Effects of Mixed-species Foraging Groups on the Feeding and Aggression of Juvenile Parrotfishes

Many parrotfishes (Scaridae) co-occur in mixed-species aggregations as juveniles, but diverge in resource use and social structure as adults. Focal observations of three juvenile parrotfishes (Scarus coeruleus, Sparisoma aurofrenatum, and Sparisoma viride) were conducted on inshore patch reefs in the Florida Keys to determine how feeding and aggressive interactions vary with group participation. All three species spent more time in groups than alone, most often in groups of less than ten individuals. Feeding rates were significantly higher for S. viride when foraging in groups than when alone. All species fed most often from Halimeda, and overall diet composition was similar for fish whether feeding in groups or alone. The frequency of aggressive interactions varied with group participation. Focal S. aurofrenatum were more aggressive when in groups than when alone, and both S. aurofrenatum and S. viride were attacked more often by damselfishes when they were alone than when in groups. In contrast, feeding rates, diet breadth, and aggressive interactions of S. coeruleus were less affected by group participation. Small mixed-species aggregations of coral reef fishes may be large enough for individuals to assume some of the benefits of group participation while at the same time avoiding the costs of competition realized in larger groups.     

Resource and habitat sharing by the stoplight parrotfish,Sparisoma viride, a Caribbean reef herbivore

Synopsis We compare the vertical distribution, substrate preferences, grazing behaviour and social interactions of the stoplight parrotfish,Sparisoma viride, with that of other scarids at a fringing reef off Bonaire (Netherlands Antilles). Earlier reports thatS. viride only displays territorial behaviour against conspecifics are confirmed by the non-aggressive nature of this parrotfish and the low time expenditure on interactions with other herbivores. The vertical distribution ofS. viride is largely identical to that of several other scarids, acanthurids and pomacentrids, whose ranges may completely coincide withS. viride territories. Comparison of the substrate use of the five most common scarids inside a singleS. viride territory yields no evidence of food partitioning. We suggest that the lack of interspecific territorial behaviour inS. viride is explained by the inability to economically defend a territory against all potential food competitors. Factors that may favour territory sharing between herbivores are fine-scale resource partitioning and shared defence, both of which would reduce the costs of territorial life. However, more detailed investigation of herbivore food selection is required before definite conclusions can be drawn.     

Parrotfish abundance and selective corallivory on a Belizean coral reef

Parrotfish are important members of coral reef communities because they consume macroalgae that would otherwise outcompete reef-building corals for space. However, some Caribbean parrotfish species also feed directly on live corals, and thus have the potential to negatively impact coral fitness and survival. This study investigates selective grazing by parrotfish on particular coral species, differences in grazing incidence among reef habitats and intraspecific discrimination among colonies of several coral species. We also investigate spatial and temporal patterns of parrotfish species abundance across habitats on the Belize barrier reef, and examine correlations between parrotfish abundance and grazing intensity across reef habitats. We found that members of the Montastraea annularis species complex, major builders of Caribbean reefs, were preferred targets of parrotfish grazing across all reef habitats, while M. cavernosa, Agaricia agaricites, Diploria strigosa, Porites astreoides and Porites porites were not preferred; Siderastrea siderea was preferentially grazed only in the spur and groove habitats. Parrotfish grazing preferences varied across habitats; M. annularis was grazed most often in shallow habitats, whereas M. franksi was consumed more at depth. Although it was not possible to directly observe parrotfish grazing on corals, we did find a positive correlation between Sparisoma aurofrenatum abundance and M. franksi grazing incidence across habitats. Finally, when we compared our results to parrotfish abundances measured by a previous study, we found that Sparisoma viride and Sp. aurofrenatum, two species known to be corallivorous, had increased abundances between 1982 and 2004. In light of escalating threats on Caribbean reef corals, it would be important for future studies to evaluate the impact of parrotfish corallivory on coral survival.     

Variation in fish density,assemblage composition and relative rates of predation among mangrove,seagrass and coral reef habitats

We tested the hypothesis for several Caribbean reef fish species that there is no difference in nursery function among mangrove, seagrass and shallow reef habitat as measured by: (a) patterns of juvenile and adult density, (b) assemblage composition, and (c) relative predation rates. Results indicated that although some mangrove and seagrass sites showed characteristics of nursery habitats, this pattern was weak. While almost half of our mangrove and seagrass sites appeared to hold higher proportions of juvenile fish (all species pooled) than did reef sites, this pattern was significant in only two cases. In addition, only four of the six most abundant and commercially important species (Haemulon flavolineatum, Haemulon sciurus, Lutjanus apodus, Lutjanus mahogoni, Scarus iserti, and Sparisoma aurofrenatum) showed patterns of higher proportions of juvenile fish in mangrove and/or seagrass habitat(s) relative to coral reefs, and were limited to four of nine sites. Faunal similarity between reef and either mangrove or seagrass habitats was low, suggesting little, if any exchange between them. Finally, although relative risk of predation was lower in mangrove/seagrass than in reef habitats, variance in rates was substantial suggesting that not all mangrove/seagrass habitats function equivalently. Specifically, relative risk varied between morning and afternoon, and between sites of similar habitat, yet varied little, in some cases, between habitats (mangrove/seagrass vs. coral reefs). Consequently, our results caution against generalizations that all mangrove and seagrass habitats have nursery function.     

Feeding complementarity versus redundancy among herbivorous fishes on a Caribbean reef

Herbivory is an important driver of community structure on coral reefs. Adequate understanding of herbivory will mandate better knowledge of how specific herbivores impact reef communities and the redundancy versus complementarity of their ecological roles. We used algal communities generated by herbivore manipulations to assess such roles among Caribbean herbivorous fishes. We created large enclosures on a 16- to 18-m-deep reef to create treatments grazed for 10 months by: (1) only Sparisoma aurofrenatum, (2) only Acanthurus bahianus, (3) no large herbivorous fishes, or (4) natural densities of all reef fishes. After 10 months, we removed cages and filmed how free-ranging reef fishes fed among these treatments that differed in algal community structure. In general, Acanthurus spp. and Scarus spp. rapidly grazed exclosure and Sparisoma-only treatments, while Sparisoma spp. preferentially grazed exclosure and Acanthurus-only treatments. These patterns suggest complementarity between Sparisoma spp. and both Acanthurus spp. and Scarus spp. but redundancy between Acanthurus spp. and Scarus spp. Despite these generalities, there was also within-genera variance in response to the different treatments. For example, large Scarus spp., such as Scarus guacamaia, fed more similarly to Sparisoma spp., particularly Sparisoma viride, than to other Scarus spp. Moreover, the three common Sparisoma species differed considerably in the macroalgae to which they exhibited positive or negative relationships. Thus, herbivorous reef fishes vary considerably in their response to different algal communities and exhibit complex patterns of compensatory feeding and functional redundancy that are poorly predicted by taxonomy alone.     

Predation Risk,Resource Quality,and Reef Structural Complexity Shape Territoriality in a Coral Reef Herbivore

For many species securing territories is important for feeding and reproduction. Factors such as competition, habitat availability, and male characteristics can influence an individual’s ability to establish and maintain a territory. The risk of predation can have an important influence on feeding and reproduction; however, few have studied its effect on territoriality. We investigated territoriality in a haremic, polygynous species of coral reef herbivore, Sparisoma aurofrenatum (redband parrotfish), across eight reefs in the Florida Keys National Marine Sanctuary that were either protected or unprotected from fishing of piscivorous fishes. We examined how territory size and quality varied with reef protection status, competition, predation risk, and male size. We then determined how territory size and quality influenced harem size and female size to understand the effect of territoriality on reproductive potential. We found that protected reefs trended towards having more large predatory fishes and that territories there were smaller but had greater algal nutritional quality relative to unprotected reefs. Our data suggest that even though males in protected sites have smaller territories, which support fewer females, they may improve their reproductive potential by choosing nutritionally rich areas, which support larger females. Thus, reef protection appears to shape the trade-off that herbivorous fishes make between territory size and quality. Furthermore, we provide evidence that males in unprotected sites, which are generally less complex than protected sites, choose territories with higher structural complexity, suggesting the importance of this type of habitat for feeding and reproduction in S. aurofrenatum. Our work argues that the loss of corals and the resulting decline in structural complexity, as well as management efforts to protect reefs, could alter the territory dynamics and reproductive potential of important herbivorous fish species.     

Local variability in population structure and density of the protogynous reef herbivoreSparisoma viride

Synopsis We compare the (relative) abundance of life phases [juveniles (JU), initial phase (IP) and terminal phase (TP) fish], social categories (territorial and group adults), and fish following alternative mating styles, in three local populations of the protogynous reef herbivore,Sparisoma viride, on the fringing reef of Bonaire (Netherlands Antilles). In order to determine the adaptive significance of variations in social organization, they are related to the density of conspecifics and other herbivores and to the availability of food, shelter and mating sites. The most striking difference is the high abundance of JU and group fish at one location (Playa Frans) and the total absence of group fish at another (Red Slave). These differences are coherent with a gradient in population density, total herbivore density, scarid grazing pressure, and reproductive output, all of which are highest at Playa Frans and lowest at Red Slave. Exposure to waves and currents shows an inverse trend. The differences in the relative abundance of territorial fish can be explained by the concept of economic defendability, which is reduced at higher population density. In a life history context, small TP group males represent bachelors that sacrifice current reproduction for better future prospects. As predicted by life history theory, early sex change is promoted at sites where the future rewards are higher (higher spawning rates of large TP males) and where the costs incurred during the bachelor phase are reduced (more spawning opportunities for group TP males). At Red Slave an alternative male mating style (streaking) appears to be promoted by the lack of a refuge for group TP males and by a dense gorgonian canopy, allowing IP males to reside inside territories. We conclude that most observed differences in population structure can be considered adaptive in an ecological and in a life history context. Population density is a major factor in both contexts. Analysis of the variability in adult density in relation to JU density and the availability of food and shelter indicates that theS. viride populations at Bonaire are not totally controlled by stochastic processes. Considering the small spatial scale and the high dispersal of the planktonic embryos and larvae, the observed variability in behavioural and life history traits ofS. viride points to a high degree of phenotypic plasticity.     

Evaluating the use of roving diver and transect surveys to assess the coral reef fish assemblage off southeastern Hispaniola

The relatively little-studied fish fauna off southeastern Hispaniola was rapidly assessed using a combination of visual survey techniques including transects and roving diver surveys. It was found that when combined, both methods provided a more complete overall species assessment than either method was able to provide in isolation. Being able to conduct rapid species assessments is becoming increasingly more important as a conservation tool. Data on species composition, sighting frequency, and abundance of all fishes were collected using both methods. Abundance was recorded in four logarithmic-based categories (roving diver method) while the number of fishes were counted within 40-m² transects (transect method). Both methods were similar in recording the most abundant species, while a greater number of rare species (especially fishery-targeted species) were recorded with the roving diver method. The most abundant groupers were Cephalopholis cruentata and C. fulva. The most abundant parrotfishes were Scarus taeniopterus, Sparisoma aurofrenatum, and Scarus iserti. The most conspicuous differences between fishes off southeastern Hispaniola and elsewhere in the tropical western Atlantic were the low abundance and smaller size of harvested species such as groupers, snappers (Fam. Lutjanidae), and grunts (Fam. Haemulidae). With the roving diver method, more time could be spent surveying (instead of placing transect lines), resulting in a greater number of species being recorded. Additionally, well-trained volunteers can adopt the roving diver method as part of their regular diving program. Transect surveys were able to provide information such as length (biomass) and actual density measures that were not recorded in roving diver surveys. Thus, these methods were complementary and should be used in conjunction when conducting rapid assessments of fish assemblages, especially to detect the effects of overfishing.     

Female defense polygyny in the territorial triggerfish <Emphasis Type="Italic">Sufflamen chrysopterum</Emphasis>

The occurrence of polygyny requires specific environmental conditions such as female aggregation or patchy resource distribution. However, it is difficult to determine the factors responsible for polygyny in species in which the territories of both sexes overlap. To overcome this, we performed female removal experiments in the polygynous triggerfish Sufflamen chrysopterum (Balistidae) in the Okinawa coral reef. Both sexes defended their territories exclusively against consexuals of the same species, and female aggregation was absent. Each male territory included 1–3 female territories, and nonterritorial males were significantly smaller than territorial males. Further, the body size of territorial males was positively correlated with that of the largest female in their territories, and larger males tended to mate with more females. The results of the female removal experiments (n = 10 females) indicated that females competed for better territories rather than larger mates. In contrast, males abandoned the territories once the females emigrated. These results strongly suggest that males defend females rather than sites and compete for larger and a greater numbers of females. Thus, in S. chrysopterum, female defense polygyny occurs in the absence of female aggregation.     

Effects of fish predation and seaweed competition on the survival and growth of corals

On Caribbean coral reefs, high rates of grazing by herbivorous fishes are thought to benefit corals because fishes consume competing seaweeds. We conducted field experiments in the Florida Keys, USA, to examine the effects of grazing fishes on coral/seaweed competition. Initially, fragments of Porites divaracata from an inshore habitat were transplanted into full-cage, half-cage, and no-cage treatments on a fore-reef. Within 48 h, 56% of the unprotected corals in half-cage and no-cage treatments (62 of 111) were completely consumed. Stoplight parrotfish (Sparisoma viride) were the major coral predators, with redband parrotfish (S. aurofrenatum) also commonly attacking this coral. Next, we transplanted fragments of P. porites collected from the fore-reef habitat where our caging experiments were being conducted into the three cage treatments, half in the presence of transplanted seaweeds, and half onto initially clean substrates. The corals were allowed to grow in these conditions, with concurrent development of competing seaweeds, for 14 weeks. Although seaweed cover and biomass were both significantly greater in the full-cage treatment, coral growth did not differ significantly between cage treatments even though corals placed with pre-planted seaweeds grew significantly less than corals placed on initially clean substrate. This surprising result occurred because parrotfishes not only grazed algae from accessible treatments, but also fed directly on our coral transplants. Parrotfish feeding scars were significantly more abundant on P. porites from the half and no-cage treatments than on corals in the full cages. On this Florida reef, direct fish predation on some coral species (P. divaracata) can exclude them from fore-reef areas, as has previously been shown for certain seaweeds and sponges. For other corals that live on the fore-reef (P. porites), the benefits of fishes removing seaweeds can be counterbalanced by the detrimental effects of fishes directly consuming corals. Received: 31 May 1997 / Accepted: 2 September 1997     

Movements of Fishes Within and Among Fringing Coral Reefs in Barbados

Movement of coral reef fishes across marine reserve boundaries subsequent to their initial settlement from the plankton will affect the ability of no-take reserves to conserve stocks and to benefit adjacent fisheries. However, the mobility of most exploited reef species is poorly known. We tagged 1443 individuals of 35 reef fish species captured in Antillean fish traps in the Barbados Marine Reserve and adjacent non-reserve over a two-month period. Trapping and visual surveys were used to monitor the movements of these fish during the trapping period and the subsequent two months. Estimates of distances moved were corrected for the spatial distribution of sampling effort and for the number of recaptures of individual fish. Recapture rates for individual species ranged from 0–100% (median=38%). Species mobility estimated by recapture and resighting were highly correlated. Most species were strongly site attached, with the majority of recaptures and resightings occurring at the site of tagging. However, only one of 59 tagged jacks (Caranx latus, C. ruber) was ever resighted, suggesting emigration from the study area. All species were occasionally recorded away from the sites where they had been tagged (20–500m), and several species, including surgeonfish, Acanthurus bahianus, A. coeruleus, filefish, Cantherhines pullus, butterflyfish, Chaetodon striatus, angelfish Holocanthus tricolor and parrotfish, Sparisoma viride, ranged widely within reefs. In contrast, few movements were observed between reefs separated by more than 20m of sand and rubble, and no emigration from the Reserve was recorded. Most reef fishes vulnerable to Antillean traps appear sufficiently site-attached to benefit from reserves. However, many species move over a wide enough area to take them out of small reserves on continuous reef. Use of natural home range boundaries could minimize exposure of fishes in reserves to mortality from adjacent fisheries.     

Determinants of territory size in the pomacentrid reef fish,Parma victoriae

Summary Factors governing the size of territories defended by the pomacentrid reef fish, Parma victoriae, were investigated, prompted by contradictory predictions in the literature concerning the effects of food supply and competitors. Observations were carried out over the non-breeding period (March–October) on a medium density population in which territories were partially contiguous. The territory size of adult fish varied between 3 and 26 m², and was inversely correlated with local densities of conspecifics. The same range in territory size was found for both males and females, which did not differ in the time they spent on territory defence and foraging activities. No correlation existed between territory size and the abundance of algal food, body size, age or time spent on territory defence. Also, there was little variation in territory size over time, despite seasonal changes in the abundance of food algae.Experimental reduction of food supplies on isolated territories of males and females had no effect on territory size. In a higher density habitat an experiment was carried out in which population density and food abundance were simultaneously manipulated. This showed that territory size was primarily determined by intraspecific interactions, as territories exhibited considerable increases in size upon removal of neighbours. No changes in the size of defended areas resulted from either artificial increases or decreases of food levels. There were also no changes in the time spent on defence of territories, foraging time or feeding rates associated with food manipulations or territory expansion, which suggested that food was not a limited resource. This conflicted with current theories proposed to explain territory defence and expansion. It is hypothesized that intraspecific interactions constrain territory size well below the optimum in terms of the abundance of preferred food algal species.     

Small‐scale demographic variation in the stoplight parrotfish Sparisoma viride

Age‐based analysis of the stoplight parrotfish Sparisoma viride was used to examine whether observed differences in their abundance and size structure among reefs in a cross‐shelf portion of the upper Florida Keys could be explained by variation in demographic rates. Annual and daily sagittal otolith increments were enumerated for 176 individuals collected from replicates of reefs in two strata, inshore and offshore reefs (2–6 m depth). von Bertalanffy growth functions fitted to size‐at‐age plots for each site were similar between reefs within each stratum (inshore and offshore), but differed between strata. Sparisoma viride on offshore reefs attained greater average standard length (L_S) at age, greater mean asymptotic size and were longer lived than fish from inshore reefs. Fish on inshore reefs attained only half the maximum age observed on offshore reefs (4 v. 8 years, respectively). No terminal phase fish >4 years of age were found on either reef type. Estimates of mortality rates from age‐frequency data of collected fish revealed higher mortality on inshore reefs. Demographic variables obtained in this study were similar to published values for S. viride from Caribbean reefs but differed significantly from published values from reefs at a similar latitude (Bahamas), reflecting high demographic plasticity on both local and regional scales.     

Impact of Herbivore Identity on Algal Succession and Coral Growth on a Caribbean Reef

Background

Herbivory is an important top-down force on coral reefs that regulates macroalgal abundance, mediates competitive interactions between macroalgae and corals, and provides resilience following disturbances such as hurricanes and coral bleaching. However, reductions in herbivore diversity and abundance via disease or over-fishing may harm corals directly and may indirectly increase coral susceptibility to other disturbances.

Methodology and Principal Findings

In two experiments over two years, we enclosed equivalent densities and masses of either single-species or mixed-species of herbivorous fishes in replicate, 4 m² cages at a depth of 17 m on a reef in the Florida Keys, USA to evaluate the effects of herbivore identity and species richness on colonization and development of macroalgal communities and the cascading effects of algae on coral growth. In Year 1, we used the redband parrotfish (Sparisoma aurofrenatum) and the ocean surgeonfish (Acanthurus bahianus); in Year 2, we used the redband parrotfish and the princess parrotfish (Scarus taeniopterus). On new substrates, rapid grazing by ocean surgeonfish and princess parrotfish kept communities in an early successional stage dominated by short, filamentous algae and crustose coralline algae that did not suppress coral growth. In contrast, feeding by redband parrotfish allowed an accumulation of tall filaments and later successional macroalgae that suppressed coral growth. These patterns contrast with patterns from established communities not undergoing primary succession; on established substrates redband parrotfish significantly reduced upright macroalgal cover while ocean surgeonfish and princess parrotfish allowed significant increases in late successional macroalgae.

Significance

This study further highlights the importance of biodiversity in affecting ecosystem function in that different species of herbivorous fishes had very different impacts on reef communities depending on the developmental stage of the community. The species-specific effects of herbivorous fishes suggest that a species-rich herbivore fauna can be critical in providing the resilience that reefs need for recovery from common disturbances such as coral bleaching and storm damage.     

Territoriality and Habitat Use by Juvenile Blue Tangs, Acanthurus coeruleus

We studied territoriality and habitat use by yellow phase juvenile blue tangs, Acanthurus coeruleus, on a small fringing reef in Barbados, West Indies. Juvenile blue tangs occurred on the reef crest, spurs, and a transition zone between the reef crest and reef flat at a density of about 8 individuals per 100m², but were much rarer on the reef flat. They were solitary and occupied stable home ranges (median=0.85m²) that increased with body size. Observational and experimental data documented aggressive defense of home ranges against conspecific and to a lesser extent congeneric, A. bahianus, juveniles (about 7.5 approaches and attacks per hour directed at intruders). Home range locations were structurally more complex and closer to a vertical face than expected by chance. Although juvenile blue tang territories overlapped considerably with those of larger and more aggressive Stegastes damselfish, which are believed to exclude solitary adult Acanthurus spp. from reef crest and spurs, the tangs avoided Stegastes and were rarely chased (<0.3 fleeing events per hour). Space use and social organization of yellow juvenile blue tangs contrast strikingly with that of both conspecific adults and congeneric juveniles.     

Aggression,interference, and the functional response of coral-feeding butterflyfishes

Functional responses describing how foraging rates change with respect to resource density are central to our understanding of interspecific interactions. Competitive interactions are an important determinant of foraging rates; however, the relationship between the exploitation and interference components of competition has received little empirical or theoretical consideration. Moreover, little is known about the relationship between aggressive behavioural interactions and interference competition. Using a natural gradient of consumer and resource densities, we empirically examine how aggressiveness relates to consumer–consumer encounter rates and foraging for four species of Chaetodon reef fish spanning a range of dietary niche breadths. The probability of aggression was most strongly associated with both total consumer and resource densities. In contrast, total encounter rates were best predicted by conspecific consumer density, and were highest for the most specialised consumer (Chaetodon trifascialis), not the most aggressive (Chaetodon baronessa). The most specialised consumer, not the most aggressive, also exhibited the largest reduction in foraging rates with increasing consumer density. Our results support the idea of a positive link between the exploitation and interference components of competition for the most specialised consumer. Moreover, our results caution against inferring the presence of ecological interactions (competition) from observations of behaviour (aggression and agonism) alone.     

Interpreting Space Use and Behavior of Blue Tang, <Emphasis Type="Italic">Acanthurus coeruleus</Emphasis>, in the Context of Habitat,Density, and Intra-specific Interactions

Synopsis We hypothesized that blue tang, Acanthurus coeruleus, territories on sites with low biogenic structure would be larger than territories on sites with relatively high biogenic structure due to differences in the amount and distribution of resources. We tested this hypothesis by tracking blue tang over uncolonized pavement and reef crest, two habitat types at opposite ends of the habitat structure spectrum. We recorded density, feeding rates and aggression events in order to evaluate our findings in the context of a territory model and the ideal free distribution model. Territories of A. coeruleus averaged nearly four times larger on pavement sites than on reef crest sites. Conversely, densities of A. coeruleus were significantly lower on pavement sites. While there was no significant difference in the average rates of movement between habitats, average turning angles were significantly higher on reef crest. There were no significant differences in feeding rates between habitats, suggesting that higher territory sizes and lower densities may allow fish on uncolonized pavement to match resource acquisition of fish on reef crest. The insignificant difference of aggression encounters between habitats suggests that movement and density differences among habitats are not solely legacies of differential settlement.     

Feeding selectivity in relation to territory size in a herbivorous reef fish

Summary Territory size in the herbivorous reef fish, Parma victoriae, (Pisces: Pomacentridae) is primarily determined by local density patterns and is independent of changes in food levels (Norman and Jones 1984). However, while individual readily expand territories in response to having their neighbours removed, they appear not to increase total food consumption. Individuals with large territories may benefit from improved food quality. Here we test the hypothesis that expanded territories increase access to preferred food types.A preliminary comparison of the relative proportions of algal species consumed and those present in the field indicated that feeding was highly selective. Strong feeding preferences were indicated by a field cafeteria experiment, in which algal species were presented to individuals in equal amounts. Selectivity indices calculated from diet and availability measures were positively correlated with the feeding preference rankings.Individuals examined from two territory size categories (<10 m² and > 10 m²) did not exhibit significant differences in feeding prefernces. However, they differed greatly in terms of the makeup of their diets. Higher ranking algae such as Champia zostricola and Rhodoglossum sp. were consumed in greater proportions on large territories. Algal abundances within territories also differed for the two groups. Some of the less abundant, high ranking food species were found in greater quantities per unit area on large territories. The differences in diet were not solely explained by changes in availability. The appropriate comparison showed that whereas individuals on large territories fed in a highly selective manner, those on small territories consumed algae in proportion to their availability. A neighbour removal experiment supported the hypothesis that territory expansion results in an increase in the consumption of preferred algal species.     

Relationship Between Male Size and Newborn Size in the Seaweed Pipefish, Syngnathus Schlegeli

Relationships between male size, number, and weight of newborn were determined in the seaweed pipefish, Syngnathus schlegeli, with paternal care of embryos in the brood pouch. While the number of newborn increased linearly with the increase in male size, the pouch volume increased exponentially with the male size. This resulted in embryo density in the pouch negatively correlating with the male size. Newborn dry weight was negatively correlated with the embryo density in the pouch. Thus, larger males were considered to brood embryos at lower densities and give birth to heavier newborn. Neither paternal size nor embryo density seemed to have an effect upon developmental stage and total length of the newborn. Substantial weight loss of embryos during incubation indicated that paternal nutritional contribution to embryos is insignificant; therefore, the tendency of larger males to produce heavier newborn may not relate to allocation of paternal nourishment. Because egg weight increased with the female size, larger males are considered to receive the eggs of larger females and give birth to heavier newborn that developed from heavier eggs. Lower embryo density in larger males is attributable to the larger size of the heavier eggs. Assuming the pouch to be a cylindrical tube and the egg to be a sphere, geometrical calculations revealed that the relationship between the volumetric fraction of the pouch used by eggs (i.e. functional volume) and the male size was negatively quadric and had a peak. Increase in egg diameter increased the male size at which the functional volume of the pouch is maximized. Thus it appears that the size relationship of mates in pipefish is related to effective use of the pouch space.     

Multi-scale spatial and partitioning analyses of the reef-fish community composition of the Yucatan fringing reef system

Coral reef and reef-fish communities are complex systems that have spatial structures that are influenced by multiple factors and processes that interact at several scales. We analysed composition data of reef-fish communities in the Yucatan Peninsula fringing reef system using a hierarchical multi-scale survey design to elucidate the origins of the species distribution patterns through multivariate canonical ordination and partitioning analysis. Twelve reef sites were surveyed along the fringing reef system, nested in three sectors, each with distinctive human interests (tourism, fishing, protection). Line transects were placed on reef lagoon, reef front, reef slope and reef terrace habitat for a total of 480 transects. The communities were composed of many rare and some dominant species (e.g., Thalasoma bifasciatum, Acanthurus bahianus, A. coeruleus, Sparisoma aurofrenatum). Redundancy analyses revealed that environmental variables explained between 11% and 22% of the variation in fish community data according to the habitat analysed. Spatial variables, represented by the geographic coordinates of transects, explained a low percentage (2–5%) of variation in the fish community data. Among the environmental variables that significantly explained (P < 0.05) the patterns of variation on the fish community were depth, topographical complexity, and the percentage of the substratum covered by algae, calcareous floor, rock and rubble. Although the total explained variation and proportion of the variation explained by each set of variables were consistently low, most of the effects on the fish community composition data were significant. Explanations are proposed concerning those results. Evincing the distribution patterns on the biological systems of multi-species as well as the causes that shape them is key for conservation planning and essential in highly threatened regions, such as the Caribbean coast of the Yucatan Peninsula.