Zonation of benthic macrofauna on Cassino Beach, southernmost Brazil

Abstract

Benthic macrofauna zonation was studied for one year (June 2004 to May 2005 with monthly sampling on Cassino Beach, Rio Grande do Sul, Brazil. Three sites (spaced 50 m apart) were selected. Three transects were anchored at each site, spaced equidistantly 2 m apart. Each transect extended from the base of the primary dunes to the inner surf zone at approximately 1m in depth, with between 7 and 8 sampling levels. Monthly, with a 20 cm diameter core, one biological sample was collected per transect at each level, a total of nine samples per level. Within transects, the distance between the levels was 20 m until the upper swash zone, from which the distance was 10 m until the 1-meter isobath. Zonation proved to be variable throughout the year. Variability was mainly a reflection of the greater instability of the lower part of the beach, which comprised the lower mesolittoral zone and the inner surf zone. This was evidenced seasonally with the formation of distinct groups of fauna in accordance with the peculiarity of each season of the year. The formation of these groups was strongly influenced by fluctuations in densities stemming from recruitments and the migration of juvenile and adult infauna, as well as superimposing of the distribution of organisms as a result of rises in sea level due to storms. RESUMOA zonação da macrofauna bentônica na praia do Cassino, Rio Grande do Sul, Brasil, foi estudada durante um ano (junho 2004 a maio de 2005) com base em coletas mensais. Para isso escolheu-se 3 locais, com 50 m de distância um do outro, sendo que em cada local foram fundeadas 3 transversais 2 m eqüidistantes. Cada transversal se estendeu desde a base das dunas primárias até aproximadamente 1m de profundidade no infralitoral, sendo 7 a 8 níveis de coleta distribuídos em cada uma das transversais. Mensalmente, utilizando-se um tubo extrator de 20 cm de diâmetro, coletou-se uma amostra biológica por transversal em cada nível, totalizando nove amostras por nível. A distância dos níveis de coleta em cada transversal foi de 20 m até o limite superior da zona de varrido, a partir da qual a distância foi de 10 m. A zonação mostrou-se variável ao longo do ano, sendo que esta variabilidade refletiu, principalmente, a maior instabilidade da zona inferior da praia, que compreendeu o mesolitoral inferior e a zona de arrebentação interna. Isto ficou evidenciado sazonalmente, com a formação de distintos grupos faunísticos de acordo com a peculiaridade de cada estação do ano. A formação destes grupos foi fortemente influenciada pelas flutuações das densidades, decorrentes dos recrutamentos e migrações de juvenis e adultos da infauna, e da sobreposição da distribuição dos organismos, em função da elevação do nível da água devido às ressacas.

A review on macrobenthic trophic relationships along subtropical sandy shores in southernmost Brazil

“…Dense beds of A. mactroides (2-6 10 3 ind. m -2 ) are broadly found across the swash zone especially between late spring and early autumn (Neves et al 2007) when they are heavily preyed, reinforcing that important link of trophic transference between macrobenthic species and bird compartments (Garcia & Gianuca 1997). …”

“…Cassino Beach), macrobenthic zonation was characterized as very dynamic through seasons despite the general 3-zone pattern (Neves et al 2007): (i) supralittoral, occupied by burrows of the ghost crab Ocypode quadrata; (ii) upper mesolittoral, inhabited by the polychaete Thoracophelia furcifera (= Euzonus furciferus) and the isopod Excirolana armata; and (iii) a large lower zone including the lower mesolittoral and the inner surf zone, which was characterized by the intertidal migrants Amarilladesma mactroides and Donax hanleyanus in addition to several infralittoral species.…”

“…The infaunal polychaete Thoracophelia furcifera is commonly registered along the upper/mid-intertidal zones from sandy beaches of southern Brazil and northern Uruguay, from the surface up to 20 cm deep (Defeo et al 1992, Brazeiro & Defeo 1996, Neves et al 2007). This small Opheliidae (, 2 cm long, ,3 mm wide), usually classified as a deposit-feeder (Fauchald & Jumars 1979), may utilize that organic matter derived from A. glacialis deposits within the substrate whilst exploiting bacteria and other microbes as carbon source (Kemp 1986).…”

“…Such intertidal migrants may achieve high densities across the beach profile especially during recruitment peaks, between late spring and early autumn (Neves et al 2007). The above species and E. armata are also significantly preyed in a solitary manner by charadriid plovers Charadrius falklandicus (southern migrant), C. collaris (resident species), Pluvialis dominica and P. squatarola (both northern migrants), which search their prey exclusively by visual means at the upper swash zone and to a lesser extent on slightly submerged sands (Vooren 1997).…”

“…Linking the primary production to higher trophic levels, such amphipod species may be characterized as potential food items in the diet of those migrant/resident sandpipers and plovers, given the macrobenthic distribution across the beach profile and the shorebird feeding strategies (Vooren 1997, Neves et al 2007.…”