Memoirs MCZ 0701

Memoirs of tbc ^uscum of Comparalibc ^oologn AT HARVARD COLLEGE Vol VII No REPORT ON THE FLORIDA REEFS By LOUIS AGASSIZ ACCOMPANIED BY ILLUSTRATIONS OF FLORIDA CORALS, From Drawings by A Sonrel, Burkhardt, A Acassiz, and Roetter With an Explanation of the Plates by L F Pourtales Pl'BLlSHED BV PERMISSION OF A D BaCHE AND CaRLILE P PATTERSON, Superintendents of the U S Coast Survey CAMBEIDGE: Prtntrtt for tfie 1880 Jluscum PREFACE greater TriE number of the originally prepared for the Plates which final accompany Report were this Report of Professor Louis Agassiz on the Coral Reefs of Florida, which for various reasons was never published make known order to Mr Sonrel, late it was of Florida Corals," He the beautiful drawings of corals lithographed my In by the intention to publish these plates, as " Illustrations with an explanation kindly supplied by Mr Pourtales ^ has also selected a few additional species, which have been lithographed and added characteristic of the as possible builders On make to the original plates in order to these illustrations as far prominent Florida species, both the and those found within the reef reef- area.^ consultation with the Superintendent of the Coast Survey, the Hon Carlile P Patterson, far as it could it was deemed advisable same time, as be found, the Report of Professor Agassiz on the Florida Reefs, extracts of which were published in the of the Coast Survey for 1851, the permission of the Annual Report of the Superintendent — a publication but before the days of deep-sea dredging sketch of to publish at the To this publishers, Messrs Report I to naturalists have appended, with Co., the "Methods of Study," and his investigations of the Florida of the Coast Survey I known Houghton, Osgood, & Florida found in Professor Agassiz's based entirely upon little Reefs under the auspices have added a sketch map of southern Florida, with the Keys, compiled from Coast Survey maps, to facilitate the reading of this Report.^ ' During his frequent visits to all parts of our sea-coast, a marine animals which can only be drawn directly from Agassiz tions, ; life, these I hope from time to time to publish in the and the Florida corals form the ' For the deep-sea * For further first corals see Pourtales, number of drawings of polyps and of other were made under the direction of Professor Museum Memoirs, with the necessary explana- part of these illustrations No IV details see the large Coast Illust Cat.M Survey charts Nos C Z Mem Mus Comp Zobl., Vol II 166, 167, 168, 169, issued since the date of Professor Agassiz's report ALEXANDER Cambridge, M.\ss., March, 1880 AGASSIZ EEPORT THE FLOMDA EEEFS OJSr KEPOET OF PROFESSOR A6ASSIZ TO THE SUPERINTENDENT OF THE COAST SURVEY, ON THE EXAMINATION OF THE FLORIDA REEFS, KEYS, AND COAST Cambridge, Sir, Augiist, 1851 — The following report of the examination made by me of the Florida reefs, keys, and coast is prepared in compliance with your request Topography of Florida To form to a correct idea of the Florida reefs, it is of paramount importance keep in mind the topographical features of the whole country The peninsula of Florida projects between the Gulf of Mexico and the Atlantic, from the 30th degree of northern latitude nearly to the 24th, as a broad, flat, low promontory, which has generally been considered a continuation of the low lands of the Southern States not the case, or, at least, But, as we shall see hereafter, this is not with respect to the southern extremity of the peninsida, which consists of the same formations as the reef itself in a physical point of view, Florida forming the peninsula, which rise is hot limited to those tracts of land, above the level of the sive shoals along its southern extremity, keys and reefs, as well as those whence they sea, for the exten- between the main-land and the extending to the west as far as the Tortugas, stretch along the western coast, in fact belong to intimately connected with it, by Again, their physical character tract of flats along the eastern shore, but southern and western shores, nor does it it is There it, is and are a similar not so extensive as on the partake as largely of the peculiar character of the peninsula, being chiefly formed of the alluvial sand, drifted ashore by the waters of the Atlantic We shall have occasion, however, to show hereafter that the narrow longitudinal islands, which extend close to the main-land almost for the FLORIDA REEFS whole length of the eastern shore, are probably a direct continuation of the keys, covered with drifted sand.* This is certainly the case with the range of keys extending from the main-land to Cape Florida, which limits to the east the bay of Miami, their formation being of coral rock, but covered by As silicious drift-sand southernmost extremity of the main-land proper, to the determine to difficult its as outlines, consists it very is it of innumerable islands, sometimes separated by narrow channels, and sometimes assuming the character of real islands only at high water, being mostly connected with the main-land by very shallow flats This especially the case along the is southwestern extremity of the peninsula The between Cape Florida and Cape Sable, shore, however, is southern the of outline better defined, presenting, in almost unbroken continuity, steep bluffs of the same coral limestone which forms the bottom of the everglades, and may be traced, without interruption, along the Miami from the seashore to the everglades South of the main-land, between extensive it and the range of keys, there are which, even at high water, are but slightly covered, and flats, which the retreat of the tide lays bare, leaving only channels between the dry flats, with occasional depressions of greater depth These mud far as Cape Sable, but may be traced flats narrow and shallow extend not only between the main-land and the keys as to the north along the western shores of the continent, and to the west along the northern shores of the keys, not only as far as Key West and the Marquesas, but even to the Tortugas There is, however, this remark to be made, — that to the west the become covered, by degrees, with deeper and deeper water flats ; mud or, in other words, that these low grounds, extending between the main-land and the main range of keys, dip slightly to the west, being gradually in the shoals the extending north of the Marquesas and the Tortugas, along western shore of the peninsula innumerable low of the lost islands, Mangrove known in the These flats country by Islands, respecting which we are interspersed with the generic appellation shall give further details hereafter The * A shoals between Cape Sable, Cape Florida, and the main range of direct investigation of tbis point, which did not come within considerable practical importance, inasmuch as aifording a far more solid it may lead to tlie tlie limits of my survey, would be of discovery of a basis of coral rock, foundation for the construction of the lighthouses wanted along that coast, than the loose shore-detritus FLORIDA REEFS keys are literally studded with these Mangrove Islands are distributed without apparent regularity of Key the ; Sometimes they sometimes, as to the north Largo, they form a continuous range between the main-land and They keys are very numerous along also them which least along that side of mud main the of innumerable small from these low Honda and Key when we attempt We Such archipela- the Pine Islands, as well The luxuriant vegetation which West have occasion to return to shall this to explain the formation of the different islands with the Florida Reef and the main-land rises mangroves, gives them a very islands, consisting chiefly of peculiar appearance archipelagoes little as to be almost impenetrable goes occur chiefly to the north of Bahia as to the northwest of at intimately interwoven, and separated by such islets, so narrow and shallow channels, or turned towards the most extensive is Sometimes these Mangrove Islands form tlats keys, The whole tract subject connected between Cape Sable and the keys, east of Bahia Honda, as far as Cape Florida, or at least as far as Soldier Key, except to very small The keys consist of is so shoal that it will forever remain inaccessible, vessels an extensive range of low islands, rising but a few feet, perhaps from six to eight or ten, or at the utnaost to twelve or thirteen feet, above the level of the They begin sea to the north of where they converge towards the main-land, extending in the Cape Florida, form of a flat crescent in a southwesterly direction, gradually receding from the main-land until, opposite from it Cape Sable, they have by a shallow sheet of water they project in a as the Tortugas, of accumulated more westerly so far retreated as to be separated forty miles wide course, with occasional interruptions, as far which form the most western group dead corals, Farther to the west of coral rocks, or together with more or less compactness They consist either of coral sand, cemented Their form varies, but is usually elongated and narrow, their greatest longitudinal extent following the direction of the course is Avhich we main range, except Key group of the Pine Islands, almost at right angles with the main range, shall Most of these and in the —a where their circumstance attempt hereafter to explain islands are small, the largest of them, such as Largo, not exceeding ten or fifteen miles in length two or three, and many scarcely a mile in their size, others only Their width varies from a quarter to a third or half a mile, the largest barely whatever the difference ; Key West they measuring a mile across all agree in one respect, ; but — that FLORIDA REEFS their steepest shore turned towards the Gulf Stream, while their more is gradual slope inclines towards the This is a point which it is mud flats important to notice, as comparison between the keys and the shore and the as with the outer reef that the seaward shore or, in which they it encircle our will assist us in bluffs of the main-land, as well reefs of other seas, in all of which we find steeper than that turned towards the main-land, is the case of circular reefs enclosing basins (atolls), than that which borders the lagoon reef proper extends parallel to the The miles south or southeast of many miles from it, few for a following the same curve, and never receding distance between the reef and the The it main range of keys main range of keys varies usually from six to two or three miles, the widest separation Key West and being south of is about seven miles Between rise at distant intervals, there reef, six is east of the this reef, Ragged Keys, where the space upon which a few small keys and the main range of keys already described, a broad, navigable channel, extendhig the whole length of the from the Marquesas to Cape Florida, varying in depth from three to and seven fixthoms, and, more than fourteen feet except off Looe Key, where the passage is not to four deep at low water, averaging from three fathoms Farther east the average depth is again the same as at Looe becomes gradually more and more shoal towards the about two fathoms, or even less, to the east of east, Key ; but it measuring usually Long Key and Key Largo, but deepening again somewhat towards Cape Florida, where the reef converges towards the main keys and the main-land reef, this Protected by the outer channel affords a very safe navigation to vessels of medium size, and would allow a secure anchorage almost everywhere throughout tbe whole length of the reef, were the numerous deep channels which intersect known the outer reef well signals As it is, to navigators, and marked by a regular system of however, the reef seems to present an unbroken range of most dangerous shoal grounds, upon which thousands of vessels, as well as millions of property, a stronger claim as already have already been wrecked These upon the attention of the government, facts have since there are, remarked, numerous passages across the reef which might enable even the largest vessels to find shelter and safe anchorase behind this threatening shallow barrier The reef proper, as we have remarked above, runs almost parallel to the FLORIDA REEFS main range of keys from Cape Florida quesas, where it is lost It follows in its in the deep Mar- to the western extremity of the whole extent the same curve as the keys, encircling to the seaward the ship-channel already men- This tioned properly the region of living corals is Throughout its whole range except in a few points Avhere mark, giving does not reach the sea comes almost within the level of low-water Tennessee Reef, and a few other shoals of less extent, In a few localities fragments of dead dangerous of the sui-face heavy breakers, such as Carysfort, Alligator Reef, to rise it it begin to accumulate upon the edges of the but perhaps not and coral coral less sand forming small keys, which reef, vary in form and position according to the influence of gales blowing from different directions, from southwest — sometimes to northeast, in direction the of Gulf the Stream but more frequently in the opposite direction, Such are Sombrero Key, the prevailing winds blowing from the northeast Looe Key, the Sambos, and Sand Key Here and there are isolated coral boulders, which present projecting masses above water, such as the Key Rocks, west of Sand Though isolated not to present into many ; Pelican Reef, east of continuous, the outer reef many broad passages over is, it ; with many others, Dry more however, not so uniform as its crest, dividing it, as it were, main keys, submai'ine elongated hillocks, similar in form to the but not rising above water, and in which the depressions alluded to corre- spond to the channels intersecting the keys into the ship channel, anchorage within the to the may be which reef, are chiefly These broad passages leading available as entrances into the safe the inlet in front of west of Carysfort Reef, with nine feet of water French Reef and Pickle's Reef, and Crocker's Reef, also with ten feet with ten feet Alligator Reef, with two fathoms ; ; ; in a passage between another between Conch Reef another between Crocker's Reef and another between Alligator Reef and Ten- nessee Reef, with two fathoms and a half; Tennessee Reef, varying ; Key Largo and and a sixth to the west of depth from two and a half to three fothoms The remark which has been made respecting the mud flats and their gradual deepening from east to west applies equally to the general features of the main reef, as well as to the intervening channel the channel shoaler, is To shallower, the ground around the keys and and there is a gradual dip towards the west, which the eastward reef becomes makes the con- marked between the keys west of Key West, in the large groups of the so-called Mangrove Islands, and the Marquesas, beyond which there is nection less FLORIDA REEFS even an extensive interruption These the Tortugas belong none the last, in the succession of the keys before we reach however, as well as the bank west of these keys, main range of keys, from which they are only less to the West of Sand Key separated bv a more extensive and deeper depression the reef itself becomes gradually less elevated, luitil where finally lost is it the ship channel, south of the Marquesas, expands into the broad depression, separating that group of keys and shoals from the Tortugas In order to understand fidly not only the topography, of formation of all these keys and reefs, which form more or risino- reefs, heio-hts nearly to the it l)ut also mode the must be remembered that the continuous walls, reaching- at unequal less above the level of the waters, are only surface, or a particular modification of those formations growing upon coral grounds under special circumstances been ascertained, whenever similar It has investigations have been made, that living corals not occur in depths exceeding twenty fathoms, the tiiat reef-building species from prosper a depth of about twelve fathoms nearly to the surface, and that diflereut Now, species follow each other at successive heights these facts, we we keep in mind of the West Indies, if shall see that all the coral-bound islands as well as of the main-land of Central America, constitute an extensive coral field, divided by broad, deep channels, over which the coral reefs extend, with different features, according to the depths in which they occur and the changes which their own growth has gradually introduced upon the ties where they are found, influenced locali- modified to some extent also by and the direction of the prevailing currents and the action of the tides The formation a reef, — for, as of the we main range of keys shall see hereafter, their primitive condition as in they have been a submarine reef before they rose as islands above the level of of this range, as we we tlie ocean, — the repeat, at gradually greater distances from the main-land, follow their course from east to west, has been simjily depth of the bottom from which the reef has of ten or twelve fathoms' depth ; and if between the Marquesas and the Tortugas, over that space formation Again, if risen there it is is owing to the It has followed the line so wide an interruption because the ground deeper is the Pine Islands have a northwesterly direction, while the main range runs more from east to west, it is no doubt because the bod}^ of water emptying from the northern part of the gulf, along the western shores of the peninsula, has, while the tract of mud flats for a time, run chiefly over that between the keys and the main-land was field, filling PLATE XX Fig Millepora alcicornis Lamarck, natural Fig Millepora alcicornis Lamarcli, branchlet seen from above, natural Fig Millepora alcicornis Lamarck, branchlet seen in Figs 4, size size profile Millepora alcicornis Lamarck, vertical and horizontal sections of corallum, showing the transverse floors (tabulse) of the calicles Fig Millepora alcicornis Lamarck, surface magnified, showing the two kinds of calicles PI XX FiORiDA Corals Pruvie.; %M Priiued byA.Meisel PLATE Lamouroux, natural XXII Udotea flabellata Fig Udotea flabellata Lamouiou.x, Fig Udotea flabellata Lamouroux, portion magnified Fig Udotea flabellata Lamouroux, surface Fig Halimeda Fig Halimeda tridens var incrassata Lamouroux, Fig Halimeda tridens var incrassata Lamouroux, segments magnified Fig Figs 8, tridens var incrassata Halimeda tridens size edge of frond, magnified of frond, magnified Lamouroux, natural var incrassata profile size view of terminal segments Lamouroux, end view of terminal segments, magnified "Florida Corals" Pruued hyAMcisei PLATE Sketch map of Southern Florida, of the XXIII Keys and Reef, compiled from Coast Survey maps ^ J ll^ > / > ».!, \}s-^' J L S T |{ A '1' S () I-' I' I, () H I I) A ... Pourtales, number of drawings of polyps and of other were made under the direction of Professor Museum Memoirs, with the necessary explana- part of these illustrations No IV details see the large Coast