70
E. Jaramillo and M. Lastra
beach in South Africa showed that the burrowing rates of Donax serra and D.
sordidus were affected at high densities of the former species, a result which
suggests that in high density beds of these clams interactions would occur.
Similarly, in a field experiment carried out by Defeo (1996) on a sandy beach
in Uruguay, density-dependent processes were considered important for
Mesodesma mactroides and Donax hanleyanus. More experiments are clearly
needed to elucidate these aspects.
3.6 Conclusions
This review has explored the role of large suspension feeders such as E.
analoga in the observed trends of sandy beach community structure in
coastal areas like Chile and California, where these animals are the most
abundant organisms. In these areas, the relationship between abundance and
biomass of the total macroinfauna does not match the worldwide model in
which morpho dynamic beach type is considered to be the key factor in
shaping macroinfaunal community structure. Although few studies have been
carried out, it seems that beach morphodynamic type affects the behavioral
aspects of these organisms, such as tidal migration and burrowing behavior.
The patchy distribution and often size-structured aggregations of large suspension feeders, such as E. analoga, Donax and Mesodesma, also suggest that
biological interactions (an almost unexplored field) may indeed be important
in shaping these patterns on exposed sandy beaches.
Acknowledgements. We thank Karsten Reise for the invitation to present this study at the
Workshop Ecological Comparisons of Sandy and Muddy Shores at Sylt, Germany. E.J.
and M.L. acknowledge the assistance of Heraldo Contreras, Marcia Gonzalez, Crist ian
Duarte (Instituto de Zoologia, Universidad Austral de Chile), Maria del Rosario de la
Huz and Maria Esther Pita Siebert (Departamento de Ecologia y Biologia Animal, Universidad de Vigo) while preparing this manuscript. E.J. also appreciates the financial
support of CONICYT (Chile), Proyecto FONDAP Oceanografia & Biologia Marina, for
research funds used in Chile, Oman and Spain, and to the Alfred Wegener Institute for
Polar and Marine Biology (AWl, Bremerhaven, Germany) and Universidad Austral de
Chile (DID) for financial aid to attend the workshop. M.L. acknowledges financial support from Xunta de Galicia and Universidad de Vigofor research funds used on the coast
of Spain, and to AWl which provided the funds to attend the workshop. We also thank
Anton McLachlan and Jenifer Dugan for reviewing a former manuscript.
E. Jaramillo and M. Lastra
beach in South Africa showed that the burrowing rates of Donax serra and D.
sordidus were affected at high densities of the former species, a result which
suggests that in high density beds of these clams interactions would occur.
Similarly, in a field experiment carried out by Defeo (1996) on a sandy beach
in Uruguay, density-dependent processes were considered important for
Mesodesma mactroides and Donax hanleyanus. More experiments are clearly
needed to elucidate these aspects.
3.6 Conclusions
This review has explored the role of large suspension feeders such as E.
analoga in the observed trends of sandy beach community structure in
coastal areas like Chile and California, where these animals are the most
abundant organisms. In these areas, the relationship between abundance and
biomass of the total macroinfauna does not match the worldwide model in
which morpho dynamic beach type is considered to be the key factor in
shaping macroinfaunal community structure. Although few studies have been
carried out, it seems that beach morphodynamic type affects the behavioral
aspects of these organisms, such as tidal migration and burrowing behavior.
The patchy distribution and often size-structured aggregations of large suspension feeders, such as E. analoga, Donax and Mesodesma, also suggest that
biological interactions (an almost unexplored field) may indeed be important
in shaping these patterns on exposed sandy beaches.
Acknowledgements. We thank Karsten Reise for the invitation to present this study at the
Workshop Ecological Comparisons of Sandy and Muddy Shores at Sylt, Germany. E.J.
and M.L. acknowledge the assistance of Heraldo Contreras, Marcia Gonzalez, Crist ian
Duarte (Instituto de Zoologia, Universidad Austral de Chile), Maria del Rosario de la
Huz and Maria Esther Pita Siebert (Departamento de Ecologia y Biologia Animal, Universidad de Vigo) while preparing this manuscript. E.J. also appreciates the financial
support of CONICYT (Chile), Proyecto FONDAP Oceanografia & Biologia Marina, for
research funds used in Chile, Oman and Spain, and to the Alfred Wegener Institute for
Polar and Marine Biology (AWl, Bremerhaven, Germany) and Universidad Austral de
Chile (DID) for financial aid to attend the workshop. M.L. acknowledges financial support from Xunta de Galicia and Universidad de Vigofor research funds used on the coast
of Spain, and to AWl which provided the funds to attend the workshop. We also thank
Anton McLachlan and Jenifer Dugan for reviewing a former manuscript.