Low Benthic Macrofauna Diversity in Dynamic, Tropical Tidal Mudflats: Migrating Banks on Guiana’s Coast, South America

Abstract

19In tropical South America, the mudflats of the Amazonian coast are unique because of their 20 large size and unrivaled migration dynamics. On Guiana´s coast, macrofaunal communities 21 are believed to be well-adapted to these dynamic conditions. In this study, the benthic 22 macrofauna was sampled in April 2012 in the Awala-Yalimapo region of western French 23 Guiana and at two sites in Suriname, Warappa Kreek and Bigi Pan, These sites are found 800, 24 920, and 1,140 km from the Amazon delta, respectively. The richness, diversity, and densities 25 of the macrofaunal communities in these mudflats are here described for the first time. Only 26 38 OTU were recorded, among which two species were common and widely distributed: the 27 tanaid crustacean Halmyrapseudes spaansi and the polychaete Sigambra grubii; the former 28 represented 84% of all individuals collected, with densities reaching up to 73,000 individuals. 29 m -2 . Most of the OTU consisted of relatively small individuals (< 10 mm in length). The very 30 low richness and diversity and the small sizes of the organisms are likely linked to the 31instability and softness of the substrate on these mudflats. This study suggests that the 32 differences in macrofaunal community composition among sites could be due to the migration 33 stage of banks rather than the distance from the Amazon Delta and associated effects of river 34 discharge. 35 ManuscriptClick here to view linked References

Prey Choice by Declining Atlantic Flyway Semipalmated Sandpipers (Calidris pusilla) at a Major Wintering Area in Brazil

“…Although there are no diet studies of Semipalmated Sandpipers in the wintering areas where large population declines were observed (Suriname, French Guiana and Guyana; Morrison et al 2012), the very high abundance of the tanaid crustacean Halmyrapseudes spaansiand (densities up to 73,000 individuals m -2 ) and its similar behaviour to C. volutator (Jourde et al 2017) suggests that this species could be the staple prey of Semipalmated Sandpipers in these areas. While there are two studies that report densities of tanaid crustaceans of similar magnitude in the 1980s and the 1990s in some habitats of these areas (Swennen et al 1982;Clavier 1999), it is difficult to evaluate from the published data how much change occurred in the extent of the habitat for these ani-mals.…”

Meiofauna versus macrofauna as a food resource in a tropical intertidal mudflat

“…Predator abundance in the study area had been determined only for G. oceanicus (Jourde et al 2017). For the purpose of feeding, the predators studied perform tidal migrations, following the rising tide by swimming or walking over the sediment on the bottom (Gibson, 2003).…”

“…However, abundances of the high fin goby G. oceanicus have been estimated from measurements in benthic cores, revealing a patchy distribution, with densities reaching 50 ind. m -2 (Jourde et al 2017). For evaluation of the maximum top-down effect, daily ingestion was calculated, taking into account the highest abundance of fish and lowest abundance of meiofauna (Dupuy et al 2015), and the highest ingestion rate measured in this study.…”

“…The macrofauna is not very diverse and is dominated by a small number of few taxa, such as tanaids, with the species Halmyrapseudes spaansi accounting for 84% of macrofauna specimens, with mean abundances from 2,600 ind.m -2 to up to 73,000 ind.m -2 corresponding to a maximum dry weight of 12.1 g m -2 (Jourde et al 2017;Nguyen et al 2018). The macrofauna also includes members of the Polychaetes and, to a lesser extent, Gastropods and Nemertea (Jourde et al 2017). The macrofaunal community is dominated by small species, such as H. spaansi, which never exceeds 6.4 mm in length (Nguyen et al 2018).…”

“…The study site has two advantages for studies of this type: i) easy extraction of the meiofauna and macrofauna by sieving, because the sediment consists primarily of particles of less than 63 µm in diameter (Dupuy et al 2015) and ii) ease of experimental manipulation of the macrofaunal community, due to its low diversity, dominated by a species of small tanaids (Jourde et al 2017, Nguyen et al 2018. Sediment was sampled as previously described.…”