Vertical distribution of meiofauna on reflective sandy beaches

Abstract

Extreme physical conditions usually limit the meiofauna occurrence and distribution in highly hydrodynamic environments such as reflective beaches. Despite sediment grains of the upper layers being constantly resuspended and deposited, the high energy of the swash zone besides depositing coarse sediments allows an ample vertical distribution of meiofaunal organisms. The effect of physical, chemical and sediment variables on the vertical distribution of meiofaunal organims and nematodes was analysed on two reflective exposed beaches. Sampling was conducted at three sampling points on each beach in the swash zone. The sediment collected was divided into four 10-cm strata (0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm). The statistical differences between strata due to factors previously established (i.e. meiofaunal composition, density of most abundant taxa) were tested using a hierarchical PERMANOVA applied under similarity and euclidian distances. An inverse relation among average grain size, content of organic matter and sediment sorting was evident. Coarser sediment characterized the upper layers, while at deeper layers the sediment was very poorly sorted and presented a higher content of organic matter. A similar pattern in the vertical distribution of meiofaunal and nematofaunal composition and density was detected. The lowest densities were associated with the first stratum (0-10 cm), highly affected by hydrodynamics. The vertical distribution of organisms was statistically different only when the interaction among factors was considered. This result suggests that zonation and vertical distribution of meiofaunal organisms are determined by the within-beach variability. Descriptors: Reflective beach, Vertical distribution, Spatial distribution, Meiofauna, Nematoda, Sediment. AbstrAct Mariana de Oliveira Martins*, Tito Cesar Marques de Almeida, Maikon Di DomenicoA ocorrência e distribuição da meiofauna em ambientes com alta energia hidrodinâmica, tais como praias refletivas, são normalmente limitadas por extremos físicos. Apesar de as camadas superficiais do sedimento serem afetadas, a alta energia na zona de espraiamento e a presença de areia grossa possibilitam que a meiofauna tenha ampla distribuição vertical. Para testar o padrão de distribuição vertical da meiofauna e de nemátodos em relação às variáveis físicas, químicas e sedimentológicas, duas praias refletivas expostas foram analisadas. As coletas ocorreram na zona de espraiamento em três pontos de cada uma dessas praias. O sedimento coletado foi dividido em quatro estratos de 10 cm (0-10, 10-20, 20-30 e 30-40 cm). A diferença entre os estratos foi analisada com o uso de PERMANOVA com modelo hierarquizado. A análise foi aplicada em matrizes de similaridade e de distância euclidiana, para estudo da composição da meiofauna e densidades específicas de táxons mais abundantes, respectivamente. O padrão granulométrico evidenciado caracterizou-se pela relação inversa entre o tamanho médio do grão e o teor de matéria orgânica aliado ao grau de selecionamento. Sedime...

Evaluation of Meiofauna in the Hyporheic Zone of the Beberibe River, Pernambuco, Brazil

“…Hydrology and geomorphology, directly or indirectly, control the distribution of organisms in the interstitial habitats (Dole-Olivier and Marmonier, 1992). Hydrodynamic processes are also important for meiofauna (Martins et al, 2015). In hyporheic zones, the important flows influencing faunal distribution patterns are likely to be the volume of surface water flow (water velocity and sudden changes in discharge), and the amount and direction of vertical exchange (Hakenkamp and Palmer, 2000).…”

Effect of sediment on meiofauna and Nematoda structure in different freshwater Amazon environments under the influence of mesotides

“…While Nematoda was the dominant group in muddy environments, Copepoda was the most abundant group on both beaches. This pattern was expected, since several studies have shown the dominance of Nematoda in estuaries or beaches characterized by fine sediments (Ansari and Parulekar, 1993; Gomes and Rosa Filho, 2009; Baia and Venekey, 2019), while Copepoda (in their adult or larval form) are more common organisms in environments characterized by coarse sediments, such as reflective beaches with high-energy hydrodynamics (McLachlan, 1977; Martins et al ., 2015). This pattern occurs due to the high concentration of oxygen in sediments with coarser grains, and this is an ideal condition for Copepoda as they are highly sensitive to interstitial depletion of oxygen (McLachlan and Brown, 2006; Armenteros et al ., 2008).…”

“…These results explain the low densities and the absence of a vertical distribution pattern for meiofauna on the beaches studied in Cotijuba, since samplings were conducted only in the first centimetres of sediment. This suggests that individuals might have migrated to deeper layers in order to avoid the resuspension that occurs in the upper layers by the energy of waves (Martins et al ., 2015).…”

“…Similarly, there was no significant difference in meiofauna density among the layers on both beaches studied. Martins et al (2015), who studied reflective beaches with quite similar sedimentological characteristics to those of Cotijuba beaches (predominance of coarse or medium sand, moderately sorted), observed that the highest densities occurred at intermediate depths of 10-30 cm, while densities were lower in the first 10 cm from the surface. These results explain the low densities and the absence of a vertical distribution pattern for meiofauna on the beaches studied in Cotijuba, since samplings were conducted only in the first centimetres of sediment.…”