Benthic invertebrates . Benthic invertebrates live primarily in 

 (infaunal) and on (epifaunal) the bottom substrata. Three groups, the 

 annelids, molluscs, and crustaceans constitute the majority of animals in 

 benthic communities in coastal Maine. Annelids are segmented worms. 

 Molluscs, such as clams and snails, have shells and soft bodies. Crustaceans 

 are crablike organisms. Fifteen hundred and eighty-two taxa have been 

 reported from the characterization area. These species are listed by region 

 in appendix E. 



Communities of benthic invertebrates occupy an important position in the 

 marine system. They take the direct and indirect products of primary 

 production and convert them to animal protein, which is passed to higher 

 trophic levels through predation. 



The burrowing and feeding activities of the benthic invertebrates alter 

 sedimentary structures and return to the water column nutrient materials that 

 have been deposited or bound in the sediments. They are dependent on the 

 overlying water to supply oxygen and food and to remove wastes. Food consists 

 of phytoplankton (particulate organic material of plant origin), bacterial 

 flora on detritus, benthic diatoms, living plants, and/or living animals. 

 Some benthic invertebrates feed on one type of food only, while others feed on 

 many types (Sanders et al. 1962). The feeding type of a particular species 

 can change with its size and age (Sanders et al. 1962). Small individuals may 

 be able to consume only one type of food but as they grow they become able to 

 handle larger, more diverse food particles. 



Benthic invertebrates live on all types of substrata and, thus are affected in 

 some way by any type of habitat disruption. Up to 957o of these animals occur 

 within 5 cm (2 in.) of the water-sediment interface (Stromgren et al. 1973), 

 because organic material (i.e., food) is more concentrated there. 



Many species which are considered to be infaunal leave the sediment at night 

 and swim in the water column (i.e., bloodworms and sandworms; Dean 1978 a and 

 b), and crustaceans, which are thought to be planktonic, enter the substratum 

 during daylight hours (Thomas and Jelley 1972). 



Larval stages of many benthic invertebrates live in the water column; usually 

 up to 5 to 6 weeks in Maine (personal communication from E. L. Bousefield, 

 National Museum of Canada, Ottawa, Canada; June, 1977). Other invertebrates 

 such as predatory snails, araphipods , and isopods develop directly into small 

 adults and never enter the water column. Invertebrates that have pelagic 

 larvae have the ability to disperse widely at this stage in their development. 

 Local or short-term perturbations have less effect on these populations than 

 on animals that develop without the larval stage and carry out dispersal as 

 adults. Natural mortality of pelagic larvae is high, possibly as high as 95% 

 to 99%. 



The primary factor influencing distribution and abundance of benthic species 

 is the nature of the substratum. Pelagic larvae metamorphose into juveniles 

 when they come in contact with a suitable substratum and some delay 

 metamorphosis for a limited time until suitable substratum is located. The 

 period of metamorphosis and settlement is probably the most critical in the 

 life of a benthic species (Thorson 1966). Predation on newly settled 

 juveniles is severe. 



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