Sixth Intern. Ostracod Symposium, Saalfelden ECOLOGY AND ZOOGEOGRAPHY OF RECENT BRACKISH-WATER OSTRACODA (CRUSTACEA) FROM SOUTH-WEST FLORIDA DIETMAR KEYSER Abstract Die ökologische und zoogeographische Verbreitung von 36 rezenten Brackwasserarten der Ostracoden aus Südwest-Florida wurde untersucht. An ökologischen Parametern wurden folgende Faktoren berücksichtigt: Salzgehalt, Substrat, Wassertemperatur, pH-Wert und Wassertiefe. Mehrere Ostracodenvergesellschaftungen werden hinsichtlich ihrer ökologischen Präferenzen dargestelt. Die hier vorliegenden Fauna wird mit ähnlichen aus dem Golf von Mexico, der Karibischen Region, sowie von der Mittelamerikanischen Pazifikküste verglichen. Introduction The Gulf of Mexico, especially the west coast of Florida, is fairly weil known in respect of its ostracod fauna. Despite this knowledge, there is a lack of information about typical brackish water Ostracoda and of the ecology of Iiving ostracods. Many of the existing publications deal with the ecology of these animals, but because the research was done only by using the dead shells they cannot give valid data for the ecology of the species concerned. The present study tries to rationalize this situation. A second problem is the evaluation of the ostracod fauna in the Gulf of Mexico in zoogeographical connotations. The taxonomie situation has been very confused over a long period oftime. Only during the past decade a number of workers have attempted to clarify the situation (Van den Bold div., Morales 1966, King & Kornicker 1970, Keyser 1976b), and it is now possible to attempt a comparison of the Ostracoda of the Gulf Coast with other faunas, especially those of the Caribbean and the Pacific. Methods The material was collected between 1969 and 1971, mainly in the mangrove region of the Everglades National Park in southwestern Florida. One hundred and eighty-three sampIes from 120 stations have been examined. The sampIes were collected with a handnet of 240 11m mesh. Salinity, temperature and conductivity were measured with a portable conductivity-meter. The salinity tolerance was classified using the 'Venice-System'; pH was determined with the use of a portable pH-meter. The substrate was divided into sand, mud, peat, silt and shell sand by in situ observation. The grain size was determined at three stations and the depth was measured with a rod. The taxonomy and the ecological boundaries of each species have been given previously (Keyser 1976a, b). 207 The species encountered were: aff. Aglaiolypris eulitoralis forma./1oridensis Hartmann 1974; Actinmythereis subquadrata Puri 1960; Aurila amygdala (Stephenson 1944); Candona annae Mehes 1913; Candona ? balatonica Daday 1894; Cypretta brevisaepta Furtos 1934; Cypria pseudocrenulata Furtos ＱＹＳＶｾ＠ Cyprideis beaveni T ressler & Smith 1948; Cyprideis salebrosa Van den Bold 1963; Cypridopsis okeechobei Furtos 1936; Cytheridella alosa (Tressler 1939); Cytheromorpha paracastanea (Swain 1955); Cytherura elongata Edwards 1944; Cytherura sandbergi Mondes 1966;Cytherura sp. aff. C. forulata Edwards 1944; Darwinufafurcabdominis Keyser 1976; Darwinula steI'ensoni (Brady & Norman 1889); Dalerocypriafastigata Keyser 1976; Haplocytheridea setipunctata( Brady 1869); Heterocypris punctata Keyser 1976; Leptorythere darbyi Keyser 1976; Limnocythere./1oridensis Keyser 1976; Loxoconcha matagordensis Swain 1955; Mungava marthapuriae Keyser 1976; Neocaudites nevianii Puri 1960; Paralytheroma stephensoni (Puri 1954); Parapontoparta subcaerulea Keyser 1976; Perissorytheridea brachilorma forma inferior Swain 1955; Perissmytheridea cribrosa (Klie 1933); Pontoparta hartmanni Keyser 1976; Radimella.l1oridana littorala (Grossman 1965); Reticulocythereis./1oridana Puri 1960; Reticulorythereis purii Keyser 1976; ThalaSSOlypria gesinae Keyser 1976; Thalassmypria vavrai Keyser 1976; Xestoleberis mixohalina Keyser 1976. Factors controlling distribution Sa/inity The salinity seems to exert considerable influence upon the distribution of the ostracods. Fig. 1 shows that there is a boundary between the oe- and ß-oligohaline zones. The Iimnic species Candona ? balatonica and Cypridopsis okeechobei for example, are Iimited by this boundary. Cyprideis sa/ebrosa seems to tolerate the higher salinity and cannot be ca lIed a Iimnic species at this time (Van den Bold 1963). Cytheridella a/osa. on the other hand, is a true Iimnic species which, however, is often washed into the ß-oligohaline zone. The next group, with a maximum in the ß-oligohaline, is made up by 5 species, Mungava marthapuriae. Candona annae. Darwinula stevensoni. Darwinulafurcab-· dominis and Cypretta brevisaepta. They often tolerate a salinity of more than 10%0. Some limnic Ostracoda, such as Cypria pseudocrenulata. Heterocypris punctata. Limnocythere.l1oridensis. Dolerocypriafastigata and Pontoparta hartmanni are more euryhaline and live mainly in the oe-oligohaline and ß-mesohaline zones where there is a low level of competition. Thalassocypria gesinae. Parapontoparta subcaerulea and Thalassocypria vavrai are euryhaline species. It seems that their maximum population density is influenced by the absence of each other. T. gesinae prevails in the ß-mesohaline, P. subcaerulea in the oe-mesohaline and T. vavrai in the lower (ß) polyhaline zone. In the upper (oe) polyhaline A.tt. Aglaiocypris eulitorales is dominant. This succession of different Cypridacea may be controlled by competition. Cyprideis beaveni. Perissocytheridea brachyforma. Radimella .I1oridana Iittorala and Cytherura sandbergi represent the euryhaline Cytheracea. Their maximum density lies in the mesohaline zone which experiences a strong tidally controlled salinity range (Den Hartog 1964). This region has the lowest amount of competition. Perissocytheridea cribrosa might belong in this group, but it prefers the polyhaline zone. 208 ______________ ｾＺＭ［ｉｩＫｮ￟ｭ･ｳｨ｡ｬＧｐｏＮ＠ %. sa, ｾＮ＠ CythericjQUa oloso Cypridopsis ｯｫｾ･｣ｨ｢ｩ＠ i oligo- u ｰｾ＠ ., r' Candena "balatonlca Mungava . morthapuriae C:Jndona omaE! ｾｰｲｩ､･ｳ＠ salebrosa Cypretta brevisaepto Darwinula furcabdominis . Oarwinulo stevensoni Cyprio pseuclocrenulata punctato Heterocypris Limnocythere Pontoporta floridensis hortmanni Dolerocypria gesinae Parapontoparta subcaerulea Tholossocypria Cyprideis vavrol beaveni Penssocytheridea Radimella Cytherura • fostigata Tholassocypria brcchiforma floridona littorola sandbergi Perissocytherideo cribrosa Reticulocythereis floridano . .. puri; ｒｾｩ｣ｵｬｯｹｴｨ･ｮ＿ｳ＠ Haplocytheridea Loxoconcho setipunctata motagordensis Cytherura sp_ off. C. foruloto Cytheruro . elongota Xestoleberis mixohali no Aurilo am)'gdolo LeptoC)'there darbyi Neocaudites nevianii Actinoc)'thereis subqu.adrota Aff. Aglaioc)'pris eulitoralts Cytheromorpha ｰ｡ｲｯ｣ｳｴｾ･＠ Poracytheroma stephensonl Fig.1 I i I . I Species distribution in the mixohaline waters 01 South-West Florida c.:=J Total range =r> not studied _ range Range of maximal obundonce ... single findings The group of thalassogenious speeies whieh are enabled to tolerate the polyhaline and IX-mesohaline eonsists of seven speeies: Haplocytheridea setipunctata. Cytherura sp. aff. C. forulata. Loxoconcha matagordensis. Xestoleberis mixohalina. Cytherura elongata. Reticulo<ythereis.f1oridana and Reticulocythereis purii. The maximum population density ofthe remaining seven speeies lies probably in the euhaline, whieh has not been eonsidered in the present study. These speeies are: Actinocythereis subquadrata. Aufila amygdala. Cytheromorpha paracastanea. Lepto(ythere darbyi. Paracytheroma stephensoni. Neocaudites nevianii and aff. Aglaiocypris eulitoralis. 209 shell sand sand sandy mud mud peat organic debris silt ----Cytheridella alosa Cypridopsis okeeehobei Candona ?balatoniea xxxx + + xxxx xxxx Mungava marlhapuriae Candona annae Cyprideis salebrosa + xxxx xxxx xxxx xxxx xxxx xxxx Cyprerta brevisaepta Darwinula furcabdominis Darwinula stevensoni Cypris pseudocrenulala lIetero(ypris punetata Limnotythere .fIoridensis + Perisso(vtheridea braehiforma Radimella .fIoridana liflorala Cytherura sandbergi + + + + + xxxx xxx x + + xxxx xxxx + xxxx xxxx + + + ------xxxx + xxxx xxxx xxxx xxx x + xxxx xxxx xxxx xxx x xxx x xxx x xxxx Cytherura elongata Xesloleberis mixohalina Al/rila amygdala xxxx xxxx Leptocwhere darbyi Neocaudites nevianii AClinocythereis subquadrafa xxxx xxxx xxxx xxxx xxxx A.fI: Aglaioeypris eulitoralis Cytheromorpha paraeastanea Paraeytheroma stephensoni xxxx xxxx xxxx 210 + xxx x xxxx lIaplo(vtheridea selipunetara Loxoconeha matagordensis Cytherura sp.aff.C..liJrulala + + + + + xxxx xxxx + xxxx + + + + + Species distribution in correlation to the substrate. xxxx main range + single findings + xxxx Perisso(ytheridea cribrosa R eliculo(ythereis .fIoridana Retieulo(y,hereis purii Fig.2. + xxxx Pontoparla hartmanni Dolerotypria fasligala Thalassoevpria Resinae Parapontoparla subeeaerulea Thalasso(ypria vavrai (yprideis beaveni xxxx xxxx Substrate After salinity, the substrate is the most important factor controlling the distribution ofOstracoda. Generally the c1assification ofthe substrate is very difficult, because the substrate types are usually obscured by some other ingredients. Especially in the brackish water region, with its quiek changing currents, a complete description of the substrate is nearly impossible in terms of microhabitat of the Ostracoda. Nevertheless, it seems worthwhile to estimate the nature of the substrate in general terms and to try to compare the Iiving populations of Ostracoda found on these different substrates. Ostracods do not live on sterile sand or shell sand (Hulings & Puri 1964). On exposed rock, in the running waters of the channels, the small ostracod population is restricted to minor sandfilled pits. Fig. 2 shows the prevailing substrate types for the different species. To establish this table the number of specimens per sam pIe was used, not the number of sampIes in whieh the ostracod species was present. There is a striking difference between the Iimnie and marine species, the latter prefer sand or shell sand while the Iimnie forms were found more on organie detritus whieh was more abundant in the Iimnie region. However, both Iimnic Cytheracea, Cytheridella alosa and Cyprideis salebrosa obviously favoured sandy ground, whieh might be due either to their creeping movement or to their feeding as scavengers. The brackish water ostracods are found on the whole range of substrates in this zone. The swimming forms were mostly collected over sandy bottoms; the creeping ones mostly on peat or sandy mud bottoms. Polyhaline species such as Cytherura. Reticulocythereis and Haplocytheridea. live mainly on sand, whereas Perissocytheridea prefers sandy mud. Typical mud favouring forms are Cyporideis beaveni and Heterocypris punctata. Cyprideis being only found in great numbers on mud. Parapontoparta as weil as Thalassocypria vavrai were also often collected on this substrate. Peat and shell sand give rise to a characteristic fauna, whieh consists of Radimella .t1oridana Iittorala, Loxoconcha matagordensis and Xestoleberis mixohalina. Silt has proved to contain only a low number of such species as Haplocytheridea setipunctata. Actinocythereis subquadrata and Paracytheroma stephensoni in the brackish water zone. A fairly rieh fauna Iives on silt in the euhaline. Shell sand seems to contain the same species whieh live on sand. No interdependence can be stated between the phytal and the present ostracod species. Loxoconcha and Xestoleberis flourished during the summer vegetation of Caulerpa and Acetabularia. but were present also at other times when no vegetation was observable. They obviously did not depend on the plants. Whether or not Cypretta and Cypridopsis need plant Iife could not be defined. They were more numerous in the vegetation, but no definite answer is possible at this time, for the amount of decaying material in these areas was also very high. Temperature (Fig. 3) The temperature during the collection interval varied between 13° and 34°C. Ostracods were mainly found in the 20" to 30"C range. Stenohaline marine ostracods 211 Fig. 3. Temperature range of each species 25 20 Cytheridella alo5O Cypridopsis okeechobei Candona ?balatonica Mungava marthapuriae Candona annae Cyprideis salebrosa Cyprerta brevisaepta Darwinula furcabdominis Darwinula stevensoni Cypria pseudocrenulata Heterocypris pllnctata Limno(ythere .f1oridensis Pontoparta hartmanni Dolerocypria fastigata Thalasso(ypria gesinae Parapontoparta subcaerulea Thalassocypria vavrai Cyprideis beaveni Perissocytheridea brachilorma Radimella f10ridana lifforala Cytherura sandbergi Perissocytheridea cribrosa Rl!ticulocythereis .f1oridana Reticulocythereis purii Haplo(ytheridea setipunctata Loxoconcha matagordensis Cytherura sp.aff. C. forulata Cytherura elongata Xestoleberis mixohalina Aurila amygdala Lepto(ythere darbyi Neocaudites nevianii Actinocythereis subquadrata Aff. Aglaio(ypris eufitoralis Cytheromorpha paracastanea Para(ytheroma stephensoni 'Xf 30 35 ｾ＠ )()()()()()()() XXX><>< XXX><>< XXXXXXXXXXXX>OO x· XX>O<:JOOOOOOOO )()()()()()()() )()()()()()()() ｸﾷｾ＠ X>OOOO<XXXXXXXX<lOOOOO<XXXXXXX XXXXXJOOOO<XX>O ----------------- xxxxxxxxxxx >oooooooooooo<x XX>OOOOO<XXXXXX xxxxxxxxxxxxxxx xxxxxxxxxxxxxxx >oooooooooooo<x<xxxx ------->OO<XXXXXXXXXXX <XXXXXXXXXXXXXX Ｍｾ＠ )()()(){)()()() xxxxxxxxxxxxx Ｍｾ -------------------- xxxxxxxxxxxxxxx XXXXXXXX><XX XXX><>< ------------------xxxxxxxxxxxxxxx xxxxxxxxxxxxx xxxxxxxxxxxxxxx xxxxxxx lklLrllli·ncu range ulll:crtain range are also stenothermal, they were found mainly at 25° 10 30°C and sometimes up to 34°C. Euryhaline ostracods seem to be also eurythermal. Limnic forms show a maximum temperature limit at 30"C. 212 Definite statements concerning the optimum temperatures cannot be given. Only laboratory experiments can give reliable data, as done for Aurila conradi (= ?Radimella./loridana) by Kornicker & Wise (1960). They could show that this species is immobilized below 6°C and can survive O°C for 24 hours. Its activity was 1imited by an upper temperature of 36°C. These temparature limits show the range of water temperatures the brackish water ostracods have to withstand in these shallow tidal areas. This preadaptation might be one cause which separates the mixohaline and the marine animals (see also Den Hartog 1964). Hydrogen-ion-concentration (pH) During the investigation the pH did not seem to have any influence on the distribution. The ostracods were found between 6.5 and 9.2 pH. In the limnic zone the difference was smaller. In the marine and polyhaline zone the animals were collected at a pH below 8, with the one exception of Aurila amygdala at 8.8 pH. ResuIts The main factor controlling the local distribution of the investigated Ostracoda was the salinity. This agrees with the findings of several authors (Hartmann 1956, 1957, 1962, Morales 1966, King & Kornicker 1970). The second most important factor in controlling their distribution was found to be the substrate. Temperature seems to have only a minor effect on the distribution in this geographically small area. Current strength influenced mainly the swimming forms, but only in sm all areas. Water depth, pH and turbidity showed no apparent influence on the ostracod fauna in the eulitoral zone. Associations (Fig. 4) Using the salinity data for each species, 5 ostracod-associations can be recognized in the brackish water zone 01' southwestern Florida. The substrate preference of each species is also given: I) Limnic-Oligohaline assemblage; composed mainly of Cypridacea, with only two Cytheracea occurring: Cytheridella alosa Cypridopsis okeechobei Candona ?balatonica Mungava marthapuriae Candona annae Cyprideis salebrosa Cypretta bevisaepta Darwinula furcabdominis (sand) (organic (organic (organic (organic (sand) (organic (organic debrisl phyta/) debris) debris) debris) debris) debris) The latter two species also occur in assemblage 2. 213 .2.... Q .2. Fig. 4. A) I. 2. 3. 4. 5. 6. 7. 8. 9. ｬ｡ｾｵｮ｣ｑｲｩ＠ Rnizophoramangle AvicenniQ nitida ｾ＠ _ Canocarpus .rl'Ctus s.renoa racemoSQLTQxOdiUm distithum Limnic-Oligohaline Assemblage Mungava marthapuriae Candona ?balatonica Candona annae Cypridopsis okeechobei Cypretta brevisaepta Cytheridella alosa Cyprideis salebrosa Darwinula stevensoni Darwinula furcabdominis Dolerocypria fastigata Pontoparta hartmanni Cypria pseudocrenulata Heterocypris punctata Limnocythere floridensis Euryhaline Assemblage 15. Thalassocypria gesinae 16. Thalassocypria vavrai 17. Parapontoparta subcaerulea C) 214 -:;j- ThdlQssia tHtudinum !L. Cault>rpa _rtulark>idK ..J,.... Acetabularia cre-nulata L 1.. Chara hornemann;1 Mariscus jamaiC«lsis Ostracode assemblages and vegetation distribution in the whitewater Bay (F1orida) B) Oligo-Mesohaline Assemblage 10. 11. 12. 13. 14. ｲｾｮｳ＠ 18. 19. 20. 21. 22. D) 23. 24. 25. 26. 27. 28. 29. E) 30. 31. 32. 33. 34. 35. 36. Cyprideis beaveni Perissocytheridea brachiforma Perissocytheridea cribrosa Radimella floridana Iittorala Cytherura sandbergi Meso-Polyhaline Assemblage Reticulocythereis purii Reticulocythereis floridana Haplocytheridea setipunctata Loxoconcha matagordensis Xestoleberis mixohalina Cytherura sp. aff. C. forulata Cytherura elongata Poly-Euhaline Assemblage Aff. Aglaiocypris eulitoralis Neocaudites nevianii Actinocythereis subquadrata Leptocythere darbyi Cytheromorpha paracastanea Aurila amygdala Paracytheroma stephensoni ｾ Q .2. Fig.4. Ｎ＠ RI"u:ropn olCmonglf> Avic.nruo niUdo logUl"lculorio ｾ＠ _ CanocorpYs f>rf'CIU5 St-rf'flOO racfmosoT TQ.lCodlum Mungava marthapuriae Candona ?balatonica Candona annae Cypridopsis okeechobei Cypretta brevisaepta Cytheridella alosa Cyprideis salebrosa Darwinula stevensoni Darwinula furcabdominis B) Oligo-Mesohaline Assemblage 10. 11. 12 . 13 . 14. Dolerocypria fastigata Pontoparta hartmanni Cypria pseudocrenulata Heterocypris punctata Limnocythere floridensis Cl ElIryhaline Assemblage 15. Thalassocypria gesinae 16 . Thalassocypria vavra i 17. Parapont opa rta sllbcaeru lea 214 dist lchum ".:.:/' Tt'ldloHio t.stud inum 1.. Cau"rpa wrtutorold@s .J... Ac.tabulorio crenulata 1- Moriscus jomOICH1S IS Ostracode assemblages and vegetation distribution in the whitewater Bay (Florida) A) Limnic-Oligohaline Assemblage I. 2. 3. 4. 5. 6. 7. 8. 9. ｲｾｳ＠ 18. 19. 20. 21. 22. 0) 23. 24. 25 . 26. 27. 28 . 29. Cyprideis beaveni Perissocytheridea brachiforma Perissocytheridea cribrosa Radimella floridana littorala Cytherura sandbrrgi Meso-Polyhaline Assemblage Reticulocythereis purii Reticulocythereis floridana Haplocytheridea setipunctata Loxoconcha matagordensis Xestoleberis mixohalina Cytherura sp. aff. C. forulata Cylherura elongata E) Poly-Euhaline Assemblage 30. 31. 32 . 33 . 34. 35 . 36. Aff. Aglaiocypris eulitoralis Neocaudites nevianii AClinocythereis sllbquadrata LeptocYlhere darbyi Cytheromorpha paracastanea Allrila amygdala Paracytheroma stephensoni 2) Oligo-Mesohaline assemblage: Cypria pseudocrenulata Heterocypris punctata Limnocythere .f1oridensis Pontoparta hartmanni Dolerocypria fastigata (independent of substrate) (mud) (peat) (sand) (sand) All these species except Cypria pseudocrenulata were found alone. Dolerocypria jastigata was also found only together with Pontoparta hartmanni. This is obviously a function of substrate selection. 3) Euryhaline assemblage; composed of the euryhaline ostracods which favour the mesohaline zone with large and quick salinity changes. Here associations are encountered which characterize a very sm all biotope. The combination of Cyprideis beaveni and Thalassocypria vavrai for example, indicates a pure mud substrate in a stagnant water region and Perissocytheridea brachi/orma. Cytherura sandbergi and Radimella floridana littorala are characteristic of sandy mud in open tidal waters. A substrate rich in debris yields Thalassocypria gesinae and Parapontoparta subcaerulea in association. The Euryhaline assemblage consists of the following species: Thalassocypria gesinae Parapontoparta subcaerulea Thalassocypria vavrai Cyprideis beaveni Perissocytheridea brachiforma Radimella .f1oridana littorala Cytherura sandbergi Perissocytheridea cribrosa (sand) (peat) (sand) (independent of substrate) (sandy mud) (shell sand, peat) (sand) (sandy mud) The latter three species are often encountered in the following assemblage. 4) Meso-Polyhaline assemblage: Reticulocythereis .f1oridana Reticulocythereis purii Haplocytheridea setipunctata Loxoconcha matagordensis Cytherura sp. aff. C. forulata Cytherura elongata Xestoleberis mixohalina (sand) (sand) (sand) (shellsand) (sand, shellsand) (sand, shellsand) (peat) Here again characteristic combinations are observed. Radimella floridana Iittorala, Loxoconcha matagordensis and Xestoleberis mixohalina are typically found in the zone of seasonal vegetation or on shell sand or peat in open waters. 80th speeies of Reticulocythereis often occur together, as do the three species of Cytherura. An explanation for these phenomena cannot be given at this time. 215 5) Poly-Euhaline assemblage: (shell sand) (shell sand) (shell sand) (sand, shell sand) (shell sand) (shell sand) Aurila amygdala Leptocythere darbyi Neocaudites nevianii Actinocythereis subquadrata A.ff. Aglaiocypris eulitoralis Cytheromorpha paracastanea Paracytheroma stephensoni (silt) Zoogeographical distribution (Fig. 5) The zoogeographieal eomparison of the study area with other parts of middle Ameriea is diffieult due to taxonomie uneertainties (Swain 1955, Curtis 1960). The present results have been eompared with two studies from the Gulf of Mexieo (Morales 1966, King & Kornieker 1970). The Caribbean Sea area is fairly weil known in respeet ofits fossil and subfossil Ostraeoda due to the work ofVan den Bold (div.). Reeent speeies were mentioned by Klie (1933, 39) and Triebel (\ 961,62). The Paeifie eoast is weil known only in South California in the USA and Baja California and the Gulf of California in Mexieo (Juday 1907, Benson 1959, Benson & Kaesler 1963, MeKenzie & Swain 1969, Swain & Gilby 1974). The Ostraeoda of the further south Iying eoast in the area are known merely from publieations by Hartmann (1955,1956,1957,1959) from EI Salvador and Coryell & Fields(l937) from Panama. Ishizaki & Gunther(l974) reeently published a paper on the Cytheruridae ofPanama. Allison & Holden (1971) dealt with the fauna of Clipperton Island and Triebel (\956) as weil as Pokorny (\968 a, b, e, 1969, 1970) deseribed ostraeods from the Galapagos. Distribution in the Gu(f of Mexico (Florida-Texas-Mexico) The ostraeod fauna of the Gulf of Mexieo is fairly uniform. This is surprising beeause the studies with whieh the present work is eompared (Morales 1966, King & Kornieker 1970) were earried out in different environments. Ten eorresponding species are eommon to all three areas: Aurifa amygdala. Radimella .floridana (littorala), Cytherura elongata. Cytherura sp. aff. C. .lorulata. Cytherura sandbergi. Haplocytheridea setipunctata. Leptocythere darbyi ('? nikraveshae), Loxoconcha matagordensis. Paracytheroma stephensoni. and Perissocytheridea brach!torma. Three further species may be eommon, but taxonomie uneertainties were present: Actinocythereis subquadrata Cytheromorpha paracastanea Xestoleberis mixohalina . = '?(A. triangularis sensu Morales), warneri sensu King & Kornicker), and = ,?(X. sp. sensu King & Kornicker,X. rigbyisensu Morales). ='?(c. Two speeies are found only in Mexieo and Florida: Neocaudites nevianii. and Perissocytheridea cribosa. 216 ,I Imixo euimnic ,;, Ｌｾ＠ ＬｾＺ｜ＮＧ＠ )1 Caribbea Pacific Texas Mexico -,u,luu ＧＱｕｉｾ＠ "UIII .. l1li , me rmii ' " p:- 11 'hnson, y ｾ＠ ...ＬｾＢ＠ ... FIG.5 -- II1II I I Zoogeographical comparison of the Ostracode- fauna Van den Bold reported both species (Neocaudites 1966b from Venezuela, Perissocytheridea 1963 from Trinidad), Klie (1933, 39) only Perissocytheridea, from the coast of South America. Questionable is the conspecifity of Perissocytheridea cribrosa and P. bicelli{ormis mentioned by Swain (1955) and Engel & Swain (1967). The absence of Neocaudites nevianii from Texas is striking. It is probably a true tropical species. 217 Naturally the ostracod fauna of Florida corresponds most c10sely to that of Texas, since the environment of the two study areas is more comparable and the geographical situation is also similar. A comparison between the Cypridacea of the brackish water zone based on the figured shell characteristics by King & Kornicker ( 1970) seems to reveal the same genera, although adefinite assignment is not possible due to lack of information of the softparts: Aglaiocvpris sp. ASlello(vpris sp. Cypridopsis sp. POlamocvpris sp. POlamocvpris smaragdilla ......................... ? = Thalasso(ypria sp. ·........ . ................... '? = Parapof1!oparla sp. ·............................... ·............... .. . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .. = Cypridopsis sp. Potamo(vpris sp.A = POlamo(vpris sp.B = The same is true for Cyprideis beaveni and unfortunately questionable between Limnocythere ./loridensis and L. sp. as weil as Reticulocythereis ./loridana and R. multicarinata. Species common between Texas and Mexico are: Megacylhere johnsoni. Perissocytheridea excavata. and Perissocytheridea rugata. In summary, the ostracod fauna of the brackish water zone is very homogenous. Unfortunately, only the fossil fauna of the Caribbean is known from the works of Van den Bold and, therefore, little can be said about the distribution ofthe Recent Ostracoda. The fossil findings, however, indicate a partly communality between the ostracod faunas of the Gulf of Mexico and the Caribbean. Gull Ql Mexico-Pacjlic coast Ql Middle America The brackish water fauna of Florida at the specific level is not similar to the ostracod fauna which Hartmann (1957) described from EI Salvador although the genera are the same. No species which Hartmann described was found in the Gulf ofMexico. Van den Bald (1964), however,encountered three species from EI Salvador in his sam pies from the Caribbean: Loxoconcha lapidiscola. Palaciosa vandenboldi and Perissocytheridea punctata. There seem to be a few species common between the Caribbean and the Pacific. Only one species has so far been found in the Pacific as weil as in the Caribbean and the Gulf of Mexico, that is Cytherura sandbergi Oshizaki & Gunther 1974, Benson & Kaesler (?) 1963, Morales 1966, King & Kornicker 1970). The connections between the Gulf of Mexico and the Pacific are almost non-existent. The ostracod faunas of these two regions, which have been physically separated since the Miocene have become widely divergent due to separate evolutions. In this connection it is interesting that Eibl-Eibesfeld (Triebel 1956) found two species on the Galapagos Islands which are conspecific with ostracods from Florida. These species are Cyprideis beaveni(= C. stenophora) and Xestoleberis arcturi. This might be related to the extinction of the tropical fauna at the west coast ofthe continents with their cold currents in equatorial directions and the survival on islands along these coasts (Ekman 1953). Hartmann (1974) explained this by the extension of the cold Pleistocene currents along the west coast of the conti- 218 nents, wh ich resulted in the extinction of the coastal tropical fauna, while the island were mostly not influenced by these currents, enabling the fauna to survive. Whether or not this can explain the occurrence of the same species on the Galapagos Islands and in F10rida remains to be demonstrated by further studies. Afangrove dependence A typical mangrove fauna could not be found at the specific level. A correspondence could only be observed at the generic level. This fauna does not seem to depend on mangroves but is typical of a tropical brackish water flat (Date 1971). Summary The ecology and zoogeographical distribution of 36 ostracod species collected in the brackish water region ofSouth West Florida has been investigated. 183 sampIes from 120 stations were studied. The ecologic parameters recorded were; salinity, substrate, water temperature, pH, water depth, turbidity and currents. I. The most important factor controlling the distribution of ostracods in this region is the salinity. 2. Five assemblages could be recognized in respect of their salinity preferences: Limnic-Oligohaline assemblage Oligo-Mesohaline assemblage Meso-Polyhaline assemblage Poly-Euhaline assemblage Euryhaline assemblage 3. Typical for the brackish water zone is the occurrence ofthe Thalassocyprididae. Heterocypris punctata, Cyprideis beaveni, Perissocytheridea brachi/orma and Perissocytheridea cribrosa are also true brackish water ostracods. Cyprideis salebrosa has been cIassified as a Iimnic species with oligohaline tolerance. 4. The next most important factor controlling the distribution is the substrate. It was cIassified into shell sand, sand, mud, sandy mud, peat, silt and organic debris. The Cypridacea of the Limnic-Oligohaline assemblage prefer substrates which are rich in debris, the Cytheracea more sandy ground. The explanation is probably their different feeding habits. The ostracods of the Poly-Euhaline assemblage prefer sand and shell sand. Cyprideis beaveni and Cypria pseudocrenulata could not be correlated with a special substrate. 5. Water temperature has only a minor effect on the distribution. Extreme temperatures are a limiting factor. Only Leptocythere darbyi shows a seasonal fluctuation which is correlated with temperature. 6. Turbidity, currents, pH and water depth do not reveal any influence on the distribution of the ostracods. 7. The zoogeographical comparison of the investigated brackish water fauna with other known faunas of the Gulf of Mexico showed a good accordance at specific level (16 species). 6 species have been reported from the Gulf of Mexico and the 219 Caribbean. 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