T H E . . . . W A S M A N N . . . . J O U R N A L . . . . O F . . . . B I O L O G Y
Volume 27, Number 1 ..................................................................Spring, 1969
An Intertidal Reconnaissance of Rocky
Shores of the Galapagos*
*Charles Darwin Foundation Contribution Number 106.
Joel W. Hedgpeth, Oregon State University Marine
Science Center, Newport, Oregon 97365.
"Abstract: Although there have been many scientific visitors to the Galapagos, little notice has been taken of the marine life on the shores of these volcanic islands. Most visitors have been concerned with the birds, reptiles, and terrestrial flora, and except for the marine iguanas and the ubiquitous red crabs, the life between the tides has rarely been mentioned. Indeed thef act that the yearly tidal range on these islands is in the order of six or seven feet, a surprisingly large range for equatorial islands, is seldom remarked upon. Nevertheless there has been extensive collecting of marine invertebrates in tidepools and shallow waters of the Galapagos and larger, more common elements of the flora and fauna are reasonably well known. A well-developed, although not always obvious biota is found between the tide-marks in many parts of the Galapagos. It is most obvious on wave-swept shores, but there are many intertidal organisms living beneath rocks and crevices, some of them at surprisingly high levels. Observations of intertidal zonation patterns were made at a number of localities in the Galapagos during TeVega cruise 17, from February 26 to march 18, 1968. These observations spanned the equator and included both warm- and cool-water environments in the archipelago."
INTRODUCTION
At first glance the shores of the Galapagos appear to be a barren jumble of slag heaps, cracked blocks of lava and basalt, and cinder piles, all funeral black. It would be difficult to improve upon the grim description of the scene by Herman Melville in Las Encantadas, and from the viewpoint of the student of intertidal zonation there is certainly a dearth of smooth surfaces covered by marine life, and even tide pools are none too common. The equatorial sun heats the rock surfaces exposed even for a few hours at low tides to temperatures that may be beyond the lethal limits for many intertidal animals, and shallow tide pools may become as warm as any truly tropical locality. marine life is abundant in deep tide pools, as described by Beebe (1924) in his less than a hundred hours on the islands (and considerably less than that on the shores) in 1923, and more conservatively by Crossland (1927), who visited parts of the islands about a year later.[footnote 1]
1 = Crossland's account is undated: according to a book by C.L. Collenette, "Sea Girt Jungles: the experiences of a naturalist with the St. George Expedition"
During Beebe's second visit to the Galapagos (1926) on the Arcturus, even less time was spent observing shore life, since most of the interest was evidently ichthyological. Most of our knowledge of the marine fauna and flora of the Galapagos is based on the various collecting expeditions of the California Acadmey of Sciences and the Allan Hancock Foundation and reports on various systematic groups published by these institutions. No summaries have been brought together, so we have a less satisfactory idea of the relationships of this apsect of the Galapagos biota than we do of the birds, reptiles, and terrestrial vegetation.
There are some conspicuous absences, however. There are no species of Littorina on rocky shores (there is a small species, Littorina porcata, among the mangroves), and no intertidal limpets. [footnote 2]
[2]In this discussion we are concerned with intertidal limpets commonly living exposed or at least open surfaces. Keyhole limpets (Diodora) are common in the Galapagos, but are subtidal or cryptic in habit.
There is, to be sure, Acmaea filosa, but it lives under rocks and does not appear to be common. There are no species of Siphonaria.Patella mexicana (or an abalone) would starve on the available food supply if it were released as an adult. However, it is more likely that larval stages of inter-tidal limpets have not succeeded in surviving the trip to the Galapagos from the mainland.
A similar situation occurs with respect to the Chatham Islands, which lie about 560 miles east of South Island, New Zealand (Knox, 1954). here only species of limpet (an endemic) occurs, and several barnacles have not succeeded in making the trip from New Zealand. This is comparable to the situation of the Galapagos, which lie some 600 miles west of the mainland but in a much more favorable situation to the parent land mass with respect to prevailing currents, and it is noteworthy that the barnacle genus Chthamalus is absent from the Galapagos although widespread along the mainland. Mussels are similarly absent from both Chatham and Galapagos islands (except for a very small species Mytilus (Hormomya) adamsianus in sheltered situations among the mangroves). It is obvious from these examples that oceanic barriers may be as formidable to many kinds of marine invertebrates asa they are to terrestrial plants and animals. As on land, colonization by sea cannot be realized by a single isolated wanderer, but requires some sort of "critical mass," some minimum number of colonizers, who may still fail if the environment is inhospitable. Whatever the situation for colonizers of the intertidal regions may be, the waters around the Galapagos are nevertheless rich and productive (Wooster and Hedgpeth, 1966).
ACKNOWlEDGMENTS
I am indebted to Stanford University and Dr. Malvern Gilmartin for the opportunity to visit the Galapagos on TeVega (may she rest in peace) cruise 17 as a member of the floating faculty from February 25 to March 18, 1968, and am therefore pleased to state as required: "This research was conducted (in part) during Stanford Oceanographic Expedition 17 with support from NSF grant GB 6870 and GB 6871." I wish to thank Dr. Donald P. Abbott and Dr. Robert I. Bowman for helpful encouragement, and Drs. Olga Hartman, Leo G. Hertlein, Victor A. Zullo, and Mr. Allyn Smith for assistance in identifications; I also wish to thank Dr. G.A. Papenfuss for obtaining an identification from Dr. Paul C. Silva for me. Also I wish to thank Mr. Roger Perry for courtesies extended to me at the Charles Darwin Station for Biological Research and for permission to carry out observations on the grounds of the Station at Academy Bay.
SUMMARY
A tripartite zonation scheme of the "standard" or Stephensonian pattern is not demonstrable on the rocky shore of the Galąpagos Islands. There is no clear upper-spray or supralittoral zone; periwinkles, aspidobranch and pulmonate limpets, and spray zone barnacles are absent. In many regions there is no mid-tidal development of algae or sedentary animals; often the only indication of such a zone is the development of patches or an irregular band of the barnacle Tetraclita stalactifera. It is suspected that in some localities the absence of intertidal algae may be related to the grazing activities of the marine iguana. The most obvious and well developed zone on open or exposed shore is the zone from about +1.0 to perhaps -1.0, foot, of corraline algae and bushy brown algae of such genera as Sargassum and Bifurcaria. This zone is similar to that on other tropical islands and mainland shores. Various anemones and zoanthid are also characteristic of this zone. Intertidal fauna is nevertheless common in the Galapagos. It occurs for the most part in sheltered areas, in crevices, caves, and under overhangss of rock, or under stones.
LITERATURE CITED
Abbot, Donald P. 1966. Factors influencing the zoogeographic affinities of the Galapagos inshore marine fauna. Chapter 14, in The Galapagos. . .
Beebe, William. 1924. Galapagos. World's End.
Beebe, William. 1926. The Arcturus Adventure.
. . . to be completely compiled later by Robert Roy van de Hoek.
Concluding Observations
by
Robert 'Roy' J. van de Hoek
Field Biologist & Geographer
Wetlands Action Network & Sierra Club
The Galapagos Islands are blessed to have the world's finest marine biologist explore and report upon the tidepools, intertidal region, and marine biology as it was known in the 1960s, now more than 30 years ago. It is important to remind readers that tidepools and mangroves are exposed to air with each daily tidal cycle, so scientists have termed these another special type of wetland. Wetlands are defined as that portion of the earth that are at the boundary between land and permanent water. Wetlands must have a period of drying to qualify as a wetland. And since tidepools, intertidal, and mangroves are out of the water for three to seventeen hours each day, depending on the zone of the intertidal, they qualify wholeheartedly as a wetland.