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.     

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.     

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.     

Spatio-temporal and intra-specific variations in the physiological and biochemical condition of the invasive bivalve Corbicula fluminea

Hydrobiologia - Corbicula fluminea is a known aquatic invasive species responsible for several ecological and economic impacts. In Portugal, it is found in all major watersheds, although to varying...     

Habitat use,feeding and territorial behavior of a Brazilian endemic damselfish <Emphasis Type="Italic">Stegastes rocasensis</Emphasis> (Actinopterygii: Pomacentridae)

This paper presents the results of the first field study of the Brazilian endemic damselfish Stegastes rocasensis. Underwater data were collected at the Fernando de Noronha Archipelago (NE Brazil), where four sites were visually assayed for local territorial and feeding behaviors, as well as habitat use. S. rocasensis preferentially fed on turf and macroalgae, and during the afternoon period. Its territory size ranged from 0.26 to 13.86 m² (1.61 ± 0.23 m²). Our findings suggest that adults preferably inhabit shallow, turf-rich areas, while sub-adults and juveniles occupy deeper areas with higher percent cover of invertebrates and hard corals, respectively. With regards to agonistic behaviors, pursuit of intruders was the most frequent reaction recorded (p < 0.001); the highest level of aggression was elicited by territorial herbivores (p < 0.001). Nevertheless, analysis of attacks elicited by different fish species within S. rocasensis’ territory showed that more attacks were launched on conspecifics than on other fish species.