scholarly journals Why the urchin lost its spines: hydrodynamic forces and survivorship in three echinoids

1996 ◽  
Vol 199 (3) ◽  
pp. 717-729 ◽  
Author(s):  
M Denny ◽  
B Gaylord

Two species of sea urchins (Colobocentrotus atratus and Echinometra mathaei) commonly co-occur on wave-swept intertidal shores in the Indo West Pacific. E. mathaei is a typical spiny urchin and is confined to cavities in the rock. In contrast, C. atratus has an unusual morphology, in which the spines are much reduced, and is found on substrata fully exposed to wave-induced velocities and accelerations. Previous researchers have suggested that spine reduction may therefore be a morphological adaptation to hydrodynamic forces. However, measurement of the drag, lift and accelerational forces on sea urchins show that the adaptive significance of spine reduction is less straightforward than it initially appears. The reduction in drag in C. atratus as compared with that in E. mathaei is to a large extent offset by an increase in lift. Instead, the 'streamlined' morphology of C. atratus seems best adapted to provide a reduction in the force imposed by water acceleration, thereby making it feasible for C. atratus to venture safely into the tumultuous flows of the surf zone.

1995 ◽  
Vol 32 (2) ◽  
pp. 77-83
Author(s):  
Y. Yüksel ◽  
D. Maktav ◽  
S. Kapdasli

Submarine pipelines must be designed to resist wave and current induced hydrodynamic forces especially in and near the surf zone. They are buried as protection against forces in the surf zone, however this procedure is not always feasible particularly on a movable sea bed. For this reason the characteristics of the sediment transport on the construction site of beaches should be investigated. In this investigation, the application of the remote sensing method is introduced in order to determine and observe the coastal morphology, so that submarine pipelines may be protected against undesirable seabed movement.


2015 ◽  
Vol 62 (1-2) ◽  
pp. 27-39 ◽  
Author(s):  
Grzegorz R. Cerkowniak ◽  
Rafał Ostrowski ◽  
Magdalena Stella

AbstractThe paper presents results of field and theoretical investigations of a natural sandy shore located near the IBW PAN Coastal Research Station in Lubiatowo (Poland, the south Baltic Sea). The study site displays multi-bar cross-shore profiles that intensively dissipate wave energy, mostly by breaking. The main field data comprise offshore wave parameters and three cross-shore bathymetric profiles. Waveinduced nearbed velocities and bed shear stresses are theoretically modelled for weak, moderate, strong and extreme storm conditions to determine sediment motion regimes at various locations on the seaward boundary of the surf zone. The paper contains a discussion on the depth of closure concept, according to which the offshore range of sea bottom changes can be determined by the extreme seasonal deep-water wave parameters.


1995 ◽  
Vol 46 (4) ◽  
pp. 751 ◽  
Author(s):  
AE Drummond

The reproductive cycles of Echinometra mathaei and Diadema savignyi on the South African eastern coast were investigated by means of gonad index and histological methods. Both species showed annual cycles, with spawning occurring during the summer months (December to March-April), but the degree of gametogenic synchrony differed markedly between the two species. In D. savignyi, gametogenesis within and between sexes was in close synchrony and there was evidence suggesting that repeated spawning with a monthly rhythm occurred. In contrast, gametogenesis in E. mathaei was poorly synchronized and spawning occurred over an extended period.


2018 ◽  
Vol 161 ◽  
pp. 322-336 ◽  
Author(s):  
Annika O'Dea ◽  
Merrick C. Haller ◽  
H. Tuba Özkan-Haller

Author(s):  
Dimitris Spanos ◽  
Apostolos Papanikolaou

The wave induced yaw drift moment on floating structures is of particular interest when the lateral yaw motion of the structure should be controlled by moorings and/or active dynamic positioning systems. In the present paper, the estimation of the yaw drift moment in the modeled natural wave environment is conducted by application of a nonlinear time domain numerical method accounting for the motion of arbitrarily shaped floating bodies in waves. The computational method is based on linear potential theory and includes the non-linear hydrostatic terms in an exact way, whereas the higher-order wave-induced effects are partly approximated. Despite the approximate modeling of the second order hydrodynamic forces, the method proved to satisfactorily approach the dominant part of the exerted hydrodynamic forces enabling the calculation of drift forces and of other drift effects in irregular waves. Hence, the subject yaw drift moment in the modeled natural wave environment is derived, resulting to a basic reference for the design of similar type floating structures.


1980 ◽  
Vol 23 (1) ◽  
pp. 81-89 ◽  
Author(s):  
Masaru Mizuguchi ◽  
Masahiko Isobe ◽  
Shintaro Hotta ◽  
Kiyoshi Horikawa

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