Coral reef restoration in the Eastern Tropical Pacific: feasibility of the coral nursery approach

Due to the worldwide degradation of coral reefs, the active restoration of these ecosystems has received considerable attention in recent decades. This study investigated (1) the feasibility of using coral nurseries for restoration projects, (2) the minimum size required for a Pocillopora damicornis (Pocilloporidae) coral fragment to survive and grow in a nursery, and (3) the optimal transplant size of a fragment when transplanted to a degraded reef at Gorgona Island (Colombian Pacific). For this investigation, 230 fragments were transplanted directly to El Remanso reef, and another 150 fragments were maintained in in situ nurseries. Every 2 months, the length, weight, and survival of the fragments were recorded. After growing for 134 days in the nurseries, the 52 surviving fragments were transplanted to El Remanso reef, and after 5 months, the same variables were measured. Among the nursery‐reared fragments, the largest (4 to <8 cm) had the highest survival and growth rates, whereas among the directly transplanted fragments, the smallest fragments (<2 cm) had the highest survival and growth rates. However, the nursery‐reared fragments acquired greater structural complexity (arborescent morphology), and they were all alive 156 days after transplantation and presented a maximum linear growth rate of over 2 cm, which was higher than that of the directly transplanted fragments. Apparently, the arborescent morphology acquired during the nursery period provides advantages to the colonies that favor greater success when transplanted. Therefore, nursery‐reared fragments of P. damicornis between 2 and 4 cm are the most appropriate for use in restoration projects.     

Successful methods for transplanting fragments of Acropora formosa and Acropora hyacinthus

In order to establish a successful method for the transplantation of branching and tabular coral fragments, we tested the effects of orientations of attachment, seasons of transplantation, and size of fragments on survival, growth, and spawning using Acropora formosa and A. hyacinthus. Vertically attached, large-sized fragments of A. formosa showed 98–100% survival rate after 18 months. The fragments transplanted in August exhibited better survival than those transplanted in November. The larger fragments had the higher percentage of spawning. The fragments that spawned had lower growth rate, while those resorbed the oocytes carried at the time of transplantation showed higher growth rate, suggesting the trade-off between growth and reproduction. Half of the fragments spawned 1 month earlier than the donor colonies. Only the vertically attached fragments of A. hyacinthus fused to the substratum, and those transplanted in February showed 100% survival rate after 14 months, indicating that this species is well suited for transplantation.     

Biological parameters and current status of European eel (Anguilla anguilla Linnaeus, 1758) from Asi River,Northeastern Mediterranean region,Turkey

The biological characteristics of eels from the Asi River, Turkey, were assessed between December 2017 and November 2018. Eels were sampled monthly using fyke nets (operated by professional fishermen), yielding a total of 509 specimens. Total length and weight were measured, sex, age and maturity stages (silver or yellow eel) were determined. Catch Per Unit Effort (CPUE) was calculated for both biomass per unit effort and numbers caught on a monthly and annual basis. The length-weight relationships (LWRs) of silver and yellow eel was W = 0.009*TL^3.22 (n = 262) and W = 0.0106*L^3.09 (n = 247), respectively. The age of the sampled fish ranged from year class II to VI. Von Bertalanffy growth parameters were estimated as L_∞=69.25 cm, K = 0.43 1/year, t₀= −0.41 and phi prime index ( ǿ )= 3.31 for all samples. The overall eel fishing mortality rate (F) was 0.31 year^-1, and the exploitation and survival rates of silver stage eels were estimated with 30% and 39%, respectively.     

Length-weight relationships of four fish species from the Yalong River,China

Parameters of the length-weight relationship (LWR) were estimated for four fish species [Beaufortia szechuanensis (Fang, 1930), Claea dabryi (Sauvage, 1874), Percocypris pingi (Tchang, 1930), and Yunnanilus sichuanensis Ding, 1995] from the Yalong River. Samples were collected seasonally from June 2018 to July 2019, using various fishing gears [set nets (mesh: 1.5 × 2.0 cm), hook, drift gill nets (three mesh sizes: 1.0; 2.0; 3.0 cm) and electro fishing]. Two new maximum standard length were recorded for C. dabryi and P. pingi.     

Length–weight relationships of four fish species from the Nujiang River,China

Length–weight relationships (LWRs) were determined for four fish species (Akrokolioplax bicornis [Wu, 1977], Barbodes wynaadensis [Day, 1873], Glyptothorax cavia [Hamilton, 1822] and Placocheilus cryptonemus [Cui & Li, 1984]) from the Nujiang River, China. Samples were collected from March 2008 to August 2016 (frequency of sampling during the study period: once per year), using various fishing gears (set nets [mesh: 1.5 cm × 2.0 cm], fish cages [0.5 cm mesh], hook, drift gill nets [mesh: 1.0 cm × 2.0 cm × 3.0 cm] and electro fishing). Two new maximum SL were recorded for B. wynaadensis and P. cryptonemus.     

Length‐weight relationships of four fish species from the Yellow River,China

Length‐weight relationships (LWRs) were estimated for four fish species [Schizopygopsis anteroventris Wu & Tsao, 1989, Schizothorax lissolabiatus Tsao, 1964, Triplophysa markehenensis (Zhu & Wu, 1981) and Triplophysa siluroides (Herzenstein, 1888)] from the Yellow River. Samples were collected seasonally from August 2016 to October 2017, using various fishing gears [set nets (mesh: 1.5 cm × 2.0 cm), hook, drift gill nets (mesh: 1.0 cm × 2.0 cm × 3.0 cm) and electro fishing]. Four new maximum standard length were recorded for S. anteroventris, S. lissolabiatus, T. markehenensis and T. siluroides.     

The Yellow Gorgonian Eunicella cavolini: Demography and Disturbance Levels across the Mediterranean Sea

The yellow octocoral Eunicella cavolini is one of the most common gorgonians thriving in Mediterranean hard-bottom communities. However, information regarding its distribution and ecology in several parts of the Mediterranean is lacking, while population trends and conservation status remain largely unknown. We investigated 19 populations of E. cavolini over three representative geographic regions: the NW Mediterranean, CE Adriatic, and N Aegean. Focusing on the upper bathymetric range of the species (<40 m), data were collected on the populations’ upper depth limit, density, colony height, and extent of injury. A three-level hierarchical sampling design was applied to assess the existence of spatial patterns, using: a) regions (located thousands of km apart), b) localities within regions (tens to hundreds of km apart), and c) sites within localities (hundreds of m to a few km apart). In the NW Mediterranean and CE Adriatic, the upper distribution limit was at depths ≤15 m, whereas in the N Aegean most populations were found deeper than 30 m. Population density ranged between 4.46-62 colonies per m², while mean colony height was 15.6±8.9 SD cm with a maximum of 62 cm. The NW Mediterranean sites were characterized by dense populations dominated by small colonies (<20 cm), periodic recruitment, and low proportion of large gorgonians (>30 cm). The CE Adriatic displayed intermediate densities, with well-structured populations, and continuous recruitment. In the N Aegean, most populations presented low densities, high proportion of large colonies, but low number of small colonies, signifying limited recruitment. Disturbance levels, as a function of extent and type of injury, are discussed in relation to past or present human-induced threats. This work represents geographically the most wide ranging demographic study of a Mediterranean octocoral to date. The quantitative information obtained provides a basis for future monitoring at a Mediterranean scale.     

Length-weight relationships of four fish species from the Hei River in northwest China

Length-weight relationships (LWRs) were assessed from four fish species in Hei River in northwest China. All specimens were collected using (fishing1 km along the river and 3 meters along the river bank) and netting (gill nets, nets: 30 × 1.2 m; mesh size: 3 × 3 cm) and shrimp cages (nets: 20.0 × 0.5 × 0.4m; mesh size: 0.5 cm) seasonally from April 2019 to October 2020. The gill nets and shrimp cages were soaked in water in the afternoon and pulled in around 10 a.m. the next day after an overnight stay. These specimens were measured for total length (L, 0.1 cm) and body weight (W, 0.1 g) while the specimens were fresh. The parameters for the LWRs were estimated with the basic statistical analyses. The study provided the new maximum total length for Gymnocypris chilianensis (21.0 cm) and Triplophysa tenuis (17.0 cm).     

Length–weight and length–length relationships of four native fish species of the Qinghai‐Tibet Plateau,China

This study presents the length–weight (LWR) and length–length relationships (LLR) of four fish species (Gymnocypris namensis Wu & Ren, 1982; Herzensteinia microcephalus Herzenstein, 1891; Triplophysa stenura Herzenstein, 1888; and Triplophysa brevicauda Herzenstein, 1888) collected from the Qinghai‐Tibet Plateau, China. A total of 291 specimens was collected using electric fishing (12V), gill nets (mesh size: 2 × 2 cm, 3 × 3 cm) and cast nets (mesh size: 2 × 2 cm), in July 1998 and October 2014.     

Red Coral Fishery at the Costa Brava (NW Mediterranean): Case Study of an Overharvested Precious Coral

Abstract The Mediterranean red coral (Corallium rubrum, L. 1758) is a slow-growing longevous gorgonian that produces a red calcium carbonate skeleton, which is in high demand by the jewellery industry. Its long history of intensive commercial harvesting has resulted in a well-documented decline of its stocks throughout the Mediterranean, becoming especially apparent during the last two decades. Based on the extensive ecological data from the Costa Brava (NE Spain) stocks, this study reviews, for the first time, socioeconomic aspects and the impact of current fishing practices on the red coral population structure and reproductive biology. A comparison of the intensively harvested populations in shallow water with that of the infrequently harvested ones in deep water, along with a population in a marine reserve as well, reveals that 98% of all shallow water colonies show a juvenile size and branching pattern as a result of harvesting. Recent data on the reproductive biology of the species show that 91% of the colonies in shallow water populations (<60 m depth) are not 100% sexually mature. These populations are clearly at the limit of their recoverability potential. The maximum sustainable yield (estimated using the Beverton-Holt model) is reached at an age of first capture of 98 years, although the current regulations allow harvesting of approximately 11-year-old colonies (corresponding to a basal diameter of 7 mm). The presented data reveal how this renewable resource is being exploited in a clearly non-sustainable and inefficient way, changing significantly the underwater landscape of the Mediterranean coast. The review of all available data suggests that the shallow water stocks are depleted. Furthermore, recent trends in poaching of juvenile colonies and mass mortality events threaten the survival of the shallow water populations. A ban on reconstituted coral from the market appears to be the only option to control this form of poaching.     

Coral transplantation as an aid to reef rehabilitation: evaluation of a case study in the Maldive Islands

As part of a study of reef rehabilitation, whole coral colonies (primarily Acropora, Pocillopora, Porites, Eavia and Favites) were transplanted and cemented in place onto three approximately 20 m² areas of Armorflex concrete mats on a 0.8–1.5 m deep reef-flat in the Maldives which had been severely degraded by coral mining. Growth, in situ mortality, and losses from mats due to wave action of a total of 530 transplants were monitored over 28 months. Natural recruitment of corals to both the transplanted Armorflex areas and concrete mats without transplants was also studied. Overall survivorship of corals 28 moths after transplantation was 51%. Most losses of transplants due to wave action occurred during the first 7 months when 25% were lost, with only a further 5% of colonies being lost subsequently. Within 16 months most colonies had accreted naturally to the concretemats. Thirty-two percent of transplants which remained attached died with Acropora hyacinthus and Pocillopora perrucosa having the highest mortality rates (approx. 50% nortality over two years) and Porites lobata and P. lutea the lowest (2.8 and 8.1% mortality respectively over two years). Growth rates were very variable with a quarter to a third of transplants showing negative growth during each inter-survey period. Acropora hyacinthus, A. cytherea and A. divaricata transplants had the highest growth rates (colony mean linear radial extension 4.15–5.81 cm y^-1), followed by Pocillopora verrucosa (mean 2.51 cm y^-1). Faviids and poritids had lowest growth rates. Favia and Favites showed the poorest response to transplantation whilst Acropora divaricata, which combined a high growth rate with relatively low mortality, appeared particularly amenable to transplantation. Natural recruitment did not differ significantly between concrete mats with and without transplanted corals. Visible recruits wer first recorded 10 months after emplacement of the mats and were predominantly Acropora and Pocillopora. On near vertical surfaces their density was almost 18 m^-2. Recruits grew fast producing many 20–30 cm diameter colonies on the mats within 3.5 years. Growth and survival of transplants are compared with results of transplantation studies in other locations. We conclude: (1) species transplanted should be selected with care as certain species are significantly more amenable than others to transplantation, (2) the choice of whether fragments or whole colonies are transplanted may profoundly influence survival, (3) considerable loss of transplants is likely from higher energy sites whatever method of attachment, (4) transplantation should, in general, be undertaken only if recovery following natural recruitment is unlikely.     

Enhanced ultraviolet radiation can terminate sexual reproduction in the broadcasting coral species Acropora cervicornis Lamarck

The effects of enhanced ultraviolet radiation (280-400 nm: UVR) on the fecundity of Acropora cervicornis were measured in field-transplanted colonies from 20 m to 1 m depth and vice versa at La Parguera, Puerto Rico. Fecundity was estimated from histological sections made from tissue samples obtained at different time intervals during the experimental period (March - August 2003). All colonies transplanted from 20 m to 1 m showed a 100% reduction in gonads per mesentery per polyp one month after transplantation, while those transplanted from 1 m to 20 m did not show any significant reduction in fecundity throughout the experimental period. The latter colonies did show however, a delay in the spawning times by releasing their gamete bundles approximately two-three weeks after the controls at 1 m and two months after the controls at 20 m suggesting an induced response as a consequence of changes in their daily light cycle due to less radiation (PAR and UVR) available at 20 m compared to 1 m. Control colonies at 20 m spawned after the full moon of June 2003, while the controls at 1 m spawned 5-6 days after the full moon of July 2003. While a possible reabsorption of the gametes occurred in A. cervicornis colonies transplanted from 20 m to 1 m, the expulsion of these gametes due to the sudden stress caused by the transplantation is not discarded. The results suggest that sudden increases in UVR can completely stop sexual reproduction in ramose broadcasting coral species, which in turn can affect the dominance of the species and the composition and structure of shallow reef environments.     

Length–weight relationships of three small fish species caught in the Yarlung Zangbo River basin,China

Length–weight relationships (LWRs) were determined for three small fish species, Glaridoglanis andersonii (Day, 1870), Glyptosternum maculatum (Regan, 1905) and Pseudecheneis sulcatus (Mc‐Clelland, 1842) from the Yarlung Zangbo River basin, China. A total of 285 specimens were collected from the Yarlung Zangbo River in May and October 2017(frequency of sampling during the study period: once per month).The specimens were caught with fishing gear including drifting gillnets (nets: 10 × 1.0 m; mesh size: 3.0 cm) and shrimp cages (nets: 4.0 × 0.5 × 0.4 m; mesh size: 0.5 cm).     

Length‐weight relationships of ten tropical finfish species from north eastern Arabian Sea,India

The length weight relationships (LWRs) of ten tropical finfish species from north eastern Arabian Sea, India were studied. Specimens were caught using a wide range of fishing gear mainly trawl nets (20–25 mm), dol nets or bag nets (20–40 mm) and gill nets (80–270 mm) operated in Maharashtra maritime waters during 2012–2016. The specimens were measured for total length, and weight, then dissected and the sex confirmed. Previously unavailable in FishBase, the detailed LWR of Polydactylus mullani is reported for the first time. Maximum total lengths presented for six species in this study are new records. The existence of a differential growth between male and female was confirmed for five species, which was not known earlier. The LWR data will be useful for deriving future sustainable management and conservation strategies.     

An adaptive management approach to an octocoral fishery based on the Beverton-Holt model

Coral reef species are frequently the focus of bio-prospecting, and when promising bioactive compounds are identified there is often a need for the development of responsible harvesting based on relatively limited data. The Caribbean gorgonian Pseudopterogorgia elisabethae has been harvested in the Bahamas for over a decade. Data on population age structure and growth rates in conjunction with harvest data provide an opportunity to compare fishery practices and outcomes to those suggested by a Beverton-Holt fishery model. The model suggests a minimum colony size limit of 7–9 years of age (21–28 cm height), which would allow each colony 2–4 years of reproduction prior to harvesting. The Beverton-Holt model assumes that colonies at or above the minimum size limit are completely removed. In the P. elisabethae fishery, colonies are partially clipped and can be repeatedly harvested. Linear growth of surviving colonies was up to 3 times that predicted for colonies that were not harvested and biomass increase was up to 9 times greater than that predicted for undisturbed colonies. The survival of harvested colonies and compensatory growth increases yield, and yields at sites that had previously been harvested were generally greater than predicted by the Beverton-Holt model. The model also assumes recruitment is independent of fishing intensity, but lower numbers of young colonies in the fished populations, compared to unfished populations, suggest possible negative effects of the harvest on reproduction. This suggests the need for longer intervals between harvests. Because it can be developed from data that can be collected at a single time, the Beverton-Holt model provides a rational starting point for regulating new fisheries where long-term characterizations of population dynamics are rarely available. However, an adaptive approach to the fishery requires the incorporation of reproductive data.     

Maximum length and age report of Sparus aurata (Linnaeus, 1758) in the Black Sea

The presence of gilthead sea bream (Sparus aurata) in the Black Sea, albeit sparse, has been known for many years. In recent years, it has been encountered in fishing nets, most commonly as by‐catch. In this study conducted in the southern Black Sea (Ordu) region, three female individuals were caught in trammel nets on October 9, 2017, and the largest individual was found to have a total length of 61.4 cm, a weight of 3080.6 g, and a gonad weight of 115.59 g. The metric and meristic characteristics of the largest individual sampled were also determined.     

Commercial fisheries,inter‐colony competition and sea depth affect foraging location of breeding Scopoli's Shearwaters Calonectris diomedea

The distribution of seabirds at sea is influenced by physical, ecological and anthropogenic factors such as sea depth, prey distribution, intra‐specific competition and commerical fishing activities. We quantified the foraging habitat preferences of Scopoli's Shearwater Calonectris diomedea in the Mediterranean Sea. We analysed habitat preferences in relation to a suite of physical and ecological variables including sea depth, net primary production and distance to other colonies (as a proxy of intra‐specific competition). Since the Mediterranean is heavily impacted by commercial fisheries, we also incorporated the distance to fishing harbours in our analyses as a proxy of the availability of discards which are a potential feeding source for Scopoli's Shearwater. Foraging birds preferred shallower waters and avoided areas close to other colonies, thereby reducing interactions with conspecifics. We also found that long‐distance trips were undertaken to areas close to fishing harbours, suggesting that these represented particularly profitable locations to compensate for the greater travelling costs involved. No differences in foraging between the sexes were recorded. This study improves our understanding of the at‐sea distribution and habitat preference of a seabird inhabiting the over‐exploited Mediterranean Sea. Our results support growing evidence that seabirds exhibit complex relationships with commerical fishing activities, which must be considered when planning conservation programmes.     

Evidence for an asymmetrical size exchange of loggerhead sea turtles between the Mediterranean and the Atlantic through the Straits of Gibraltar

The permanent eastward current at the Straits of Gibraltar may trap small Atlantic loggerhead sea turtles (Caretta caretta) inside the western Mediterranean until their swimming and diving skills improve enough to allow them counter-current swimming abilities through the current. A captivity experiment with twelve loggerhead sea turtles (straight carapace length or SCL range: 25.3-48.0 cm) revealed that the average critical velocity of this species within the considered length range was 0.38 ± 0.16 m s^− 1 or 1.01 ± 0.24 bl s^− 1. As a consequence, loggerhead sea turtles are predicted to require a minimum SCL of 36.0 cm to swim counter-current through the Straits of Gibraltar, where the water velocity ranges 0.31-0.37 m s^− 1. Genetic analysis of 105 specimens using one mitochondrial marker and seven microsatellites, as well as the recapture of three tagged individuals, support this conclusion; all Mediterranean individuals found in the Atlantic side of the Straits were not smaller than 36.0 cm SCL and the average length (47.3 cm SCL) was significantly higher than that of the Mediterranean turtles in the Mediterranean side of the Straits (31.6 cm SCL). Furthermore, the average length of the turtles of any origin moving from the Mediterranean to the Atlantic was much larger than 36.0 cm (SCL: 54.5 cm SCL), which may indicate the intervention of a different, yet unidentified mechanism restricting east-westward movement. The Algerian current, running along northern Africa, may at least partially explain the delayed departure of loggerhead sea turtles from the Mediterranean Sea to the Atlantic Ocean, as it would force the eastward drift of loggerheads occupying the southwestern Mediterranean. Exchange through the Straits is asymmetrical, and Atlantic turtles are found to enter the Mediterranean at a length of about 20.5 cm. However, once in the Mediterranean they would be retained there for up to 7.9 years, due to the surface circulation pattern. This increases the time span at which turtles are exposed to a high mortality rate, caused by fishing.     

Reproductive features and gonad development cycle of the soft bottom-gravel gorgonian Leptogorgia sarmentosa (Esper, 1791) in the NW Mediterranean Sea

Abstract

Leptogorgia sarmentosa (Cnidaria: Octocorallia) is a common soft bottom-gravel gorgonian in the northwestern Mediterranean Sea. This study examined the annual reproductive cycle of a L. sarmentosa. population at a depth of 30 m, and further determined the sex ratio, the intra-colonial gonadal output variability and the age at first reproduction. L. sarmentosa was gonochoric and the population studied was characterized by a sex ratio slightly biased towards female colonies (1 male:1.6 female). Secondary branches had higher polyp fertility (number of gonads per polyp) compared to primary branches, but because of the number of polyps on the former, most of the sexual effort was actually contributed by the primary branches, as in other gorgonian species. Male colonies became fertile above a height of 21 cm, but female colonies had gonads even in the 1–10 cm height class. Spawning occurred between late August and early September, although there was no direct observation of broadcast spawning or surface brooder strategy. The maximum gonad size was 550 μm in males and 500 μm in females, with a mean diameter of 270 μm for spermaries, and 190 μm for eggs. The number of gonads per polyp prior to spawning reached 4–5 spermaries polyp!1 in male colonies, and 3–4 eggs polyp!1 in female colonies. Spawning did not appear to be synchronized with the full moon. L. sarmentosa appeared to have a different reproductive strategy to other Mediterranean gorgonians (living on hard bottom substrata), probably because of its different habitat preferences and biological (morphology, diet, prey capture rates, growth, biochemical levels) features.