Chapter 12 



Commercially Important 

 Invertebrates 



Authors: Lee Doggett, Susan Sykes 



Over 1500 benthic (bottom dwelling) invertebrate species live in the marine 

 and estuarine systems of Maine. The most important phyla, in terms of numbers 

 of species and individuals represented, are Mollusca (snails and clams), 

 Annelida (principally polychaetes) , and Arthropoda (primarily crustaceans). 



These three phyla are important consumers that feed on the direct 

 (phytoplankton and macroalgae) or indirect (detritus and animals) products of 

 primary production and convert them into animal protein. The energy generated 

 is passed on to higher trophic levels through predation (by fish, birds, other 

 invertebrates, and humans). Detritus is colonized by bacteria and becomes a 

 major food source for some invertebrates (deposit feeders). Also, the 

 burrowing and feeding activities of invertebrates, particularly annelids, 

 release sediment nutrients into the water column. 



Species of molluscs, arthropods, and annelids live in the subtidal and 

 intertidal zones (these zones are defined in chapter 4, page 4-59) of the 

 marine and estuarine systems. Molluscs and arthropods are found on all bottom 

 types whereas annelids are more common on unconsolidated bottoms. Some adult 

 arthropods and annelids move into the water column during periodic migrations. 

 Many of the species in these phyla have pelagic (living in the water column) 

 larvae and, as such, are part of the water column habitat. 



The sensitivity of species of these phyla to environmental variation and 

 perturbations varies considerably. Some crustaceans are particularly 

 sensitive to environmental change, but some polychaetes are very resilient. 

 Intertidal invertebrates tend to be less sensitive to environmental impacts 

 than subtidal invertebrates. Although landings of commercial forms may 

 fluctuate greatly, they are generally less sensitive to habitat alteration 

 than other invertebrates. The choice of a species as a biological indicator 

 depends on many factors, including the type of variation or perturbation, 

 natural life cycle events, natural predation, and in the case of commercial 

 species, potential changes in abundance due to overharvesting. 



12-1 



10-80 



