water such as is often associated with dense aquatic vegetation.
Grass shrimp tend to avoid fast currents and migrate in the direction of
tidal currents.*73*
COMMENTS ON FEEDING LARVAE ENVIRONMENTAL ASSOC_ -
Larvae are relatively intolerant of salinities higher than 5 ppt but are
more tolerant of higher salinities after they reach stage IV.*73*
Environment Associations - 3 (DRAFT) - Life History
Species shrimp, grass
Species Id M070010
Date 26 AUG 96
LIFE HISTORY
Morphology/Identification Aids
Several diagnostic features distinguish the caridean shrimps, to which the
genus Palaemonetes belongs, from the penaedean shrimps. In the caridean
forms, the pleura of the second abdominal somite overlap those of the first,
and the third walking legs lack claws or chelae. Palaemonetes spp. and
other members of the family Palaemonidae may be distinguished from members
of the families Alpheidae, Processidae, and Hippolytidae by having the
second walking leg with an unjointed carpus (the segment just proximal to
the chela). The absence of mandibular palps in Palaemonetes distinguishes
this genus from the other palaemonid genera Macrobrachium and Palaemon.
Furthermore, unlike Palaemonetes, Macrobrachium bears hepatic spines and
Palaemon floridanus has a prominent striped pattern on the carapace and
abdomen.
Other morphological features of Palaemonetes, as well as many other caridean
genera and families, include the following: well-developed rostrum bearing
both dorsal and ventral teeth, a smooth carapace and abdomen, rounded
abdominal pleura 1-4, well-developed eyes with globular pigmented corneas,
well-developed spines on the telson (two pairs dorsally, two pairs
posteriorly), and chelate walking legs 1-2 (the second legs are stronger
than the first). Grass shrimp are transparent to yellowish brown. Few
exceed 50 mm in total length. Males can be separated from females by the
presence of the appendix masculina attached to the appendix interna of the
endopod of the second pair of pleopods. Also, the endopod of the first
pleopod is larger in males than in females of the same age. External
genitalic details of males may also be used to distinguish between the five
species.*73*
Spawning:
The spawning season of grass shrimp extends from February through October
but may vary with species and geographical location. An exception is P.
paludosus, which spawns all year in southern Florida. In the prespawning
female, the ripening ovaries are discernable as greenish or grayish brown
masses of tissue dorsal and posterior to the stomach, and additional setae
develop on the ventral surface of the abdomen and thorax. After molting,
the female is receptive to the male but apparently the male recognizes her
condition only if physical contact is made with her exoskeleton.
During copulation, which must occur within 7 h after molting, the ventral
surfaces of the partners are positioned so that their genital apertures are
close together. A spermatophore is quickly extruded by the male into the
genital sternites of the female where it remains until oviposition. Before
oviposition, which occurs within 7 h after sperm transfer, part of the
spermatophore dissolves (probably due to enzymatic secretions from the
female's oviduct) and the spermatozoa are released. Ova are fertilized
externally as they are extruded, then manipulated against the plepods and
setae on the ventral surface of the abdomen where they adhere.
The eggs hatch 12 to 60 days after fertilization, depending on species and
geographical location. In warmer climates, the incubation period is usually
shorter. Osmotic swelling of the inner membrane, struggling by the larva
(protozoea), and ventilatory movements by the female assist in freeing the
larva from the egg membrane. The female molts again within a few day after
spawning and may produce an additional brood, depending on the species or
Life History - 1 (DRAFT) - Life History
Species shrimp, grass
Species Id M070010
Date 26 AUG 96
time of spawning.*73*
Fecundity:
The fecundity of P. pugio in Rhode Island is greater than that of other
shrimp populations that have been studied. For example, in June, the
average number of eggs per female was 486 in Rhode Island; 372 in Texas; and
up to 247 in South Carolina. There was a significant positive correlation
between the length (X) of an ovigerous female and the number of eggs (Y).
Development of Larvae:
Larvae are planktonic and feed upon zooplankton, algae, and detritus.
Depending on the species and environmental conditions, there may be from 3
to 11 morphologically distinct stages during larval development. Transition
from one stage to the next occurs during molting. Intraspecific genotypic
variability in the number of larvae and the morphology of different stages
may enhance dispersal.
The morphology and behavior of larvae and postlarvae differ. Larvae lack
long appendages and swim almost continuously with the head down and the
dorsal surface oriented toward the direction of horizontal movement. The
duration of larval development may range from 11 days to several months for
P. pugio, depending on environmental conditions. The final larval stage
metamorphoses to a postlarva, which closely resembles the adult.*73*
Maturation and Life Span:
Juvenile P. pugio mature when they are 1.5 to 2 months old and about 15 to
18 mm long; their life span is 6 to 13 months. The older, overwintering
shrimp usually spawn early in the year and die by the next winter. Most
young-of-the-year spawn late in the year as adults. Postlarvae that survive
the fall and winter spawn in the following spring.*73*
Predation:
In estuaries, numerous fish species and other aquatic carnivores, some of
which are valuable sport and commercial fishes, eat large quantities of
grass shrimp. Grass shrimp are also eaten by forage fishes such as Fundulus
spp., which in turn are preyed upon by larger fishes. As prey, grass
shrimp play an important role in the transfer of energy from the producer
and decomposer levels to higher consumer levels.
Grass shrimp frequently inhabit water near underwater structures and are
particularly attracted to dense stands of underwater macrophytes. These
stands not only support an abundance and diversity of food for shrimp, but
also provide a refuge from predators. Grass shrimp are more prone to
predation when displaced from preferred substrata such as macrophytes and
oyster shells.*73*
Parasites:
Grass shrimp are hosts for numerous species of parasites and ectocommensals.
The most abundant are coccidia, microsporidians, trematodes, isopods, and
leeches. Diseases and parasites do not appear to be major factors in
limiting the abundance and growth of grass shrimp in the Gulf of Mexico.*73*
Growth Characteristics:
Because populations of grass shrimp may produce more than two broods a year,
length-frequency distributions may be polymodal and growth rates are
Life History - 2 (DRAFT) - Life History
Species shrimp, grass
Species Id M070010
Date 26 AUG 96
difficult to characterize. Growth rates vary somewhat between species,
sexes, habitats, and times of year.
In colder coastal waters, growth patterns are different. Salinity is yet
another factor that affects growth. *73*
Bioassays:
In as much as grass shrimp have been recommended for use as bioassay test
organisms (American Public Health Association 1975), much information has
been published about mortality and sublethal effects of various toxicants on
grass shrimp. Workers evaluating the effects of kepone and other
insecticides (heptachlor, toxaphene, dieldrin, and endosulfan) conclude that
P. pugio adults were usually less sensitive and showed a lesser tendency to
bioconcentrate these toxicants than did the fish that were tested. On the
other hand, grass shrimp are much more sensitive than fish to endrin
dithiocarbamates, various chlorophenols, DDT and parthion. On the basis
of a study of 12 insecticides, it was concluded that grass shrimp are more
sensitive to organophosphorous insecticides, and less sensitive to several
organochlorine insecticides at high salinity than at low salinity. Low
temperatures enhanced the survival of shrimp exposed to both groups of
insecticides. Also, for most organophosphorous compounds tested,
crustaceans were more sensitive than marine fishes by several orders of
magnitude.
Heavy metals such as cadmium are more toxic to grass shrimp than to
mummichogs, Fundulus heteroclitus. Concentrations of heavy metals (mercury,
cadmium, and chromium) are acutely toxic to adult grass shrimp, usually in
the order of 100 to 1,000 ppb. Except in areas of sewage or industrial
outfalls, such concentrations far exceed those in estuaries. Therefore,
grass shrimp are too resistant to be of much value in heavy metal bioassays.
Increased temperature or decreased salinity increases the sensitivity of
grass shrimp to heavy metals. Sublethal effects of heavy metals on grass
shrimp have included loss of a predator avoidance response, developmental
abnormalities in larvae, and a reduced tolerance to salinity fluctuations.
Attempts have been made to evaluate the effects of exposure to petroleum
hydrocarbons on survival and various physiological phenomena in grass
shrimp. Several conclusions have been drawn from this research: (1)
concentrations of petroleum hydrocarbons normally found in saltwater (10 to
20 ppb) and its sediments are too low to have acutely toxic effects on grass
shrimp; (2) when sediments and water are exposed chronically to oil
pollution or during a large oil spill, hydrocarbon concentrations could
cause acute toxicity; (3) metabolism reproduction and growth may be reduced
or altered if oil concentrations persist near 1 ppm; (4) grass shrimp
rapidly depurate accumulated petroleum hydrocarbons when they are returned
to oil-free water; and (5) the toxicity of oil is correlated with the
relative proportion of the aromatic fraction present.
Some investigators have evaluated the effects of biocides, such as those
used to remove fouling organisms from cooling systems of powerplants
(generally chlorine), on grass shrimp. In one study, it was concluded that the
detrimental effects of chlorination on grass shrimp were negligible under
normal powerplant operations.
Additional investigations indicated that P. pugio was less sensitive than
mysid shrimp to drilling muds but that both were several orders of magnitude
more sensitive than fishes; grass shrimp were more sensitive than pinfish
(Lagodon rhomboides) to a simulated refinery effluent containing phenol,
Life History - 3 (DRAFT) - Life History
Species shrimp, grass
Species Id M070010
Date 26 AUG 96
sulfide, ammonia, and some other components; and grass shrimp were more
sensitive than other crustaceans to ionizing radiation. Radiation affects
metabolic pathways involved in the synthesis of non-essential amino acids
used in osmotic regulation.*73*
Behavioral Ecology:
Field studies have shown that the movement and distributional patterns of
grass shrimp may be influenced by both photoperiod and tidal cycles.
Swimming of European species, Palaemonetes varians, peaked in morning and
evening. The only documented observation on nocturnal movement of P. pugio was
reported that some shrimp are buried in the sediments during daylight.
Studies indicate that grass shrimp in tidal creeks migrate seaward
(downstream) or drift with the current during ebb tides and migrate upstream
into tidal creeks during incoming tides.
During laboratory experiments on agonistic behavior in P. pugio. and P.
vulgaris, females were dominant over males and large shrimp were dominant
over smaller ones. In interspecific pairings, P. vulgaris generally
dominated P. pugio and P. vulgaris is known to displace P. pugio from the
preferred shell substratum. Such displacement may favor coexistence between
these two sympatric species by reducing the future potential for agonistic
behavior. Distributional differences between two sympatric species are
believed to be caused by displacement of P. vulgaris by Palaemon floridanus
from the preferred red algal substratum.*73*
REFERENCES FOR LIFE HISTORY- 73
Life History - 4 (DRAFT) - Management Practices
Species shrimp, grass
Species Id M070010
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Adverse Draining wetlands, marshes, ponds, lakes
Adverse Constructing/maintaining bulkheads, seawalls, and dikes
Adverse Dredging
Beneficial Maintaining unique or special habitat features [wetlands, caves,
Beneficial Controlling pollution [thermal, chemical, physical]
Beneficial Controlling water levels
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 73
REFERENCES FOR ADVERSE MANAGEMENT PRACTICES - 73
COMMENTS ON MANAGEMENT PRACTICES -
Because grass shrimp depend on aquatic vegetation in many coastal waters,
alterations of estuaries that destroy vegetation could seriously reduce
their abundance. In one instance, weirs built in marshes to benefit wildlife
produced dense masses of aquatic vegetation that supported an abundance of
grass shrimp far higher than that in nearby less densely vegetated waters.
In another study in West Bay, Texas, dredging, bulkheading, and filling of
coastal marshes caused a permanent loss of intertidal vegetation. The
reduction of detrital input into the adjoining aquatic systems caused a
noticeable decrease in abundance of grass shrimp.*73*
For discussion of pollution as related to grass shrimp, see Life History:
Bioassays.
Management Practices - 1 (DRAFT) - References
Species shrimp, grass
Species Id M070010
Date 26 AUG 96
References
73* Anderson, G. 1985. Species Profiles: Life Histories and
Environmental Requirements of Coastal Fishes and Invertebrates
(Gulf of Mexico) -- Grass Shrimp. U.S. Fish and Wildlife Service
Biol. Rep. 82(11.35) pp 19.
References - 1