macroalgae, but photo- and chemosynthetic 

 bacterial productivity have yet to be 

 estimated. There are several estimates 

 of benthic microalgal production in tem- 

 perate, shallow-water habitats (Table 2), 

 but only Marshall et al. (1971) deal spe- 

 cifically with the New England region. 

 Table 2 shows large regional differences 

 in primary production, probably dependent 

 upon local biological, physical, and chem- 

 ical conditions, and the time of the year 

 of the measurements. In addition since 

 it appears that microalgal production is 

 lower at higher latitudes, the estimates 

 by Marshall et al. (1971) cannot be used 

 to generalize for the whole New England 

 region. Phytoplankton productivity in 

 several temperate estuarine environments 

 is given in Table 3. As in the case of 

 benthic microalgae, large regional differ- 

 ences in productivity exist for phyto- 

 plankton making general statements of 

 little value. No estimate of phytoplankton 

 production on New England tidal flats is 

 available and conflicting evidence exists 

 as to whether tidal flat production levels 

 are higher or lower than production levels 

 in deeper coastal waters. Phytoplankton 

 productivity above the flats may be low 

 because these areas are covered by water 

 only a portion of the day and the water 

 over the flats Is turbid because of tidal 

 action. Conversely, primary production 

 may be stimulated by the increased warmth 

 of water over the flat and the closer 

 proximity of nutrients available in the 

 sediments. 



Few studies have attempted to deter- 

 mine organic sources and estimate input 

 and utilization rates of organic matter in 

 New England coastal environments. The few 

 data available, while not specifically 

 from tidal flat habitats, suggest that the 

 flats rely on external sources of organics 

 transported by tidal action. Nixon and 

 Oviatt's (1973) comprehensive study on a 

 smiall Rhode Island coastal embayment 

 demonstrated that the system depended 

 heavily on imports of organic matter from 

 adjacent salt marsh grasses and micro- 

 algae. Welsh (1980) found a western 

 Connecticut mud flat to be a nutrient 

 importer in which mud flat sediment 

 scavenged nutrients derived from both an 

 adjacent salt marsh and tidal creek. In 

 fact, the sediments were so effective in 

 trapping passing nutrients that very 

 little were transported to the adjacent 



open estuarine environment. The periodic 

 contribution of detrital material to the 

 sediment of Barnstable Harbor, Massachu- 

 setts sand flats was related to the 

 annual productivity-decay cycles of 

 Spartina alterniflora (Whitlatch 1981). 

 Other data support the view that detritus 

 imported from salt marshes, eel grass beds, 

 and phytoplankton contribute significantly 

 to the annual budget of organic matter 

 entering shallow water estuarine systems 

 (e.g., Day et al. 1973; DeJonge and Postma 

 1974; Wolff 1977). 



Data are available that contradict 

 the "energy subsidy" thesis. In a variety 

 of southern New England coastal ponds and 

 estuaries, Marshall (1970) found that most 

 of the organic matter contributed to the 

 sediment came from sources within the sys- 

 tem (Table 4). While it is difficult to 

 extrapolate directly from these data to 

 tidal flat habitats, they do point to ben- 

 thic micro- and macrophyte production as 

 significant contributors of organic car- 

 bon. Marshall (1972) later pointed out 

 that the rates at which organic matter was 

 added to those systems he studied was less 

 than the rates at which it was being uti- 

 lized. He suggested that rapid recycling 

 of organic materials within the habitats 

 could explain the imbalanced carbon bud- 

 get. In addition, there is a debate 

 regarding the importance of salt marshes 

 as energy subsidizers of estuarine and 

 coastal environments (see Nixon 1980 for a 

 review). Early studies suggested that 

 marsh grasses were exported in large quan- 

 tities to become the major contributor of 

 detritus to the coastal zone. More recent- 

 ly, studies have indicated that much of 

 the detritus associated with Georgian 

 estuaries is not derived from marsh grass 

 but comes from algal sources (e.g., Haines 

 1977; Haines and Montague 1979). Produc- 

 tion of organic materials by chemosynthe- 

 tic bacteria has been overlooked and may 

 contribute appreciably to the tidal flat 

 carbon budget (see section 2.2.4). In any 

 event, it is obvious that more research 

 carried out with a holistic (whole system) 

 perspective will be needed to clarify this 

 situation. The contribution of salt marsh 

 organic materials to tidal flat habitats, 

 for instance, may be determined by hydro- 

 graphic characteristics (e.g., flushing 

 rates, topographic conditions) of the 

 individual systems and the proximity of 

 the salt marshes to the tidal flats. 



15 



