BENTHIC DISTURBANCE BY FORAGING PREDATORS: EFFECT OF WHITE CROAKER, MICROPOGONIAS FURNIERI, ON SEDIMENT STABILITY IN SW ATLANTIC TIDAL FLATS

MOLINA, L.M.; VALIÑAS, M.S.; PRATOLONGO, P.D.; PERILLO, G.M.E.

Bahía Blanca, Argentina

Simposio; ECSA 44 Symposium: Science and management of estuaries and coasts: A tale of two hemispheres; 2008

Estuarine and Coastal Science Asociation

<!-- /* Font Definitions */ @font-face {font-family:SimSun; panose-1:2 1 6 0 3 1 1 1 1 1; mso-font-alt:宋体; mso-font-charset:134; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:3 680460288 22 0 262145 0;} @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 159 0;} @font-face {font-family:"@SimSun"; panose-1:2 1 6 0 3 1 1 1 1 1; mso-font-charset:134; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:3 680460288 22 0 262145 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:SimSun; mso-ansi-language:ES; mso-fareast-language:ZH-CN;} p {mso-style-unhide:no; mso-margin-top-alt:auto; margin-right:0cm; mso-margin-bottom-alt:auto; margin-left:0cm; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:SimSun; mso-ansi-language:ES; mso-fareast-language:ZH-CN;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt; mso-fareast-font-family:SimSun;} @page Section1 {size:595.3pt 841.9pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> A common feature of many of large predators is that they cause substantial local sediment disruption and generate obvious patch structures, such as pits or furrows. These biogenic structures may have different effects on soft sediment communities, altering population dynamics, creating a temporal mosaic of successional patches, and increasing variability at different spatial scales. Depressions in soft sediments become areas of reduced shear stress, enhanced deposition, and enlarged residence time for suspended material. Sediment deposition in depressions is enhanced because of a reduced shear, but a remaining question to be resolved is to which extent the sedimentation process into pits is selective for particles of differing settling velocities. Micropogonias furnieri (white croaker) is a major predator in SW Atlantic tidal flats that commonly produces elliptical depressions in the soft mud by direct attack on benthic infauna. The aim of this study was to test the effects of the M. furnieri feeding activities on the infaunal vertical distribution, as well as sediment deposition and stability. Six fish exclusion were performed and cages deployed for a month, after that sediment corers (10 cm in diameter and 12 cm in depth) were taken and separated in three layers (upper, mid and lower) about 4 cm thick. Differences between treatments and depths were tested through a two way ANOVA. Sediment stability was measured using a Cohesive Strength Meter device (CSM), by taken one measurement per cage. The Critical Shear Stress thresholds were estimated and then compared through a one way ANOVA. Sediment samples were also taken in control sites, inside and outside depressions, to compare sediment size distributions. Sediment inside depressions showed a higher preponderance of sand, when compared to sediment outside pits, and sediment stability was greater inside fish exclusions. However, infaunal distribution did not show significant differences between treatments. These results support the idea that M. furnieri has a great effect on sediment dynamics and stability, not because of its effect on infaunal communities, but by changing microtopography and altering sedimentation patterns. Keywords: Micropogonias furnieri, feeding pits, sediment stability