Juveniles of a number of reef fish species develop in shallow-water ‘nursery’ habitats such as mangroves and seagrass beds, and then migrate to the coral reef. This implies that some reef fish ...species are distributed over the mangrove-seagrass-reef continuum in subpopulations with different size distributions that are spatially separated for considerable periods of time. To test this assumption, and to determine ontogenetic dietary changes (which may drive fish migrations from nursery habitats to the coral reef), we selected 9 herbivorous and carnivorous reef fish species whose juveniles are highly abundant in nearby nursery habitats.13C:12C and15N:14N ratios were measured in fish muscle tissues and in potential food items collected from each of the 3 habitats, and fish gut contents were identified. All δ13C signatures of fishes sampled from the coral reef were close to the carbon isotope signatures of food items on the reef, and were significantly depleted compared to those of fishes from the nursery habitats (with the exception ofScarus iserti). Gut-content analysis of herbivorous fishes entailed problems with identification of the ingested food items, but there was no change in the δ13C or δ15N signatures of the muscle tissue as a function of fish size. Regression analysis showed significant positive relationships between δ15N content and fish size in all carnivorous fish species; this was correlated to the decreasing dietary importance of small crustaceans and the increasing consumption of decapod crabs or prey fishes with increasing size. The combined study of stomach contents and stable isotopes showed that the juveniles and adults of these reef fish species are separated ecologically and spatially for a considerable period of time, and that herbivorous fishes do not change their trophic status with increasing size, whereas carnivorous fishes feed on increasingly larger prey at increasingly higher trophic levels prior to their migration from the nursery habitat to the coral reef.
There has been much controversy over the degree to which mangroves and seagrass beds function as nursery habitats for the juveniles of fish species that live on coral reefs as adults. In previous ...studies we have shown that the juveniles of at least 17 Caribbean reef-fish species are highly associated with bays containing mangroves and seagrass beds as nurseries, and that juveniles of these species are absent in bays lacking such habitats. In this study we therefore hypothesised that on islands lacking these bay nursery habitats, adults of these fish species will be absent or show low densities on the coral reef. Densities of the 17 species were compared between the reefs of Caribbean islands with and without mangroves and seagrass beds. On reefs of islands lacking these habitats, complete absence or low densities were observed for 11 of the 17 species, several of which are of commercial importance to fisheries. This finding suggests a very important nursery function of such habitats and implies that the densities of several fish species on coral reefs are a function of the presence of nearby bays containing mangroves and seagrass beds as nurseries. The results indicate that degradation or loss of these habitats could have significant impacts on reef-fish stocks in the Caribbean.
Fish community structure of a non-estuarine inland bay on the Caribbean island of Curaçao was determined in the mangroves, seagrass beds, algal beds, channel, fossil reef boulders, notches in fossil ...reef rock, and on the adjacent coral reef, using visual censuses in belt transects. Fish communities varied among biotopes, but some overlap was present. Fish density and species richness were highest at the boulders and on the coral reef, and extremely low on the algal beds, whereas the total number of individuals calculated for the entire bay was highest on the seagrass beds. Differences in fish densities between biotopes were related to differences in structural complexity and amount of shelter. Fishes in the bay largely consisted of 17 (mainly commercially important) reef fish species, which used the bay biotopes only as a nursery during the juvenile part of their life cycle. Small juveniles of these species were most often found in the mangroves, whereas at intermediate sizes some were found in the channel. Large individuals and adults were found on the reef, and densities of several of these species were higher on the reef near the bay than on reefs located farther down-current. Fishes which spent their entire life cycles in either the bay or on the coral reef were also found, and the latter group showed a strong decrease in abundance with increasing distance into the bay. The density distribution of individual fish species was not homogeneous within the bay. In the mangroves and seagrass beds, spatial distribution of fishes was correlated with distance to the mouth of the bay, water transparency, amount of shelter, and the structural complexity of the biotope. Juveniles of 3 reef species showed an increase in size on the seagrass beds with distance from the mouth into the bay, whereas 1 bay species showed a decrease in size with this distance.
We studied the settlement patterns of three Caribbean coral reef fishes in three different habitat types: mangroves, seagrass beds, and coral reefs. The settlement patterns of the three species were ...not random and could best be explained by active habitat selection during settlement. "Acanthurus bahianus" preferentially settled on the shallow reef flat and in adjacent seagrass beds, "Lutjanus apodus" settled exclusively into mangroves, and "Ocyurus chrysurus," settled into both mangroves and seagrass beds. The settlement patterns of these three species reflect their habitat utilization during later juvenile stages. This study, therefore, suggests that the higher juvenile densities in mangroves and seagrass beds are determined by habitat selection during settlement rather than by post-settlement processes. This habitat selection during settlement is in accordance with the assumed importance of mangroves and seagrass beds as juvenile habitats of coral reef fishes and underlines the pressing need for their conservation.
Mangroves and seagrass beds are considered important nursery habitats for coral reef fish species in the Caribbean, but it is not known to what degree the fish depend on these habitats. The fish ...fauna of 11 different inland bays of the Caribbean island of Curaçao were compared; the bays contain 4 different habitat types: seagrass beds in bays containing mangroves, seagrass beds in bays lacking mangroves, mud flats in bays containing mangroves and seagrass beds, and mud flats in bays completely lacking mangroves and seagrass beds. Principal component analysis showed a high similarity of fish fauna among bays belonging to each of the 4 habitat types, despite some differences in habitat variables and human influence between bays. Juveniles of nursery species—fish species using mangroves and seagrass beds as juvenile nurseries before taking up residence on reefs—showed highest abundance and species richness on the seagrass beds, and on the mud flats near mangroves and seagrass beds, but were almost absent from bays containing only mud flats. The high abundance and species richness on the mud flats near nursery habitats can be explained by fishes migrating from the adjacent mangroves/seagrass beds to the mud flats. Seagrass beds near to mangroves showed a higher richness of nursery species than did seagrass beds alone, suggesting an interaction with the mangroves resulting in an enhancement of species richness. Comparison of fish densities from the 4 different habitat types indicates that for the nursery species the degree of dependence on a combination of mangroves and seagrass beds as nurseries for juvenile fish is high forOcyurus chrysurusandScarus iserti, the dependence on seagrass beds is high forHaemulon parrai,H. sciurus,Lutjanus apodus,L. griseus,Sparisoma chrysopterumandSphyraena barracuda, and the dependence on mud flats near mangroves/seagrass beds is high forL. analis. The dependence on mangroves and/or seagrass beds is low forChaetodon capistratus,Gerres cinereus,H. flavolineatumandL. mahogoni, which can also use alternative nursery habitats.
Day-night changes in fish communities were quantified in 6 associated shallow-water biotopes within a single bay: mangroves, seagrass beds, algal beds, channel, fossil reef boulders, and notches in ...fossil reef rock. All biotopes, except the algal beds, showed a strong reduction in fish density and species richness at night, caused by absence of diurnally active fishes and migrations of Haemulidae and Lutjanidae to the seagrass beds. The fish fauna of the different biotopes showed a relatively high dissimilarity between day and night. This dissimilarity is largely caused by absence of Acanthuridae, Chaetodontidae, Labridae, Pomacentridae, Scaridae and Sparidae at night. These fishes seek shelter at night in, amongst others, the channel, notches and boulders. The balloonfish Diodon holocanthus utilised almost all biotopes as shelter as well as feeding sites. The wide distribution of its preferred food (molluscs) probably explains its distribution in most biotopes at night. The noctumally active Haemulidae and Lutjanidae, on the other hand, migrated from their daytime shelter sites to the seagrass beds at night to feed. Some of these fishes also migrated to the algal beds to feed. The preference of Haemulidae and Lutjanidae for the seagrass bed as a feeding biotope, instead of other bay biotopes, appears to be related to the relatively high availability of their preferred food (Tanaidacea and Decapoda) as determined by digestive tract analysis. Other bay biotopes showed much lower densities of such food items compared to the seagrass beds.
The value of mangroves for fish species is usually explained in terms of high food abundance or shelter against predators as a result of high turbidity and structural complexity. In a field ...experiment, artificial mangrove units (AMUs) were designed as open cages, each of which was provided with a different degree of structural complexity and shade. Fish species that were attracted to the AMUs were identified and counted and the effects of shade and structural complexity, as well as the interaction between the two factors, were tested. Diurnal fish showed a preference for the greatest structured complexity and for a moderate increase in shade. Two nocturnal species common in local mangroves as well as seagrass beds showed statistically significant effects: densities of Haemulon sciurus were positively related to both shade and structural complexity, whereas only shade had a significant positive effect on densities of Ocyurus chrysurus. The experiment indicated that the attractiveness of mangrove vegetation for H. sciurus may be influenced by the structural complexity of the habitat as well as by the degree of shade, and that both factors are equally and separately important. Individuals of O. chrysurus that are attracted to mangroves are more likely to be influenced by the presence of shade than by the degree of structural complexity. The data thus indicated that the positive relationship between fish densities in mangrove habitats and the degree of shade and structural complexity, or both, is species-specific.
Quantitative data on leaf litter removal activity of macrozoobenthic organisms in the mangrove forests of East Africa are virtually non-existent. In the present study, litter removal activity was ...determined in two contrasting types of mangrove stands in Gazi Bay (Kenya). In the relatively elevated
Ceriops tagal vegetation, which is only flooded during spring tides, the detritivorous snail
Terebralia palustris (Linnaeus) was the major macrobenthic organism responsible for litter removal. Analysis of the
δ
13C value of the foot tissue of the snail indicated a segregation in the food consumed by individuals below and above a size of 50 mm, in agreement with the observation that only larger individuals were feeding on the leaf litter. In the low lying
Rhizophora mucronata stand, which is flooded by each high tide, the crab
Sesarma guttatum (H. Milne Edwards) was responsible for most of the litter removal (consumption and burial).
The availability of water in the
C. tagal stand, caused by tidal inundation or by rainfall, was a determining factor in the amount of litter being removed. When the stand remained dry around neap tides, the median litter removal, as a percentage of the litter fall, was only 0.8%. Under wet conditions around spring tide this percentage was much higher: 41.6% by night and 25.2% by day, respectively. These figures reflect the behaviour of
T. palustris, which is inactive under dry conditions in order to avoid desiccation. Median litter removal in the
R. mucronata vegetation, expressed as a percentage of the litter fall, was 40.3% by day and 21.7% by night. No relation was observed between lunar cycle and activity of the litter processing crabs. Taking into consideration differences in inundation frequency and duration, and in litter removal activity by benthic animals as related to tidal height and day/night cycles, we estimate that in this East African mangrove, on average, 11.2% and 18.6% of the fallen litter is processed by macrobenthic animals in the
C. tagal and in the
R. mucronata vegetation, respectively. Our results indicate that removal of fallen leaf litter in mangrove forests is not effected by benthic communities dominated by crabs only, but that activities of litter feeding snails may also be significant.
Mangroves and seagrass beds have received considerable attention as nurseries for reef fish, but comparisons have often been made with different methodologies. Thus, relative importance of different ...habitats to specific size-classes of reef fish species remains unclear. In this study, 35 transects in 11 sites of mangroves, seagrass beds and coral reef were surveyed daily, in and in front of a marine bay on the island of Curaçao (Netherlands Antilles). The density and size-frequency of nine reef fish species (including herbivores, zoobenthivores and piscivores) was determined during a five-month period using a single methodology, viz. underwater visual census. All species were ‘
nursery species
’ in terms of their high densities of juveniles in mangroves or seagrass beds. Relative density distribution of the size-classes of the selected species over mangroves and seagrass beds suggested high levels of preference for either mangroves or seagrass beds of some species, while other species used both habitats as a nursery. Spatial size distribution of the nine species suggested three possible models for Post-settlement Life Cycle Migrations (PLCM).
Haemulon sciurus,
Lutjanus griseus,
L. apodus, and
Acanthurus chirurgus appear to settle and grow up in bay habitats such as mangroves and seagrass beds, and in a later stage migrate to the coral reef (Long Distance PLCM). Juveniles of
Acanthurus bahianus and
Scarus taeniopterus were found only in bay habitats at close proximity to the coral reef or on the reef itself, and their migration pattern concerns a limited spatial scale (Short Distance PLCM). Some congeneric species carry out either Long Distance PLCM or Short Distance PLCM, thereby temporarily alleviating competition in reef habitats.
Haemulon flavolineatum,
Ocyurus chrysurus and
Scarus iserti displayed a Stepwise PLCM pattern in which smallest juveniles dwell in the mouth of the bay, larger individuals then move to habitats deeper into the bay, where they grow up to a (sub-) adult size at which they migrate to nearby coral reef habitats. This type of stepwise migration in opposite directions, combined with different preference for either mangroves or seagrass beds among (size-classes of) species, shows that reef fish using in-bay habitats during post-settlement life stages may do so by choice and not merely because of stochastic dispersal of their larvae, and underline the necessity of these habitats to Caribbean coral reef systems.
.
The HADES data from p + Nb collisions at a center-of-mass energy of
GeV are analyzed employing a statistical hadronization model. The model can successfully describe the production yields of the ...identified hadrons
,
,
,
K
0
s
,
with parameters
MeV and
MeV, which fit well into the chemical freeze-out systematics found in heavy-ion collisions. In addition, we reanalyze our previous HADES data from Ar + KCl collisions at
GeV with an updated version of the model. We address equilibration in heavy-ion collisions by testing two aspects: the description of yields and the regularity of freeze-out parameters from a statistical model fit as a function of colliding energy and system size. Despite its success, the model fails to describe the observed
yields in both, p + Nb and Ar + KCl . Special emphasis is put on feed-down contributions from higher-lying resonance states as a possible explanation for the observed excess.
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