Reprinted from the Proceedings of the 4Th Pacific Science Congress, Java, 1929; from Vol

Home , East Indies, Flores Sea, Gulf of Tomini

Reprinted from the Proceedings of the 4th Pacific Science Congress, Java, 1929; from Vol. III, 1930, pp. 1-6 (preprint, pp. 1-6, issued at Congress, May, 1929).

The Hydrographic and Faunal Independence of certain isolated deepwater seas in Eastern Asia. by CARL L. HUBBS University of Michigan, U. S. A.

One of the most fascinating phases of zoogeography, since the publication of WALLACE'S "Island Life", has been a comparison of the faunas of isolated regions. The faunas of islands are not the only ones segregated from one another : so also are those of mountain tops, of rivers, of continents and oceans themselves. Among the most interesting cases are those of isolated deepwater basins-freshwater lakes, saline inland seas, deep fjords, and partially enclosed seas, such as the Black Sea and the Mediterranean Sea. It is probable that a number of such seas exist in the highly complicated Indopacific region. Two seas of this sort have interested me, and they form a striking contrast with one another. The Sea of Japan, nearly enclosed by land or by straits which nowhere are depressed as much as 180 meters below sea level, receives through Chosen Strait at its south end a branch of the warm Kuro Shiwo, and through its northern straits cold subarctic waters, which of course dip down beneath the warm layers coming up from the south. DR. CHARLES HENRY GILBERT, whose recent death was a severe blow to the zoology of the Pacific, has related to me the taking by the Albatross during its 1906 cruise in Japan, of tropical pelagic animals over a subarctic bottom fauna. Unfortunately little has been published on the faunal and hydrographic relations of the Sea of Japan. One definite point has however been determined : the macrouroids, ordinarily the most abundant in species and individuals of the deepsea fishes, were nowhere found in the Sea of Japan, although numerous and successful hauls of the trawl were made at appropriate depths, and although these fishes were everywhere taken in the Okhotsk Sea and along the eastern shore of the Japanese chain. The macrouroids have not penetrated into the Sea of Japan, probably because the rim of the basin is everywhere above the bathymetric range of the family. The Sulu Sea and connected waters to the northeastward, together

B. 1 bounded by Luzon. Samar, Mindanao, Sulu Archipelago, Borneo and Palawan, are likewise largely isolated from the surrounding ocean and seas, but offer a sharp contrast with the Sea of Japan, in hydrography as well as in fauna. These waters are connected with South China Sea on the west and northwest, with the Pacific Ocean on the northeast and east and with Celebes Sea on the southeast and south, by numerous straits, in some of which the surrounding rim is depressed to between 350 to 550 meters. Since the more open waters surrounding the Sulu Sea are all Tropical (the open surface water in all remains above 25° C. all winter) there is no available cold surface water to sink into the depths of Sulu Sea. The temperature of the surrounding waters 0 often drops to somewhat below 10 at depths between 350 and 550 meters, but such cold waters are held back from the Sulu Sea by the fact that in the connecting channels the temperature at such maximum 0 depths is warmed to above 10 (Figure 1). In the Sulu Sea proper, including Mindoro Sea, the bottom temperature drops to 10° at about 550 meters depth, then remains constantly slightly below 10° to depths greater than 2000 meters (Figure 2). In Mindanao, Surigao and Visayan seas, and other island-surrounding waters between the Sulu Sea on the southwest and Luzon, Samar and Mindanao on the northeast, all more or less connected with Sulu Sea,—the bottom temperature also remains nearly constant at depths greater than 550 meter, but is generally about 11. 5°, averaging almost 2° warmer than Sulu Sea proper at similar depths (Figure 3). In two localities, namely Tanon Srait between Negros and Cebu, and Ragay Gulf in southern Luzon, much higher bottom temperatures prevail, 0 approximately 17 in depths between 400 and 700 meter. In the more open waters surrounding Sulu Sea and the inland waters to the northeast, fairly uniform bottom temperatures prevail. Every- where in these waters there is evident a continued decline in bottom temperature with increasing depth. The temperature curves for the South China Sea (off the Philippines, Hongkong and Formosa), and for the Pacific Ocean off the east coast of Luzon and Mindanao, are remarkably like those for the waters about the East Indies South of the Philippines—Celebes Sea, Gulf of Tomini, Strait of Makassar, Flores Sea (Figures 4 to 6). There are, to be sure, some exceptionally

warm records for the South China Sea, but these are0 in passages in which the bottom temperatures drop to colder than 7 at depths greater than 950 meters ; the exceptionally warm records at about 365 meters in the Pacific Ocean are for Pujada Bay, Mindanao, and perhaps do not represent the usual condition in the ocean off the Philippines.

2 Fig. 1.- Solo Arch i pe lago

Fig.1.- Celebes Sea to Flores Sea

• FL§ 6.- South ChLna Sea

8 3 In Sulu Sea and associated waters, unusually warm at great depths because they are shut off from the deep polar drift, there is a rich and distinctive deepsea fish fauna. So distinct is this fauna, that GILBERT and HUBBS made of the area a distinct faunal subregion, the Philippine, coor- dinate with the East Indian. The shallow-water fauna of the area does not of course, show such distinctness. Since the macrouroid fishes are the only deepsea group of the Philippines which has been fully reported upon, we must look to GILBERT and HUBBS' contribution on this family for a discussion of the deepwater fauna of the Philippine subregion. They reported (U. S. Nat, Mus., Bull. 100, Vol. 1, part 7, pp. 376-377). "This subregion includes the waters about the central Philippine Islands, north of the Tawi Tawi group, and south of west-central Luzon, and exclusive of the Pacific Ocean along the east coast of Luzon. While sharing many of its species with the East Indies, this subregion is inhabited by a number of peculiar and often singular forms: Bath ygadus sulcatus; Gadomus magnifilis; Coryphaenoides semiscaber (representing the East Indian C. tydemani); three species of Coryphaenoides, each known only from its type dredged in the depths of the Jobo (Sulu) Sea — namely C. paradoxus, C. dubius, and C. camarus; Coelorhynchus quin- cunciatus and thompsoni, C. velifer, C. macrolepis, C. carintier. C. acuti- rostris; Hymenocephalus gracills (closely related to the Hawaiian H. tenuis); H. longiceps; H. s. torvus (representing H. s. striatissimus of Japan, Formosa, and eastern Luzon, and H. s. aeger of the East Indies; intergrading with striatissimus off northern and northwestern Luzon, and with aeger about the Tawi Tawi group); Malacocephalus luzo- nensis; Ventritossa macronemus (most nearly related to V. misakia of Japan and eastern Luzon); Ventritossa lucifer; Lionurus decimalis. "The Philippine subregion appears to lack certain species of the East Indies, as the Albatross failed to obtain them during monhts of intensive dredging within the limits of the subregion. These species follow : Bathygadus filamentosus, B. entomelas, Gadomus Coryphaenoides asprellus, C. tydemani, C. heyningeni, C. aequatoris, C. orthogramnius, C. sp. Weber, Coelorhynchus plat- orhynchus and acantholepis. Hymenocephalus s. aeger, H. grimaldii, Malacocephalus? laevis, Lionurus infranudis, L. evides, L. vittatus, L. richardi, and L. parvipes, Mataeocephalus adustus, Cetonurus robustus. "In contemplating such a peculiar fauna occupying a comparatively restricted area, one is led to examine the hydrographic data of the region to determine whether the physical conditions of life may be obviously unusual. Such an examination does, in fact, indicate that the basic conditions of depth and temperature throughout this subregion

4 are in peculiar relationship to each other. Briefly stated, the region consists largely of a partially inclosed cup, broken up by islands to the northward, and communicating with more open bodies of water only by narrow channels, much shallower than the depths of the Jobo (Sulu) Sea, which in consequence are rendered peculiarly warm. The temperature records of depths greater than 400 fathoms vary little from 50° F., and nowhere was the temperature found to fall as low as 49°, although depths of over 1,000 fathoms were investigated. "At the northern end of the Philippine subregion, in the China Sea off southern Luzon, it was found that the temperatures do not remain warm at greater depths. Here the fauna resembles, in general, that of the moderate depths to the southward, and as it contains no additional northern elements we consider it a derived portion of the Philippine fauna. It is characterized particularly by the exclusive or nearly exclusive occurrence of Coelorhynchus veliter, C. macrolepis, and C. cariniter Of the other, species peculiar to the Philippine subregion, this northern district shares with the south only Coelorhynchus thompsoni. Hymenocephalus striatissimus torvus, and Ventritossa luciter (one specimen), fishes inhabiting the moderate depths. The remaining fishes inhabiting the China Sea off southern Luzon are not among those peculiar to the Philippine subregion." In looking over the reports on other deepsea animals dredged by the Albatross about the Philippines (all published as parts of Bulletin 100, United States National Museum), it is evident that in general the deepsea fauna of the Philippine subregion is exceedingly rich, and contains a high proportion of distinctive elements. As the other groups collected on the same cruise particularly the fishes — are subjected to study, it will be very interesting to note how well they conform in their distribution to GILBERT and HUBBS' summary (1. c., p. 371) on the macrouroid fauna of the Philippine subregion. "The region of the Job o or Sulu Sea forms a partly inclosed basin connected with open waters by narrow and comparatively shallow channels ; the water of the sea is consequently rendered warm, retaining a temperature of more than 49° F. to depths of over 1,000 fathoms. Though of comparatively small size, the Philippine faunal subregion, comprising these waters of unusually high temperatures at great depths, contains a large proportion of peculiar and frequently very distinct species, which have probably been evolved in this region of peculiar environmental conditions. The process of their evolution has doubtless been aided or hastened by their isolation, more or less complete, in this partly inclosed sea".

5 Explanation of Figures. All six figures are graphs showing the relation between bottom temperature (plotted as alscissae) and depth (ordinates) for certain specified regions, in South China Sea and about the Philippine and East Indian islands. The data were all compiled from the records of the Albatross 1907 1910 Philippine expedition (publisheid as Doc. 741, U.S. Bureau of Fisheries). The depth data in fathoms and temperature records in degrees Fahrenheit, were converted into the metric system and Centigrade scale. No statement is made in the records cited as to whether the temperature readings were corrected for pres- sure: if they were not, the comparisons and conclusions made in the present paper would not be invalidated. The surface temperatures indicated were obtained by averaging for each area the readings given in the Albatross report for all stations where the depth equals or exceeds 100 fathoms (183 meters). For a discussion of each curve, see the text.