Comparative predation rates on larval snappers (Lutjanidae) in oceanic, reef, and nearshore waters

The life cycle of most reef fishes involves pelagic larvae entering the nearshore environment to settle to benthic substrates. Settlement is considered to be highly risky as larvae encounter high rates of predation mortality associated with shallow nearshore habitats. This potential bottleneck may be particularly significant for many tropical snapper (Lutjanidae) species which bypass the reef to settle to very nearshore seagrass areas. To test the hypothesis that predation-related mortality increases as naïve late-stage fish larvae leave the offshore oceanic environment and enter the nearshore to settle, relative nocturnal predation rates on tethered late-stage snapper larvae were measured in oceanic, coral reef, and nearshore surface waters of the lower Florida Keys, USA. Both relative predation rate and probability of predation in oceanic areas seaward of the reef was significantly greater than over reef or nearshore seagrass/hardbottom habitats. This surprising result may be due to differences in the density or spatial distribution of potential predators between deep offshore (near flotsam at the surface) and shallow nearshore environments (demersal). These findings suggest that successful late-stage snapper larvae should avoid surface waters in deep oceanic areas and move upward in the water column as they pass over the reef and other shallow nearshore environments prior to settlement.     

BIODIVERSITY OF PLANKTONIC DINOFLAGELLATE SPECIES IN MANGROVE PONDS,PELICAN CAYS,BELIZE

Information on the population structure of planktonic dinoflagellates is reported in the coral reef‐mangrove ecosystem at Pelican Cays, Belize. Six sites examined included: Cat Cay, Douglas Cay, Elbow Cay, Fisherman's Cay, Lagoon Cay and Manatee Cay. A spectacular and rich dinoflagellate taxa including oceanic, coastal and offshore species are illustrated. The presence of oceanic species in the studied cays is an unexpected observation since dinolfagellate assemblages are virtually enclosed within ponds bordered by coral ridges that limits water exchange with the open ocean except during storm events. I am also reporting significant differences in the dinoflagellate associations among the studied cays. Dominant taxa included 16 Proroperidinium species, 11 Gonyaulax species, and ten Ceratium species. Only six planktonic species were harmful. Bloom forming species included Ceratium furca and Gonyaulax polygramma. A much more diverse authotrophic and heterotrophic dinoflagellate population characterizes the Pelican Cays than previously suspected. Some species are reported the first time: Protoperidinium belizeanum sp. nov., P. pyrum Balech, P. steidingerae Balech, P. depressum (Bailey) Balech, and P. divergens (Ehrenberg) Balech. These results demonstrate that the Belizean coral reef‐mangrove ecosystem is a delicate and species‐rich environment, and as such, should be protected and preserved.     

Potential for adaptation to climate change in a coral reef fish

Predicting the impacts of climate change requires knowledge of the potential to adapt to rising temperatures, which is unknown for most species. Adaptive potential may be especially important in tropical species that have narrow thermal ranges and live close to their thermal optimum. We used the animal model to estimate heritability, genotype by environment interactions and nongenetic maternal components of phenotypic variation in fitness‐related traits in the coral reef damselfish, Acanthochromis polyacanthus. Offspring of wild‐caught breeding pairs were reared for two generations at current‐day and two elevated temperature treatments (+1.5 and +3.0 °C) consistent with climate change projections. Length, weight, body condition and metabolic traits (resting and maximum metabolic rate and net aerobic scope) were measured at four stages of juvenile development. Additive genetic variation was low for length and weight at 0 and 15 days posthatching (dph), but increased significantly at 30 dph. By contrast, nongenetic maternal effects on length, weight and body condition were high at 0 and 15 dph and became weaker at 30 dph. Metabolic traits, including net aerobic scope, exhibited high heritability at 90 dph. Furthermore, significant genotype x environment interactions indicated potential for adaptation of maximum metabolic rate and net aerobic scope at higher temperatures. Net aerobic scope was negatively correlated with weight, indicating that any adaptation of metabolic traits at higher temperatures could be accompanied by a reduction in body size. Finally, estimated breeding values for metabolic traits in F2 offspring were significantly affected by the parental rearing environment. Breeding values at higher temperatures were highest for transgenerationally acclimated fish, suggesting a possible role for epigenetic mechanisms in adaptive responses of metabolic traits. These results indicate a high potential for adaptation of aerobic scope to higher temperatures, which could enable reef fish populations to maintain their performance as ocean temperatures rise.     

Successful sexual reproduction of the scleractinian coral Porites panamensis: Evidence of planktonic larvae and recruitment

Porites panamensis is a hermatypic brooder coral endemic to, and distributed along, the Eastern Tropical Pacific, and is considered a species vulnerable to local effects because it has limited capacity for long‐distance dispersal (and low genetic diversity). Although larvae of P. panamensis have been previously shown to recruit to artificial settlement platforms, they have never been observed in the water column. The present study describes the reproductive behavior of P. panamensis, with a focus on using molecular tools to document evidence for a larval planktonic stage and for successful recruitment. Larvae collected from the water column, and recruitment on natural and artificial substrata were documented. Phylogenetic analysis of two ribosomal markers, 18s rRNA and ITS (ITS1‐5.8‐ITS2), and one mitochondrial marker, cytochrome oxidase subunit 1 (cox1), confirmed the taxonomic identity of larvae, and showed that larvae and recruits have genotypes similar to adults of P. panamensis. Lipid vacuoles and Symbiodinium sp. were present in the gastrodermis of all larvae. A total of 12 and 371 recruits settled on artificial and natural substrates, respectively, and the recruitment rate differed significantly over time. By documenting the reproductive success of the species, we show the potential for existing individuals both to maintain the population in the study area and to contribute to maintenance of the coral reef community in the coming decades.     

Reef waters stimulate substratum exploration in planulae from brooding Caribbean corals

This study tested the hypothesis that waters surrounding reefs with healthy coral populations are more likely than degraded sites to induce planulae to navigate downward and begin benthic probing. In the laboratory, larvae from two brooding Caribbean coral species, Agaricia tenuifolia and Porites astreoides, were introduced to seawater collected at (1) 1 m above shallow, healthy reef with high-coral cover, (2) 1 m above shallow, degraded reef with high-macroalgal cover, and (3) ~400 m ocean-ward of the reef in deep, blue water. Counter to the hypothesis, water from both the healthy and degraded reef caused the larvae to swim downward and begin benthic probing. These results suggest that substances carried in reef waters may contribute to macro-scale habitat selection by planulae and that understanding how these waterborne cues mesh with other stimuli used by planulae to select a settlement site may be valuable for deciphering a site’s recruitment potential for corals.     

Allometric growth and functional development of the gut in developing cod Gadus morhua L. larvae

The development of the gut epithelium in cod Gadus morhua was studied during the larval period in intensive rearing systems. Cod larvae were fed enriched rotifers from mouth opening. On 17 days post‐hatch (dph) one group of larvae were fed Artemia sp. nauplii while another group were fed both rotifers and a formulated diet (co‐fed). At the end of the experiment (30 dph) larvae receiving live feed were almost three times larger than the co‐fed larvae, although no clear signs of pathological effects due to feeding regime were found in any larvae sampled for morphological studies. The midgut volume in larvae fed live feed increased by a factor of 38 during the experiment, and in particular volume increased rapidly between 24 and 30 dph. The enterocyte size increased between 12 and 24 dph from 652 ± 64 to 1479 ± 144 μm³ (mean ±s .e .). When enterocytes reached their maximum size, several morphological changes in the gut epithelium were initiated, such as increased number of mitochondria per enterocyte, increased size of the nuclei and a considerable increase in microvilli surface area. The mitochondrial membrane structures changed during the experiment, suggesting a maturation process of the mitochondria. The midgut development was strongly related to larval size rather than age. On 30 dph co‐fed larvae were equal in size to Artemia sp. fed larvae on 24 dph. This was reflected by equal values of estimated midgut volume, midgut length and total number of enterocytes and the number of mitochondria per enterocyte. The microvilli surface area, however, was significantly larger in co‐fed larvae on 24 dph compared to live‐feed larvae on 30 dph. This increase in absorptive surface was probably a response to suboptimal feeding conditions. The strong correlation between gut development and larval size and the lack of clear pathological effects, suggested that the gut tissue is flexible and can withstand periods of suboptimal nutrition at this stage.     

Differential survival of nursery‐reared Acropora cervicornis outplants along the Florida reef tract

In recent decades, the Florida reef tract has lost over 95% of its coral cover. Although isolated coral assemblages persist, coral restoration programs are attempting to recover local coral populations. Listed as threatened under the Endangered Species Act, Acropora cervicornis is the most widely targeted coral species for restoration in Florida. Yet strategies are still maturing to enhance the survival of nursery‐reared outplants of A. cervicornis colonies on natural reefs. This study examined the survival of 22,634 A. cervicornis colonies raised in nurseries along the Florida reef tract and outplanted to six reef habitats in seven geographical subregions between 2012 and 2018. A Cox proportional hazards regression was used within a Bayesian framework to examine the effects of seven variables: (1) coral‐colony size at outplanting, (2) coral‐colony attachment method, (3) genotypic diversity of outplanted A. cervicornis clusters, (4) reef habitat, (5) geographical subregion, (6) latitude, and (7) the year of monitoring. The best models included coral‐colony size at outplanting, reef habitat, geographical subregion, and the year of monitoring. Survival was highest when colonies were larger than 15 cm (total linear extension), when outplanted to back‐reef and fore‐reef habitats, and when outplanted in Biscayne Bay and Broward–Miami subregions, in the higher latitudes of the Florida reef tract. This study points to several variables that influence the survival of outplanted A. cervicornis colonies and highlights a need to refine restoration strategies to help restore their population along the Florida reef tract.     

A finite interval of initial swimbladder inflation in Latris lineata revealed by sequential removal of water‐surface films

A finite interval of initial swimbladder inflation in striped trumpeter Latris lineata larvae occurred over 4 days at 16° C. Water‐surface films were removed on different days to form treatments: 4, 8, 9, 10, 11 and 12 days post hatching, dph (day 4, 8, 9, 10, 11 and 12 treatments, respectively). No swimbladder inflation was recorded prior to water‐surface film removal. When the water‐surface films were removed in day 4 and 8 treatments, initial swimbladder inflation was first recorded in larvae 9 dph at mean ± s .e . 35·0 ± 5·4%(n = 4) and 45·0 ± 7·9%, respectively. Water‐surface film removal at days 9, 10 and 11, resulted in initial swimbladder inflation the following day at 62·5 ± 2·5, 62·5 ± 7·2 and 11·3 ± 5·5% in larvae 10, 11 and 12 dph, respectively. No swimbladder inflation was recorded following water‐surface film removal on day 12. There was no significant difference in initial inflation among larvae in day 4, 8, 9 and 10 treatments, ranging from 65·0 ± 4·1 to 73·8 ± 6·9%(P > 0·05). Initial inflation was significantly lower in the day 11 treatment (11·3 ± 5·5%)(P < 0·05). During the inflation interval (9–12 dph) swimbladders displayed one of three morphologies; liquid dilation, gas inflated and collapsed. Collapse of the swimbladder lumen was first apparent in larvae without swimbladder inflation from 11 dph and progressively developed thereafter in all larvae with non‐inflated swimbladders. Larvae >6·1 mm standard length lost the ability to undergo initial swimbladder inflation. This study demonstrates that the interval for initial swimbladder inflation in striped trumpeter is short, finite and related to larval size. The end of the inflation interval was marked by onset of abnormal swimbladder morphologies, but not to closure of the pneumatic duct.     

Revisiting the connectivity puzzle of the common coral Pocillopora damicornis

Understanding levels of connectivity among scleractinian coral populations over a range of temporal and spatial scales is vital for managing tropical coral reef ecosystems. Here, we use multilocus microsatellite genotypes to assess the spatial genetic structure of two molecular operational taxonomic units (MOTUs, types α and β) of the widespread coral Pocillopora damicornis on the Great Barrier Reef (GBR) and infer the extent of connectivity on spatial scales spanning from local habitat types to latitudinal sectors of the GBR. We found high genetic similarities over large spatial scales spanning > 1000 km from the northern to the southern GBR, but also strong genetic differentiation at local scales in both MOTUs. The presence of a considerable number of first‐generation migrants within the populations sampled (12% and 27% for types α and β, respectively) suggests that genetic differentiation over small spatial scales is probably a consequence of stochastic recruitment from different genetic pools into recently opened up spaces on the reef, for example, following major disturbance events. We explain high genetic similarity among populations over hundreds of kilometres by long competency periods of brooded zooxanthellate larvae and multiple larval release events each year, combined with strong longshore currents typical along the GBR. The lack of genetic evidence for predominantly clonal reproduction in adult populations of P. damicornis, which broods predominantly asexually produced larvae, further undermines the paradigm that brooded larvae settle close to parent colonies shortly after the release.     

Habitat selection by recruits establishes local patterns of adult distribution in two species of damselfishes: Stegastes dorsopunicans and S. planifrons

Local patterns of adult distribution in organisms that disperse young as pelagic larvae can be determined at the time of recruitment through habitat selection or, shortly thereafter, through post-recruitment processes such as differential juvenile survivorship and interspecific competition. This study addresses the importance of habitat selection by recruits in establishing the local pattern of adult distribution in two sympatric Caribbean damselfish species, Stegastes dorsopunicans and S. planifrons. Both species inhabit shallow reefs but show little overlap in their distribution; S. dorsopunicans predominates in the reef crest and S. planifrons occurs primarily on the reef slope. Furthermore, S. dorsopunicans is associated with rocky substrate, while S. planifrons occupies live coral. The substrate cover follows a similar pattern with coral being much less common on the reef crest than on the reef slope. Monitoring recruitment every other day in reciprocal removal experiments and artificial reefs indicates that the observed pattern of local adult distribution is a product of habitat selection for both species. The presence or absence of conspecifics did not influence recruitment patterns for either species. Stegastes dorsopunicans recruited primarily to shallow, rocky areas, appearing to cue on both substratum type and depth. Stegastes planifrons recruited exclusively to coral substratum independent of depth. These results indicate that local adult patterns of distribution can be explained by habitat selection at recruitment, and that substrate type and depth may be important cues. Received: 27 May 1997 / Accepted: 4 January 1998     

Nutrient cycling in early coral life stages: Pocillopora damicornis larvae provide their algal symbiont (Symbiodinium) with nitrogen acquired from bacterial associates

The waters surrounding coral reef ecosystems are generally poor in nutrients, yet their levels of primary production are comparable with those reported from tropical rain forests. One explanation of this paradox is the efficient cycling of nutrients between the coral host, its endosymbiotic alga Symbiodinium and a wide array of microorganisms. Despite their importance for the animals' fitness, the cycling of nutrients in early coral life stages and the initial establishment of partnerships with the microbes involved in these processes has received little scrutiny to date. Nitrogen is an essential but limited nutrient in coral reef ecosystems. In order to assess the early nutrient exchange between bacteria and corals, coral larvae of the species Pocillopora damicornis were incubated with two coral‐associated bacteria (Alteromonas sp., or Vibrio alginolyticus), prelabeled with the stable nitrogen isotope ¹⁵N. The incorporation and translocation of nitrogen from Vibrio‐ and Alteromonas bacteria into P. damicornis coral larvae and specifically into the coral‐symbiotic Symbiodinium were detected by nanoscale secondary ion mass spectrometry (NanoSIMS). A significant increase in the amount of enriched ¹⁵N (two to threefold compared to natural abundance) was observed in P. damicornis larvae within 8 h of incubation for both bacterial treatments (one‐way ANOVA, F_5,53 = 18.03, P = 0.004 for Alteromonas sp. and F_5,53 = 18.03, P = 0.0001 for V. alginolyticus). These findings reveal that coral larvae acquire nutrients previously taken up from the environment by bacteria. The additional nitrogen may increase the survival rate and fitness of the developing coral and therefore contribute to the successful maintenance of coral reefs.     

Seasonal recruitment,habitat associations and survival of pomacentrid reef fish in the US Virgin Islands

Patterns of distribution and abundance of coral reef fish depend in part on recruitment of a pelagic larval stage, on subsequent dispersal among habitats, and survival of new recruits. We studied recruitment of five species of Stegastes and two species of Chromis damselfish onto reef habitats of St. Thomas, USVI during one year. The two study sites, Flat Cay and Outer Brass Island, were on the southern and northern sides of St. Thomas, respectively. At both sites, recruitment occurred largely in the summer months, although one species (Stegastes planifrons) showed significant winter recruitment at Flat Cay. The onset of increased summer recruitment in 1992 of other species occurred several weeks later and was shorter in duration at Outer Brass Island than at Flat Cay, perhaps indicating differences in oceanographic conditions (currents etc.) or spawning cycles between sites. The two Chromis species showed lunar periodicity of settlement at Flat Cay. At Flat Cay, recruits of three species (S. leucostictus, S. diencaeus and S. planifrons) were associated with conspecifics possibly due to preferential settlement. Similarly, new recruits were more often found near live coral than coral rubble, and very few occurred on sand habitat. Substratum complexity was a poor predictor of recruitment within a habitat, although larger juveniles of some species were more common on more complex substrate. Contrary to other studies, there were no apparent depth preferences among recruits, although larger juveniles of two Stegastes species were found more often in deeper water. It appears that within habitats, newly arriving larvae may be attracted first to the presence of conspecifics and secondarily take up position adjacent to live coral. Apparent survivorship of some Stegastes species and one Chromis species was higher at Outer Brass Island than at Flat Cay, and may partly compensate for lower recruitment of some species at Outer Brass Island.     

Recruitment and larval connectivity of a remnant Acropora community in the Arabian Gulf,United Arab Emirates

Coral cover and community structure in the Arabian Gulf have changed considerably in recent decades. Recurrent bleaching events have dramatically reduced the abundance of previously dominant Acropora corals and have given space to other more thermally resistant coral taxa. The loss of Acropora spp. has reduced reef structural complexity and associated biodiversity. Sir Bu Nair Island (SBN) is a nature reserve in the United Arab Emirates that sustains some of the last dense and extensive Acropora stands in the southern Gulf. This study investigated coral recruitment at a southern coral reef on SBN and examined larval dispersal and reef connectivity between SBN and other local and regional reefs through an agent-based model coupled with a 3D hydrodynamic model. Recruitment was surveyed with settlement tiles deployed from April to September 2019. Contrary to other reefs in the Gulf, we found that Acropora is indeed the major coral recruiter settling at SBN reefs, followed by Porites. The models indicate that SBN reefs are mostly self-seeding but also connected to other reefs in the Gulf. SBN can supply coral larvae to the neighbouring islands Siri and Abu Musa, and nearby reefs along with the north-eastern Emirates, Iranian coast and Strait of Hormuz. Findings highlight the importance of SBN to protect remnant populations of the locally almost extinct Acropora in a region where natural coral recovery is increasingly sparse.

     

Larval ontogeny and morphology of giant trahira Hoplias lacerdae

In the present study, the morphology and behaviour of giant trahira Hoplias lacerdae larvae were investigated, from hatching to complete absorption of the yolk sac, under laboratory conditions. In the first day post‐hatching (dph), the larvae presented a big ovoid‐shaped yolk sac that underwent regression during larval ontogeny. The mouth opened 3 dph, when the pectoral fins were evident. From this day, the larvae were able to perform sudden bursts of activity and appear to be able to swim a few centimetres before sinking again. The branchial apparatus was defined at 5 dph, and by 6 dph the operculum was formed. The internal organs such as intestine, liver, kidney and external sensorial structures were present at 7 dph. The yolk sac remained until 7 dph.     

Post-larval French grunts (Haemulon flavolineatum) distinguish between seagrass, mangrove and coral reef water: Implications for recognition of potential nursery habitats

Environmental cues like sound, magnetic field, oceanic currents, water chemistry or habitat structure are believed to play an important role in the orientation of reef fish towards their settlement habitat. Some species of coral reef fish are known to use seagrass beds and mangroves as juvenile habitats. Once oceanic larvae of these fish have located a coral reef from the open ocean, they still have to find embayments or lagoons harbouring these juvenile habitats. The sensory mechanisms that are used for this are still unknown. In the present study, experiments were conducted to investigate if recruits of the French grunt (Haemulon flavolineatum) respond to habitat differences in water type, as mangrove/seagrass water may differ in biotic and abiotic compounds from coral reef water. Our results show that post-larvae of a reef fish that is highly associated with mangroves and seagrass beds during its juvenile life stage, choose significantly more often for water from mangroves and seagrass beds than for water from the coral reef. These results provide a more detailed insight in the mechanisms that play a role in the detection of these juvenile habitats.     

Effects of monsoon-driven wave action on coral reefs of Guam and implications for coral recruitment

Benthic cyanobacteria can respond rapidly to favorable environmental conditions, overgrow a variety of reef organisms, and dominate benthic marine communities; however, little is known about the dynamics and consequences of such cyanobacterial blooms in coral reef ecosystems. In this study, the benthic community was quantified at the time of coral spawnings in Guam to assess the substrate that coral larvae would encounter when attempting settlement. Transects at 9, 18, and 25-m depths were surveyed at two reef sites before and after heavy wave action driven by westerly monsoon winds. Communities differed significantly between sites and depths, but major changes in benthic community structure were associated with wave action driven by monsoon winds. A shift from cyanobacteria to crustose coralline algae (CCA) accounted for 44% of this change. Coral recruitment on Guam may be limited by substrate availability if cyanobacteria cover large areas of the reef at the time of settlement, and consequently recruitment may in part depend upon wave action from annual monsoon winds and tropical storms which remove cyanobacteria, thereby exposing underlying CCA and other substrate suitable for coral settlement.     

Using Agent-Based Models to Aid Reef Restoration: Enhancing Coral Cover and Topographic Complexity through the Spatial Arrangement of Coral Transplants

High coral cover and topographic complexity are favorable qualities of a healthy coral reef. Because coral reef restoration is expensive and coral growth is naturally slow, there is a need to strategically arrange coral transplants to maximize coral cover and topographic complexity. Similarly, it is important to understand how differences in the life history characteristics of coral transplants can influence changes in the structural attributes of coral reefs. This study utilizes agent‐based computer modeling to explore the different spatial scenarios of coral transplantation using corals with contrasting r‐ and K‐selected life histories. Spatial indexes are used to compare coral cover and topographic complexity at incremental time scales, within which disturbance events are of minor importance in spatial structuring. The outcomes of the model suggest that even‐spaced grided transplanting arrangements provide the fastest increase in coral cover and three‐dimensional habitat space (topographic complexity) across large temporal scales (<30 years) for corals with r‐selected life history strategies.     

Ontogeny of body density and the swimbladder in yellowtail kingfish Seriola lalandi larvae

The ontogeny of larval body density and the morphological and histological events during swimbladder development were investigated in two cohorts of yellowtail kingfish Seriola lalandi larvae to understand the relationship between larval morphology and body density. Larvae <3 days post hatch (dph) were positively buoyant with a mean ± s.d . body density of 1·023 ± 0·001 g cm^?3. Histological evidence demonstrated that S. lalandi larvae are initially transient physostomes with the primordial swimbladder derived from the evagination of the gut ventral to the notochord and seen at 2 dph. A pneumatic duct connected the swimbladder to the oesophagus, but degenerated after 5 dph. Initial swimbladder (SB) inflation occurred on 3 dph, and the inflation window was 3–5 dph when the pneumatic duct was still connected to the gut. The swimbladder volume increased with larval age and the epithelial lining on the swimbladder became flattened squamous cells after initial inflation. Seriola lalandi developed into a physoclist with the formation of the rete mirabile and the gas‐secreting gland comprised low‐columnar epithelial cells. Larvae with successfully inflated swimbladders remained positively buoyant, whereas larvae without SB inflation became negatively buoyant and their body density gradually reached 1·030 ± 0·001 g cm^?3 by 10 dph. Diel density changes were observed after 5 dph, owing to day time deflation and night‐time inflation of the swimbladder. These results show that SB inflation has a direct effect on body density in larval S. lalandi and environmental factors should be further investigated to enhance the rate of SB inflation to prevent the sinking death syndrome in the early life stage of the fish larvae.