Growth rates increase in spring and may 

 remain high throughout the summer in 

 shallow waters. Primary production, 

 therefore, tends to be higher in near- 

 shore than oceanic waters because the 

 shallower waters are continuously well- 

 mixed and the phytoplankton have a con- 

 stant supply of nutrients from the sedi- 

 ments. Growth rates are also higher in 

 southern New England than northern New 

 England probably due to higher water 

 temperatures and the presence of larger 

 amounts of anthropogenic nutrients in 

 southern areas. 



Phytoplankton species composition 

 varies along the New England coast. Dia- 

 toms are most abundant in northern waters 

 while the warmer, southern waters have 

 higher concentrations of dinoflagellates. 

 Hulburt (1556, 1963) found that several 

 central New England shallow estuaries 

 exhibited large concentrations of one or 

 two species of phytoplankton and that 

 species diversity was generally lower than 

 in more oceanic waters. These patterns 

 are assumed to reflect the more physically 

 unstable inshore conditions that favor 

 motile species (e.g., dinoflagellates) 

 that do not sink to the bottom in shallow 

 waters. 



Occasionally, outbreaks of the dino- 

 flagellate, Gonyaulax excavata , occur in 

 New England nearshore waters. This "red 

 tide" organism produces a toxin that is 

 harmful to marine species when ingested 

 (e.g., suspension-feeding clams, mussels). 

 If the toxin accumulates in shellfish in 

 sufficient quantities, it may be fatal to 

 the host organism as well as to humans 

 when contaminated shellfish are eaten. 

 The intensity and duration of red tide 

 outbreaks are variable in New England, but 

 massive outbreaks create a severe health 

 problem and economic impact upon the 

 shellfish industry. 



2.2.4 Photosynthetic and Chemosynthetic 

 Bacteria 



Although photosynthetic bacteria are 

 commonly found in the sediments of New 

 England tidal flats, relatively little is 

 known about their ecology or role in the 

 tidal flat food web. These organisms are 

 restricted to the upper few millimeters of 



the sediment and appear as purplish films 

 especially during the warmer months of the 

 year. Chemosynthetic bacteria, on the 

 other hand, tend to be most abundant in 

 the redox layer of tidal flat sediments 

 and derive energy from the oxidation of 

 inorganic compounds such as sulfide, 

 nitrite, and ammonia. While relatively 

 little is known about these bacterial 

 types, recent studies in New Hampshire 

 tidal flats (Lyons and Gaudette 1979) and 

 a Massachusetts salt marsh (Howarth and 

 Teal 1980) have shown that chemosynthetic 

 bacteria may contribute significantly to 

 primary production. How much of this 

 energy is transferred to higher trophic 

 levels within the tidal flat ecosystem is 

 not known. 



2.3 THE DECOMPOSERS 



While considerable attention has 

 focused on coastal embayments and estuar- 

 ies as areas of high primary production, 

 much of the organic material entering 

 these systems is in the form of organic 

 detritus (e.g., dead and decomposing salt 

 marsh plants, eelgrass, phytoplankton). 

 Recent evidence points to in situ utili- 

 zation of the bulk of detritus (Haines 

 1977; Woodwell et al. 1977) as well as 

 importation of additional detritus into 

 shallow water from adjacent coastal water. 

 Combining these organic inputs with those 

 coming from terrestrial and aquatic 

 sources and human activities (e.g., 

 Kuenzler et al. 1977; Welsh et al. 1978), 

 it appears that the utilization of detri- 

 tus in inshore waters outweighs the con- 

 sumption of the products of primary pro- 

 duction. 



Decomposition processes become in- 

 creasingly important to the fauna on tidal 

 flats because of (1) a high relative 

 proportion of shallow water areas that 

 promotes the occurrence of autochthonous 

 (indigenous) detrital producers (e.g., 

 benthic micro- and macroalgae), (2) low 

 velocity current regimes that increase the 

 probability of organic particles settling 

 out from the water column, and (3) an 

 increase in the ratio of length of shore- 

 line to volume of water resulting in 

 increased amounts of allochthonous (trans- 

 ported) detrital material entering from 



12 



