Benthic Community zonation in a breakwater on the north coast of the state of Rio de Janeiro, Brazil

The present study presents the vertical zonation pattern of the intertidal benthic organisms on granitic boulders in the Farol de São Tomé beach (22º02'S, 41º03'W), Rio de Janeiro State. Four sampling profiles using 20 x 20 cm quadrats through a photo quadrat technique revealed four horizontal bands: (1) Littoral Fringe characterized by empty space and Littorina; (2) Upper eulittoral mainly occupied by Chthamalus and bare rock; (3) Lower eulittoral characterized by Chthamalus, Phragmatopoma, Ulva and Centroceras; and (4) Sublittoral Fringe characterized by Ulva, Phragmatopoma and Hypnea. The high variability in the relative abundance of the dominant species among the profiles may be attributed to the high topographic irregularity, reflecting in different wave action intensity at the same height, and consequently favoring the establishment of different species. The frequent substrate alternation from granitic rock to Phragmatopoma sandy reefs might contribute to the small-scale spatial variability. The implantation of a breakwater on an area without natural rocky shores allowed the study of intertidal benthic communty zonation, and provide a baseline for the experimental studies.

A new genus and species of polyclad flatworm found in the mantle cavities of gastropod molluscs in the high-intertidal zone of the Pacific coast of Central America

A commensal relationship is described between the polyclad flatworm Paraprostatum echinolittorinae Faubel & Sluys gen. et sp. nov. and gastropod molluscs living on the Pacific coast of central America. Although the worms are relatively large in comparison with their hosts, the latter sustained no apparent damage. Considering the fact that the molluscs live in the upper eulittoral zone and littoral fringe of the shore, it is unlikely that the polyclads could survive for long outside the hosts. Diagnostic characters for the new genus and species are a long penial stylet joined to the proximal vesicle and absence of Lang's vesicle. It is pointed out that Aprostatum clippertoni Bock, 1913 and A. longipenis (Kato, 1943) have been incorrectly transferred to the genus Euplana Girard, 1893 and that Discoplana malagensis Doignon, Artois & Deheyn, 2003 should be transferred to the genus Ilyella Faubel, 1983.

Cooperative Interactions and Environmental Control in the Intertidal Clustering of Nerita Textilis (Gastropoda; Prosobranchia)

Abstract1. Somalian populations of the intertidal gastropod Nerita textilis Gmelin show a vertical separation between resting (mid-upper eulittoral) and feeding (lower eulittoral) zone. During high tides and mostly diurnal low tides some snails remain scattered (SF), while other form aggregations (AF) at lower levels of the rocky shore. During the mostly nocturnal low tides both SF and AF migrate downward to feed on microalgae. 2. Lower and upper aggregations are mostly frequented around neap (NT) and spring tides (ST), respectively. Clustering significantly reduces the exposure to waves during high tide, and probably overheating and dehydration during diurnal low tide. 3. About 90 percent of the total population enters into the cluster system throughout each NT-ST-NT cycle. Clustering begins to increase at NT and falls at ST, reaching a maximum (52 percent of the population) between NT and ST. The relative frequency of transition between SF and AF shows a spike after NT and falls after ST. The inverse transition (AF to SF) is negatively correlated to the amount of AF. 4. Return to the original cluster after one feeding excursion is high (76 percent) and decreases slightly at increasing intervals (about 40 percent after 14 feeding migrations), but it becomes significantly lower after one or more rest phases spent in SF. 5. The field study suggests that the periodical (NT) increase in density at the lower rest-zone (tide-pools belt), long-lasting chemical marking of collective rest sites and releasing mucus trails during feeding excursions cause the clustering. According to this hypothesis, a primer group stops at each aggregation site at NT, mostly returning to it by self-trailing after each feeding migration, while the progressive recruitment of snails from SF is caused by the interindividual trail-following during the return migration from the feeding ground. 8. The same model can explain the clustering behaviour of other intertidal gastropods, though the importance of the different parameters (periodical variation in zonation, marking of rest places, trail-following) probably vary among the different species.