New mechanisms studied for creek formation in tidal flats: From crabs to tidal channels

Abstract

Mechanisms for the formation of creeks in tidal flats are rarely discussed in the peer- reviewed literature. Moreover, while there are general theories about how creeks form in tidal flats, there is no data to support these theories. It is generally believed that marshes inherit creeks from previous tidal flats that plants colonize, and that further modify the creeks. Recently, we have discovered new mechanisms for creek formation in three dif- ferent environments of Argentina in which tidal creeks are actually originating in both fresh and salt marshes. One of the most sur- prising and interesting findings is that creek formation can actually be a product of the intense action of crabs ( Chasmagnatus granu- lata ). In these settings, crabs first interact with a halophytic plant ( Salicornia ambigua ), developing zones of high-density of crab holes, which then are utilized by groundwater and tidal action to form channels.This specific interaction forms a series of rings that, to the best of our knowledge, have not been described elsewhere in the literature. In this article, we examine the advances made by an interdisciplinary project working at a recently discovered site within the Bahía Blanca Estuary (Figure 1).The project involves researchers and Ph.D. students from diverse disciplines, including oceanographers, biolo- gists, chemists, engineers, and geographers tackling the variety of problems centered on channel formation, but also covering aspects of soil mechanics, turbulence processes, sediment and nutrient transpor t, phyto- and z ooplankton, benthic communities, and air-sea- land interaction processes, to name a few. Bioengineering or ecosystem engineering is common in many of Earth’s environments, but what makes this site unique is the develop- ment of the Salicornia rings circling a center area full of crab holes (Figure 2a). Salicornia ambigua is a bi-annual halophyte marsh plant that inhabits a region of about 0.5 to 1 m below the highest astronomic tide, an area flooded only on spring tides.The site was discovered by O. Iribarne in the summer of 1999–2000 and since then, we have developed a couple of 3-year research projects to try to understand the complete cycle, from the initial plant-crab interaction, to the formation and further evolution of the channels.