Dynamics of fish assemblages on a continuous rocky reef and adjacent unconsolidated habitats at Fernando de Noronha Archipelago, tropical western Atlantic

Abstract

In recent years, many studies investigated how density-dependent factors, such as shortages in microhabitat and food availability influence the structure of reef fish assemblages. Most of what is currently known, however, comes from comparisons of isolated patch reefs and from correlations between fish abundance and one or few microhabitat variables. In addition, most studies were done in the Caribbean and Indo-Pacific regions, whereas the South Atlantic region has been, to date, understudied. The present study evaluated spatial and temporal variations in reef fish abundance and species richness in a continuous rocky reef and adjacent unconsolidated habitats in a Southwestern Atlantic reef, using underwater techniques to assess both fish numbers and microhabitat variables (depth, rugosity, number of crevices and percent cover of live benthic organisms, bare rock, sand, and limestone). Higher species richness was observed at consolidated substratum stations on both sampling periods (May and October), but fish abundance did not show a significant spatial variation. Topographical complexity and percent cover of algae (except coralline algae) were amongst the most important determinants of species richness, and correlations between fish size and refuge crevice size were observed. The non-random patterns of spatial variation in species richness, and to a lesser extent, fish abundance, were related to differences in substratum characteristics and the inherent characteristics of fishes (i.e. habitat preferences) and not to geographical barriers restraining fish movement. This study highlights the importance of concomitantly assessing several microhabitat variables to determine their relative influence in reef fish assemblages.Em anos recentes, vários estudos investigaram como os fatores dependentes da densidade, por exemplo, a diminuição na disponibilidade de microhabitats e alimento, influenciam a estrutura das assembleias de peixes. A maior parte do que é atualmente conhecida, no entanto, é oriunda de comparações de recifes isolados e de correlações entre abundância de peixes e uma ou poucas variáveis relacionadas ao microhabitat. Ainda, a maior parte dos estudos foi realizada nas regiões do Caribe e do Indo-Pacífico, enquanto a região do Atlântico Sul tem sido, até o momento, subestimada. O presente estudo avaliou as variações espaciais e temporais da abundância de peixes recifais e da riqueza de espécies em um recife rochoso contínuo e em habitats não-consolidados adjacentes em um recife do Atlântico Sudoeste, utilizando técnicas subaquáticas para avaliar tanto os valores dos peixes como as variáveis do microhabitat (profundidade, rugosidade, número de fendas e porcentagem de cobertura de organismos bênticos vivos, rocha nua, areia e cascalho). Uma maior riqueza de espécies foi observada nos pontos de substrato consolidado em ambos os períodos de amostragem (maio e outubro), mas a abundância de peixes não mostrou uma variação espacial significativa. A complexidade topográfica e a porcentagem de cobertura de alga (e...

Non‐linear thresholds characterize the relationship between reef fishes and mangrove habitat

“…Perhaps the most obvious explanation for our results would be the positive relationship between topographic complexity and species richness in this region. In this previous examination by Walker et al (2009), in situ rugosity measurements yielded the best explanation of fish assemblage patterns, a pattern that is consistent with several other studies in the tropical western Atlantic region (e.g., Gratwicke and Speight 2005, Kuffner et al 2007, Medeiros et al 2011. We would like to point out that our GAM analysis found no significant relationship between distance from mangroves and species richness.…”

“…, Medeiros et al. ). We would like to point out that our GAM analysis found no significant relationship between distance from mangroves and species richness.…”

Substrate Association and Patterns of Microhabitat Use by Fishes at Fernando De Noronha Archipelago (Brazil)

“…Spatial variations in benthic composition are less likely to affect the density of mobile species, but should play an important role in determining populations of site-attached species with stronger habitat preference. On the other hand, the high abundance of algae in the study area, a common feature of most Southwestern Atlantic reefs (MEDEIROS et al, 2010), strongly suggests that food is not a limiting factor for herbivores and omnivores of the study area, but space and availability of crevices seem more important (MEDEIROS et al, 2011). Future studies determining the extent of local mobility of wanderers should bring up new information.…”

Community structure of shallow rocky shore fish in a tropical bay of the southwestern Atlantic

“…In comparison, there are few studies involving the associations among fishes on tropical rocky shores (CONI et al, 2007NUNES et al, 2007aNUNES et al, , 2007bMEDEIROS et al, 2009a;2009b;MAIA-NOGUEIRA et al, 2010;MEDEIROS et al, 2011). Thus this region still remains largely unknown.…”

“…LUCKHURST; LUCKHURST, 1978;FERREIRA et al, 2001;WILSON et al, 2007;MEDEIROS et al, 2011;PEREIRA-FILHO et al, 2011;CONI et al, 2013). Topographic complexity is an important factor that is generally positively associated with reef fish species richness and diversity, particularly as it provides shelter from predators BEETS, 1993).…”