COMPARISON OF PHYTOPLANKTON PRODUCTION BETWEEN 

 NATURAL AND ALTERED AREAS IN WEST BAY, TEXAS' 



Jane Corliss and Lee Trent" 



ABSTRACT 



Phytoplankton production was compared between an undredged marsh area, a bay area, and an adja- 

 cent marsh area altered by channelization, bulkheading, and filling. Average gross production (mg 

 carbon/liter/day) in the altered area (canals) was 8% higher than in the marsh and 48% higher than 

 in the bay during June, July, and August 1969. Gross and net production were significantly higher 

 in the canals and marsh than in the bay; differences between the canals and marsh were not significant. 



Large areas of shallow bays and marshes are 

 being dredged, bulkheaded, and filled for water- 

 front housing sites along the Gulf of Mexico 

 coast. When these sites are developed, shallow 

 marsh and bay areas are deepened or filled with 

 spoil, thus changing the environment for marine 

 organisms. Major changes to the bayshore en- 

 vironment as a result of these alterations in- 

 clude: (1) reduction in acreage of natural 

 shore zone and marsh vegetation; (2) changes 

 in marsh drainage patterns and nutrient inputs; 

 and (3) changes in water depth and substrates. 

 The effects of these environmental changes on 

 the productivity of estuarine organisms are 

 poorly understood. 



Basic production in estuaries results from four 

 types of plant life: phytoplankton, attached 

 algae, sea grasses, and emergent vegetation. 

 Production of sea grasses and emergent vege- 

 tation is reduced or lost when natural marsh 

 areas are dredged and filled for housing sites. 

 Whether or not this reduction in primary pro- 

 duction by sea grasses and emergent vegetation 

 is compensated for by an increase in production 

 by phytoplankton and attached algae is not clear. 

 The objective of this study was to compare ph.y- 

 toplankton production between housing develop- 

 ment canals, natural marsh areas, and the open 

 bay in a shallow Texas estuary. 



' Contribution No. 319, National Marine Fisheries 

 Service Biological Laboratory, Galveston, Tex. 77550. 



" National Marine Fisheries Service, Biological Lab- 

 oratory, Galveston, Tex. 77550. 



Manuscript accepted June 1971. 

 FISHERY BULLETIN: VOL. 



69, NO. 4, 1971. 



STUDY AREA AND METHODS 



The study area in West Bay, Texas, included 

 a natural marsh, an open bay area, and the canals 

 of a waterfront housing development ( Figure 1 ) . 

 The developed area, which included about 45 

 hectares of emergent marsh vegetation, inter- 

 tidal mud flats, and subtidal water area prior 

 to alteration, was reduced to about 32 hectares 

 of subtidal water by dredging and filling. The 

 water volume (mean low tide level) was in- 

 creased from about 184,000 to about 394,000 

 kliter. 



Sampling stations were established in dead-end 

 canals in a housing development, natural marsh 

 ai-eas, and an open bay area (Figure 1) . Water 

 depths at mean low tide at stations 1 through 5 

 were 1.6, 2.6, 0.5, 0.2, and 1.0 m respectively. 



Primary production was measured on six 

 occasions at each station between June 18 and 

 August 14, 1969. Measurements were made 

 using the light- and dark-bottle technique de- 

 signed by Gaarder and Gran (1927). Water 

 samples were taken 15 cm below the surface at 

 all stations. A 4-liter bottle having a vent at 

 the bottom with a 30-cm rubber tube attached 

 was used to take the subsurface samples. Num- 

 ber 10 netting (0.060-mm mesh) was placed over 

 the mouth of the bottle and the bottle was sub- 

 merged, mouth down, until the container filled. 

 The netting was used to eliminate most of the 

 zooplankton from the samples. 



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