Recruitment Of Coral Reef Fishes Research Articles

The influence of Sargassum biomass and thallus density on the recruitment of coral reef fishes

The influence of Sargassum biomass and thallus density on the recruitment of coral reef fishes

Recruitment of coral reef fishes along a cross-shelf gradient in the Red Sea peaks outside the hottest season

Knowledge on the early life history, ecology, and biology of marine species is crucial for future projections of the resilience of coral reef ecosystems and for adequate management strategies. A fundamental component of population dynamics is the recruitment of new individuals, and in some marine populations, this may be a limiting factor. Recruitment peaks of coral reef fishes commonly occur during the warmer months of the year in many subtropical and temperate locations worldwide. In the Red Sea, very little is known about the influence of temperature on reproductive patterns of coral reef fishes and studies on recruitment are missing. The Red Sea is one of the hottest and most isolated tropical seas in the world. We hypothesized that sea surface temperatures (SSTs) during the Red Sea’s hottest season may exceed the optimum for successful recruitment of some coral reef fishes, which therefore has to occur during other, cooler seasons, unlike recruitment among coral reef ecosystems around the world. We identified taxa among fish recruits by matching mitochondrial DNA sequences (using COI, commonly known as “barcoding”) and assessed potential biological and environmental drivers of recruitment. We studied three reefs located along a cross-shelf gradient for 12 consecutive months in the central Red Sea to capture seasonal changes in biotic and abiotic parameters along this gradient. Our results indicated that recruitment peaks did not occur during the hottest SSTs for most taxa, especially at the hottest inshore and mid-shelf reefs, and identified fish recruitment to be mainly and strongly correlated with the biomass of planktonic invertebrates. Moreover, temporal patterns of fish recruitment differed within and among taxonomic families among the reefs.

Patterns of recruitment of coral reef fishes in a monsoonal environment

The abundance of newly settled recruits of coral reef fishes was monitored at a total of 11 sites at two islands and two coastal locations in the central Philippines for a 20-month period (February 2008 to September 2009) that included two monsoon cycles. Recruitment occurred throughout the year. Most of the abundant species exhibited protracted recruitment seasons. This confirms the expectation of extended breeding of reef fishes at lower latitudes. The annual pattern of recruitment of reef fishes as a group was predictable. Annual fluctuations of sea surface temperature and wind strength largely explained the pattern. Rainfall, however, did not significantly influence the pattern of recruitment. Peaks in density and species richness of recruits occurred during the southwest monsoon and the second inter-monsoonal period of the year (July to October) when temperatures were highest and when most of the sites were sheltered from winds or when winds were weak. Conversely, lowest density and species richness were observed during the northeast monsoon (November to March) when temperatures were lowest and most sites were exposed to winds. The same pattern could also be seen in the recruitment of both damselfishes (Pomacentridae) and wrasses (Labridae), notwithstanding a tenfold difference in abundance of recruits between the two families. The pattern was fairly consistent across most sites, among most of the species that were examined, and between the 2 years that were sampled. This study is one of the few to provide insights into the influence of environmental factors on the recruitment patterns of fishes on Indo-Pacific coral reefs situated at lower latitudes.

Predator identity and recruitment of coral-reef fishes: indirect effects of fishing

Studies of food and interaction webs are often simplified by combining different species of predator into guilds, especially predators that are closely related. Such combinations require the assumption that predators are functionally redundant or at least have similar effects on prey abun- dances and community structure. However, few studies have rigorously tested this assumption, par- ticularly with exploited species of marine predators. Moreover, fishing can strongly alter the relative abundances of different predatory species, further highlighting the need to examine the top-down effects of different predators on lower trophic-level species within marine communities. Throughout the greater Caribbean, intensive fishing has depleted populations of Nassau grouper Epinephelus striatus, while populations of the less-targeted coney Cephalopholis fulva have proliferated. In the present study I experimentally tested the effects of these different grouper species on recruitment of other coral-reef fishes to spatially isolated reefs. Recruitment to reefs occupied by Nassau grouper was similar to that on predator-free control reefs, and both treatments accumulated higher relative recruit abundance and diversity than reefs occupied by coney. Thus, even closely related predator species can have substantially different effects on lower trophic levels. Shifts in dominance of preda- tory species may therefore lead to dramatic changes to prey communities. These findings underscore the importance of addressing both the direct and indirect effects of fishing on marine communities.

Larval supply and juvenile recruitment of coral reef fishes to marine reserves and non-reserves of the upper Florida Keys, USA

For marine organisms, decoupling between the planktonic larval stage and the benthic-associated juvenile stage can lead to variable patterns of population replenishment, which have the potential to influence the effectiveness of marine reserves. We measured spatial and temporal variability in larval supply and recruitment of fishes to coral reefs of different protection levels and tested whether protection level influenced the relationship between supply and recruitment. We sampled pre-settlement larvae and newly settled recruits from four reefs (two reserves and two non-reserves) in the Florida Keys National Marine Sanctuary, USA. Replicate point measures of larval supply over 14 months and 17 monthly measurements of recruitment varied significantly among months and sites. Sites with the same protection level had significantly different patterns of larval supply as well as larval and recruit diversity, but recruitment magnitude differed only by protection level, where densities were greater at reserves. Differences in larval supply among sites included two particularly large peaks in larval abundance at one site, possibly associated with the observed passage of small-scale oceanographic features. To examine whether relationships between larval supply and recruitment varied by protection level, we selected one species that was present in both the light trap samples and the monthly recruitment surveys. Recruitment of the bicolor damselfish Stegastes partitus was significantly and positively related to larval supply at three of the four sites thus, protection level did not influence this linkage. Since local variability among sites can lead to spatial differences in population replenishment, characterization of larval supply and recruitment to potential marine reserve sites may help to identify optimal locations in a region and contribute to more effective reserve design.

Temporal and spatial patterns in the recruitment of coral-reef fishes in Barbados

We monitored the recruitment of 8 fish taxa at 10 d intervals for 1 yr on 5 fringing coral reefs along a 15 km stretch of the west coast of Barbados, using benthic standard monitoring units of recruitment of fishes (SMURFs). SMURFs are designed to sample taxa that settle onto coral rubble, including cryptic species, and to minimize post-settlement predation. We deployed SMURFs in reef habitat to separate meso-scale processes from the small-scale influences of benthic habitat. Recruit- ment of most taxa occurred year-round, but was highly variable, with on average more than 50% of recruits collected on only 14% of the sampling dates, indicating the importance of frequent sampling. Temporal patterns within taxa were concordant across reefs, indicating coast-wide synchronous set- tlement, but differed among taxa. Within reefs, 2 taxa settled more frequently on SMURFs sur- rounded by non-preferred substrate, 1 exhibited the opposite pattern, and the remaining 5 showed no substrate associations. Recruitment to individual SMURFs was seldom correlated among taxa. Among reefs, recruitment of 4 taxa was consistently lower on the central coast and higher at the north and south ends, consistent with a previously identified tidally induced flow regime that reduces onshore larval transport near the center of the west coast; the remaining taxa exhibited other spatial patterns, challenging the generality of the role of hydrodynamics. Overall, this study expands the tax- onomic range of recruitment studies, shows spatially coherent (over kilometers) but temporally vari- able (over tens of days) recruitment and reveals substantial diversity in patterns among concurrently settling taxa.

Possible effects of downwelling on the recruitment of coral reef fishes to the Eilat (Red Sea) coral reefs

We compared water current measurements with data on the recruitment of reef fishes to a coral reef in Eilat, Red Sea for two consecutive recruitment seasons. There was a clear correlation between the daily number of recruits and the magnitude of the downwelling flow, suggesting that an increase in offshore (near bottom) flow induces higher recruitment. The higher recruitment may be the result of larval swimming against the flow. Although the exact mechanism explaining this correlation is unclear, it may involve odor transport from the reef by the downwelling currents, which reaches competent larvae in deeper water and directs them to potential settlement sites.

Experimental analysis of recruitment patterns of coral reef fishes in seagrass beds: Effects of substrate type, shape, and rigidity

Habitat choice of reef fish larvae at settlement is one of the mechanisms proposed to explain spatial patterns in the distribution of fishes and the corresponding spatial structure of communities. Field experiments using Pomacentridae were conducted at Iriomote Island, southern Japan, in order to determine if rare recruitment of coral reef fishes in seagrass beds is due to larval settlement preference. When three types of natural patch treatments (branching coral patch, seagrass patch, and control without patches) were established in cleared seagrass squares in the center of a seagrass bed, four pomacentrid species, Amblyglyphidodon curacao, Dischistodus prosopotaenia, Cheiloprion labiatus, and Dascyllus aruanus, recruited exclusively onto the coral patches, indicating that larvae distributed in the seagrass bed may have preferred a coral rather than seagrass substrate as a settlement habitat. The effects of differences in physical shape (grid structure for branching coral vs. vertical structure for seagrass leaves) and rigidity (rigid substrate for coral vs. flexible substrate for seagrass) between coral and seagrass substrates on such recruitment patterns were investigated using artificial coral and seagrass units. When artificial habitat units with predator exclusion cages were established in the cleared seagrass squares as above, high densities of A. curacao and D. prosopotaenia recruits were observed on the rigid rather than flexible habitat units (both unit types having similar shape), whereas differences in recruit numbers of the two species were unclear in differently shaped units. These results demonstrated that even though pomacentrid larvae are distributed in the seagrass bed, they do not settle on the seagrass substrate owing to their habitat choice being partially based on a preference for substrate rigidity. Moreover, non-recruitment of C. labiatus and D. aruanus on artificial habitat units suggested that the presence of living coral substrates rather than physical shape/rigidity of substrates are an important cue for habitat choice of these fishes.

Settlement and recruitment of coral reef fishes in moderately exploited and overexploited Caribbean ecosystems: implications for marine protected areas

In order to evaluate the impact of heavy exploitation on settlement and recruitment rates of coral reef fishes, the abundances of pre-settlement and pre-recruitment fishes were monitored at Discovery Bay, Jamaica, where fish stocks are heavily exploited and at several sites around the British Virgin Islands (BVI) where exploitation is moderate. Light traps set concurrently at Discovery Bay and at three fringing reefs in BVI caught many species of pre-settlement reef fishes, except grunts and parrotfish, and one BVI site (Hans Creek) may be an area of particularly high settlement. In contrast, heavily exploited fish stocks at Discovery Bay had greatly reduced settlement rates compared with all three sites in BVI. Settlement rates of unexploited species were more similar in Discovery Bay and BVI. Abundances of juvenile fish caught in wire-mesh traps were monitored over several years in Discovery Bay and at three sites in BVI. Consistently low numbers of exploited species were taken at Discovery Bay compared to the BVI sites, indicating that settlement and recruitment rates have been low in recent years. Exploited fish populations in the small marine protected area (MPA) at Discovery Bay are expected to increase very slowly as a result of settlement and recruitment limitation.

Short-term temporal patterns of early recruitment of coral reef fishes in the tropical eastern Pacific

Short-term temporal patterns of recruitment have been described in a variety of coral reef fishes and have often been related with lunar and tidal cycles. While the relative importance of lunar and tidal factors in determining recruitment patterns has been difficult to assess, most studies have been done in the Caribbean and Indo-Pacific, where tidal amplitudes are small. We studied the short-term temporal dynamics of fish recruitment at Gorgona Island (tropical eastern Pacific), where there is a large tidal amplitude (~4.4 m). Every other day during three consecutive months in 1998, we directly measured the magnitude of reef fish recruitment to standardized coral units (SCUs) isolated from natural reefs. A total of 40 species from 21 families settled on the SCUs. Of 11 species with sufficient numbers for meaningful statistical analyses, two (Lutjanus guttatus and Pomacanthus zonipectus) had lunar recruitment with peaks near the new moon; three combined species of antennariids showed semilunar recruitment with peaks near moon quarters; and eight other species showed sporadic and aperiodic recruitment pulses. The contribution of lunar (moonlight intensity) and tidal factors (tidal amplitude and net tidal flow) to recruitment dynamics varied among species, although it was generally low (<18%) even among species with periodic patterns, except perhaps in L. guttatus. In this species, recruitment magnitude correlated negatively with moonlight intensity, accounting for 34.5% of the variance. Post-settlement predation by roving predators may be one cause of this relationship. In the remaining species, particularly those with sporadic and aperiodic recruitment pulses, stochastically varying weather and oceanographic events may be more important in determining temporal variation in recruitment.

Variability in Recruitment of Coral Reef Fishes: The Importance of Habitat at Two Spatial Scales

We investigated spatial and temporal variability in recruitment of coral reef fishes to ST. Croix, U.S. Virgin Islands, with the goal of assessing the importance of habitat and physical oceanogrpahic processes in determining patterns of distribution at two spatial scales. Recruitment was monitored visually each month, using SCUBA, at sites spaced equally around the island and on transects within each site. Spatial patterns of distribution were consistent within seasons and between years at both spatial scales. Although recruitment showed a seasonal pattern, there were few inter—annual differences at any spatial scale. At the largest scale, recruitment varied significantly among sites around the island, and a unique pattern of distribution was observed. On the windward shore, recruitment ranged from hig on the eastern (upcurrent) end to low on western end of the island. Recruitment showed the opposite pattern on the leeward shore, ranging from low on the eastern end to high on the western end. At the transect scale, certain features of the habitat significantly predicted recruitment density. None of the microhabitat features that prerdicted recruitment at the small scale could explain patterns of recruitment observed at the large scale. In contrast, physical process affecting larval availability or transport were more important than habitat in determining the spatial patterns of recruitment at this scale. Thus, physical oceanographic processes appeared to be responsible for patterns of recruitment to the two shores of St. Croix, and to sites along those shores. Despite consistent patterns of recruitment to sites, habitat selection did not appear to be important at the site scale. Once delivered to a site, however, settlers or new recruits distributed themselves based on habitat preferences.

Variability in recruitment of coral reef fishes

Many benthic marine organisms are characterized by a long-distance dispersal phase; it has been suggested that this factor may control the population dynamics of many species as well as promote variability in assemblage composition and coexistence between competing species. Various components of variability in recruitment of tropical marine fishes to experimental reefs were examined during 1978–1981 in St. Croix, U.S. Virgin Islands. The fishes studied include the beaugregory, Stegastes leucostictus (Muller & Troschel), bridled goby, Coryphopterus glaucofraenum Gill, goldspot goby, Gnatholepis thompsoni Jordan, French grunt, Haemulon flavolineatum (Desmarest), and ocean surgeonfish, Acanthurus bahianus Castelnau. Variability in settlement on replicate reefs was a species-specific phenomenon that appeared to be correlated with social behavior. Schooling species (French grunt, ocean surgeonfish) showed clumped, highly variable recruitment that presumably resulted from aggregative settlement. Non-schooling species showed random, less variable recruitment patterns. The temporal component of recruitment variability was very large; not only were there strong seasonal fluctuations in abundances of recruits, but abundances varied from year to year by factors of 2 to 10. The spatial component of variability, measured here on the scale of 1 km, appeared to be very low and was unlikely to contribute significantly to differences in fish assemblages.

Recruitment of Coral Reef Fishes: Effects of Distribution of Predators and Shelter

Factors affecting recruitment and early survivorship of juvenile coral reef fishes were studied on St. Croix, United States Virgin Islands. The faunal assemblage studied included diurnally active fishes found in the rubble/sand habitat. The most abundant members were: beaugregory (Stegastes leucostictus), foureye butterfish (Chaetodon capistratus), mahongany snapper (Lutjanus mahogoni), surgeonfishes (Acanthurus bahianus and A. chirurgus) and French grunt (Haemulon flavolineatum). During the period 1978—1981, set of experimental reefs constructed from Strombus gigas shells were built in various locations relative to a major reef. Recruitment of juveniles of almost all species in the rubble/sand fish assemblage occurred more heavily on reefs that were built 20—40 m away from the main reef (into the lagoon) than on those built at the edge of the backreef. A series of experiments revealed that this is probably due to two factors: differences in available shelter and differences in encounter rates with predators. Seagrass and algae, which provide shelter to very small juvenile fishes, are absent in a "halo" zone close to the reef due to the feeding activities of reef—associated grazers (fishes and urchins). Experiments with artificially produced halos and artificial seagrass and algae showed that part of the explanation for the observed spatial pattern of fish recruitment is the spatial pattern of the shelter provided by seagrass and algae. Experiments in which potential prey fish were tethered demonstrated that the risk of predation for small juvenile fishes was considerably higher close to the reef than it was 20 m away. The results of these experiments suggest that patterns of settlement and juvenile survivorship of coral reef fishes are affected by complex interactions with other reef organisms (in this case, he activities of reef—associated grazers that modify available shelter) and by the frequency of encounters with predators. If they survive, all of the juveniles, regardless of where they initially settle, eventually migrate to a nearby reef. The species studies here differed in the degree to which juveniles use the sea—grass/algal habitat as a refuge from predation; these differences suggest that spatial patterns of recruitment, interacting with predation, may influence both population abundances and species composition of older juveniles on the reef.

Seasonality and recruitment of coral reef fishes

Information is given on the times of recruitment of 54 species of coral reef fishes which inhabit the lagoon at One Tree Island, Great Barrier Reef. The information is based on observations of juvenile settlement over nearly 3 years. Most of the fishes have fairly long breeding seasons and reproduction occurs mainly during the summer months from about September to May. Recruitment of juveniles reaches a peak in January-February when temperatures are highest. This also corresponds with the period of greatest primary production and it is suggested that breeding cycles may be timed to ensure that larval metamorphosis and settlement of juveniles occur at the time of year most favourable for growth. Although strongly seasonal, recruitment patterns show little year to year constancy and it is likely that prevailing weather conditions have a significant influence on recruitment success.