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COMPOSITION AJ\JD DISTRIBLITION OF

EPIFAUNA ON PROP ROOTS OF RHIZOPHORA MANGLE L. IN LAKE SURPRISE, FLORIDA

by Gary L. Nickelsen

A Thesis Submitted to the Faculty of the College of Science lll Partial Fulfillment of the Requirements for the Degree of

~~ster of Science

Florida Atlantic University Boca Raton, Florida December 1976 (0 Copyright by Gary L. Nickelsen 1976

11 CO~WOSITION AND DISTRIBUTION OF EPIFAUNA ON PROP ROOTS OF RI-IIZOPHORA MANGLE L. IN LAKE SlffiPRISE, FLORIDA

by Gary L. Nickelsen

This thesis was prepared under the direction of the candidate's thesis advisor, Dr. G. Alex Marsh, and has been approved by the members of his supervisory committee. It was submitted to the faculty of the College of Science and was accepted in partial fulfillment of the requirements for the degree of Master of Science.

SUPERVISORY COMMITfEE: ~~Jttw~ / - · J~~ ·/( . /// c~( ~ ~H ~ t_____., I t/ Sk~ ··m~:

Dean, College of Science /97t

111 AC KNO\VLEDGB [ENTS

I wish to express my appreciation to Dr. c;. Al ex Iarsh for his

assistance in this study and his thorough revie~v of the manuscript . Drs.

Ralph ~1. Adams and Sheldon Dobkin are also thanked for their review and

criticism of the manuscript. I also \vish to thank Dr. Joseph L. Simon

and Mr. Ernest D. Estevez of the University of South Florida for their

genuine interest and invaluable assistance in the initial development

of t his study.

Dr . Manley L. Boss, who initiated several stimulating discussions

of my work and offered advice and encouragement throughout this study,

is gratefully acknowledged . I would also like to thank Dr. Robert B.

Grinun for assistance in identification of algae, and Dr . Tin1othy S.

Cotton and Ms. Carol Jones for designing the computer programs us.ed in

this study.

I am indebted to Mr. Bruce R. Johnson for his honest criticism of

the manuscript, and to Mr . Richard E. \Valesky for his valuable opinions and for permission to use his unpublished data . I also thank ~lessrs .

Gary A. Pettit and Larry Brown for their assistance 1n the field , and

Don and Debra Burgess and Daniel Bell for their aiel 111 constructing the

figures used in the manuscript. Credit for the development of the Com munity Fullness index is shared with Mr. Gary S. Kleppe 1 of Fordham

University.

A special thanks goes to ~lr . John Golden for his encouragement and friendship throughout this study.

lV Most of all I wish to thank my wife Susan who assisted in the field, typed the manuscript, and contributed to this thesis in many other ways. Her love, patience, and w1derstanding have been unfailing throughout this study.

v ABSTRACT

Author: Gary L. Nickelsen Title: Composition and Distribution of Epifauna on Prop Roots of Rhizophora mangle L. in Lake Surprise, Flonda Institution: Florida Atlantic University

Degree: ~~ster of Science

Year: 1976

The invertebrate epifauna associated with prop roots of a single strand of the red mm1grove, Rhizophora mangle L., in Lake Surprise, Florida was sampled in !v~y and November, 1975. A total of 108 species was collected. Dominant species included the amphipods Elasmopus pocillirnanus and

Erichthonius brasiliensis, the polychaetes Syllis ~· and Vermiliopsis bermudensis, and the tanaidacean Apseudes propinquus. Fringe roots hosted greater numbers of species and individuals and a greater abundance of sponges and epiphytes thm1 roots 1n the interior of the strand. The root connnuni ty was characterized by three assemblages. The algae-amphipod-tanaidacean assemblage was prominent on fringe roots . The sponge- polychaete assemblage (excluding serpulids) was represented well in both areas, but \vas more prominent at the fringe. The bare root-serpulid as-

) sernblage dominated much of the interior. Overall mean qiversi ty (H 5 m1d equitability (E) were 2.60 and 0.65 respectively. Faunal density was 13,200 ind/rn2 of root surface.

Vl TABLE OF CONTENTS

ACKNO\VLEDGE!v!ENTS lV

ABSTRACT ... Vl LIST OF TABLES viii

LIST OF FIGURES lX

INTRODUCTION . . 1

HI\TERIALS AND METHODS 4

Description of Study Area 4 Sampling Stations . . . . 4 Physico-Chemical Sampling Procedure 6 Biotic Sampling Procedure 7

RESULTS 9 Physico-Chemical Conditions 9 Community Composition . 11 Horizontal and Vertical Distribution 23 Seasonal Variation 26 Diversity 32 DISCUSSION . . . 37 Epiphytes 37 Sessile Fauna 39 Motile Fauna 42 Connnuni ty Structure 48 TI1e Prop Root Counnunity as an Indicator of Environmental Conditions 54 SUM01ARY 59 LITERI\TURE CITED 62 ADDITIONAL REFERENCES USED FOR IDENTIFICATION OF SPECIES 67

Vll LIST OF TABLES

1. Light intensity readings 15 em below the surface. Readings given in lux for each station are means of 4-7 trials . 12 2. Ranking by abundance of all non-colonial epifaunal species collected in this study. Percent and cumulative percent composition, total number of root sections on \-vhich each species occurs (#Sect.), mean density (individuals/m2), and Biological Index (BI) are listed for each species 13

3. Ranking by Biological Index (BI) values of dominant non colonial epifaunal species collected in this study. A Amphipod, P = Polychaete, T = Tanaidacean, 1-1 = 1-Iolothurian 21 4.. Ranking by surface area of all sponges attached to mangrove roots collected in this study. Displacement vollUl1e 1s also given for each species ...... 22 5. Ranking by Biological Index (BI) of dominant species at fringe and interior areas for May and November collections. A= Amphipod, P = Polychaete, T = Tanaidacean, 1-1 = 1-Iolothurian 25

6. Summary of Community Fullness values for May and November collections. Subtotals represent contributions of indicated taxa to "fullness" of conunw1ity ...... 35

Vlll LIST OF FIGURES

1. 111ap of area showing collecting site (X) and stations (A-F in top insert) in Lake Surprise ...... 5 2. Approximately bi-weekly surface salinities at Lake Surprise and total monthly rainfall at Royal Pa1Jn Station, Ever- glades Na tional Park, April 1975-December 1975 10

3. Distribution and abundance of major non-colonial taxa on fringe mangrove roots. A = Amphipods, P = Polychaetes, T = Tanaidaceans, I Isopods, G = Gastropods, 0 =All Others ...... 27 4. Distribution and abundance of major non-colonial taxa on interior mangrove roots. A = Amphipods, P = Polychaetes, T = Tanaidaceans, I Isopods , G = Gastropods, 0 = All Others ...... 28 5. Distribution and abundance of sponges and epiphytic algae on fringe mangrove roots ...... 29

6. Distribution and abw1dance of sponges and epiphytic algae on interior mangrove roots 30 7. Abundance of polychaetes (including serpulids) in relation to sponge surface area on mangrove root sections with in significant (> .5 ml displacement volLUTie) algal cover. Solid line is estimated line of best fit . . . . . 44 8. Abundance of amphipods in relation to algal 2olume on mangrove root sections with insignificant (> .5 em) sponge cover. Solid line is estimated line of best fit ..... 46

9. Species frequency curve for mangrove prop root community in Lake Surprise ...... 55

LX INfRODUCf ION

' The mangrove commw1ity 1s a major tropical ecosystem. According to McGill (1958) the many species of mangroves dominate nearly 75% of the world's shoreline between 25°N and 25°S latitude. In south Florida, three species of mangroves (Rhizophora mangle, Avicennia germinans and Lagw1cularia racemosa) occupy 700 square miles along the coasts. The red mangrove (Rhizophora mangle L.) typically dominates the intertidal zone of protected areas and plays a vital role in the ecology of estuarine areas (Heald et al. , 197 4) . "-Jhe widespread occurrence of tropical mangrove communities has stimulated many studies of the trees themselves and of the flora and fauna associated with them. Davis (1940) discussed the role of mangroves in accwrrulating sediments and building land areas. Davis also gave a general accow1t of the ecology of several mangrove co1nmunities in Florida. Other studies include an investigation of the structure and Inetabolism of the red mangrove (Galley et al., 1962); the zonation of Indo-West Pacific (Jvtacnae, 1967, 1968) and South African (Macnae, 1963) mangroves and their associated flora and fauna; and the zonation of the epibenthic and infauna living on and in the mud in mangrove swamps (Wal sh, 1967;

Rutzler, 1969; Sasek.unar, 1974). Odum (1970) and Odum and Heald (1972)

1 described the complex tropic structure of an entire mangrove community and Heald and Odum (1970) discussed the importance of mangrove ecosystems to sport and commercial fisheries.

1 2

One aspect of mangrove ecology that has received relatively little attention is the often diverse and abundant epibiota associated with

prop roots of ~· mangle. Burkholder and Almodovar (1973) investigated quantitatively the distribution and productivity of marine algae attached to the prop roots of red mangroves in Puerto Rico, and Rehrn (1974) studied

qualitatively the distribution and ecology of marine epiphytes on ~· mangle from Tampa to Key Largo, Florida. Many other studies of the mangrove community have made reference to the epifatma, but detailed in-

vestigations of the ecology of anDnals living on red mangrove roots are

generally lacking. ~~ttox (1949) studied the ecology of the mangrove osyter Ostrea rhizophorae in Puerto Rico, and Robertson (1959) described the molluscan fauna of mm1groves in the Bahamas. The only comprehensive studies that have exrunined community structure and distribution of prop root epifauna and the ecological factors governing these communities are those of Kolehmainen (1973) and Kolehmainen et al. (1974) in Puerto Rico. Descriptions of faunal dis

tribution were restricted primarily to the phylum level m these studies. Species diversity was indicated merely by numbers of species present. , The importance of red mangroves to various fisheries has been

well docwnented (Idyll et al., 1968; Odum, 1970; Heald and Odum, 1970; Odum and Heald, 1972; Heald et al., 1974). Leaves, as they decompose

after falling into the \vater, form the foundation of a detritus food chain. They become protein enriched \vi th coatings of bacteria and fungi

! and are ingested by detritivores. The consumers of leaf material then become prey for larger animals occupying food webs that may include commercially important shrimp and grunefish occurring in the mangrove estuary. 3

Idyll (1965) pointed out the value of mangrove estuaries as nursery grounds for the pink shrimp Penaeus duoranm1, and Heald and Odum (1970) listed ten species of gamefish known to be dependent on mangrove estu aries during some part of their lives. .. Since red mangroves inhabit such a large portion of tropical coastlines and are an important contributor to various sport and com mercial fisheries, a full understanding of their ecology is essential. Because the organisms living on the prop roots of red mangroves are more sensitive to pollution and changes in the environment than the trees themselves (Kolehmainen, 1973), this epifaunal co~nunity may prove to be a useful indicator of environmental stress in the mangrove ecosystem. Providing baseline information on species composition and patterns of diversity of this root epifauna is necessary to discern the effects of abnormal perturbations in the environment. The intent of this study is to provide quantitative information on the epifauna associated with the prop roots of a single strand of the red mangrove, Rhizophora mangle, in Lake Su1~rise, Florida. Species com position, distribution, and seasonal changes in the fauna will be inves tigated, as well as the roles of dominant species in the structure of this important community. MATERIALS AND MET! !ODS

Description of Study Area Lake Surprise, located on the west side of Key Largo, Florida (25°ll'N; 80°23'\1) was chosen as the study site (Fig. 1). Lake Surprise is a semi-enclosed, shallow hypersaline lagoon approxlinately 2.1 km long and 1.2 km wide and is bisected by U. S. Highway 1. The lake shoreline i s bordered by red mangroves of the type described by Davis (1940) as a ''f-'lature Rhizophora Consocies" and by Teas (1976) as a Coastal Band conrrnunity. The mud bottom of the lake slopes gently to a maxlinum depth of 2m and is dominated by extensive growths of turtle grass, Thalassia testudinum, and occasional large patches of Acetabularia crenulata. Studies were conducted in a strand of trees on the northwest shore

of the lake, approxlinately 150 m from U. S. Highway l. Sea water enters this portion of Lake Surprise through a single channel connected to Blackwater Sound. No significant tidal variation was fow1d in Lake Sur prise by this author, nor has any been observed by previous workers (Chesher, 1974). Due to the restricted flow of water and the protection afforded by the mangroves that surround the lake, conditions are generally calm, and salinities remain high throughout the year.

Sampling Stations Prellininary observations revealed obvious differences in the abun dance and composition of epifaw1a and epiflora between the most seaward

4 5

Luk.· Surp ri M~

Barnes Sound

1 N Blackwater Sound ~

KILOMETERS

0 l 2

••• .... 0

Fig . 1. ~ l ap of area showing collecting site (X) m1d stations (A-F in top insert) in Lake Surprise. 6 roots and those located more centrally in the strand. In order to sam ple the different faunal assemblages, three s~Jling stations were estab lished on each of two bottom contour lines in a peninsular strand of trees (Fig . 1). The mangrove peninsula extends approximately 15 rn into the water and is 10 m wide at the base, narrowing to 5 rn at its seaward edge. Stations were established at the 30 em and 100 ern depth contours and marked with string. Stations were located 2-3 m apart on both sides of the peninsula and at the tip of the strand on each contour.

Physico-Chemical Sampling Procedure Water samples were collected 15 em below the surface for labora tory analysis of salinity (Mohr titration), turbidity (Hach turbidimeter, f.lodel 2100), and dissolved oxygen (Winkler titration) on 10 May and 12 f.1ay 1975 and on 22 November 1975. Light intensity readings were taken

15 on beneath the surface at each station with a General Electric Expo sure Meter (Type PR-1) sealed in a plastic bag. Readings were later converted to lux by calibration with a Weston Model 756 Slll1light Illumi nation Meter. Surface water temperatures were recorded with a stem thermometer. Additionally, the daily fluctuation of dissolved oxygen concen trations was investigated at Station C on 21 June 1975 and 22 November 1975. Early morning, noon, and late afternoon water samples were fixed at the collection site with Winkler reagents and transferred to the lab oratory for analysis. Surface salinity was recorded approximately every two weeks be tween 10 !vlay 1975 and 22 November 1975. 7

Biotic Sampling Procedure Four roots were selected at each station for faunal studies. In order to collect those species living primarily on epiphytic algae or sponges, care was taken to include both of these major sessile groups on the roots collected at each station. Although root diameter did not seem to greatly influence the amount of attached growth, an attempt was made to collect roots of similar diameters to facilitate comparisons of faunal density. Before removal, roots were marked into 10 em vertical sections beginning 10 em above the water line and continuing to the bottom of the root. Due to the angle of some roots, not all sections were the same length. Roots penetrating the substrate were first clipped at the bottom with large pruning clippers. Sections were then clipped off one at a time after first being enclosed in a nylon cloth collecting bag approximately 10 em in diameter and 20 em deep with 0.3 mn nylon mesh net- ting (Nitex No. 308) sewn into the bottom. Visual inspection revealed little or no loss of root material or fauna with this sampling technique. Root sections were later placed in appropriately labeled jars and filled with 7-10% sea water-formalin stained lightly with rose bengal.

~laterial remaining in the collecting bags was rinsed into the sample Jars. In the laboratory each root section was scraped of all material. Sponge surfaces in contact with the substrate (either the root itself or

I other sponges) \vere traced on aluminum foil. This foil was cut out and weighed and compared to a knovm area of foil for conversion to surface area (to the nearest 0.1 cm2). The clean root section was \vrapped in 8

foil and its surface area calculated in a similar manner to the nearest

0.1 cm 2. The material scraped from the roots Has rinsed into a 0.5 mm

s1eve. All animals retained in the sieve were placed m plastic vials according to major taxa and preserved in 8% fonnalin. These animals were later identified to species whenever possible and counted.

An estimate of sponge volLUlle for each root section was determined by placing each species in a graduated cylinder filled with water and measuring the displacement to the nearest ml. Algal volLUlle was meas ured in the same manner, but no distinction was made as to species. In stead, a total algal volume for each section was recorded. Data were analyzed with the aid of a Univac 1106 computer. RESULTS

Physico-Chemical Conditions Salinities in Lake Surprise ranged from 43.9 o/oo to 51.9 o/oo during the study period. Highest values were recorded prior to the on set of the rainy season, and dropped to 43.9 o/oo a few days after the first significant rains in May (Fig. 2). High evaporation rates con tributed to a general rise in salinities during the summer months, coun teracting the diluting effects of rainfall. Periods of reduced salinity occurred after a time lag of approximately one month following periods of heavy rainfall due to the accumulation of fresh water from land runoff. Since bi-weekly water samples were collected at various times of day and under a variety of weather conditions, temperature data \vere not gathered at these times. However, Rehm (1974) reported yearly high sur face water temperatures in Lake Surprise of 32°C and 33°C in August of 1971 and 1972 respectively, and a yearly low of 23°C in January 1972. Mean turbidity values recorded on the sampling dates ranged from

19.7 to 0.4 Jackson Turbidity Units (JTU). Highest values were recorded in May on a moderately \vindy day, and lowest values occurred in November on an extremely calm day. These values indicate the variable turbidity encountered in Lake Surprise. Dissolved oxygen concentrations also varied with 1local weather conditions. Cloud cover appeared to have an important influence. Early morning, noon, and late afternoon dissolved oxygen values were 3.89,

9 10

II• 12 52 II I I I I I I I I I I I I I I I I 11 I I 51 I I I I I I I I I I I I I I IO I I I I I I 50 I I I I I I I I I I 9 I I I I I I I I I I 49 I I I I 8 0 I I -. I I 0 I I ·~ ...... I Hainfall = I I 0 ~ I 48 7 ~ I I ~ I ~ I - ~ I < I I ~ I ~ I 6 I z z .n I ~ ~ I I I ~ I < I I 5 ~ < I (f) I I 4-6 I I I I I ·t. I I I I \ I Salinity ·t-5 I I I 3 I I I I I I I 2 H I I I I I I I I I I I I I I I I ' ' 1 I ' ' I ' ' I ' ', I I I I D

Fig . 2. Approximately bi-weekly surface salinities at Lake Surprise and total monthly rainfall at Royal Palm Station, Evergl ades National Park, April 1975-December 1975. ll

4.64, and 3.68 mg/1, respectively, on an overcast day in June (minimum saturation= 65%) and were considerably higher at 9.80, 13.69, and 17.49 mg/1 on a clear day in November (minimwn saturation= 146%). Light intensity values 15 em below the surface at each station are presented in Table 1. Values are given in lux and percent of the value recorded at the station receiving the most light. Interior stations D, E, and F were heavily shaded by the mangrove canopy, and light intensity averaged approximately 60% of that at the partially shaded fringe stations. On overcast days the differences between interior and exterior stations were less pronounced than on clear days. Although water chemistry varied with local weather conditions, values of each parameter recorded at each sampling period were nearly identical throughout the mangrove strand, indicating thorough mixing of the water .

Con~unity Composition A total of 40,200 non-colonial invertebrates representing 92 species was collected from approximately 2.9 m2 of root surface examined during this study. Overall faunal density was 13,200 ind/m2 of root surface. Crustaceans comprised 57% of the total fauna and 26% of the species (amphipods, 48 % of fauna and 14 % of species; isopods, 2% and 10%; tanaidaceans, 7% and 2%). Polychaetes were the second most abundant group and comprised 37% of the fauna and 38 % of the species . The total nwnber of individuals in each species of epifauna collected js given in ! Table 2 along with percent and cumulative percent composition, total number of root sections on which each species occurred, mean density on occupied root sections, and Biological lndex (BI) value (Sanders, 1960). 12

TABLE 1.--Light intensity readings 15 em below the surface. Readings given in lux for each station are means of 4-7 trials.

STATION

A B c D E F

May

lux 1345 1345 1280 1184 1119 1227

% max* 100.0 100.0 95.2 87.8 83.2 91.2

November

lux 888 2905 1775 689 775 646

% max 30.6 100.0 61.1 23.7 26.7 22.2

mean lux** 1117 2125 1528 937 947 937

% max 52.6 100.0 71.9 44.1 44.6 44.1

* Percent of the value (lux) recorded at the station receiving the most light. ** Mean of combined f,lay and November values. TABLE 2. --Ranking by abundance of all non-colonial epifaunal species collected in this study. Percent and cumulative percent composition, total nun1ber of root sections on which each species occurs (# Sect. ), mean density (individuals/m2), and Biological Index (BI) are listed for each species.

0, Rank 'o Cumul . Individuals/ By No . Species Individuals Fauna % # Sect. m2 BI

1 Erichthonius brasiliensis 9153 22 . 77 22.77 208 2871 . 80 626 2 Elasmopus pocillimanus 5355 13 . 32 36.09 255 1841.42 750

3 Filograna implexa 3940 9. 80 45 . 89 96 3964 . 71 243

4 Melita appendiculata 3271 8.14 54.03 111 1726 . 64 187

~ 5 Branchiosyllis occulata 3057 7.60 61 . 63 151 1586 .10 307 lN

6 Sy11is ~ · 2692 6. 70 68 . 33 245 1006 . 73 540

7 Apseudes propinquus 2200 5. 47 73 . 80 218 1043.46 401 8 Vermiliopsis bermudensis 1788 4.45 78 . 25 167 1286 . 65 364

9 Sy11is gracilis 1533 3. 81 82 . 06 203 882 . 93 312 10 Synaptula hydriformis 712 1.77 83.83 153 480 . 77 204

11 Syllis l?_rolifera 697 1. 73 85.56 169 416.80 113

12 Cymadusa compta 586 1. 46 87 . 02 128 530.52 102

13 Bagatus stylodactylus 573 1.43 88 . 45 121 556 . 81 169 TABLE 2.--Continued

Rank % Cumul. Individuals/ By No. Species Individuals Fauna % # Sect. m2 BI

14 Leptochelia savignyi 530 1. 32 89.77 145 405.02 147 15 Lysidice ninetta 452 1.12 90 . 89 22 532.85 93 16 Gitanopsis tortugae 428 1.06 91.95 104 373.73 64

17 Hyale ~ · 401 1. 00 92.95 78 480 .13 172 18 Amphiura stimpsoni 284 . 71 93.66 68 293 . 45 19

f-.' 19 Cerithiopsis emersoni 276 .69 94.35 22 7 51.15 34 .j:>. 20 Syllis cornuta 226 .56 94.91 94 266.80 83 21 Unknown Anemone 221 .55 95.46 35 792 .10 36 22 Excorallana tricornis 210 .52 95.98 51 460.45 10

23 Leucothoe spinicarpa 185 .46 96.44 34 395.80 17 24 Mi tre lla argus 126 .31 96.75 61 188.40 15

25 Spirorbis knightjonesi 122 .30 97.05 10 923.17 29 26 Tubulanus pellucidus ll4 .28 97.33 70 154.33 15 27 Syllis spongicola 113 .28 97.61 47 236.70 4 TABLE 2.--Continued

Rank % ClTITlul. Indivi~uals By No. Species Individuals Fauna % # Sect. rn BI

28 Loirnia medusa 110 .27 97.88 43 207.43 14 29 Harninoea elegans 105 .26 98.14 56 227.37 23

30 Exogone dispar 78 .19 98.33 47 178.03 42

31 Ceratonereis rnirabilis 63 .16 98.49 36 177.10 26 32 Arnphipholis squamata 48 .12 98.61 29 150.20 3

I-' 33 Bu11a striata 41 .10 98.71 19 201.35 4 (J1 34 Hydroides dianthus 40 .10 98.81 30 118.13 2 35 Unknown Simple Ascidian 37 .09 98.90 27 122.57 3

36 Dorvi11ea rubra 33 .08 98.98 31 111.50 10 37 Lysianopsis alba 30 .07 99.05 23 158.20 13

38 Paracerceis caudata 26 .06 99.11 19 141.40 2

39 1\laera ~· 23 .06 99.17 10 206.85 0 Unknown Polyclad Turbe11arian 23 .06 99.23 14 147.30 1

41 Hypsicornus circlTITlspiciens 21 .05 99.28 12 167.90 12 TABLE 2.--Continued

Rank % Cumul. Indivi~uals/ By No. Species Individuals Fauna % # Sect. m BI

42 Autolytus prolifer 16 .04 99.32 9 205.40 2

43 Excora1lana sexticornis 15 .04 99.36 8 171.80 0

Eunice- antennata 15 .04 99.40 11 123.33 3 Cypridina squamosa 15 .04 99 . 44 12 131 . 70 0 46 Branchidontes exustus 14 .03 99.47 13 98.92 3

1-' 47 Luconacia incerta 12 .03 99.50 7 139.40 4 0\ Platynereis dumerilii 12 .03 99.53 10 204.58 10

49 Limnoria platycauda 11 .03 99.56 5 292.25 1

Lumbrineris inflata 11 .03 99.59 3 549.70 0

Marginel1a lavalleeana 11 .03 99.62 7 153.33 0

52 Syll~s ferrugina 9 .02 99.64 9 108.30 0

Odontosyllis ~· 9 .02 99.66 9 86.43 0 54 Paracaprella tenuis 7 .02 99.68 6 125.53 0

55 Corophium tuberculatum 6 .01 99.69 6 117.65 2 TABLE 2.--Continued

Rank % CliDlul. Individuals/ By No. Species Individuals Fauna % # Sect. m2 BI

Callipaliene brevirostrum 6 . 01 99.70 3 257.50 2 Modulus modulus 6 . 01 99 .71 6 118.70 0 58 Erichsonella attenuata 5 . 01 99.72 5 118.00 1 Dodecaceria corallii 5 . 01 99.73 5 102.03 1 t'-1arphysa sanguinea 5 . 01 99.74 5 102.40 0

I-' Cirriformia ~ · 5 . 01 99 . 75 4 153.35 3 ---.] CollUTlbella rusticoides 5 .01 99.76 5 120.70 3 Ischnochiton papillosus 5 .01 99.77 5 87.50 4

Thais rustica 5 . 01 99.78 3 137. 30 0 4 168.70 0 Thais- haemastoma cana1iculata 5 .01 99.79 66 Sphaeroma quadridentatlUTl 4 .01 99.80 2 228.40 9

t-1esanthura ~· 4 .01 99. 81 4 114.80 0 Branchiomma nigromaculata 4 .01 99.82 4 105.10 0 Pista palmata 4 .01 99.83 4 86 . 65 0 TABLE 2.--Continued

Rank % Cumul. Indivi~uals/ By No. Species Individuals Fauna % # Sect. m BI

Fabricia ~· 4 . 01 99.84 4 106.70 0 Achelia sawayai 4 .01 99 .85 3 133.20 0

Gr~1ulina ovuliformis 4 . 01 99 .86 4 184.80 0

73 Grandidierella bonnieroides 3 . 01 99 .87 3 103.55 1 Lumbrineris tenuis 3 .01 99.88 2 203.40 0

f-' Oreaster reticulatus 3 .01 99.89 3 80.95 0 00 Diastoma varium 3 . 01 99 . 90 3 133.90 0

77 Samythella sp. 2 .01 99 . 91 1 115.50 0 Unknown Harpacticoid Copepod 2 .01 99.92 2 160.60 2 Anoplodactylus pectinus 2 .01 99.93 2 163.80 1 Amph1ura fibulata 2 .01 99.94 1 185.20 0 Cerithium muscarum 2 . 01 99.95 2 133.55 0 Chthamalus fragilis 2 . 01 99.96 1 167.50 0

83 Ligia ~· 1 99.97 1 98 .50 5 TABLE 2.--Continued

Rank % Clllllul . Individuals/ By No. Species Individuals Fauna % It Sect. m2 BI

Annandia maculata 1 1 130.40 0

Thelepus setosus 1 1 88.10 0

Nereis aclllllinata 1 99 .98 1 111.00 0

Fabricia sabella 1 1 140.60 3

Odontosyllis eno~ 1 1 159.00 0 1--' Bunodeopsis globulifera 1 99.99 1 76.50 0 \.0

Geukensia demissa l 1 49.10 0

Crepidul a fornicata 1 1 121.40 1

Thais haemastoma floridana 1 100.00 1 159.00 0 20

The Biological Index is useful in detennining dominance and is based on the abundance of each species in a series of samples. The most abundant species on each root section was awarded 5 points, the second most abun

dant species 4 points, and so forth to 1 point for the fifth most abun dant species. Points were totaled for each species for all 334 root

sections with the maximumpossible points being 1310.

The 10 dominant species are ranked m Table 3 by their BI values. Amphipods and polychaetes accounted for most of the dominant species. The arnphipod Elasmopus pocillimanus was the most frequently encountered

species, occurring on 76% of the root sections, and the amphipod Erichthonius brasiliensis Has the most abundant species with 9,153 indi viduals collected. Both species were fow1d in relatively high numbers where algae was abundant. The serpulid polychaetes Vermiliopsis ben11udensis and Filograna implexa predominated on bare root surfaces 1vhere they were found in extremely high densities. The polychaetes Syllis sp. and Syllis gracilis were found in greatest numbers on sections v.;ith abundant sponge growth. Branchiosyllis occulata, although occurring in

high nwnbers, was limited primarDy to root sections hosting the sponge

Chondrilla nucula and was encow1tered on only 45 % of the root sections. The only dominant species other than runphipods or polychaetes were the tanaidacean Apseudes propinquus and the holothurian Synaptula hydrifonnis. Both species were collected primarily from epiphytic algae. Colonial species are not included in Tables 2 and 3 but were, nevertheless, important members of the epifaunal comrnun fty. Dominant sponges, based on surface area (Table 4), were Chondrilla nucula, Lissodendoryx isodictyalis, and Halicomites stellata. The bryozoan 21

TABLE 3.--Rm1king by Biological Index (BI) values of dominm1t non colonial epifaw1al species collected in this study. A = Amphipod, P = Polychaete, T = Tanaidacem1, H = J-lolothurim1.

Rm1k Species BI

1 Elasmopus pocillirnm1us (A) 740 2 Erichthonius brasiliensis (A) 626

3 Syllis ~· (P) 540

4 Apseudes propinquus (T) 401

5 Venniliopsis bermudensis (P) 364 6 Syllis gracilis (P) 312

7 Brm1chiosyllis occulata (P) 307

8 Filogrm1a implexa (P) 243

9 Synaptula hydrifonnis (H) 204 10 1'-lelita appendiculata (A) 187 22

TABLE 4.--Ranking by surface area of all sponges attached to mangrove roots collected in this study. Displacement voltu11e is also given for each species.

Surfacelrea Volume Rank Species em rnl

1 Chondrilla nucula 2569.2 1494 2 Lissodendoryx isodictyalis 1586.3 969 3 Halicomites stellata 1349.8 83 4 Dysidea fragilis 596.7 109 5 Leucosolenia canariensis 465.2 128 6 Haliclona pennollis 272.7 119 7 Geodia gibberosa 211.3 440

8 Halisarca purpura (?) 172.3 26

9 Haliclona canaliculata (?) 66.2 12

10 Axine11a 2£· 26.1 10 11 Tethya diplodenm 5.7 5

12 Halichondria melanadocia (?) 2.5 1 23

Arnathia vidovici and the componnd ascidian Perophora viridis were abnn- dant and often fonnd partially overgrown by sponges. An W1identified colonial anemone and an tmidentified hydroid were also collected, but were rare. Dominant epiphytes included Ceramium sp., Chondria sp., and Jania capillacea 1vhich were abW1dant on roots fringing the mangrove peninsula, but poorly represented in the interior. Polysiphonia subtilissima and Bostrychia binderi dominated in the interior, but were not nearly as abW1dant as fringe epiphytes.

Horizontal and Vertical Distribution In order to group similar stations, comparisons were made of the falffial similarity between all possible station pairs for each collecting period. Similarity values were obtained by Sanders' (1960) index of af- finity (S), which is the sum of the lmvest percent composition of all species present in two samples, and by Sorensen's (1948) index (K):

K = ~ X 100 ab A+B where Kab similarity of samples a and b A mnnber of species 111 sample a

B number of spec1es ln sample b c mnnber of species common to both samples Both _indices showed relatively high similarities among fringe stations A, B, and C and among interior stations D, E, andJ. !>'lean values for the fringe stations were S = 53.7, K = 80.2; for interior stations, S = 68.1, K = 71.1. .t-1ean values between fringe and interior stations were lower (S = 42.9, K = 64.0). Therefore, stations A, B, and C (fringe) 24

and stations D, E, ffi1d F (interior) were grouped, based primarily on the above values of faunal similarity. The two station groups were also differentiated on the basis of greater relative ablmdances of sponges and epiphytes at the fringe. The two station groups differed notably in the nwnber of individuals and species. More than 34,000 individuals were collected from the fringe compared to less than 6,000 from the interior. The number of non-colonial species were 88 and 60 respectively at the two sites. Although the greater abundances found at the fringe were due in part to

a greater root surface area sampled (approximately 2 t~1es that of the interior), faw1al density within fringe stations was approximately 3 times that Hithin interior stations. Therefore, other factors such as the amount of food and shelter provided by sponges and algae were probably influential.

The 5 dominant species (ranked by BI) are listed in Table 5 for each station group and season. Amphipods more clearly dominated the fringe while polychaetes predominated in the interior. The preponderance of serpulids in the interior was due to the proportionately greater amow1t of bare root surface there than at the fringe. The amphipod Elasmopus pocillimanus, the tanaidacean Apseudes propinquus, and the polychaetes Syllis sp. and Vermiliopsis bennudensis were the only species found among the dominants at both station groups. The amphipods Erichthonius brasiliensis and Melita appendiculata, most often fow1d where algae were

I abundant, dominated at the fringe, but occurred in small numbers in the interior. The polychaete BrffiKhiosyllis occulata had a similar distribution and was fo\.md with the sponge Chondrilla nucula, which was abw1dant TABLE 5.--Ranking by Biological Index (BI) of dominant species at fringe and interior areas for May and November collections. A = Amphipod, P = Polychaete, T = Tanaidacean, H = Holothurian.

MAY FRINGE MAY INTERIOR

Rank Species BI Rank Species BI

1 Erichthonius brasiliensis (A) 348 1 Vermiliopsis bermudensis (P) 102 2 Elasmopus pocillimanus (A) 331 2 Apseudes propinquus (T) 91 3 Syllis sp. (P) 220 3 Elasmopus pocillimanus (A) 83 4 Apseudes-propinquus (T) 153 4 Syllis gracilis (P) 71 5 Vermiliopsis bermudensis (P) 134 5 Hyale sp. (A) 52 N (Jl NOVEMBER FRINGE NO\TEJ\1BER INTERIOR

Rank Species BI Rank Species BI

1 Elasmopus pocillimanus (A) 289 1 Filograna implexa (P) 73 2 Erichthonius brasil1ensis (A) 260 2 Syllis ~· ----cP} 71 3 Svllis ~· (P) 208 3 Synaptula hydriformis (H) 66 4 Branchiosyllis occulata (P) 181 4 Syllis gracilis (P) 58 5 Melita appendiculata (A) 147 5 Vermiliopsis bermudensis (P) 56 5 Hyale ~· (A) 56 26

only at the fringe. The amphipod Hyale ~.,which iru1abited the upper most region of the water column at both areas, was a dominmlt species

m the interior where a much greater proportion of the root length was 1n shallow water.

Sponges showed a marked difference in abundance bet1veen the fringe and interior. Total sponge surface area equivalent to 31% of the avail able root area was recorded for the fringe stations compared to 12% for the interior stations , and total sponge volwne at the fringe was nearly

10 times that in the interior. Epiphytes were also more abundant at the fringe 1vi th a total volLDlle nearly 6 times that of the interior. Vertical sections were tested for faunal similarity in the same manner as horizontal zones in order to distinguish any zonation patterns. No distinct groupings of sections could be discerned, however, except that the root section above the surface harbored few organisms and was distinct from all other root sections . Some vertical trends in faunal abundance were obvious though. The greatest number of individuals and non-colonial species at the fringe 1vas located near the middle of the roots and decreased toward the surface and bottom (Fig. 3). In the in terior, the bottom 20 em of the roots were the most densely populated (Fig. 4). The same trends also held true for colonial species and epi phytes (Fig. 5, 6).

Seasonal Variation

Several changes 1n the composition and structure1 of the root com munity were evident . The total mnnber of individuals from f\lay to Novem ber increased from 15,000 to 25 ,000 1vhile the total nwnber of non-colonial species decreased from 77 to 67 . Those species showing the most striking I I I I (surface) I I I I , ------!------,------r------,------r------

> <{ ~

E u :r: 1- a.... w 0 ------,------~------N ---J

> 0 z

100

1 500 1000 500 0 500 1 000 1 500 SOD 0 500 250 0 250 250 0 250 250 0 250 250 0 250 A p T G 0 ABUNDANCE OF MAJOR TAXA

Fig . 3. Distribution and abundance of major non-colonial taxa on fringe mangrove roots. A= Amphipods, P = Polychaetes, T = Tanaidaceans, I = Isopods, G = Gastropods, 0 =All Others. I I I (surface) I ------l~------;------!------1 I > < ~

E 30 u :r: I C... L.U (surface)

0 ------·------~------1 - --·------N I co I I > 0 z

250 0 250 750 500 250 0 250 500 750 250 0 250 250 0 250 250 0 250 250 0 250 A P T I G 0 ABUNDANCE OF MAJOR TAXA

Fig . 4. Distribution and abundance of major non-colonial t axa on interior mangrove roots. A= Amphipods P = Polychaetes , T = Tanaidaceans, I = Isopods, G = Gastropods, 0 =All Others . 29

(surface ) ------

J: 1- a.. w 0

> 0 z

100

400 200 0 200 400 50 25 0 25 50 SPONGE (e m")

ABUNDANCE OF SPONGE AND ALGAE

Fig. 5. Distribution and abundance of sponges and epiphytic algae on fringe mangrove roots. 30

(surface)

E u 30 0 I 1- a.... w C) - ~~-~~!~~-:~------

> 0 z

200 1 00 0 1 00 200 25 0 25 SPONGE (em' )

ABUNDANCE OF SPONGE AND ALGAE

Fig . 6. Distribution and abundance of sponges and epiphytic algae on interior mangrove roots. 31 seasonal fluctuations were the amphipods Elasrnopus pocillirnanus and Melita appendiculata, the polychaetes Branchiosyllis occulata and Filograna irnplexa, and the holothurim1 Synaptula hydriforrnis. Of the 92 species collected, 52 were folllld in both May and Novern- ber, 25 in May only, and 15 in November only. Thus, more than 40% of the species were seasonal or became so sparsely distributed at certain times that they were not included in collections. From May to November there was a decrease in the nwnber of species from 72 to 63 at the fringe, but an increase from 42 to 49 in the inte- nor. There was no evidence of seasonal migrations of species from the fringe to the interior, however. Both areas showed approxjmately a two- fold increase in individuals from May to November, from 13,452 to 21,423 at the fringe and from 1,752 to 3,573 in the interior. Sponge surface area m1d volume, and algal volume also increased from May to November . Total sponge area increased 72% 1vhile sponge vohnne increased 51%, with greater total gains (but smaller percent gains) at the fringe. Epiphytic algae increased 75% in volume between seasons, but gains were restricted to the fringe . Interior stations maintajned a nearly constant low algal volwne. Seasonal changes in dominant species were evident at both station groups (Table 5). Elasmopus pocillimanus increased in abundance and occurred on more root sections in November than in May, andre- placed Erichthonius brasiliensis as the dominant fringe species .

I Branchiosyllis occulata and ~1elita appendiculata also increased in abundance in November and replaced Apseudes propinquus and Venniliopsis bermudensis as the 4th and 5th dominant fringe species. Filograna 32

implexa, Syllis ~.,and Synaptula hydriformis becwne the top three dominants in the interior in November, while Elasmopus pocillimanus and Apseudes propinquus declined to 7th and 13th respectively.

Diversity A common method used in describing comn1unity structure involves the use of species diversity indices. A widely used index of species diversity which is relatively sample-size independent is the infonnation

function (Shannon and l\'eaver, 1963):

s L.: P·1 ln P1· i=l diversity of a swnple s total number of species p. 1 proportion of individuals of the total san1ple that belongs to the ith species.

Hs is influenced by both the mnnber of species and the evenness of distri bution of individuals wnong the species . A means of determining the equitability (evenness) component of diversity is provided by the index

of Pielou (1966):

where E equitability of sample Shannon-Weaver index for srunp le s total number of species in srunple At Lake Surprise, the mean overall diversity and equitability of the two station groups for both collections was 2.60 and 0.65 respectively.

Diversity and equitability varied only slightly bet\veen the fringe and 33

interior and between sample periods. Diversity values for the fringe

in May and November were 2.57 and 2.53, respectively, and were 2.59 and

2. 73 for the interior. Equitability values in f\'lay and November were 0.60 and 0.61 for the fringe, and 0.69 and 0.70 for the interior. Higher

species numbers at the fringe were accompanied by greater dominance of

a few species, and diversity values remained slightly lower than the

more evenly distributed interior.

As noted previously, the index of Shannon and Weaver is sensitive

to the number of species and the relative distribution of individuals

among them. It is insensitive to fmmal density, however. Thus, two

communities having the same number of species and proportions of indi-

viduals, but differing by a factor of 100 in the number of individuals

in each species, would be considered identical on the basis of the Shannon-Weaver index. Yet, the impact of the more "dense" conrrnw1i ty on the environment \·JOuld be greater and intra- and interspecific interac-

tions would occur much more frequently. The more "dense" con11Tiw1i ty

\·JOuld also place greater demands on the inrrnediate environment in tenns

of energy and nutrient requirements.

To further characterize communities beyond that possible by Hs alone, the following index of Commw1j ty Fullness is proposed: s CF I [ ln(ni + ni/N) + (ln[ni + N/S]) (5 +SlnS) i=l

\vhere CF "fullness" of the conllTiunity

S total number of species

ni number of individuals belonging to the ith species

N total nwnber of indivjduals . 34

This index is sensitive to the number of species (species richness), evenness of distribution (equitability), and the abundance of each species . The species richness component of the index is determined by (ln[ni + N/S]) (S +SlnS), and the abundance and equitability component

is detennined by ln (ni + ni/N). Providing the number of species does not decrease, an increase in the nwnber of individuals to any species always increases the "fullness" of the community (an increase 1n an abundant species often results in greater dominance and a decrease in Hs)· The addition of individuals to rare species increases the evenness of the community and is reflected 1n a greater increase in CF than that caused by adding individuals to abundant species. Finally, the addition of ne\V species to the conrrnuni t y, representing new pathways of nutrient and energy transfer, increases the community fullness by the greatest

amount. CF values range from l. 39 for a "co1m1uni ty" of one individual, to infinity for a community with an infinite number of species and individuals.

If sampling techniques are identical, CF values obtained from collections differing in the amount of area sampled can be compared by dividing each value by the appropriate area to obtain a CF value/unit area. To be representative of the total coJnn1w1ity, sample size (number of individuals) should be such that a species accwnulation curve (Sanders,

1960) has leveled off.

CF values were used m the present study to determine the contri-

f butions of major taxa to community fullness and are presented in Table 6. Polychaetes were clearly the most influencial contributors to community fullness in both ~1ay and November, accounting for 37% and 42% of 35

TABLE 6.- -Swnmary of CornmW1ity fullness values for ~ la y and November collections . Subtotals represent contributions of indicated ta.xa to "fullness" of coi1UnW1ity.

MAY

AbW1dance and Species Equitability Richness Taxon Component Component Subtotal Value/m2

Amphipoda 53 . 36 81.83 135.19 93.88 Polychaeta 87.17 169.02 256 .19 177.91

Tanaidacea 12.05 13.71 25 . 76 17.89

Isopoda 21.12 51.51 72 .63 50.44 Gastropoda 17 .11 57 . 32 74 .43 51.69

Other 35.03 86 . 05 121.08 84.08

Total 225.83 459.44 685.27 475.89

NOVEMBER

AbW1dance and Species Equitability Richness 2 Taxon Component Component Subtotal Value/m

Amphipoda 47 . 00 66.41 113.41 77.15 Polychaeta 93.59 187.33 280.92 191.10 Tanaidacea 12.99 ] 4. 86 27.85 18 . 94

Isopoda 12.81 20.03 32.84 22 . 34 Gastropoda 22.28 76 . 06 98.34 66.90 Other 31.95 83.81 115.76 78.75

Total 220 . 62 448 . 50 669 .12 455.18 36 the total CF value respectively. Amphipods were the second most prominent group (disregarding the artificial "other" group) with 20% and 17% of the total value in the tHo collections. Gastropods followed Hith 11% and 15 %, isopods Hith 11 % and 5%, and tanaidaceans with 4% and

~ 4 0 • Polychaetes and gastropods showed obvious gains from ~1ay to Novem- ber in their partial CF values, while all other groups except tanaidaceans experienced losses . Tanaidaceans, represented by tHo species, showed a very slight increase betHeen seasons.

The total CF value changed only a small amount from 477.89/m2 in

~1ay to 455 .18/m2 m November. A reduction in the species richness component from 459.44 to 448.50 reflected a decrease of 10 species. A slight decline in the abundance and equitability component from 225.83 to 220.62 resulted from an overall increase in dominance which offset gains in faunal abundance. DISCUSSION

' Red mangrove prop roots provide a stable substrate that is colo nized by a variety of marine organisms preslmmbly in the manner of typ ical fouling corrnnunities. Many studies of fouling communities have re vealed that bacteria and other microorganisms initially colonize the fouling substrate, followed by sessile macroinvertebrates (Zobell and Allan, 1935; Scheer, 1945; Wood, 1950). As the sessile fauna develops, it provides a source of food and shelter for many motile invertebrates (McDougall, 1943; Rodriguez, 1959; Kolehmainen, 1973). Generally, the more complex the sessile fauna becomes, the richer and more abundant 1s the associated motile fauna (Poore, 1968). In areas where tides and wave action are minimal, submerged mangrove roots usually support an abundant sessile and motile fauna (Kolehmainen, 1973) and a rich variety of epiphytes (Rehm, 1974). The calm conditions in Lake Surprise are ideal for such development. Sponges and epiphytes, the dominant sessile forms in Lake Surprjse, played a major role in detennining the abundance and distribution of the motile fauna found on the mangrove roots, and the factors governing the distribution of these sessile groups were in strumental in determining the structure of the entire root connnuni ty.

g>ipht_te~ Rehm (1974) studied epiphytes on red mangrove prop roots 1n Lake Surprise and distinguished between a sun community, characterized by those species on fringe roots, and a shade community, inc1uding those

37 38

species on highly shaded roots . Sun species had a greater overall abundance thm1 shade species. Similar trends were noted in this study. Differences between the fringe a.'1d interior in the total volume of epiphytes can be partially attributed to the different morphologies of species adapted to each of these habitats. Fringe species are larger than interior species and have a more extensive thallus network. Fringe species may extend 20 ern or more from the root, whereas interior species, having relatively short thalli, rarely extend more than a few centime- ters from the root. Interior epiphytes occur higher on the root than fringe epiphytes, possibly as a result of the reduced amount of light in the interior. Well-illuminated algae are known to be more productive and achieve a greater standing crop than shaded algae (Rehm, 1974; lleald et al., 1974). The more voluminous fringe epiphytes are also better competitors for substrate space than are the interior epiphytes since they are better able to limit the settlement of potentially competitive spores and larvae by sweeping the adjacent root surface 1vhen water movement IS sufficient. This effect has been suggested for fucoids (Lewis, 1968). Interior epiphytes are less successful than fringe species in competing 1vi th sessile invertebrates, and pressure from sponges, their chief competitors, may cause these epiphytes to extend higher on the interior roots. Interior epiphytes can conq)ete successfully 1vi th sponges but apparently only where the epiphytic grmvth is very dense. Fringe and interior epiphytes differ widely in their influence

l on the epifauna. Fringe epiphytes provide a greater surface area from which epifauna can feed, m1d differ from interior epiphytes in their ability to trap suspended matter. The larger fringe species are more 39

efficient in slowing the movement of the surroW1ding water, causing larger suspended particles to settle and become trapped in the thallus network. Because of the shelter and a ready supply of detritus for food and building material provided by the fringe algae, many epifaW1al spe cies are attracted to this habitat. Nagle (1968) showed that in sea grass communities, the greater the abundance of epiphytes, the 1nore de tritus that was trapped, and the more abundant were tube-building am phipods. The same relationship was evident at Lake Surprise where the tube-building amphipod Erichthonius brasiliensis was abundant only on the fringe algae.

Sessile FaW1a

Sponges were the most prominent faunal group living on the prop roots in Lake Surprise. They were clearly the most successful of the sessile invertebrates and were the single most important faunal group

in determining the structure of the entire root commw1ity. Sponges cover bare root surfaces that, because of a lack of shelter, are unin habitable by most motile invertebrates. Sponges thereby provide habit able space on their own surfaces or within their tissues. The variety and nLunber of invertebrates living on or 1n sponge tissue is sometimes quite high (Pearse, 1932, 1950; Long, 1968; Dauer, 1973). Sponges on prop roots are commonly encrusting and tend to overgrow, and to be over grmm, by other encrusting sponges, often forming large growths of sev eral species in many layers. Since most sponges are efficient filter feeders and are capable of bringing large quantities of particulate matter to their surfaces, a buildup of detritus can occur in the many crevices around the sponges, attracting many motile org(lllisms who use 40

detritus as a source of food, tube-building material, or protective cover.

An encrusting, rather than erect , sponge form is probably an ad-

aptation for existence on vertical surfaces. Kitching~! al. (1934) discovered that encrusting sponges flourished on vertical substrates but were much less abundant, and sometimes absent, from nearby horizontal surfaces. Since sponges generally do not grow well where they are sub-

jected to heavy sedimentation (De Laubenfels, 1947; Konnecker, 1973), it is likely that an encrusting form on vertical surfaces is advanta- geous 1vhere silt accwnulation may be a problem. Protruding outgrowths from vertical ?Urfaces would easily collect a thick layer of silt , whereas a thin encrustation growing close to the substrate would not.

In very calm conditions, a heavy build-up of silt could prove detrimen- tal to some sponges .

Sponges are excellent competitors and are known to overgrow and smother other sessile invertebrates (McDougall, 1943; Edmondson, 1944; De Laubenfels, 1950). While barnacles and serpulid polychaetes observed in the present study were often overgrown and apparently killed by sponges, there was no evidence of any damage to sponges overgrown by other sponges. It has been suggested that in cases where several sponge species coexist in a llinited space, cooperation between species, rather than competition, may occur (Sara, 1970). Cooperation occurs mainly in the fonn of reductions of microclimate fluctuations and possible modifi- I cations of the physico-chemical characteristics of the surrolmding water. In Lake Surprise, thin encrusting sponges may shield underlying sponges from large sediment particles while allowing water and small food 41 particles to pass through their tissues . The horizontal and vertical distribution of sponges throughout the mangrove strand in Lake Surprise was not uniform. Fringe roots \vere longer than interior roots and had a greater total root surface available for sponge attachment . In addition, fringe roots had a much greater proportion of their length in water deep enough to be suitable for sponge growth. Near the middle of the root, where sponges were most abundant, the effects of exposure due to wave action, dilution at the surface during rains, and heavy silting from resuspended bottom sediments are at a m1n1mum. Interior roots, reaching only 30 em below the surface, are more exposed by occasional high wave action, and support a less abundant sponge fauna . The middle portion of fringe roots also represents the oldest portion of the roots in terms of length of time available for colonization. As described by Kolehmainen (1973), the root tip gro1vs downward, \vhile the whole root gradually sinks due to the weight of attached foulers . The result is that the top and bottom portions of the root are the last to occupy the water colurrm, initial sponge colonization on these portions lS delayed, and sponges are less abundant than in the middle of the root. The sponges found in this study are not unique to the mangrove habitat . Chondrilla nucula is often abundant on pilings (Hechtel, 1965), as is Haliclona pennollis (Poore, 1968). Lissodendoryx isodictyalis, which has been characterized by Hartman (1958) as a typical fouling

~ sponge, is also common on pilings and other substrates (De Laubenfels,

1947). Dysidea fragilis has been recorded on mangrove roots elsewhere in the tropics and is also found on turtle grass, Thalassia testudinum 42

(Hechtel , 1965) and on rocks in a variety of habitats (Konnecker, 1973). ivlost of the sponges at Lake Surprise are widely distributed through the tropics, although Lissodendoryx isodictyalis and Dysidea fragilis also extend into temperate regions (Hechtel, 1965). The tubes of serpulid polychaetes occupied a much smaller portion of the roots than did sponges but often occurred in high numbers. These species occurred primarily near the surface where the largest amount of bare root surface occurred. Competitive pressure from sponges that are capable of overgrowing the wonns is absent from the highest part of the roots. The greatest proportion of sponge-free root space occurred in

the shallmv interior, \vhich accow1ts for the dominance of Venniliopsis bermudensis and Filograna implexa there. Two other serpulids, Hydroides dianthus and Spirorbis knightj onesi, occurred in lmv numbers. Of the remaining sessile forms , Amathia vidovici, a stoloniferous bryozoan, and Perophora viridis, a compound ascidian, were frequently found overgrown by sponges and algae, and \vere probably preyed upon by many invertebrates. Other sessile invertebrates, represented by nine spe cies, occurred in such small numbers as to be relatively insignificant.

Motile Fauna The diverse and abw1dant microhabitats provided by epiphytes and sponges on the prop roots \vere occupied by many motile forms. TI1e great est n1.ID1ber of species, represented primarily by polychaetes, \vere asso ciated with sponges. faunal density, on the other hand \vas highest among the epiphytes, which were inhabited by a large mnnber of crustaceans. The body form of polychaetcs makes them well suited for life among the small crevices and openings created by sponges, rather than 43 on algae lvhere special appendages are sometimes necessary for attachment. The m_unerical relationship between polychaetes and sponges is illustrated in Fig. 7. A positive correlation exists between sponge surface area and abundance of polychaetes. The correlation is not as clear between sponge volume and polychaete abundance, indicating that most polychaetes largely prefer the surface of sponges rather than the interior. However, large numbers of Syllis spongicola and Lysidice ninetta were found within the tissues of Lissodendory:x: isodictyalis and

Haliclona permollis. Dauer (1973) found a positive relationship between sponge surface area and the number of associated polychaete species in the Gulf of Mexico. Dauer suggested that polychaete diversity was influenced by the shape of the sponge, which determined how much sediment could accwnulate and hmv much area was provided for refuge. In Lake Surprise, root sections with the greatest mrrnber of sponge species also had the greatest number of polychaete species, apparently due to a large number of Inicrohabitats. The distribution of polychaetes closely followed that of sponges. Excluding the serpulids, which were not associated with sponges, most polychaete species were present near the middle of the fringe roots and near the bottom of the interior roots where sponge diversity was greatest. Errant polychaetes of the genus Syllis \vere the most frequently encoLmtered species associated ~vi th sponges. All of these identified species collected have 1vide distributions and in many cases are cosrno

j politan. Members of this genus are not exclusively sponge dwellers, but are able to take advantage of the detritus-filled crevice habitats provided by sponges. Branchiosyllis occulata was the most numerous errant tJ) 300 UJ 1- UJ <( I 250 u I / 0

....J>- 0 200 I - / 0 a.. LL 0 0::: 150 UJ ., / ..,. cc I n +:> ~ ::::> 100-1 0 0 z oO 0 / 0

20 40 60 80 100 120 140 160 180

2 SPONGE AREA (CM )

Fig. 7. Abundance of polychaetes (including serpulids) in rel at ion to sponge surface ar ea on mangrove root sections wit h insignificant ( < . 5 rnl displacement volume) algal cover. Solid line is estimated line of best fit~ 45 polychaete and has been reported to live in the internal canals of sponges (Dauer, 1973). Branchiosyllis did not frequently occur inside sponges in Lake Surprise but was most often collected on the surface of Chondrilla nucula. Quite often these polychaetes made grooves on the surface of the sponge, and Chondrilla ~vas rarely collected without at least a few individuals of Branchiosyllis present. The sur face of Chondrilla may provide Branchiosyllis refuge from predators. Other sponges are apparently incapable of overgrmving the smooth surface of Chondrilla, and no crevices are available for polychaetes or other spe- Cles lvhich might prey on Branchiosyllis . Some isopods and amphipods inhabit the internal spaces of sponges. The amphipod Leucothoe spinicarpa is a conunon inhabitant of sponges

(Pearse, 1932; Jones, 1948) and in this study was particularly abw1- dant in the sponge Lissodendoryx isodictya1is. Fox and Bynum (1975) fow1d the same association in a North Carolina estuary . Lissodendoryx in Lake Surprise also hosted the isopod Excorallana tricornis. Paracerceis caudata, which occurred at Lake Surprise, has been reported to live on the surface and in the canals of sponges (Pearse, 1932) but may also be abundant where sponges are poorly represented (tv1arsh, 1973). It could not be determined if Paracerceis was associated with sponges in this study. Most crustaceans observed in this study lived among the epiphytes rather than among sponges. The abundance of amphipods , the dominant

I crustacean group, showed a positive correlation 1v ith the abw1dance of algae (Fig . 8) . Nagle (1968) found the same relationship between amphipods and epiphytes of eelgr;:tss. 1000 I 0 0 0

(J) / 0 0 I 0 800 0.. I 0 :c- 0.. ~ <( 600 -I 0 L.L. 0 I / 0 ~ UJ c:a 0 0 ~ 400 ~ / Q\ ~ :::> z

200

I - 0 / 0

4 8 12 16 20 24 28 32 36

3 VOLUME OF ALGAE (CM )

Fig. 8. Abundance of amphipods in relation to algal volume on mangrove root sections with insignificant ( < . 5 cm2) sponge cover. Solid line is estimated line of best fit. 47

Although sampling techniques in the present study generally pre cluded the detennination of exact locations of crustaceans on epiphytes, a zonation of species, detennined primarily by patterns of detritus dep osition, may exist within the algal 1nasses. Many crustaceans use detri tus as food or building material and achieve their greatest abundance near the base of epiphytes where the greatest amount of detritus accu mulates (Nagle, 1968). The tube-building amphipod Erichthonius brasiliensis, for example, was particularly abundant near the base of prop root epiphytes in Lake Surprise. Cymadusa compta, primarily a detritivore, has also been reported to inhabit the base of epiphytes on eelgrass (Nagle, 1968). Conversely, species that primarily eat diatoms occur near the outward edges of epiphytes where the slight accwnulation of detritus does not hinder diatom growth. The preference of the tanaidacean, Leptochelia savignyi, for the edge of eelgrass has been partially attributed to this fact (Nagle, 1968). The choice of substrate by other crustaceans found in this study 1s largely Lmknown. Elasmopus pocillimanus, a presumed detritivore, did not appear to be selective 1n its choice of habitat since it was fow1d in large nwnbers among both algae and sponges. Other abundant species such as the tanaidacean Apseudes propinquus, the isopod Bagatus stylodactylus, and the amphipod r-.lelita appeadiculata were clearly phytal species, but their locations within the algal masses are unknown. ~lelita was not completely restricted to algae but Has also fow1d in small num bers among sponges. Feeley and Wass (1971) found~· appendiculata on sponges 1n Chesapeake Bay but did not indicate that it >vas found on algae.

Conversely, Fox and Bynum (1975) reported this spec1es to be common on 48 algae in a North Carolina estuary but did not indicate that it occurred on sponges. In view of the much greater abundance of Melita on algae than on sponges in Lake Surprise it is apparent that, when given a choice, this species prefers an algal habitat. The small holothurian Synaptula hydrifonnis is also a known associate of algae (Deichmann, 1954) and is probably able to hold on to algae by means of tiny spicules embedded in its integument. Synaptula had no evident preference for a particular type of alga and occurred in approximately equal densities at the fringe and interior of the study area. Synaptula appeared higher on the list of dominants in the interior due to the absence of great numbers of amphipods. The relationships between many of the motile and sessile organisms on prop roots appear to be mutualistic. Nagle (1968) demonstrated that epiphytes realize a greater productivity when cleaned of detritus by associated epifauna. Detritivores, meanwhile, obviously benefit from food and shelter provided by the algae. The same relationship is as sumed for sponges and their epifaw1a. Crustaceans clean the surfaces of sponges (Long, 1968), and many polychaetes probably do like\vise, thereby preventing the oscules of sponges from clogging. At the ·same time, sponges accumulate detritus and provide food and shelter for epi faunal associates. The entire relationship between the motile and ses sile faw1a may be viewed as an adaptation for survival at the conununity kvel.

Co~nunity Structure The prop root conununity can be characterized as having three faunal assemblages, consisting of the sponge-polychaete assemblage, 49 consisting of the sponge-polychaete assemblage (excluding serpulids), the algae-arnphipod-tanaidacean assemblage, and the bare root-serpulid assemblage. The three major sessile groups (sponges, epiphytes, and serpulids) were in direct competition for space on the roots. Serpulids are capable of relatively fast growth (Edmondson and Ingram, 1939) and soon dominate the portions of the root available for colonization. Many epiphytes also rapidly colonize available substrates (Tomlinson, 1972). The slower growing sponges, however, are much better competitors and eventually overgrow serpulids (McDougall, 1943; De Laubenfels, 1947). Epiphytes, when moderately dense, are able to withstand the competitive pressure exerted by sponges and are not overgrown (Pyefinch, 1950) . Sponges, however, cover the root surfaces and surround the epiphytes. \\fhen the epiphytes die, sponges completely cover the area, preventing any growth of new ephiphytes . A balance between sponges, serpulids, and epiphytes is probably maintained as old sponges die and fall off the roots or are torn off by stonns, and the newly exposed root surface is recolonized by epiphytes, serpulids, and other sessile invertebrates . The increase in epiphytes at the fringe stations between the two sampling periods appears to be the result of seasonal growth. Rehm (1974) indicated that Jania capillacea and other fringe species die back during the stmuner and are most abtmdant in the winter and spring. Humm (1964) reported sig11ificant seasonal varjations in the abundance of epiphytes in Biscayne Bay. Sponges appear to be less affected by seasons ! in the tropics, although some species may grow faster in the calm, less turbid conditions of the swnmer months due to an increase in pumping rate (Reiswig, 1973). The sponge assemblage, therefore, is more stable 50

temporally than the epiphyte assemblage and is characterized by a less dramatic change in seasonal abundances of polychaetes and other associated motile fauna.

Comparisons of faunal similarity with other prop root communities are hindered by a general lack of information. The only comparable list of species is provided by Kolehmainen (1973). Similarity between Lake

Surprise and Jobos Bay, Puerto Rico prop root fauna is low (K = 8.81), with only 10 species in common. The fauna in Jobos Bay lS comprised primarily of decapod crustaceans and ascidians, whereas at Lake Surprise the fauna consists mainly of amphipods and polychaetes. In contrast to the low similarity with Jobos Bay is the relatively high similarity be- tv;een the prop root and turtle grass epifauna in Lake Surprise (K = 35 .1). Of 160 species collected from the two habitats, 34 were con@on to both (R . Walesky, unpublished data). Thus, it appears that a distinct prop root epifauna may not exist . Instead, prop roots may be colonized by invertebrates that are attracted to a variety of substrates. Further conclusions, however, must await additional research. Envirorunental factors are influential in determining communi ty composition and structure. The calm conditions and insignificant tidal flux at Lake Surprise have already been mentioned in this respect. In addition, salinity and temperature probably play major roles in deter- mmmg species composition of the prop root corTll11unity. The high salinity of Lake Surprise undoubtedly restricts the presence of many species, but the rapid drop in salinity in May may be more important! ln determin- mg species composition. Sinmons (1957) found the rapidity of salinity

change in the hypersaline Laguna ~ J adre to have a greater effect on the 51 fanna than actual high salinity values. Goodbody (1961) recorded mass mortality of mangrove root invertebrates in Jamaica following heavy rains and subsequent reductions in salinity of 15 o/oo and more. Re ductions in salinity were not as extreme 1n Lake Surprise and dropped only 8 o/oo following the .t'-1ay rains, but this rapid reduction in salin ity may have been partially responsible for the 13% decrease in motile species between May and November.

High summer temperatures in Lake Surprise may also have been re sponsible for the reduction in species. Thorhaug et al. (1973), in a study of thermal pollution in Biscayne Bay, predicted a SO% reduction in macrobenthic invertebrate species resulting from a temperature in crease from 26°C to 33°C. Kolehmainen {1973) detennined that tempera tures of 35°C or more were limiting to the mangrove root epifanna in Puerto Rico. The maximum temperature of 33°C reported for Lake Surprise

(Rehm, 1974) may not be.high enough or of long enough duration to se verely affect the root epifauna, but a few species may not have been able to tolerate this relatively high temperature and therefore did not occur during the warmest months. A synergistic effect of salinity and temper ature may limit the occurrence of some species as suggested for the

Lagnna Jvladre by Simmons (1957). No other studies on prop root conunnnities give density data for comparison, but s1nce prop roots m many locations often harbor few or ganisms (Kolehmainen, 1973), the density of the motile fauna at Lake Surprise, at 13,200 ind/m2 of root surface, 1s probably' relatively high.

It is difficult to determine density per meter of bottom due to varia tions in the number of roots occupying any given area. A rough estimate 52 for the mangrove zone of Lake Surprise, taking into consideration differences in the density of fringe and interior roots, is 5,000 to 20,000 ind/rn2 of level bottom. Other epifaunal connnunities for which density values are known include Thalassia beds in Lake Surprise, which hosted approximately 470 ind/m2 of grass surface and approximately 4,900 ind/rn2 of level bottom

(R. Walesky, unpublished data). Mean density for epifauna of Zostera in the York River, Virginia, calculated from Marsh (1973), was approxi mately 9,000 ind/m2 of level bottom, with a maximum density of nearly

25,000 ind/n1 2 of level bottom. Nagle (1968) found generally similar values (9,000-37,000 ind/m2 of level bottom) for Zostera at Cape Cod. ]\lean values for a northen1 Florida Juncus marsh, \vhich included some in fawlal species, were 540 and 381 ind/m2 of level bottom (Subrahmanyam et al., 1976}. Thus, density of the prop root epifauna appears to be equivalent to or greater than that of several other epifaw1al connnunities. Where the prop root epifauna is well developed, it makes a major contribution to the overall productivity of the mangrove ecosystem. The high density values per root surface area in Lake Surprise can be attributed to root length, 1vhich typically is greater than sea grass, and the abundance of food <:md shelter provided by sponges and epiphytes. Density values in this study were influenced primarily by a fe1v species such as the amphipods Erichthonius brasiliensis, Elasmopus pocillimanus and Melita appendiculata, and the polychaetes, Branchiosyllis

i occulata, Venniliopsis bennudensis, and Filograna implexa. Comparable data on other prop root connnunities is lacking, but a mean diversity value of Hs = 2.60 at Lake Surprise is probably relatively 53 high. A total of 108 species , including colonial species, was collected in this study compared to 119 species found by Kolehmainen (1973) . How- ever, Kolehmainen's collection consisted of more than 100 roots from 8 different stations in Jobos Bay, Puerto Rico compared to only 48 roots in a single mangrove strand in the present study. Compared to other epifaunal communities, the prop root community is only moderately diverse. Mean diversity values for other studies include 1-ls = 2.89 for Thalassia ln Lake Surprise (R. Walesky, unpublished data), Hs = 3.04 for Zostera m the York River, Virginia (Marsh, 1973), and Hs 2.49 for Juncus in northern Florida (Subrahmanyam et al., 1976). The Community Fullness index (CF) pen1lits one to determine the contribution made by various taxa, in terms of diversity and abundance, to the "fullness" of the whole community. "Fullness" is defined as the richness of species and individuals in a corrnnunity. It is assumed that the richer the fauna, the more complex are the overall intraconununity biotic relationships and the more complete and efficient is the use of biotic llild abiotic resources.

It is obvious from the CF values in Table 6 that polychaetes and amphipods are the most significant groups in determining this aspect of community structure. These two groups occupy the greatest number of niches and are the most prodigious users of the corrununity's resources. Polychaete CF values, which in both collections (177. 91/m2 in May llild 191.10/m2 in November) Here much higher than those of any other group, 1 reflected a relatively large number of species, h'hich represented many realized niches. Although amphipods had only slightly more than one- third as many species as polychaetes, the high densities of amphipods 54 resulted in a proportionately higher abundance and equitability campo- nent of CF (despite reduced equitability). Thus, these CF values sug- gest a more complete utilization of the conunw1ity' s resources by amphipods . The overall CF value changed little between collections, dropping from 475.89/m2 in May to 455.19/m2 in November. A decline in species and a slight increase 1n dominance was counteracted by an increase in total faunal abundance. This small change in CF between collections agrees well with similar small changes in Hs and E.

The Prop Root Community as an Indicator of Environmental Conditions Compared to published diversity values of many other marine habitats, diversity of the prop root epifauna in Lake Surprise appears low. This apparently lmv diversity coupled with relatively high dominance by a few species is characteristic of communities in unstable or stressful environments (Sanders, 1965). Sanders illustrated that a cumulative frequency curve (ctnnulative % of s~nple vs. cumulative % of species) deviates more widely from the theoretical maximwn diversity baseline (Equit- ability= 1) for tmstable commw1ities than stable communities. In Fig. 9 a cwnulative frequency curve is presented for the prop root conununity in Lake Surprise. T1w curve deviates widely from the line of theoretical maximwn diversity, with 10% of the species representing approximately

86% of the faw1a. This approximates values given by Sanders for an unstable benthic community.

Hypersaline bays are listed by Sanders (1965) as ex~nples of phys- ically unstable environments. A few species are not limited by the 55

100 , , , ,, , , , , 90 , , , , , , , , 80 ,, , ,' w MANGROVE ROOT EPIFAUNA , ,' ....J , , a.. 70 ,','4. # "' ~ , ~ , ~ <( ,' ,.~ c./) ,~ 60 ,'ov u. ,' ~ 0 , ,'v ~"' ,':\....l... , c,' -~ 50 ,' .,_4- ,'().,:. w ,'.;:;,~ > ,'+'~ 1- 40 ,,~,. <( , ,',c '?""" , .,_-...... J ,'o4 :::> 30 ,'~~«; , , ~ , , :::> , , u , , 20 , , , , , , , , , , 10 , , , , , , ,'

10 20 30 40 50 60 70 80 90 100

CUMULATIVE % OF SPECIES

Species frequency curve for mangrove prop root corrm1w1i ty 1n Fig . 9 . j Lake Surprise . 56 physical conditions in Lake Surprise and are able to attain high densities on the prop roots, while many other species are excluded either completely or periodically.

Knowledge of the structure of root connnlll1ities may prove useful in recognizing major factors influencing the entire sublittoral portion of rnangrove ecosystems. Sessile invertebrates, once established, are unable to avoid harsh environmental conditions, and the severity of local conditions is reflected in the diversity and composition of this portion of the community (McCain, 1975). Motile fauna, on the other hand, are capable of moving to avoid harsh conditions (Nagle, 1968; Kolehmainen et al., 1974). Thus, the composition and structure of epifaunal communities may be altered in response to environmental stress. Suspended detritus, which serves as food for many species, is of major importance m mangrove estuaries . The abundance of filter feeders in the root con111llll1ity is tied closely to the amount of suspended material in the water. These species and others utilizing detritus may be useful as indicators of turbidity. There is evidence, for example, that many species of fouling polychaetes are more ablll1dant in moderately turbid waters (Crippen and Reish, 1969). Tube-building amphipods show similar trends (Barnard, 1958; Cory , 1967). ~lcNulty (1970) found a direct relationship between the amolll1t of suspended organic material and the abund:mce of Erichthonius brasiliensis and other amphipods. 1 Sponges may also be indicative of the amount of suspended material. Burton (1947) suggested that in nearby areas sponges may be larger in waters having more suspended Jetritus. C:ertain types of sponges may 57 also be indicators of water quality. In a study of Jamaican sponges,

Reiswig (1971) showed that sponges of low tissue density >vere able to inhabit waters of high particle concentration because of efficient fil- tration mechanisms . Sponges of high tissue density, such as in the

Order Keratos<:~., were restricted to clearer water. Different areas, therefore, may develop different types of sponge communities, depending on the quantity and quality of suspended material. Long-term changes in water quality would thus likely result in qualitative changes in the sponge fauna. Periodic censuses of sponge populations could prove useful in determiniug the extent of changes in water quality over a wide area or over a long period of time. TI1e role of the prop root conlffiw1ity in the mangrove ecosystem is not well known. Epiphytes contribute to the total productivity of the ecosystem (Burkholder and Almodovar, 1973), and the epifauna probably contribute to the breakdown and cycling of organic material. The sessile flora and fauna provide shelter for invertebrates that may be im- portcmt links in food webs of commercially important species. Amphi- pods especially are known to be a food source for many fishes (Simmons, 1957; Cory, 1967). Prop roots may also provide food or shelter for .commercially important species such as young individuals of the spiny lob- ster Panulirus argus (Kolehmainen, 1973) and some species of mullet

(Rehm, 1974). _The contribution of the prop root comrnw1ity to the total mangrove ! ecosystem varies with the richness and diversity of its fauna. Since the composition and structure of the corrunw1ity differs from place to place and is determined primarily by local environmental conditions, 58 knowledge gained from studying this community could be useful in provid ing infonnation on the factors influencing all species throughout the entire mangrove ecosystem. SUMMARY l. A study of the epifaW1a associated \vith prop roots of the red man grove, Rhizophora mangle L., in Lake Surprise, Florida provided quantitative information on species composition, distribution, and seasonal changes in the faW1a.

2. Epifaw1a and flora were collected from three stations on each of two

depth contours (30 em and 100 ern) in a single mangrove strand in May

m1d November, 1975. Stations were grouped into fringe (100 em depth) and interior (30 em depth) stations based on faW1a1 similarity and abW1dm1ee of sponges and epiphytes.

3. A total of 40,200 non-colonial invertebrates representing 92 species

\vere collected from 2. 9 m2 of root surface. Amphipods, with 48% of the faW1a and 14 % of the species, and polychaetes, with 37% of the faW1a and 38 9o of the species, dominated the motile faW1a. Colonial invertebrates, represented by 16 species, were dominated by sponges (12 spp.).

4. Fringe roots hosted greater n~iliers of non-colonial species (88) and individuals (34,000) than interior roots (60 spp., 6,000 individuals). Sponges covered the equivalent of 31% of the availal?le root surface at the fringe and 12 % in the interior. Epiphytic algal volwne at the fringe h'as 6 times that in the interior. Spatial differences 59 60

1n faunal abundances were attributed to the greater area of submerged root surface and relative abw1dance of algae at the fringe.

5. Seasonal fluctuations of the falma were apparent. Tl1e number of non-colonial species decreased from 77 in .May to 67 in November

1vhile the number of individuals increased from 15,000 to 25,000. Less than 60% of the species were collected at both sampling periods. Seasonal differences in species composition may have been partially influenced by salinity and temperature. Abundances of motile fauna were influenced primarily by sponges and epiphytes, both of which increased in abundance from May to November.

6. The prop root coiTUnunity consisted of three assemblages. The algae- amphipod-tanaidacean assemblage, comprised of epiphytes inhabited primarily by the amphipods Erichthonius brasiliensis and Melita appendiculata and the tanaidacean Apseudes propinquus, 1vas prominent at the fringe but not in the interior. The sponge-polychaete assemblage (excluding serpulids) consisted of sponges such as Chondrilla nucula and Lissodendoryx isodictyalis inhabited primarily by the polychaetes Branchiosyllis occulata a'ld several species of Syllis. The sponge-polychaete assemblage occurred at the fringe and in the interior but was more prominent at the fringe. The bare root-

serpulid assemblage was made up largely of Filograna implexa and Venniliopsis bennudensis, whjch were dominant species in the 1n

l terior 1vhere the greatest proportion of bare root space occurred.

? 7. Average faLmal density was 13,200 ind/m~ of root surface and approx-

imately 5,000- 20,000 ind/m2 or level bottom, depending on root length, 61

location within the mangrove strand, and the munber of roots occupy ing a given area. Species diversity (Hs) and equitability (E) values remained fairly constant between fringe and interior stations, and between seasons . Overall mean values for the mangrove commw1ity for both seasons were Hs = 2.60 and E = 0.65. An index of "Corrununity Fullness" (CF), which is sensitive to species richness, equitability, and faunal abundance, also remained fairly constant between seasons.

8. The role of the prop root corrunw1ity as an indicator of environmental conditions was discussed. The composition and structure of the epi faunal conmllmi ty is sensitive to environmental conditions, and may be indicative of factors affecting all species in the n1angrove ecosystem. LITERATURE CITED

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Warmke, G. L. , and R. T. Abbott. 197 5. Caribbean seashells. A guide to the marine mollusks of Puerto Rico and other West Indian Is lands, Bermuda and the lower Florida Keys. Dover Publications, Inc. New York. 348 pp.

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