American malacological bulletin (1987) (17970394709)

Title: American malacological bulletin

Identifier: americanmal4519861987amer (find matches)

Year: 1983 (1980s)

Authors: American Malacological Union

Subjects: Mollusks; Mollusks

Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)

Contributing Library: Smithsonian Libraries

Digitizing Sponsor: Biodiversity Heritage Library

Text Appearing Before Image:

264 AMER. MALAC. BULL. 5(2) (1987)

Text Appearing After Image:

Fig. 7. Northern Indian River Lagoon: 1 = Halodule wnghtii Ascherson: Elysia serca; 2 = Halophila: E. serca; 3 = Caulerpa prolifera: E. n. sp. "AF"; 4 = Syringodium filiforme Kiitzing (no ascoglossans); 5 = Drift algal substrates (e.g. Acanthophora)—Chaetomorpha sp.: Ercolania funerea; filamentous Rhodophyta: Hermaea cruciata Gould; 6 = Bryopsis: Ercolania fuscata (Gould), Placida kingstoni, Cladophora sp.: Er- colania fuscata; 7 = Polysiphonia sp.: Ercolania fuscovittata (Lance); 8 = Epiphytic diatoms (on Codium): Elysia evelinae Marcus; 9 = Codium isthmocladium: Placida sp., Elysia canguzua Marcus. Diet unknown: E. chlorotica Gould. mangrove-colonized shorelines. Qualitatively, however, these areas are very similar to areas in the Florida Keys. Man-O'War Cay, Belize: This small mangrove cay is a rookery; the water up to 50 m from the island has an odor of guano, suggesting a high nutrient content. There is a rich growth of Bryopsis extending from below the mangroves to about 40 cm depth, followed by a dense meadow of Cauler- pa racemosa to about 1 m. In June 1985, we found a great mass of Chaetomorpha, estimated at a volume of 23 m3, con- taining a total of four Ercolania funerea (Costa). SUBTROPICAL BARRIER-ISLAND LAGOON: In sub- tropical Florida, barrier islands enclose a long salt lake, the Indian River Lagoon. In its undisturbed state, examples of which are unfortunately disappearing rapidly, the Indian River Lagoon received most nutrient input via a very restricted watershed and very limited oceanic exchange, with produc- tion dominated by seagrasses and apparently a near- equilibrium of production and respiration. The balance of pro- duction and respiration is evidenced by a fine silica sand bot- tom of low organic content (Gilbert and Clark, 1981). Currents are slow and wind driven except near inlets (von Zweck and Richardson, 1980). Temperature varies widely and rapidly on both diurnal and seasonal scales because of the high sur- face area: depth ratio of the lagoon (Smith, 1983). Salinity varies with rainfall, and is highest at the end of the dry season. In recent years, much of the lagoon has moved toward a high- turbidity system with increased nutrient influx accompany- ing urbanization and agricultural expansion, and the seagrasses are steadily declining. The ascoglossans of the northern Indian River Lagoon (Sebastian to Haulover Canal) are represented in Fig. 7, a composite of species observed since 1972 in this habitat. Two significant changes have occurred during this period; in the absence of prior data, we are unable to determine whether these are permanent or cyclic changes. From 1972 to about 1976, Chaetomorpha was a dominant alga in the lagoon and was heavily colonized by Ercolania funerea (Costa); at the Haulover Canal in Titusville in 1973, for example, we were able to collect thousands of slugs simply by scooping hand- fuls of algae into a bucket. In later years, however, the abun- dance of the alga steadily declined and today the alga occurs as only as isolated threads and small clumps in drift algal masses in most of the areas where it was formerly abundant. A second noteworthy change is the colonization of the North Indian River by Caulerpa prolifera (Forsskal) Lamouroux cir- ca 1980. Absent from this part of the river in 1975 (Gilbert and Clark, 1981), C. prolifera now forms patches in the sandy bottom at a depth of about 0.5-1.0 m; an undescribed Elysia, morphologically similar to E. subornata Verrill, eats this alga and occurs from Sebastian to Titusville. MANGROVE CHANNEL FLOOR (MCF): This habitat oc- curs in mature mangrove areas in which channels have erod- ed the peat foundation, sometimes producing a soft, organic mud/silt substrate; waters are mesotrophic to highly eutrophic, depending upon the extent of mangrove drainage. In the best-developed MCF habitats, mature mangrove canopy provides partial or complete shading, and the extent of drainage produces a moderate tidal flow; in some loca- tions, a sand bottom could be present. The peat walls of the channel often support growth of Caulerpa verticillata. Key Largo, Lake Surprise (Fig. 8): Drainage from mangrove areas feeds through Jewf ish Creek and into a tidal roadside canal; this canal empties into the Lake Surprise Lagoon onto a delta about 1 m deep. Sediments are partly organic, partly calcareous silt with some shell chaff. Cauler- pa paspaloides and Halimeda incrassata (Ellis and Solander) Lamouroux dominate in patches between the mangrove fringe and the Thalassia beds; "islands" of dense patches (1 m diameter) of Avrainvillea nigricans Decaisne occur near the mangrove fringe. The roadside canal itself is colonized by some Thalassia and Penicillus, but like the Twin Cays chan- nel floors described below, has a depauperate ascoglossan fauna, possibly because of the high silt load. A well-developed epimanglic community is present at the mangrove fringe, described separately below. Twin Cays, Belize, Main Channel (Fig. 9). In broader parts of the channel, the sediment is fine calcareous sand/silt. The diversity of algae and slugs is low here, and densities were too low to sample. Twin Cays, Hidden Creek (Fig. 10): Sediment here is

Amerikanisches malakologisches Bulletin 1987 indischer Fluss Kieselalgen Mikroskopie Pflanzen

1987

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