Estuaries Vol. 7, No. 4B, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA p. 531540 December 1964 Distribution and Abundance of Submerged Aquatic Vegetation in Chesapeake Bay: An Historical Perspective’ ROBERT J. ORTH, AND KENNETH A. MOORE Virginia Institute of Marine Science of the College of William and Mary Gloucester Point, Virgina 23062 ABSTRACT: An historical zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG summary of the distribution and abundance of submerged aquatic vegetation (SAV) in the Chesapeake Bay is presented. Evidence suggests that SAV has generally been common throughout the bay over the last several hundred years with several fluctuations in abundance. The decline of Zosrera marina (eelgrass) in the 1930’s and the rapid expansion of Myriopl?yZlum spicutum (watermilfoil) in the late 1950’s and early 1960’s were two significant events involving a single species. Since 1965, however, there has been a significant reduction of all species in most sections of the bay. Declines were first observed in the Patuxent, Potomac and sections of other rivers in the Maryland portion of the Bay between 1965 and 1970. Dramatic reductions were observed over the entire length of the bay from 1970 to 1975. Particularly severe losses were observed at the head of the bay around Susquehanna Flats as well as in numerous rivers along Maryland’s eastern and western shores. Changes in the lower, Virginia portion of the bay occurred primarily in the western tributaries. Greatest losses of vegetation occurred in the years following Tropical Storm Agnes in 1972. Since 1975 little regrowth has been observed in the Chesapeake Bay. Other areas along the Atlantic Coast of the U.S. during the same period have experienced no similar widespread decline. It thus appears that the factors affecting the recent changes in distribution and abundance of submerged vegetation in the bay are regional in nature. Causes for this decline may be related to changes in water quality, primarily increased eutrophication and turbidity. Introduction A distinct feature and one of Chesapeake Bay’s important natural resources are the beds of submerged aquatic vegetation (SAV) that have occupied many of the shallow water areas (Anderson 1972; Stevenson and Confer 1978; Orth et al. 1979; Orth and Moore 198 1). In addition to its high pri- mary productivity, SAV is important be- cause it is a food source for waterfowl, a habitat and nursery area for many species of commercially important fish and inver- tebrates, a shoreline erosion control mech- anism, and a nutrient buffer (Thayer et al. 1975). Because of the recognized values of SAV beds to the Chesapeake Bay, and in partic- ’ Contribution No. 1187 from the Virginia Institute of Marine Science, School of Marine Science, Glouces- ter Point, Virginia. ular its waterfowl populations, there has been some interest historically in the dis- tribution and abundance of these vegetated areas. This has resulted in various field sur- veys by both state and federal agencies at different times and locations, utilizing, for the most part, different methodologies. Un- fortunately, much of the information from these surveys went unpublished or re- mained as state or federal reports. We have attempted here to summarize all the perti- nent information available and to provide a summarization of both the recent and past changes in SAV abundance. We have organized the discussion of SAV distribution into three zones. The area be- tween the mouth of the Chesapeake Bay to just above Smith Island is designated the lower bay zone; the area between Smith Is- land and Kent Island is designated the mid- dle bay zone; and the area between Kent Island and Susquehanna Flats is designated Q 1964 Estuarine Research Federation 531 016~6347/64/04BO531-1 0$01.50/O