Fish spawning aggregations (FSAs) are vital life-history events that need to be monitored to determine the health of aggregating populations; this is especially true of the endangered Nassau grouper ...(
Epinephelus striatus
). Hydroacoustics were used to locate Nassau grouper FSAs at sites on the west end of Little Cayman (LCW), and east ends of Grand Cayman (GCE) and Cayman Brac (CBE). Fish abundance and biomass at each FSA were estimated via echo integration and FSA extent. Acoustic mean fish abundance estimates (±SE) on the FSA at LCW (893 ± 459) did not differ significantly from concurrent SCUBA estimates (1150 ± 75). Mean fish densities (number 1000 m
−3
) were significantly higher at LCW (33.13 ± 5.62) than at the other sites (GCE: 7.01 ± 2.1, CBE: 4.61 ± 1.16). We investigate different acoustic post-processing options to obtain target strength (TS), and we examine the different TS to total length (TL) formulas available. The SCUBA surveys also provided measures of TL through the use of laser callipers allowing development of an in situ TS to TL formula for Nassau grouper at the LCW FSA. Application of this formula revealed mean fish TL was significantly higher at LCW (65.4 ± 0.7 cm) than GCE (60.7 ± 0.4 cm), but not CBE (61.1 ± 2.5 cm). Use of the empirical TS to TL formula resulted in underestimation of fish length in comparison with diver measurements, highlighting the benefits of secondary length data and deriving specific TS to TL formulas for each population. FSA location examined with reference to seasonal marine protected areas (Designated Grouper Spawning Areas) showed FSAs were partially outside these areas at GCE and very close to the boundary at CBE. As FSAs often occur at the limits of safe diving operations, hydroacoustic technology provides an alternative method to monitor and inform future management of aggregating fish species.
Extensive aquaculture in coastal and estuarine wetlands can support both increased food production and wider ecosystem services when underpinned by effective management to promote productivity and ...hence food webs that support both commercial species and biodiversity. Changing hydrology, specifically water movement, within wetlands significantly impacts the physico-chemical properties of the water body and hence can be employed to manipulate productivity and alter patterns of recruitment of commercial species and may also transfer non-native species from the supplying water bodies. The reconstructed wetlands of Veta la Palma in the Doñana Natural Park are subjected to either a 1% or 5%d−1 water exchange with water drawn from the adjacent Guadalquivir estuary. This site provides an excellent opportunity for examining the effect of water management on the food webs that support both the birdlife and aquaculture activities for which this habitat is managed. Stable isotopes were used to examine food webs in three replicate lagoons under each water management scheme. In lagoons receiving higher water exchange, phytoplankton productivity appeared to be more important than benthic production in supporting food webs. Increased water exchange also changed the shape of the food webs, facilitated the colonisation of at least one non-native species and increased the importance of non-native species in the diets of large commercially harvested fish (>60% of seabass diet). Lagoons with high water flows also had between three and four times greater shrimp biomass than those of low flow lagoons. Non-native fauna were opportunistic omnivores, eating marginally more non-natives in lagoons with greater water exchange. Overall non-native cordgrass Spartina densiflora contributed only slightly more to food webs compared with the native reed Phragmites australis, despite the lagoon edge occupancy ratio of 9:1, respectively. Non-natives also appear to enhance food provision for large predators and wetland birds, by increasing biomass, without competing for resources with native species, supporting the dual management objectives of aquaculture and waterbird conservation.
Extensive aquaculture productivity appears to be positively correlated with water exchange rates.
•Veta la Palma is a rare site where aquaculture and bird conservation activities are simultaneously promoted.•Greater water exchange increases the carbon supply from phytoplankton to the food web changing the shape of food webs.•Water exchange impacts recruitment opportunities for both commercial and non-native species.•Greater water exchange increases the proportion of non-natives in the diet of commercial species.•Non-native fauna are well integrated into the food web and provide both direct and indirect support to the extractive aquaculture activities
A series of experiments investigated the potential role of microbial mats in nutrition of the early settlement stages of Penaeus semisulcatus. From 3 days post-metamorphosis, the microbial mat ...supported high growth and survival rates in postlarvae, equivalent to that supported by a control diet of Artemia nauplii and mussel. Examination of gut contents indicated that benthic postlarvae feed indiscriminately on the microbial mat. However, when postlarvae were fed separated size-fractions of the microbial mat, only the fraction containing a high concentration of infauna (mainly nematodes) was able to support the same growth as intact microbial mat. This appears to be due to the low nitrogen content (0.4-0.9 mmol g⁻¹) of the various size-fractions, compared to that of infauna (4.0 mmol g⁻¹). The stable isotope composition of the dietary size-fractions and postlarval shrimp tissue supports the hypothesis that the shrimp assimilated C and N primarily from the associated infauna. This may be due to selective feeding that is not apparent from stomach contents, due to rapid digestion of fauna soft tissues, or to differential assimilation of infaunal prey relative to other microbial mat components. The results demonstrate that microbial mats may support survival and growth in early-stage penaeid shrimp postlarvae on intertidal mud flats.
In a restored wetland (South of Spain), where different flow regimes control water exchange with the adjacent Guadalquivir estuary, the native Palaemon varians coexists with an exotic counterpart ...species Palaemon macrodactylus. This controlled m\acrocosm offers an excellent opportunity to investigate how the effects of water management, through different flow regimes, and the presence of a non-native species affect the aquatic community and the trophic niche (by gut contents and C-N isotopic composition) of the native shrimp Palaemon varians. We found that increased water exchange rate (5% day−1 in mixed ponds vs. 0.1% day−1 in extensive ponds) modified the aquatic community of this wetland; while extensive ponds are dominated by isopods and amphipods with low presence of P. macrodactylus, mixed ponds presented high biomass of mysids, corixids, copepods and both shrimp species. An estuarine origin of nutrients and primary production might explain seasonal and spatial differences found among ponds of this wetland. A combined analysis of gut contents and isotopic composition of the native and the exotic species showed that: (1) native P. varians is mainly omnivorous (2) while the non-native P. macrodactylus is more zooplanktivorous and (3) a dietary overlap occurred when both species coexist at mixed ponds where a higher water exchange and high abundance of mysids and copepods diversifies the native species' diet. Thus differences in the trophic ecology of both species are clearly explained by water management. This experimental study is a valuable tool for integrated management between river basin and wetlands since it allows quantification of wetland community changes in response to the flow regime.
•Flow regimen is a major determinant of physicochemical habitat of a wetland.•Water exchanges wetland-estuary modify its aquatic community and trophic links.•Omnivory and physiological tolerance key in the resistance of a wetland community.•Trophic niche of P.varians seems not to be shrunk by the presence of P.macrodactylus.•The shrimp P. varians has a key role in the stability of the aquatic faunal community.
Penaeid shrimp can be useful ecological indicators of linkages between shallow tropical coastal habitats, acting as integrators of carbon and nitrogen sources due to their generalist feeding habits ...and their mobility between habitats and with tidal cycles. In the current study, the contribution of mangrove, seagrass and microbial mat to the nutrition of two penaeid shrimp species,
Penaeus semisulcatus
and
Metapeneus ensis
, in a shallow arid embayment in the Arabian Gulf was assessed through a combination of analysis of stomach contents and dual carbon and nitrogen stable isotope signatures. Shrimp tissue stable isotope signatures identified seagrass as a major source of carbon and nitrogen for both species, contributing 21–38 % (1–99 ‰). Microbial mat was also detected as a significant nutritional source for early-stage
Metapenaeus affinis
postlarvae (1–27 %). However, mangroves were not identified as a significant source, with the range of results including the possibility of a zero contribution. Moreover, the greatest possible contribution of mangroves as source of carbon was less than for the other primary producers. This may be due the high salinity and wide temperature range limiting mangrove productivity as well as the low export of dissolved and particulate organic material out of the mangroves due to low rainfall.
The feeding ecology of the green tiger shrimp Penaeus semisulcatus was studied in inshore fishing grounds off Doha, Qatar, using a combination of stable isotope (delta13C and delta15N) analysis and ...gut contents examination. Samples of post-larvae, juvenile and adult shrimp and other organisms were collected from intertidal and subtidal zones during the spawning season (January-June). Shrimp collected from shallow water seagrass beds were mostly post-larvae and juveniles and were significantly smaller than the older juveniles and adults caught in deeper macroalgal beds. Gut content examination indicated that post-larvae and juvenile shrimp in seagrass beds fed mainly on benthos such as Foraminifera, polychaetes, benthic diatoms and small benthic crustaceans (amphipods, isopods and ostracoda), whereas larger shrimp in the macroalgal beds fed mainly on bivalve molluscs and to a lesser extent polychaetes. In shrimp from both seagrass and algal beds, unidentifiable detritus was also present in the gut (18, 32%). delta13C values for shrimp muscle tissue ranged from -9.5 +/- 0.26 to -12.7 +/- 0.05 0/00, and delta15N values increased with increasing shrimp size, ranging from 4.1 +/- 0.03 to 7.7 +/- 0.11 0/00. Both delta15N values and delta13C values for shrimp tissue were consistent with the dietary sources indicated by gut contents and the delta13C and delta15N values for primary producers and prey species. The combination of gut content and stable isotope data demonstrates that seagrass beds are important habitats for post-larvae and juvenile P. semisulcatus, while the transition to deeper water habitats in older shrimp involves a change in diet and source of carbon and nitrogen that is reflected in shrimp tissue stable isotope ratios. The results of the study confirm the linkage between sensitive shallow water habitats and the key life stages of an important commercially-exploited species and indicate the need for suitable assessment of the potential indirect impacts of coastal developments involving dredging and land reclamation. PUBLICATION ABSTRACT
Decapod crustaceans have adopted a full range of reproductive strategies from the release of large numbers of small eggs (Penaeoidea) to the release of relatively low numbers of large advanced larvae ...(Nephropidae). As larval size determines trophic position in planktonic food webs, all food sources from phyto- to zooplankton are exploited, with many species changing trophic level during ontogenetic development. Comparative studies on digestive enzymes, levels of activity and changes during ontogeny, together with measurements of gastroevacuation rates and food energy values appear to reveal a general pattern. While herbivorous decapod larvae adapt to low food energy values with high enzyme activity levels, rapid food turnover and low assimilation efficiency, carnivorous larvae exhibit low levels of enzyme activity but compensate by extending retention time of high-energy food to maximise assimilation efficiency. New studies on digestive enzyme levels during development in the penaeid
Litopenaeus vannamei, the caridean
Lysmata debelius and the cirriped
Elminius modestus, appear to agree with previous observations.
The present study aimed to investigate the potential use of the differing natural nitrogen stable isotope ratios in plant- and fish-sourced dietary components in the assessment of their relative ...utilisation in compound diets. Pacific white shrimp postlarvae (2.0
±
0.6 mg ww) and juveniles (414
±
11 mg ww) were fed eight experimental isoenergetic and isonitrogenous diets at each of two protein levels (46 and 23%). Diets were formulated with either fish meal or soy protein isolate as the only protein source, or in ratios of 50:50 and 10:90 based on nitrogen content. Contrasting nitrogen isotopic values (
δ
15N) of the fish meal and soy protein allowed estimation of the relative contribution of both ingredients to muscle tissue growth using an isotopic mixing model. The dietary effects on nitrogen turnover rates and on the isotopic diet–consumer discrimination factors (
Δ
15N) were also assessed. Nitrogen half lives in muscle tissue were estimated from turnover rates and growth after using an exponential model of isotopic change. In all cases, analysis of postlarval and juvenile muscle tissue indicated a biased nutritional contribution from fish meal, so that in postlarval shrimp fed the 46% protein diet containing a 50:50 ratio of the two ingredients, 69% of nitrogen in muscle tissue originated from fish meal; while in animals fed diets containing the 10:90 ratio of the two ingredients, the relative contributions of nitrogen from fish meal and soy protein were 32 and 68%, respectively. Juvenile shrimp fed the same 50:50 diet, incorporated 73% of nitrogen form fish meal and 27% from soy protein. The mixed diets with higher soy inclusion supported growth equivalent to that of the control and fish meal-based diets, possibly due to the disproportionate contribution of fish meal to growth. Muscle tissue of shrimp fed either 100% fish meal or soy-based diets showed contrasting
Δ
15N values that were positively correlated to soy protein inclusion level. The magnitude of these values further increased when shrimp were fed diets containing the lower protein level. The results demonstrate the potential for application of natural stable isotope analysis of diets and tissue in evaluation of plant-source ingredients and the optimisation of their use in diets containing very low levels of fish meal.
While most copepods are holoplanktonic, decapod larvae are meroplanktonic with a pelagic larval development ranging from days (Penaeidae) to weeks (most Palaemonidae, Palinuridae). Reproductive ...strategies result in either the early release of larvae in large numbers of small planktonic forms (Penaeidae) or smaller numbers of advanced larvae after parental incubation (Brachyura, Palaemonidae, Nephropidae, Palinuridae). Commercially-cultured decapod larvae exhibit a wide range of feeding strategies exploiting most of the trophic levels found within the planktonic ecosystem. Studies on these crustacean larvae demonstrate how their digestive physiology is adapted to different feeding strategies during larval development, and provide an insight into the design of appropriate artificial feeds for commercial culture. Comparative measurements of digestive enzyme levels reveal that trypsin-like protease appears to dominate in all larvae investigated. Highest levels occur in herbivorous penaeid and brachyuran larval stages. In contrast, carnivorous lobster and caridean larvae show low protease activity at first feeding and appear to rely upon high-energy digestible live prey for their nutrition. Ontogenetic changes in enzyme type, activity and content are displayed during the penaeid mysis and caridean, brachyuran late zoeal stages as larvae transfer to higher trophic levels. The range and extent of these changes are reviewed for the commercial larval groups of commercially important species.
Competition for coastal land use and overexploitation have reduced or degraded mangrove coverage throughout much of their distribution, especially in South-east Asia. Timber production was the ...initial motivation for early mangrove reforestation projects. More recently, benefits from protection against erosion and extreme weather events and direct improvements in livelihoods and food security are perceived as justifications for such restoration efforts. This study examines the socioeconomic impacts of a community-led reforestation project in the Philippines through a survey of the local fishers. Revenues from mangrove fisheries, tourism and timber result in an annual benefit to the community of US$ 315 ha−1 yr−1. This figure is likely to be considerably more if the contribution of the mangrove to the coastal catch of mangrove-associated species is included. This estimate only includes direct benefits to the community from mangroves, and not intangible benefits such as coastal protection, which paradoxically is perceived by the community as one of the most important functions. More than 90% of all fishers, regardless of where they fished, thought the mangrove provided protection from storms and typhoons and acted as a nursery site and should be protected. Those fishing only in the mangrove perceived more benefits from the mangrove and were prepared to pay more to protect it than those fishing outside. This study concludes that replanting mangroves can have a significant economic impact on the lives of coastal communities. Acknowledgement of the value of replanted mangroves compared with other coastal activities and the benefits they bring to the more economically-vulnerable coastal dwellers should support better informed policy and decision-making with regard to coastal habitat restoration.
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