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Marine Ecology

plants, species, sargassum and water


The submerged plants growing about the Tortugas are not many, since marine algae most abound on rocky shores and rocks are conspic uously lacking in the Tortugas physiography. Of the higher plants several interesting spermatophytes are very abundant, viz : (1) Thalassia testudinum Koenig and Sims, which occurs on exten sive areas in shallow water. The leaves and stems of this plant, the turtle-grass, are cast up in long rows by the waves, particularly after storms, on the sandy beaches of the islands.

(2) Another component of this mass of debris is the manatee-grass, Cymodocea manatorum Ascherson, which has much more slender leaves and a peculiar inflorescence. It was the author's good fortune to secure both of these plants in bloom, and the Cymodocea in fairly large quantity by going down in a diving helmet in about 3 to 4 meters of water and walking about on the bottom, making a close observation of the beds of this grass. Algae were also collected in the same manner.

(3) Two other spermatophytes, which were obtained by the deep-sea dredging apparatus carried by the Laboratory yacht, were two species of Halophila, growing in 17 to 19 fathoms of water out in the Gulf Stream. These were H. engelmannii and H. baillonis Aschers. The occurrence of these plants in this locality and their interesting relations to the region have been discussed by the writer in another paper.' These

and the calcareous alga which are given in a list below are quite abun dant. Representatives of the Rhodophyceie and the PhEeophycefe are not nearly so plentiful. The Udotea and Penicillus are quite com mon in sandy shallows and various species of Halimeda contribute a large share to the detritus making up the land. Codium and Acetab ularia are frequent on rocks, shells, or other submerged objects afford ing a firm foothold. Gracillaria is mostly brought up on shells and sponges in the dredges along with species of Halophila, while Sargassum bacciferum, and occasionally Valonia, Didyosphceria, Lyngbya, Hypnea, and Lawrencia, drift about the islands and in the Gulf as large mats or rafts. These are washed up on the shores in long windrows, and while floating these mats of Sargassum furnish an abiding-place for numerous small animals, especially several species of crabs. One which is fairly common matches exactly the yellow-brown fronds of the Sargassum and can be seen only with difficulty in a tangle of the gulfweed when thrown into an aquarium.