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A WET-SEASON CHARACTERIZATION OF THE TIDAL MYAKKA RIVER

submitted December 12, 1985

to ·Or. Jeffrey lincer, Coordinator Ringling MacArthur Reserve Proj~ct Board of County Commissioners, Sarasota, Florida

by the Mote Marine Laboratory 1600 City Island Park Sarasota, Florida

Ernest D. Estevez, Ph .D. Principal Investigator

Mote Technical Report No. 1 5 a PREFACE

The September 1985 survey of the Myakka River represents the mo st intensive, collaborative and productive project undertaken by the Mote Marine laboratory in so short a period of time. Never before have we attempted to link the design and execution of each study element to the findings of preceding (and even ongoing) tasks, but have done so as a result of preparation, cooperation, and experience. Due to the enormous amount of data generated during the study we have elected to produce a report in two volumes. This first volume presents results in a greatly reduced and graphic version and moves immediately to discussion and analysis. Methods employed for each task are described in an appendix to Volume I . The second vo l ume is a compi l ation of all original data, presented as hard copy of files maintained on an IBM personal computer at the Laboratory. The survey seems incomp l ete despite the extensive, new information it has generated. Many questions natural ly arose during report preparation which we hope to pursue by continued research and more careful scrutiny of data al ready in hand . Nevertheless, this report should prove useful to a variety of persons interested in the Myakka River. We certainly believe that any new studies undertaken within the tidal river will be much improved by the present report.

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~------.------~I ACKNOWLEDGEMENTS

It is a pleasure to recognize the following persons and offices for their support in this investigation.

Becky's Bait Bucket Kathy M. Hammett Paul E. Camp John F. McCarthy Jay B. Dobkin Jonathan Mill er Patricia M. Oooris Irene Randolph Dick Emerson Karen Ridenour Michael S. Flannery Soi l Conservation Service Carter R. Gilbert Snook Haven Fish Camp PROJECT STAFF

Princi pal Investigator Ernest D. Estevez Project Coordinator Bruce Fortune

Tasks

Presettelment Vegetation Barry Wharton!

Modern Shorel ines Beth Hu ssey

Marsh and Forest Structure Ernest D. Estevez

Physical Factors Kell ie Dixon Ernest D. Estevez

Bathymetry Bruce Fortune

River Bed Characteristics James Cul ter

Benthic Fauna James Culter Nora Maddox Jenny Mapes Mike Mill igan

Oyster Eco l ogy Jay Sprinkel Jay Gorze l any

Fisheries T. Duane Phil l ips

Data Management Greg Blanchard

Text Processing laurie Fraser

Graphics Denise Latulippe

!Consultant CONTENTS

Volume I Page Title Page i Preface i i Acknowledgements iii Project Staff iv Contents v Introduction I Summary of Findings 7 Description of the Lower Myakka River Study Area 12 Shoreline Vegetation 27 (.;1e) Marsh and Forest Structure 52 Physical Factors 66 Bathymetry 109 River Bed Characteristics 125 Benthic Invertebrates 136 Oyster Reefs 175 Oyster Predator Inventory 210 Oyster Reef Associated Fauna 218 Fisheries 234 Commentary 246 ( ___ 'f 8 ) Literature Cited 255 Appendices 263 I . Methods 264 2. Supporting Data 282

Volume II Data Reports INTRO DUCTION

Problem Statement The quantity and quality of river water supplied to an estuary have long been known as the most important factors in controlling the productivity of estuarine and many marine living resources . The timing of flows is known to be as important as the volume of discharge, and the role of cyclic and non-cyclic variation in flow and water quality has been amply documented in estuaries throughout the world. No less an intimate relationship exists for estuaries of the Florida west coast . These estuaries and their usually small tributaries are productive and richly diverse environments, long valued for their yields of sport and commercial fisheries, recreational quality, and contribution to the quality of human life. Estuaries are threatened today by the direct and indirect impacts of increased human occupation. Shoreline changes, chemical discharges, habitat loss, and upland development on the Florida west coast are increasing as rapidly as the resident population. Demands for potable water are also increasing, and it is this threat which most imperils the long-term productivity of nearby estuaries. The Ri ng l ing-MacArthur Reserve i s a 33,000 acre tract of flatwoods, wetlands , and other landforms typical of west central Florida. It is adjacent to the Myakka River and Myakka River State Park in Sarasota County . The tract has l ong been recognized by resource managers as a valuable regional asset in terms of its potential as a source of potable water, recreational area, and wildlife habitat . Sarasota County initiated an acquisition and development program for the tract by means of (a) a public referendum in which the intent, scope and financing of the program were defined; (b) acquisition through negotiations between the Board of County Commissioners and Trustees of the holding foundation; and (c) sel ection of consultants for design, construction, and impact assessment. At present, consultants have been selected for design of treatment and distribution faci l ities, on-site hydrology, ecology, history and

-1- archaeology, and land-use planning. Development of water resources on the Ringling-MacArthur Reserve may affect the timing, quantity, and quality of flows to the Myakka River estuary via reductions in leakage of the water table into the bed of the Myakka River and reductions of surface discharge by groundwaters to ponds in the southwest sector of the Reserve. Furthermore, Deer Prairie Slough and, to a lesser extent, Big Slough drain other Reserve lands, each flowing southwesterly to the Myakka estuary . Alterations of surface and/or groundwaters on the Reserve may therefore have significant off site imp acts, since the Reserve represents 13% of the total river watershed and approximately one-third of the watershed below State Road 72 . Hydrological and engineering studies performed in 1985 indicated that on-site supp lies of potable water from the surficial aquifer may not be as extensive as originally believed . This finding has l ed engineers to a preliminary conclusion that water from the Reserve may have to be augmented by other water sources, possibly even the Myakka River, in order to be a reliabl e supply . Withdrawal of water will affect the discharge of freshwater to the downstream estuary, but the consequences of reduced flow are presently undefined. Direct and indirect impacts to the estuary cannot be defined until (i) the resources are better defined; (ii) a system for harvesting, storing, and distributing water is selected; (iii) other activities in the watershed are considered; and (iv) the existing relationship of estuarine resources to freshwater supply is known. The first two tasks will be performed as regular development activities. (Another aspect of development will be the assessment of on-site impacts.) The third task has been accomplished in part by past U.S . Geological survey (USGS) stud ies of the Myakka River. Additional hydrological studies of Charlotte Harbor by the USGS and Florida agencies also may provide information on the relationship of lower river sa linity to streamflow . If exploitation of water resources on the Reserve could have a singular, significant effect on streamflows, or significant effect in concert with other activities, the Southwest Florida Water Management District (SWFWMD) will, according to Chapter 400-1.601 of their rules, consider : a an assessment of ex i sting downstream resources;

-2- o an evaluation of impacts to be expected under various withdrawalsj o inclusion of these factors in issuance of consumptive use permits; o compliance monitoring during and after development of the new supply system. The SWFWMD may require that the developer of the resource assume responsibility for the tasks listed above. In the Peace River, for example, SWFWMD required that General Development Corporation meet certain research and operational requirements in connection with a consumptive use permit for their water treatment plant. SWFWMD has also required Manatee County to anticipate downstream impacts of additional reservoir withdrawals. The study included vegetation mapping, water chemistry, and biological sampling in the tidal area of the Manatee River. The SWFWMD has performed comparable impact assessments in the Alafia River. Also, Mote Marine Laboratory is presently conducting studies of the Waccasassa, Weeki Wachee, Crystal and Withlacoochee Rivers for SWFWMD in order to assist the District in determining optimal flow regimes. Because studies are required by SWFWMD and by the resolution attending the Sarasota County referendum, it was clearly in the County's interest to perform preliminary studies and prepare for a larger plan of study. The study described by this report provides the first systematic scientific description of the estuarine ecology of the lower Myakka River.

Study Design The first phase of studies in the river downstream of the Ringling MacArthur Reserve had several goals and objectives. First, it was necessary for the study to be performed rapidly in order to be useful. However, so little was known about the river it was necessary to design a sampling program with flexibility and rapid transfer of findings critical to other tasks. Secondly, the study had to deal with methodological uncertainties due partly to an unfamiliarity with the river; to the application of innovative techniquesj and to natural variability. Finally, and most importantly, the study had to result in a description of the river which would be useful on its own merit and also guide the refinement of subsequent studies. All sampling and measurement was registered to stations derived from a

-3- thorough series of transects employed for the shoreline survey, between the southwest corner of the Reserve and Charl otte Harbor (Figure 1 and Table I). Bathymetric profiles were run at alternate shoreline transects; mollusc samples were taken at alternate bathymetric profiles; infauna was collected at alternate mollusc stations, and so on. Unique stations were created for only a few, limited purposes .

Organization of the Report

-4-

PHASE I -- SUMMARY OF FINDINGS

1. Channel morphology and vegetation dispersion patterns in the lower Myakka River have not changed greatly during the past 140 years, at least so far as historical records reveal. 2. The river upstream from Snook Haven may have meandered in recent history, and island configuration appears to have changed in the river between Deer Prairie Creek and Tarpon Point. 3. Since the middle of the nineteenth century, mangroves may have extended their range upriver from El Jobean to a pOint nearby Deer Prairie Creek. 4. A total of 72 vascular plant species were identified on the Myakka River from 102 transects which were established between 1-75 and Charlotte Harbor (ca. 22 miles). 5. Black needle rush (Juncus roemerianus) was the most common species on the lower Myakka River, occurring at 49 of the 102 transects surveyed. 6. An analysis of plant community similarity showed vegetational changes from upriver to downriver and a transitional plant community assemblage located between river miles 6.0 and 13.0. 7. Compared to other rivers in the west Florida Gulf coast region, the Myakka River exhibited a conspicuous scarcity of freshwater marsh within the study area. 8. Freshwater flow from Deer Prairie Creek was found to influence vegetation on the main river's shorelines . 9. Drought-induced damage to bulrush was evident downstream of Big Slough. Density of live bulrush decreased in a downstream direction. 10. Juncus density was biphasic, with peaks near Deer Prairie Creek and E1 Jobean. Density was largely controlled by dead shoot abundance, which was low between Big Slough and Myakka Bay. Height of dead Juncus varied inversely with dead shoot density. 11. Red mangroves occurred upstream to a point above Deer Prairie Creek. Most trees were short (10 ft), and saplings were the most common size/ age class.

-7- 12. Mangrove forest structure was relatively uniform upstream from El Jobean to U.S. 41, then values for all measured parameters decreased rapidly. 13. Flowering and wood borer damage in mangroves reflect the input of nutrients and freshwater to the main river . 14. The basin area included in the study area can best be characterized as extremely flat. Most natural drainageways in the river corridor are shallow sloughs , the Myakka River channel being the only one well defined and naturally entrenched throughout its course. 15. The river channel in the study area ranges in width from 60 ft upstream to over 13 ,000 ft at the mouth. 16 . Most of the difference in bank length is attributable to the widening of the river channel into Charlotte Harbor in Zone 4. 17. River widths were most frequently less than 500 ft. The mean depth of all transects was 5.2 ft, illustrating the shallow nature of the river and indicating a low confined discharge volume potential in the upper river area. The river was divided into four zones based on river widths. 18. Shallowest river segments were found near the Deer Prairie Creek, which may indicate the shoaling potential of this tributary. The elevated bed in the vicinity of Deer Prairie Creek may affect the penetration of tidal water and could function as an important salinity control for upriver areas. 19. The relative location of the main channel within the river bed upstream of El Jobean follows no definite pattern . The river bed flanking the channel graded from level bottom to steep slopes. Sloping beds were most common and terracing of the river bed was observed at only 8 transects. 20 . The potential for wind driven mlxlng is poor upstream of Myakka Bay and Myakka Bay may have the best potential for wind driven mixing. 21. Sediments of the Myakka River basin consist primarily of quartz sands 0.5mm to 0.12Smm in size, with sediments of upriver areas being visually more coarse and having fewer silt/clay particulates than downstream areas . 22. Substratum in the upper river is differentiated into center stream (high current speed) and bank areas (low current speed), with the center being well scoured or coarse sands and bank areas having finer sediments derived mostly from shoreline slump.

-8- 23. Areas well outside of running water act as sinks for fine particulates and terrestrial debris. This is true for all sections of the river. 24. Areas downstream of Ramblers Rest Resort generally exhibited bottom of uniform sediments. This was particularly true of areas downstream of Transect 32, where the river noticeably widened. 25 . USGS salinity data collected during the 1985 drought include measurements of 15 parts per thousand (0/00) as far upriver as the Interstate bridge. 26. Before Hurricane Elena, salinity values of 1.0 0/00 occurred upstream as far as Deer Prairie Creek. After the hurricane, the 1.0 0/00 isohale was located in Myakka Bay. 27. Before Hurricane Elena, the lower river was unstratified with regard to salinity and dissolved oxygen. After the hurricane and for the rest of September 1985, both parameters were stratified in and downstream of Myakka Bay. 28. Invertebrate community structure did not reflect hydrographic conditions at the time of sampling. 29. A weak estuarine fauna (few numbers and species) was found as far upstream as Snook Haven. The poor representation of estuarine fauna there may be due to difficulty of upstream larval recruitment. 30. live Corbicula maniliensis at a station above Blackburn Bridge indicate little or no saltwater influence of any significance beyond this point. 31. Numbers of species and faunal density were typical for a river estuarine system, and increased from freshest to most estuarine stations with the exception of Station B19. Station BI9, with notably sparse fauna, was the most highly stressed transitional area. 32. Station B53 appeared to be within a well established estuarine area. It is likely this area seldom undergoes drastic salinity reductions (i.e., to 10-15 ppt) for any length of time. 33. Individual oysters were found on red mangrove prop roots and seawalls from the U.S . 41 bridge to Charlotte Harbor . Oyster reefs were found only from El Jobean to Charlotte Harbor, and were similar based on most parameters.

-9- - 34. The reefs were comparable to some of the better reefs observed in other estuaries. Commercial size oysters were present in the reefs, but more large oysters occurred south of El Jobean. 35 . The oyster Condition Index (mean weight to cavity volume ratio) values were high compared to values from other estuaries. 36 . Oyster morphology varied along the river, and it appeared that low salinities controll ed upstream oyster recruitment more than substrate availability. 37. The primary oyster predator during September was Me10ngena corona, which did not appear to be a controlling factor on oyster bars, though it may be of local importance. 38. Melongena dispersion appeared to be strongly limited by salinity and were not found upstream of Tippecanoe Bay. A salinity of 11 0/00 may represent a critical value for this species. 39. Me10ngena did not display a diurnal migrationj however, increases in both abundance and predation activity were observed at high vs. low tide. 40. Oyster associated fauna communities appeared to be strongly correlated with salinity, with several unique species present which can be used as salinity indicators. 41 . Oyster faunal abundances and diversity were generally low, most likely due to heavy runoff, high river stage, and l ow salinities. 42. Several commensal spec ies which are harmful to oysters were observed, though their concentrations during September were not high enough to cause substantial damage to the oyster populations. 43. Fish egg and larvae densities were extremely low. Two groups could be discerned: freshwater species collected only at upriver stations; and estuarine species col lected only in the lower river. 44. The portion of the river in the vicinity of Tarpon Point appeared to be a transition zone for ichthyoplankton during the wet season. 45. Night trawl collections of juvenile and adu lt fishes contained more individuals and significantly more species than daytime col l ections.

-10- 46. Fishes and macroinvertebrates were more abundant in the lower more saline portions of the river due to the presence of a number of estuarine and marine species. 47. Freshwater species were restricted to the upper river above Big Slough. Several euryhaline species were present throughout the river. 48. Distribution of fishes and macroinvertebrates during the wet season were related closely to salinity. 49. Overall, sampling and analysis met predetermined goals for precision, accuracy and comp leteness . SO. Parameters measured in the study were classified as having response periods of short term, mid-range, or long term duration. Most parameters had mid-range to long term response times. 51. Accurate indi cators of wet season conditions were salinity and dissolved oxygen; marsh structure; benthic densities; oyster related indices, and fishery catches. 52. The river between Myakka Bay and Deer Prairie Creek was identified as the wet season estuary . 53. A worst case scenario resulting from reduced freshwater inflow to the Myakka River was prepared using results of Phase I studies and literature. Twenty-one potential impacts were identified.

-11- DESCRIPTION OF THE LOWER MYAKKA RIVER STUDY AREA

Introduction

The lower Myakka River study area includes approximately 23 river miles of the river corridor, bounded roug hl y by Interstate 75 and S.R. 776 (El Jobean Bridge), the latter situated about 3 river miles above the mouth of the river (Figure I) . The focus is on the river corridor, which includes the river channel, its adjoining forested and marshy floodplain, and some riverside sandy uplands. Th e Myakka River winds through a low, flat, sandy tableland district within the Southwestern Flatwood physiographic region (Brooks, 1981a; Davis, 1943; Harper , 1927). The river originates in eastern Manatee County near Myakka Head and flows generally so uthward a distance of about 66 river miles before emptying into Charlotte Harbor. The dominant topographic feature is the Pamli co marine terrace, an ancient plain formed during the Pleistocene times . The topography is flat to gently sloping , and elevations are generally below 5 ft above sea level along the river corridor, except around river mile 20 where it reaches nearly 10 ft above sea level. Local relief is very subdued save in areas where river meandering has been hi storically active and created locally irregular terrain, most ly above river mile 14. The Myakka River channel enters the study area as a narrow, tightly meandered, freshwater stream . It gradually widens downstream and becomes brackish around Snook Haven at river mile 17 (National Park Serv ice, 1984). Further downriver the channel begins to straighten while both its width and salinity increases. After an island-dotted stretch between river miles 14 and 6, the river widens dramatically and appear s more like a narrow bay than a river. It gently winds its way to Char lotte Harbor, where its two mile wide mouth effectively disguises the narrow river it began as several miles upstream. The river basin is relatively narrow and i s dissected by several small, largely unbranched tributaries and associated drainage canals . Its more important tributary streams are Big Slough, Salt Creek, and Oeer Prairie Creek, all located east of the river. Drainage west of the river is accomplished by

-12- several short streams and a few canals. The long Curry Creek Canal connects the water of the Myakka with Roberts Bay about 6 miles west of the study area. Surface water cond itions can vary from no flow during dry spells (upstream of the study area) to flood stage during rainy periods. Groundwater discharge is more important during the dry season (Joyner and Sutc li ffe, 1976). Surface geological deposits along the river corridor belong to the mid-P l eistocene age Fort Thompson Group and primarily consist of clastic and shelly sediments. Mid-Miocene age Hawthorn Formation/Statenville type deposits are exposed about 3 miles above the study area (Brooks, 19B1b) . Soi l s within the study area are ch iefly sandy and poorly to very poorly drained. The adjoining pine and pine-cabbage palm flatwoods are underlain by sandy, high acidic and low acidic soi l s, respectively. Along the river are found sma ll pockets of Bradenton fine sand (a hammock soil) and Sandy Alluvial Land (an alluviated swamp/hammock soi l) , both confined to above river mile 14. Unclassified tidal marsh soils appear downstream and form an ever widening strip. Sma ll islands and bank areas between Big Slough and Charlotte Harbor have unclassified tidal swamp soils (in Sarasota County) and various types of very poorly drained brackish soi l s (in Charlotte County), both of which support mangrove vegetation (Wildermuth, 1959; Henderson, 1984). Four principal plant associations occur in the river corridor. The low upriver association, a frequently flooded freshwater assemblage of popash heads mixed with buttonbush-popash-water locust meadows, and willow pOints, is found along low banks and islands in the river and marsh in scattered localities near Snook Haven (its main distribution lay upstream of the study area). The low downr i ver assoc iation, a frequently tidally-submerged brackish water assemblage consisting of brackish marsh and mangrove communities, is l ocated between Snook Haven and Charlotte Harbor. The mangroves, however, reach upstream only as far as U.S. 41. Also comprising part of this association are thin strips of red cedar, Brazilian pepper, prickly pear cactus, and various other xeric plants wh ich are typically found on low natural levees fronting the brackish marsh belt (personal communication, Jonathan Miller, 9/19/85). The oak-cabbage palm hammock association consists of dense forests flanking the river and/or brackish marsh. Four varieties of hammock forest have been defined by Miller and Morris

-13- (no date) according to dominant tree species : 1) laurel oak hammock; 2) laurel oak-cabbage palm hammock; 3) live oak-cabbage palm hammock; and 4) cabbage palm hammock. These hammock forest communities are found upstream from Rambler's Rest Resort, except for the cabbage palm-dominated hammock which is found more along the bracki sh marsh belt downstream. A fourth principal plant association may be included, that of the pine flatwoods/saw palmetto prairies , portions of which come up to the river bank as form low bluffs. The primary land use since the 1840's has been cattle ranching and farming. A wave of land speculation swept through the lower Myakka area during the 1880's - 1890's but had little effect on the cattle industry. The land remained largely unimproved well into the 20th century (McCarthy and Dame , 1979). Timber, ch i efly pine and probably some oak and red cedar, wa s cut over during and after this time (Wildermuth, 1959; Covington, 1957). The 1950's-1960's witnessed a frenzy of residential developments, mostly centered near El Jobean and Port Charlotte (in Charlotte County), with extensive bulkheading and finger-canal construction hardening the river bank along this stretch. Scattered housing has recently appeared above U.S. 41 and the recent completion of Interstate 75 may encourage development where it crosses over the river (National Park Service, 1984).

Presettlement Conditions

This study phase focuses on one aspect of the environmental history of the river - -its presettlement environment. Although historical investigations have been carried out on the Myakka River (McCarthy and Dame, 1979; National Park Service, 1984) , these primarily have dealt with its cultural history. No studies to date have examined in any detail the natural historical aspects of the river. The main objective is to reconstruct, with the aid of historic documents and records, the environmental setting of the lower Myakka River corridor as it appeared during the presettlement period. By "presettlement" we are referring to the period of time prior to significant occupation along the lower Myakka corridor by American settl ers after the 1870's, and some time after 2000 or 3000 B.C . when the modern environmental regime of southwest Florida was

-14 - ushered in. The reconstruction targets several environmental aspects, chiefly the river corridor's topography, vegetation, and hydrography. Particular emphasis is placed upon relocating the upstream limits of saline influences as reflected in soil/vegetation and water salinity, and tidal forces. The reconstruction was based on records of the original public land survey of the region in the 1840's. These records contain extensive documentation of the presettlement environment. They were recorded on the spot by experienced field surveyors according to a more or less prescribed format and along cadastral (land) lines whose present day locations have been fairly well pinpointed (Cazier, 1976; White, 1983). Although the original surveys were primarily intended to establish legal land boundaries preparatory to a region's settlement, data on a variety of environmental features also were recorded by the surveyors, including types of terrain, soils, vegetation, and hydrography. The survey was implemented under the direction of the General Land Office. In addition to the General Land Office Survey (GLOS) records, five other historic sources proved very useful. These include two maps prepared by surveyor-naturalist Bernard Romans (1774, 1776), John Lee Williams' (1837) classic historical geographical Territory of Florida, J.e. Ives's (18S6) south Florida map, and the travelogue-adventure books by F. Trench Townshend (187S) and Anthony and Julian Dimock (1908) . The last sources actually date to early post-settlement times, but because the Myakka River was still apparently pristine in most respects, these sources were treated as if they reflected true presettlement conditions. Because the investigation moved repeatedly up and down the study area, there was need for a locational grid reference. Actually, two locational systems were used: a river mileage system computed expressly for this report by the author; and the land line grid (township and section lines). A conversion table which ties the two systems is provided in the appendix . [Editor's note: all river mile references have been converted to the system used by Mote Marine Laboratory.)

-15- Results

The Myakka River enters the study area at the north boundary of Section 6 of Township 39S, Range 20E (just below river mile 20.5). Coming into the township from the north, surveyors encountered a narrow, winding river flanked by hammocks of live oak, cabbage palm, red map 1e, and bay trees. The bank-to-bank river width, estimated from the plat map, was about 130 ft, with river hammock adjacent to the east measuring about 265 ft in width. The surrounding upland was pine flatwoods, which surveyors characterized as varying between "prairie or very thinly timbered pine land" east of the river to a "very open pine land ll giving way to land where the "timber is much more abundant" west of it (Figure 2). Th e river gently wound southeastward through Section 6 and intersected 1 i ne 6S about 1,250 ft west of corner 6SE (ri ver mil e 18 .5). It was recorded as being about 130 ft wide. A strip of hammock varying in width between 50 and 550 ft paralleled the river on the east . Where the hammock crossed line 6S it was described as a "scrub hammock [of] saw palmettos and oak [prob ab l y live oak

ll and/or laurel oak] along the Miaca , and measured 528 ft wide. The upland was a mosaic of pine and pine -cabbage palm flatwoods, the latter termed 113rd Pine and [Cabbage] Palmetto Land". The river next intersected line 7E about 1,420 ft south of corner 6SE (river mile l8.0), was some 200 ft wide, and coursed east-southeastward. Pine flatwoods encroached onto the river bank from the north, pinching out the hammock which was present just west and east of the line. The river crossed Section 8's southwest quadrant accompanied by a gradually broadening strip of hammock . Where it crossed line 8S (river mile 16.7) the river was about 130 ft wide. The hammock expanded to over 500 ft wide east to west, and was characterized as an "oak and [cabbage ] palmetto scrub hammock". A short tributary branch flowed westward through the head of the hammock and joined the Myakka at river mile 16 .5.

- 16 - Entering Section 17 the "Miaca Creek" continued to wind southeastward. Just below the branch confluence, the hammock began to constrict and petered out at approximately river mile 15.0 just west of line 17E . The river then brushed against line 17E (at approximately river mile 14.9), briefly swung southwestward and turned southeastward, then crossed line 17E (at roughly river mi l e 14.7) about 660 ft north of corner 17SE. Next, the upriver most pocket of the Myakka River marsh, described simply as a "small marsh", was recorded at and below the lower intersection (river mile 14.7) of the river with line 17E . The marsh was bounded on its east by the river. and on its west by a "small run" that flowed northward a short distance before joining the Myakka River. The plat is mute on whether the marsh was brackish or not. Between river mile 15.0 and 14.7 the river was fl anked by sandy upl ands described as "mostly 3rd rate 1and covered with scrub [saw palmetto?] and scattering [of] [cabbage] palmetto". About midway through Section 21 (at approximately river mile 14.0) "marsh" appeared along the river's east bank and by line 21S had grown to about 430 ft wide east-west. The ri ver also widened somewhat along this stretch, from 165 ft (at line 165) to 230 ft (by line 215) across. At roughly river mile 14.2 another smal l tributary branch, shown to be about 0.7 miles long, flowed northeastward and emptied into the Myakka. The surrounding uplands continued to be "3rd rate" pine-cabbage palm land. Still following southeastward the river left line 215 (at roughly river mile 13 .3) and cut across the NE quadrant of Section 28. It was joined by a narrow tributary stream at about river mile 12.8. The plat shows this tributary originating within Section 29 about 1.3 miles west of the river and flowing eastward . Just below its confluence with the Myakka and just west of 1 ine 28E, a belt of river marsh wedged in along the west bank. Where the river intersected line 28E (at about river mile 12.6) the river had widened to 330 ft and flowed through a 1,400 ft wide belt of marsh . The Myakka River then flowed across the southwest portion of Section 27, its channel widening to around 400 ft and then constricting somewhat before entering Section 34 to the south (at roughly river mile 11.6). The river marsh continued to widen and by line 275 had expanded to a width of about 2,050 ft. Today's Deer Prairie Creek joined the Myakka River at approximately river mile

-17 - 12.1. The plat shows this creek heading inside Section 1, about 4.6 miles north-northeast of its confluence, flowing southwest. The first mention of saline influences was recorded where the Myakka River crossed section line 27S (river mile 11.6). The river, 264 ft bank to bank, was recorded here as "Miaca creek, salt water". The adjoining marsh, however, was not recorded as "salt" {less than a half-mile below it was}. What "salt" meant is uncertain, but it seems likely that, since surveyors failed to use "brack; sh" {a term used then}, they general i zed brackish and sal; ne as

Il sa lt". If so, then they should have been somewhat downstream of the freshwater/brackish water "line" and brackish conditions should have been present upstream. This probab ly also applies to the marsh vegetation. Why they did not call the marsh "salt[y]" may well have to do with the expectable presence of one or more freshwater marsh grass species which can tolerate brackish conditions, such as sawgrass, soft rush, or cattails. Data presented below from the Townshend and Dimocks accounts also point upstream of line 27S for the limit of brackish water. Between line 27S and 34E (river mile 11.6 and 10.9) the Myakka River channel widened only slightly. The marsh belt was shown constricting somewhat , then expanding again before it exited Section 34. Lack of suitably near bearing trees suggests the marsh was essentially devoid of tree cover . A "small salt water creek" is shown joining the Myakka at roughly river mile 11.1. It appears as a short tributary originating less than a mile northeast, crosses line 34E and flows southwest into the river. The first recording of "salt marsh" was made along line 34E (river mile 10.9). Here the salt marsh formed a half-mile wide apron cut along its center by the river, which at this pOint, informs the plat, was somewhere between 265 and 330 ft wide. From a literal reading of the GLOS data it would seem the uprivermost extent of salt marsh laid between river mile 10.9 an 11.6. Its actual extent, however, could have been farther upriver, for reason s suggested earlier. Two short, narrow tributaries originating in the pine flatwoods northeast of the river are shown flowing generally southwestward , disecting the riverine salt marsh and joining the river at river mile 10.5 and 10.2 . Both of these were recorded as small "salt water creeks" . The creek at ri ver mile 10.5

-18- is today's Salt Creek, the other an unnamed tributary. The river corridor between river mile 10.1 and 7.1 at the Sarasota-Charlotte County line was surveyed by Irwin. In addition to running section lines, he also meandered the river. Unfortunately, Irwin did not append any environmental notations to his meander data. At river mile 10.1 the "Myakka River" was very broad: "The River on the west bank runs S680E, has no current other than the tide, water of Salt, it is but an arm of Charlotte Harbort! . This is the upriver-most direct mention of tidal forces in the GlOS records of the lower Myakka. Based on these data, the river had widened dramatically before it crossed line 35S, where it was nearly 3,300 ft across. The marsh adjacent to the east of the channel was about 1,300 ft wide at line 35S, but just above river mile 8.8 it abruptly terminated and pinelands reached to the river's edge . Be low the 1arge "sand bar or island" the ri ver narrowed cons i derab ly and by 1i ne IS-2S (river mile 8.8) was about 1,880 ft broad . 8ig Slough joins the river at river mile 9.5. Although mistakenly left off the plat, the field notes picked Big Slough as it crossed line IN heading southwest toward the river and recorded it as being 66 ft wide. Its confluence was not detected by surveyors for unknown reasons. The river across Section 12 broadened considerably to about 3,630 ft wide while turning from southeast to east. At the bend another large "sand island" and smaller bars or islets dotted the channel, and below the river gradually narrowed to 2,500 ft wide. Records mention no salt marsh and instead show "pine woods" flanking the river . It is plausible that higher water levels associated with wet season surveys had submerged the marsh strip which 6 years earlier had been exposed during a dry season survey. The river's course entering the next township, T40S, R21E turned south-southeast . A "small salt creek" crossed line 13E and flowed east to the river just below river mile 6.5. Just above this point a "bayou" breached the north river bank. The plan shows a rather confused picture of this bayou, which a comparison against modern maps indicates actually confused three drainages --today' s Rock Creek and two unnamed drainages nearby- - to form one large stream.

-Ig- Below river mile 4.5 the river narrowed to around 3,000 ft wide, then turned back toward the east at river mile 3.5. It rebroadened to about 4,300 ft by river mile 2.5 and a mile in width again by river mild 1.5 . Here the river turned south for its final 1.5 mile leg into Charlotte Harbor. Along this stretch the pinelands fronted the river banks, broken only by some salt marsh located along the north bank between roughly river mile 2.1 and well below river mile 1.5, just west of Tippi canoe Bay. Two mangrove trees were pinpointed on the bank fronting this salt marsh at river mile 1.7. This is the most upriver indication of mangroves preserved in the GLOS data on the Myakka. That mangroves were not mentioned in association with the channel islands upstream may suggest only that "timber" sized trees were absent from them . In light of later acco unts , it is possible that so me mangroves were present on these islands but were not recorded in the field notes , especially if they were bushes and not trees.

Discussion

Zones The historic data permit recognition an delineation of three natural zones segmenting the river corridor longitudinally (Figure 3) . The fo 11 owi ng description locates, defines and characterizes each of these zones in terms of their distinctive hydrography , vegetation, and the salinity indicators these two attributes contain. Zone 1 comprises the river corridor between river mile 21.5 and 15.0 (also extending a couple of miles upriver), and may be defined as that stretch of the river where the channel was creek-like in narrowness, highly meandrous in course , was still freshwater but whose water level s oscillated a few feet due to tidal influences downstream, and was flanked by an oak-cabbage palm hammock strip along the east bank, and sandy uplands of flatwoods (of varying mixtures of pine and cabbage palm) and saw palmetto prairies along the west bank .

-20- The vegetation along the river corridor included a narrow strip of oak-cabbage palm hammock along the eas t bank, and flatwoods and prairies along the west bank. The hammock forest was characterized by oak (mostly live oak but presumably including some laurel oak as well) and cabbage palm, with some stands bearing only cabbage palm, others only live oak, and still others a mixture of the two (and possibly laurel oak) . The vegetation along the river's west bank consisted of pine flatwoods, pine-cabbage palm flatwoods, cabbage palm flatwoods, and saw palmetto prairies with occasional pines and cabbage palms. Their mosaic probably aligns in part with the distribution of high acidic (sour) and low acidic (sweet) soil areas. Zone 2 compr ises the river corridor between river mile 15 .0 and 9.0 and may be defined as that stretch of the river where the channel remained narrow but was gradually widening, cons iderably less meandrous in course, the water brackish and subject to direct tidal influence, and flanked by an expanding brackish marsh belt backed by flatwoods and saw palmetto prairies. The vegetation alone Zone 2 reflected the transition from fresh to brackish surface and so il water conditions. Oaks drop out and cabbage pa lm and pine comprise the only trees noted along the river corridor. The cabbage palms were found bank side, as i slands in the marsh, and in the adjoining uplands. Mov ing downstream, the upper end of the zone was marked by the upstream-most outlier of marsh (the same as depicted on modern USGS maps), followed by about a half mile stretch where "3rd rate pine and scrub" lands pinched up against both banks. Then, roughly at river mile 14.0, the marsh belt started, first as a narrow band along the east bank of the river, then flanking both banks by and below river mile 12.7. The brackish marsh belt widened gradually downstream to a peak width of over 3,300 ft (including a 330 ft wide river channel) by river mile 10.1. By river mile 9.0 the brackish marsh belt had ceased expanding. The species composition of the brackish marsh is poorly known from the historic sources, which simply mention there being "marsh grass" (Jones) I or rushes (Townshend) . Only bulrush was specifically noted by the Dimocks. Townshend and the Oi mocks also observed II ta' 1" or Ilbeaut; ful ll ferns along the banks in th i s and probably the next upstream zone, which could be referring to the leather fern, a fresh/brackish water tolerant plant. The marsh grasses could have been

-21- any of one to several species present in today's marsh which are tolerant of both brackish and fresh water conditions, such as smooth cordgrass, sand cordgrass, blank needlerush, soft-stem bulrush, and sawgrass. Zone 3 comprises the river corridor between river mile 9.0 and 0.0 and may be defined as that stretch of the river where the channel widened greatly, the water was brackish, shoaly, and tidally influenced, the channel dotted with numerous bars and islands (some of which supported mangrove bushes and trees) in the upper reach of the zone, and which gave way to a very broad, slightly deeper, mile wide channel relatively free of bars or islands . The marsh belt had been truncated in the upper two river miles of the zone, thereafter forming occasional pockets downstream and the mangrove appeared along the banks in association with the marshes at the lower end of the zone. Red cedar appeared for the first time, occupying low natural levees and channel islands; the river was fed by several small branches and wide mouthed bayou like creeks; and the adjoining uplands supported chiefly pine flatwoods containing few cabbage palms. The brackish marsh at the upper end of the zone was at first quite wide , but was soon reduced to a narrow strip by river mile 7.1 and below that to occasional pockets along the banks. The description by the Oimocks of "mile-wide meadows of partly submerged bulrushes" applies to the upper end of this zone or the lower end of Zone 2. Reid's record of a "narrow strip" of brackish marsh at river mile 7.1 and the lack of their mention by Irwin downstream until river mile 2.2 and below indicate that the marsh belt had abruptly ended and had been replaced by pinelands interrupted by occasional pockets of brackish marsh. The vegetation of this zone appears to have been more diversified than that of the upstream zones, if relative number of species mentioned is any indication. Soft stem bulrush and probably other brackish water tolerant grasses, such as smooth cordgrass, black needlerush, and saltgrass, carpeted the brackish marshes . The Oimocks observed that the marsh, at least where it was stll a broad belt, was "dotted with tall [cabbage] palmettos , singly and in groups". At least some of the channel islands or bars were sand covered and presumably devoid of significant vegetation, according to the GLOS data. Pine flatwoods, apparently with few cabbage palms, touched the river banks below

-22- river mile 6.5, and stretched off into the distance west and east of the river. These were interrupted by occasional brackish marsh areas, at least one of which contained mangrove trees (Irwin's bearing trees) at river mile 1.7. The Ives (and indirectly GLOS) data show that significant belts of mangrove swamp were present just below the study tract, and Townshend did not report riverside mangrove swamps until he reached the vicinity of Hog Island well below the study area. The presence, however, of mangrove on channel islands perhaps as high up as river mile 8.5 suggests there may have been some mangrove grow i ng along the banks or interspersed across the marsh belt opposite these islands. Limits of Tidal Influence The problem of pinpointing the upstream limits of tidal or saline influences is acute for three reasons. First, tidal influences per se penetrate farther upriver than saline influences, and the features recorded in historical documents are affected variably by each factor . Second, none of the lower Myakka historic sources provide species identifications for the various marsh grasses which were present in the study area, and without these (e .g. , specific mention of dominance by cordgrass or black needlerush, both frequent indicators of salt or brackish marshes), identification of saline associated marshes becomes exceedingly difficult. Third, although several of the presettlement observers more or less locate the limits of tidal or saline influences, each observer did so in a non-standardized fashion, so it is highly probably that their individual threshho1ds of sal inity recognition fel l at different pOints al ong the salinity gradient. All that seems certain is that the various observers recognized saltwater somewhere not too far below the fresh/brackish contact . Moreover, since each's observations were made during different years and during different times of the year, normal short and long term fluctuations must be considered. Two of the observers, Jones (GLOS) and Town shend, recorded their observations during the late spring - early summer and winter seasons, respectively. The Oimocks were mute on the season of their excursion. In light of these shortcomings, the only recourse remaining for establishing saline limits was to strike a compromise among all three sources and hope that it approximates the actual limits, and use the presence/absence of cabbage palms and oaks for additional substantiation.

-23- The presettlement position of the freshwater/brackish water transition, which was reconstructed using direct evaluation of salinity by the historical observers (and indirectly through their vegetation descriptions) appears to have been in the same locality as today's transition. Although the GLOS data places it well downstream (roughly between river miles 11.5 and 12.5) from today's , the Dimock and Townshend data points upstream to around river mile 14 .5, perhaps a bit higher. This still falls about 3 river mi les below the present upstream limit of brackish-water conditions as reflected in the distribution of marsh vegetation described el sewhere in this report. This difference does not necessarily indicate a post-settlement upstream shift of brackish-water conditions, for it is likely that the early observers first noted such conditions where these had already become pronounced and not where the first indications appeared upstream, probably in the form of outlier pockets as in today's setting. Therefore, the evidence, uncertain as it is, fails to indicate significant change in the general reach where freshwater and brackish conditions intermingle. Although minor changes in the composition of the vegetation have occurred, there is no evidence of significant modification in its zonation. The general positions of the river hammock and brackish marsh belts appear unchanged, although there are some data to indicate a post-settlement, upstream migration of mangroves from about river mile 7.9 to river mile 12.5. The hammock appears to have expanded in extent since presettlement times. Whereas it originally formed a strip along the east riverbank. presently it flanks both riverbanks and has encroached a bit into the adjoining uplands. This expansion is probably attributable in large part to t he early 20th century practice of suppressing pine woods fires, augmented by an increase in sandy alluvial land soils along the insides of meander loops. Despite the long term impacts of decades of timber removal, cattle grazing, drainage improvements, urbanization, and the invasion of exotics such as Brazilian pepper, the vegetation still approximates its original mosaic.

-24- Conclusion In reviewing the historic evidence, the lower Myakka appears much like it did in presettlement times . The upstream extent of estuarine conditions, as reflected in brackish water conditions and brackish type vegetation, has probably not shifted from its presettlement situation. Both freshwater and brackish water vegetation communities retain in large part their original configuration along the lower river corridor. Aside from recently intense development along the l ower reaches approaching El Jobean, the most visible changes, such as channel meandering, sand bar deposition, and bank erosion, are chiefly the result of the operation of natural processes, although certainly affected to some extent by anthropogenic processes as well.

-25- SHORELINE VEGETATION

Introduction

The goals of this study were to document patterns of plant community dispersion in the lower Myakka River in relation to sal inity; to determine zones of constancy and transition within plant communities; and to assess geomorphic influences on the Myakka River shoreline. Since plant communities are relatively long-lived and stationary, their composition and distribution are reliable indicators of physical and chemical conditions occurring along portions of the river. The data generated from this survey ca n be used to evaluate the physiographical structure of the river and help to determine the role of freshwater in the ecology of the downstream, estuarine component of the Myakka River. The shoreline survey covered the banks of the Myakka River from a point near t he Interstate 75 bridge to the mouth of the river near the southeastern tip of Hog Is 1and. The character of the banks change phytol og i call y and geomorphically along the tidal river. Th ese changes in shoreline character occur in a progression from upriver to downriver . In an earl ier description of shoreline vegetation in the river, Morris and Miller (1974) defined three riverine vegetational associations from the State Park to the Sarasota County line; low-upriver, oak/cabbage palm hammocks, and low-down river associations. An intensive study of the nearby Peace River describes vegetation changes from fresh to saltwater (Environmental Quality Laboratory. 1979) . Ongoing studies by MML of the Weeki Wachee, Crystal, Withlacoochee, and Waccasassa Rivers describe the alignment of biological communities including shoreline vegetation from upriver to downriver areas. A review of these riverine shoreline studies leads to the conclusion that the character of bank vegetation reflects the estuarine setting of the shorelines and can be related to long-term effects of river flow, sal inity, and other t idal influences. Placement of the shoreline survey transects defined the geographical boundaries and established a grid of the work area for the Phase I study. The shoreline survey and bathymetry crews described all transects for subsequent use

-28- by the other tasks. Subsets of the 50 shoreline survey transects were used for bathymetry, bed classification, mollusc survey, submerged aquatic vegetation, and salt marsh tasks. Data from the survey were tallied immediately for occurrences of marsh and mangrove species in order to determine marsh task sampling sites. Preliminary results sent to Barry Wharton to aid his analysis of the historic physiography of the river included: 1) species lists of 16 transects coinciding with section lines; 2) descriptions of all transects; 3) occurrences of marsh species; and 4} occurrences of 26 indicator species for all transects.

Results A list of the plant species indentified on each transect and bank is provided in the Data Appendix (Volume II) . A total of 74 species was identified (Table 2). Twenty-seven species were trees or shrubs; 35 were herbaceous groundcover, and 12 species were vines or epiphytes. Table 3 lists the species in order of number of occurrences . Black needle rush (Juncus roemerianus) was the most common species on the lower Myakka River, occurring at 49 of the 102 transects surveyed . Cabbage palm (Sabal palmetto), found on 39 transects, and Brazilian pepper (Shinus terebinthifolius), found on 33 transects, were the second and third most common species, respectively. These two trees had the greatest dispersion along the length of the river, indicating high tolerances to a wide range of salinities. Wax myrtle (Myrica cerifera) was the fourth most prevalent species (26 occurrences). Zamia floridana (coontie) was found on three transects near the mouth of the Myakka and is a threatened species (Ward, 1979). Distribution and Shoreline Types The distribution of the 20 most common species is shown in Figure 4. No strong pattern of zonation relative to salinity was evident. However, when a different set of species is used, salinity zonation becomes apparent. Figure 6 illustrates the distribution of twelve species found along the river which are known from other studies to indicate conditions of long-term salinity (Carlton, 1975; Eleuterius, 1981; Jackson, 1952; long and lakela, 1978; and Penfound, 1952). The locations of discontinuities between plant communities are best

-29- illustrated by these indicator species . For example, the last downstream occurrence of swamp lily (Crinum americanum) and bulrush (Scirpus validus) are the same {river mile 13}. River mile 11 is approximately the last downstream occurrence of live oak (Quercus virginica), the first upstream occurrence of white mangrove (languncularia racemosa), and the center of the distribution of Juncus roemerianus. River mile 9 marks the first upstream occurrence of black and red mangroves (Avicennia germinans and Rhizophora mangle). At river mile 4.5 the estuarine Juncus marshes end and the presence of nicker bean (Caesalpinia crista) indicates a more marine shoreline vegetation. Eight physiographic shoreline types were found along the tidal Myakka River: freshwater forested shoreline, freshwater marsh, brackish marsh, salt marsh, palm/oak hammock~ mangrove, tropical hammock~ and isolated pine flatwood. Figure 5 illustrates the distribution of these shoreline types on each bank. Freshwater forested shorelines occurred on t he west bank from river mile 21 .0 to 15.6 and on the east bank from river mile 21.0 to 15.0. A canopy of swamp or upland species such as laurel oak, cabbage palms, or willow (Salix---- caroliniana) fringes these shorelines, and contains an understory of species such as water hemlock (Cicuta mexicana), beauty berry (Callicarpa americana) or saw palmetto. A profile of transect 1, east bank, i s characteristic of shorelines found in this fresher portion of the river (Figure 7). Banks along the forested shorelines are quite steep, with shorel ine elevations reaching as high as 10 feet in some instances . Only five transects, all on the east bank between river miles 19 .8 and 16 .9, were occupied predominately by freshwater marsh species. A profile of transect 8 east illustrates this shoreline type (Figure 8). Freshwater marsh shorelines are found in shallow water areas. Often they occur where a small creek joins the river. Characteristic species of freshwater marshes include cattails (~ spp.), sawgrass (C1adium jamaicense) and bulrush. Brackish or mixed marshes were found from river mile 16.6 to 6.7 on the east bank and from river mile 12.7 to 9.4 on the west bank. Brackish marshes were defined by the presence of both salt marsh and freshwater marsh species, the absence of a dominant canopy, and by low elevation. Shorelines of higher elevations in this same region of the river supported palm/oak hammocks, found

-30- from river mile 15 . 1 to 5.6 on the east bank and from river mile 14.8 to 10 .8 on the west bank. Profiles of these shoreline types are shown in Figures 9 and 10 . Palm/oak hammocks were defined by the presence of palms, live oak, or other cano py, as well as the presence of some saltwater indicator species, distinguishing this shoreline type from freshwater forested shoreline. Salt marsh shorelines were distinguished by the dominance of Juncus and the rarity of any brackish marsh species such as leather fern or bulrush. Salt marshes occurred frequentl y from river mile 11.8 to 6.7 on the east bank and on only three transects between river miles 13.4 and 11.8 on the west bank . Further insight into the marshes of the Myakka River can be gained by referring to the salt marsh task, which describes structural aspects of these marshes. A profile of the marsh shoreline is seen in Figure 11 . These salt marshes are usually a monotypic expanse of needle rush (Juncus roemerianus). Needle rush grows unbranched, with the meristematic tissues at the base of the shoot. DenSity, height, and weight of these shoots changes seasonally and varies according to edaphic factors, thereby making them excellent indi cators of environmental stress. Dominance by one or more mangrove species (Avicennia germinans, languncu1aria racemosa, and Rhizophora mangle) was the criterion used to define the mangrove shoreline type. These species , indicating high salinities and low elevations, were found found from river mile 9.4 to Charlotte Harbor (river mile -2.3) on the east bank and from river mile 7.1 to the mouth of the river on the west bank (Figure 12) . Often, mangrove shorelines include a berm with a low swa le behind. The berm may be vegetated by understory species including the halophytes saltwort (Batis maritima), sea lavender (limonium carolinianum) and sat1meadow cordgrass (Spartina patens). Subtropical hammock occurred within the mangrove zone where elevations and sal inities were higher. Hammocks supported a rather interesting plant community including white stopper (Eugenia axil1aris), sea grape (Coccoloba uvifera) and coontie (Zamia floridana) (Figure 13). Subtropical hammock was found intermittently on the east bank from river mile 7.1 to the mouth, and on the west bank from river mile 2.5 to the mouth. Pine uplands were found adjacent to the shoreline on four transects between river miles 15 . 1 and 4.0 (Figure 14).

-3 1- Tributaries Several tributaries to the main river were investigated. The shorelines of Deer Prairie Creek were surveyed at 2 transects (22-23). Palm/oak hammocks bordered the upstream area of the creek and a brackish marsh shoreline was found on the north bank of the creek near the confluence with the river. Brackish marsh was also found just downstream from Deer Prairie Creek amidst salt marsh which suggests that freshwater flows from the creek have influenced the river vegetation. Tran sect 31 crossed another major tributary to the south, Big Slough. Both shores of t he slough were bordered by Juncus marsh and the southern shoreline contained a patch of leather fern. Tippicanoe Bay, fed by Knigh t Creek, was surveyed at three transects (48, 48A, and 48B). The north shore was vegetated by mangroves while the southern shoreline was vegetated by saltmarsh and/or mangroves. Freeze damage to the mangroves was evident in Tippicanoe Bay; live mangrove height did not exceed one meter. Juncus marsh appears to be replacing mangroves in the areas of worst freeze damage. Community Analysis Transect data were analyzed for similarity by two methods. In one case, 100 transects from both banks were grouped into 20 units. In the other case, 50 transects from the east bank only were grouped into 10 units . For example, transects IW through 3W and transects 3E through 5E were used as two units with 5 replicates each in the first analysis, or one unit with 5 replicates in the second analysis. Samples were analyzed using Czekanowski's (Bray-Curtis) Indices of Similarity and dendrograms were produced using group-average sorting (Figures 15 and 16). Values of similarity between zones were low. For the first analysis the highest similarity (71%) occurred between units 6 and 7. Units were grouped loosely into three major community types oriented as a linear model: (1) an estuarine/marine community -- encompassing transects from river mile -2 .3 to 6.0. (2) a riverine commmunity -- encompassing transects from river mile 13 .0 to 21.0, and (3) a transitional community -- encompassing transects from river mile 6.0 to 13.0.

-32- Physiographically, this transitional zone includes the braided channel portion of the river from an area just upstream of Deer Prairie Creek to the beginning of Myakka Bay. Exceptions to the linear model produced from all 100 transects occurred in three instances. The first irregularity occurred between units 11 -14 in the transitional zone. These units were 67% more similar to one other although they were not simi lar adjacent units . The second deviation wa s the 58% similarity between units 15 and 18 in Myakka Bay, separated by four miles of river. The third exception was the grouping of units 9 and 10. These units span the mouth of Deer Prairie Creek and had a 62% similarity, meaning that they resembled upstream riverine transects. In other words, plant community structure immediately downstream of Deer Prairie Creek was more similar to commu nities more than a mil e upstream than to those areas adjacent to the Creek, implying that freshwater from Deer Prairie Creek has an effect on marsh vegetation along the main river. The second community analysis was ba sed on east bank transects and produced a different similarity pattern (Figure 16). Values were lower than obtained by the first analysis, with the highe st index of similarity at 67% . The most dissimilar units were farthest apart. Every unit was most similar to an adjacent one, indicating a serial relationship from upstream to downstream. The grouping of units 3 - 5 and the high similarity of units 6 and 7 indicates a major break in community structure between units 6 and 5, near Warm Mineral Springs.

Discussion Limits of Transect Methods The transect survey method is a fairly intensive effort to describe the distribution of shoreline plant species at a large number (102) of sites. Because the survey sites are disjoint, the first and last occurrence of a spec ies ;s only as precise as the distance between transects (ca. +0.4 miles). While transects were intentionally established at sites where important plant

-33- assemblages were present, indicator species undoubtedly occurred outside some transects, as may have occurred in the case of red maple . Adverse survey conditions were experienced during Hurricane Elena, which caused water levels at least two feet higher than usual. The presence of dead bulrush farther downstream could not be established until water level subsided, and other occurrences may have been missed for the same reason. Finally, the number of species which are present or conspicuous within a two week period is limited according to the seasonality and phenology of each species. Annual species, which respond more directl y than perennials to env i ronmenta l factors, may not have been present during the survey. Species Diversity in Comparison to Other Rivers The number of species identified during this shoreline survey of the Myakka River was less than the number of species identified for the Peace River in a study conducted in 1979 by Environmental Quality Laboratory (EQL); 72 species were identified for the Myakka River compared to 95 for the Peace River. Sampling methods were not the same for both studies, however. In addition, the community structure of the Peace River vegetation appears to be significantly different from that found on the Myakka River. For example, two species indicative of freshwater swamps --bald cypress (Taxodium distichum) and red maple (Acer rubrum)-- were present on the Peace River but not along the Myakka River . Species diversity was much higher on the Myakka River than on the Weeki Wachee. Crystal and Withlacoochee Rivers (Table 4). Results are more comparable, since survey techniques were identical in these studies. High species diversity along the Myakka River is attributable to the presence of both forested freshwater shorelines upstream and subtropical hammocks (absent in other rivers) adjacent to the shoreline near the mouth. Physiography of the River The general structure of Florida Gulf coastal riverine systems, including the Myakka River, ;s that upstream shorelines are close together and have steep banks -- a result of geomorphic controls and a relatively narrow floodplain

-34- and that downstream shorelines are spread farther apart with shallow banks formed by the slope of the intertidal salt marsh floor . Salinity dictates the types of plant associations present on shorelines affected by tide. Marshe s bordering freshwater portions of the river are usually comprised of sawgrass (Cladium jamaicense) or cattails (!YQh! spp.), while those bordering saltwater consist of black needle rush (Juncus roemerianus) and cordgrass (Spartina alterniflora). This gradient is modified by elevational and geological variations of the shoreline, resulting in different plant communities. Highly elevated banks in both fresh and saltwater portions of the Myakka River are adjacent to the upland pine f l atwoods community; limestone outcrops in freshwater areas may be vegetated by Laurel oak (Quercus laurifolia) and saw palmetto (Serenoa repens) while those located in areas of higher elevation within the salt marsh support Cabbage Palm (Sabal palmetto) and Spanish Bayonet (Yucca aloifol ia). In those areas where tributaries flow into the river, marsh species occur. For example, at the confluence of Curry Creek and Myakka River (Transect 3) a cattail marsh was found. Only one occurrence of sawgrass (Cladium jamaicense) was found on the river, which is unusual compared to the other river systems mentioned above . There was no extensive sawgrass marsh, although it was seen along the river. This situation, coupled with the scarcity of freshwater marsh, suggests one of the following conditions: I) The geomorphic character of the Myakka River is unlike that of other Gulf coastal riverine systems reviewed; freshwater marsh does not occur because shoreline elevations are prohibitively high; or 2) Saltwater influences the upper reaches of the study area to a greater degree than in the other rivers. Salinity Tolerances of Shoreline Plant Species Table 5 presents a classification of some species found in the Myakka River which can be used as indicators of salinity. Transitional species include some which also may reflect salt or freshwater conditions. For example, bulrush (Scirpus validus) thrives in freshwater but can tolerate low salinities. Juncus

-35- roemerianus, the dominant salt marsh species, can in turn tolerate brackish conditions . More specific salinity tolerances for each species can be determined as more syno ptic and long term salinity data are collected. The upper curve shown in Figure 17 represents dry season salinity from the mouth of the With1acoochee River to a point located near river mile 6. The lower line represents salinity in the river during the wet season. It i s evident that the dry season salinity curve reflects a pattern of plant species replacement. Limits of plant distribution and salinity also are correlated in the Weeki Wachee River {Figure IS}. It is reasonable to expect that plant distributions and salinity are correlated in the Myakka River, too, but the nature of the relationship will be spec ific to that system. A finer mapping of plant communities and more salinity data for a longer period of time will be needed to evaluate the form of this relationship. o c• •c .. E •~

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- Table 2. Taxonomic list of shoreline species from the Myakka River.

Osmundaceae Osmunda regalis var. spectabilis pteridaceae Acrostichum danaeaefolium Pteridium aquilinum polypodiaceae Phlebodium aureum Polypodium polypodioides var. michauxiana Vittariaceae Vittaria lineata Cycadaceae Zami a f1 or; dana Pi naceae Pinus elliottii Cypressaceae Juniperus silicicola Typhaceae ~sp. Poaceae Andropogon glomeratus Andropogon perangustatus Chloris glauca D;stichlis spicata Spartina alterniflora Spartina bakeri Spart i na patens Stenataphrum secundum Cyperaceae Cladium jamaicense Fimbristylis castanea Scirpus validus Arecacea Saba 1 palmetto Serenoa repens Bromel iaceae Tillandsia sp. Tillandsia unseoides Juncaceae Juncus roemerianus Smilaceae Smilax sp. Agavaceae Yucca aloifolia Amaryllydaceae Crinum americanum Orchidaceae Table 2. Continued.

Encyclia tampensis Sal icaceae Salix caroliniana Myricaceae Myrica cerifera Bataceae Batis maritima Fagaceae Quercus laurifolia Quercus virginiana var. v;rg;n;ana Polygonaceae Coccoloba uvifera Rumex vertiallatus Aizoaceae Sesuvium portulacastrum Fabaceae Caesalpinia crista Errthrina herbacea Ga actia macreei Schrankia microphylla Anacardaceae Schinus terebinthifolius Toxicodendron radicans subsp. radicans Aquifo1iaceae Ilex sp. v; taceae Ampelopsis arborea Parthenocissus guinquefolia Vitis sp . Hypericaceae Hypericum hypericoides var. hypericoides Cactaceae Opuntia sp. Lythraceae Lythrum lineare Rhizophoraceae Rhizophora mangle Combretaceae Conocarpus erectus Languncularia racemosa Myrtaceae Eugenia axillaris Apiaceae J Cicuta mexicana Pl umbag i naceae Limonium carolinianum 01eaceae Fraxinus caroliniana Convolvulaceae Ipomea sagittata Table 2. Continued.

Verbenaceae Callicarpa americana Avicenniaceae Avicennia germinans Solanaceae lycium carolinianum Goodeniaceae Seaevola plumieri Asteraceae angustior

, Table 4. Species Diversity Along Several Riverine and Estuarine Shorelines .

River County No. of Species Myakka Sarasota, Charlotte 72 Weeki Wachee 52

Crystal 37 Withlacoochee 50 Waccasassa

Table 5. Saltwater Indicators Transitional Species Freshwater Indicators Avicennia germinans Acrostichum danaeifolium Ampelopsi s arborea Baccharis halimifolia Cladium jamaicense Baccharis glomerulifl ora Batis maritima Juncus roemerianus Callicarpa americana sorrTchia frutescens lythrum lineare Cicuta mexicana Caesalpinia crista Quercus v;rg;niana Cladium jamaicense Coccoloba uvifera Scirpus validus Crinum americanum Distichlis spicata Galactia macreii Eugenia axillaris Hy~eriCUm hypericoides Iva frutescens Me anthera nivea JUncus roemerianus Phlebodium aureum Languncularia racemosa Pinu s elliott; Limonium carolinianum Pteridium aquilinum Lycium carolinianum Quercus laurifolia Pluchea purpurascens Quercus virginiara Rhizophora mangle Salix caroliniana Sesuvium portulacastrum ~us validus Solidago sempervirens Soli ago fi stula Spartina alterniflora Spart; na baker; Spartina patens Yucca aloifolia Zamia floridana rrythrina herbacea MARSH STRUCTURE

Introduction

Physical features of a marsh reflect the physiological condition of individual plants and the vigor of the system (Oviatt et al., 1977) . Although direct measurements of primary production and energy flow are preferred as indicators of marsh condition, comparisons of shoot density, height, and vitality also can be used, especially for rapid economical surveys . The purpose of this study element was to identify structural characteristics of marshes along the tidal reach of the Myakka River as a means of evaluating the shores ide effects of salinity regimes . Originally emphasis was intended on sawgrass (Cladium jamaicense), cattails (Typha spp.), black needlerush (Juncus roemerianus) and saltmarsh cordgrass (Spartina alterniflora). Structural features in marshes dominated by these species were to be described across the length of their range . Because the shoreline survey documented a scarcity of ~, Cladium, and Spartina marshes in the river, measurements were instead made on the leather fern (Acrostichum aureum), and mangroves, mostly the red mangrove (Rhizophora mang le). Stations were selected from the suite of shoreline transects and additional observations (Figure 19). Standard areas of marsh were clipped and returned to the laboratory for analysis, but fern measurements were made ---in situ to prevent their destruction. Mangrove measurements also were made in the field due to the impracticality of samp li ng. Additional methods are given in the appendix.

Results

Leather Fern Leather ferns of Florida are represented by two species, Acrostichum .-' aureum and A. danaeifolium, in brackish and fresh water, respectively (Lakela and Long, 1976) . Acrostichum danaeifolium occurs in the tidal portion of the Myakka River from Snook Haven to Big Slough, as isolated plants, clumps in

-53- Juncus marshes, and islets. The ferns are most common in Juncus marsh and typically are found growi ng along and behind natural berms adjacent to the shoreline. Mean lengths of fronds from upriver sites were greater than at downriver sites (Figure 20). There were no signs of dead leather fern anywhere along the river, even downstream of Big Slough. The fern's absence in the expansive Juncus marshes from Tarpon Point to the county line does not, therefore, seem due to recent drought related stress, but instead reflects the effect of longer term mechanisms.

Bulrush The soft-stem bulrush (Scirpus validus) is distributed widely along the lower Myakka River. The shoreline survey observed bulrush on transects between river miles 12 and 18. A second survey for bulrush was made after floodwaters had receded, and revealed that live bulrush occurred as far downstream as Tarpon Point. Patches of dead bulrush were found below Tarpon Point to the county 1 ine. Shoot density and height decreased in a downstream direction. The density of line shoots decreased by the density of dead shoot s was constant and low (Figure 21) . The height of live shoots did not vary in relation to river location but the mean height of dead shoots upstream of Deer Prairie Creek was twice that of shoots below the creek. Bulrushes downstream of Tarpon Point were seriously damaged by high salinities resulting from the drought. Above-ground tissue was short, usually dead, and decomposing. Bulrush in the river at the mouth of Deer Prairie Creek bore flowers and maturing seeds, which were seen elsewhere only in Big Slough .

Black Needle Rush Juncus roemerianus has the most extensive range in the Myakka River of any shoreline marsh or mangrove spec ies. It occurs as broad belts between the river and uplands, and as wide islands in mid-river. Large marshes are dissected by tidal creeks and may have low berms vegetated by fern or mangroves. Needle rush grows at the mouths of all streams entering the river between

-54- Rambler's Rest and El Jobean except for Big Slough, which is a dredged waterway. The density of Juncus shoots varied as a complex function along the river {Figure 22}. Total shoot density increased from Snook Haven to the vicinity of Deer Prairie Creek, decreased along the river to Big Slough and remained relatively low to Myakka Bay, then rose again at downstream-most stations. Dead shoots determined the total shoot pattern (Figure 22), which indicates the effect of earlier growth and decay in each area. The density of dead shoots (and consequently total shoots) varied inversely with the height of dead shoots (Figure 23). Density decreased from Deer Prairie Creek to Big Slough but dead shoot height increased. From Big Slough to Myakka Bay densities were relatively low but heights were relatively high. Downstream of Myakka Bay densities increased but heights decreased. Live shoot heights varied greatly but were much lower near El Jobean than elsewhere in the river.

Mangroves Woody halophytes of the Myakka River and estuary include the red mangrove {Rhizophora mangle}, black mangrove {Avicennia germinans}, white mangrove (Laguncularia racemosa) and buttonwood (Conocarpus erectus). Red and black mangroves have the widest distribution, occurring from Charlotte Harbor to just upstream from Deer Prairie Creek. Black mangroves are the largest of Myakka River mangroves, especially downstream from El Jobean. White mangroves are very common, especially near Myakka Bay. Freeze effects were very noticeable. Mangroves on the east shore downstream from El Jobean near Ghost Point have been damaged severely, presumably by freeze stress, resulting in extensive intertidal areas of dead trees. Regrowth from black mangrove stumps has begun and some recruitment by propagules was evident. Characteristics of red mangroves were used to assess upriver variation. Relatively tall canopy (10 ft) occurred near the mouth of the river (except for dead trees at Ghost Point) and near Big Slough, but the majority of canopy heights were between 6-10 ft (Figure 24). The height of red mangrove canopy decreased rapidly upstream of Deer Prairie Creek.

-55- Stranded propagules were found as far upriver as marker 3 {river mile 10 .6}, whereas rooted propagules (seedlings) occurred farther upstream, to marker 5 (river mile 11.8) (Figure 25). Saplings (plants taller than seedlings but lacking a trunk at breast height) were found still farther upstream at Transect 20 above Deer Prairie Creek (Figure 26). Trees (trunk dbh 1.0 cm) occurred as far upstream as rooted propagules. Overall, saplings were the most common size class along the river, but rooted seedlings were relatively more abundant downstream than upstream. Combined densities for all size classes produced a bimodal distribution (Figure 27) with peaks at the river mouth and near Big Slough, and lower densities along the shores of Myakka Bay. Flowers, fruit, and propagu1es occurred in trace amounts along the river but were more abundant in the lower reach at Transect 40, at the mouth of a creek flowing to Myakka Bay, and also were more abundant upriver from Big Slough to Deer Prairie Creek. Trees between Deer Prairie Creek and the U.S . 41 bridge were heavy in flower (more than 50 per tree). The estuarine, wood -boring isopod Sphaeroma terebrans, occurred in red mangrove prop roots across a broad reach of the lower river . Animals were observed from Transect 46 upstream to Transect 21. and bored roots were observed between Transects 48-20. Bored roots were most abundant (relative to total root number) between Salt Creek and Big Slough (Figure 28) . Sphaeroma also were found inhabiting live Juncus shoots near Big Slough, the first record of such an occurrence. The distribution of other salt marsh fauna;s discussed in the section on benthic macroinvertebrates.

Discussion

The dispersion, abundance and condition of marshes and mangroves along the tidal Myakka River are useful indicators of medium to long-range salinity influence, as well as other abiotic stress (freezes) or biotic stress (wood -borers).

-56- Freshwater marsh occurred over a small range, often in mixtures with brackish species, and was not sampled. Better mapping of freshwater marshes will be needed to understand their location relative to salinity. Leather fern frond length decreased over its range as ambient salinity increased, which is consistent with known effects of water stress. Drought-related impacts to bulrush probably were severe, since few dead shoots were still present. In all likelihood, bulrushes were killed earlier in the year and dead shoots had decomposed by September. The density of live shoots decreased at sites farther downstream, also in response to salt-stress. Juncus abundance, on the other hand, was controlled by the density of dead shoots. Dead shoot densities can be explained by two equally possible models. On the one hand, dead shoot density can be relatively high where new growth is low . On the other hand, high dead shoot density can be caused by suppressed rates of decomposition. Both explanations may be involved but too few data are available at this time to know . Mangroves represented a departure from trends seen in marsh species by being relatively more constant throughout their range and by ending abruptly. The fine structure of their upriver limit deserves extra description because small differences in the location of floating and rooted propagules, seedlings, and saplings, may reveal the role of currents in determining their distribution . The distribution of Sphaeroma along lower river shorelines implicates Big Slough as a source of freshwater and the middle river as an area of high particulate turbidity (Estevez, 1978). Sphaeroma may be very useful as an indicator of salinity-mediated stress to mangroves, and possibly Juncus, too. The occurrence of Sphaeroma in Juncus at the mouth of Big Slough must reflect an enormously large population of wood-borers. Certain places along the river were noteworthy as transitions or endpoints in marsh or mangrove distribution or condition. Deer Prairie Creek and Big Slough were most important in this regard. Deer Prairie Creek discharges were manifest in live bulrush density (lowest values); Juncus density (highest values); Juncus reproduction (only occurrence); mangrove canopy height (lowest values for live canopy); and mangrove reproduction (highest values). Effects of the creek may be mediated throu9h changes in high tide salinity

-57-

I (upstream); low tide salinity (downstream); altered current structure during low flows; instream nutrient availability; and micrometeorology.

Conclusion Patterns and trends in marsh structure were determined using rapid survey techniques that could be improved by the use of more replicates, and perhaps sampling on one shore only. Bulrush and needlerush conditions varied as a function of river position. The effect of earlier hydrologic and salinity conditions could not be evaluated, although bulrush was affected most . Reproduction, recruitment, and biotic stress (e.g. wood-borers) deserve continual monitoring relative to salinity. Overall, the range of marsh and mangrove condition indices demonstrated the structuring influences of salinity and the potential for adverse impacts to shoreline vegetation caused by chronic changes in salinity regimes. Salt marshes and mangrove forests deteriorate under constantly elevated salinity (Snedaker and DeSylva, 1977). Of equal relevance to the issue of salinity impacts is the observation that mangroves decline when just dry season discharges are reduced (Saenger et al., 1983). Marsh and mangrove productivity in the Myakka River probably depends on the total amount of freshwater entering the system, as much as the wet season peak. If true, it will be necessary to protect dry season discharges from significant reduction.

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Sl.OOHS Sn:lNnr .1MDI3H N'f'3W PHYSICAL FACTORS

Introduction

Physical data from the Myakka River include stages and discharges at Myakka City, the river near Sarasota (State Park), and the river near Venice (Blackburn Bridge). Other physical and chemical data are available at U.S. 41 and S.R . 771 from agencies and Mote Marine Laboratory . Part one of this section reviews selected U.S. Geological Survey data for discharge to describe the long term characteristics of the river, and USGS and SWFWMD data to describe the drought of 1984-85. Stage data then are used to illustrate the hydrologic setti ng of the RMR Phase I investigation. Part two of this section reviews historical salinity data for the river and introduces new data produced in Phase I. Important historical data include 1972-1975 data at U.S. 41 and S. R. 771 (MML); 1979 - 1985 salinity data near El Jobean (FDNR); and 1984-1985 data along the tidal river (USGS). New data presented in part two include 3 high tide and 2 low tide profiles of surface and bottom salinity from Charlotte Harbor to the Interstate 75 bridge crossing. Part three of this section summarizes Phase I results of dissolved oxygen, temperature, pH and other chemica l sampling in the river. Emphasis is placed on surface to bottom differences in dissolved oxygen in relation to discharge. This section ends with a discussion of the hydrological and hydrographic information, and implications for river management and subsequent studies.

Discharges to the Estuary

The actual amount of freshwater entering the tidal portion of the Myakka River is unknown. Unmeasured sources include the river watershed below the most downstream gage sites {Myakka River State Park and Blackburn Bridge}; the lower end of Big Slough; coastal watersheds; the Peace River (via brackish tidal waters from Charlotte Harbor); and groundwater.

-67- On balance, there is a long term record of discharges at the state park, which reflects about 42 percent of the entire watershed. Statistics on normal monthly means (all days) are given in Tabl e 6. About 79 percent of river discharge occurs from June to October, inclusive. Another 12 .7 percent occurs during January-March, the winter "~t season". Two dry periods occur in a typical year, in April-May and November-December. Monthly Variation Coefficients of variation in Table 6 range from 0.8 to 1.7. August-November has the lowest variation, but even these values are at least 0.8, meaning that monthly values are widely distributed. Figure 29 illustrates the departure from mean monthly flows, of the means based on the flows from 10 wettest and driest months . Wet conditions depart from the mean more than dry conditions do, but both covary in a similar pattern and share the greatest similarity to mean flows in May and November, two months with the lowest standard deviations over the period of record (Table 6) . Seasonal Variation Discharge and rainfall covary at Myakka River State Park as shown in Figure 30. Discharge increases during periods of increasing or steady, high rainfall but decreases rapidly when rainfall lessens. Variations in rainfall, runoff, and discharge result in some periods with higher variability than others (Table 7). The summer wet season has the lowest coefficient of variation and the spring dry season has the highest. The range of summer wet season variation is much greater than other seasons, but relative to their respective means, the summer wet season has the narrowest range (x 2.4) and the spring dry season has the widest range (x 6.2) of the four periods. This apparent contradiction is caused by the number of zero flow periods in the spring dry season. The frequency distributions of discharge during each of the seasons are shown in Figure 31, which illustrates the relationship of mean dischar&es to actual discharges. Discharges during the summer wet season are more evenly distributed across the range of discharges than in other periods. Discharges in other periods are dominated by low-end values, meaning that very wet conditions are relatively rare during these periods .

-68- Wet Season Characteristics Most of the wet season discharge (57 percent) occurs in August and September (Figure 32). July and October contribute approximately equal discharges. August and September discharges are correlated best among wet season months (Table 8), although June-July, and July-August are also loosely correlated. Dry Season Characteristics According to unpublished USGS discharge analyses, there are about 30 days each year during which discharges in the Myakka River are zero. The published low flow frequency for the river through 1984 (Table 9) shows that trace discharges (less than 0.05 cfs) occur for at least 30 consecutive days with a 2 year recurrence frequency. Four consecutive months of zero flow may be expected to occur every 20 years, on the average (Hughes, 1981). May is the driest month of the year in the Myakka River. More days have no discharge in May than any other month and May has more continuous periods of no flow than any other month (Figure 33). It is interesting to note that 23 percent of all zero discharge months occur in June but no zero discharge months occurred in July (until 1985) . The effect of dry periods is evident in the flow duration curve for the river (Figure 34). It is a cumulative frequency curve giving the percentage of time (in the period of record) that specified daily discharges were equalled or exceeded. A discharge of 5000 cfs is rarely exceeded, whereas a 500 cfs discharge is exceeded about 15 percent of the time . A 20 cfs discharge is exceeded 65 percent of the time, meaning that Myakka River discharge is below 20 cfs about one-third of the time . The 1984-1985 Drought The period between spring of 1984 and fall of 1985 was exceptionally dry. River levels at the state park (an area not affected by tides) fell continuously after August 1984, and monthly variation in stage was much reduced (Figure 35). Data from SWFWMO illustrate the departure of wet season months in 1984 and 1985 (Table 10). June and July 1985 were months of zero flow. August 1985 had much higher discharge than in 1984, but the flow was only 53 percent of the mean for the period of record. Based on provisional USGS data, September 1985 had a

-69- discharge equal to 118 percent of the mean for the period of record , making it an "average" year. Hydrologic Setting of the RMR Phase I Study All Phase I sampling and measurement was conducted during a period of flow affected by Hurricane Elena, which occurred during the Labor Day weekend of 1985. River stage and discharge were not remarkably high in September, but the rapid pulse of runoff associated with the storm may have been atypical (Figure 36). River banks were flooded at least to the Charlotte County line and current velocity was high in the river upstream of U.S . 41. Figure 37 illustrates the flow-duration curve for all September daily discharges . Mean flow for the peri od of record (700 cfs) is equalled or exceeded 40 percent of the time, placing the mean close to, but above, median flows . The September 1985 mean flow was 656 cfs, which is equalled or exceeded 45 percent of the time. September 1985 was the 15th wettest September in the past 50 years.

Sal inity

Three types of salinity data are available for the Myakka River: values from single samplings at specific places; time-series, usually monthly, at one or a few stationsj and measurements made over a large number of stations for well-defined tidal and flow conditions . Early Studies A survey by Woodburn (1960) may represent the first salinity measurement made in the tidal river for ecological purposes. A surface salinity of less than 1.0 part per thousand (0/00) was recorded at the El Jobean bridge in September 1960, a very wet month (mean monthly flow - 2247 cfs, exceeded only once in the period of record). The first time-series of salinity was reported by Dragovich et al. (196B) for monthly readings in 1965, a relatively dry year. Figure 38 illustrates hydrographic properties of the river at a station probably located near the Sarasota-Charlotte County line (river mile seven). Salinity varied from zero to about 15.0 0/00, with freshwater conditions in the lower river during the winter

-70- wet season, August, and September. It is noteworthy that surface to bottom variation in salinity was low. Alberts et al. (1970) produced the first composite salinity structure for Charlotte Harbor, including the lower Myakka River . They described a general surface variation in salinity of 5-15 0/00 in the river south of El Jobean, and were first to note that "the discharge of the Peace River is well defined by the tongue of low salinity water which (crosses the harbor and) follows the east and north sides of the estuary," placing Peace River discharges near the mouth of the Myakka River. From May 1972 until May 1975 surface salinity at El Jobean was recorded weekly over a variety of tidal conditi ons by Mote Marine Laboratory. Salinity ranged from 0.5-32.8 0/00 (Figure 39) during a relatively dry period. Data for 1973 illustrate a winter wet season period of lowered salinity; a spring dry season in which salinity rose and remained above 20.0 0/00 until the end of June; a summer wet season with salinities below 5.0 0/00; and a drying period in fal l . The 1974 summer was a period of rapid salinity change due to the occurrence of a tropical storm during a very dry spring. Measurements were taken at U.S. 41 for a shorter, coincident period (May 1972 - May 1973). The river below El Jobean was sampled on a less intensive basiS, beginning in 1976. Texas Instruments (1978) occupied one station near Cattle Dock Point for 10 months in 1976. Environmental Quality Laboratory (1979) made monthly salinity measurements at El Jobean from 1976-1978 and found that salinities were comparable to those at the mouth of the Peace River. Beginning in 1979 the Florida Department of Natural Resources has made monthly salinity measurements in the vicinity of El Jobean as part of their shellfish sanitation program. Results of their studies are presented in the section of this report concerning oyster ecology. Recent Studies The U.S. Geological Survey has made several sampling trips along the length of the tidal river in 1984 and 1985 as part of the USGS/Florida agency environmental study of Charlotte Harbor . Their results are presented in Figure 40 for one high tide and two low tides. Surface to bottom differences were unimportant in all 3 surveys. Saltwater penetration was extreme during the

-71- final period of the 1984-1985 drought (July 1985) when a 5 day mean stage of 0.90 ft was recorded at the state park. Salinity was approximately 15 0/00 at the Interstate 75 bridge crossing and 28 0/00 in Charlotte Harbor at the river mouth. The penetration of saltwater wa s less during period s of higher river stages and low tide. At a stage of 3.94 ft a low tide salinity of 1.0 0/00 was measured at U.S. 41, and at a 5.82 ft stage the 1.0 0/00 isohale occurred near the county line. Harbor salinities corresponding to these conditions were 17.5-21.0 0/00 and 10 .5-11 .5 0/00, respectively. Phase I Salinity Results Salinity profiles of the tidal Myakka River were made on 3 surveys in Phase One of the downstream study. The first run, slightly after a high tide on August 27, 1985. preceded Hurricane Elena and resembles the USGS low tide profile of August 28, 1984 except that salinity in Myakka Bay was lower in 1984 (Figure 41). The difference may have been due to increased flow (stage = 6.26 ft in August 1985 compared to 5.82 ft in August 1984) and tidal action. The river was not vertically stratified prior to the hurricane but became highly stratified by September 10, 1985 (Figure 42), when the 5 day antecedent mean stage was 7 . 83 ft. Surface to bottom salinity differences ranged from 15.0 0/00 at the river mouth to 1.0 0/00 at the head of Myakka Bay. The 1.0 0/00 isohales at the surface and bottom converged near river mile 7 at high tide but the same salinity was located near river mile 4 (bottom) and 2 (surface) during low tide. Stratification probably continued through the month until the third survey on September 24, 1985, by which time average river stage had declined to 5.87 ft. Less flow was reflected in a lower degree of surface to bottom sali nity difference, not more than 10.00/00 (Figure 43). The upriver extent of saltwater was greater under lower flows. The 1.0 0/00 isohale moved upriver by about 2 miles even though predicted tidal heights (2.0 ft mlw) were the same on the dates of both surveys. The Relationship of Di scharge and Salinity

-72- Stage and discharge are related to salinity in ways specific to particular estuaries. Determination of the relationship requires data on each factor and also on tides, winds, and the physical structure of the system. The data must cover a range of values for each variable to make predictive model s accurate. Historical data for the Myakka River are too few for definite relationships to be determined. Recent and ongoing monitoring of discharge and conductivity will be helpful in this effort, but until such analyses have been made we must rely on sketchy historical data for some insight to the physical organization of the estuary. The point in the river at which a particular bottom salinity occurs, 10.0 0/00, for example, bears a strong relation to both tide and discharge. The actual location of the 10.0 0/00 isohale is known for only a few high or low tides (Figure 44), but the data suggest a sensible relationship. Figure 44 compares 5 day antecedent mean stage at the park to river miles at which the 10.0 0/00 isoha1e was found at the bottom, for high and low tides . Saltwater moves farther upriver at low stage (low discharge), and on high tides, than at high stage or low tide . Tidal effects are of course complicated by the continuum of possible low and high tide heights. The red tide data at El Jobean in 1973 were used to evaluate mean monthly surface salinity in relation to normal monthly mean discharge (Figure 45). A log-log plot was used to collapse the range of values. The curve suggests that surface salinity drops at an increasing rate in response to increasing discharge, to a rate of about 300 cfs, and that beyond that rate, surface salinity drops even more rapidly. It is interesting to ask whether the river changes to a stratified system at or above 300-500 cfs discharges. Records on time or tide for 1973 salinity data are unavailable, so tidal differences certainly must mask relationships between discharge and salinity . Moreover, discharges are plotted as monthly meanSj shorter periods of antecedent discharge also would improve the correlation. Reasonable correlation coefficients were obtained when 1973 data were tested using linear, logarithmic, and quadratic models. The best fit (R2 • 0.778, significance level = 0.005) was obtained by the equation:

-73- (A) Surface Salinity at El Jobean' 24 .49954 (6.35412 x IO-2)(discharge) + (7.74978 x IO-5)(discharge2) (3.32548 x IO-8)(discharge3) where discharge was based on normal monthly means at the state park and expressed as cfs.

The regression does not consider tidal effects or wind, but gi ven limitations of the analysis, predicted salinities compare favorab ly to observed salinities at El Jobean (Figure 46), although predicted values exceeded observed ones in both wet and dry seasons . Figure 47 is an application of equation (A) to normal monthly mean discharges at the state park for the period of record (1936-1984). In general, highest predicted surface salinity occurs in May and lowest salini ty occurs in September . The influence of rainfall and runoff in each season appears to be reflected in salinity patterns at the river's mouth.

Other Factors

Information on such parameters as dissolved oxygen, temperature, or light in the tidal Myakka River is not extensive, particularly if long-term or river-wide data bases are considered. The best time series are for temperature, pH and nutrients, and come from the red tide studies in 1972 - 1975. Oata on dissolved oxygen along the length of the river are available from some of the USGS. surveys and the Phase One Study. Temperature Surface water temperature at El Jobean in 1973 is depicted in Figure 48, juxtaposed against salinity data. The winter wet season (January-March) was a period of low temperature as well as low salinity. The spring dry season (April, May) was a period when both parameters had intermediate, increasing values. The summer wet season (June-October) was a time when water temperatures were highest and salinities lowest . The fall dry season (November, December) was a time when temperature va1ues were decreasing and salinity values were increasing.

-74- The seasonal covariance of temperature and salinity is a stable relationship, especially where water temperature is concerned . The 1973 temperature data closely resembled temperature data for other years. Moreover, there was very little difference in surface water temperatures at E1 Jobean and U.S. 41. For 30 paired observations between April-December 1972 (range 12.S-32.00 C), the usual difference between U.S . 41 and E1 Jobean was only about I.SoC. Regularity of temperature variation in the Myakka River estuary is significant. Seasonal changes occur independently of discharge (salinity), and are therefore predictable environmental cues for ecological events in the estuary. Temperature controls other ecologically critical parameters, especially dissolved oxygen in shallow water. However, little temperature variation along the river or from surface to bottom was seen during Phase I because most measurements were made in September, a relatively stable month. In fact, the total range of surface water temperature was only 4.790 C, from 26.1-30 .90C. Vertical variation of temperature was minimal, on the order of O.I -O.SoC, except at Charlotte Harbor stations were vertical temperature differences of 1.O-3.00C were measured. Dissolved Oxygen Amounts of respirable oxygen dissolved in water are critical for the maintenance of a diverse estuarine fauna, although much is left to be learned about the amounts and conditions which are actually necessary for particular species. Chapter 17-3, Florida Statutes, defines a mean value of 5.0 milligrams per liter (mg/l) and an instantaneous value of 4.0 mg/1 as threshho1ds beyond which water quality standards are violated. Dissolved oxygen values in the tidal Myakka River bore a highly significant relationship to salinity under particular flow regimes. Prior to Hurricane Elena, surface and bottom values were very similar (Figure 49). Oxygen concentrations increased steadily from near Snook Haven (3.5-4.2 mg/l) to the opening of the river into Myakka Bay (7.7 mg/1). Myakka Bay values decreased along an upstream to downstream axis by about 2.0 mg/1 and Charlotte Harbor values were slightly larger. Surface concentrations were only slightly higher than bottom concentrations.

-75- Conditions changed dramatically during the aftermath of the hurricane. High tide data from September 10, 1985 depict a highly stratified river, particularly in and downstream of Myakka Bay (Figure 50) . Essentially all of the river upstream of Myakka Bay was in violation of state water quality standards, as was most of the bottom water in and downstream of Myakka Bay. The lowermost river and Charlotte Harbor (river miles 2.0 to -2.0) had vertical differences in oxygen concentration of up to 5.0 mg/l, even two weeks after the September 10 survey (Figure 51). Oxygen stratification was relatively more abrupt in Charlotte Harbor on low tide than high tide, and the persistent input of oxygenated water from Big Slough became apparent on low tides (Figures 52, 53). Causes for higher concentrations of dissolved oxygen in Big Slough are not presently known but may include better mixing or higher primary production . Even at low tides, however, Myakka Bay was the river zone where surface to bottom differences in dissolved oxygen became apparent. The Relationship of Salinity and Dissolved Oxygen Although temperature affects dissolved oxygen, as previously stated, not much effect was expected or seen in September because temperature values varied little. Salinity does not appear to affect dissolved oxygen under low flow conditions, at least to the point beyond which the river becomes density stratified. Once the river stratifies, however, oxygen and salinity differences from surface to bottom covary directly. A comparison of Figures 42 and 50 illustrates that river mile 7, near the entry of the river to Myakka Bay, was the place where vertical differences in both parameters became evident. A sharp increase in bottom salinity between river miles 5.0 and 4.5 was paralleled by an equal decrease in bottom concentrations of dissolved oxygen. For the river below river mile 7.1, surface to bottom salinity and oxygen va lues were very highly correlated (Figure 54). An increase of 2.0 0/00 in surface to bottom differences in sa linity results in an increase of about 1.0 mg/l in oxygen stratification. This can be expressed as a linear equation of the form: (delta oxygen) • (0.416)(de1ta sa1inity)+(0.116).

-76- Discussion

This review of selected historical data and Phase I results establishes a few facts about the tidal Myakka River and suggests the nature of new information needed to understand and manage the river. There are two definite sets of hydrographic co nditions, or seasons, in the river, which can be called the spri ng dry and summer wet seasons. A minor wet period occurs in winter, and a minor dry period occurs in fall. These conditions have most ecological meaning in relation to prior or subsequent conditions, e.g., the spring dry season is usually drier than winter, but is warmer and much drier and cooler than summer . What are the essential or important factors in each season, relative to the ecology of plants and animals inhabiting the estuary? Is it enough that temperature varies seasonally or do salinity variations overwhelm temperature? Is the combination of salinity and temperature more important as a structural or functional pacemaker in this river than either parameter alone? The first step toward answering such questions must be an understandi ng of physi cal conditions in the river, over space and time, and with sufficient intensity to accurately predict the values of salinity, temperature, and dissolved oxygen at the surface and bottom, over the known range of flows for the river. If a picture must be drawn of the Myakka River and estuary based on hydrological data reviewed so far, it would emphasize the relative dryness of the system. The river commonly has low or no flow, with rapid salinity changes. The river appears to be a system in which extremes of wet season flow are greater than dry season extremes, whether flows so great as to comp letely "flush ll the estuary to its mouth occur with any regularity to be seen. The frequency of extreme salinity reductions at the river mouth obviously" must be determined if any thought is to be given to harvesting "surplus ll flows. If it happens that major flushes of the river are rare, then reductions in flow will always be expressed in a modified salinity structure within the tidal river. We now know that severe droughts result in the penetration to Interstate 75 of salinities greater than 15 0/00, so additional flow restrictions almost certainly will advance salt wedges farther, as well as bands of intermediate

-77- salinity -- but to what extent, for how long, and with what effect? The knowledge that the lower river may switch from an unstratified system during low flows to a stratified one during high flows may be a key to the success of future studies. Salinity and dissolved oxygen measurements are needed at surface and bottom, on high and low tides, at several sites along the river under a full range of flows especially where stratification occurs. Based on Phase I results, it may be useful to envision stratified river conditions as an extension of similar events in upper Charlotte Harbor (Fraser, 1981). At this pOint we cannot even discount the possibility that stratification in the lower river is the result of harbor-wide stratification and would occur independently of Myakka River flows. The wet season hydrographic survey identified some areas of interest in addition to the river mouth and upper Charlotte Harbor . Principal among these is Myakka Bay, where wet season conditions changed most rapidly and surface to bottom conditions diverged. Needed is a careful investigation of the river near the county line, where the braided channel emerges into the head of Myakka Bay . The Big Slough area had some effect on the river in the wet season, and from a physical or chemical perspective, was the most upriver area of interest. However, we can safely add some other, more upriver areas deserving of study based on the review of historical data. Data from 1972-1975 show clearly that tidal water of low salinity (1 .0 - 10.00/00) reaches U.S . 41 during years of average wetness. The extent to which salinity or other factors would be changed at U.S. 41 as a result of induced flow reduction must certainly be part of any future modelling effort. The tidal portion of Deer Prairie Slough will need to be scrutinized because of its direct involvement with water development on the Reserve. Sites upstream of Deer Prairie Slough which may be important as hydrological or hydrographic landmarks cannot be identified on the basis of the wet season survey. Conclus i on This first review and consideration of hydrological data for the eventual purpose of defining withdrawal impacts leads to one preliminary conclusion. On the one hand, surplus water may occur only when the river is made totally fresh by high flow, and even then, discharges may not be surplus if withdrawals

-78- significantly shorten the duration of zero-salinity cond i tions at E1 Jobean. This approach ignores the role of freshwater so defined as surplus, once it enters Charlotte Harbor, but that is a consideration well beyond the scope of this present study or any soon to come. On the other hand, critical points may exist in the hydrological character of the river which operate to define discrete sets of downstream response within which the occurrence of particular flows can be considered surplus. Without such a mechanism we must assume that plants and animals inhabiting the Myakka River estuary are more resilient or adaptable than existing ev idence allows . Therefore, new hydrological and hydrographic investigations should be accompanied by more ecological studies modelled after ones summarized by the following reports.

,

-79- Dlrterence from Me.n Monthly Flow (ct •• 100)

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Percent ot Zero-Discharge Month. (N = 26) MYAKKA RIVER MONTHLY STAGE VARIATION Min. Max. for 1982-85

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10 5. 1"1 "" :. •• j cJI =- =- =>0 _ :=.. =- c- CIoo c- =- ell <=000 ""] ell,,' ". j o , , [) IflHI FIG liRE -River discilo.rge, precipitation, nnd hydro- logic:1.\ propert.ies o.t sl:l.tiOlt 5, r.[yakka River, Flu., Jaounry 1064 to J:muary 1065, (Open bars=surf:lcCi solid bars= bottom.) • " .

" ., i \/ • i i • /\ I .0 I \' '~, I -' 1. I ~ > '\ , 'V\ I. i .\,i " '\ I , '... ;;" r, . : I 'J , \ : "< .' .. • r , ! r r, / \ ! i " \ • r ', .... \ i . , ..II r' \ ,' !J i, i \ , '\ ' , r \ ' • i r' r , ,r , '\ ' \ I \' , r' r \ . , , '\ ' , \ : r ,r ' 0 • : \, \ ,r' \ . r i ! ~ , I I , , , T,! , I I , ' \. I .. ~\ .I'''' \. 'I ~ --- 1972 ---- '1I1~ ...... 1117 • ...... --- '075

JUNE JU~' AUGU$T SE.TU'UIIOCT08ERNOVE".SER IIECE "' 8(R

SURFACE SALINITY AT EL JOBEAN ,

July 115, 1985 (USGS) High Tide. ® February 16, 1984 (USGS) Low Tlde=@ Surface , August 28, 1984 (USGS) low Tide . © Bottom

35

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1S RIVER MILE FOR 10 0100 at BOTTOM

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• ~ o '! '! '! o '! '! ...... " ...... Table 6. Statistics on normal monthly means (all days) of Myakka River discharge. Period of record, 1937-1984 (Myakka River State Park).

--Value Jan Feb Mar Apr' May Jun Mean, cfs 105 .0 121.0 154 .0 81.8 27.4 178.0 S.d. 143.0 145.0 241.0 120.0 46.5 253.0 C.V. 1.4 1.2 1.6 1.5 1.7 1.4

% 3.5 4.0 5. 1 2.7 0.9 5.9

-Value- Jul Aug Sep Oct Nov Dec Mean, cfs 436.0 648.0 700.0 402 .0 82.2 64.7 S.d. 476.0 497.0 558.0 325 .0 76 .2 89 .0

• C.V . 1.1 0.8 0.8 0.8 0.9 1.4 % 14.5 21.6 23.3 13.4 2.7 2.2

S.d.: Standard Deviation C.V.: Coefficient of Variation Table 7. Characteristics of four hydrological periods for the Myakka River.

Inclusive Cumulat i ve Discharge! Period Months % Mean c1s Min. c1s Max. c1s Mean C.V. Wi nter Wet Jan-Mar 12 .7 380.0 1.6 1,827 1.37 (3) (4.2) (126.6) (0.53) (609) Spring Dry Apr-May 3.6 109.0 0.0 676 I. 58 (2) (1 .8) (54.5) (0 .0) (338) Summer Wet Jun-Oct 78.7 2,364.0 510.5 6,277 0.98 (5) (15.74) (472.8) (102.1 ) (1,255) Fall Dry Nov-Oec 4.9 147.0 1.2 557 1.15 (2) (2.45) (73.5) (0 .6) (279)

ISum of all values for indicated months from Table I (% and mean cfs) and USGS unpublished data (minimum and maximum cfs). Mean C.V . computed from Table 1. Numbers in parentheses were computed by dividing sum by number of months. Table 8. Correlation of wet-season months, based on unpublished USGS data (normal monthly mean discharge, cfs) at Myakka River State Park, for the period 1937-1984 .

Jun Jul Aug Sep Oct 1 .473 .234 .154 -.128 June 1 .455 .173 -.187 July 1 .583 .030 August 1 -.087 September 1 October Table 9. Magnitude and frequency of annua l low flows on the Myakka River near Sarasota, for July 1937 to June 1977. Adapted from Hughes (1981)1.

Recurrence Lowest average flow, in cubic feet per second, for interval indicated number of consecutive days. in years I 7 14 30 60 90 120 183 2 0 0 0 (*) J.I 7.2 12 32 5 0 0 0 0 0 . I .9 5.5 10 0 0 0 0 0 0 .05 2. I 20 0 0 0 0 0 0 0 J.I 30 0 0 0 0 0 0 0 .8 50 0 0 0 0 0 0 0 .5

*Less than 0.05 cfs .

IThis table has been superceded by Hammett (1985) which was not available to the authors . Table 10. Stream flow at Myakka River State Park from SWFWMD , 1985 . POR , period of record.

Mean Monthl~ Flow , mgd POR 1984 1985

June 118.0 42.2 0 July 289.3 74.2 0 Augu st 427.6 47.2 228.0 September 459.4 115 .1 539.8 October 262 .4 79.2 89.4 BATHYMETRY

Introduction

The first European to draft an accurate map with bathymetric soundings of the Myakka River was an Englishman, Bernard Romans, during the early 1770's (McCarthy and Dame, 1983). The Myakka River was sounded at eight pOints for a distance of at least two or three miles upstream. It was not until the 1840's that a more accurate mapping of the Myakka River was accomplished by the General Land Office Survey (GLOS) . A detailed description of the GLOS report is in cluded in Presettlement Environments of the Lower Myakka River Corridor, (Wharton, 1985). The historical evidence shows a basic stability in the overall configuration of the river corridor from presettlement times to the present. The GlOS data, however, suggest a shift in the position of the river channe l from river mil e 15 to 19, and provides evidence for changes in island position near the U.S. 41 bridge. River depth and the general location of islands taken from Roman's notations compare closely with present day conditions (Wharton, 1985) . Numerous studies in the last 25 years have been made by the United States Geological Survey (USGS) on the hydrogeology, magnitude and frequency of flooding, and flow characteri stics of the Myakka River and surrounding area. Until recently, however, the Myakka River has been a neglected river in terms of ecological investigations. A bathymetric survey was done in September 1985 to aid in bed characterization and station selection for water chemistry, fisheries, oyster, and salt marsh tasks. Preliminary work involved assembling navigational charts and maps of the area, locating channel markers, determining working depth ranges and evaluating bottom types. The survey was made using a recording fathometer on a shallow draft skiff. Using the preliminary shoreline vegetation transects as reference pOints, alternate shoreline sites were surveyed from bank to bank, usually across a line normal to the long axis of the river.

-111- Area of Survey The area surveyed for this report included approximately 25 river miles of the lower river corridor, bounded roughly by the southwest corner of the Ringling MacArthur Reserve to the north and the southeast tip of Hog Island to the south. The basin area included in the study area can best be characterized as extremely flat. Topographic contours of less than 5 feet extend up the river corridor to Curry Creek (river mile 19.3) and streambed elevation is below sealevel for the entire study area (Hammett et al . , 1978).

Description of the River Corridor Most natural drainageways in the river corridor are shallow sloughs, ranging in width from a few feet to more than one mile. The Myakka River channel is the only one that is well defined and naturally entrenched throughout its course (Joyner and Sutcliffe, 1976). The river channel at the northern boundary of the study area has steep. occasionally undercut banks and is narrow, ranging between 60-100 feet in width. Its course is highly meanderous and occasionally marked by meander cutoffs and small oxbows. Two small creeks enter the river from the east at approximately river mile 19 (transect #4) and river mile 13.5. The river begins to widen at approximately river mile 13, becoming a wider, highly braided channel with marsh present as a continually widening strip between uplands or hammocks and the river . Deer Prairie Creek and Big Slough, major tributaries of the Myakka River, enter the main channel from the east at river miles 12 and 9.5, respectively. Warm Mineral Springs enters the river from the east side between these two tributaries. The Sarasota-Charlotte County line crosses the river at mile 7, where the river widens significantly and resembles a narrow bay rather than a river channel. From El Jobean (river mile 2.8) to the southeast tip of H09 Island, the most southerly transect in the study area, the river can best be characterized as a broad, shallow estuarine area.

-112- Transects Thirty-one cross sectional transects were run at alternate shoreline survey sites, roughly at one mile intervals (see Figure 55). The mouth of Curry Creek, Deer Prairie Creek, and the midpoint of Tippecanoe Bay were also surveyed. An identification number was provided for each location, from number 1 at the southwest corner of the Ringling MacArthur Reserve to number 53 at the mouth of the Myakka River near the southeast tip of Hog Island. Each cross section was also assigned a reference distance measured upstream from the calculated drainage basin margin located at Cattle Dock Point. Two cross sections downstream of Cattle Dock Point were assigned negative numbers (Table II).

Results

The bathymetric survey was made between August 28 and September 4, 1985. August was a wet month relative to an earlier period of prolonged drought. Periods of intense rainfall occurred daily during the survey and the passage of Hurricane Elena through the Florida Straits into the Gulf of Mexico contributed to extreme high tides. This advantageously allowed for complete bank to bank fathometer traces in most places . Although exact times of fathometer traces were noted, the applications intended for bathymetric data produced by this report did not require comparison to simultaneous stage heights of nearby gauging stations. All depths are therefore relative to the high tide river surface and are not absolute.

Shoreline Length A computer-aided analysis of shoreline length was made using USGS topographic quadrangles of the study area. The river was divided into four zones based on river widths (Figure 55). and a comparison was made of west and east bank shoreline lengths by zones (Table 12). The shoreline was longer on the east bank in Zone I (the furthest upstream zone) by apprOXimately 2,000 feet. In Zone 2, however, the west bank was longer by roughly 2,500 feet. In Zone 3. the east bank was longer by approximately 2,500 feet. From Curry

-113- Creek to Cattle Dock Point (transect 3 to 50) the west bank length is 115,490 feet (21.9 miles) and the east bank length is 125,486 feet (23.8 miles), a difference of approximately 1.9 miles . Most of this difference in length, however, is attributable to the widening of the river channe l into Charlotte Harbor in Zone 4.

River Width and Depth River widths were most frequently less than 500 feet, with 45% of transects and approximately 60% of the length of the study area falling in this category (Figure 56). The mean depth of all transects was 5.2 feet. Because al l measurements were made during a period of high discharge and high tides, a mean depth of only 5.2 ft illustrates the shallow nature of the river and ; nd; cates a low confi ned d; scharge vo lume potent i ali n the upper ri ver area. Maximum recorded depth was 13.8 feet at transect 9 (river mile 16.5) (Figure 58), although this cannot be regarded as the deepest area in the entire river. For instance, unverified data suggest a deep hole in the main channel just upstream of Big Slough. As shown in Figure 57, the most common values of maximum depths were between 7 to 12 feet (57% of all values). Shallowest river segments were found near Deer Prairie Creek (Figure 58), which may indicate the shoaling potential of this tributary. Figure 59 illustrates typical cross sections for each river zone (note that scales change by zone). The river channe l enters the study area as a narrow, steep banked meandering stream (Zone 1). It becomes a wider, highly braided channel in Zone 2. At the Sarasota-Charlotte County line the river widens dramatically in Zone 3. From the county line to the State Road 776 bridge at El Jobean, Zone 3 has an average width of 2,765 feet , compared to 526 feet in Zone 2. Zone 4 from E1 Jobean to the southeast tip of Hog Island basically becomes a broad, shallow estuary.

Channel Location and Shape

-114- The relative location of the main channel within the river bed north of El Jobean follows no definite pattern (Figures 60-62). Maximum depths seem to be divided equally between the west bank, the middle river, and the east bank. This suggests the study area north of El Jobean is dominated by a meandering channel able to move the river bed during periods of high discharge. From El Jobean south the greatest depths in each transect followed the west bank (Figure 63). The channels ranged in shape from trapezoids to smoothly rounded depressions. Secondary channels were present in Zones 1-3. Their occurrence corres ponded with drainage feature s such as marsh creeks, sloughs, or tributaries. The river bed flanking the channel graded from level bottom to steep slopes. Sloping beds were more common than level bottom and terracing of the river bed was observed at only 8 transects.

Discussion

The possibility that the Zone 1 river channel has moved since historic times implies that some measure of sediment was introduced to the lower river, which would affect tidal action, currents, and biological events. Th e elevated bed near Deer Prairie Creek may contain sediment from such origins, or represent ancient erosion in Deer Prairie Slough. The elevated bed may affect the penetration of tidal water during certain di scharges and could function as an important salinity control for upriver areas. Bathymetric data reveal that the potential for wind driven mixing in Zones 1 and 2 are poor due to narrow channels and restricted fetch. On the other hand, turbulent mixing may be higher in upper river zones . Zone 3, Myakka Bay, is not as wide as Zone 4, but it is much more shallow; therefore, mixing by wind may be better than in any other zone.

-115-

, w z o N

"W ~ N

N W Z S

w z o N • 0 0 0 ~

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Maximum Mean Transect River Depth Depth Width No. Mile ( ft) (ft) ( ft) 53 2.4 12.8 6.1 13,090 52 1.7 11.1 6.6 9,032 50 0 11.4 5.9 3,889 48 (Tippecanoe) 1.5 4.1 3.6 1,833 46 1.5 9.4 5.3 8,409 44 2.6 12.1 7.8 2,664 43 3.5 10.0 5.2 2,980 41 4.4 8.6 5.1 3,003 39 5.6 6.6 4.0 3,042 37 6.7 8.9 3.7 2,317 35 7.7 7.6 3.7 2,587 34 B B.I 7.7 4.4 270 34 A 8.1 7.2 4.6 893 32 8.9 11.4 7.5 501 30 9.4 11.4 6.4 462 29* 9.9 13.81 3.2 362 27 10.4 7. 2 3.4 824 25 B 10.9 3.5 3.2 3B5 25 A 10 .9 5.0 3.2 508 23 (Deer Prairie) 11.8 5.8 3.5 62 21 12 . 2 4.9 3.8 616 19 13.0 6.8 4.7 424 17 13.7 7.4 5.9 539 15 14.2 12.0 8.2 216 13 14.8 7.3 6.6 246 II 15.5 13.3 7.6 131 9 16.5 13.8 4.1 115 7 17.7 11 .8 7.8 154 5 18.4 9.8 5.6 77 3 (Curry Creek) 19.3 4. 1 3.1 131 1 20.2 8.0 6.4 60 *Side channel only. Table 12. Comparison of west and east bank lengths in study area .

West Bank East Bank Zone Tran sect (ft) (ft) I 1-15 29 ,B 52 31,875 II 17-34 40 . 221 37,654 III 35-44 34,013 36,640 IV 46 -53 24,799 32,724 128,885 138,893 (24 .4 mi (26.3 mi or 39 .3 km) or 42 .3 km)

CUMULATIVE LENGTH West Bank East Bank Zone Tran sect ( ft) ( ft) I 1-15 29,852 31,875 II 17 -34 70,073 69,529 III 35-44 104,086 106,169 IV 46-53 128,885 138,893

• RIVER BED CHARACTERIZATION

Thirty river bed sites were examined by divers to qualitatively evaluate sediment type and presence or absence of detritus and limestone outcroppings. The survey was conducted in the month of September during a period of heavy rainfal l and subsequent high river discharge . Uppermost river stations had the narrowest bank to bank width and the greatest water veloc ity. The river gradual ly widens downstream and reaches its widest pOint in Myakka Say . Table 13 characterizes the bottom at each station. Substratum type appeared to be a function of current speed . The upper river region (transects 1, 3 and 5) was relatively narrow with a strong current. As a result, the central channel at these locations was scoured to limestone with patchy pockets of coarse quartz sands. The banks in these areas generally sloped steeply to maximum stream depth. Submerged nearshore sediments consisted of slumped bank material and was the primary infaunal habitat. Patchy sediments of the central channel were generally free of organic material. Nearshore sed iments frequently consisted of layers of sand and detritus. There were almost no fine, particulate materials (organic or inorganic) present within the sediments . At Transect 7 near Snook Haven the riverbed was completely covered with coarse sands and there were no limestone outcroppings. The shoreline sediments were of a finer consistency and interlaced with terrestrial detritus. Thi s pattern of coarse quartz sands covering the channel portion of the river and finer shoreline sediments was typical for most of the river bed. Overall, sed iment s gradually became finer as the river widened downstream. At Tran sect 9 there were limestone outcroppings present near the east bank. These outcropp ing s were the furthest downstream rock substratum detected by the survey. Beginning in the region of Transect 13 the river bed was usually of nearly uniform consistency with only smal l differences between nearshore and channel sediment s. Areas that contained sediments of notably different consistency than the main river basin were transects 23, 31, 48 and the dredged canal on the west bank of transect 37. These areas contained sed iments of much

-127- finer consistency (silty-muddy sand) presumably due to slower stream velocities. Sediment Analysis In addition to qualitative river bed descriptions, quantitative grain size analyses were performed at three benthic core stations: B7, B27 ,and B53. Methodologies used for these analyses can be found in the appendix. Table 14 summarizes the sediment parameters for each station. Value s for median and mean grain size and sorti ng coefficient are presented as phi (0/) values . As an aid to interpretation Table 15 presents interpretive values for each of the sediment parameters. Based on these tables and the values for mean and median grain size, sediments from these three stations can be classified as medium to coarse sand (B27 and B53) and medium to fine sand (B7) . Sorting is a measure of the evenness of distribution of the total sediment weight over all particle sizes. Sorting coefficients for these three stations were very similar being moderately well sorted. Skewness is a measure of the asymetry of the particle grain size distribution. Positive values indicate a grain size distribution slanted or "skewed" to finer particle sizes. A value of zero indicates grain size distribution skewed to larger particle sizes. Skewness values ranged from nearly symmetrical, 0.02 at Station B7 and 0.09 at Station B27, to a more positive skewness of 0.14 at Station B53. Kurtosis is a peak measure of the grain size distribution curve. A low value indicates a very peaked curve (concentration of sediments among only a few particle sizes}j higher values, representing a less severe curve are indi cative of wider distribution of particle sizes. Stations B7 and B53 with kurtosis values of 0. 74 and 0.76, respectively, are classified as platykurtic (moderately peaked), while Station B29 with a kurtosis value of 1.3B i s considered leptokurtic, or moderately flat. Silt/clay content of the river sediments increased from upstream (B7, 0.44%) to downstream (B53, 1.33%). The percent organic composition increased from upstream to downstream in a similar manner. Based on median and mean grain size data it appears that the grain size of river sediments increase from upstream to downstream, which contradicts the visual observations noted in the previous section. This apparent discrepancy results because sediment cores were taken in the same area as the faunal cores to insure the sediments would be descriptive of the faunal habitat. At Station

-128- 87 , for example, this location was closer to the east bank to avoid the scoured mid -channel. Thus, although the sediments generally were comprised of clean quartz sands, they were primarily of two fine particle sizes: 0.125 mm and 0.063 mm . The sediments at Station 827 were taken from the center portion of the river since this area was less heterogeneous in sediment structure. The sediments in thi s area were well washed and consisted primarily of clean quartz sands distributed over three particle sizes: 0. 5mm, 0.25mm and 0.125mm . The sediments of Station 853 were also of these three particle sizes but also a larger percentage of fine sand (O.063mm) and silt/ clay sized particles (0.063mm). Sediment structure is , therefore, regulated by current speed with overall coarser sediments in the main upstream channel and finer sediments downstream. Photographic Documentation Photographic records of the surface sediments were made at the transects where the river bottom wa s described. A core sample was taken and placed on a white enamel pan and photographed on the surface. In addition, at Stations 87, 827 and 853, in situ sediment profile photographs were taken . Figure 64 i s a representative photograph exhibiting the sediments of Transect 7 (benthic Station 87) . Figures 65 , 66 , and 67, represent profile pictures of Stations 87 , 827 and 853. These photographs were used as an aid in interpreting sediment data .

-129- Table 13. River bed characterization for thirty sites along the Myakka River during the month of September 1985. The river water level was high and fast moving during period of observation.

Transect River No. Mile Bottom Description

I 21.0 River relatively narrow in this area, water fast moving. Banks are steep with middle of river scoured to limestone . Some small pockets of coarse sand (ca. O.5mm) in limestone depressions. Bank areas consist of shore slump where sediments become finer with organic detritus and root hairs from shoreline vegetation.

3 19.74 Where Curry Creek JOlns Myakka River. Swift current. Center of river with large smooth limestone slabs. As with Transect 1, there were small pockets of coarse sand . Banks consist of finer sand mixed with detritus. West bank near cattai l s very fine organic muck and strong hydrogen sulfide concentration. H2S gas bubbles from disturbed sediments. Curry Creek wa s flowing west. 5 18 .75 Center of River well scoured to limestone as with Transects 1 and 3. Banks not as steep as Transects 1 and 3 with slump sediments projecting across the river bottom for about 5 meters. Terrestrial debris present in sediments. 7 17 .92 River noticeably wider than previous transects , current not as strong . Middle of river with coarse sand sediments; no limestone found. Sediments near shore finer with organic detritus. 9 16.53 River deepest near east bank (left side when fac ing downstream), with limestone outcroppings. Sediments near east bank and middle coarse sand. West side of river shallower with finer sands mixed with detritus.

II 15.56 East side of river deepest with fine sand bottom and terrestrial detritus. Coarse sa nd over middle and west portions of river bottom . No evidence of rock bottom or outcroppings. Table 13. continued . Tran sect River No. Mile Bottom Descr i ption

13 14.84 Very uniform bottom, with sands generally finer than previous transects . Middle sediments slightly more coarse than bank areas which were fine grained and darker . No rocks. 15 14 . 18 Very uniform bottom sediments with bank regions being finer and darker in color mixed with detritus . 17 13.66 Uniform bottom sediments, fine nearshore sands to slightly more coarse middle sediments . The bivalve Corbicula noticeably present near banks . Sediments much finer in west marsh embayment. 19 13 .01 Very shal l ow area . Sediments un i form, mixed fine and coarse sands . 21 12.19 Uniform shallow bottom. Sediments near shore only slightly finer and darker than mid channel. 23 11.99 Located in Deer Prairie Creek. Sediments of fine muddy sand, muddier near shore, permeated with root hairs. 25 11.08 River shal l ow, sediments finer than upstream areas, with nearshore areas coarser and lighter in color than midstream. 27 10 . 57 River bottom very uniform in composition across entire transect, consisting of fine relatively cl ean sand. 28 10.17 Sediments uniform, typically muddier near shore, but mostly fine clean sand. 29 10 . 17 Sediments very similar to transect 28 but slightly lighter in color. 30 9.42 River deepest near west bank with fine relatively clean sand. Shallow water has finer sediments especially near mangroves of east bank. 31 9.42 Located in Big Slough, bottom covered with 3-6 cm of silty flocculent mud, shallower and not quite as muddy near salt marsh. Sediments in the area very dark brown to black. Table 13. continued. Tran sect River No. Mile Bottom Description

32 B.79 Deepest area west of center with coarse dark sand. West bank with fine relatively clean sand. East side silty with high organic content. 34 B.19 Main channel. Deepest area in the center with a substratum of fine sand with fragments of crushed shell. The west bank muddy. peat type consistency containing root rhizomes; oysters also present. East bank muddy, not peat consistency but with root rhizomes. 35 7.69 East bank near Juncus muddy with Juncus roots and grading to fine sand about 10m offshore. Center stream with a fine sand substratum mixed with some shell material. West pass with coarse grained sand and dead bivalve shells scattered throughout. 37 6.67 East portion of river very sha llow with relatively clean coarse sand substratum. Middle portion of river encompassing channel with fine somewhat muddy sand . Substratum from west bank dredged blind canal very silty with a pudding- like consistency. 39 5.57 Sediments generally similar across entire river consisting of fine moderately muddy sand. Polychaete tubes first noticeable on this transect (Diopatra). 41 4.47 Sediments from east and middle of river very similar consisting of a fine muddy black sand. West bank near canals very muddy with silt. 43 3.50 East and west bank sediments appear identical cons isting of a fine sand. Center portion of river muddier, black in color. 44 2. 53 East bank area with fine muddy sand brown-black in color. Sediments become coarser toward middle and became relati vely clean fine sands on west bank.

46 1.50 Northeast point a clean medium sand. Midstream substratum finer and muddier . West bank area very shallow with dense seagrasses over a fine muddy substratum. Tabl e 13 . continued. Transect River No. Mile Bottom Description

48 1.50 Located in Tippecanoe Bay, surrounded by salt marsh, sediments consist of fine black sandy mud. 50 o Substratum across entire river very similar consisting of clean medium fine sand. Estuarine type benthic fauna conspicuous including Ensis (razor clams), Pectinaria (polychaete) ana-the brachiopod Glottidia. 53 -2.33 Sediments of this area very similar from shore to shore consisting of clean relatively fine sand, somewhat more coarse in midstream. Seagrasses present along both shore areas. BENTHIC INVERTEBRATES

Introduction

Nineteen discrete locations were sampled for benthic epifauna and infauna of the Myakka River. Invertebrate distributions were determined by the analysis of four types of samp les: I) bucket dredge (qualitative); 2) collection of macroinvertebrates from selected salt marsh locations (qualitative); 3} incidental catches within the fisheries otter trawls (qualitative); and 4} benthic diver operated core samplers at four locations (quantitative). The dredge, salt marsh and trawl samples were used primarily for molluscan and crustacean macrofauna with the bulk of the infauna being described from the diver cores. Table 16 lists the transects sampled by dredge, trawl and core with the station locations exhibited in Figure 68. Data obtained by dredge and trawl samples are labeled by transect numbers. Benthic core data are labeled by transect numbers and the prefix "B" (e.g., B7, B19, B27, B53).

Results

Table 17 lists the benthic macro in vertebrates collected by the four methods. A total of 156 discrete taxa were identified from these collections. This number is within the range of what would be expected for thi s type of river system based on similar studies of the Manatee River (Culter and Mahadevan, 1982) and the Weeki Wachee, Crystal, Withlacoochee and Waccasassa Rivers (Estevez, 1985) . The largest number of taxa were collected by diver operated quantitative box cores, which accounted for 111 taxa, 90 of which were not col lected by any other method. Forty-six taxa were col lected by bucket dredge (18 unique taxa); 23 by trawl (15 unique taxa); and 10 taxa (3 unique) were collected within the intertidal zone of salt marshes .

-138- Table 18 categorizes the taxa by major invertebrate group and lists the abundance of each group (percent total individual counts). Crustaceans were the best represented group with a total of 52 taxa collected by all methods. Crustaceans also were the most abundant group at Stations 819, 827 and 853, accounting for an average of 57.7 percent (s • 18) of the total individual s at these stations. Molluscs were the second most common group taxonomically with a total of 50 taxa collected. However, molluscs were not as abundant as crustaceans or polychaetes, having an average mean abundance of 14 .5 percent (s - 5.2) of total indi vidual s where they occurred. The annelids accounted for a total of 40 species: 34 Polychaeta ; 5 Oligochaetaj and 1 Hirudinea. Polychaetes were also relatively abundant, accounting for an average of 23.4 percent of the total individuals collected (s - 14.6) over all stations. The most abundant taxa at each station are li sted in Table 19 based on total faunal counts for the benthic core samples. There was relatively little overlap in dominant taxa between stations. Dominant taxa were represented by 7 polychaetes, 3 oligochaetes, 3 amphipods, 3 bivalves, and one each of gastropods, i sopods, tanaids, cumaceans, ostracods, and insects as well as the phyla Nemertina and Nematoda.

Mollusca Molluscs can be a valuable tool in hydrobiological studies because: 1) the group is well described taxonomically; 2) they are generally habitat specific and vary greatly in tolerance to environmental changes and their mode of feeding; 3) as adults most molluscs are relativelY sedentary or travel only short distances; and 4} molluscan shell remains provide a semipermanent record of their occupancy in a given location (Taylor et al., 1970) . Mollusc spec imens collected represented two classes: the Pelecypoda (bivalves) and Gastropoda (snails). Twenty-one species of pelecypods were identified representing sixteen different families . Sixteen families of gastropods were represented for a total of twenty-five species. A phylogenetic listing of molluscan taxa and the method by which each was collected can be found in Table 17. Fourteen transects (Table 16) were sampled qualitatively by bucket dredge for surface infaunal and epifaunal invertebrates. Two locations

-139- were sampled at each site to provide information on community variation within a given area of the river. The portions sampled were: 1) a shallow water area, usually along one bank; and 2) the deepest portion of the river. Both live and dead molluscs (shell remains) were identified to obtain a more comprehensive description of each station. A complete species list of molluscs collected by dredge is presented by location and life status in Table 20. Thirty-three species of molluscs were collected in the dredge samples, fifty percent of which were dead specimens, fifty percent live. Five taxa occurred alive or dead at 50% or more of the stations sampled, Tellina sp. A (86%); Mulinia lateralis (71%); Rangia cuneata (64%); Tagelus plebius (57%); and Amygdalum papyri urn (50%) . Eleven species were found at only one station, (four taxa from Station 53, four from Station 44, one each at Stations 34, 37, and 50). The distributions of the dominant molluscs collected by dredge are presented in Figures 69 and 70 for the shallow and deep water samples, respectively. Generally, the shallow and deep water samples exhibited the same trends with the deep water specimens having a wider range . The limnetic bivalve Corbicula manilensis was found alive only at Transect 1. Dead Corbicula were found as far downstream as Transect 34. The Corbicula could represent washdown specimens, although the hydrographic data suggest that salinities may be low enough at times in that area to allow Corbicula to survive. Additional trends of mollusc distribution are discussed following presentation of the benthic core data . Quantitative benthic core samples were taken at five locations (B7, B19, B27, B40 and B53). The number of molluscs collected by core at each station is exhibited by taxa in Table 21. A total of 29 molluscan taxa were enumerated from the core samples as opposed to 33 taxa from the bucket dredge samples. Twelve taxa were collected by core samples but not the dredge, while 16 taxa were collected by dredge but not core. The core and dredge data augment and support the distributional data seen by each method individually, since the majority of molluscan taxa (for both methods) were collected in the lowre river inclusive of Transect 37 and downstream locations. The distribution of Corbicula, a limnetic bivalve, was discussed above.

-140- The upper river area (Transects 1-5) was not as typically fresh as was expected. The paucity of molluscs in this area and the occurrence of brackish water species did not reflect the hydrographic conditions at the time of sampling. No Corbicula was found within the core samp les downstream of Transect 1, but the bivalve Rang ia cuneata was found at Station B7. Rangia was also documented by dredge to occur or have occurred as far downstream as Transect 41. Rangia was found viable only down to Station 17. Rangia is typically associated with communi ties of low salinities (0 -18 0/00, Castagna and Chanley, 1966) in subtidal zones and rarely found in intertidal areas (Heard, 1982; Lasalle and de la Cruz, 1985). A survey by the Florida Department of Natural Resources lists the farthest downstream occurrence of Rangia near Tran sect 39 (Godcharles and Jaap, 1973). Another mollusc found only at the upriver areas was a sma ll Hydrobiid snail. Hydrobiids in general occupy a wide range of salinities (0-25 0/00) . They are considered primarily a tidal marsh inhabitant feeding on detritus and associated microflora. Also found at the uppermost stations were the bivalves, Mytilopsis leucophaeata (live specimens) and Ischadium recurvum (dead remains). While Mytilopsis is a fresh to brackish water inhabitant, Ischadium recurvum is usually an estuarine inhabitant. Its presence at Transect 1 suggests that salinities this far upstream are mesohaline for a duration sufficient to allow colonization of the substratum by Ischadium l arvae. This evidence is su pported by the historical hydrological data. Intermediate river stations (Transects 5-34) exhibit a dynamic community with respect to salinity, based on molluscs and mollusc remains . This region seems to represent a large transitional zone between limneti c and true estuarine conditions . A greater number of species were dead than alive within this region. In addition to Rangia, the predominant species, Tellina sp . A, Arnygdalum papyri urn, Tagelus plebius and Ischadium recurvum are characteristic of tidal marsh to estuarine communities. The presence of shell remains up to Transect 5 and 9 is evidence of periods of increased salinities for sufficient duration to affect the structure of benthic communities. The presence of dead R. cuneata at Transects 21 and 28 and C. manilensis at Station 21 supports the conclusion that limnetic conditions occur in this area as well.

-141- Tellina sp. A is tolerant of a wide range of salinity occurring from Transects 13-41. If it is like other Tellinidae, Tellina sp. A is probably a detritus feeder and inhabits shallow waters throughout the region (Abbott, 1974). Amygdalium papyrium is occasionally a tidal marsh inhabitant but is better adapted to saline (ca . 19 0/00) bays and inlets (Andrews, 1971). It is commonly found associated with the seagrass Ruppia maritima (Abbott, 1974). Tagelus plebius is common to mesohaline bays, in subtidal to lower intertidal fine sand and mud. It can be found associated with shoots of Spartina and is preyed upon by large fish (rays and drum) and blue crabs (Heard, 1982). Like T. plebius, Ischadium recurvum is not considered a typical marsh spec i es and is better adapated to estuarine habitats. The benthic core Station B19 exhibited only one bivalve specimen of Tagelu5 plebius, which normally inhabits brackish water communities. This station exhibited the fewest species of all invertebrate types, which may indicate this region was subjected to a longer duration of salinity fluctuations than other portions of the river. The downstream transects (37-53) exhibit a more stable estuarine community with increased diversity. Common to most stations were Amygdalum papyri urn, Nassarius vibex, Mulinia lateralis and Tellina sp. A. Both M. vibex and M. lateralis are found in sandy-mud substrata and are tolerant of wide salinity ranges (16-31 0/00 for ~ . vibex and 8-25 0/00 for ~. lateralis, Abbott, 1974). The l ive molluscs found within the benthic cores of Stations B27 and B40 supported the invertebrate trawl data in the finding that the middle portion of the study area was a transitional lone (from brackish to estuarine) at the time of sampling. Mytilopsis leucophaeata and Polymesoda caroliniana, the most abundant bivalves at Station 827, are typical euryhaline river or estuarine inhabitants occupying fine sand to mud substrata. This was the only station where these two species were found. The molluscs of Station 840 were typical of inhabitants of low to medium salinity habitats of shallow estuaries and bays and included: Acteocina canaliculata, Tellina texan a and Amygdalum papyrium (Emerson and Johnsen, 1976). I. texana was collected at 3 of the 5 benthic stations. The salinity at these stations ranges from 0.01 to 23.92, suggesting an ability to

-142- withstand wide salinity fluctuations. Although A. papyrium is better adapated to saline bays and inlets of salinities of 19 0/00 (Andrews, 1971), it is occasionally found in tidal marsh areas near Ruppia maritima (Abbott, 1974) . Each of these dominant taxa also were found at Station 3 (53) where the greatest diversity was observed. It is possible this station does not undergo radical salinity fluctuations due to the increased width of the river and the greater influence of tidal waters. This station exhibited a true estuarine infauna. The 24 species of molluscs comprised 19% of the total fauna. Equally important to diversity was the increased density observed at this station. Total mollusc individuals numbered 150, as compared to 73 at 840; 15 at 827; one at B19; and 10 at B7. The dominant taxon was Mysella planulata, comprls1ng 15% of the molluscan taxa. The species represented are generally tolerant to salinity changes and inhabit shallow, estuarine bays and intertidal sand flats. Mysella p1anu1ata frequently attaches to pilings, buoys, and grasses in shallow water (Abbott, 1974). Salt Marsh Molluscs Marsh zones exhibit distinct species assemblages. Salt marsh inhabitants are often exposed to harsh conditions which restrict the number of species (Heard, 1982). Unlike other areas in the river, the marshes can undergo rapid daily changes i n salinity, D.O., temperature and pH. In spite of these harsh conditions, the marsh is an area of high productivity, and valuable as habitat. Most mo l luscan marsh species are consumers of epiphytes and detritus. They account for a major portion of the energy flow between autotrophs (food producers) and heteretrophs (requiring nourishment from outside sources) (Subrahmanyan et a1., 1976). Six species of molluscs were qualitatively identified in Myakka River salt marshes. These taxa did not exhibit a definitive pattern of dispersion along the river sal inity gradient. From a total of 41 specimens collected for the six species, Neritina reclivata accounted for 15 individuals, Littorina irrorata 13, Crassostrea virginica 6, Polymesoda caroliniana 3, Ischadium recurvum 3, and Hydrobiidae sp. 1 individual. Neritina reclivata is a convnon marsh inhabitant withstanding salinities ranging from 1 0/ 00 to over 40 0/00

-143- (Heard, 1982). Heard (1982) has observed Neritina climbing on Spartina stalks to graze on encrusted algae and other microflora. In turn, Neritina provide food for wild ducks, blue crabs, and birds. Being habitat specific, tl. reclivata was not found in the transect or benthic stations. The bivalve Polymesoda caroliniana is a ubiquitous inhabitant of bracki sh estuaries and low salinity Juncus marshes. The species is euryhaline but is usually associated with freshwater (river) sources. Once established in the marsh, this species ;s able to withstand very long periods of exposure at low tide (Gray and Hackney, 1982). The primary predators of P. caroliniana are Callinectes sapidus (the blue crab), and racoons (Heard 1982). Littorina irrorata was also observed in Myakka River salt marshes. Strictly littoral, ~. irrorata was not found in the transect dredgings or the benthic sampling. Tolerant of both low and high salinities, they are able to survive for long periods out of water (Abbott, 1974). littorina irrorata is primarily an omnivore and detritus feeder and is a food source of the blue crab. Adults are commonly found crawling up Juncus at high tide (Subrahmanyan et al., 1976). Although not typically considered a marsh species, Ischadium recurvum was identified at three of the salt marsh locations. Preferring more estuarine environments, 1. recurvum is often found attached to oysters and the ribbed musse l Geukensia demissa (Heard, 1982). The hydrobiid snail was found at only one salt marsh location during the September 1985 sampling. Members of the family Hydrobiidae are normally found in large numbers in Gulf tidal marshes. It is possible they were overlooked at other stations due to their small size. According to Heard (1982) at least six species can be found in tidal marsh habitats. Hydrobiids feed on detritus and associated microflora . Crustaceans Fifty-two taxa of the class Crustacea were collected from the Myakka River. These taxa represented three subclasses: Cirripedia, Ostracoda and Copepoda; and 6 orders (not of the previous subclasses): Amphipoda, Cumacea, Decapoda, Isopoda, Mysidacea and Tanaidacea (Table 17). The amphipods were dominant in both species numbers and individuals collected. Seventeen distinct

-144- amphipod taxa were collected, by al l methods. These species accounted for 39 percent of the total crustacean individuals collected by core samples. Oecapoda were also represented by 17 taxa, although they were not numerically dominant, accounting for only 2 percent of the core fauna. Most of the decapod taxa were epifaunal species collected by trawl catches; only 5 taxa were collected in core samp 1es . I sopods were represented by 8 taxa, only 3 of whi ch were co 11 ected in core samples. They accounted for sl ight1y less than 10 percent of the crustacean individuals collected by core samples. The remaining groups of crustaceans were not taxonomically well represented (only 1 or 2 species), but a cumacean, Cyclaspis sp., and an ostracod, Parasterope pollex, were quite abundant, representing 22% and 24%, respectively, of the crustacean fauna collected by core. These two species are highly motile and typically occur in "swarms" in estuarine areas. Crustaceans as a group are often more tolerant of salinity fluctuations than molluscs or annelids. In addition, many crustaceans are highly mobile and can relocate if conditions become adverse . The dispersion and density trends for the crustaceans followed a salinity gradient, al though as with the molluscs, the patterns did not accurately reflect the salinities at the time of sampling. As would be expected, the euryhaline taxa were found at most sampling locations, whereas those less tolerant of wide salinity variations were more restricted . The only exception was the amphipod Ampelisca abdita, a typical estuarine/marine species which was collected from the freshwater of Station 87, along with Grandidierella bonnieroides and Gammarus t igri nus, which are euryhaline taxa. The dispersion trends for al l crustacean taxa collected by core dredge and trawl samples are il l ustrated in Table 22. The benthic core Stations 87, 827, 840 and 853 each exhibited a greater number of taxa than adjacent trawl and dredge stations. However, the trawl and dredge samples usually contained species also collected by core. The unique species collected by trawl (Table 17) were almost all decapods inhabiting the estuarine areas (Transect 50). These decapod taxa are highly motile and could easily avoid capture by diver core. They also appear to be mostly limited to the true estuarine areas, since few of the taxa were collected from other trawl stations (Table 22).

-145- Distribution of the crustaceans collected by dredge are graphically depicted in Figures 71 and 72, for both shallow (nearshore samples) and deep (mid channel) areas . Table 22 shows both areas combined. Many of the most common taxa. Ampelisca, Grandidierella, Mesanathura, Rithropanopeus, were found in both deep and shallow areas . Distributional trends were not notabl y different between the two areas; however for downstream areas, the shallow samples exhibited a more diverse representation of taxa. This was probably due to the large expanse of submerged macrophytes in the nearshore areas of the lower river. Such vegetated areas are typically rich in associated crustacean fauna. There was also a distinct increase in number of species collected from upstream to downstream stations; the same trend was exhibited by trawl data, as well as core data (Table 23). The combined core, trawl and dredge data shown in Table 22 provide background to the structure of the Myakka River benthic communities. The upper river area (Transects 1-5) which exhibited some freshwater molluscan affinities had sparse crustacean fauna. No crustaceans were collected at Transect 1, and only three taxa were collected at Tran sect 5, Gammarus trigrinus (amphipod), Mesanthura pulchra (isopod) and Rhithropanopeus harrisii (decapod) . These three taxa are euryhaline and tolerant of very low salinities (ca. 1 0/00). Gammarus is often a dominant upper estuarine specis typically found in debris (Bousfield. 1973). Mesanthura can tolerate a wide range of salinities and also;s commonly found in debris where its feeding mode is similar to that of an earthworm, that is, processing detrital materials (Shultz, 1969). Rhithropanopeus is common in fresh to estuarine areas, both subtidally and intertidally in mud banks and grassbeds or pilings, among shells and under debris . Rhithropanopeus harrisi; ;s not habitat specific and is the only xanthid crab which can tolerate limnetic to euhaline conditions. It feeds on detritus, crustaceans, molluscs, and decaying animal matter. Rhithropanopeus can be an important food item for fish, birds, and raccoons (Heard, 1982) . All three of the above taxa were also found at other downstream locations . Thus, the uppermo st river stations, having freshwater hydrographic conditions at the time of sampling, did not exhibit any exclusively freshwater crustacean taxa, only three very tolerant taxa.

-1 46- Another salinity tolerant amphipod, Grandidierella bonnieroides was collected at the first benthic core Station, B7, as well as three amphipods usually found only in brackish to marine water, Podocerus cf. brasiliensis, Ampelisca abdita and ~. holmesi. Podocerus was collected only at Station 87, while Grandidierella occurred at over 66% of the stations. Ampelisca holmesi occurred at seven other stations, all much further downstream (B27 , B37, 840, 841, 844, 850 and 853). Ampelisca abdita was found at 6 other stations also downstream (837, 840, 841, 844 , 850 and 853). The Ampelisca spp . and Podocerus are all tube building species in sand or silty sand substrata . Podocerus is also known to be an important food item for sheepshead fish (Thomas, 1976) . The presence of these species at Station B7 are indicative of more saline conditions prior to the initiation of the study. As with molluscs , a large portion of the river could be termed an intermediate transitional zone. With the molluscs this was defined by Transects 7-34, but the crustacean zone seems to extend farther down river from Transect s 7-44. This transitional area can be further divided into two sections, Transects 9-25 and Transects 27-44. The area encompassed by Transects 9-25 wa s notably sparse in crustacean fauna, with each transect exhibiting only 2-4 taxa. This included a benthic core station, B19, which had the lowest number of species and total individuals for all core stations (Table 23). There were no taxa unique to this area, but the species which did occur were mixohaline (tolerant of a wide range of salinities). This indicates that the region may undergo frequent changes in salinity of a magnitude great enough to structure a "stressed" benthic community. Only two taxa in this region were found which had not been collected at Transects 5 and 7, Balanus improvisus (barnacle) and Hargeria rapax (tanaid). Balanus first occurred in this study at Tran sect 21, and while many barnacles are upper estuarine inhabitants, they are generally not to 1erant of freshwater condit ions. The tana i d, Hargeri a, is a tube dwe 11 i n9 species which feeds on detritus and organic particulate and is tolerant of fresh to hypersal ine conditions (Heard 1982). It is known as an important food resource for many estuarine fish, including the killifish (Fundulus spp.), but it was not particularly abundant in the Myakka River. The lower portion of the crustacean delineated transitional zone (Transects 27-44) showed notable

-147- increases in the numbers of species recovered. Species such as Edotea triloba (isopod), Penaeus duorarum and Palaemonetes ~ (decapods), and Corophium louisianum (amphipod) are generally tolerant of brackish to marine conditions but not freshwater . The transect stations downstream of the El Jobean bridge (850 and 853) exhibited a typical estuarine fauna, with a dramatic increase in number of species (particularly 853 core samples) (Table 8A) and a community composition having fewer freshwater tolerant species. Twenty-four crustcean taxa (46 percent of the species found at all stations) were only found at Stations 850 and 853. Most of the decapod and isopod taxa found were in this area. While many of the upper river taxa were detritus and debris feeders, taxa from this area also represent predators (Alpheus, Portunus) and deposit feeders (Ampelisca, Cyclaspis, Myodocopa sp.). The crustacean fauna of the Myakka River was well represented by a diversity of taxa. With the except i on of the downri ver "estuari ne lf area (Transects 50-53) the fauna did not reflect current hydrographic conditions. None of the areas sampled exhibited a freshwater crustacean fauna. An exceptionally large transitional area (Transects 9-44) exhibiting salinity stressed communities (Transects 9-25) exhibited low species diversity and number of individuals. The overall dispersal and abundance is regulated by salinity variations , with both the number of taxa and number of individuals increasing at downstream stations.

Annelids Analysis of annelid communities provides useful information in determining changes in the environmental conditions of the river. Annelids, like molluscs, generally lack the mobility found in other faunal assemblages, i.e., fish, crustaceans, etc. Consequently, they cannot readily avoid adverse conditions. A short term environmental change, if severe enough , may be reflected in the changing community structure but may go unnoticed through intermittent water quality analysis.

-148- Annelids were primarily represented by two classes: Oligochaeta and Polychaeta. Two specimens of a third class, Hirudinea, were collected at the freshwater location B7. Oligochaeta were represented by two families: Naididae and Tubificidae. A single representative of the family Naididae, Piguetiella michiganensi s occurred at Station B19, where the salinity was less than 1 0/00 (Table 24). Piguetiella michiganensis is a freshwater species having the ability to enter the water column and swim for short periods of time. Consequently, its presence at Station B19 may not be truly indicative of the permanent infaunal commu nity. Tubificidae accounted for the majority of the oligochaetes and was represented by three species: Limnodrilus hoffmeisteri, Tubificoides brownae, and limnodriloides sp. Limnodrilus hoffmeisteri wa s collected only at freshwater Station B7, where it comprised 13% of the total benthic fauna. This is a cosmopolitan freshwater spec ies very tolerant to environmental stress. Limnodrilus hoffmei steri is frequently reported in upper oligohaline regions of estuaries where it can withstand slight salinity fluctuations . Accurate, specific determination of immature tubificids collected at Station 87 was not possible, though they were probably young h. hoffmeisteri. Tubificoides brownae and Limnodriloides sp. were only collected at the most saline Station 853, where the salinity ranged from 16-24 0/00 during the sampling period. Tubificoides brownae, an estuarine species, is common on both coasts of North America and has been frequently collected from estuaries within this salinity range on the west coast of Florida. All species of Limnodriloides are either estuarine or marine. Various species within this genus have been reported from the west coast of Florida. Additional mature specimens are necessary for specific determination. The polychaete fauna was very diverse and abundant in the Myakka River, compris ing up to 45% of the total benthic fauna at Station B40 . Thirty-four taxa of polychaetes represented by 21 families were identified. Three distinct communities could be distinguished based on the salinity regime: the upstream region, less than 1 0/00; the middle region, generally 6-12 0/00; and the downstream region, generally 16-18 0/00.

-149- The upstream region (Stations B7, B19, and B27) was characterized by low abundance and diversity. Six species were collected throughout this region (Table 24), with Laeonereis culveri being the dominant species . Nereid polychaetes are generally limisted in their dispersion by low salinities. High salinity is not reported to be limiting (Oglesby, 1965). Laeonereis is often found living in freshwater areas and is able to tolerate salinity fluctuations from 0.5 to 30 0/00. It is an important intertidal burrowing non-selective deposit feeder from throughout the Gulf coast (Carpenter, 1956; Hedgpeth, 1950; Mazuskiewicz, 1970). Boccardiella sp., Aricidea philbinae, and Lumrineries verill; were collected from this region only. Mediomastus sp. and Aricidea taylor; were occasionally encountered but were more abundant at locations further downstream. Station B27 was more of a transitional region between Stations B19 and B40. Two taxa were collected at Station B27: Lumbrinereis verrilli (a burrowing deposit feeder) and Amphicteis gunneri (a surface deposit feeder). The former species was equally distributed between Stations 619 and B27, while the latter was more abundant at Station 40. Station B40 was characteristic of the middle region. Although this region contained only seven taxa, the number of individuals collected was much greater than the upstream region, with the polychaetes comprising over 40% of the total benthic fauna. Streblospio benedicti dominated the polychaete community, comprising 26% of the total benthic fauna (Table 24) and was not collected at the other stations. Strebbl ospio, an intertidal tube dwelling deposit feeder, is often considered a pollution or stressed environment indicator. It is common in salinities from 10-17 0/00 (Cowles, 1931) and often occurs in high densities within fine organically enriched sediments and mudflats (Light, 1978). It can occur in a variety of substrates, however , and its presence does not always indicated polluted conditions. Neanthes succinea, Pectinaria gouldii and Amphicteis gunner; were the only other dominant polychaetes at this station, comprising 3%, 4%, and 6% of the total fauna, respectively. Polydora ~ and Diopatra cuprea were only collected at Station 640, both comprising less than 1% of the total fauna.

-150- The farthest downstream station (853) contained the highest polychaete diversity and abundance within the study area. Twenty-six species within 19 familis were identified at this station, reaching a density of 463 individuals (#/m2) . Twenty species were collected only at Station 853. Paraprionospio _____ pinnata, the most abundant species at Station 853 (Table 19), comprised 13% of the total fauna. Other dominant polychaete taxa were Neanthes succinea, Spiochaetopterus £. oculatus and Mediomastus ambiseta, comprising 3%, 4%, and 4% of the total fauna , respectively. Neanthes and Mediomastus are both nonselective deposit feeders. Neanthes (a nereid) is tolerant of a wide range of salinities but typically is estuarine. Mediomastus can occur in high densities in organically enriched sediments and for that reason ;s sometimes considered a pollution indicator (Reish, 1979) . Spiochaetopterus is a tube dwelling su spension feeder and can occasionally feed by gathering surface particular with its palps. Three species, Pectinaria gouldii, ~. succinea and Spiochaetopterus f. oculatus, were collected both at Stations 853 and 840. Pectinaria is a tube dwelling selective deposit feeder which constructs its tube from fine quartz and grains. The only other species occurring at a station other than B53 were Mediomastus ambiseta and Aricidea taylori . A single specimen of each species was collected from Stations B7 and B19, respectively. Taken together, the oligochaete and polychaete fauna formed a dominant component of the benthic communities of the Myakka River. The study area could be separated into three distinct regions by analyzing the dominant annelid species within the communities. The upstream or freshwater-oligohaline region was characterized by low abundance and diversity. The dominant oligochaete wa s a salt tolerant freshwater speCies, Limnod rilus hoffmeisteri. The dominant polychaete was a freshwater tolerant brackish water species Laeonereis culveri. The middle region was devoid of oligochaetes. The polychaetes were a major component of the community, with Streblospio benedict; being the most abundant species. Neanthes succinea, Pectinaria gouldii and Amphicteis gunneri also formed an integral part of this community. The downstream region had the highest abundance and diversity. The only oli90chaetes present were typical estuarine forms. The most abundant species in this region was the polychaete Paraprionospio pinnata, a tube dwelling spionid which feeds on surface

-151- particulates by gathering material with grooved peristomial tentacles. It is commonly found in sandy mud and muddy substrates from 3 to 1300 meters (Foster, 1971). Other dominant components of the polychaete community were Spiochaetopterus f. oculatus, Mediomastus ambiseta and Neanthes succinea. The overriding factor determing the community structure of the Annelida was apparently salinity. The lack of a strong polychaete commuunity at the uppermo st river stations, where crustaceans and molluscs indicated a brackish/estuarine community, illustrates that perhaps polychaetes react more instantaneously to changes in salinity. In addition to the species of the major phyletic groups, there were 13 taxa classified as miscellaneous taxa (Table 18). Included were representatives of Platyhelminthes (2 taxa), Bryozoa (I group), Hirudinea (I taxon), Brachiopoda (I taxon), Insecta (6 taxa) , Echinodermata (I taxon), and Urochordata (I taxon). Only the urochordate Branchiostoma spp. occurred in significant numbers (6.5% of individuals at Station B53). Branchiostoma is an estuarine species and generally would not be found in freshwater areas. One individual of Branchiostoma was also found at Station B27, indicating estuarine conditions. The brachiopod Glottidia pyramidata, the echinoderm Micropholis gracillina, and one flatworm, Euplana gracilis, are strict estuarine taxa and only occurred at Station B53. These species could not survive extended periods of salinities lower than 10-15 ppt. At the other end of the salinity range the dipteran insect spec i es found in the Myakka River are primarily freshwater inhabitants. Five of the insect taxa occurred only at Stations B7 and B19. The other insect, Cryptochironomus spp. (larvae), was recovered only from Station B27 . Many species of insects have aquatic larvae which are tolerant of brackish waters. The presence of insect larvae at the three uprivermost core stations could be a result of stream drift or could indicate a transition from the brackish-estuarine fauna seen in the molluscs and crustaceans to a freshwater insect fauna. This faunal transition would coincide with the hydrographic alterations (salt to fresh) seen in the Myakka River.

-152- Benthic Community Parameters In general the Myakka River benthos seems to have a rich and varied faunal community, especially considering that only one sampling has been conducted . The descriptive community parameters (species richness, faunal density, diversity and equitability) were calculated based on the faunal core data. Species richness {expressed as species numbers} ranged from only 9 taxa at Station 819 to 86 taxa at Station 853 (Table 25). With the exception of Station B19 the values can be considered moderate to high for a system of this nature. Faunal density (#/m2) ranged from 247 to 14,890 individuals per square meter at Stations B19 and 853, respectively. Diversity reflected the species richness trends ranging from 1. 17 to 3. 00 nats at Stations 819 and 853, respectively. Equitabi1ity or the measure of evenness of distribution of fauna around the taxa ranged from 0.56 (most uneven distribution) at Station B19 to 0.83 (the most even distribution) at Station 87.

Discussion

The invertebrates collected for this study were typical for Florida west coast estuarine areas. Studies in Tampa Bay (Mahadevan et al ., 1977; Simon and Conner, 1976), the Manatee River (Culter and Mahadevan, 1982), the Weeki Wachee, Crystal and Withlacoochee Rivers (Estevez, 1985) have resulted in collections of many of the same species. Adequacy of Sampling In order to assess the adequacy of sampling effort for the benthic infaunal survey, species area or species saturation curves were constructed (Figure 73). A curve was developed for each station by accumulating the number of new taxa found in each additional replicate. Each curve ;s the average of three possible combinations of rep l icates to approximate the ideal curve (all possible replicate combinations). An adequate number of samples is that number which provides the majority of taxa present within a habitat (sampling station). This approximation ;s generally considered to be the asymptote of the curve or the point at which the increase in additional taxa between the last and next to last replicate is less than 10 percent of the total. Figure 73 shows that all

-153- stations reached an acceptable level of saturation with seven replicate cores. An additional four cores were processed for Station 19 because the increase between replicates six and seven was greater than 10 percent. However, graphic analysis of this curve indicated a relatively small amount of information was gained by the addition of four replicates; therefore, in this case seven replicates are also judged as sufficient. Information for seven cores from each station was used in this report. Role of Salinity The invertebrate fauna examined by this study indicate salinity is the primary community structuring force. Examination of the mollusc, crustacean, polychaete and miscellaneous components indicates each of these groups reacts at a different rate to changes in salinity. This was evident by the slightly different zones of fresh, transitional and estuarine waters delineated by each group. Overall, based upon the faunal distributions at the time of sampling, it appears the annelids are most sensitive (fastest reacting), followed by the molluscs. The crustaceans may have the strongest ability to tolerate pronounced salinity shifts and therefore exhibit the greatest lag time in a restructuring of the fauna. River estuarine systems are generally divided into zones based upon defined salinity regimes (Table 26). Most invertebrates also have dispersion patterns that can be directly attributed to salinities within these systems. Benthic invertebrates collected in the Myakka River during September 1985 also exhibited distributions determined by salinity. The distributions, however, were not related directly to salinities observed at the time of sampling due to the unusual hydrological conditions prior to and during the sampling events. For example, benthic communities described by Table 19 indicate the recent occurrence of mesohaline conditions very near the area of Station B7, but hydrological measurements made during this time depict a limnetic system as far downriver as Transect 37 (see Figure 42), and oligohaline conditions (O.S-S ppt salinity) to Transect 38. Even at Transect 53 salinities for this period were below 25 ppt. Because four sampling methods were used in this study, molluscs and some crustaceans were more thoroughly described with respect to distribution.

-154- \ ..

T= Trawl Be= Benthic Cor. BO= Bucket Dredge

Location of trans.ct. where de.crlptlve bottom observations were made and location. of cor., dredge, and trawl station •. 0 0 0 '" 0 N, ..'" 0 0 0 ~ 0 , 0 0 0 0 0 0 0 0 0 0 0 0 ~ 0 0 0 0 n 0 N 0 0 0 0 0 0 0 0 0 0 '" 0 0 0 0 u 0 0 .. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .. 0 0 0 0 0 '" .. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 u u 9 0 0 0 '" 0 0 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 9 0 0 0 0 0 a 0 0 0 .. 0 0 0 0 0 0 0 0 0 0 0 0 .. 0 0 • 0 0 0 0 0 0 :l 0 0 0 0 0 ~ 0 0 ... 0 0 N 0 0 " ~ 0 0 0 .. 0 ~ 0 0 8 0 0 0 0 0 ~ 0 N 0 0 0 0 0 ~ 0 0 0 0 0 0 0 0 0 0 0 n 0 00 0 ~ '"~ ."• .. ..~ Q• u 0 i5 i5 0 0 0 0 0 0 0 0 0 0 '"~ 0 0 0 0 0 0 0 0 0 0 0 ~ 0 0 0 " 0 0 0 0 0 0 ... 0 0 0 ~ 0 0 0 0 0 0 0 <0 ... 0 ~ <0 n 0 0 0 0 0 0 0 0 0 0 0 ~ 0 0 0 '" 0 0 0 0 0 0 0 N 0 0 0 n n n

~ N •C 0 -• '"• 0 t)- 0 0 •" V> -• 0,- • '"~ 0 0 0 0 0 0 '"0 0 0 0 0 ~ 0 0 0 0 .. 0 0 0 ~ 0 5 5 .. 0 0 0 0 ... ., 0 0 0 0 0 0 0 0 ~ 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 ~ 0 " 0 0 0> 0 0 0 0 0 0 0 0 0 ~ 0 0 0 0 0 0 0 0 '" 0 0 0 \! , ~ 0 0 0 0 0 0 0 0 .. 0 0 0 •" 0 il 0 0 , •0. ~.. ~ 0 0 0 0 0 0 0 0 0 0 .. 0 0 o " 0 0 0 o ~ 0 0 0 0 ~ 0, o \l " 0 9 '" 0 0 0 0 ~ 0 0 0 ~ 0 0 .. u u 0 0 0 0 0 0 0 ... ~ 0 0 '" 0 0 0 0 " 0 0 5 c 0 0 0 < 0 0 0 • .. 0 0 0 0 0 0 D 0 0 0 o ., 9 0 n , o 0 0 0 0 o 0 0 0 0 .... 0 0 0 0 0 0 0 0 0 0 0 0 0> 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .. 0 0 0 0 .. 0 0 0 0 0 '" 0 0 0 0 0 0 .. 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 " 0 0 0 0 " 0 0 0 0 0 0 0 '" 0 0 0 0 ~ 0 0 0 0 0 0 0 0 0 0 0 0 o 0 0 " u 0 0 0 0 D 0 0 0 0 D 0 0 , 0 0 D 0 0 D .. '" 0 D '"" " 8 0 v v 0 0 i5 0 0 0 0 0 i5 0 0 0 0 0 0 0 0 0 0 0 0 0 on 0 0 0 0 .,'" 0 0 0 0 0 0 , 0 0 0 0 0 '" 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 n 0 0 2 n , 0 0 - 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 n n ~ 0 0 - n 0 0 v 0 0 0 0 0 0 0 0 '" 0 0 0 0 0 0 0 0 0 0 0 0 '" 0 0 0 0 0 0 0 0 0 .. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 on .. 0 0 0 0 0 ., 0 0 0 0 0 n 0 0 0 0 0 0 0 .. 0 0 0 0 0 0 0 0 0 .... 0 0 0 0 0 0 '" 0 .. •> 0 0 :::l 0 0 .... 0 v 0 - ., 0 '" 0 0 - 0 0 0 - 0 0 0 0 0 0 0 '" " 0 0 0 - n n '"- .,'"- "• .. 0 0 0 - 0 0 on 0 0 0 0 0 0 n - n -'" ....- '"- ....., ..- 0 '" - •c '" 0 .,-• • 0 u- 0 0 0 0 ... 0 0 0 0 ., 0 0 ", '" 0 0 0 0 0 0 -, " 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 - 0 0 0 0 0 0 0 0 0 " 0 0 0 ... 0 0 0 0 0 0 0 0 0 0 0 " .. 0 0 0 0 0 0 0 .. 0 0 ., 0 0 '" 0 0 0 0 0 0 0 0 '" 0 0 0 0 0 0 0 0 0 0 ~ 0 0 0 0 0 0 0 0 0 0 0 0 8 ., 0 0 0 0 0 0 0 0 0 0 .. 0 •> 0 0 0 :J 0 15 0 0 0 ~ 0 0 0 0 0 - 0 0 0 " 0 0 0 0 0 - " 0 0 - c 0 c 0 0 " c 0 0 - c 0 0 ... .. 0 0 0 0- - .,- .. 0 0 • 0 0 0 .. 0• 0 0 - 0 0 '" 0 - 0 .. 0 u 0 0 0 0 -~ 0 0 0 0 - 0 0 ~ 0 0 .. 0 0 .. 0 0 0 0 - 0 0 0 .. 0 0 0 0 0 - 0 0 0 0 0 0 0 0 n 0 " •0 -" 0 -• "• -0 <..> STATIONS/ ';\ INCREASE 90 B 53/ 8.3'" 80

U) w 70 "w ..U) ... 80 0 rr: 5 w.. ::> 40 Z'" w > B 40/ 3.2% t- 30 ..... B 27/ 8.0 '11 ::> 87/ 8.7$ 20 '"::> " 10 819/ 0 %

3 4 8 10 11 .0 1 158 .0312 . 0468.0824 . 0180 .0838 . 1 0 82 . 1248 . ,.04 . 1560 . 1718 REPLICATE (CUMULATIVE AREA m2 ) Table 17 . Composite list of benthic invertebrate species for the Myakka River collected by cores, bucket dredge, trawl and qualitative salt marsh samp lings for fall 1985. The term "dead" under dredge indicates only shell remains and no live spec imen s were found. Benthic Salt Core Dredge Trawl Marsh PLATYHELMINTHES Turbe 11 ari a Euplana gracilis x Polycladida sp. x NEMERTINA Nemertina spp. x NEMATODA Nematoda spp. x BRYOZOA Bryozoa spp . x BRACH WPODA Glottidia pyramidata x ANNELIDA Polychaeta Orbiniidae Leitoscoloplos spp . x Paraonidae Aricidea philbinae x Aricidea taylor; x Sp;onidae APoprionosrio pygmaea x Boccardiel a spp. x Carazz;e11a hobsonae x parasr;onospio pinnata x Poly ora 1i g ; x Streblospio benedicti x Poecilochoetidae Poecilochaetus johnsoni x Chaetopteridae Spiochaetopterus costarum oculatus x Cirratulidae C;rratulidae spp. x Capitellidae Mediomastus ambiseta x Maldanidae Table 17. continued. Benthic Salt Core Oredge Trawl Marsh Maldanidae spp . x Phyllodocidae Phyllodocidae sp. x Eumida sanguinea x Phfllodoce arenae x Siga ionidae Sigalionidae spp. x Hesionidae Gyptis brevipalpa x P;1 argidae Ancistrosyl1is jones; x Sigambra bassi x Sigambra tentaculata X Syll idae Exogone dispar X Nereidae Laeonereis culver; X Neanthes succinea X Glyceridae Glycera americana X Goniadidae Glycinde solitaria X Nephtyidae Nephtys picta X Onuphidae Diopatra cuprea X Lumbrineridae X ¥:~~~~ verrillsp. i X ae Pectinaria gouldi; X Ampharetidae Amphicte;s gunner; X MeT inna maculata X 01 igochaeta Naididae Piguetiella michiganiensis X Tubificidae Unid. Tubificidae w/o cap. chaetae X Limnodriloides sp. X Limnodrilu s hoffmei ster; X Tubificoides brownae X Hirudinea Table 17 . continued. Benthic Salt Core Dredge Trawl Marsh Pisicolidae Pisicolidae spp . x MOLLUSCA Pelecypoda Mactridae Rangia cuneata x x x Mulinea laterali s x x Tell inidae Tellina sp. A' x Te 1li na texana x Macorna tenta x x Solecurticrae- Tagelus plebius x x Dreissenidae MttilOPSi S leucophaeata x x Cor ul idae Corbicula manilensis x Polymesoda caroliniana x x x My til idae Amygdalum papyrium x x Ishadium recurvum dead x leptonidae Mysella planulata x Semelidae Abra aegualis x lasaeidae Lasaeidae sp. x Arcidae Anadara sp. x dead Anadara transversa x Cyrenoldidae CarenOida floridana dead Car 1idae Dinocardium r. vanhyngii x laevicardium marten; x x Solenidae Ensis minor x Mactridae Mactra fragil ; s x Trati idae Asthenothaerus hemphilli x Ostreidae Crassostrea virginica x x x Gastropoda

- Table 17. continued . Benthic Salt Core Dredge Trawl Marsh Hydrobiidae Hydrobiidae sp. x x x Acteocinidae Acteocina canaliculata x x Nassariidae Nassarius vibex x x Vitrinell idae Vitrinella helicoidea x Vitrinellidae sp. x Naticidae Polinices dUhlicatus x Natica maroc iensis x x Sinum maculatum x pyramidel 1idae Turbonilla conradi x Turbonilla dalli x Turbonilla interrupta x Turbonilla sp. x Odostomia semi nuda x Odostemia sp . x dead Columbellidae Mitre"a lunata x x Caecidae Caecum 9Ulchellum x Crepidul i ae cre~idula plana x x x Cerit i idae Diastoma varium x x Haminoeidae Haminoea succinea x Turridae Turridae sp. dead Kurtzie"a sp . dead Epitoni idae Epitonium lamellosum x Melongenidae Melongena corona x x Neritidae Nerit; na sp. dead Neritina reclivata x x Acteonidae Acteon 9unctostriatus dead Littarin; ae Littorina irrorata x Table 17. continued. Benthic Salt Core Dredge Trawl Marsh ARTHROPODA Crustacea Ostracoda Parasterope pollex x Podocopa spp. x Copepoda Calanoida spp. x Clclo~oida spp. x Cirripedia Balanus improvisus x x x Balanus sp. x Mysidacea Bowmaniella sp. x x Cumacea Alm racuma sp. x (yet aspis sp. A* x Tanaidacea Hargeria rapax x Isopoda Edotea tril oba x Ericnsonel'a crenulata x Euceramus praelongus x Janira sp. x Mesanthura pancidens x Mesanthura pulchra x x Sphaeroma terebrans x Xenanthura brevi tel son x Amphipoda Acuminodeutosus nagle; x Am~elisca ab ita x x Am~elisca holmesi x x Ampelisca sp. B x Ampelisca sp. C x Batea cf. catharinensis x CorophTUm lacustre x coroshium lou;s;anum x Cyma usa campta x Dulichia appendiculata x Gammarus tigrinus x x Ganvnaridae sp. x Grandidierella bonnieroides x x listriel" d. barnard; x [lsianopsis alba x Mel ita sp. x T.ble 17. continued. Benthic S.lt Core Dredge Trawl Marsh Podocerus cf. brasil iensis x Oecapoda Alpheus heterochaelis x Al~heus norman; x Am idexter symmetricus x Cal1inectes sapidus x Libinia dubia x Paleomonetes ~ x Pagurus carolinensis x Pagurus longicarpus x Penaeus duorarum x Persephona mediterranea x Pinnix. cf. 1unzi x Pinnixa sp . x x Pinnixa pearse; x Portunus gibbesii x Rithropano~eus harrisi; x x x Upogebi •• finis x X.nthid.e sp. x In secta Diptera Chaeoboridae Chaoborus punctipenni s x Ch; ronomi dae Chironomus spp. x Coelot.nypus spp . x crfptochironomus spp. x Po ypedilum spp. x T.nyt.rsus spp. x ECHINODERMATA Stelleroide. Asteroidea Micropholis graci11 ima x UROCHORDATA Branchiostoma spp . x TOTAL COUNTS: 111 46 23 10 TOTAL UNIQUE TO METHOD: gO IB 15 3 TOTAL TAXA ALL METHODS: 156 *Letters refer to taxa as yet undescribed or of uncertain taxon om i c status housed in MML's invertebrate collection. Table 19. The most abundant taxa (based on total faunal counts) for five benthic stations on the Myakka River for September 1985 . In cases where taxa are represented by equal numbers of individuals, all are listed. Percentage Composition by Station Taxon B7 BI9 B27 B40 B53 Nematoda spp. 14.3 2.1 2.2 13 .0 Laeonere i s culveri (P) 13.2 3.6 Limnodrilus hoffmeister; (0) 13.2 Polypedilum spp . (In) 11.0 3.6 Rangia cuneata (B) 9.8 Mesanthura pulchra (I) 2.2 67.7 14 .4 3.4 Lumbrineris verrilli (P) 2.2 7.1 2.1 Aricidea taylori (p) 3.6 Aricidea philbinae (P) 3.6 Piquetiella michiganensis (0) 3.6 Hargeria rapax (T) 3.6 0.1 Nemertina s 3.6 2.1 2.8 0.2 1.1 41.2 6.5 5.2 Uri4t~t~~~(B) (B) 4.1 capil liform chaete (0) 4.1 0.2 Streblospio benedicti (P) 26.4 Acteoci na canal i culata (G) 9.0 0.1 Ampelisca abdita (A) 1.1 6.5 0.7 Amphicteis gunner; (P) 2.1 5.6 Parapr i onosp io innata (P) 13.5 Parasterope pollex Os) 2.1 12.1 Ampelisca holmesi (A) 1.1 1.0 4.5 11.5 Cyclaspis sp. A (C) 10.9 TOTALS: 69.2 100.0 80.5 67.0 62.2

A = Amphipoda B '" Bivalvia C '" Cumacean G • Gastropoda In = In sect a I = Isopoda o = Oligochaeta Os '" Ostracoda P = Polychaeta T '" Tanaidacea Table 21. Quantitative distribution of molluscan taxa at five benthic stations on the Myakka River for September 1985.

Taxon 87 819 827 840 853 Total Rangia cuneata 9 9 Hydrobiidae I 2 2 5 Tell ina texana 2 8 II 21 Tagelus plebius I 2 I 4 MftiloPSiS -eucaQfiaeata 4 4 Polymesoda caroliniana 5 5 Acteocina canaliculata 32 2 34 Amtgda lum QaQ~r;um 14 9 23 Nassarius vibex I 4 5 Vitrinelliaae-ip. juv. 2 2 Tellina sp. juv. 15 10 25 Macorna tenta 9 9 Mlsel'a planulata 22 22 Natica marochiensis 7 7 Turboni1'a conradi 5 5 Abra aequalis I I Mul inia lateralis 12 12 Lasaeidae sp. 5 5 Odostomia sp. II II Vitrinel1a helicoidea 5 5 Mitrella lunata 9 9 Turbonilla dalli I I Odostomia semi nuda 2 2 Caecum Qulchellum 9 9 Crepidula plana 3 3 Turbonil,. sp. 2 2 Anadara sp. I I Turbonill a interrupta I I Diastoma vari urn 2 2

TOTAL TAXA 2 I 5 7 24 29 TOTAL INDIVIDUALS 10 I 15 73 145 244 x # Ind./Taxon 5 I 3 10 6 8 Std . Deviation S 5.7 1.4 11.2 5.1 8.5 Table 23. Quantitative distribution of crustacean taxa at five benthic stations on the Myakka River for September 1985.

--Taxon B7 BI9 B27 B40 B53 --Total spp.(O) 3 I I I 6 2 33 14 14 61 I 25 12 38 I I 16 187 205 I I

I I 40 23 65

I I I 2 3 2 2 (0) 2 197 199 I I I 2 3 I 6 2 9 I 9 2 12 3 3 2 2

I I I I

I I I I sp. A(C) 177 177

I) 10 10 5 5 4 4 2 2

I I B(A) I I C(A) I I Table 23 . Continued.

--Taxo n B7 BI9 B27 B40 B53 Total Dulichia a~~enai c ulata(A) I I Lxsiano~sis alba(A) I I Mesantfiura ~auciaens(l) I I Pagurus carolinensis(D) I I

TOTAL TAXA 7 3 10 14 19 32 TOTAL INDIVIDUALS 10 35 64 105 608 820 x # Ind ./ Taxa I 12 6 8 32 26 Std. Deviation S 0.8 18.4 12.5 8.6 69 .1 57.3 A - Amphipoda Ci - Cirrepidia Cu - Cumacea 0 - Oecapoda I - Isopoda M - Mysidacea 0 - Ostracoda Table 24. Quantitative distribution of polychaeta and oligochaeta (0) at five benthic stations on the Myakka River for September 1985.

Taxon B7 B19 B27 B40 B53 Total

Laeonereis cu1ver; 12 1 13 Limnodrilus hoffmeisteri (0) 12 12 Unid. Tubifididae cap. chaetae(O) 11 4 3 18 amb; seta 2 51 53 spp . 1 1 2 2 4 1 1 1 2 3 (0) 1 1 2 20 22 2 2 94 94 15 52 67 11 5 16 2 2 1 1 c. 1 62 63 219 219 solitaria 16 16 10 10

9 9 7 7 5 5 5 5 3 3

3 3 2 2 'dae spp . 2 2 Maldanidae spp . 2 2 Sagambra tentacul ata 2 2 Eumida sanguinea 1 1 Exogone di spar 1 1 Gyptis brevipalpa 1 1 Table 24. Continued.

Taxon B7 Tot al -- BI9 B27 B40 B53 -- Leitoscolog:los spp. I I Limnodriloides sp.(O) I I Nephtys Pi§ta I I phyl1odoci ae 'p. I I Poecilochaetus jOhnson; I I Sigalionidae spp. I I Sigam6ra bassi I I TOTAL TAXA 5 5 4 7 29 40 TOTAL INDIVIDUALS 38 6 10 144 420 668 x # Ind ./Taxon 8 I 3 21 16 17 Std. Deviation S 5.6 0.4 1.0 33 .2 42 .3 38.9 Table 25. Descriptive community parameters for five benthic infaunal stations on the MY~kka River, sampled by diver core (7 replicates, total area .1092m ) during September 1985 .

Shannon- Species Faunal Weaver Equi tabil ity Richness DenSi~y Di versity Pielou's Sta . S #/m H' J'

B7 23 833 2.62 0.83 BI9 9 247 !.17 0.56 B27 25 888 2.33 0. 72 B40 32 3260 2.64 0.78 B53 86 14890 3.00 0.67