Allan T. Souza

Non-random reef use by fishes at two dominant zones in a tropical, algal-dominated coastal reef

Habitat use and the processes which determine fish distribution were evaluated at the reef flat and reef crest zones of a tropical, algal-dominated reef. Our comparisons indicated significant differences in the majority of the evaluated environmental characteristics between zones. Also, significant differences in the abundances of twelve, from thirteen analyzed species, were observed within and between-sites. According to null models, non-random patterns of species co-occurrences were significant, suggesting that fish guilds in both zones were non-randomly structured. Unexpectedly, structural complexity negatively affected overall species richness, but had a major positive influence on highly site-attached species such as a damselfish. Depth and substrate composition, particularly macroalgae cover, were positive determinants for the fish assemblage structure in the studied reef, prevailing over factors such as structural complexity and live coral cover. Our results are conflicting with other studies carried out in coral-dominated reefs of the Caribbean and Pacific, therefore supporting the idea that the factors which may potentially influence reef fish composition are highly site-dependent and variable.

From water to land: how an invasive clam may function as a resource pulse to terrestrial invertebrates

Resource pulses are episodes of low frequency, large magnitude and short duration that result in increased resource availability in space and time, with consequences for food web dynamics. Studies assessing the importance of resource pulses by invasive alien species in the interface between terrestrial and aquatic ecosystems are rare, especially those in the direction from water to land. This study assessed the importance of massive die-offs of the Asian clam Corbicula fluminea (Müller, 1774) as a resource pulse to the terrestrial invertebrate community after an extreme climatic event using a manipulative experiment. We used 5 levels of C. fluminea density (0, 100, 500, 1000 and 2000ind·m(-2)), with terrestrial invertebrates being censused 7, 30 and 90days after C. fluminea addition. We also assessed the possible effect of plots position, where plots that delimited the experiment were assigned as edge plots and the remaining as core plots. Clear differences were detected in abundance, biomass, richness and diversity of terrestrial invertebrates depending on the C. fluminea density, time and position. Interestingly, the highest abundance of adult Diptera was observed 7days after C. fluminea addition, whereas that of the other terrestrial invertebrates was on day 30, both with C. fluminea densities higher than 500ind·m(-2) located on the edge of the experimental design. This study highlights the importance of major resource pulses after massive die-offs of invasive bivalves, contributing with remarkable amounts of carrion for adjacent terrestrial systems. Part of this carrion can be consumed directly by a great number of invertebrate species while the remainder can enter the detrital food web. Given the high density and biomass attained by several invasive bivalves worldwide and the predicted increase in the number, intensity and magnitude of extreme climatic events, the ecological importance of this phenomenon should be further investigated.

Habitat use and behavioural ecology of the juveniles of two sympatric damselfishes (Actinopterygii: Pomacentridae) in the south‐western Atlantic Ocean

Spatial distribution, microhabitat use and territorial and feeding behaviours were compared between the juveniles of two sympatric territorial damselfishes Stegastes variabilis and Stegastes fuscus on a small tropical reef in the south-western Atlantic Ocean. Juvenile S. variabilis were most abundant at sites subject to stronger hydrodynamics and with mixed benthic cover, whereas juvenile S. fuscus were most abundant at sheltered sites with dense turf algae cover. No differences regarding feeding habits were detected, with both species preferentially feeding on turf algae. Also, despite similarities in territory area and agonistic encounter rates, the identity and proportion of intruders involved in agonistic interactions differed significantly between species. These interdependent traits suggest strong asymmetric competition, with juvenile S. fuscus dominating high-quality sites and evicting juvenile S. variabilis to low quality, marginal areas of the reef.

Differences in the macrozoobenthic fauna colonising empty bivalve shells before and after invasion by Corbicula fluminea

Bivalve shells can potentially alter the structure of aquatic benthic communities. However, little is known about the effect that different shell morphologies have on their associated fauna. This study aimed to understand how empty shells, from four different freshwater bivalve species, affect macrozoobenthic communities, using the River Minho (Iberian Peninsula) as a study area. Three native (Anodonta anatina, Potomida littoralis, Unio delphinus) and one non-indigenous (Corbicula fluminea) species were used for this research. Comparisons among species and between scenarios (i.e. before and after invasion by C. fluminea) were performed. Our results suggest that macrozoobenthic community structure did not vary among treatments, with the exception of species richness, which was higher on shells of native species. Furthermore, little difference was detected when comparing scenarios with and without C. fluminea shells, despite dissimilarities in size and morphology between species. The empty shells of C. fluminea partially (in terms of density and biomass, but not in species richness) replaced the role of empty shells of native species as a physical substratum for the associated macrozoobenthic community.

Structure, growth and production of a remarkably abundant population of the common goby, Pomatoschistus microps (Actinopterygii: Gobiidae)

The common goby, Pomatoschistus microps, is a relevant species from estuarine food webs, playing important roles as predator of polychaetes and crustaceans and as prey for larger fishes and crustaceans. The Minho estuary (NW Portugal) is a relatively well-preserved and productive system. To assess the population structure and production of P. microps in this estuary, monthly samples were undertaken in three different areas along an estuarine gradient in the lower estuary. The density of P. microps varied considerably among seasons and sampling stations, with higher densities occurring in summer and autumn. The lowest densities were found closer to the sea. In general, the density of females was higher than the density of males in all sampling stations, while juveniles were more abundant within a salt marsh area. Compared with other European estuaries, our data showed a remarkable higher density and production values of P. microps. This may be related to the high freshwater input and the low salinities found in this estuary. In addition, we hypothesize that the lower density of the sympatric species P. minutus and the high availability of bivalve shells observed in the Minho estuary may have also contributed to the present results, once P. minutus and P. microps often display a diet overlap and the bivalve shells are crucial for the common goby reproduction.

Behavioral changes of a Brazilian endemic damselfish Stegastes rocasensis when guarding egg clutches

This study aimed at comparing the feeding, territorial and agonistic behavior of the Rocas Gregory Stegastes rocasensis when guarding egg clutches. This was accomplished through underwater observations of 80 S. rocasensis individuals observed in four sampling sites in the Fernando de Noronha archipelago (SW Atlantic). Several differences were detected in the behavior of S. rocasensis, such as the reduced size of the territory, the feeding preferences and the aggressiveness towards intruders. Males guarding eggs defended territories twice as small as the ones that did not present egg clutches inside their territories. Additionally, they fed mostly on turf algae, while individuals without eggs in their territories fed mostly on turf and macroalgae. Fish guarding egg clutches elicited agonistic reactions mainly towards planktivores and omnivorous fishes, which could potentially prey on their eggs, while individuals without eggs clutches in their territories elicited agonistic reactions mainly towards herbivorous fishes. The results of the present study reinforces that damselfishes are able to identify the intruder’s identity and elicit agonistic reactions only toward species that may represent a threat to their eggs and/or farmed algae.

Physical legacy of freshwater bivalves: Effects of habitat complexity on the taxonomical and functional diversity of invertebrates

Bivalves may play a major role in structuring aquatic communities. This may be especially relevant in aquatic communities dominated by non-native invasive bivalves, which can contribute to the increase of habitat homogenization. In this study, we assess how habitat homogenization, through the reduction of empty bivalve shells identities, influences the macroinvertebrate assemblages. Towards this end, a manipulative experiment with the empty shells of two native (Potomida littoralis and Unio delphinus) and one non-native (Corbicula fluminea) species was performed. Seven treatments were prepared, three of them consisting of homogeneous substrates using shells of one species, and four of them consisting in heterogeneous substrates using more than one species. The associated fauna colonizing different treatments was analyzed through taxonomic and trait-based approaches. Our results showed that the substrate complexity influenced the density of macroinvertebrates, with the heterogeneous treatments significantly yielding more dense assemblages. Also, the trait patterns differed among the levels of habitat heterogeneity, influencing mainly organisms that feed on microphytes of both small and big sizes, that inhabit areas with slow to moderate water flow, and that have short and long live cycles. Further, the functional diversity was not influenced by the substrate heterogeneity. Therefore, the habitat homogenization, through the accumulation of non-native C. fluminea empty shells in the river bottom, did not affect the functional diversity of the macroinvertebrate assemblages.

Assessing the effects of temperature and salinity oscillations on a key mesopredator fish from European coastal systems

A population dynamics model was developed to assess the short and long-term effects of temperature and salinity variations in the common goby Pomatoschistus microps in a Portuguese estuary (Minho estuary, NW Portugal). The population was divided into juveniles, females and males, which constituted the models state variables. Linear regressions between the observed and the predicted density of juveniles, females and the total population were significant. Parameters sensitivity and uncertainty analysis were estimated. The model was able to satisfactory describe the P. microps population dynamics, and thus was used to simulate the effects of climatic changes on the fish population. Simulations indicated that the common goby population is sensitive to both temperature and salinity changes. Overall, scenarios of more than 3 °C increase caused significant population decreases. Similarly, increased salinities led to a population shrinkage, whereas scenarios of salinity decrease generated an opposite variation on the population. According to the IPCC predictions for climatic tendencies, the population of the common goby will tend to decrease in the near future, experiencing marked oscillations (decrease or increase) during climatic extremes, namely droughts and floods, respectively. These results may be a useful for future planning and management of estuarine systems given that the common goby is an important species of estuarine food webs in many temperate ecosystems.

Community structure of reef fishes in shallow waters of the Fernando de Noronha archipelago: effects of different levels of environmental protection

Marine protected areas (MPAs) are important tools for the evaluation of the biodiversity and status of marine systems. However, not all MPAs are equal in their design and management; therefore, it is important to understand how different levels of protection affect the fish communities. In the present study, the shallow reef-area fishes of seven areas in Fernando de Noronha archipelago (north-eastern Brazil) with dissimilar habitat characteristics and different levels of environmental protection (no-take MPA and MPA) were compared. In total, 140 visual censuses were performed, in which 12958 fishes of 27 families and 50 species were recorded. Differences were recorded between no-take MPAs and MPAs in the benthic composition, abiotic data and fish-community structure and composition. These differences were associated with a higher diversity, richness, density of larger fishes and top target fish families, and biomass per census (nearly 2-fold higher in the no-take MPA). Our findings suggested that the differences in the ichthyofauna were probably more related to the different levels of protection than to dissimilarities in the habitat structure among areas, and that the local no-take MPA (National Marine Park of Fernando de Noronha) is effective in maintaining the shallow reef-area fish communities healthy and diverse.