4.11
Relationship of Indian Ocean Epiplanktonic
Calanoids to the W orId Oceans
A. FLEMINGER and K. HULSEMANN
Circumglobal distributions are widely accepted as commonplace among epiplanktonic
species of zooplankton and especially for those copepods occurring in warm oceanic
waters (SEWELL, 1948). Nevertheless, the warm-water belt lying roughly between
latitudes 40° Nand 40° S is not a continuous circle. Interruptions include a virtually
perfect warm-water barrier, the Americas, separating the Atlantic and Pacific Oceans, the
extensive Afro-European barrier separating the Atlantic from the Indian Ocean as far
south as latitude 35° S and the mosaic of land masses and shallow seas comprising the
Austral-Asian boundary intervening between the Indian and Pacific Oceans. These barriers
appear a priori to be formidable deterrents to panmixis and in all likelihood they have
prevailed in their relative positions at least since the end of the Tertiary (DARLINGTON,
1965).
DAHL (1894) was among the first to suggest that the circumglobal warm-water belt is
not faunistically homogeneous. On exceedingly limited evidence DAHL noted the existence
of many differences among the species of copepods known at the time from the Atlantic
Ocean on one hand and from the Indian and Pacific Oceans on the other. Appropriate
support for his view has been scanty and largely unnoticed. One source is SCHMAUS'
(1917; SCHMAUS and LEHNHOFER, 1927) discovery that the equatorial epiplanktonic
species, Rhincalanus cornutus, is geographically poly typic and actually consists of 2 distinctively different populations, one restricted to the Atlantic Ocean and the other ranging
through the Indian and Pacific Oceans. Equally significant is JONES' (1965) observation
that the equatorial epiplanktonic species Candacia pachydactyla parallels R. cornutu5
in having constant morphological differences distinguishing the Atlantic form from the
form found throughout the Indian and Pacific Oceans. In addition, LANG (1967) presents
evidence that within the Eucalanus elongatus species group, E. inermis is found only in
the eastern equatorial Pacific and it is replaced to the west in the Indo-Pacific region by
E. elongatus s.s.
Drawing upon his admirable efforts to document the limits of diversity in the genus
Calanus s.l., BRODSKY (1965) argued at length on the need to analyze and compare epiplanktonic populations systematically from the vantage point of a world-scale view.
Judging by the perspectives of warm-water distributions obtained from such a view of
the genus Clausocalanus (FROST and FLEMINGER, 1968) in addition to the others
mentioned above, BRODSKY'S points are well taken. FROST and FLEMINGER found 2 categories of warm-water distribution within Clausocalanus. One pattern is circumglobal
and apparently sustained by warm-water epiplanktonic species capable of breeding
effectively to about 40° north and south latitudes. The second pattern is non-circumglobal
and the breeding range is apparently restricted to lower latitudes between the Equator
and perhaps 30° north and south.
Relationship of Indian Ocean Epiplanktonic
Calanoids to the W orId Oceans
A. FLEMINGER and K. HULSEMANN
Circumglobal distributions are widely accepted as commonplace among epiplanktonic
species of zooplankton and especially for those copepods occurring in warm oceanic
waters (SEWELL, 1948). Nevertheless, the warm-water belt lying roughly between
latitudes 40° Nand 40° S is not a continuous circle. Interruptions include a virtually
perfect warm-water barrier, the Americas, separating the Atlantic and Pacific Oceans, the
extensive Afro-European barrier separating the Atlantic from the Indian Ocean as far
south as latitude 35° S and the mosaic of land masses and shallow seas comprising the
Austral-Asian boundary intervening between the Indian and Pacific Oceans. These barriers
appear a priori to be formidable deterrents to panmixis and in all likelihood they have
prevailed in their relative positions at least since the end of the Tertiary (DARLINGTON,
1965).
DAHL (1894) was among the first to suggest that the circumglobal warm-water belt is
not faunistically homogeneous. On exceedingly limited evidence DAHL noted the existence
of many differences among the species of copepods known at the time from the Atlantic
Ocean on one hand and from the Indian and Pacific Oceans on the other. Appropriate
support for his view has been scanty and largely unnoticed. One source is SCHMAUS'
(1917; SCHMAUS and LEHNHOFER, 1927) discovery that the equatorial epiplanktonic
species, Rhincalanus cornutus, is geographically poly typic and actually consists of 2 distinctively different populations, one restricted to the Atlantic Ocean and the other ranging
through the Indian and Pacific Oceans. Equally significant is JONES' (1965) observation
that the equatorial epiplanktonic species Candacia pachydactyla parallels R. cornutu5
in having constant morphological differences distinguishing the Atlantic form from the
form found throughout the Indian and Pacific Oceans. In addition, LANG (1967) presents
evidence that within the Eucalanus elongatus species group, E. inermis is found only in
the eastern equatorial Pacific and it is replaced to the west in the Indo-Pacific region by
E. elongatus s.s.
Drawing upon his admirable efforts to document the limits of diversity in the genus
Calanus s.l., BRODSKY (1965) argued at length on the need to analyze and compare epiplanktonic populations systematically from the vantage point of a world-scale view.
Judging by the perspectives of warm-water distributions obtained from such a view of
the genus Clausocalanus (FROST and FLEMINGER, 1968) in addition to the others
mentioned above, BRODSKY'S points are well taken. FROST and FLEMINGER found 2 categories of warm-water distribution within Clausocalanus. One pattern is circumglobal
and apparently sustained by warm-water epiplanktonic species capable of breeding
effectively to about 40° north and south latitudes. The second pattern is non-circumglobal
and the breeding range is apparently restricted to lower latitudes between the Equator
and perhaps 30° north and south.