Gammarus setosus

Taxobox | name = "Gammarus setosus"
regnum = Animalia
phylum = Arthropoda
subphylum = Crustacea
classis = Malacostraca
ordo = Amphipoda
familia = Gammaridae
genus = "Gammarus"
species = "G. setosus"
binomial = "Gammarus setosus"
binomial_authority = Dementieva, 1931

"Gammarus setosus" is a small invertebrate, approximately 1 cm in length. Its green-grey body is segmented with several jointed appendages and two larger antennae near the head [cite book |author=N. A. Campbell & J. B. Reece |year=2001 |title=Biology. Sixth edition |publisher=Pearson Education, Inc., Benjamin Cummings, San Francisco, California |id=ISBN 0-805-36624-5 |pages=1175 pp] . As with all members of the Malacostraca, "Gammarus setosus" has mouthparts located at the head segments, with their legs branching from each thoracic section, and most of their abdominal sections [cite journal |quotes=no |author=V. J. Steele & D. H. Steele |year=1970 |title=Biology of "Gammarus" (Crustacea, Amphipoda) in Northwestern Atlantic |journal=Canadian Journal of Zoology |volume=48 |issue=4 |pages=659] . Typically, "Gammarus setosus" is found in the benthic sub-tidal or low inter-tidal regions. They can be found in the waters off the coast of British Columbia, but have been observed in nearly all of the world's oceans cite journal |quotes=no |author=S. Chavanich & K. A. Wilson |year=2000 |title=Rocky intertidal zonation of Gammaridean Amphipods in Long Island Sound, Connecticut |journal=Crustaceana |volume=73 |issue=7 |pages=835–846 |url=http://www.springerlink.com/content/r11x84020p626g32/ |doi=10.1163/156854000504840 |format=Dead link|date=May 2008] .

It has been documented that the different species of gammaridean amphipods tend to accumulate in zones corresponding to the abundance of the algae that they eat. In a study involving the inter-tidal distribution of such organisms, it was found that "Gammarus" species were more likely to be located in areas where one of their important food sources, "Chondrus crispus" was prevalent . In addition to algae, "Gammarus setosus" often consumes animal material that has settled to the sea floor. There have been a few cases in which "Gammarus" species have preyed upon other small, weak or stressed marine organisms cite web |author=R. Newman |title=Freshwater shrimp. A general description of "Gammarus" shrimp |url=http://www.bcadventure.com/adventure/angling/bugs/shrimp/shrimp.phtml |accessdate=2005-10-23] . However, due to their primarily scavenging nature, they are identified as detritivores and serve a crucial role in the diet of other invertebrates, fish and even some whales [cite journal |quotes=no |author=B. D. Wisenden, A. Cline & T. C. Sparkes |year=1999 |title=Survival benefit to antipredator behavior in the amphipod "Gammarus minus" (Crustacea: Amphipoda) in response to injury-released chemical cues from conspecifics and heterospecifics |journal=Ethology |volume=105 |pages=407–414 |url=http://www.mnstate.edu/wisenden/pdfs/1999%20gammarus%20survival%20Ethology%20105%20407-414.pdf |doi=10.1046/j.1439-0310.1999.00399.x|format=PDF] . Occasionally they are eaten by terrestrial organisms, namely shorebirds and insects that dwell near the ocean [cite journal |quotes=no |author=K. Wudkevich, B. D. Wisenden, D. P. Chivers & J. F. Smith |year=1997 |title=Reactions of "Gammarus lacustris" to chemical stimuli from natural predators and injured conspecifics |journal=Journal of Chemical Ecology |volume=23 |pages=1163–1172 |url=http://www.springerlink.com/content/u171616n1g653k3n/?p=c54e8509f6aa45da8dac6f2e6f50aef6 |doi=10.1023/B:JOEC.0000006393.92013.36] .

Reproduction occurs through a process in which the male carries the female on his back for a length of time, often up to a week. "Gammarus setosus" may reproduce many times in a year, which is often the length of their lifespan, generating up to 100 young per episode . Relative success of growth and reproduction has been shown to correspond to the length of the photoperiod in a given habitat. "Gammarus setosus" can survive in most intensities of light that will occur in their natural environment but are more active at night cite web |publisher="Gammarus" |year=2004 |title=A general description of "Gammarus" |url=http://www.lawrencehallofscience.org/foss/fossweb/teachers/materials/plantanimal/gammarus.html |accessdate=2005-10-23 |publisher=Lawrence Hall of Science |date=2006-10-03] or in the darker, lower light intensity of the sea floor [cite journal |quotes=no |author=V. J. Steele & D. H. Steele |year=1986 |title=The influence of photoperiod on the timing of reproductive cycles in "Gammarus" species (Crustacea, Amphipoda) |journal=American Zoologist |volume=26 |issue=2 |pages=459–467 |url=http://icb.oxfordjournals.org/cgi/content/abstract/26/2/459 |doi=10.1093/icb/26.2.459 |format=abstract] . At temperatures above 20°C, reproduction and growth are greatly accelerated and lifespan becomes significantly shorter [cite journal |quotes=no |author=T. Neuparth, F. O. Costa & M. H. Costa |year=2002 |title=Effects of temperature and salinity on life history of the marine amphipod "Gammarus locusta". Implications for ecotoxicological testing |journal=Ecotoxicology |volume=11 |issue=1 |pages=61–73 |url=http://www.ingentaconnect.com/content/klu/ectx/2002/00000011/00000001/00391035 |doi=10.1023/A:1013797130740] . Ideally, "Gammarus setosus" lives in water around 15°C but can survive in temperatures approximately 10°C above or below this valuecite journal |quotes=no |author=Lois G. Kruschwitz |year=1978 |title=Environmental factors controlling reproduction of the amphipod "Hyalella azteca" |journal=Proceedings of the Oklahoma Academy of Science |volume=58 |pages=16–21 |url=http://digital.library.okstate.edu/OAS/oas_pdf/v58/p16_21.pdf] .

Salinity is a less important factor, as it has a greater tolerable range and will not vary as much in a given environment. A salinity of 33 ppt is ideal; however, at times "Gammarus setosus" are caught in tide pools, where they must survive in water that can reach upwards of 40 ppt . On the other end of the spectrum, survival is possible in salinity as low as 10 ppt . In fact, some "Gammarus" species thrive in the very low salinity of freshwater lakes .

Although not as vital to reproduction or growth, currents in the water column are very important for movement. Floating comprises the primary mode of locomotion, yet they can also swim in short, concentrated bursts. Descriptive of their body orientation while manoeuvring themselves, "Gammarus" are often referred to as side-swimmers .

References