Activity rhythms of two cirolanid isopods from an exposed microtidal sandy beach in Uruguay |
| |
Authors: | B Yannicelli R Palacios L Giménez |
| |
Institution: | (1) Sección Oceanografía, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay Tel.: +598-2-5258618; Fax: +598-2-5258617 e-mail: byannice@udec.cl, UY;(2) Programa de Desarrollo de las Ciencias Básicas (PEDECIBA), Universidad de la República, Montevideo, Uruguay, UY |
| |
Abstract: | Activity rhythms of two cirolanid isopods, Excirolana armata and Excirolana braziliensis, were studied based on both seasonal field observations and laboratory experiments, at an exposed microtidal sandy beach
in Uruguay. The natural emergence patterns of both species were observed in the field for 1 year, twice in each season, and
correlated to sea level, expected tidal cycles and diel cycles. Laboratory experiments were carried out in order to detect
endogenous rhythms of activity and observe how emergence of both species was affected by changes in light and/or sediment
thixotropy. We also compared behavioral strategies of sympatric species that occupy different beach levels. Sea level (and
thus swash zone position) during field sampling did not follow expected tidal cycles for most sampling occasions. E. armata was observed in activity most of the time, but activity only correlated with sea level on three out of eight occasions, and
only once was correlated to expected tidal cycle. Laboratory results showed that emergence under constant conditions was rare;
changes in sediment thixotropy stimulated emergence, but the response was not cyclical; light had little effect on this response.
On the other hand, E. braziliensis was fairly scarce in the water column, but swimming individuals were observed always during the night. They displayed an
endogenous circadian activity pattern in the laboratory which augmented in response to changes in sediment thixotropy. The
natural light/dark cycle modulated both spontaneous and response emergence by increasing day/night differences in activity.
In this study E. armata, a midlittoral species more exposed to sea level variations, seemed to rely entirely on different physical and/or biological
cues to trigger emergence at the appropriate time. E. braziliensis, found mostly in the upper intertidal zone, emerged in a circadian rhythm, which was stimulated by changes in sediment thixotropy
and reinforced by light cycles. The results of this study led us to conclude that on microtidal, unpredictable beaches, local
physical and biological factors can combine to determine different activity strategies in organisms from different intertidal
levels.
Received: 23 March 2000 / Accepted: 30 August 2000 |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|