Bijdragen tot de Dierkunde, 53 (2): 233-243 — 1983
Amsterdam Expeditions to the West Indian Islands, Report 28.
Predation as a factor influencing the occurrence and
distribution of small Crustacea in West Indian
groundwaters
by
Jan H. Stock
Institute of Taxonomie Zoology, University of Amsterdam,
P.O. Box 20125, 1000 HC Amsterdam, The Netherlands
Summary 1. INTRODUCTION
from inland Hadziid are known groundwaters Amphipoda During groundwater explorations (1800 sta- of 14 West Indian islands, Thermosbaenacea from those of tions in in the West 43 islands) Indies, great both 9 islands. Only 4 islands show joint occurrence of numbers of animals hypogean were en- Even in islands of hadziids occur groups. joint occurrence, countered in this significantly more often alone in a given locality, than in (see previous reports series). The combination with Thermosbaenacea or Copepoda most frequently represented groups were
Cyclopidae. The latter two do not show signifi- groups any Oligochaeta, Gastropoda, and four crustacean for the cant avoidance of each other. Some possible causes taxa: Ostracoda, cyclopid Copepoda, Am- non-random occurrence of small groundwater Crustacea phipoda, and Thermosbaenacea. are discussed; it seems most likely that hadziids predate on Groundwaters river other Thermosbaenacea or (in springs, Crustacea, such as Cyclopidae. wells, caves,
This have influence the and beach of islands predation may have, or had, on interstitia) the following
of the under considera- actual distributionpatterns groups have been investigated (fig. 1) during a ten tion. years' period (1973-1982) by the Amsterdam
Expeditions: Aruba, Curaçao, Bonaire, Isias Résumé Los Roques, La Tortuga, La Blanquilla, Los
Des Hadziides des Amphipodes sont connus eaux souter- Testigos, Margarita, Barbados, St. Lucia, raines intérieures de 14 îles des Antilles; des Thermos- Martinique, Dominica, Guadeloupe, Antigua, îles baenacés sont connus de 9 îles. C’est seulement sur 4 Barbuda, St. Eustatius, Saba, St. Barthélémy, les deux rencontrent; mais même dans ces que groupes se St. dernières îles, il est nettement plus fréquent de trouver les Martin, Tintamarre, Anguilla, Anegada,
Hadziides seuls à certaine association St. St. une localité, qu’en Virgin Gorda, Tortola, John, Thomas,
des Thermosbaenacés des avec ou avec Copépodes St. Croix, Vieques, Culebra, Puerto Rico, deux derniers s’évi- Cyclopidés (tandis que ces groupes ne Mona, Hispaniola (Haiti), Jamaica, Grand de On discute tent pas façon significative). sur plusieurs Cayman Brac, South Caicos, raisons du fait la distribution de Cayman, possibles que ces Providenciales, Great Crustacés souterrains de taille réduite présente ce Inagua, Mayaguana, caractère l’idée la les Crooked San Salvador «non-random»; plus plausible est que Island, Island,
de Crustacés Hadziides sont des prédateurs aux dépens Eleuthera, and New Providence. tels les Thermosbaenacés et les Cyclopidés. Ceci peut que The will present paper discuss the occurrence avoir — ou avoir eu — une influence sur la distribution and distribution of three crustacean actuelle de groups, ces groupes. viz. the family Cyclopidae of the Copepoda, the
hadziid group of the Amphipoda Gammaridae,
and the order Thermosbaenacea, in inland
Of these the *) Report 27 has been published in Bijdragen tot de Dier- groundwaters. cyclopids are en- kunde, 53 165-177 countered almost but hadziid (1): (1983). on every island,
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Fig. 1. Map of the West Indies, showing the islands mentioned in the text (§ 1). Heavy dots: Boundary ofthe distribution distribution the Ther- area of the generically diversified fauna ofhadziid Amphipoda. Light dots: Boundary of the area of mosbaenacea. Heavy strokes: Position of the Anegada Trough.
Fig. 2. Distribution of hadziid Amphipoda (H, black dots) and Thermosbaenacea (T, triangles) in the West Indies.
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restricted certain calcareous for the International amphipods are to 3rd Symposium of
and of islands (Stock, 1977, more recent data Groundwater Ecology (Lodz/Chestochowa, our own), viz. Aruba, Curaçao, Guadeloupe- 1981), which was published recently (Stock,
Grande St. the the based Terre, Antigua, Barbuda, Martin, 1982). In present paper, data on
Tintamarre, Anguilla, St. Croix, Puerto Rico, the completely sorted samples of the 1973
Hispaniola, and Jamaica (fig. 2). Members of through 1982 campaigns are included, and
hadziid also several the the group are known from Marie- provisional results of earlier draft
Galante and Cuba have been in definite (Stock, 1980) (Dancau, put now a more shape.
visited 1973; Holsinger, 1977), not during our investigations. Besides, marine or anchihaline
considered in this hadziids, not paper, are 2. ACKNOWLEDGEMENTS known from certains islands in the Leeward
The fieldwork in the various West Indian islands has been group (Bonaire, Curaçao, La Tortuga), in the made ofthe Netherlands Foundation possible by grants for Bahamas, and from Puerto Rico. the Advancement of Tropical Research (WOTRO), The
Thermosbaenacea are more limited in their Hague; the Treub Maatschappij, Utrecht; the Beijerinck distribution. They have been found in the Popping Fonds, Amsterdam, the Fonds Landbouw
and the Amsterdamse Univer- inland waters of nine islands, viz. St. Croix Hogeschool, Wageningen, siteitsvereniging, Amsterdam. (Stock, 1976), Cuba (Botosaneanu et al., 1973:
The has been executed a team of 1 sampling by changing 14; Orghidan, 1973: 38) ), Anegada, Virgin composition, consisting of Lazare Botosaneanu, Nico Gorda, Tortola, St. John, Culebra, Puerto Broodbakker, Sylvia van Lieshout, Jos Notenboom, Jan and Rico, Hispaniola (our own records). Stock, Maarten Stock, Steven Weinberg, and Francisca
Moreover, marine or anchihaline thermos- Zijlstra.
Many on the various islands, too to be considered in this persons many baenaceans, not paper, are mentioned in various individually, helped us ways: by known from Curaçao (Stock, 1976, and granting permissions, by providing transportation or unpublished data). accomodation, by guiding us to caves and wells, etc.
During the fieldwork it looked as if the three
under consideration crustacean groups were, although not entirely mutually exclusive, only 3. MATERIAL AND METHODS rarely found in each other's presence. For the
Most samples have been collected with a vertical combination hadziids—thermosbaenaceansthis closing net of the Cvetkov type (see Bou, 1975), or with is already clear from the above enumeration of biophreatical pumps (Bou, 1975; Mittelberg, 1980). The localities: the former have been found 14 on entire sample was preserved in formalin 4% and sorted the latter 9 but 4 islands, on islands, only later in the laboratory under a dissecting microscope. islands (Cuba, Hispaniola, Puerto Rico, and Chlorinities have been measured with an EEL electric
chlorinimeter, or according to the ASTM method D512. St. Croix) have both groups represented in their In the the present paper term "hadziids" is applied to a groundwaters (fig. 2). of of group strictly stygobiont Amphipoda the family Gam- The whether or not the absence of question the treated maridae, essentially genera by Stock (1977) the one of and the group crustaceans, and Bousfield (1977), or by Barnard & Karaman (1982) simultaneous under the name "Hadziids and Weckeliids". presence of the other is statistical- Only the
inland-water are considered the ly significant, is examined in detail in the genera (thus excluding anchihaline the marine or hypersaline genus Saliweckelia or Possible for the observed present paper. causes genus Protohadzia). distribution also discussed. patterns are The hadziids are particularly rich in species in the
On the Lesser is Neotropics. Antilles, only one genus
A shortened and draft of this with endemics preliminary present, Metaniphargus, on a number of
islands. On several other the Greater Antilles genera, in paper has been presented as a congress lecture addition to Metaniphargus , are known (see for anenumera-
Thermosbaenacea to be in Cuba tion in in ') appear more common Stock, Botosaneanu, press). than these single records in the literature suggest The thermosbaenaceans of the West Indian inland
(Delamare Deboutteville, in litt., 1977). waters comprise uniquely Monodella-like forms. The
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Halosbaena has been marine to anchihaline not con- calculate the genus even pattern, one can expected sidered. The entire is stygobiont. group number of The joint occurrence. taxon m is The number and Cyclopidae comprise a large of genera in fraction stations present a of the others also sampled, subgenera, some of them strictly stygobiont, 1 this fraction + 0 ■ Sq' being n . known from epigean waters. (0 m m + ) the is in fraction Likewise, taxon n present a (0„
1 of the stations + 0 ' So' This m + n) sampled.
4. STATISTICAL METHODS leads to the following equation of the expected
number of stations of occurrence joint (em + n): 4.1. Test 1 e = + 0 Sq' + 0 m + n (Om m + n ) ■ ■ (0„ m + n ) ■
1 The or absence of n taxa 2 ■So" S or more e = + presence (1, m, • 0 , simplified: m + „ (0m
l islands is A test for 0 + O on k different + f n) compared. m n)(0„ m + n)-S ( .
variable for k essen- Since the value for e is based on the scores on one categories, m + n
2 test 1975: is observed values 0 and the tially a x (Meddis, 60) m 0„, expected sample
size island will be N = 2e + 0 + 0„, appropriate. per e m + „ m
2 and the number of scores to be used in the x
4.2. Observed values test will be EN . One of the of the (0) e requirements
2 is that the observed X test EN must sum to t up The observed of frequencies solitary occurrence number of the for scores, TiNq. So, frequencies in of each taxon (0/ 0 ) are recorded n e f°r 0 and for 0 should be to m + n> m n adjusted unrelated pairs (0; with Op 0 with 0 ) m n EA with factor 0 by multiplication a T,Nq •
with the observed of ~ along frequency the x T,N . The corrected are e expected frequencies samples containing two taxa at a time (0 „). 1 m + then: E = LN ■ • e E = LN„- m + n 0 EA/ m+ „; m
The total number of positive stations (i.e., sta- 1 • 0 etc. LA," m, tions of the observed yielding any taxa studied) 2 X can now be computed as follows:
= is = 0 per category ( island) expressed by Sq m
+ 0„ + 0 stations, m + „. Negative containing (2 0 Y O 2 O 2 none of the taxa studied, are not considered.
observed The number of scores per category,
Nq, is 0 + 0 + 2 0 This not seem m n m+ n . may One of the inferences of the present test is but be understood if bears in obvious, can one of the that it should not be used if any expected mind that taxon m occurs at 0 stations alone, m frequencies is less than 5 (Meddis, 1975: 61). and at 0 stations with taxon + m n together n, This rules the of this for the out use test majori- whereas taxon n occurs at 0„ stations alone and ty of the islands sampled during our program. 0 The total at stations jointly with taxon m. m + „ For the following islands, the solitary and joint number of scores for taxa m and n is thus 0 + m of crustacean occurrence certain groups was
0 + 0„ + 0 = 0 + 0„ + 2 0 m + „ m + „ m m + n . testable:
The total numberof scores for all islands, the N Hadziids-cyclopids: Haiti-Curaçao-Aruba; 2 EAf of the x test, is . 0 Hadziids-thermosbaenaceans: Haiti;
Thermosbaenaceans-cyclopids: Anegada-Tor-
tola-Haiti. 4.3. Expected values
The expected frequency of joint occurrence
and the basis of 5. RESULTS e of taxa m n, calculated on ( m + n)
each the separate occurrence of m and n on 5.1. Hadziids and cyclopids island, can be estimated as follows:
If that observed the hadziid one supposes the frequencies During present investigations,
and the of the taxa m n per island are realistic, Amphipoda have been sampled in
deviate from random and islands: although they may a following Aruba, Curaçao, Bonaire,
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Tortuga, Marie-Galante, Guadeloupe, Bar- occur solitary than jointly, is not due to random buda, Antigua, St. Martin, Tintamarre, fluctuations but to other effects.
Anguilla, Puerto Rico, Haiti, and Jamaica.
Although on almost all these islands Cyclopidae 5.2. Hadziids and thermosbaenaceans occur as well, most data could not be used for
because of The relevant summarized in table testing a variety of reasons: (1) On data are II,
Bonaire and Tortuga only haline hadziids of the for the only island of which sufficient samples of
both Haiti. genus Saliweckelia are known, whereas for the groups are available,
2 have used inland-water For LN = 88 and = value of 8.92 present study we 0 df 3, a x
has been which is species only; (2) we have not sampled personal- computed, significant at
island of and better than the It that the ly the Marie-Galante, we are not 5% level. seems likely
of hadziids and ther- sure that the sampling methods used there were observed joint occurrence identical with mosbaenaceans deviates from the ours; (3) several islands have significantly
insufficient occurrence be if the taxa were yielded "positive" stations, e.g. to expected not
which 1 in each other's Antigua or Tintamarre, on only station avoiding some way presence. yielded hadziids, although the number of sta- tions the Table II. Observed sampled was large enough; (4) com- and expected frequencies of solitary
and of hadziid and ther- for the joint occurrence Amphipoda (1) puted "expected frequencies" test were mosbaenaceans in Haiti. For symbols: see text § 4. than (3) lower 5, making the use of the test risky.
As the Observed a result, only Frequencies 0, 33 25.76 e, + 3 for three islands and (0) (Aruba, Curaçao 0 29 113.52 3 N,
could be used for statistical 0, 13 E, 25.58 Haiti) treatment; + 3
jV 88 E 22.48 these data are recorded in table I. At the bottom 0 3
5 75 £ 19.96 of this table, the Expected Frequencies (e) and 0 2 + i the Expected Frequencies after correction for 5.3. Thermosbaenaceans and introduced. cyclopias (indicated by E) are
2 For EN = 272 and = value of 0 df 3, a x In table III the relevant data for the solitary and 16.71 has been found, being significant at about joint occurrence of these groups on Anegada, the 0.1 % level. It seems likely that the observa- Tortola, and Haiti are summarized. tion that hadziids and cyclopids do more often 2 For = 168 and = value of LNQ df 3, a x
0.77 has been computed, which is not signifi-
cant. It must be concluded that the solitary
Table I. Observed and of expected frequencies solitary occurrence of thermosbaenaceans and and of and joint occurrence hadziid Amphipoda (1) and their do cyclopids, joint occurrence, not cyclopid Copepoda (2) in three West Indian islands. For deviate from random fluctuations. symbols: see text § 4.
Haiti Aruba Curaçao 6. DISCUSSION
22 62 13 97 O, LO, = 6.1. Ecological implications 0 93 4 14 E0 =111 2 2
0 24 6 2 =32 1 + 2 1.0, + 2
hadziids and are ex- N 163 78 31 EN = 272 Apparently, 0 0 cyclopids
S 139 72 29 LS = 240 each other to and 0 0 cluding a significant extent,
hadziids so are and thermosbaenaceans. On the e 38.72 9.94 8.27 + 1 2 other hand, thermosbaenaceans and cyclopids N 192.44 85.88 43.54 EN - 321.86 e r in islands in occur jointly the a not = way E, 18.59 52.40 10.99 LE, 81.97
E LE significantly different from random fluctua- 78.59 3.38 11.83 = 93.80 2 2 E, 32.72 8.40 6.99 ZE =48.11 tions. + 2 l + 2
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and of Table III. Observed expected frequencies solitary occur both are used; these islands are listed at
and of and ther- joint occurrence cyclopid Copepoda (2) The the top of the table. Mann-Whitney test mosbaenaceans in three West Indian islands. For (3) sym- value Z of which yields a for 0.61, is likewise not bols: see text § 4. significant.
Anegada Tortola Haiti
Table IV. Chlorinities (in mg/1, 0-10 recorded as "10", 0 5 3 72 T,0 = 80 2 2 of hadziid 11-20 recorded as "20", etc.) in 40 samples 0 1 5 6 L0 = 12 3 3 Amphipoda and 40 samples of Thermosbaenacea from 0 5 7 26 = 38 + 2 + 3 2 3 Haiti.
N 16 22 130 T,N = 168 0 0
S 11 15 104 LS = 130 0 0 Hadziids: 10, 10, 10, 20, 20, 20, 20, 20, 20, 20, 30, 30, 30,
30, 30, 40, 40, 40, 50, 50, 50, 50, 50, 60, 70, 80, 80, 90, 8.00 30.15 T,e = 43.60 e 5.45 + 2 + 3 2 3 110, 130, 140, 150, 190, 190, 200, 240, 310, 450, 3320, T,N N 16.90 24.00 138.30 = 179.20 e e 5640. E 4.69 2.81 67.50 Y.E = 75.00 2 2
E .94 4.69 5.63 LE = 11.26 3 3 Thermasbaenacea: 10, 20, 20, 20, 20, 20, 20, 20, 20, 30, 30, E 5.11 7.50 28.27 T.E = 40.88 2 + 3 2 + 3 40, 40, 40, 40, 50, 50, 50, 50, 50, 50, 60, 60, 70, 80, 80,
100, 100, 100, 110, 150, 190, 200, 240, 310, 390, 420, 510,
2440. A number of be 1640, possibilities can postulated to explain the fact that hadziids rarely occur
with thermos- simultaneously cyclopids or Table V. Chlorinities (in mg/1, 0-10 recorded as "10", in 100 of hadziid baenaceans in the 11-20 recorded as "20", etc.) samples same sample: Amphipoda and 100 samples of cyclopid Copepoda, from (a) Certain abiotic factors determine the Guadeloupe, Antigua, Barbuda, St. Martin, Anguilla, St. presence or absence of members of each taxon. Croix, Haiti, Curaçao and Aruba. The only factor in the groundwaters of these
calcareous that shows tropical, mostly islands, a Hadziids: 10, 10, 20, 20, 30, 30, 90, 90, 130, 140, 140, 150, considerable of is The 160, 180, 190, 190, 200, 200, 200, 210, 220, 230, 240, 240, range values, chlorinity. 270, 290, 290, 290, 290, 290, 300, 320, 330, 380, 390, 410, waters examined during our program ranged 410, 470, 470, 480, 550, 580, 590, 600, 660, 660, 680, 690, from fresh to For the pur- entirely polyhaline. 690, 690, 710, 710, 800, 830, 890, 910, 920, 950, 1000, of this the chlorinities pose study, we compared 1040, 1120, 1240, 1240, 1250, 1280, 1280, 1280, 1310, of 40 localities with Thermosbaenacea, with 1320, 1400, 1440, 1460, 1470, 1480, 1480, 1580, 1630,
1800, 1880, 2160, 2500, those of 40 localities with hadziids (table IV). 1640, 1720, 1760, 1760, 1880, 2640, 2800, 2840, 3100, 3320, 3600, 4000, 4160, 4990, These the comparisons have been made on 6280, 8120, 8250, 8910, 17820. basis of chlorinity determinations from Haiti,
the island which hadziids and being only on Cyclopids: 10, 20, 20, 20, 20, 20, 30, 30, 40, 40, 40, 40, 50, thermosbaenaceans coexist in numbers large 70, 70, 100, 120, 120, 160, 240, 240, 240, 240, 250, 310,
statistical 320, 320, 320, 360, 360, 360, 400, 400, 480, 560, 560, 560, enough to allow treatment (as we 590, 680, 680, 720, 760, 800, 840, 880, 920, 920, 920, 920, have demonstrated above, this coexistence on 920, 950, 960, 960, 980, 1000, 1040, 1040, 1080, 1080, the that same island does not mean they 1080, 1160, 1160, 1280, 1280, 1280, 1320, 1320, 1360, coexist in the frequently same locality). 1360, 1390, 1400, 1440, 1480, 1480, 1480, 1560, 1640,
Using a test for unrelated scores on two 1680, 1720, 1760, 1760, 1880, 1880, 1920, 2000, 2160,
2280, 2380, 2630, 2800, 3320, 3340, 3600, 3630, 4000, variables (one rankable, the chlorinities; the 4360, 4900, 4990, 6280, 9400. other nominal, the taxa), such as the Mann-
Whitney test (Meddis, 1975, table 3.4.1 and §
5.5), we can compute a value for Z = -0.66, These tests make it likely that chlorinity is which is not significant. not the ecological (master) factor that deter-
In the the same way, chlorinities of 100 mines the distribution of the three groups under localities with cyclopids have been compared study. A correlation between distribution and with 100 localities with Here hadziids (table V). chlorinity was a priori rather unlikely, since in
islands which too, only on the taxa are known to one and the same locality, the chlorinity
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fluctuates the in but also for entire islands considerably during year, single localities,
in the semi-arid such those islands in the such particular islands, as (several Virgin group, as
of the Leeward Group, where periods of rains Anegada, Tortola, St. John and Culebra,
and droughts alternate, and with these the yielded dense populations of thermosbaena-
and rise. the but islands of the chlorinities drop Nevertheless, ceans no hadziids; several
faunal of certain rule Lesser such composition a locality as a Antilles, as Aruba, Curaçao,
does the St. not change during year. (One most Marie-Galante, Guadeloupe, Barbuda,
is the of abundance of had- interesting exception groundwater Martin, Anguilla yielded an
Blauw Baai Cave, Curaçao, in which marine or ziids but no thermosbaenaceans).
in polyhaline stygobionts penetrate dry periods, What kind of interaction exists between had-
whereas limnic groundwater elements abound ziids and other small crustaceans is a matter of
of Food is in periods strong rains.) speculation. competition highly unlike-
such since of debris of of Other abiotic factors, as light penetra- ly, supply higher plants, or
tion and is or temperature do not play any important microscopical plants such as yeasts fungi,
since in the available in wells and role, they are pretty constant abundantly many caves
examined. examined the groundwaters during our survey. Moreover,
A number of biotic factors of the hadziids of dif- possible are mouthparts are a quite
discussed in paragraphs b-d. ferent order of magnitude than those of the
It is well known that (b) cyclopids are quite cyclopids, making different food requirements
abundant in surface waters. It could be extremely likely.
that The postulated they penetrate only occasionally most plausible explanation is then, that
in which hadziids feed smaller Crustacea when hypogean waters, form the exclusive on these
The that this available. In absence of the habitat for hadziids. supposition are crustaceans,
would be factor of in the observed hadziids the usual food for a importance may turn to source
avoidance of hadziids and cyclopids, is unlikely subterranean amphipods, viz. decaying leaves,
if bears in mind that hadziids and thermos- and loam in one fungi yeast growing on caves, even-
baenaceans avoid bat etc. (both strictly hypogean taxa) tually manure,
each other's likewise. presence
(c) Since cyclopids (length 1 to 3 mm) and ther- 6.2. Zoogeographic implications mosbaenaceans 2 3 (length to mm) are con- The curious distribution of the Thermos- siderably smaller than hadziids (length 3 to 8 baenacea and the the former be limited the hadziid Amphipoda over mm), may to ground- of the groundwaters West Indian islands can be water in microporous substrates, the latter to
that of explained in at least two entirely different macroporous substrates. Although it is ways: and vicariant and feasible that the larger hadziids will be absent (1) by dispersal events, (2) by biological interactions. from microporous substrates, it is improbable
that would avoid cyclopids macroporous
substrates. it Moreover, seems important to 6.2.1. Dispersal and vicariance. — The
islands where the hadziids of note that on are of Thermosbaenacea of the presence genus
small size hadziid size 3-4 Monodella in the northeastern of the (e.g., Curaçao; body part An-
mm—cf. Stock, the same absence of tillean 1977), arc (Cuba, Haiti, Puerto Rico, Culebra,
in hadziid habitats is observed in cyclopids as and several of the British and U.S. Virgin islands with hadziids. be large-sized Islands), may interpreted as a good example
Hadziids interact with (d) other Crustacea, of dispersal via a North American-Caribbean such thermosbaenaceans and Track as cyclopids. In (see Rosen, 1976: 436 et seq., fig. 3).
this is the This idea is the of my opinion only plausible explana- supported by presence a tion. As soon as hadziids are absent, the other species of Monodella in several localities in Texas two show This is taxa up. not only true for (Edwards Aquifer, see Stock & Longley, 1981).
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of St. dates from the intercon- The occurrence Monodella on Croix, one time Anegada was of the U.S. Virgin Islands (Stock, 1976) seems nected with the other islands of the Puerto somewhat puzzling at first glance, since St. Rican Bank.
Croix is separated from the remaining Virgin The other possibility, viz. that the thermos-
Islands the baenaceans found have by a stretch of very deep water, nowadays on Anegada
about Anegada Trough (length 250 km, max- "stranded" or "crawled out of the sea" recent- imum 4574 St. about is hard depth m, see fig. 1). However, ly (i.e. 8000 years ago or less), to
Croix be of the since marine Monodella-like appears to a plate fragment accept, no ancestor
and is known Virgin Islands Bank, "belongs, according actually from the West Indies. So, a to its geological structure, to the Virgin Islands, recent evolution of inland-water Monodella and Lesser that would second viz. the not to the Antilles start with require a assumption,
Sombrero or Saba" (Weyl, 1966: 173, in simultaneous extinction of its marine ancestor. translation). Mitchell, 1954, suggests that the In the light of the relictary distribution of
formed in Anegada Trough was relatively recently Monodella (and Thermosbaena) the peri-
I inclined attribute (Quarternary). Mediterranean belt, am to a
On the other hand, the presence of various similar age to the West Indian members of the
related thé Monodella species, closely to New genus, thus an origin during the final stages of
World taxa, in the peri-Mediterranean belt, the Tethys Sea, in the (late) Miocene epoch.
well be sea-level in The absence of Monodella the can very explained by drops on many the later islands of the Antillean Tertiary (Fryer, 1965; Stock, 1976). geologically younger
movements of the the Volcanic but in During regressive sea level, arcs (e.g. Antilles, par- marine interstitial of ancestral ticular calcareous islands like populations on young
Monodella have stranded and have seem to to Guadeloupe/Grande-Terre, Marie-Galante, developed into continental groundwater in- Barbuda, Barbados, the Roques archipelago,
their habitants. At any rate, actual localities are etc.) becomes comprehensible then. all found on or near the late-Tertiary Tethyan seaboards. The distribution of the hadziids is more or
A similar envis- in "stranding" can easily be less similar to that of the thermosbaenaceans,
on the islands of the Antillean of tracks". The is aged chain, terms "generalized group which have undergone considerable positive virtually absent in South America (but for one vertical tectonic the Miocene. movements since species, found in a cave near the sea in
A difficult is the island case presented by of Venezuela, Metaniphargus venezolanus Stock &
well in Anegada (British Virgin Islands), one of the Botosaneanu, 1983), but is represented islands on which Monodella abounds. This island the northern half of Central America. Several
with the has been connected others on the species are known from the Edwards Aquifer in
Puerto Rican Shelf land until by a bridge Texas.
but the In the and southern of the 10,000-8,000 B.P., connections were eastern parts peri-
and sometime and Caribbean Leeward flooded, between 8,000 area (Lesser Antilles,
6,000 B.P., Anegada drastically reduced in size group, Venezuela) only a single genus, by transgressive sea-level movements (Heat- Metaniphargus, occurs in inland groundwaters, wole & MacKenzie, 1967; Heatwole et al., but in Central America, North America and in
for further references see Dunne & the Greater few 1981; Antilles, quite a genera are
If of Brown, 1976, 1979). represented. one wishes to speak "tracks",
carries rich track is the Since Anegada a groundwater a North American-Caribbean most
of population Thermosbaenacea (genus likely here as well.
I take it that island it is Monodella), for granted the In my personal opinion more likely that never was inundated completely by seawater, the hadziids, just like the thermosbaenaceans, the and that thermosbaenacean population originated from marine ancestors. Some of the
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lateral in direction to that older hadziid Amphipoda may be of similar age movement a opposite
of Cuba and the as the thermosbaenaceans (late Miocene). Hispaniola, along Cayman
had Rico Trench fault Several species must, however, have a Trough/Puerto system,
which would much more recent origin. For one of the not place Jamaica appreciably
of curasavicus closer of the other Antilles. subspecies Melaniphargus to any
the The of Thermosbaenacea and a Stephensen, 1933, inhabiting exclusively presence
fauna Pleistocene-Recent coastal plains of Curaçao, generically diversified hadziid on Cuba,
well for and Rico as as M. bullipes Stock, 1980, from Hispaniola Puerto (fig. 1), might
Marie-Galante and from indicate that these islands have once been Metaniphargus n. sp.
Guadeloupe (islands that emerged less than 1 interconnected. Several possibilities, some of
the late Pliocene million years ago), a much more recent evolu- them as recently as (ca. 5
been million tabulated tion from marine ancestors has postulated years) are by Hedges (1982,
(Stock, 1977, and Stock & Vermeulen, in press). table I). Mitchell (1954) supposes that if the
connected with Outside the West Indies, the presence of had- Puerto Rican bank ever was
ziids certain islands is known well it lost the connection in the on young as Hispaniola,
in lava Connections between the (e.g., Liagoceradocus acutus Andres, 1978, Pleistocene or earlier.
tunnels of Lanzarote in the Canary Islands). islands within the Puerto Rican bank have been
These observations the idea extensive and due in give support to that recent; to eustatic rises sea
if hadziids these connections to some, not most, belong to recently level, were lost only 8,000
stranded waves that started to colonize the 10,000 years ago (Heatwole et al., 1981). The
of members of inland groundwaters. common possession Monodella on
several islands of the Puerto Rican Bank sup-
do if the Greater the existence of interconnections. Geologists not agree as yet ports recent
Antilles were plate fragments once attached to a
continental landmass each — (and/or to other) or 6.2.2. Biological interactions. It can
if had continental be accidental that islands in which they never attachments. hardly
More exists about the Lesser An- abound agreement hadziids (such as Curaçao, Aruba,
tilles, of which no past attachments are assumed Barbuda, Anguilla, etc.) lack inland-water
(Hedges, 1982). Thermosbaenacea, whereas islands in which
Data based the Malacos- Thermosbaenacea abundant on groundwater are (such as
traca do not contradict a view that Jamaica has Anegada, Virgin Gorda, Tortola, and Culebra)
been attached continental lack hadziids. The in be due never to any or pattern might part
insular landmass in the whereas interactions members of area, Cuba, to among these two
the Hispaniola and Puerto Rican plate might groups.
well have had mutual connections. If the thermosbaenaceans origin Since are generally con-
of the earlier inland-water hadziids and ther- sidered "primitive" crustaceans ("living
mosbaenaceans dates from the Miocene, it is fossils" in the words of Botosaneanu &
plausible to infer that interconnectionsbetween Delamare Deboutteville, 1967), it is tempting to
the three islands still existed in that that — in the older epoch. assume they were once
I wish to illustrate the statements in the Caenozoic — more widely distributed over the
previous paragraph by the following observa- West Indian islands. Fryer (1965) made it
tions: probable that the peri-Mediterranean Ther-
The absence of Thermosbaenacea on mosbaenacea evolved from marine ancestors
Jamaica and the absence of a hadziid fauna that that "stranded" during geotectonic oscillations
is diversified in the late Miocene. Stock on generic level (only the peri- (1977) thought it not
Caribbean is the that the hadziids likewise genus Metaniphargus present on unlikely descended,
the from marine from Pliocene island; Stock, 1983), supports interpretation ancestors, Miocene,
of Hedges, 1982, that Jamaica has undergone a or Pleistocene strandings. The presence of had-
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ziids islands scribed above on that emerged relatively recently (dispersal, vicariance, biological
(Lanzarote, Grande-Terre, Marie-Galante) interactions) is supported by at least some
the idea that if evidence. the actual of gives further support to some, Presumably, pattern
hadziids insular and intrainsular distribution not most, belong to younger waves occurrence that started to colonize the inland ground- is based on a complicated combined action, not
of waters. necessarily during the same geological epoch,
the nonmarine Thermos- the various In the of In the West Indies, processes. case ground-
10 such thermosbaenaceans baenacea are restricted to chlorinities of to water organisms as
2440 mg/1 (limnic and oligohaline waters and hadziids, the following evolutionary
scenario is contradicted fact: according to the Venice System). Hadziids are, not by any
the islands where thermosbaena- of the Monodella from marine at least on (1) origin group
distributed ceans occur as well, predominantly ancestors by stranding (vicariant process, called
the and do in waters of same chlorinity, not regression model);
difference in inland-water show a significant overall salinity (2) adaptation to conditions;
the preference. If we consider, however, the (3) dispersal over emerged plates (e.g.,
of the hadziids islands Puerto Rican distribution over all the plate), eventually over adjacent in the West Indies, including those that do not plates (e.g., Cuba/Hispaniola);
of of marine harbour thermosbaenaceans, we find that over (4) stranding more recent waves
15% of the hadziid stations have higher descendants (hadziids);
locali- of the invaders inland- salinities than in any thermosbaenacean (5) adaptation new to ty. Eleven percent of the hadziid stations water conditions, followed by dispersal;
extermination of the older classifies as mesohaline, and one percent even (6) by prédation as polyhaline. This halophily may be taken as groundwater Crustacea (thermosbaenaceans)
from the an indication for a more recent descent by younger ones (hadziids); marine for the in in ancestors hadziids, com- (7) survival of thermosbaenaceans islands
thermosbaena- hadziids and parison to the more halofugous without in large islands offering a
number of habitats the ceans. greater allowing
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Received: 22 August 1983
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