CREATION OF SEAGRASS BEDS 



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Ronald C. Phillips 



Department of Biology 

 Seattle Pacific University 

 Seattle, Washington 98119 



INTRODUCTION 



Seagrasses are marine vascular 

 plants which, except for one genus, oc- 

 cur in shallow protected coastal waters 

 on muddy sand substrates. Phyllospadix 

 grows on very high energy coasts on rock 

 in the North Pacific. In the Indo- 

 Pacific region, Thalassodendron and 

 Amphibol is may occur on rock, but Phyl- 

 lospadix is the only genus limited to 

 growth on rocky substrates. The sea- 

 grasses function principally in detri- 

 tus-based food chains. Dr. Pomeroy (at 

 this meeting) stated that about 90% of 

 the biomass enters the particulate and 

 dissolved phase, while 10% is used by 

 grazers. 



U.S. Fish and Wildlife Service bio- 

 logists from the west coast are probably 

 most concerned with eelgrass ( Zostera 

 marina ) because of black brandt ( Branta 

 bernicla nigricans ) whose summer and 

 winter ranges and migratory routes are 

 governed almost primarily by the major 

 concentrations of eelgrass. The brants' 

 diet is about 80% eelgrass and they are 

 wholly dependent on it. On the west 

 coast, brandt are the principal animal 

 using eelgrass. 



Seagrasses function in a submerged 

 environment with roots' binding sediment 

 and leaves' forming baffles which trap 

 sediments. This function was very well 

 illustrated in the early 1930's during 

 the so-called "wasting disease" in the 

 North Atlantic, when up to 99% of all 

 the eelgrass ( Zostera marina ) disap- 

 peared. Soon after, up to 0.3 m (1 ft) 

 of sediments eroded in many areas. 

 Seagrass leaves die and decompose, 

 forming detritus which feeds a number of 

 long complex food chains. Many of our 

 commercial animals, such as clams and 

 oysters, use this detritus. Shrimp and 

 certain fish are still the result of 

 detritus food chains, whether these 

 detritus chains are marsh or seagrass 

 derived. 



TRANSPORTATION 

 GENERAL ECOLOGY OF SPECIES USED 



The two species that I am most in- 

 volved with for transplanting in the 

 Caribbean region are turtlegrass ( Tha- 

 lassia testudinun ) and shoalgrass ( Halo- 

 dule wrightii ) and in the temperate zone 

 on both coasts, eelgrass. Thalassia 

 seems to grow best in water temperatures 

 from 20°C to 32°C (68°F to 90°F), a 

 range of water salinity of 20 °/oo to 

 35 o/oo, rather gentle water currents of 

 2 to 3 knots but of low energy, and rel- 

 atively clear water. I have observed the 

 best Thalassia growth down to 9 to 10 m 

 (30 to 33 ft), although reports state 

 that it does grow deeper. Substrates 

 are mixed silty mud and sand. Seagrasses 

 will tolerate some sedimentation, but I 

 do not know how much. I have observed up 

 to 20 cm (7.9 inches) of sediment dumped 

 on Thalassia and Halodule at Port Aran- 

 sas, Texas, over 6 mo. While Thalassia 

 reacted very poorly, Halodule appeared 

 to thrive. 



Halodule has a broader tolerance 

 level for all environmental parameters 

 listed above. Temperature extremes for 

 Halodule may extend from 15°C to 35°C 

 (59°F to 95°F), while salt tolerances 

 are much wider, from perhaps 20 ° /oo to 

 45 °/oo, even to 60 ° /oo in some areas 

 in the Laguna Madre, Texas. There is 

 evidence that temperature or salinity 

 variations exist within subspecies in 

 the distributional range of seagrass 

 species. After transplanting from the 

 Laguna Madre into the normal salinity of 

 Redfish Bay, Texas, I cannot tell the 

 difference between the transplants of 

 Halodule from the two locations and 

 indigenous growth in Redfish Bay. It is 



This report is based upon research sup- 

 ported in part by the National Science 

 Foundation under Grant ID074-24358. 



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